Wheel Backspace

[bobw]

I'm planning on putting 14" wheels on my Alpine with a rotary engine conversion. In searching around the forum, it seems like 14" wheels are possible with very little or modification to the sheet metal.

Somewhere I found specifications for Alpine wheels that seemed to indicate they had a 4 1/2" backspace. I fitted a 14" X 6" wheel with a 3 1/2" backspace and a P175R14 tire to get an idea of how they would fit. It looks like the 4 1/2" backspace would be just fine for the rear wheels, but there is no more than 1" clearance between the tire and the upper control arm in the front (with 3 1/2" backspace wheel). I can't get a real accurate measurement for this spacing because the hub doesn't have a rear bearing. (The car came with regular hubs on the rear and knock off hubs on the front. Bearings are on order.) I measured the backspacing of the rim that was on the rear and the backspacing measures 4 1/8". It also clears the control arm OK.

I can't seem to find the web site where it said the backspace was 4 1/2" again. I'm inclined to go with the 4 1/8" backspace as I think it will clear the control arm in front and still be inside the wheel well in the back. Any advice on the best solution would be appreciated.

Thanks,
Bob White

 

[slippery_biscuit]

For what it's worth, I recently put 13x7 wheels with P205 60's rubber on my car. The wheels have 4" of offset and I have about 1/2" of clearance with the steering arm.

 

[bobw]

Thanks for that data point. If I went with 4 1/8 backspace, that would put me at 3/8" clearance. What cleareance would be considered a minimum? I suppose if I'm too close I could use a thin spacer.

Bob W.

 

[Bill Blue]

Bob, 1" clearance is probably excessive. Try for something like 1/4-1/2". You need the close fitting wheel in order to keep the centerline of the tire in correct relationship to the turning center of front suspension. As that distance becomes greater, the car steers harder.

Bill

 

[Bill Blue]

Thanks for that data point. If I went with 4 1/8 backspace, that would put me at 3/8" clearance. What cleareance would be considered a minimum? I suppose if I'm too close I could use a thin spacer.

Bob W.

When it rubs, you have gone a little past the minimum.

Bill

 

[bobw]

Thanks Bill, I'll order 4 1/8" backspace rims and see how it comes out. And if it isn't rubbing, I'm OK!

Bob W.

 

[bashby]

4" backspace could go with 4-1/4"

I have 15x6 with a 4" backspace and could have gone to 4-1/4" without rubbing. Can send photos if you like. on a Series 5

 

[Chuck Ingram]

I have 15x6 with a 4" backspace and could have gone to 4-1/4" without rubbing. Can send photos if you like. on a Series 5

What size tires are you running?I need new rims for the 62 and am debating 14 or 15 inch rims.
Thanks

 

[bashby]

Tire size

I am running 195/55-15's which is pretty close to the stock tire diameter.

 

[bashby]

trim the front valance

I should have mentioned that I did have to trim the front valance so that the wider tires would not hit (rub) when turning corners. Took off ~1/4"-3/8" on the curve.

 

[bobw]

Thanks bashby,

I would like to increase the diameter of my tires to match the 205/60 15" that were on the RX-7. The rear end ratios are very close and the 175/70 14" are about 5% smaller dia. I expect I will have to trim the valance some also. I don't mind that, but I don't want to have to flare the fenders.

How much clearance do you have with the 4 1/4" backspace? A photo would be appreciated.

I'm still trying to figure out where I got the 4 1/2" number.

Bob W.

 

[afssanders]

Backspace

I have fitted 17X7s on my Sunbeam. I'm building my car to drive. If I didn't care about it rubbing while I was driving it I would of went bigger. When we had our Cougar I put those wheels on it to see if they would fit. To my surprise they did. They were 16" wheels. I think they were 5 maybe 6" wide.
I measured my car about 20 times before ordering the wheels. In my opinion 7 inch width is max if you plan on not having to worry about the tires rubbing. I had to turn(bend) my upper front fenders edges up a bit to make sure the tire never rub. I have bottomed out the car to make sure that they didn't. In the back it was a minor trim of those huge return edges.
To get a 7" width wheel on your car you'll also have to get a 17" wheel to clear your upper ball joints. My point here is more about the front space and not the back space.
I have a 1-5/8 front space. I would say to be on the safe side. A person that doesn't want to do anything should order 1-1/2 front space. Most front wheels drive cars are just that.

I have quite a few pictures of my wheels on my car. Keep in mind that I channeled my car 2". Which means I moved my front suspension up into the car 2 inches. I did this to lower it without loosing travel in the suspension.

http://gallery.me.com/mnwheelers#100348

 

[bobw]

It took a while, but I finally got the wheels I ordered from Stockton Wheels. It was 7 weeks before they were delivered. Well, I got 3 of them. UPS sent one of them to Hodgkins, IL instead of Albuquerque. It will be back next week if all goes well.

After everything was fitted up I found that the P175/70R14 was almost the same diameter as the original 6.00-13's. No valence trim required. The P175's are a little over one inch wider. I will try these to see how well I like the match to the rotary engine.

After the comments here, I ordered the wheels with a 4 1/4 inch backspace instead of 4 1/8. The fit couldn't be better. The rim and upper support are about 1/16 inch apart, and the rim is slightly above the support, so the actual clearance is a little more than 1/16.

Higher resolution pictures are available at:
http://bob-white.com/photos/alpine/wheel-backspace/index.html

 

[bashby]

15" wheels

I have 195/55-15 BFG G-Force on my Series 5.

 

[bashby]

15x6 Minilites on Series 5

15x6 Minilite's with 4" backspace with 195/55-15's tires

 

[Series6]

wow

1-Very nice car
2-Did you have to modify the front valance?

 

[bashby]

15x6 wheels valance trim

Thanks, "she" is still a work in progress, swapping in a Nissan intercooled turbo 1.8 liter and 5-speed.
I had to trim the front valance about 1/4" on the corner so that the tires did not rub when turning (straight ahead they were okay).

 

[Series6]

wow, part 2

Thanks, "she" is still a work in progress, swapping in a Nissan intercooled turbo 1.8 liter and 5-speed.
I had to trim the front valance about 1/4" on the corner so that the tires did not rub when turning (straight ahead they were okay).

I plan to use the same tires on the new project. I was concerned about altering the look of the well lip. You'd never miss 1/4 inch..

It drives/rides well with those tires?

 

[bashby]

BFG G-Force tires

I like the driving (they stick really well) and the ride is good as well I am on my 4th set on my daily driver (~25k per set with AWD) so you could say that I like them.

 

[bobw]

I plan to use the same tires on the new project. I was concerned about altering the look of the well lip. You'd never miss 1/4 inch..

If you make the backspace 4 1/4 inch, you may not even need to take 1/4 inch off. I was surprised to find the diameter of the 175/70R14's were almost the same as the 6.00-13's. According to a tire size program I found on the web, the 195/55R15 is slightly smaller in diameter than 175/70R14. If that's the case, the interference must be a result of the 155's being wider plus the quarter inch less backspace.

Bashby, your clearance seems to be more than 1/4 inch more than mine. I wonder if the Minilites are measured the same way. Here is a close up of my measurement. I didn't realize how small it would be in the last picture. Hopefully this will be better.

I'll try to get a picture of my car with the wheels on it now that I can roll it out of my confined workspace again. Although the car isn't pretty yet.


Bob W.