Front to Rear Tire Size Ratio

[DocDirk]

Hello all you handling enthusiasts!

I'm finishing my WC build and am wondering about the size ratio of 265 15's front and 295 15's in the rear. When the kit first arrived I had thought the fronts were 245's and talking to some folks they said the ratio 245/295 would impact the handling in such a way as to give the most neutral cornering characteristics. Now that my eyes have recovered and I noticed the fronts are 265 I'm wondering....is there an accepted "optimal" ratio between front and rear sizes to avoid pushing or oversteering, etc. in turns? This is my first real performance car and my ignorance is vast.. (and there seems to be a lot of room for a bigger tire in the rear if I were to choose to push it to 315 or 335... )

Thanks ahead of time for responses

Dirk

[WildBill3]

Hi Doc I know how you feel.We run a 295/315 setup that corners well.And yes I think 335's will go if we have the right offset on the wheels allthough we are on 18's.But We still have alot of room with the tires being so short.I have never ran anything smaller than a 275 on the front.Ther are alot of other factors that get a well balanced car mostly in the set up of the suspension as well as driver input.Good hunting...WB3

[Larry N Johnson]

Dirk,

You did not say street manners or track manners.

My personal experience is that you want similar diameter tires so the car sits level, not too much rake. With 295/50x15 rears, I personally like 235/60x15 fronts. Close to the same diameter. You sort out handling with tire pressures, sway bar rates, spring rates, etc.

These are Goodyear Eagle GT II upon arrival:


Track tires same idea (see Roger Kraus Cobra Tires):
26.5x10-15's rear are 26.7" diameter
and
26.5x8-15 fronts are 26.2" diameter.



Depending on you roadsters front/rear weight bias, anti-sway bars, spring rates, are rear suspension setup, tire pressures vary. On my FFR at 55% rear weight bias, IRS, sway bars, and 500/500 lb/inch springs front and rear, we have found that 24 psi front and 25 psi rear on Goodyear racing slicks provide superior grip in corners.


Each car is different so my experiences will differ from the next person's.

Good luck sorting it out.

Larry

[Stroked 66]

Larry,
Do you know where to get a set of the GTII's now? Seem like everywhere I look they are on B/O. Thanks, Tony

[Larry N Johnson]

Originally Posted by Stroked 66

Larry,
Do you know where to get a set of the GTII's now? Seem like everywhere I look they are on B/O. Thanks, Tony

Tony,

Have to make some phone calls. I did a Google "Goodyear 295 50 15" and got several sources. My favorite, TireRack.com is back order. The others are harder to check, have to phone them I guess. They are around and come and go. They can be had...patience and persistance. Best of luck; do not give up.

Larry

[DocDirk]

So as I understand it...it's too simplistic to say that any given set of tires must have a front to rear ratio to perform well... the jist of what I'd been told was that going to 335's on the rear would cause the car to "push" in turns, wanting to go straighter than a smaller rear tire would. I see your point on diameters, Larry, thanks. I'm just wondering if I could increase the rears to 335 for straight line traction and (given the identical setup) not cause a net loss of decent street cornering manners.... and yes, I understand no such question has a simple answer!

Thanks and ride safely

Dirk

[Larry N Johnson]

Originally Posted by DocDirk

So as I understand it...it's too simplistic to say that any given set of tires must have a front to rear ratio to perform well... the jist of what I'd been told was that going to 335's on the rear would cause the car to "push" in turns, wanting to go straighter than a smaller rear tire would. I see your point on diameters, Larry, thanks. I'm just wondering if I could increase the rears to 335 for straight line traction and (given the identical setup) not cause a net loss of decent street cornering manners.... and yes, I understand no such question has a simple answer!

Thanks and ride safely

Dirk

If your roadster will fit 335's and it will help straight line traction and accelleration, then go for it. Here is an example of a 325/50x15 tire drag racing in an SPF:

Greg Schroeder from Scottsdale, AZ says

easy start video
10.91 @ 128.75 pass

- What gear ratio is yours?
Ford 8.8 3.73 with Detroit Truetrac, Tremec TKO 600 and the tires for drag racing are Mickey Thompson ET Street Drag radials, 325/50 15, actual height 27 inches tall.


- What engine?
Roush 427R-095 with single plane intake manifold
Switched carb to Pro-Systems 1000 cfm double pumper
switched to 2 inch primary headers
switched to Buckshot Racefab side pipes

- Total weight?
race weight should be 2550lbs with me in the car and gas.

My SPF number is 2040. Mine was one of the last ones with the Ford 8.8 3.73. I'm not sure exactly which number car they switched, but the new SPF cars come with a Dana rear end which I believe is the same type in a new Pontiac GTO.

[DocDirk]

Thanks for the replies! I don't know enough about performance automobiles .... but I'm finding out more! Just got my Vehicle ID # from California CHP, next it's off to BAR and DMV next week....fingers are crossed! Would a rank amateur performance car driver be able to tell any difference between 295 rear tires and 335's? Or is that more the kind of difference one only notices at the extremes of performance demands such as road racing or drag racing? I'll be heading up to Infineon Raceway for driving school when all the mechanical kinks have been worked out, but for the first few weeks I'll just be getting used to the toy

Might be legally drivable in less than a week! Oboyoboyoboyoboyoboy!!

Dirk

[Larry N Johnson]

Originally Posted by Stroked 66

Larry,
Do you know where to get a set of the GTII's now? Seem like everywhere I look they are on B/O. Thanks, Tony

In stock 295 50 15 today
http://www.breezeautomotive.com/details.php?prod_id=692

The 235 60 15's are ar TireRack.com