Auto X Slick Tire : temps vs width?

[MrGas]

Ok, I am putting together My Solo Vee. My question is: would wide tires 9.5 / 11" get up to temp in a Auto X run . lets assume Hoosier R25B compound. Or would a narrower tire set up come to temps Quicker? (7 / 9") Thus giving more traction? ie quicker run. The car will be under 1000# w driver. In my DOT tire experience 1900# car could road race 20 minutes in AZ 100 deg heat and not have the tires come up to proper operating temps. Good : they lasted for ever. Bad : less sticky. Opinions ? options? I have a wide variety of wheel to use all 13" . 5.5" set .6" Pair. 7" set. 8" pair. Thanks in advance. Greg.

[Albatross]

Seems to me the only good answer is to have your pit crew take tire temps immediately after completion of a run...Don't dilly-dally through the paddock and then....take the temps. Take'm immediately at the end of the run! What tires do the fastest guys in your class use. Begin there.

[tonychilton]

I run either a 75 Lola supervee (1060# with driver) or a home built Amod 1400# with driver also from the 70s called the bandit (1400# with driver).

I run some autoX and a lot of hillclimbs

In the Lola I went down in size from 12s and 10s eventually to what it was designed for 8s and 6s. In a two mile hill climb on r25Bs I could finally get heat in the tires and some heat in autoX. Traction increased and times decreased dramatically over wider tires.

I bought the bandit last spring and ran it this summer as it came with 12s and 10s . They never built up much heat at all. The tire came with sticker Avons but they were apparently ages old as they were hard as rocks. I got some new used Avons (Formula Atlantic take offs) and while it sticks much better now there is still little heat getting into the tires even with all the wing. Not sure what I'll do but it may be predicated on the tires I can get.

Upshot : I'd start with narrower tires and only go to larger ones it seems you are overheating them or loosing traction. I also think the Avon hillclimb compounds are better than the R25B but they cost significantly more.

[Jnovak]

Higher tire temps are way more important than wider tires. The cf of tires can increase by over 25% with tire temps.

[mwizard]

I saw a couple of FV cars at Nationals and they ran 10+ in wide tires front and rear. In the FF 25B's heat up enough to grip in about 3 turns and we use a slightly smaller tire on the front. , but we have major suspension advantage over FV cars. You may need to do your own experimentation unless a FV guy chimes in.
Mark

[Barry Ott]

[QUOTE=....My question is: would wide tires 9.5 / 11" get up to temp in a Auto X run . lets assume Hoosier R25B compound.... [/QUOTE]

Well, I'd say it depends

Obviously, getting good data is tough because you can't stop to check temps in the stop-box so you end up taking data when you get back to grid, which is really too late. I've always assumed that the numbers I read are lower than the "right" numbers. Another big variable is if you have a co-driver, which I almost always do. Jeff Speer from Hoosier told me that R25B's want to be between 110 and 140 degs. For my car ('95 VD FF, 7.0 fronts and 7.2 rears, 1104#'s with driver, two drivers, PPIR surface) I regularly measure high 130's during summer events. I am much more likely to cool my tires than cover them to keep heat in. Cool spring and Fall events are different, I usually cover the tires to keep heat in, especially if it's cloudy and/or breezy. For my car, I would run bigger tires if it was practical (but it's not).

Barry

[Darth Vee]

I run 71/2 fronts and 9inch backs on 20 inchers. I'm not a championship driver, I just have fun driving but try to run as fast as I can, finished last this last Nationals, not fast enough. Still had fun. Great bunch of guys in Cmod. I run a Lynx B with a caracal rear.

[Lynn]

Most SoloVees use the following Hoosiers in R25B compound:

Front: 20.0 x 7.5-13 A2500 on 8" wheels
Rear: 20.0 x 9.0-13 A2500 on 10" wheels

I have been told that 20.5 x 7.0-13 A2500 on 6" wheels on the front and the 20.0 x 7.5-13 A2500 on 8" wheels for the rear will result in more heat in the tires. I don't know of anyone who has tried it. These are the sizes for wet tires, too.

There are Avon tires in similar sizes, but they are expensive and very hard to get.

BTW, the minimum weight for a SoloVee with driver is 1000 pounds.

[no-cones]

Happy Holidays All.
Tony, which Avon compound are you using?
I might be able to help with this discussion, because I have been planning to do some testing.
I am going to purchase the Autocross Storm package with the gopro and test some tire combinations. Here is my plan.
In April when I start to run again I am going to use my current tires Avon A11 9x20x 13 front and 10x20x13 rear. Then after two events switch to a very fresh set of Avon A11's. After a few events switch to a comparable size Hoosier 25b. Depending on time of year purchase a new set of which one proves to be the better tire.
I would really like to have a set of A15's but these are very difficult to get and require some advanced planning. I have also been warned they will only last a few events.
I have used both Hoosier and Avons and have made some personal observations. The Avons work well here in Florida when the weather is hot, their side walls seem stiffer than the Hoosiers. However when the temp drops there performance decreases dramatically.
I will be glad to share this data with anyone that is interested. Please keep in mind the numbers might not be the ultimate because this driver has quite a few miles on his odometer.
Richard

[MrGas]

Thanks every one for the responses! So it is sounding like my theory is correct about narrower tires and heat. I am new to Slicks not to Racing. Any Pics of said set ups? and I like to see vee pics any way! this is my strart a Lynx B copy. last owners pic.

[Neil_Roberts]

A major factor is how often you plan on buying new tires. New R25s are good to go right off the trailer. As they get older, it takes more heat to wake them up.

[tonychilton]

I'm using A11s on the Bandit. I have yet to understand the Avon numbering system. It appears to be figured out by incantation.

[-pru-]

I'm using A11s on the Bandit. I have yet to understand the Avon numbering system. It appears to be figured out by incantation.

I agree!

I found a Avon compound range PDF via Roger Kraus Racing (sorry, could not attach due to forum size limits).

At very high level, I understand the following regarding compounds from the different suppliers :

Avon ~ Hoosier ~ Goodyear
A11 ~ R35 ~ R160
A15 ~ R25 ~ R120

From what I have read/heard, the Avon A15 is closer to a slick version of a Hoosier WET or Goodyear R80 WET in terms of compound.

[mwizard]

I agree!

I found a Avon compound range PDF via Roger Kraus Racing (sorry, could not attach due to forum size limits).

At very high level, I understand the following regarding compounds from the different suppliers :

Avon ~ Hoosier ~ Goodyear
A11 ~ R35 ~ R160
A15 ~ R25 ~ R120

From what I have read/heard, the Avon A15 is closer to a slick version of a Hoosier WET or Goodyear R80 WET in terms of compound.

What does this mean? I have not seen Hoosier wets on any scale of stickiness.
Mark

[-pru-]

What does this mean? I have not seen Hoosier wets on any scale of stickiness.
Mark

Mark,

For the answer to that question, I recommend calling Roger Kraus. They can provide durometer readings for both the Avon A15 and Hoosier WET.

Take care,

[formulasuper]

Not an autocrosser here but have always wondered if roadracing rain tires with their super sticky soft compound would work for the short duration of an autocross run on dry pavement. Surely it's been tried, right?

[mwizard]

Mark,

For the answer to that question, I recommend calling Roger Kraus. They can provide durometer readings for both the Avon A15 and Hoosier WET.

Take care,

Krause and Co are a bit busy this wkend with the 25 hrs at Thunderhill.
Mark

[Tuiguy]

For a 900 lb autocross formula car Avon A15 cross ply tires work very well, They are comparable to Hoosier 25 compound, and wear about the same. Hoosier wets are heavily grooved, which reduces footprint and works them harder in the dry. They are slightly softer and tend to grain or overheat in dry conditions even on a short 30 t0 40 second autocross course. Best for wet, but not a great choice for dry.

[no-cones]

This post is to share the date from a Saturday practice session and a Sunday event in central Florida. Air temp both days reached the mid 70's track temp 66F Saturday and 85F Sunday. These were the temps when I ran.
Saturday was a practice with 6 runs on a 40 second course Sunday 3 runs on a 50 second course. Note. Saturdays course had no real left turns
The data was collected using Solo Storm. I would be happy to share the logs if someone will tell me how to post them.
Car Solo Vee. Avon tires A11 compound bought used with full rubber beginning of last season. Front 9x20x13 Rear 10x20x13 tire pressure 12.5F 13R
Saturday max lateral 1.32g right turn
Sunday 1.66g right turn 1.16g left I might be better at turning right than left or a calibration issue or it was the turn.
Will be putting a fresher set on for next Sunday's event
Hope this helps and would be glad to keep sharing. Richard

[mblanc]

max lateral
Sunday 1.66g right turn 1.16g left

I would not look at 'max G' at all. Don't pick out one or two little peaks, and pat yourself on the back for that peak number.

Instead, I would look at the graph of the G line, and analyze it.

I'd look at how high it normally is during most of the corner, and concentrate in increasing that sustained avg #, for a longer period of a time.

pick a number, (1.4?) and compare, how LONG are you holding at or above that G ?
what causes the variations ? surface ? driver ?
what can you do to improve it: line? more coasting? more throttle?

What about where you are not WOT, and the G is low? why are you slow there?

[no-cones]

I was in no way patting myself on the back but just trying to provide helpful data that is relevant to the topic. Hoping this info will provide useful info for someone selecting tires and how they behave under different conditions.
Yes I looked at all the things you suggested but was uncertain which number I could post that would actually be useful. I will be glad to post the whole log if it would help but need to know how.
R

[MrGas]

Thanks No-Cones. lmk what info you get on the new set of tires.