Rear wheel clearance for 15x6 smoothie wheels

[ReddingScott]

I am changing to 15" wheels to accommodate a Wildwood front disc brake conversion. I bought one Allied smoothie wheel, size 15x6 with 3.75 backspacing.
No problem on fronts but rear, of course, has little clearance on the outside wheel well lip. The old tires on the old stock 14" rims were Coker 205/75R15 and there is about 1 inch of clearance with these. Figuring that I need to stay close in size, I am considering a 215/65r15 or a 205/70r15. Wheel diameters are very close as well as width.

The original 14' wheels were 5.5" and these new ones are 6". Am I going to have any clearance issues with this set up? and which tire size would work best?

Many thanks!

Scott
Redding, Ca.

[RICH MUISE]

Welcome to the forum.
The problem is the 3.75 backspace, it won't let you run a very wide tire. Most of us are able to fit 7" wide rims on the back, but with a 4.25 backspace. I'm actually running a 235/70-15 tire on the back. Neither my fender lip or wheelwell are modified. I do have my rear narrowed 3/4 inch per side, but the mentioned tires did fit on before it was narrowed. Since you've only purchased one wheel (which is a good size for the front), if it were me,I'd check to see if they are available in wider wheel with a deeper backspace. Not sure what you meant by "figuring I need to stay close in size", but most of us run narrower wheels and tires on the front and as big as posible on the back. Just looks better.
btw, I am running 215/70-15's on the front with a 6" wheel/3.50 backspace.
Lots of recent posts on this topic.

[ReddingScott]

Rich,

Appreciate the help! I guess I am not all that concerned about running larger tires on the rear. I just want them to clear and have enough of a load rating to work properly. I just found a 215/65r15 that measures up very well with the Coker. Its only about a quarter of an inch wider than the Coker. I might just order one to see if it works in the rear. If not, I could use it on the front. Ideas?

Thanks again,

Scott

[RICH MUISE]

Just my suggestion about checking to see if you can get a deeper backspace wheel for the back. You really need at least a 1/2" or so clearance on the back at the fender lip to prevent rubbing when the car is leaning into a curve.

[ReddingScott]

Sorry to keep bugging you!  I can get a 15x7 wheel for the rear and they have a 4.25 inch backspace. But won't I be adding to the problem by using a 7 inch instead of a 6 inch rim, or not? If it won't matter, I'll use a 7 inch rim on the rear with the deeper backspace.

Thanks!

[lalessi1]

15 x 7 with 4.25" backspace wheels should work fine with tires up to 235/70 section width. I am running that wheel with 225/60 tires on my stock rear (and front) setup.

[RICH MUISE]

What lynn said. In rereading your first post, I think maybe you need to take a second look at how much space you have in the back with the 6" wheel. You said it was close, but it really shouldn't be, even with the shallower backspace. I guess that's subjective depending on what "close" is. You are correct in that a 7" wheel with a 4.25 backspace will actually be 1/2" closer to the fender than a 6" wheel with a 3.75 backspace.

[lalessi1]

One of the "fun facts" to know... the rim width does not move the tire out the same amount. For any given section width there is a "measuring rim width" that will give you that dimension. A wheel wider than that will increase the measured tire width but not by the same amount. Even though your rim is 1/2" closer to the fender, the tire will not move that 1/2" where the interference actually is. This is because a 6" wheel with 3.75" B.S. and a 7" wheel with 4.25" B.S. have the same offset and that keeps the centerline of the tire in the same place for both wheels.

[ReddingScott]

Thanks to you all who have replied-it has helped a great deal.

I have decided to order one tire to go onto the 15x6 smoothie with 3.75 backspace for testing purposes. Its a 215/65R15 Cooper Cobra Gt . According to the data, the diameter of the Coker tire I am taking off (205/75R14), even with the 15 inch rim, the tire diameters are almost identical and the width of the Cooper is only .24 inch wider than the Coker. With the current Coker tire on the car, there is 1 inch of clearance on the lip of the fender.

My plan is to mount the tire on the smoothie and test fit it into the rear rear well. If it is a go, I am good. If not, I'll use it on the front and come up with another plan for the rear.

Ideally, a 15x6 smoothie with a 4.25 inch backspace would cure all problems but I was unable to find one anywhere. If I need to, I can try a 15x7 with the deeper backspace.

Again, many thanks to all who have responded thus far and I will update this with results.

[rmk57]

You may have to jack the car on the frame and unbolt the shock so the rear end drops enough to squeeze the tire in.

I'm running 235/70/15 on a 6 inch steel rim and that's what I have to do.

[RICH MUISE]

When you're ready for new shocks, switch to 56(55?) Ford Monroe shocks and you won't have to unbolt them any more. I'd have to look up the number, but there's threads from a few months back on them.

[ReddingScott]

Ok, here is my report on rear wheel clearance on my Fairlane. I ordered one Allied 15x6 smoothie wheel with 3.75 backspace and mounted a 215/65R15 Cooper Cobra tire on it. I mounted it on the car and as the advice stated, I had to loosen the shock to get the tire on. After it was mounted and the car lowered to the ground, I have 1/2 inch clearance on that fender lip that comes closest to the tire.

The magic question is: Will that be enough clearance in everybody's mind to make this set up work?

Many thanks for all of your help in this. I want to make a good decision and order the rest of the wheels and tires if this is a go.

Thanks!!

Scott

[RICH MUISE]

I would think you're ok, but just barely. Actually alot depends on your suspension. If it's old and worn out, your more likely to have some rubbing in curves, but as I said, I think you'll be ok.
New springs and new shocks will help alot, and you may be planning on that anyway. JMHO
BTW, that's about how much clearance I had before I narrowed the rear end, had old 4 leaf springs and NO shocks, and I did not have an issue with rubbing, albeit I was not driving it hard because I also had NO rear brakes, lol.

[ReddingScott]

Rich,

Thanks for the help and advice-I think I will go ahead with the changeover. I am not a hard driver and baby the thing most of the time. I appreciate the suspension issues. My springs are original but will put in new shocks. Can you look up the Monroe number I should be looking for? Would appreciate it. I could go with a smaller tire yet but then I get out of the white raised letter sizes that I want.

Ideally, a 15 x 6 smoothie wheel with a 4 inch or 4 1/4 inch backspace would be ideal but I have not been able to find one.

Thanks again, you have been a big help.

Scott

[lalessi1]

You clearance is CLOSE but OK to me. You can buy steel wheel with any backspace... Wheel Vintiques, Wheelsmith.. more expensive, an extra $50 to $75 per.