Wheel and Rim Compatibility

Q: Wheel and Rim Compatibility

I am planning on buying 15X8 wheels with a 4″ backspace. I would like to go with 225’s up front and 275’s out back. Will this work without body modifications? Anyone currently running this setup? I have seen 275’s on 1st gen camaros, but never had a chance to talk to the owner.

A: It would be helpful to know if you’re talking about 60 or 50 series tires. This would greatly affect the fit question.

1st issue, the wheel. The factory 14×7 and 15×7 typically have a 4″ backspacing. If you keep the back spacing the same, but make the tire and wheel wider, most of that new width goes to the outside. 4.5 inch backspacing on an 8 inch wheel would distribute the new width equally to the inside and outside. In measuring my car (’68), I found that I had room for 5″ backspacing on an 8 inch wheel. This allowed me to fit a 265/50R-15, and not have it stick out of the wheel well.

Now for tire sizes… If you are talking about 50 series tires, a 275/50-15 would most certainly protrude beyond the wheel opening. That tire will be about 10.82 inches wide, and will most likely be sticking out about an inch. If you use this tire and wheel combo, you will have to raise the car high enough to clear this tire, but it’s up to you to decide it that looks good to you.

Where the 50 or 60 series issue come up is related to the tire height. A 275/50-15 about 25.8 inches tall, a 275/60- 15 will be about 28 inches tall! You’re going to have to lift the rear of this car alot to clear a 28 inch tire.

Check the inside of your wheel well. The potential con- tact areas will be… the top inside area of the inner wheel house, The leaf spring, and then the lower shock mount are the moste likely places where it might rub.

I would suggest the following steps.

• Remove your present wheel and tire, and measure the backspacing.

• But the tire and wheel back on the car. Now measure the amount of clearance you have, both on the inside and the outside. Allow at least half an inch for side to side movement of the axle, plus a margin for up and down movement, and then you can determine how much larger than your present tire you can fit. Pay attention to where you want the wheel/tire center- line, and what backspacing is needed to make it fit.

• The end result will be that you will know that you can go x inches wider than present, but need y inches of backspacing to make it work.

A: Why do all this measuring? I could tell you that you could fit tire size x on wheel y. This would work for a smaller tire, with much larger margins for error. But when you get into the big stuff, you have less room for mistakes. Each car is somewhat different, and the clearances onmy car may not be the same as yours.

Q: Rubbing and Fit

You mentioned that you were running a five inch backspacing on a 15 inch rim with a 265/50-15 on the rear of your 1968. Did they rub or hit at all (over big bumps, etc.)? I assume that you did not modify your rear suspension and that your springs were in good shape. Right?

If this combination gave you trouble free performance, I would love to see a picture to help get an idea of the appearance. Also, what are you running up front

A: The car got about 800 to 900 miles usage before going dormant to get the interior sorted out. That included about 700 miles of highway driving (trip to Reno), and the rest was low speed cruising on various road conditions. We did a lot of driving in and out of various driveways and parking lots that were off camber or had steep drives.

The rear suspension consists of all new parts including 5 leaf springs, KYB shocks, bushings, and shackles. No rubbing or hitting in the rear was noticed.The parts are all stock re- placements.

Presently the rear sits a bit high by my preferences, about 3 inches above the tire. I hope that the springs will settle. If not, I’ll have to remove a leaf to adjust the ride height. No problems with the ride being too stiff or harsh.

I was running 225/60R-14s on 14×7 ralleys, which were in rough shape (the wheels). I have since changed to 225/60R-15s on 15×7 Ralley IIs. The front tires would occasionally hit the inside of the wheel wells when I drove to quickly into a driveway. The front springs have had 1 coil removed to get the nose down.

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