275/60 on 15x8 fitment

MNwe4

Member
Thought I'd post some pics and info since many of the old images on this site are lost. To start my body and rear end are as close to centered as I could get them. Nothing fancy, just did body bushings a decade ago and have dropped lower control arms with adjustable uppers. The wheels are 15x8" with 4" of backspacing. As it sits in these pictures the rear height is 28.5", so taking the extra tire height out of the equation I think it's still up 1-1.5" in the rear.

You can see where the outside of the tire is in relation to the wheel arch trim and there is about 1/3-1/2" from the tire to the frame.

I don't love the rake the car has, so I wanted to tuck these up more. I've seen some photos of lowered cars on 275's, but how is it possible without a frame notch or cutting the trim and rolling the fender?

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hensleyt

Active Member
Wish I had a good pic of my car. But it’s not that close anywhere.
Could the drop lower arm be bringing the axle assembly forward and shorting the wheelbase?
Not wanting to question you , are you sure that’s a 4 in and not a 3.5 backspace.
I run 28X9 MT drag radial and on the street a 275 -60 Cooper and I can put my fingers between the tire and finder and I have room at the frame as well.
 

MNwe4

Member
Thanks for joining the conversation. The wheels are Eagle Alloys 111's and specs show the 15x8 has a -12 mm offset. Online calculators show that as 4" backspacing. I've seen old links from Summit list 3.966" as well.

In a 275/60 the MT ET Street SS is listed as having a section width of 11.1" and the Sportsman ST (same as Cooper Cobra) has 10.7", both measured on a 15x8 wheel. Tread width is also down from 9.3 to 8.9, so I could see how a non drag radial would just be able to tuck up there.

Now if I could only figure out how to imbed the images vs having them as attachments so they're quicker to see and won't get lost if the site ever goes down again...
 

hensleyt

Active Member
-12mm is almost 1/2 in 13mm is 1/2 in
0 mm offset on a 8 in wheel is 4 in backspace so -12mm would be about 3 1/2 backspace.
and yes the ET is wider by 3/8 inch or .400 with is just .200 or 3/16 on each side
you have moved the tire outboard a full 1/2 in , a bigger tire + 3/16 = 11/16 or 17.5 mm. that very nearly 3/4 of a in.
that is a lot my friend.
and it looks in the pic the lower control arms have shorten the wheelbase at least a 1 in to me. getting the tire close to the frame in the front side.
you will need to center the wheel in the wheel well. with the lower arm ,reset pinion angle and center the the diff in the frame with the top control arm.
IMO I would put the lower arm in the OE position.
Hows drooped arm kit did you use?
 

MNwe4

Member
I think the picture is a little deceiving because I can fit my hand in front of the tire and the rear and top of the arch follows the contour of the tire nicely. The lower control arms are not adjustable and are UMI along with the drop brackets. Going from memory, but I believe we put the pinion angle 1.5* down. No way I'm going back to the stock hole as dropping them greatly improved traction. Car runs 10.70's and would go faster if I wasn't out of injector.

Back to the wheel topic, I understand the math and logic you're following, but believe there's one key thing missing that even I didn't realize for a long time. A 8" wide wheel is not 8" from outside edge to outside edge. It's 8" inside the lip where the tire mounts. Backspacing is from the outside edge to the mounting pad. It so happens that from the tire mounting surface to the outside edge of the rim is about 1/2", or 12mm. Here's info from Weld's specs:
71LP-508B35A15x85x4.75-253.5
71LB-508B45A15x85x4.7504.5

The right two columns are offset then backspace. As you can see if it had -12.5 mm offset the BS would be 4".

I'm confident that going to a 255 would allow it to tuck into the wheel well safely and I bet people have set the rear down with a 275 on a 7" stock wheel, but I don't see how it's possible to tuck a 275 drag radial on a 8" or wider wheel based on my pics and measurements without doing a frame notch or cutting the trim and rolling the fender.
 

hensleyt

Active Member
Thank you for setting me straight on offset and backspace
It wasn’t hard to see I’ve been wrong for some time.
For me I have a set of full throttle GN. 8 in with the coopers. The fit is perfect and under the fenders with OE trim on the street and never rub.
I run Arrow racing wheel 4 in back space at the strip with 28x9 Hoosier slicks steel drum at 12 lb it just barely touched sometime down the lane , probably on the hit.
I switch to MT BP and I have lots of room everywhere
I’m sure I can run the MT SS or the ET R on my wheels with no problem the Pro will be a little close it’s just a tad wider than the Hoosier. The steel drum dose tuck the wheel in I think about a1/8 maybe 3/16 can’t remember.
I run UMI upper and lower and I think they make good stuff.
I wish I had sprung for adjustable upper and lower but I have no problem just need better 60 foot.
I seen the pic and read the drop arm and I jumped to the conclusion shortened wheelbase and pic looks like wrong offset with tire setting outside.
I chose this wheel and tire combo because it was a proven setup and there was no DOT tire restriction in Hawaii.
We lost all the pics in the wheel and tire combo some time ago dirty shame. If it wasn’t a day project to get my car out of the trailer I would take some picture at the same spot you took yours. Lots of people have run that tire on a 8 in wheel with no problem. some have been in the 10s with the 255.
 

MNwe4

Member
Yea, when you're trying to fit stuff to the 1/4 inch on these cars it gets tricky. The hope was that I could get a 15x8 with 4.5" backspacing (like Welds) and with the extra .5" BS I could use a thin spacer if needed and bring it in a little more and be able to tuck the 275 and not hit the fender trim. Then I got under the car and saw that I can't really go any closer to the frame without it rubbing on turns (it doesn't touch at all now).

I could probably lower it 1" back to factory and it would only be 1" higher than the front due to the 28" tire in the rear and 26" tire in front. I don't see how I drop the rear 2" from where it is now (to 1" lower than stock) and not hit the trim on bumps. That would require going to the 255 drag radial. I should probably just replace the sagging front springs to get the car closer to level and go from there.

Thanks for the good conversation. Would love to see pics next time you have access to your car. It is a shame that all the photos were lost, which is kind of why I made this post.
 

hensleyt

Active Member
I just put 255 /60- 17s on my wife’s old truck because it was as chip as 235/ 75 -15 and the new wheels looks good on the old truck. But the old truck gave me much more room to work with.
I may inherit my son’s 86 Ttype if I do I think I’ll try a set of 17 on it.
I went 28 tall to keep the cars RPM at bay at the drag strip and Hawaii track prep was not really that good and needed contact patch. When the Hoosier went away MT suggest the Bracket Pro. To be truthful the Hoosier stuck better. I’ve moved back to Az and when I finish the building this house I’ll be ready to hit the track again. I put 215/65-15 out front and the car doesn’t seem to look so butt high it’s the same bight as the 235 but it just looks different
 

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