How to choose tires for 4WD Touring Sedans

by Eric Perez

Part1 Intro Identifying the Track Surface Tire Terminology Quick Tire Setups Tire Setup Theory Effects of Chassis variables on Tire Setups Solving Common Handling Problems Rubber Tires: 1.Traction Tires 2.Temperature Tires 3. Hybrid Tires Summer Tire Testing Panther Tire Review Wrap up

Intro

Now-a-days you hear and read a lot about tires in

the magazines, at the track, and on web discussion boards all over the world. What is it about this topic

that interests us racers so much? All your car has to prevent it from sliding all over the track are those

small areas underneath the tires. Maximizing the traction on those four spots is what tire and car

setups are all about. Even if you have the perfect chassis setup and the best tuned engine, without the

proper tires, you won't be better off than if you used

Slick 50 as a traction additive!

There are many things that need to be considered to effectively select the tires that are needed for your car to perform at its best. The first question

that you need to ask yourself is whether you are willing to sacrifice some

cash to get your sedan to hook up. I will be giving you some general tire setup that will work for most surfaces. If you are willing to sacrifice some

longevity for enhanced performance, then let's get to it. No, I have not

forgotten about you the budget racer (I consider myself a racer on a budget). I know tires are one of the most expensive items on a racer's

budget, especially if you run gas cars and routinely run 20 min Mains. Nobody likes spending $40 on a tire set -to then find out that the car

handles worse than it did with run-down practice tires. That's why it's better to conduct an experiment when you know the outcome. Always

check with the racers that are winning to get an idea of what types of tires work best at the track. There is no sense in spending money doing tire

R&D when the knowledge base is already there. If the local racers are keeping you in the dark, then ask the Hobby Shop sales associate; at least

you'll know what tires are the big sellers. Just remember that a little quick and painless investigative work up front can save you a big headache in

the future. When you do buy your tires, remember to throw the junky open-cell foam insert that most tire manufacturers include with their tires

in to the trash-can and instead use molded foam inserts.

Identifying the Track Surface: A tire is designed to be used at a

certain temperature and surface. So the first step in properly

selecting tires is to correctly identify the surface where you are

planning on racing your car. Tires that work on a particular track &

temperature will probably not

work or not work as well in other conditions. It is not uncommon to have winter, fall/spring and summer

setups. As the temperature and track conditions change, some types of tires will adapt better to the change than others. If you happen to run on

a couple of different surfaces you will probably end up with an optimal tire setup for each track or you could shot down the middle and get a tire set

that will work on most of the surfaces.

CONCRETE ASPHALT

ROUGH SMOOTH SEALED UN-SEALED

CLEANED &

BLOWN

W/TRACTION

ADDITIVE

CLEANED &

BLOWN

W/ TRACTION

ADDITIVE

SMOOTH BUMPY SMOOTH BUMPY

HOT or WARM

COLD HOT or WARM

COLD

Tire Terminology:

A quick brush up on tire terminology: There are

two main types of tires. These are rubber and foam tires. Rubber tires are further separated into

two categories, temperature rubber and traction rubber. As the name implies, temperature tires

rely on heat to soften the tire. As the tire softens, it heats up even more, causing the outermost

rubber layer to break down generating hi-levels of traction. Traction rubber tires rely on the softness

of the tire and its adhesive quality to generate traction. These tires feel very soft and sticky. With

this type of rubber tire, traction increases

gradually with increased heat, but it's more related to the softening of the rubber and not due to rubber break-down as is the case with the rubber

used for making temperature tires. Most of the traction rubber tires are marketed as long-lasting or long-wear high traction tires.

Quick Asphalt Tire Setups: For the best performance on asphalt, you will need to run foam tires. This

is especially true if you have serious HP and the space to use it. When the temperature is right, there is no beating foam tires on asphalt. Popular

choices are reds, blues or double orange in the front and orange, purple or

pinks in the rear.

Temperature rubber tires in my experience seem to work the best if you have to run rubber on asphalt. On asphalt I would recommend Pro-Line S2

or H13 with a hard molded insert for the front; and on the rear use S3 with a med./hard or med. molded foam insert. If you are on a tight

budget, Duratrax slick tires for the Street Force GP are sold for less than $10 and that's for a full set of four temperature tires!

Quick Concrete Tire Setups:

Traction rubber tires work very well on concrete. As the heat factors increases, so does the traction level, but heat is not as critical because the

tire is already soft to begin with. If it's too hot (in the upper 90's), then you might need to go with a slightly harder compound tire or a belted one.

You may also need to increase the hardness of the insert to help the tire retain its shape a little better. If temperatures are right, you can get

better traction with a temperature rubber tire. If that is the case, then a H13 with a hard insert in the front coupled with an S2 with a hard insert in

the rear should provide increased performance. If tire longevity is not important then S2 in the front with S3 in the rear can be a lethal

combination for your competition.

Tire Setup Theory:

The golden rule: Tires are 80% of a car's setup. You could play with your suspension for a week straight until you get the car to go around the track

without spinning the rear end. You could also take your wheel wrench and change the tires in under a minute and have a better handling car -It's

your choice…

It's true, for an ill handling car, a tire change would be the easiest but not

the most cost-effective way of getting the car to handle properly. Even if you make a tire change, it probably won't get you 100% of where you

need to be. You still need to work on overall chassis setup; but even this is secondary to having the right tires. If there is a big flaw on your chassis

setup, then a tire change is not going to save you, at least not enough to get you anywhere near the A-main.

Some people have the philosophy that you must learn to drive a car that oversteers severely and will spin out the moment you touch the steering

wheel. Others, consider it normal for the car to plow through the corners and grab a handful of wood every time you enter a corner at more than 5

mph. Folks, I'm going to let you in on a secret: If the D-main drivers traded cars with the A-main drivers, they would probably do a whole lot

better( It's got nothing to do with engine HP ). I can't do well in a race unless my car is easy to drive. The fact is that if I can drive it to the finish

line, then the average racer would do even better than I -with my own car! Driving is important, but having a well-behaved car is also a big part

of the winning equation.

Effects of Chassis setup on Tire Selection

Chassis Setups: Lately the "hot" setups for the latest breed of "racing" sedans (insert your

car here)... is ultra stiff suspensions w/ super thick anti-roll bars, front one-ways and solid rear diffs. If you have foam tires and a track that is

oozing out traction additive -maybe. If you have a great computer radio and a degree in computer programming and are a very smooth driver,

then this is a good setup! The only bad part of these new stiff setups is that it makes the car super twitchy and you can't make any mistakes in

the driving department. Try this setup w/ the wrong tires or on a rough track that needs the suspension to work and your car will be everywhere

on the track. You will make the boards your home. Not only that, you will look like a fool doing doughnuts in the straight-a-way with a "race" car.

If you just recently got your car and don't have it hooked up, the last thing you need is an ultra responsive stiff suspension. You need a car

that's forgiving and that you can get used to. You also need a car that understeers a little and pushes slightly when on power. This type of car

anyone can drive; it's consistent and less error prone than the twitchy stiff chicken.

How do I get my car to handle like that?, you may ask yourself, as your

car grabs another handful of 2X4 wood...there goes the shiny aluminum

turbo fast suspension arm set (Wasn't the aluminum junk supposed to make me faster -you thought?)

To get a car that's easy to handle, you need to get the suspension to work

smoothly. The front always must be stiffer than the rear. The shock oil must always be thicker in the front. Also, the front tires must have less

grip than the rear. This is achieved by using a stiff insert in the front and a softer one in the back. Many times you will need to use different tire

compounds between the front and the rear. What matters is that you have

consistent front-to-rear traction. You need to know exactly how the car is going to behave when you're braking, accelerating, taking a fast corner or

a slow one. For you to feel comfortable with your car, it has to feel

consistent at all points in the track. Don't forget that if you start with the manufacturer's suggested setup, then choosing the proper tires will get

you 80% toward that "perfect" setup. The rest is chassis fine tuning...Bare in mind this is assuming you have everything under "control" in the

driving department.

Solving Common Handling Problems

Oversteering: The most common problem that racers run into is that their car

oversteers. This means that the car over-reacts when you try to turn the front wheels. As a result of high levels of front traction the rear brakes

loose and wants to trade places with the front whenever you ease up on the throttle and try to turn the front wheels. Let's have a quick top level

look at how to correct this handling problem. Some cars seem to work well with the same tire/insert combination at all four corners, but most

cars will tend to have varying levels of oversteering when this is

attempted.

(Oversteering) Primary Change: Change front tire to a harder one (less traction) or go to a softer rear tire

(more traction). Don't waste your time and money on trying to correct a severe error in tire choice with suspension adjustments. If the tire

selection is "way" off, then do yourself a favor and change the tires. You can always use the offending set as play tires or for breaking-in new

engines at a parking-lot. Sometimes when tire choices are very limited I

suggest you swap out the tires, front to rear (assuming you have different compounds). On some occasions this works real well, on other the

problem is reversed ie. the car goes from oversteering to understeering.

(Oversteering) Secondary Changes:

1. Reduce steering servo travel (throw). 2. Set front camber to –0.5 and rear camber to -1.5 .

3. Increase front caster if you need to take-away low-speed steering. Reduce front caster if you want to remove high-speed steering.

3a. Increase rear toe-in to add on-throttle stability. 3b. Increase front toe-in (will make steering less responsive at the

beginning of a turn). 4. Decrease chassis droop or down-stops on car (more suspension travel

will get the car to roll more and be less responsive).

5. Increase front ride-height and/or lower the rear to get more static weight on the rear tires.

6. Increase the shock oil viscosity in the front to get less steering in the middle of the turns.

7. Go w/ stiffer springs in the front shock and/or install front anti-roll bar. Go to the next softer spring in the rear shock. Body roll creates traction.

Too much body roll promotes instability and roll-overs. 8. Reduce front differential action by tightening the ball differential. If

your car has a gear-diff, you can use thick silicone diff fluid or heavy high-temp grease to slow-down power transfer. A tight front diff will make the

car push a little under power, thus making the car easier to drive. You want the rear diff to be fluid, so that you can send power easily to either

rear wheel.

Understeering:

If the car understeers, this means that the car is not responsive to your attempts at rounding the corners. The car plows through the corners, with

no front grip until: A) The car slows down enough for your front tires to grip, or B) You hit a board and your car ricochets into the corner (sort of

like playing billiards with a $300 r/c car). To fix this handling ailment you need to increase front traction and/or reduce rear traction. Basically, do

the opposite of the changes outlined in items 1-8. Sometimes when tire choices are very limited I suggest you swap out the tires, front to rear

(assuming you have different compounds and/or inserts). On some occasions this works real well, on other the problem is reversed i.e. the

car goes from understeering to oversteering.

Unresponsiveness:

If the car feels unresponsive to steering inputs and easily brakes the rear loose in the corners -and your suspension is not ultra-stiff, then it's time

to change to stickier tires (tires that provide more grip)

This is just a general guideline. Don’t make too many changes at once;

then you won’t know exactly what fixed your problem. I read this piece of advice some time ago, and it’s helped me quite a bit: “Work on the side

of your car where the problem is first”. If you need more rear traction,

work with the rear end first. If after making the changes you still need more traction, then remove some traction from the front. Don't forget it is

all a balance, the car will not work properly unless you have the right amount of front to rear traction.

Rubber Tires

Intro:

I remember the days when "racing" tires would last a couple of runs. The tires would develop a bald spot, or the soft foam-insert would shift inside

the tire and wear a groove around the inside edge. These days, the one-run tire is a thing of the past. I'm a little smarter with insert selection, and

tire technology continues to move forward at an alarming pace. Now,

most of my tires out-live the rims they are mounted on. That's actually a great feeling… The only draw-back of these new breed of tires is that the

new mold-releasing agents make the tires harder to glue on to the rims. This means you have to be more careful about tire preparation and the

glue used on the tires needs to be of high quality. To help the glue do its job better, clean the tires and wheels w/ motor spray or denatured alcohol

and make sure the insert and tire are seated correctly. There is also the problem that with an overwhelming number of different tires and

compounds, belted and un-belted and more types of inserts than flavors in a Baskin-Robbins… Soon enough you will not be better off with 20 sets

of tires than you were when you had 3 sets. I have so many choices in my tire suitcase, that sometimes, even I forget what tire insert combination

has more traction than another… and, yes, it's all about traction!

Traction Rubber Tires: The traction tire is of the type that does not depend on the temperature to

soften the rubber to increase traction. Traction rubber feels sticky and will

hook up immediately when the tires hit the track, thus warm-up is usually not even needed. Adhesion is achieved by molecular bonds between the

tire and the track surface. Examples of these tires are Pro-Line H13, Take-Off's WSA,WSB,A25,B30 Panther's LP230,231 and other soft rubber long-

lasting tires like the new HPI 24mm R compounds. Most of the major tire manufacturers have some version of these long-lasting rubber tires. These

tires will last "forever". I have still to wear out an H13 with a properly selected molded insert. I have H13 tires that have been commissioned for

almost a full year; the rims are a little beat up, but the tires are like new... Traction tires perform well in colder climates because they do not

rely on heat to develop grip. Depending on your location, there are some tires that can be run the entire season. Traction tires work very well on

unprepared concrete, even if it’s a bit dusty. They are not the best for unprepared asphalt, but with a lot of tuning experience, you can make

them work in the tar tops. Because of their high traction and decreased

wear, these are great nitro sedan tires.

On the pictures above, you will notice that small scores or ridges

are actually formed on the tire's surface. These are the typical

wear patterns that you will see on temperature tires. Notice that the tire's surface remains clean and that the wear patterns have

actually increased the tire's gripping ability. The tire shown on the

right is a very well worn Take-Off WSA tire. It has been seeing racing action since last year. Shortly after the photo-shot the tire

was retired to provide a good shot of the inside of a belted tire. A moment of silence for this battle hardened tire...All in the name of

Science.

Temperature Rubber Tires:

Temperature tires rely on the track and rubber's temperature to make them stick. You can recognize these tires by the characteristic thermal

break-down of the rubber. It looks like the rubber is literally burning off

the tire and clinging to the tire's surface. Examples of these tires are Proline's S2,S3... HPI Pro-Compound, etc… In the winter months these

tires don't work very well because the lower temperatures prevent the rubber from breaking down. When the track starts to heat up, they work

very well. The hotter the tire, the more traction they give; heat is this tire's friend! The only draw-back is that if the heat level is too high, the

tire will get oily and lose some grip. Also with increased heat levels, tire life is sacrificed. Tire longevity is really the only drawback of the

temperature tire. Seeing how the tire consumes itself to provide traction, this should not be a surprise. Tire durability issues are further enhanced

when the tire has some type of tread pattern or grooves cut into the tire carcass. These patterns prevent the melted rubber from sticking to the

tire which will accelerate wear because the tire is continuously exposing fresh rubber. Temperature rubber tires perform well on both concrete and

asphalt surfaces. If the temperature is right, this tire will give you the

best traction (when compared with other rubber tires). When the track is a bit dusty, temperature tires take a performance hit because dirt gets

stuck on the tires.

In the photos above, you can see that the tires have picked up

quite a bit of track debris. On the left (Panther Firm-Compound LP Slick), you can make out the small pieces of rubber that are

clinging to the tire's surface. This broken-down rubber gives the

tire its characteristic tacky feel.

Hybrid Rubber Tires:

The third and last type of tires are Hybrid tires. These basically borrow some characteristics from both the temperature tires and traction tires. An

example of a combination tire is HPI’s B1540 tire. They are good choices if you run in varied surfaces and don't want to spend a bunch of money.

They are also good because they tend to outlast the temperature tires, yet still retain some of their properties. Some of the new breed of long-lasting

rubber tires actually are part of this hybrid group.

Here we show the inside of a Take-Off WSA belted (radial) tire.

The fiber-belt is permanently bonded to the rubbers surface.

I haven't talked much about other tires that have special treaded patterns or are belted. Belted tires tend to last longer than unbelted tires,

especially if they are temperature tires. Temperature tires get softer as

they heat up; the tires balloon a little when you accelerate. This can

accelerate wear and cause the car to feel inconsistent. On real hot days

the car seems to hop in the corners. This isn’t always a huge performance hit; just remember that when the tire’s diameter changes, this can cause

the car to have over/under-drive. This could accelerate wear-and-tear on

the car's drive train. You should not use a high level of over-drive unless your car has a one-way bearing. Over-drive helps you get out of the

corners when you’re on the throttle. You don’t really want under-drive or your rear end is going to slide when under power.

Tire Temperature Ratings: Some of the newer breed of tires are coming out with temperature

ratings. This is but another way of fine-tuning the traction level to the track conditions. Does this mean that you can't use a cold weather tire on

a hot day? No -but you won't get maximum grip. With some rubber

compounds, as their temperature goes up in the warm-ups, the traction will either increase, stay the same or it will be reduced very quickly. Be on

the lookout when the car suddenly starts to act funny, and at what point in the race it starts happening. This is normally the case when you had

great traction in the warm-ups, and then the traction just vanishes! This loss of traction is mainly caused by the gradual increase in tire

temperature over a period of time. When you are practicing, take your temp gun and aim it at your tires every couple of minutes until you reach

maximum temperature. Typically, tire temps will be 15-20F higher than the ground surface. Make track/tire temp readings a regular part of your

setup notes; getting to know how temperature tolerant your rubber tires are will help you make the right tire choices even before you set foot on

the track.

Molded Inserts: Molded inserts come in many flavors. There

are three characteristics that need to be mentioned with inserts: 1) The firmness of

the foam material used to make the insert. Typical nomenclatures for foam density are

soft, soft-medium, medium, hard/firm, extra hard/firm. 2) There is also the width of the

insert. Most narrow or medium-narrow inserts are for 24mm tires. Most of the time these

can be used on std. 26mm rims and LP tires

without many problems. The low profile std. 26mm inserts are a little bit wider. They will

give you a slightly flatter contact patch. 3) Last on the list is the thickness of the insert.

The thickness will depend on the following tire carcass design attributes: Standard, Low-Profile (LP), Extra Low-

Profile(LP2), Round and/or Belted. Note: Some of the newer Losi LP and

Pro-Line LP2 are of the extra low-profile type of tires. These require the

use of very thin molded inserts. The Std. 26mm thick insert was designed for full height tires. Most of these tires are now extinct because racers

have switched over to lower profile tires that have less side wall flex and

also give the cars a lower ride height. Make a mental note: Most of HPI's tire line-up still needs a std. thickness insert to fill the tires taller profile.

Because HPI's 24mm tires are both narrower and taller than other tire types it may be difficult to find molded inserts that fit the tire properly,

thus You probably should use HPI 24mm molded inserts.

Here we explain the specs on a popular Yokomo ZR-038F molded

insert. Notice the three dimensions on the lower left-hand side of the label.

The most important part of selecting an insert is that the tire is properly supported and that you don't have too thick or too thin of an insert. Either condition will yield inconsistent traction. The profile of the insert is also

important. A flat tire will yield more straight-line traction, but a round tire

will react better on the corners; it's all compromise.

Misc. Information: Most 24mm tires can be used on

26mm rims and visa-versa. There is so much variation on what

manufacturer "A" calls 24mm and what manufacturer "B" calls 24mm

that nine out of ten times, the tire will fit on either 24/26 rim with no

objections. The insert is really more

important than the rim's width. The softer the tire, the harder the insert.

Typically, the front tire has a relatively hard insert to help reduce

front traction. Don’t use the spongy

open-cell foam that most tire manufacturers include w/ their tires. Sponge

inserts don’t work that well, especially when trying to support the weight of a heavier nitro sedan. Instead, buy molded inserts that help keep the

tires' contact patch in good shape. The end-effect is that your tires will

give you better and more consistent traction and will last twice as long.

Rubber Tire Overview:

To wrap up the rubber tire section, some brands do work better than others, but you’ll have to experiment to see what works for you. I

currently use Pro-Line, HPI, Duratrax, Take-off and Ofna tires. These are just a small number of the many companies selling tires and inserts. I

know a lot of people that swear by (insert other tire manufacturer here). All I can say is that I’ve spent a lot of money on tires and inserts and I

can only comment on the tires that I have used. If you follow the

manufacturers application chart and select a good insert, then you will probably get good results and long tire life. Make a handful of setup

changes and you’ll have a great handling car.

Hot Track Tire Experiments:

Recently, I brought my entire tire suitcase to the local track on a hot 95F day, with only one thing in my mind -Tire setups. Swapping tires actually

became my primary mode of operation. The number one thing that I noticed was that cool or mild-weather traction tires would not really wear

out, even if you cooked the tire to 130F! What actually happened was that

the tires lost their grip, some by a large margin. This usually wasn't apparent until the car had been on the track for at least 3-5 min. During

this day-long experiment, there was one tire compound that I kept reaching for -It was the H13 with a 26mm hard insert. I have a group of

H13s that I've been using since last summer/fall. It has been my experience that this tire is not suited for the rear because it lacks the

necessary grip, but as front tires H13 shine! My testing has confirmed that H13 tires are very temperature tolerant. They work at 60F, and also work

at 130F; few tires on the market are as versatile as the Proline's H13. They seem to work best when kept closer to 100F, but they are still

functional and long-lived for summer racing too. With a properly selected rear tire you should be able to continue to be competitive at the local

track during the entire season. Seeing how the H13 is very popular as a control tire for the some of the big National races; this news should not be

a huge eye opener. The Texas summer is long and very hot; hopefully, as

the season unwinds, I'll have more hi-temp data to share with you.

Panther LP-Slick Tire Review: A short time ago i decided to take the plunge and try-out the new Panther

Sedan LP-Slick tires. After a few testing sessions, I'm not impressed with their hot weather performance. Most manufacturers give you an idea of

the temperature rating of the tire. I prefer traction and temperature

ratings on tires; this takes some of the guess-work out of choosing tires.

HPI, Sorex, Take-Offs and Even Pro-line, to a small extent, have been doing this for some time now. Panther tires should have gotten on the

bandwagon; instead, they went with soft, Med/Soft and Firm compound

labels (It sort of leaves you in the dark as far as application temps are concerned). With the softest tires in the rear and the med/soft compound

in the front, the car was planted. After the warm-up, the rear tires lost their grip; shortly thereafter, the car was pushing under-power and I was

losing the rear in the turns; It was "spin city..." I decided to experiment with other combinations, so I changed to firm in the front and med/soft in

the rear. The car handled better, but the med/soft tire lost its grip after the warm-up; and again, it was "spin city". I tested the "firm" tire

compound in another occasion and again handling was not to par with other more popular tires on the racing circuit. From the way the car

handled it seemed that the rubber compound that Panther used to mold the tires is not suited to very hot temperatures. During testing tire temps

peaked close to the 130F mark. After a few 5 minutes runs tire wear seamed to be taking it's toll on the firm tires. It's interesting to note that

the softer panther compounds seemed to wear more like traction tires,

whereas the firm tire was wearing very similar to a Pro-Line S2/S3 yet, yielded less traction. It was very apparent that the tires were not at home

under the hot Texas sun, who knows? Maybe these tires will be the hot ticket in the fall when it cools down a bit. I'll keep you posted...

Wrap-up:

This is only the first part of this two (2) Article Series. To view the

section on foam tires, click here.

If you would like to discuss any of the topics presented in this article in

more detail, feel free to e-mail me or post a reply on the message board

in the Tech Article Discussion Forum under the topic "Sedan Tire Tech-Talk".

Whoop some R/C car butt!!!

Eric Perez Team NitroRC.com

How to choose foam tires for 4WD Touring Sedans (Part 2)

by Eric Perez

Foam Tires Intro

Shore Rating Types of Foams

Tire Wear Tire Selection

Chassis setup Racing with Foam

Compound Chart Manufacturer Index

Wrap up

Foam Tires

Intro:

The other main type of tire is the foam tire. Foam tires unlike rubber ones don't use an insert, instead the entire tire is actually made of a

homogeneous foam-rubber compound that is molded in the shape of a doughnut and glued to a plastic rim. Good foam tires are more expensive

than rubber slicks, but they already come assembled with the rim and trued. They are basically ready-to-run. With rubber tires you need to buy

rims, plus inserts and do a good job assembling the tires. When you add up the dollars, rubber is more expensive but will tend to last longer.

More on the cost of ownership: The main disadvantages of foam tires are that they tend to give less run-time than a rubber tire, and the rims are

not as robust as those used for rubber tires. If you tap a wall or get hacked, the soft foam tires could be damaged or chunked (torn).

Sometimes the tire can be fixed with thin CA, but usually lightly chunked tires become "practice" tires.

On hot asphalt, foam tires will give you the highest level of traction

available. Foam tires can be run more aggressively because of better

traction recovery characteristics when you spin the tires. Rubber tires have a harder time regaining their grip after they break loose. Another

benefit of quality foam tires is that you don't need to worry about unglued edges. I still recommend checking the tires rim edge between rounds; but

it's not as critical as with glued rubber tires.

Shore Rating:

Foam tires are rated by the hardness of the foam. Most of the time you will be working in the 30-60 Shore range. The manufacturer measures the

shore rating by using a tire durometer. This tool has a small steel pin that

is spring loaded and indexed to a circular gauge, very similar to a tire pressure gauge. To measure the tire hardness you roll the durometer on

top of the tire; the compression force that the foam has exerted on the steel pin can be read on the dial. Repeat it over several locations on the

tire and the average is the tire's shore value. There are other features that must be considered when describing a foam tire; like tire

construction, composition and rubber/silicone content of a foam tire. These will typically be similar if you stick to a particular tire manufacturer.

Foam tire construction can be one single piece of foam or it can be multiple rings glued together to cover the rim surface. Multi-ring tires are

more expensive to manufacture but are less prone to suffer damage from the occasional rub or run-in with another car.

Types of Foam:

Another important characteristic of the tire is the silicone/rubber content of the foam. Hi

silicone/rubber content tires are sometimes classified as exotic foam or long-wear foam.

These as the name implies have longer wear life. They also provide better traction than

pure foam tires because the tire doesn't dry out as fast. Yes, foam tires do have a shelf

life; this starts as soon as you open the package and expose the foam to air. Keep

your foam tires off the car and inside a

plastic zip-lock bag or other air-tight container and keep them away from

sunlight… and don't feed them past midnight :) Typically, you can guess the rubber

content of the foam by the weight of the tire. Pure foam tires are very light and spongy,

whereas silicone/rubber tires are a bit heavier and more elastic.

Tire Wear:

Another thing to consider when running foams is tire wear. The number one enemy of foam tires is the abrasiveness of the track surface. Smooth

tracks make tire durability a non-issue, rough asphalt parking lots might force you to run harder compounds to let the tires last through the end of

the day!

Another element of tire wear is related to the suspension geometry itself.

If the suspension is not adjusted correctly or if the material used to make the rim is too flexible, the foam tire will not wear evenly. This means that

the tire diameter won't be the same across the contact patch. This can

induce handling problems in the car by creating an apparent camber angle or stagger (tires of different diameters on car). Typically, the softer the

tire, the faster it will wear, and the easier it is for the tire to deform and for the contact patch to get coned out. All of these characteristics lower

the useful life of a foam tire.

If you have access to a tire truer, it will greatly increase the useful life of the tires. It will also allow you to reduce the tires diameter to reduce side

wall flex and make the contact patch more consistent. For most, a tire truer is a very big investment in the neighborhood of $200-350 depending

on quality and features. If you are going to be running foam tires for most

of the season, then a tire truer will almost pay for itself by allowing you to run the tires for a longer time. Not only this, but traction will feel more

consistent from run to run. If you happen to have a lot of time on your hands, you can purchase foam doughnuts and mount/true your own tires

at half the cost of buying the tire RTR.

Foam Tire Selection: Most racers run a front tire with a shore rating

in the 60-40 range. This is more commonly referred to as tire dot color codes. The dot code

for 60-40 is blue, red and orange. For the rear 30-40 shore or pink, purple, orange is more

common. Tire selection is going to depend heavily on surface roughness, temperature,

track preparation and chassis setup. Keep this in mind when you are going into a late

afternoon main. The track is going to be hotter than in the morning. It's not uncommon for the

cars that were hooked-up in the morning to be traction rolling in the afternoon. If you are on

the verge of rolling over when track temps are

not up to par, then change to harder tires or make suspension adjustments to anticipate

higher traction levels later in the day.

Chassis Setup for Foam Tires:

We already know that foam tires have the highest possible level of traction than any other type of tire -Under the right conditions. What will

all this extra traction mean in the setup department? The extra traction

will be translated into extra body roll. If the chassis dampening is set too soft, then the car will roll-over.

Roll Over problems seem to be one the primary problems of beginning

racers when they switch to foam tires. They forget to stiffen the shocks and the car spends more time on it's lid than on the tires! What can you

do to "stiffen" the car if you don't have a box full of shock springs and a gallon of shock-oil at hand? The first thing is to do is to lower the ride

height of the car. This will lower the center of gravity of the chassis, and make it harder for it to roll-over. The next thing to do, would be to

decrease the droop on the suspension arms. This will limit suspension arm

movement and help keep the car from swaying too much on the corners.

When I'm setting my car up for the large asphalt tracks I usually take my parking lot setup and set the camber to -2 deg all around. This is done to

prevent the tires from coning out. Another setup change is done in the suspension department. I increase the shock fluid viscosity and go to the

next stiffer springs front and back. I do this to take some sensitivity out of the chassis. If I still need less traction, then it's either a tire change or I

stiffen the shocks some more or I dial out some traction with anti-roll bars to get the car tuned for the corners.

I like to keep tabs on tire wear with a caliper. I measure the inside and outside diameter of the tire. If the outside is wearing more than the inside

then you need to increase the negative camber. If the inside of the tire is wearing faster then I reduce negative caster. On tracks with a lot of high

speed right hand turns I also like to rotate the tires left to right to promote more even tire wear and extend their life.

Racing with Foam Tires:

I tend to do less tire swapping when I run

foams, than when running rubber. This is because there are only a few tire choices

available when you are running foams -

that is, after you find a brand that yyou are happy with. Once you find your brand you

will probably only need 3 to 5 different compounds. There is going to be a

Hot/Warm/Cold base tire selection, but after you make your in initial choices, the rest is done with chassis setup.

It's not uncommon for electric racers to use traction additives on their foam tires. Electric race times are relatively short when compared to a 10-

15 minute nitro main, This is one of the reasons why I don't recommend their use for racing conditions. Results are just not repeatable enough for

me. Why introduce an additional sometimes uncontrollable variable into your traction formula?

Where do you start? Whatever the guys wining the races are using -that's what I start with! After the initial "roll-over" phase use your judgment as

to the tires traction/wear/cost and take it from there. I like Super G's and TRC tires, there are a couple of new brands out there. If the tires aren't

lasting you at least 4 Sunday races then you might have a very rough track or you are using very soft compounds. If you are clue-less as to

what the compounds that you need then run RED (50) fronts tires and PURPLE (40) rear tires -that should be a good starting point.

A special note: If the track is very cold with outside air temps in the 40-

50F then you may be better of using low-temp belted rubber tires. I've

done this in the past with great results. While the "foam" guys where complaining about no traction I was clocking the laps with my rubber

tires.

Once again -When running foam tires you will tend to have more traction that what you need and taking traction away with suspension settings is a

lot easier than "creating" traction with suspension settings. This allows the beginner more room for error when setting up a car that runs on foam

tires. The only drawback is that you need to stay away from the walls!

TRC'S compound chart:

COMPOUND DUROMETER HARDNESS WEAR RATE

Silver 25 Soft/Medium Moderate

Platinum 25 Soft/Medium Very good

White 26 Medium/Soft Good

Green 29 Medium Good

Gray 31 Medium Moderate

Pink 34 Medium Moderate

Blue 36 Firm Moderate

Purple 42 Medium Excellent

Red 54 Firm Excellent

2Blue 55 Firm Excellent

Tire Manufacturer Index:

I've compiled this short list of tire manufacturers to help you find what

you're looking for. This is in no way an endorsement from my part -I can't guarantee that they will work for you! Looking at what the winners are

using is going to be a lot more valuable to you than what my favorite tires are.

Manufacturer Types of Tires

TRC Foam

Super G Foam

Jaco Foam

Yokomo Rubber/Foam

Tredz Rubber/ Foam

Proline Rubber/Foam

Ofna Rubber/Foam

HPI Rubber

Take-Off Rubber

Sorex Rubber

RD-Logics Rubber

Duratrax Rubber

Team Losi Rubber

Panther Rubber

Wrap-up: Hopefully, this article opened your eyes on the need for proper tire setups

and their application in 4WD Touring Sedans… And, yes, it's all about

traction! Once again, if I didn't mention your tire of choice, don't feel bad. Sometimes, you need to stick with a particular manufacturer to simplify

your choices. Hey, my tire suitcase is overflowing, and most of the time I only really need 2 or 3 tire sets to get my car hooked up. What's with the

big tire suitcase? It's just part of the psychological warfare that goes hand-in-hand with R/C racing!

Whoop some R/C car butt!!!

Eric Perez Team NitroRC.com

If you have any questions or would like to discuss any of the topics

presented in this article, feel free to e-mail me.