Best Tire size/rear gear combo? - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 8 Old 03-25-2018, 06:01 PM Thread Starter
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Best Tire size/rear gear combo?

We are building a 363 for a 85 carbed GT with a faceplated TKO600. My question is concerning the rear end. We have 8" welds for the rear. We will be racing on DR's and was debating on a 275-50-15 (10.5 wide by 26" tall) with a 4.10 gear. The other choice is a 255-60-15 (9.5 wide by 27.5" tall) with a 4.30 gear Both gears calculate that they would trap at about the same rpms, so which tire/gear combo would work the best for hooking up? One concern I had was, would the 8" rim be too narrow for the 275-50 and pull the sides of the tire up so it wouldn't hook? So I guess I'm asking, is it better to have a wider/shorter tire with less gear or a taller, narrower tire with more gear? Any pros or cons you see would be appreciated. Thanks!


Just an old carpenter with a 94 Cobra and a Son with a nasty 85GT! I'm Show and he's Go!!
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post #2 of 8 Old 03-25-2018, 06:46 PM
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I like a tall sidewall myself being a stick also with plenty of torque.

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post #3 of 8 Old 03-26-2018, 01:48 PM
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Hoosier bias ply 27x10.5 or et street r bias 28x10....It will be tough to get a good consistent 60 foot with drag radials and a stick.

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post #4 of 8 Old 03-26-2018, 08:42 PM Thread Starter
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Originally Posted by sradtodrag View Post
Hoosier bias ply 27x10.5 or et street r bias 28x10....It will be tough to get a good consistent 60 foot with drag radials and a stick.
Is that Hoosier 27 x10.5 the ones they call Quick Time Pro? You have to run a bias front with that type of tire, correct?

Just an old carpenter with a 94 Cobra and a Son with a nasty 85GT! I'm Show and he's Go!!
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post #5 of 8 Old 03-28-2018, 07:21 AM
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I always did fine with radials and a stick. In my car, how it worked depending a whole lot more on the tire composition and suspension than if it was a radial. I could easily pull the front tires on the 1-2 shift using a TKO600 with M&H street legal drag radials, and if they spin they still push the car along.

Aside from the obvious RPM change by changing diameter, a shorter tire has less footprint and can't be run quite as low on air. The shorter tire, if you have stock arm angles, gives better geometry for the same ride height.

A narrower rim will take weight off the outer tire edges or even pull the edges up, especially with a short tire. You can offset this with less pressure if you don't run into drifting around at high speed or if you don't go so low the tire wads up. I wouldn't run much less than a tire manufacturer says.

The entire interaction between things is complex.

If you just have marginal power, like below 500-600 HP, something like an M&H drag radial will be a very good tire. It will handle well, be good on the street or marginal track prep, last a while, and hook way better than many other DOT legal tires. If you have a ton of power you'll have to watch the tire choice, the MT ET Street SS is a good tire. It will work almost like a slick or one of the minimum tread drag radials.

Hoosiers just don't last in my car. The rubber rolls up and the sidewalls go away in a few passes, while a MT tire will last 15-20 passes.

This is a 295 55R15 DOT street legal full tread MT ET SS that fits in the mildly hammered stock wheel wells of a 3200lb car. This is an easy 1.2 second 60 ft street legal tire. The best I've been on an M&H street legal is high 1.3 second 60.
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post #6 of 8 Old 03-28-2018, 08:04 AM Thread Starter
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Thanks for the detailed info Tom!

Just an old carpenter with a 94 Cobra and a Son with a nasty 85GT! I'm Show and he's Go!!
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post #7 of 8 Old 03-28-2018, 01:11 PM
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Go with the bias ply, they recover easier from a spin and they take the hit better when your dropping the clutch a 5000+ rpms..

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post #8 of 8 Old 03-29-2018, 02:32 AM
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Tom brings up some excellent points, but I'd have to side with the votes for bias ply tires in your application. Not only will they be more consistent and recover far better (spin on a drag radial and you're done; not so on a bias ply) but also a lot easier on parts. I'd suggest the Hoosier QTP 27x10.5 for you. On an 8" rim, narrower and taller is going to be better.

What Tom says about Hoosiers' sidewalls going away is correct, but whether it's a bad thing or not really depends on the power level. When I was running 11's, I could literally get 4 YEARS out of a set of 26x9 slicks without any loss of traction. But when I did replace them, they would fall down into an unstructured pile of rubber after taking them off the rim - where as a new tire would stand and keep its shape unmounted. When I got in the 10's, I got a little over two years out of the QTP's I switched to (the same ones I recommended to you). Now I run tiny 26x8.5 Hoosier slicks and have 1.5 seasons on them, and they're starting to fall off a little now that I'm high 9's/low tens; but these tires were designed for outlaw 8.5 racing and they have much stiffer sidewalls than the other two I mentioned. I should note, by "fall off a little" I mean going from 1.41 60' to 1.44 60' times. Still pretty good, especially on a 3,500lb car with a pretty basic suspension setup and 3.08 gears and a glide.

Keep in mind two things - Tom is making more power than you or I make, and I always drive to the track on my racing tires. Oh, bias plies with also wear a lot longer than drag radials.

AlexLTDLX

'84 LTD LX - 9.83 at 140.09. Whippled 365 SBF with a glide and 3.08 gears. Driven to and from the track 60 miles without even changing tire pressure.
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