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-   -   Optimal Road Racing Tire Width (https://www.rx7club.com/race-car-tech-103/optimal-road-racing-tire-width-837147/)

Irentat 05-02-09 07:38 PM

Optimal Road Racing Tire Width
Hey all,

I have an FC but don't want to limit the responses to that model.

I understand optimal tire contact pressure but it seems that a wider tire would be more beneficial even if you lower the optimal contact pressure.

Bottom line, what is considered the best width for our cars in road racing conditions? Let's not consider cost but only traction as our final factor.

I have seen others on this board with up to 335's but know many others run 245's competitvely.

Any feedback is accepted.


Gene 05-02-09 09:47 PM

What kind of racing are we talking about? There are often class restrictions.

Irentat 05-02-09 10:39 PM

No class restrictions.

jgrewe 05-02-09 11:21 PM

You are only changing the shape of the contact patch with wider tires if they both run the same pressure. Wider is better in general until it rains. With no restrictions, get some slicks then you look at the temps. We run 9.5 wide slicks and get them over 200F so we could use bigger if we were allowed.

alex.hay 05-03-09 05:32 AM

yep thats right... the best racing tyre is the biggest one that you can get up to optimal temp, if you can get a 305 slick to the right temp it will provide alot more grip than a 240 slick, but if you cant, and your not running at optimal temps, you will have less grip than maybe a smaller tyre that IS the right temp...

this is why you see Time attack cars running a smaller tyre than in road racing, as they can only get so much heat up in one out lap for their hot lap...

Irentat 05-03-09 05:30 PM

So I am running 245 F / 255 R and CAN get them up to proper temps currently. Does this mean I should try and go wider next time I need tires?


speedturn 05-03-09 07:33 PM

Your general question about tire width is missing the importance of wheel width. Racing tires are made to fit on a certain width rim. The tires and rims must be matched to work together.

Most racing classes will specify a certian limit on wheel dia and width, and then the racing tire manufacturers will design a tire that works best with that size rim.

Also, from racing tire manufacturers there are choices of tire compounds available. The soft tires are fast, but they don't last long, so the cost per lap is very expensive for them. If you run lots of laps, you may overheat them. If your suspension or chassis is not balanced, you may run a softer compound on one end and a harder compound on the other end of the car. The ass heavy Porsches I race against sometimes run a Goodyear 430 hard compound on the rear, and a soft 210 compound on the front. If the tire temp is not optimal, then you need to choose a different compound, or adjust your driving style to make the tires you have work.

mustanghammer 05-03-09 09:10 PM

Ignoring the rules from all sanctioning bodies the answer is simple: The biggest tire and wheel package that can be fitted to the car. I have never met a racer that said he/she had enough tire under their car.

Black91n/a 05-03-09 11:39 PM

Yes, but a wider tire creates more drag, so under some conditions, especially if its a track with lots of straight and/or the car has low HP, then a narrower tire with less drag can be faster. The stopwatch is the only real way to tell.

wrankin 05-04-09 07:30 AM

To second the above post - I seem to recall a discussion a while back over on www.improvedtouring.com about just this subject. One poster made the comment that on certain tracks he was faster with a slightly narrower tire (205 v. 225 in this case) but only on specific tracks. He also did not specify which tire brand he was testing here, but I suspect it was a harder compound and he was having problems getting the 225 up to temp on those tracks.


Irentat 05-04-09 10:14 AM

Originally Posted by Black91n/a (Post 9179174)
Yes, but a wider tire creates more drag, so under some conditions, especially if its a track with lots of straight and/or the car has low HP, then a narrower tire with less drag can be faster. The stopwatch is the only real way to tell.

OK, I assume that my 400 RWHP is sufficient and is confirmed by my tire temps getting up to factory reccommened level (maybe even to the upper end of their level). I will consider how wide I can actually go then.

wrankin 05-04-09 12:17 PM

Horsepower and car weight are definitely big factors - impacting your ability to heat up the tires. Different tire compounds also affect this (obviously). All of these will go into determining the proper tire width as well as the possibility of going with a staggered setup.

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