What is the best wheel/tire size to run for optimal road track performance?

[sixty9boss302]

Hey guys i need your help. Especially anyone involved in road racing. I'm looking to buy new wheels/tires and I'm having trouble deciding on what to get. One option is to get 17's and slap some 315's on the back because that looks awsome. The second idea I had was go up to 18's and wrap them in 275's.

What I really want to know is what is the best performing (road course not drag strip) wheel size and tire size setup? Not looking for what brand to buy but what rim size and what tire width an ratio will handle best?
Thanks.

 

[autoXr1]

1. Sometimes class rules dictate which tire/wheel size you will be running.
2. Sometimes suspension/wheel well/brake system clearance issues are at hand.
3. Front/rear weight distribution, power-to-weight, and overall weight influence this.
4. Suspension plays a significant part.
5. Rolling resistance influences decisions.

Bottom line, you ask 50 different road racers what they like to use on their car, you'll likely get as many answers. That said, GENERALLY speaking....for Mustangs...use the widest wheels that will fit within the wheel wells, then use the narrowest tire that is recommended (by the manufacturer) to fit on that wheel. This method GENERALLY results in the best tire sidewall support with minimal rolling resistance and the flatest contact patch. Wider is not often better when it comes to tires...it really depends upon if the wheel can support a flat contact patch and offer good sidewall support.

For softer, "sport" suspensions, a large diameter (18-19") wheel is generally desired. For much firmer "race" suspensions, a slightly smaller (16-18") wheel is desired. The tire IS part of the suspension...this is where tire sidewall firmness, aspect ratio, and especially tire pressure play into it.

Sorry, I am not going to get into a discussion over which specific tire/wheel combo is best for YOUR car. Just me....

 

[sixty9boss302]

double post

 

[sixty9boss302]

In that case critique my options:
18 x 9 inch rim with...
265/40/18 = .6 in. larger diameter than stock
275/35/18 = good diameter but from what you said i think this might be too wide
17 x 9 inch rim with
265/40/17 = .4 in smaller diameter than stock (don't like goin smaller)
275/40/17 = perfect diameter but too wide?
and 17 x 10.5 inch rim with
305/35/17 = .3 in smaller diameter than stock
315/35/17 = perfect diameter but too wide?

how wide is too wide on the front?

sorry for all the questions but its hard to find this info so i need experienced guys suggestions.

 

[sixty9boss302]

Just thought about this alot. I think I have to go with the 17x9's and 10.5's. 255/45/17 in the front and 285/40/17 in the back. The overall diameter of each is almost identical and its only slight larger than stock. Only question now is, will 285 be too skinny on a 10.5 inch rim???
Thanks

 

[Michael Yount]

AutoXr provided a good overview. You need to be willing to experiment and see what works. When I was racing SCCA, my car actually benefitted from changing between two different size tires depending on what track I was running at. So there's not one simple answer to the question.

What I'd add is that the weight of the wheel/tire combo has a big impact on handling (unsprung weight) and on acceleration/stopping. All else equal, the lighter the combo, the better -- and most folks (especially street cars) don't even think about the weight of the wheel/tire. If you look at most tests, the lightest combos available and the best acceleration/handling times come from 15" or 16" combos. This is largely due to the fact that once you get to the 17" combos the weight starts going up. This assumes that you're comparing the same section width tire/compound and the same width wheels simply in different diameters and aspect ratios. However, there is a trade off. If you're serious about road racing (multiple laps) you're gonna have to do something about the brakes. And the benefit of larger brakes in front usually is worth the trade off of going to a larger diameter combo to clear the rotors. If you're autocrossing, you may come up with a different answer - 45-60 seconds worth of hard use on the brakes at lower speeds is totally different than 45-60 minutes worth of hard use on the brakes at higher speeds. Go to a NASA or SCCA regional event; hang around the Mustang/Camaro guys and see what they're running. Decide what you're gonna try - but be prepared to experiment. It's highly unlikely you'll stumble onto the best combo the first time out.

 

[sixty9boss302]

Thanks for the advice.

 

[autoXr1]

"...285 be too skinny on a 10.5 inch rim???"

It's just about right. My 285 VictoRacers are on a 18 x 10" wheel. That said, check with the manufacturer. Sidewall construction can vary significantly from one manufacturer to the next. For example, some sizes of Kumho VictoRacers are "recommended" for a relatively narrow rim and tend to overhang the wheel a bit....which is a bit odd for a roadrace tire/wheel combo. Many references out there suggest going roughly 1 inch narrower treadwidth than wheel width. So, obviously, there are no "set-in-stone" rules. Again, pick out a few tires you think you would like to try, then research the recommended wheel widths for each tire.

 

[RickyB]

on HPTV on Joe's stang he used new brakes from Roush 14 inchers ...but be prepared, it was about 3 grand for the setup

 

[sixty9boss302]

I'm not worried about brakes yet....road racing for me is a long long ways away. It's like an ultimate goal to shoot for. What i should have said i was looking for is a setup good for tearing around curves on back roads. I've done alot of reading and I understand that a tire can be too wide and cause sloppy handling. It seems like a lot of people on this site just try to squeeze the largest tire they can on a rim. I want to konw wut the best relationship is for handling. I think i am gonna buy 18 x 9 ' s and get some 245/40/18 rubber. I like to hear everyones advice on this.

 

[Michael Yount]

Keep in mind too - the best setup/wheels/tires for "tearing around curves on back roads" will likely be entirely different than the best set up for a properly maintained road racing circuit. You encounter all kinds of different pavement conditions on the street which call for a much more compliant/supple suspension than is needed on the track. Optimize for one, and you'll compromise the other. Just for grins, I'd be curious what the 18" combo your considering weighs compared to 1) what's on the car now and 2) a really light combo.

 

[sixty9boss302]

I had thought about that too:
Stock weight is 48 # per wheel/tire.
18's w/ 245 would be 51 # and my other option
17's w/ 255 and 285 would be 56 # and 60 #.
Now i'm curious what a really light combo would be.

 

[Michael Yount]

As combos go, that 18" is pretty light compared to stock. Do you have wheel/tire weights separately? Starts to let you see what impact size (wheel and tire) are having on things.