IDOXLR8

I just mounted some 28x10.5x15 (S-stiffer sidewall) ET Drags on Bogart RT Bolted wheels. I tried fitting them on my car last night and the tire basically pressed up against the rear bumper . Since I have adjustable LCA I plan on centering the tire. My question is how much clearance should I have btw the tire and the wheel well? Is an inch enough? I understand that tire growth affects the center of the tire. I am just wondering how much the tire will grow. The car is a 6 speed car and should trap over 130 mph. Thanks in advance.

Injuneer

I had a 28.0" QTP, and it bolted on with no interference. When it grew enough at 125mph trap speeds, there was evidence of the tire tread hitting the sheet metal front edge of the body fender opening. I moved the axle back 1/4" and the problem went away. And there was no rubbing on the rear bumper cover.

Then I switched to ET Drag 28x10.5-15W. As you noted, the tire, although supposedly 28.1" diameter, wouldn't come near fitting in the wheel opening, hitting the rear bumper cover. I cut about 1/2" off the rear cover, and the wheel fit on, but it was obvious it was going to hit, so I eventually cut another 1" more off the rear bumper cover.

I left the axle where it was, because I assumed the growth would put it into the front edge of the fender again. Unfortunately, the car hasn't been run yet, but it has been taken up to speed on the chassis dyno with no problems. I also am switching from poly bushings in the LCA's to rod ends, so that the axle can't move forward when the bushings compress on launch.

There are some pictures on this page that show the "fit" with only about 1/2" cut off the rear bumper... you can see why I cut another 1" off.

http://cjcfo.fbody.com/members/injun...l.com/PhotosK/

IDOXLR8

Thanks for the useful info. What kind of kind of procedure did you follow to cut the bumper? Thanks in advance.

Injuneer

I just marked the location of the cut with some masking tape, then cut into the cover with a very sharp hunting knife... the cut can than be sanded smooth. There is sheet metal behind the cover, if you take more than 1" off, so the sheet metal has to be "rolled" back after you cut the cover. Touch up the edges of the cover with some touch-up paint.

A friend of mine put 29.5" ET Drags in a 30th SS, and left the actual front edge of the bumper intact. They cut a wedge shape out from behind the front edge, and then pushed the front edge of the cover back and glued it somehow. That way you still have the original edge on the bumper.

http://cjcfo.fbody.com/members/injun.../DCP03836a.jpg

I have also seen an NHRA "Stock" class F-Body running 30's, with an aluminum strip shaped to cover the leading edge of the rubber bumper cover with a slight overlap to the outside, to provide a small "guard" to keep the rubber off the bottom of the bumper cover.