What Size Tire (Wheel Diameter)?

So, on my autocross/track car right now are 225/50r16 tires (which, I think are too much sidewall, lots of sidewall flex).

Looking at buying the next set, and wondering if I should change diameters? I have 7 in wide wheels (biggest I can fit up front without cutting and adding fender flares, which I'm not willing to do at this point) in 15", 16" and 17" sizes

Mustang 10 holes:
15x7, 20.7 lb ea \
225/45r15 tire weight 22lb
Total wheel/tire weight: 42.7 lb
Outside diameter: 23 inches

Enkei J10's (Currently on the car): 
16x7
16.7 lb ea
225/50r16 tire weight 25lb
Total wheel/tire weight: 41.7lb
Outside Diameter: 24.9 inches

Focus EAPs:
17x7
20.3 lb
225/45r17 tire weight 24lb
Total wheel/tire weight: 44.3 lb
Outside Diameter: 25 inches

225 is the largest I can fit on the car without changing anything else (read: flares), and for the Falken RT660 (which is likely what I'll buy for it) the prices between the three diameters are within $5 ($133-$138ea) of each other, so cost isn't a factor.

Pros for 15's: Better gearing (23" diameter vs 24.9", almost 8% smaller).
Cons for 15's: Not lighter with THIS 15 inch option, but other, lighter 15 in wheels exist

Pros for 16s: Current wheels are fairly light and I know the 225/50r16 fits
Cons for 16s: Difficult tire sizing.

Pros for 17s: Tire size availabilty 
Cons for 17s: Heavier, potentially larger diameter (though 225/45r17 is only 0.1" larger than the 16" option)

I *could* go to 215's to stay with 16 inch but would be giving up width to do so. Though, the section width (8.5" vs 9.2") is much less than the current 225/50r16 RE-71R tires, the measured tread width is *almost* the same (7.5" for the 215 Falken vs 7.6" for the 225 RE-71R).
Linky for 215's
Pros for 16 inch 215's: 3lb lighter weight (22lb ea), and gearing advantage (-5.2% from current 16inch package, down to 23.6" diameter
Cons for 16in 215's: Almost $15 more expensive, giving up width.

What are your thoughts about the different options here? Please let me know.

Linky for 15 inch Tires
Linky for 16 inch Tires
Linky for 17 inch Tires

17x7 with a 225. Done. It's a common size that will be supported in the future. 

In reply to mazdeuce - Seth :

So will the 225/45 R15

I support using the diameter for extra gearing and the cheaper tire options.

spacecadet (Forum Supporter) said:

In reply to mazdeuce - Seth :
I support using the diameter for extra gearing and the cheaper tire options.

Though here, it's.. Negligible cost difference.

mazdeuce - Seth said:

17x7 with a 225. Done. It's a common size that will be supported in the future. 

this but I'd look into the 225/40

In reply to bobzilla :

Would be nice, but it seems that the only options in that size are Hoosier R7/A7, and the new Continental 200TW, which are almost $100 EACH more expensive than the 225/45r17 Falkens.

In reply to TXratti :

Fine.... since you won't cut the fenders and go with 8.5" wheels and 245's... 

215/40 or 45/17. I was going to suggest seeing if wider and shorter (like 235/40) could be made to fit, but on 7" wheels the functional difference between 215s and 225s is probably negligible and at least offset by the better gearing and less sidewall compliance (and going wider is even more pointless). 215/40 is even shorter than your 15" option but a bit more expensive, 215/45 is still almost 1/2" shorter than the other two options and in the same mid-$130 range. The 215/40 would probably wear the best also, not sure if that's enough to offset the extra $25 per tire but probably at least close.

I think the big thing would be the gearing difference between them. Is the 15" going to make the gearing too short? 

I'd lean toward the 17 probably, just because I like the bigger wheels look. If you went 17", could you stuff a 235/40 under there by rolling the fenders, instead of a cut/flare? Since it's shorter than a 225/45? Or raising the car a touch to more tire under it? That's what I'd be looking to try to do.

z31maniac said:

I think the big thing would be the gearing difference between them. Is the 15" going to make the gearing too short? 

I'd lean toward the 17 probably, just because I like the bigger wheels look. If you went 17", could you stuff a 235/40 under there by rolling the fenders, instead of a cut/flare? Since it's shorter than a 225/45? Or raising the car a touch to more tire under it? That's what I'd be looking to try to do.

 

The ultimate answer is wider wheels and rolling/ cutting fenders. 225 is the widest that fits up inside the wheel well, it BARELY clears the fender as well as the strut. Now that I think about it, the Falkens run so wide, they might not fit without pushing the wheel out a bit anyway. 235/40 MIGHT work, the car fits fairly tall anyway, I'd just not be jazzed about a 235 on a 7 in wide wheel. This is almost a stop-gap until I pick the right size and commit to chopping fenders and going wider.

TXratti said:

z31maniac said:

I think the big thing would be the gearing difference between them. Is the 15" going to make the gearing too short? 

I'd lean toward the 17 probably, just because I like the bigger wheels look. If you went 17", could you stuff a 235/40 under there by rolling the fenders, instead of a cut/flare? Since it's shorter than a 225/45? Or raising the car a touch to more tire under it? That's what I'd be looking to try to do.

 

The ultimate answer is wider wheels and rolling/ cutting fenders. 225 is the widest that fits up inside the wheel well, it BARELY clears the fender as well as the strut. Now that I think about it, the Falkens run so wide, they might not fit without pushing the wheel out a bit anyway. 235/40 MIGHT work, the car fits fairly tall anyway, I'd just not be jazzed about a 235 on a 7 in wide wheel. This is almost a stop-gap until I pick the right size and commit to chopping fenders and going wider.

Buy once, cry once. I'd go ahead and just decide how much wheel/tire you can use for class or power level and commit to flares. 

Play with your various wheel width and offset options on https://www.willtheyfit.com/.  If you take measurements off of your current setup (distance to fender, distance to spring, hub, etc) and have your widths and offsets handy you can find some other creative solutions to fitting more tire/width.  

17's are likely your easy button in terms of cost and options as others have stated.  

z31maniac said:
Buy once, cry once. I'd go ahead and just decide how much wheel/tire you can use for class or power level and commit to flares. 

True, but tires are consumables and these wheels I already have... could buy something now and then go a different direction later. 

Of note, the lower profile options with the 23" diameters put my theoretical top speed at ~145mph in 5th, which I doubt I'd get to, even at somewhere like Road America.  (250hp/2900 lb)

TXratti said:

z31maniac said:
Buy once, cry once. I'd go ahead and just decide how much wheel/tire you can use for class or power level and commit to flares. 

True, but tires are consumables and these wheels I already have... could buy something now and then go a different direction later. 

Of note, the lower profile options with the 23" diameters put my theoretical top speed at ~145mph in 5th, which I doubt I'd get to, even at somewhere like Road America.  (250hp/2900 lb)

I would definitely want the lower gearing for a track car. I was specifically think of AutoX where the lower gearing might bouncing off the revlimiter or a shift to third on a faster course. 

In reply to z31maniac :

True. It's still fairly up there. In the current gearing, 61mph, vs 66mph at the top of 2nd (the difference between 23in diameter and 24.9 in diameter). Which could make the difference, on a fast course. I just remember my 6 Spd NB miata... A data-verified 53mph top speed in 2nd gear. Forever shifting to 3rd.

On the one hand, 225/45R15 is one of the only smaller sizes of high performance tires with availability that isn't (currently) in decline. On the other hand, no tire size for 15 inch, let alone 16 inch, wheels will have the long term availability of numerous great tire options as the 225/45R17.

In the short to mid term, the 15's would probably be great. However, I'd be prepared to make the change again to 17's (or even 225/40 18's) in the long run.

I mean, in anything that isn't 200tw limited, Spec miata 205/50r15 takeoffs (effectively 225 street car size) are cheap and fit on the 15x7s. And spec miata is going to be around for a while I'm sure.

Yes, if you can run R-Comps, 15's should also continue to be pretty good for the foreseeable future.

Yeah the more I think about it, the more that sounds like Used R comps on the 15s for the track, and something like a Continental ECS on the 17x7s for street driving/ wet track days.

I vote 15s given this limited info.  But why not 15x8 (or more)?  225 on a 7 seems like a bit of a waste.  I'm guessing that is a next step?

In reply to ProDarwin :

It was partially a thought towards 'How much can I fit and not cut up the fenders?'. I think, after talking to some folks, I can fit 8 in wheels in an et35 (or et40 and 5mm spacer) and not-balloon tires (probably 215/225 max width). But mostly it was the fact that all of the wheels that I have are 7 inches wide.

ProDarwin said:

I vote 15s given this limited info.  But why not 15x8 (or more)?  225 on a 7 seems like a bit of a waste.  I'm guessing that is a next step?

Yeah, I ran 205 RComps on 15x8s on NA track rat.

In reply to z31maniac :

R comps run wiiide. 205 Hoosiers and Toyo RRs are the same width as 225 street tires.

Very likely could be a waste, wanting to run more tire and trying to shake the ES craziness where they put 225's on a 6in wheel. Which works (is faster than 205s), but is a very corner case in terms of tire sizing.

225/45r17 is a common OE tire size for 17x7 wheels, but is different dynamically than 225/45r15