I finally got around to picking up some 28x9 slicks for my '67 Belvedere II. I'd been running M/T 26x8.5x15's that I bought back in 1992. I only raced them until 1994 on a '67 Barracuda with 360 with 340 manifolds, a stock 904 converter and 3.91's that ran a best of 13.96@98mph. In 2005 I started back, running the M/T's on the Belvedere with that same 360 and 3.91's, running 8.80's in the 1/8th mile. For the last 2 years it's been with a 440 and 4.30's running down to 8.0 times. Ended last year with a 7.73 and started off this year with a 7.66 (must have been good air, MPH went up 1 to 89mph).
I don't seem to slip at the line much, but folks tell me those tires are so old they should be "gassed out" and slippery. They're down to pretty close to the wear indicator bottoms, but still seem okay. Ran them mostly on 15x7 steel wheels I pulled from vans (rims are marked CANADA) and this last time on Centerline knockoffs measuring 15x7. They may be worn out, but all last year when I felt the car slip, the other cars I run with were slipping as well. Probably some slippage in there with the weight of my car and it running a 7.73 but I couldn't really tell.
Sooooo, today the Hoosier 28x9's arrived and I put them on rims. One went on a steel 15x7 and one went on a Greg Weld Racing (DO NOT BUY THESE RIMS FOR YOUR MOPAR) 15x8. The GWR rims are dual-bolt-pattern and suck on Fords/Mopars using offset washers to locate them. You can cruise the Ford forums to see what kinds of trouble others are having as well. Last year when I used them once I bound up a few bolts and had to drive home on the slicks. This was a fitment test with a different rim than the steelies.
The key here seems to be offset, the resulting centering of the slick in the wheelwell is the big issue.
Mounting on the 15x7 steel, the slick looks like it bulges out a lot with very rounded sides. On the 15x8 aluminum it doesn't look as squeezed out, but actual measurement shows 11" section width as the Hoosier info shows while the 15x7 mounting shrinks that down almost 1/2". This was measured with a rim measuring device used on our balancing machine.
The offset of the steel wheel is .35" positive, on the GWR rim it is .33" positive. I measured this by taking the full width of each rim and comparing to the backspace as measured from the edge of each rim to the mounting surfaces.
Proof is in the pudding, the slicks show enough room on the spring sides but get close on the fender lips. Steel rim fits better, the .02" offset difference doesn't seem like much but added to the lower section width it makes a difference. S/S springs keep the slicks from making any contact up in the wheelwell against the inner fender, and seem to be stiff enough that any side to side movement will keep things clear of contact as well, at least with the steel rims. I plan on running them this weekend, that will be the test.
I've got some pictures of different fitment areas, will post them soon. Overall, the 2" taller tires are supposed to drop RPM's about 300. A tire diameter calculator I found this past week showed a difference in "effective gear ratio" from 4.30 to 4.10 and that doesn't seem like much of a change. When I went from 3.55's to 3.91's on my Barracuda the times at the track didn't change much either.
B II
I don't seem to slip at the line much, but folks tell me those tires are so old they should be "gassed out" and slippery. They're down to pretty close to the wear indicator bottoms, but still seem okay. Ran them mostly on 15x7 steel wheels I pulled from vans (rims are marked CANADA) and this last time on Centerline knockoffs measuring 15x7. They may be worn out, but all last year when I felt the car slip, the other cars I run with were slipping as well. Probably some slippage in there with the weight of my car and it running a 7.73 but I couldn't really tell.
Sooooo, today the Hoosier 28x9's arrived and I put them on rims. One went on a steel 15x7 and one went on a Greg Weld Racing (DO NOT BUY THESE RIMS FOR YOUR MOPAR) 15x8. The GWR rims are dual-bolt-pattern and suck on Fords/Mopars using offset washers to locate them. You can cruise the Ford forums to see what kinds of trouble others are having as well. Last year when I used them once I bound up a few bolts and had to drive home on the slicks. This was a fitment test with a different rim than the steelies.
The key here seems to be offset, the resulting centering of the slick in the wheelwell is the big issue.
Mounting on the 15x7 steel, the slick looks like it bulges out a lot with very rounded sides. On the 15x8 aluminum it doesn't look as squeezed out, but actual measurement shows 11" section width as the Hoosier info shows while the 15x7 mounting shrinks that down almost 1/2". This was measured with a rim measuring device used on our balancing machine.
The offset of the steel wheel is .35" positive, on the GWR rim it is .33" positive. I measured this by taking the full width of each rim and comparing to the backspace as measured from the edge of each rim to the mounting surfaces.
Proof is in the pudding, the slicks show enough room on the spring sides but get close on the fender lips. Steel rim fits better, the .02" offset difference doesn't seem like much but added to the lower section width it makes a difference. S/S springs keep the slicks from making any contact up in the wheelwell against the inner fender, and seem to be stiff enough that any side to side movement will keep things clear of contact as well, at least with the steel rims. I plan on running them this weekend, that will be the test.
I've got some pictures of different fitment areas, will post them soon. Overall, the 2" taller tires are supposed to drop RPM's about 300. A tire diameter calculator I found this past week showed a difference in "effective gear ratio" from 4.30 to 4.10 and that doesn't seem like much of a change. When I went from 3.55's to 3.91's on my Barracuda the times at the track didn't change much either.
B II
