Front / Rear Tire Size Ratio

[DocDirk]

Like many Cobra enthusiasts I like cornering. I have enjoyed using the Cooper Cobra tires - 265 15 fronts and 295 15's rear. Their hardness rating is 425. The boys at Roger Kraus asked me why I was running on "rocks". I changed from power steering at 13:1 to manual rack & pinion at 20:1 because the car felt squirrelly no matter who adjusted what with suspension, alignment, steering pump output pressures etc etc. with manual I have much more road feel and finally some return-to-center. I'm thinking of switching to the Mickey Thompson S/R tires as many forum users like them but their widest front tire is 8" meaning I would be running 8" fronts with 12" rears.

I'm wondering if the ratio change would cause the car to necessarily push in hard cornering.
Should I considering going to a 10" rear with the 8" front?n(I am less concerned about contact patch for pure launching)
Is there an ideal front / rear ratio for corner carving? I think I recall that in an older post someone with a lot of experience suggested 245 front with 275 rear being uniquely good for all around driving.
The steering with manual is much firmer of course. Is there signifant difference in steering with progressively smaller front tires?

Thanks in advance for any input.

Dirk

[FWB]

I use the SR's but you might want to check your rim size for the front.

i have a 26 x 10 on my front and the 12 on the rear.

sometimes i do experience a little pushing in the corners. with the extra wide rear stance our cars have compared to the front, i dunno if your going to completely eliminate that with tire size. i have adjusted alignment specs too with mixed results.

oh on another subject....we need a group pic for the owners group....it shows a question mark for it. maybe we can rob one of verns logo's he has pirated on his site....

[DocDirk]

Thanks Fred! Do you have any idea how much steering resistance reduction there might be with a 10" tire or an 8" tire vs my current 265 fronts?

Dirk

[Frank Messina]

How old are your tires? I'm asking because Cooper doesn't currently offer a 265-60-15. That aside, depending on your wheel clearance a good combination with a 295-50-15 would be either 235-60-15 or 245-60-15 on the front. You don't want the fronts to be the same diameter as the rears and most definitely not larger. If the car felt squirrely it could be your tires are overinflated. Every tire shop on the planet wants to send you out with 35+ pounds of air in the tires. They'll be rocks for sure especially on a car as light as a Cobra. Too bad you took the power steering off, as that wasn't your problem. You needed more caster and less air pressure. Also you could reduce the assist by adding a Heidt's valve to the power steering without slowing down the steering which does wonders for the feel.

I have 235-60-15 front and 295-50-15 on the rear at 23 and 26 lbs respectively. My car is IRS and weighs about 2400 lbs. I just replaced my Dunlop GT Q's which I loved with Mickey Thompson Sts. The MTs are made by Cooper and so far feel like the Dunlops although I haven't really pushed them hard yet as I only have about 100 miles on them. FWIW

Frank

[FWB]

Frank, i'll mention this cause you may not know, our cars, the west coast and the kellison are heavy weights...most weigh in over 3000 lbs. and the rear track width is wider ..(a lot) than the front

[vatdevil]

A larger front to rear stagger will affect the cars balance, but how depends on many factors. Spring rate, sway bars, tire pressure, ect..also have an effect. You can counter the stagger by varying air pressures front to rear.

The cooper tires you have are garbage. SRs are much better.

Autocross is best place to learn how to properly setup of your car.

You don't need power steering on these cars and manual steering provides much better feedback to the driver.

[FWB]

Originally Posted by DocDirk

Thanks Fred! Do you have any idea how much steering resistance reduction there might be with a 10" tire or an 8" tire vs my current 265 fronts?

Dirk

can't really say....i am surprised you gave up the P/S though. i'm looking to put P/S ON mine....parking and slow driving is a bit much on the arms.
i struggle when i have to do a "K" turn.

as far as going autocrossing to determine correct tires or set up.....well, a bit over the top for a car i just want to drive well. my car cannot autocross and i'd like to just leave it at that because i don't have the typing strength to explain why.
i will say when you build a car you eventually have to make a decision on how it will be used and choose engine, trans and suspension geared for that.
some people like dogs as pets.....others eat them....lol

[cycleguy55]

Figure out what YOU want to do with the car and set it up for that. Some want to autocross, some want to cruise, some want to show and shine - to each their own.

I just purchased a West Coast Cobra with PS & PB, and I'm going to leave both on the car, though I am going to chase down and install one of the valves used when Saginaw PS pumps are hooked up to Mustang II racks.

[Mother]

I use Nitto 555's front and rear. The rims are 17's. The fronts are 295 R40's and the backs are 315 R35's Both sets of tires are 25.68" tall, keeping with the correct height of under 26 inches in height. I corner hard and do not have a problem with much skating. Tires do not last that long due to wear usage. But the smiles and pure joy more than make up for the cost. Besides the car has a 1/2 inch ID fuel line, and a 3/8 inch return, running on 94 % octain. Ya think I care about replaceing tires? Besides the kids can make their own money like I did. No silver spoon where the sun don't shine for them.

[G-Pete]

Originally Posted by Frank Messina

That aside, depending on your wheel clearance a good combination with a 295-50-15 would be either 235-60-15 or 245-60-15 on the front.
Frank

I agree, 245 front 295 rear here - great cornering...and as Frank stated, check your tire pressure....