I'm looking for some drag radials for my 94 formula. I looking at either a set of BFG drag TA's , MT ET street radials, or a set of M&H drag radials. I'm not sure how big I can go? I would like to run a set of 275/60-15's. I think I could run a set of 255/50-16's on my stockers. Not sure anyone have any thoughts on this?

 

Wrong forum.... let's go to "Wheels and Tires". Moving......

275/60-15 is a 28" tire. I run 28" slicks.... one set (QTP 28x11.5-15) fit fine simply by pushing the rear axle back a bit with adjstable LCA's. But a set of ET Drags (28x10.5-15W) took considerable massaging of the inner fenders, and cutting at least 1" off the leading edge of the rubber bumper cover. Drag radials will gro less at high speeds than a bias-ply slick, but they are still too big.

I don't know why you would want to run 28" tires on a stock setup. You have 3.42 gears. Running a 275/60-15 will make it feel like you swapped in a set of 3.13's (if there was such a ratio available). 28" tires are typically run on 800HP power adder cars.

Running 15" wheels can be a problem. You would need at least a 15x8" wheel with a 5.5" backspace. Not all 15" wheels will clear the rear brakes. Some require grinding the fins off the brake caliper. There's a "sticky" on the "Wheels and Tires" forum covering drag tire FAQ.

Just get the 255/50-16's, and run them on your stock wheels.

 

would a 26.66 dia wheel fit well without rubbing?

 

Anything less than 28" will fit in the wheel well without rubbing on the edges of the wheel opening. The other issue is how deep the tire sits in the wheel well, and that depends on the wheel width/offset/backspace. If the wheel sticks out to far, the fender lip will squat down on the sidewall or tread and cut it. If the wheel sits too deep in the wheel well, the inner edge of the tire sidewall may rub on the inner fender liner.

 

The driver side tire still sticks out past the fender well now cause I dont have an adjustable PHB yet but if like you said the 26.66 Dia tire wont rub then I guess Ill go with 275/40/17 on the front and 275/40/18 on the rear

 

what size tire will fit a 11.5in rim? I measured the back one today and thats what size it appears to be. The tires that are on the rear now dont seem to fill the rim and the side walls are angled in.

 

How did you measure the wheel width? I suspect you took the overall outside dimension. That's not correct. The width of the wheel is measured inside the bead retainer flanges, where the tire beads sit. Most likely, you have a 10.5" wheel.

 

I did measure from the inside to the outside. I figured sliding the tape measure inside the wheel between the spokes to the outside lip Id get the measurement. They are Z06 Rims and the tire thats on it is a 285/35/18 and the sidewalls are slopped inwared torward the tread. It just doesnt look right on the rim is why i measured it. I figured the rim is too wide for the tire and I believe the tires on it are suppose to fit up to an 11" rim.

 

When you said anything less than 28" will fit without rubbing, did that include even if your tire naturally sticks out beyond the finder because the rear end isnt center?

 

You have two different problems. A large diameter tire will hit on the lower edge of the quarter panel, at the fender opening, and it will hit the rear bumper cover. Then there's the rest of the edge of the fender opening. If you put the tread or the sidewall directly under that edge of the fender, when the body drops, the edge of the fender comes down on the tread or the sidewall. In general, you select the wheel offset to position a large diameter tire INSIDE the fender line.

So.... 2 problems. 1) Wheel offset controls whether the inner edge of the tire rubs on the inner fender liner, or whether the outer edge of the tire is outside the body and subject to damage from the fender lip. That will happen whether you are using a 25" tire or a 28" tire.... it a problem with the side-to-side positioning of the tire under the fender. 2) If the diameter is large enough, the tread of the tire starts to hit the body at the edges of the fender opening, particularly at the bottom of the quarter panel, or the leading edge of the bumper cover, where the body starts to tuck in. That problem is solely a problem of excessive diameter, and not really related to wheel offset.

This is a 28" slick, against the edge of the quarter panel. The entire rear axle assembly was moved back to make that clearance. And the tire still grow enough at 140MPH that most of that clearnace disappears:



This pic shows the leading edge of the bumper upp against the 28" tire. In the photo, at least 1/2" had already been cut off the bumper cover to make room. It wasn't enough.



With another 1" or so cut off the bumper cover, the problem went away, even at 140MPH speeds:





Tire is close to being outside the fender, but does not rub on the top of the fender lip:

 

"Inside the wheel" has nothing to do with slipping the tape between the spokes of the wheel. It means measuring the width of the wheel INSIDE the bead retention flanges. Not the outside edge of the wheel.

 

I understand you generally want the tire inside the fender lip. But until I get the cash to get an adjustable pan hard bar to move my rear end to where it should be that just wont happen. I wondered about the tire size because I may trade my rims and tires for someone elses and they have a 27.1" dia tire on their rear end. I want to make sure its not going to hit that lip with that size. It is 1.25" larger in dia than my current tire that doesnt hit the lip.

 

27.1" diameter isn't a problem with the fender lip. It will reduce rear wheel torque, like swapping in lower numerical rear gears. Speedo will require correction. If you can live with that, go for it.

 

how much will it lower torque?

 

By the % change in diameter of the tire. 1" difference is about 4%.