Club Cobra

Club Cobra (http://www.clubcobra.com/forums/)
-   ALL COBRA TALK (http://www.clubcobra.com/forums/all-cobra-talk/)
-   -   Front to Rear Tire Size Ratio (http://www.clubcobra.com/forums/all-cobra-talk/93407-front-rear-tire-size-ratio.html)

DocDirk 12-04-2008 10:12 PM

Front to Rear Tire Size Ratio
 
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 12-05-2008 05:16 AM

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 12-07-2008 02:51 PM

Tire Ratios
 
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:
http://www.primequip.net/images/65%2...s%20arrive.JPG

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.

http://www.rogerkrausracing.com/imag...Cobra_CC-2.jpg

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 12-07-2008 06:54 PM

Goodyear 295's
 
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 12-07-2008 08:31 PM

Quote:

Originally Posted by Stroked 66 (Post 903403)
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 12-08-2008 01:34 PM

Ratios
 
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 12-08-2008 02:01 PM

325/50x15
 
Quote:

Originally Posted by DocDirk (Post 903560)
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
Quote:


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 12-11-2008 12:14 PM

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 12-12-2008 02:56 PM

Source 295 50 15
 
Quote:

Originally Posted by Stroked 66 (Post 903403)
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


All times are GMT -7. The time now is 10:10 PM.

Powered by vBulletin® Version 3.8.0
Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
Search Engine Friendly URLs by vBSEO 3.6.0
The representations expressed are the representations and opinions of the clubcobra.com forum members and do not necessarily reflect the opinions and viewpoints of the site owners, moderators, Shelby American, any other replica manufacturer, Ford Motor Company. This website has been planned and developed by clubcobra.com and its forum members and should not be construed as being endorsed by Ford Motor Company, or Shelby American or any other manufacturer unless expressly noted by that entity. "Cobra" and the Cobra logo are registered trademarks for Ford Motor Co., Inc. clubcobra.com forum members agree not to post any copyrighted material unless the copyrighted material is owned by you. Although we do not and cannot review the messages posted and are not responsible for the content of any of these messages, we reserve the right to delete any message for any reason whatsoever. You remain solely responsible for the content of your messages, and you agree to indemnify and hold us harmless with respect to any claim based upon transmission of your message(s). Thank you for visiting clubcobra.com. For full policy documentation refer to the following link: