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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

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( Foam Tires - Part 2 >>)


 

 

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