A couple of tire fitment test questions

[jwatts]

I am working on a 1966 Chevelle. My plans are for it to be more of a restomod that handles rather than a full blown pro touring car. I have been doing a lot of research on what tires and wheels I want to go with. The car is set to be out of the body shop in a few weeks and I can get back to work on it myself. This leads me to a few questions I have.



First, I have 295/50-15s on 15x8s on the rear. I plan to go with anywhere from 18s to 20s on the rear by the time the car is complete. I was thinking of renting a tire/wheel measurement tool to make sure I can get the wheels and tires I want to fit under the car. If at all possible I would like to run 295s on the back on either 9.5 or 10 inch wide wheels when I am done. Could I remove one of my 295/15s from the wheel and use it with the tire/wheel fitment tool? I know the height will likely be a shorter than the final tires I plan to use. Would I be ok using one of my 295s to test the width and what backspacing I would need on my new wheels? I don't think the height will be any issue, but the width will be close.

Second, I plan to swap the rear drums for either LS1 Camaro or C5 Vette disks. Should I do this prior to checking fitment? Will swapping from drum to disk change the overall width of the rear end at all, or enough to matter when it comes to backspacing?

[astroracer]

You currently have a 295 on the car and it fits. There will be no difference, width-wise, between a 295/50-15 or a 295/45-18. The 15" tire is about 26.6" in dia. the 18" tire is about 28.5" tall. 1" difference radially then the 15.
If the 15" set up fits with no issues all you need to do is measure the back space on the 15" wheel (it's probably close to 4 1/2") and make sure the 18" wheel you want comes in that back space. And it should, that is a zero offset wheel and is a common set up.
I would do some judicious measuring and see if a 305 or 315 couldn't be stuffed in there. (and you don't need a "wheel fitment tool" to do it.) A straight edge and a measuring tape will do the job.

And do the brake swap before you order wheels!
Mark

[jwatts]

Thanks for the reply. my main concern is with the width on a wider wheel. Currently they are on 8 inch wheels. They are ballooned out and not near as wide as they would be on a 9.5 or 10 inch wheel. At least I think they would be wider on a different wheel. I may measure it all out and factor in a little extra tire width when I do my measuring. I would love to get a 305 under it. I have seen similar cars with 305s so it may be an option. When the body man put the inner and outer fenderwells in I had him trim the pinch weld as much as he could to allow more clearance for tire height. He also went ahead and trimmed the rear fender lips before he put them on so I could get all the clearance possible width wise.

[astroracer]

Your course of action should be to measure the car, as it sits on the ground.
Measure from the inner and outer fenders to the sidewall of the tire. Make yourself a drawing so you can record those dimensions (I HAVE to do this anymore as I can't remember this stuff like I used to be able to. :( ).
Measure to all points around the tire that may be a clearance issue. Check the exhaust too if it runs through the area. Doing this will give you the parameters needed to figure out HOW BIG of a tire will fit.
Now, pull the rims and do all of the same measuring to the wheel mounting face on your NEW rotors. This will set the parameters for HOW BIG of a wheel will fit and what offset will be necessary to stuff a big one in there.
If you can post a pic of your drawing I can help you muddle through the numbers. This is really pretty simple once you've done it a few times.
Mark

[Typhoon1015]

I am running a 275 35 18 front and 295 35 18 rears on my 66 chevelle. Cant do any more than a 295 without minitubbing imo.

[jwatts]

I am running a 275 35 18 front and 295 35 18 rears on my 66 chevelle. Cant do any more than a 295 without minitubbing imo.

That's what I figured. 295s are good enough for me though.

[jwatts]

Your course of action should be to measure the car, as it sits on the ground.
Measure from the inner and outer fenders to the sidewall of the tire. Make yourself a drawing so you can record those dimensions (I HAVE to do this anymore as I can't remember this stuff like I used to be able to. :( ).
Measure to all points around the tire that may be a clearance issue. Check the exhaust too if it runs through the area. Doing this will give you the parameters needed to figure out HOW BIG of a tire will fit.
Now, pull the rims and do all of the same measuring to the wheel mounting face on your NEW rotors. This will set the parameters for HOW BIG of a wheel will fit and what offset will be necessary to stuff a big one in there.
If you can post a pic of your drawing I can help you muddle through the numbers. This is really pretty simple once you've done it a few times.
Mark

Mark,

I appreciate the advice. Once I get the car back home I will draw up a diagram and get some measurements. I will get a set of rotors, even if they are trashed, to get some measurements with.

[astroracer]

You have a plan. if Justin could list his wheel specs that would give you a ballpark. Width, Backspace, Offset if any.
Mark

[jwatts]

You have a plan. if Justin could list his wheel specs that would give you a ballpark. Width, Backspace, Offset if any.
Mark

I PM'd him. Turns out we both have the wider 68 and up width rear end. His wheel specs and mine should be the same. I just need to measure and verify. Thanks for all the help.