Wheel widths and tire sizes Q

[Slow old poop]

What is the minimum width rim onto which I can install 245/17 Hoosiers? Will they fit onto 7.5 in. wide wheels?

What is the maximum width rim onto which I can install 235/17 Toyos? Will they fit on 9-in wide Mustang rims?

The reason I ask is that I have 235 Toyos and 245 Hoosiers, one set of 7.5 in wheels, and am trying to figure out what size wheel I should order. I plan to use the Toyos for practice and the Hoosiers to set fast laps in TT.

I also gave four used Toyos to my buddy and crew member, Brent the Fabricator, who bought a set of 9 in. Mustang rims. He thinks those 9 in. rims are too wide for 235 Toyos.

For me, I'll just order a set of Mustang wheels for the 245s, but that doesn't solve Brent's problem.

Opinion?

Rich

 

[jtmcinder]

You can put the 235s on the 9s, but I would not put the 245s on the 7.5s. In the former case, make sure that the shop/person who does the mounting spends a moment or two cleaning up the rim before putting the new tires on. The issue is losing the bead-seal in a corner, so a clean rim is important. In the latter case, the 245s can be mounted on 7.5s, but they won't perform well at all.

7.5 is about as small as you want to go for the 235s, but even that isn't close to optimal. Tires are the most important thing, so you really don't want to skimp here. Make them happy. Put the 245s on the 9s (and, maybe, next time get 255/40/17s) and get some 8s or 8.5s for the 235s (which can later be 245/40/17s if you get 8.5s).

- Jtoby

 

[Slow old poop]

Thanks.
So, what's the ideal rim width for the 245-40/17 Hoosiers?
I'm ordering the wheels, so I want to get the right size.

Rich

 

[1stGenRocks]

whats the best size to have on 7.5 inch wheels? 225/45 is what i have now but i need to get new tires soon. mainly a street car with occasionaly autox and drag. i know 3 completly different setups

 

[jtmcinder]

245/40/17 Hoosiers want a 17x8.5

If you have 17x7.5, then I'd go with 225/45/17. If you have a 16x7.5, then you can wedge 245/45/16s on, since the extra sidewall will absorb some of the thinness of the wheel.

Personally, I still prefer 245/45/16 over 245/40/17 (even though they are the same width and diameter). I've found that being about to "tune" using pressures is more effective with more sidewall (although I've not copmpared the same tires in these sizes, back-to-back). Plus, I "only" have Koni Sports, which might be the best OTS shock, but they are damned skinny for a twin-tube. That seems to be why they aren't good at damping small imperfectives in the pavement, so a bit more sidewall seems to give me more grip.

If you have kick-tush shocks (as do ACM and Tevenor), then stop messing around and go all the way to 285/30/18. But if you only have a good system, 245/45/16 might be the best bet, followed by 245/40/17.

- Jtoby

 

[stealthTT]

Per Toyo the recommended size for their 235/40/17 is 8.0-9.5. I was told by some experienced road racers that you want to be one half size under the max size recommended for racing. So 9.0 should be good for a 235/40/17.

http://www.toyo.com/docs/tires/product_spec.asp?lpid=18968&name=Proxes RA-1

Hoosier (as well as racers) recommend taking the tire width and subtracting .5 inch. So a 245 is 10 inches wide. Subtract .5 inch and you get 9.5 inches. 17x9.5 is what I'd order.

http://www.hoosiertire.com/faqrr.htm

 

[mavisky]

So you're saying a 275/40-17 on a 17x9 +20 rim might not be the best bet for a car on GC's and AGX's

 

[jtmcinder]

9.5 is overkill for 245s. Even by your own rule of sidewall width minus .5, it would be closer to 9 than 9.5. And experience says that 8.5 is plenty for a 245. Why carry the extra unsprung and high-moment mass if it isn't going to add much if any lateral grip?

- Jtoby

 

[Ludachris]

Per Toyo the recommended size for their 235/40/17 is 8.0-9.5. I was told by some experienced road racers that you want to be one half size under the max size recommended for racing. So 9.0 should be good for a 235/40/17.

http://www.toyo.com/docs/tires/product_spec.asp?lpid=18968&name=Proxes RA-1

Hoosier (as well as racers) recommend taking the tire width and subtracting .5 inch. So a 245 is 10 inches wide. Subtract .5 inch and you get 9.5 inches. 17x9.5 is what I'd order.

http://www.hoosiertire.com/faqrr.htm

I was actually told the same thing by a guy who races in World Challenge. He asked me the wheel width and suggested 235 for a 8.5-9" wide wheel. He said to get the smallest width tire recommended for the wheel width which sounds strange to me. He must know a thing or two but I still don't know if I want to go 235 instead of the 255's I was planning on going with.

 

[drivemusicnow]

... There are some people who for whatever reason swear by the "skinnier tires wider wheels" mentality. The arguement goes something like this:

Less sidewall flex, you won't "roll" the sidewall under cornering and the tire will not flex from side to side.

Then some go on to argue that this makes faster lap times and a more predictable and smooth transition while breaking traction.

They don't tell you that this ends up with decreased tire life. They also don't say that while yes, the tire sidewall is extremely stiff when stretched, the smaller bumps then have to be completely absorbed by your suspension, or you'll lose traction.

I PERSONALLY think that running stretched narrower tires decreases overall grip, and would therefor increase laptimes (same car/driver/comfort level etc).

In the end it is what you are comfortable with. On a 9 inch wide wheel, I would put a 255 wide hoosier, and maybe up to a 275 wide toyo.

 

[stealthTT]

Doh! Monday morning math strikes again. There are 25.4 mm in an inch, not 24.5.

So it changes to:

235 would be 9.25 minus .5 = 8.75 8.5 or 9 would be ideal according to Toyo.

245 would be 9.65 minus .5 = 9.15 9 would be ideal according to Toyo.

Of course traction is more complicated than a nice easy rule of thumb. A wider tire will work with some cars and not others. You have to consider weight, springs, struts, sway bar, etc. when choosing the wheel width. The guys I spoke to with NASA prefer a wider wheel. It reduces roll-over, but decreases comfort.

If you can take a corner faster, you don't have to scrub the speed. So the weight of the wheel is offset by the increased cornering speed. Looking at NASA cars, they tend to have wide wheels and tires. I think the extra weight is negated by the improved cornering speed. A runner-up at Nationals in TTB, the 2700lb S2000 was running 275s on 10.5 inch wide wheels. He put buslengths on people in the Carousel at Road America.

But when you make a compromise for street driving, you have to throw comfort into the equation. Then you'd want a skinnier wheel so there was more give or compliance in the tire. You use the compliance in the tire to soak up the impacts that would dent a soft rim and cause a pounding to your backside. But if it's a dedicated track car like SlowOldPoops, you sacrifice comfort for performance. In his case I'd still get the 9inch wide wheel for the 245's.

I plan to buy Toyo 275's and run them on 17x10s, but I plan to use them on the street. if they were track only, I'd buy 10.5's

Another point to consider is that every tire is different.

 

[Evan K.]

I have 255 Toyo RA-1's on 8.5" rims. I just went out and looked at them and the tires look to fit perfect. The outer edge of the tread on the tire seems to line up directly over the outer edge of the rim.

I have 235 POS tires on my EVO rims. The tires are just a little too skinny to me. EVO guys usually run 255 RA-1's on there EVO rims with good results.

Remember to measure the tires you are actually going to use. Hoosiers run wide.