Tire Clearance - How much is necesary?

[68 SuperRam]

So need new tires - so looking to change the wheels also.

How much clearance is best to have between the rear tires and the inner wheel well?

Same goes for the rear fender lip?

With wheel off - have about 6 1/2 inches from the wheel mounting surface (face of rotor on rear axle) to inner fender and about 4 1/2 inches from mounting surface to edge of out fender lip.

Currently running 245 50 16 - with a 4in backspace. Looking to go to a 17 - any recommended size?

Rubs slightly on outer fender lip - so probably best to get a bigger backspace.

Thanks



12 bolt axle / disc brakes / DSE 2in drop leaf / original outer fender lip (not - rolled)

[68 SuperRam]

So i heard that the norm is have between 1/2 in and 3/4 in clearance between the rubber and the inner fender wheel well and the same for the rubber to the outer fender lip.

I have about 4 1/2 in from the wheel mounting surface to the outer fender lip and about 6 1/2 in from the wheel mounting surface to the inner fender well. Based on this I was told that I could do a 275 tire on a 9.5 wheel - with a 5.5in backspacing.

Does this make sense? Seems kinds of tight.

Running a 12 bolt / disc / 2 in drop DSE leaf springs

[Wall]

Another thing to consider is some tires run wider than others. Before I installed mini-tubs in my Firebird I had read a 275 on a 9.5 would fit with the right backspacing. I had some 18x9.5's on BFG 275'd and tried mocking them up in the wheel well with the rear end out of the car and they did go up in there but there was no clearance on either side. So there was no way they would work with.

Years ago I know BFG's ran wider than some other tires like Nitto. I know people have done it without issues but in my opinion I think a 275 is a gamble with stock tubs, you have to get the right backspacing and the right tires etc.

[68Formula]

Assuming you're not running a panhard or watts link I'd go with your original assumption for clearance. I've seen videos where the rear shifts alot in lateral corning on a leaf car. Also will depend on the sidewall thickness which will vary by compound and section height.

I'm running solid blocks instead of rubber for the leaf mounts (which I'm hoping will limit movement a little). With 275s on 9.5" rim and 5.5" backspace and discs, if I put a board against the tire, it lines directly up with the lip. I'm not lowered, but if I had enough travel, it's already edge to edge. So if I did lower it, I'd need to roll the fender. This seems to be fairly consistent to your measurements. Since you're lowered, you probably really need a 255 to keep enough clearance (with the appropriate backspacing).

As for tire width, not only may there be slight variation in with between brands, but they also list the section width based on an assumed rim width. According to tire rack, for each half inch difference between the measured rim width listed, versus your actual, section width changes by .2". For example, if they section width as 11 measured on a 10" rim, and you use a 9.5" rim, then width will be 10.8 on your rim. Most 275/40s are around 10.8-11 section measured on a 9.5". According to your measurements you only have 11" total!

There was also an interesting discussion which talked about possible benefits of running on the narrow side of recommended rim for a specified tire on the rear setup (while the opposite for the front setup):
https://www.pro-touring.com/threads/...ize-questions:

So, all that being said, the widest rim based on your data, would probably be a 9" with 5.25" backspacing. But you might be even better off with an 8.5"/5" or 8"/4.75" if available in your wheel choice.

[68 SuperRam]

Guys - thanks for the feedback and knowledge sharing - to the points raised best to be on the narrower side to avoid any clearance issues.

If I were to go with a 17X8 with 4.75 in BS - in the rear - would it look weird if the front had 17x8 with a 4 in BS? Would it be best to get a 17x7 instead in the front - so that the face of the tire to the face of the actual wheel - could appear to be the same for the front and back?

[68Formula]

Guys - thanks for the feedback and knowledge sharing - to the points raised best to be on the narrower side to avoid any clearance issues.

If I were to go with a 17X8 with 4.75 in BS - in the rear - would it look weird if the front had 17x8 with a 4 in BS? Would it be best to get a 17x7 instead in the front - so that the face of the tire to the face of the actual wheel - could appear to be the same for the front and back?

I just spent the last week with borrowed setup, my current setup, and my new rims doing fitment checks, and trust me you don't want to use an 8 with 4bs on the front. The optimum front setup stated by many is 8/4.75, and from all my different measurements, that's absolutely spot on. With that you likely can fit a 245/45, but get the rims first and do you checks. Worst case a 235/45 would be no problem. The buldge difference front/rear wouldn't be that noticeable with either.

Oh, and yeah besides the fitment issues, a 4.5 on an 8 for the front would actually stick out slightly more than the same rim even with the wider rear tire. The front would be basically flush to the outside of the fender (so under compression you'd hit) while the rear would appear tucked in. But that'd be the least of your worries.

[Wall]

For reference here's my car not long after I bought it (before I completely tore it down and made it undrivable for years). It had hideous mid 90's "billet" wheels so I bought these american racing wheels. They were 17x7 on 225s and 17x8 on 245s, can't remember the offset but I'm pretty sure came off of a Chevy S-10 and stuck out a little further than a normal set would.