Wheel clearance_ brake backing plate set up

[Steve D.]

63 convertible

I bought some 15 X 6 _ 4" backspace (0.47 " offset) wheels. Before mounting all of the tires, I had one mounted (215 70R15) on one of the new wheels and then test mounted the new wheel on each of the 4 corners. Clearance is fine on both front locations with no binding with wheels turned to limit. The new wheel also had sufficient clearance on the driver rear. But on the passenger rear, the edge of the rear spring touches the tire right at the wheel rim. The old wheel for the passenger rear has a 3.5 in backspace. This seems like a geometry issue, so I measured the shortest distance from the edge of the spring to the brake backing plate on both the driver and passenger sides. The distance is shorter on the passenger side. I assume this distance is affected by the alignment setting, but changing the alignment setting to create wheel clearance is not an elegant solution. Any other ideas for creating clearance? I can get a wheel with 3.5 in backspace, but I was trying to end up with a set of wheels with matched specs with offset close to the original.

Steve

[Gene M.]

Re: Wheel clearance_ brake backing plate set up

Steve,
Is it possible the spindle is for a disk brake setup? I ran into this problem years ago. If I recall correctly the position of the mounting flange is a bit shorter on the disk brake spindle. But it may have just been machining difference in a replacement spindle. Solution at the time was a thin spacer. I later changed to Corvette wheels and it was a non issue. Sorry I can't help anymore than that but it was a long while ago.

[Steven B.]

Re: Wheel clearance_ brake backing plate set up

Steve, I agree with Gene. A thin spacer will work---but be careful as thicker spacers will add to stress on bearings and studs. I broke a couple of passenger side rear studs on my '77 because the spacer was too thick.

Steve

[Steve D.]

Re: Wheel clearance_ brake backing plate set up

Steve/Gene

I can't discern any noticeable difference in the set up from side to side. I need to gain about 3/8" to 1/2" clearance which seems like a lot for shimming. Or is it?

Steve

[Steven B.]

Re: Wheel clearance_ brake backing plate set up

Steve, 3/8-1/2" spacers are available. The ones I used were 3/8". If you use spacers this wide you will need very good grade studs and likely longer than stock depending on your lug nuts (stock vs. mag/custom wheel nuts). If I were in your shoes, after what I have experienced replacing studs, reattaching my fender and refinishing a wheel after it got scraped hitting the pavement and pulling it from a ditch, I would get some wheels made to spec.

Steve

[David L.]

Re: Wheel clearance_ brake backing plate set up

Steve,

Years ago I had several original 63 Corvette 15" X 5 1/2" wheels. The gross width of these wheels measured 6 9/16" (6.56") with the backspacing measuring 3 23/32" (3.72") which would make the offset 0.44" or 9/16" (3.72" - 3.28" = 0.44"). The original tire was a 6.70-15 which I believe the width of the tire is 6.70".
The offset of your 15 X 6 wheel is almost the same (0.47"). The width of your 215-70R15 tire calculates as 8.46". This would mean that your 215-70R15 tire is about 7/8" wider (8.46" - 6.70" / 2 = 0.88") on each side.

My 1966 Corvette has original 65-66 15 X 5 1/2 wheels (offset = 0.44", same as 63 wheels) with P205-75R15 tires (width theoretically 205/25.4 = 8.07"). I do not have a problem with clearance to the spring (photo enclosed). The end of the spring is above the edge of the rim. Do you have a photo showing your problem?

Dave

[Steve D.]

Re: Wheel clearance_ brake backing plate set up

Dave

Unfortunately I did not take a photo of the new wheel when I had it in the passenger-rear location. The attached photo shows the current status. The fact that the same wheel (the new one, not the one in the photo), when installed in the driver-rear location has sufficient clearance still suggests to me that there is a set-up solution to this. (That is either hope or denial)

Steve

Clearance 4-29-12.jpg

[Duke W.]

Re: Wheel clearance_ brake backing plate set up

When Chevrolet went to wider wheels they decreased offset to +.06" in order to provide sufficient clearance. The KO wheels including the adapters have +.06" offset as do the '67 Rally wheels and bolt-on aluminum wheels.

It is a good idea to keep offset the same as OE, but there are two OE offsets: +0.44" for the 5.5" steel wheels and +.06" for all 6" wheels, and you now know the reason why offset was reduced with 6" wheels.

Whenever installing 6" wheels on earliers C2s I always recommend getting dimensionally identical replicas of the '67 6" Rally wheel- 15 x 6JK, +.06" offset.

Duke

[Steve D.]

Re: Wheel clearance_ brake backing plate set up

Thank you.

Steve

[David L.]

Re: Wheel clearance_ brake backing plate set up

Steve,

In your photo the end of the spring appears to be almost touching the backing plate and very close to the brake drum, not the wheel. Maybe you need a rear wheel alignment.

Dave

[Steve D.]

Re: Wheel clearance_ brake backing plate set up

Dave

The wheels have been aligned, and all is smooth up to 80 MPH (I haven't ventured beyond that). I will check with the alignment guy and see what he says about the spacing. As I noted in the original post, the distance between the spring and the backing plate is less on the passenger side than on the driver side.

Steve

[Timothy B.]

Re: Wheel clearance_ brake backing plate set up

Steve,

Do you have a reproduction spring on the car. The last two leafs look longer to me so I will go and look at my original 63 spring. Could the last leafs be longer causing the problem, try to measure them for length.

Take that spring cover plate down and check that center bolt to see if all is centered and the bolt is not broken.

[Steve D.]

Re: Wheel clearance_ brake backing plate set up

Tim

Can't be sure, but I think so. The ends of the upper leaves are turned up like original, but I guess it's possible that the bottom leaf got replaced. I'll check the bolt.

Steve

[Timothy B.]

Re: Wheel clearance_ brake backing plate set up

Steve,

When you check the center bolt, measure from the center bolt hole (main leaf) to the outside (by the wheel) and compare that each side of the main leaf measures the same. Someone MAY have drilled the center hole in the lower leaf not on center.

You can remove the spring plate by having the weight of the car on the tires and nothing will move, that's what I would look at first.