333pg333

I'm looking at getting a parts pile for my trackcar and of course the obligatory bodykit comes into it. Now if you have a bodykit of any sort you naturally have to fill those new bigger wheel wells with wider wheels and tyres. Most of the big hp/tq race 951s seem to have 10's and 12's or thereabouts. However it has been brought to my attention by another poster that he feels that by going much wider than we fit on our current road cars you get beyond the point of diminishing returns. With increases to frontal drag area and something about Laminar flow and under advisement of a suspension guru, my fellow poster was advised against going up to these bodykits and commensurate wheels and tyres.
So what's the opinions out there? The car will obviously be lighter (by how much I don't know yet) and will have a very high powered engine installed. Is there an issue with not getting enough heat into the tyres to justify 335's at the rear? Ideally I would like 11's up front too but not sure if that's possible with the particular kit I'm thinking of.
Please comment.

Duke

So winter has finally arrived ey

333pg333

The trackcar won't be ready for sometime, but I was gathering stuff along the way and I found a good, not too expensive bodykit that would at least allow me to put on wider wheels. So I just wondered if there were any varying opinions out there and better yet some of the racers out there like Hans who might have done some half decent testing of temps, trackwidth, drag even???

anders44

I run 295 cups now 333pg333, they actually get plenty hot on our tight tracks. I was worried about 335/345 myself, but I think it should be good, and hey, worst case, you can run summer tires

Ill bring a pyro on next trackday so i have exact numbers

Jason Judd

My understanding is that, if you have the HP, get as much rubber under you as you can!

bigdeano

If you go wider and feel you've diminished in power... just add more power! Good problem to try to create for yourself in my opinion!

Dave951

If you really want to answers to some of those aerodynamics questions you have in your head your going to need access to a wind tunnel. Then once you collect some data related to the desired setup (You'll need someones car that already has the exterior mods you want) you can compare them against the factory data. The factory data should be available somewhere. From this you should be able to determine some effects of the increase in frontal area...etc

Granted that is a pretty difficult task to accomplish, so then the next best thing is see what worked for everyone else. Hopefully someone who has attempted to test these effects will chime in.

Just thought of something else. If your an expert clay modeler and really handy you might be able to design a "water tunnel". Make a model of the standard and kitted bodies. Definitely easier said then done. Then you'll need something to propel the water like a small electric boat motor and something to use so you can watch the water flow around the model bodies. I believe a stream of dye would work for this. Taking velocity measurements...etc and collecting and comparing. Just a thought though its still pretty out-there.

gt37vgt

ah no to resonably accuratly extrapolate the difference in drag. One only needs to log engine parameters at 2 or three given cruse speeds with the 2 different wheel and body set ups.
the tps and manifold pressure required is genrally directly proportainal the the hp being made .
so if there is a signifiant differnce in drag you will require more manifold pressure to maintain a given cruse speed .
so the faster you can do this the better as it is not linier.
Injector duty cycle is another good power comparitor providing you AF ratios are consistant

gt37vgt

also just some real world accounts of lap times and tire temps when making big changes would be a good giude.

gt37vgt

also i think how long you are able to realisticly stay on the track is a big factor if you think you would spend 4 solid hrs on the track massive rubber would make more sense . I'f you want to be schooling feraris after 2 laps you will need a smaller tire that is already up to temp

N-Dub

In karting we work to not have too much rear end grip, as it is too stuck and bogs more on the motor stealing power that you could be using to power out of the turn. But I think your race car will have more than 30 hp but can't pull 4 lateral g's. . .

Slantnose!

Not the same thing here...
Anyway, my son has a FRC Corvette (350hp/3100lbs & 4:10, etc.) and can tell a difference between the 315's & 335's...has much better grip/wear & quicker times with the larger size at the rear.
However, likes running the 295's vs. 315's up front for better feel/response though.

gt37vgt

also remeber this simple truth.
the surface area of the tire contact patch is a function
tire pressure and wheel load only.

tire width has no impact on surface area of the contact patch.

tire width will change the shape contact patch but not the surface area .

evil 944t

I agree with your 1st point.. but..

How so? We are talking about a car tire, not a motorcyle tire. A car tire 1" wider will have a 1" wider contact patch, The shape stays the same..

Nothing but pressure/diameter(incease or decrease the diameter) will change the contact patch..

333pg333

I'm out of my tread depth here but also what about if you don't have enough traction due to too narrow tyres and then minimise your contact patch as you skip, bounce, and slip? Whereas if you had greater grip allowing you to put more power down then you are increasing your contact area by comparison?
Obviously there is a point of diminishing returns and as Adam says you won't get enough heat into the tyre to warrant it's extra size but at some stage I think my above point should be true....I think
As to what point that is, I don't know. I'm not about to make clay models and do wind and water testing. Guess I'll have to see what other high hp/tq racers use out there and go from there.