Radial Race Tires

[JBH]

I want to try radial race tires (DOT) before I start altering the suspension geometry for bias-ply slicks.

 

Here's why: I had the Avon CR500 (175/55-13 and 205/55-13) on the car and they worked really well on road courses. Looking for more traction I found a set of Avon ACB0s (6.0X21-13 and 7.0X2-13) and tried those even though they are bias-ply and my camber was set at 1.2 and 1.7 degrees front & rear respectively. They are horrible - the car slides through turns and I have to be careful with throttle so as to not break the rear end loose.

 

If I look at section widths as a measure of contact area, the CR500s are 7" and 8" front and rear. The ACB0s are 6" and 7.2". It is interesting that both tires are the same width sidewall to sidewall. The ACB0s bulge out a lot more than the CR500s.

 

So the fact that the ACBs have less contact area explains part of the problem. I don't know what impact the camber has - I do know that bias ply slicks should run close to zero so that may be part of the problem too. Ultimately, I may change the DeDion ears and front camber to run bias ply, but I thoght I would give radials a shot.

 

First question: does any one have experience with radial tires for road racing?

 

Second question: I researched three major radial tires suppliers (click on the picture shown below for manuf. data). Does anyone have thoughts on the right tire combinations for a Caterham? I think there is a limit to front tire width before it begins to rub the front wing support rod.

http://www.usa7s.com/aspnetforum/upload/1819059296_tire choices.JPG

 

Sorry for the long post - there is a lot to assimilate here.

[Kitcat]

Call Tire Rack. They love these kinds of questions. I thought all of the current DOT legal race rubber was radial (Toyo/Hoosier, Kumo, etc), but I am certainly no expert.

[slngsht]

Also, look up Radial Tire. They are a local shop in the DC area, and support alot of the SCCA guys. Very knowledgable.

[James A]

The ACB10s DO NOT like camber, you should set it at 0.25. Also, and maybe this is true with every race tire, ACB10s seem to get very hard quickly and that is it, forget doing laps with them. I used ACB10s for track days for a couple of years but have since changed my camber and stick with redials now.

Your camber settings look good for radials, I would stick with those.

I have experience with Hoosier A6 autocross tires and like them, I get on the order of 80 - 90 runs on them and that is terrific. About half way through their life I do start using Formula V traction treatment, the stuff really works!

[Ian7]

I'll offer this for thought, qualified first by saying I don't know what your intended usage is (fast track day, auto-x, full race, etc). Nonetheless,

 

A common mistake is over-tire-ing a car that weighs this little. Very often, ultimate grip is better with a slightly smaller contact patch that heats up to and stabilizes at a more appropriate temperature. Requires lot$ of testing of lot$ of tires, but thats part of the fun, right...?

[JBH]

My intended usage is fast track day. Most people like the ACB10s, but you are right, the camber should be close to zero. This requires changing the Dedion ears in the rear (not a big deal) and resetting the front. I ordered the ears, a new set of wheels and I got a good deal on a set of ACB10s so next year I'll try that set up. But while the car is set for radials, it seems a good time to try that set up.

 

Here's what I am thinking...I'll go with the Hoosier 185/60 and 225/50 front and rear. They should offer a fair amount of contact area - more than the CR500s while keeping the ratio of contact patch front/rear close to the CR500s.

 

I sort of understand the comment about too much tire - I assume you mean that in lightweight cars, it is easier to get heat into a small area. I am not sure I agree. Friction creates heat and as long as the weight over the contact area is uniform, the tire should heat up just fine. One just has to drive the car a bit harder

[slomove]

I have the ACB10 for the track and like them very much. But they are known to be pretty horrible on the road because they follow every rut and will lead you left or right depending on the curvature of the pavement.

For the front tires I run 1/2 degree negative as compromise with my radial road tires to no ill effect other than slightly uneven wear.

 

But then, I am not the fastest on the track and that gives me always a good excuse :lol:

 

Gert

[roll a 7]

I have run the ACB10s quite a few times on tracks and find them very slippery.

 

The best tire I have found for autoX is the Kumho V710. It is available in only one 13" size so I use them @ both ends. A truly great tire! When I get back onto a road course I'm sure this will be the best tire yet on my car. Some testimonials from road racers can be found on the Tirs Rack website.

[Boxologist]

the current standard for radial road race tyres is teh Hoosier R6.

 

Grassroots motosports had an issue a few month back and they had an untested i dea that the hankook z214 would do well on a lighter car like a miata. their test subject was a WRX wagon. I know a local autoXer using the z214 on his z3, he likes them. I know a bunch using the v710s, they are unwilling to commit to several sets of hoosiers per year. V710s in 14" are on closeout at tirerack. Attn steveT!

 

look into the SCCA D/E mod yahoo group. there's a nice thread thats active right now concerning camber angles and has someinfo air pressures regarding bias tyres.

 

from the guys who did my alignment, as little camber as possible is desirable and when i spoke to caterham usa (cody iirc) his advice and experience was to stay low with the camber, close to book tolerances, and go a little more on castor if possible.

 

my opinion is traction is traction and wider is better.

[Kitcat]

One of the auto-x tire manufacturers (Hoosier?) noted 2 years ago that going to v wide tires hurt times because the tires didn't warm up to operating temperatures in a typical 30"-60" auto-x run, followed by 15-25' wait for the next run, since the 7 is so light. I am sure on a road course that would be less of a concern.

 

When I spoke to RMSC about it when replacing my stock 195's they suggested going up to 205 and avoiding 225's, for the same reason.

 

My auto -x experience, in my Miata, was Hoosiers were best (tho v short -lived) then Kumos, then Toyo RA1's. But the Toyos stayed grippy, even after 8 years. The Kumos only had so many heat cycles then they were shot. Hence the 205x15 RA1's on my Prisoner wheels. They are a nice comprimise between all out track tire and a comfortable street tire.

 

JBH: 185 up front & 235 at the back would really imbalance my car and would cause huge "push" since the back would have so much more grip. Why are you thinking about such a large stagger (massive engine power?)

[JBH]

JBH: 185 up front & 235 at the back would really imbalance my car and would cause huge "push" since the back would have so much more grip. Why are you thinking about such a large stagger (massive engine power?)

 

This is my rationale - I am not sure if it is right and that's where I need some help.

 

The 175/55 and 205/55 CR500s that were on the car had a section width of 6.9" and 8.1" respectively. Thats a contact area ratio, front/rear, of 0.85.

 

Using Hoosier's section width data for the 185/60 and 225/50 tires, the ratio of contact area should be 0.83. If that is correct, I am adding slightly more grip in the rear.

 

So yes, going into the turn the car will push a little more. However, it has been my experience that I can break the rear end loose coming out of a turn if I apply full throttle, so by adding more grip in the rear, hopefully I can be more aggressive in exiting. Turn exits are where I tend to to catch and pass most cars. More grip in the rear also tends to favor trailbraking - something I like to do often (sometimes not by choice)

 

I do not think this tire combination would work at all for Autocross applications

 

If I am missing something, let me know.

[Kitcat]

I am no expert.

 

I do trust experience over theory and you already are running considerable stagger w/no ill effects so bumping it up a notch may work great.

 

At the track, I catch people, if I do, by a combo of late braking & quick turn in. I got nuttin out of the hole (93hp) so my car is set up differently than yours. I have 205x15 all around. I am toying with going to 225 in the back just to keep the tail more planted, esp in trail braking, which as with you, isn't always planned! Such instances have been the only times my car has suddenly wanted to go backwards, an experience I prefer to avoid:).

[ayseven]

I'm sorry, but I have no idea what you're talking about, and I am sure most people don't. But I do like to call in the experts from time to time when my expertise in anything is exceeded. So I would call Michelin, Toyo, and all the other TIRE MANUFACTURERS to ask them what they know about it. Quite a bit I would guess. I'm just a nobody, but I would consider tire pressure/temperature (the two are obviously linked) as a very large part of the equation not really explored much so far in the discussion.

 

As the English like to say: "I'll get my coat"...

[JBH]

I think most people know what I am talking about, but unless they have experience with Caterhams, and the tire options they are just guessing - this includes the experts.

 

The reason I run staggered width is because my car's weight distribution (with me in driver seat) is 642 lbs in front and 745 lbs in the rear. It is not a huge difference, but enough to warrant the use of wider tires in the rear. So the question is, what is the right ratio of widths front/rear - that's what I am trying to figure out.

 

I know the CR500s work really well, so in the new tires I order, I want to keep that ratio constant. It may work, it may not. But by trying, I'll get some important information that can guide my next tire selection. I know it's trial and error, but sometimes that's the only way to learn. If the car pushes excessively, I'll go to smaller tires in the rear.

 

You are correct about tire temperatures and pressures. I tried different pressure combinations front and rear on the ACB0s. After talking to Sasco about the Avons, they agree I was right in the ballpark for tire pressures (hot).

 

I ordered the Hoosier 185/60 and 225/50 so I will post results after I run them a bit.