[KobraKurt]

I'm really struggling with this decision. I love the "classic" look of 15" wheels but am extremely concerned about the limited number of tire choices. So, here's the question - what are the tires that will fit on 15" wheels? I'd love to have the Goodyears with the large "Goodyear" text but understand that they are sticky and won't wear well. Don't want the Goodrich logos.

If I can't find acceptable tires I guess that I'll go with 17"

Other factors effecting the decision - 302 EFI w/345HP, 3.55 rearend, no racing or autocross, 5 lug wheels

HELP!!!

 

[fredzo]

I'm glad you asked this question. I'm in the same boat. I like the open-spoke look where you can see the disk and caliper through the spokes of the wheel. I'm tending toward 17" wheels at this point.

I'm to the point where, when I see an interesting looking set of tires and wheels on a car, I stop and check the wheel/tire size.

This process can get a little obsessive, no?

 

[AJ]

I agree, I wanted my car to look period correct but the 17" wheels look a lot better in my opinion. So my car is now period correct with the exception of the 17" wheels!

Andy

 

[KobraKurt]

I'm more than obsessive at this point in time. This is a major decision for me.

I'll be going w/PSE Halibrands - with a deeper offset in the rear (getting the axle narrowed 2" on each side).

Your in Arlington?!?!? I spend a lot of time in the DC area on business. In fact, I'll be there the 17th thtough the 19th or 20th (hurst on my build time). Let me know if you'll be around and I can stop by to see your build.

 

[mn12]

I know Good Year Eagle GT II's come in 15" White letter. I currently have 235/60 15's on my Tbird

 

[fredzo]

You've got mail.

 

[SteveSS]

I'm a while from ordering yet, but this is also an issue I struggle with. I think "open-spoke" 17" wheels look great, but IMO they don't go with the Cobra body. It's totally a matter of personal opinion, but I like the 15" or 16" look with white-lettered tires. I think the poster car on FFR's web site has 16", and it looks great.

If performance is your first priority (you mentioned limited tire choices), I would think 17" might be better. If appearance is your first priority, 17" gives a modern look while 15" is a better match for the curvy Cobra body IMO. I think the choice of tires has more effect on the look, though. If you don't want BFG, then maybe 17" would be better.

 

[Dan Mitchell]

I struggled with this question myself. Ultimately it came down to how am I REALLY going to use the car (not what would I like to do with the car). For me I had to admit to myself that It would rarely ever see the track and street racing is out of the question. 99.9% of the time it would be a street car so good looks and comfort were the top priority. I ended up with the 15" BFG tires(good wear,good ride). If I do end up racing it I can get some cheap 17" tires just for the track.
Dan

 

[keithallenwilder]

Along the lines of the wheel discussion, I am wondering about springs. Will the factory Mustang springs raise the ride height of the Cobra because of the weight difference? Or, is it not a matter of the springs expanding but contracting that should be a concern.

 

[Gatorac]

A couple of things to consider when choosing wheels.

1. What brakes will you be using? Some brakes require larger wheels to clear the calipers. Some calipers stick out past the wheel mounting surface.

2. If you use 15" wheels up front, you must consider the lower control arm. If you use the donor control arm you are limited on the width of a 15" wheel. The FFR LCA will allow you to use a wider 15" wheel.

3. What style wheel will you be using? This is more personal preference as some wheels look better in the appropriat size.

Along the lines of the wheel discussion, I am wondering about springs. Will the factory Mustang springs raise the ride height of the Cobra because of the weight difference? Or, is it not a matter of the springs expanding but contracting that should be a concern.

No. First off, the ride height is adjustable. Second, the front to rear weight ratio is different on the Cobra, so the rear weight on the Cobra is pretty close to the donor. (Get the coilovers if you can. Adjusting the donor springs kinda sucks)

 

[RickWv]

Remember why some of us have to use 17" rims. If you go with 15" rims your choice of brake size is restricted.

Just something to think about.

 

[travissmithoh]

Kurt,

You've got all winter to pick out wheels!!

Personally I love the more modern 17" Cobra R wheels.

I plan to go this way... Someday... After I win the Lotto... And buy the kit...

Trav

 

[Ophitoxaemia]

ive got a set of both 15" and 17". no good tires for a 15x10 wheel.

no racing or autox???????? you are missing the best part

-james

 

[raceral]

Please listen to me.. I am a "expert" on this... Go with the 15's... with the 17's they ride like a buckboard... you hit a cigarette butt and you feel it.. now they handle on the track.. but go for the ride quality.. wish I had...

 

[Ophitoxaemia]

with the live axle the difference between the 17" race tires and 15" schwishy tires was dramatic. there is less difference between them now that i have IRS. partly this is because my 15"ers are much heavier than the 17"ers and so the ratio of sprung to unsprung weight is better.

-james

 

[Ozona]

With coil overs and 17" Cobra R rims, solid axle, FFR upper & Lowers the cars ride really well.

Amazingly so.

I'm not going with Cobra R's, but a different 17" rim. I chose the 17" due to brakes and tire availability.

 

[JM_OBRIEN]

Originally posted by raceral:
Please listen to me.. I am a "expert" on this... Go with the 15's... with the 17's they ride like a buckboard... you hit a cigarette butt and you feel it.. now they handle on the track.. but go for the ride quality.. wish I had...

Now the wheel size matters none with ride quality, it's the size tire you stick on them that matters. Naturally you can see that the 17" tire will have more of a contact patch than a 15" which will give a smoother ride and stick to the road alot better than the 15". Your ride will only be better on a 15" if you're using a tire with a taller sidewall than the one on the 17". Remember the sidewall is the determining factor, not the diameter of the wheel.

I would say go for the 17"er's and try to find a tire that you can live with, this will give you tons more options(brakes,wheels,tire types and possibly/hopefully a racing future)

Sorry to rant but I have much experience with all tire types and sizes in race/street cars.

 

[JM_OBRIEN]

Think of the tire size difference as comparing a lawn mower tire to an atv tire, the smaller tire can fit in more holes, bumps, roots, whatever. Now think of the holes, bumps etc. as potholes.....

 

[CRZN 427]

I will be coming to this decision soon also.

I have a couple points I want to air, and possibly clarify.

1. The 15" or 17" wheel will have different aspect ratio tires, won't they?
That should mean that the circumference of the tread should be about the same.
Thus, the shorter, stiffer side walls of the tires on the 17" wheel give a harsher ride where as the tires on the 15" wheel has more side wall rubber to absorb some of the road imperfections and improve the ride.

2. The traction from a tire is a product of weight and coefficent of friction.
Given that two tires, one a 15" and one a 17" on the same road surface and are made of the same compound, the handling charactistics (other than the above side wall stiffness) will be the same. The width (area, or contact patch) has no effect on the tire's ability to grip the pavement.
I understand that the shorter side wall will have less roll over and therefore possibly more contact area, but area is not a factor in calculating the fricton force.

I do, however, accept that the 17" wheel can support larger brakes.
This makes for a brake that has more mass and therefore will take longer to overheat and fade under similar driving conditions.
The dissipation of heat is the primary energy transfer in braking. The tires need to handle the heat as well as the brake pads and discs.
The larger wheel will also pass more air to aid in brake cooling and resist fade better.

For a street car it comes down to the choices in looks and cost.
IMHO the performance will be essetially the same.

 

[JM_OBRIEN]

As for your first point, the aspect ratio will be different of course if you going for a particular tire circumference, but if you want a better gripping tire WITH road comfort, you can do it just as easily with the 17".

And the contact patch of say a 255/45/17(26.03in tall) will be much greater than a 225/60/15(25.62in tall) and I promise most people would not be able to tell the difference in ride quality. You would be able to notice how sloppy the 15"er's were and you'd have a hell of alot more grip.

A good example, take two comparable tires like above, dip both in water, then on dry concrete and you'll see the larger contact patch, it's hard to make believer's until you can actually take a ride with the 17"'s then come back and switch to 15"s. Trust me, 15"er's are good to look authentic, and easier to set-up for drag racing but that's it!!