Help Determining wheel size on a C4 IFS & IRS 55.1GMC
 

Hello All I am at the point in my project that I need to hone in on wheel size
and tire size for my project.

Up to this point my truck has been sitting on 15" tires and wheels
borrowed from a 62 Impala minus my calipers and rotors.

To complicated matters I have bought a C5-C6 caliper adapter kit to increase my front braking power.

I do know that with the C5-C6 caliper my wheel size will at the minimum be 17"
which I'm good with.

So here is what I am asking, what is the most straight forward way in determining what wheel will fit in my fender wells?

My rear will be stock C4 set up, and I do not have any corvette rims to
test with.

Re: Help Determining wheel size on a C4 IFS & IRS 55.1GMC
 

I'd never seen this tool before you posted here: https://67-72chevytrucks.com/vboard/...d.php?t=851928

To be honest when I saw that post I wondered why someone would bother, but I can see it could fit your needs and answer the questions cheaper than buying the wrong size rims

To go with it, I'd head down the local tire shop, tell them what you are doing and ask if you can borrow a few tires in different sizes from their pile of used tires waiting for recycling

You could do the same thing with a tape measure, plumb bob and googling tire sizes. Not as visual and you'd order your new rims and tires with some trepidation

Re: Help Determining wheel size on a C4 IFS & IRS 55.1GMC
 

It's a big decision for sure. We did tons of trial and error with tires scavenged from anywhere we could find. At one point, we even cut out cardboard templates following various wheel and tire dimensions to test different scenarios. Numerous practical issues come to mind like: will the wheel fit over my calipers; will the tire rub on the frame or the inner fender; will the turning circle be impacted, etc.

But almost as important is visual aesthetics. Questions like: What stance are you going for? Do you want bigs and little's for some tire rake or same size all around? I like it when the top of the wheel opening in the fender lines up with the top of the wheel in both the front and back. Form over function I know but it's important to me.

Re: Help Determining wheel size on a C4 IFS & IRS 55.1GMC
 

17 inch is still a decent looking size without getting into the cartoon truck look. Sidewalls are still tall enough to look and ride decent. I had them on my 2K cad dts and have them on my 98 BMW 528I.

Tire size wise, this comparison chart lets you compare two tires and you can even change rim sizes by several inches. Plus it is just fun to play with. https://tiresize.com/comparison/

Searching shows that the C-4 guys can't agree on how to measure from wms to wms let alone get a measurement. You do need the weight of the truck on the rear suspension so that the axle shafts are pretty parallel to the shop floor or sitting how they will be running down the road. You may have to cheat and slide under it and measure from rotor surface to rotar surface and then pull a wheel and measure from that surface to the wheel mount surface and X2 and add that to the inside measurement.

Snooping on Rock Auto the rotors average 2.5 inches tall sitting on the table. Meaning from back surface to wms would add 5 inches to the width if you cheat and measure it that way. Bed is 50 inches plus a few thick frog hairs and outside to outside of the rear fenders is 74-1/2 subtract 1 inch for fender lip on each side and you have 72-1/2 minus what you are comfortable with as far as clearance on the inside and out. My 255 tires are 10 inches wide and that doesn't leave a lot of comfort zone with less than an inch on the inside and not much more on the outside.

Re: Help Determining wheel size on a C4 IFS & IRS 55.1GMC
 

Thanks guys for your input, I do appreciate it!

Idealy I would like same size wheels / tires and not to exceed 17"!

Had not thought about getting as close to total rear end weight as would be,
adding the wood weight and tail gate etc!

My vision is to have a sleeper ( on steroids may be) looking 55.1 GMC.
Meaning the interior will be as comfortable as I can make it.

keep these thoughts and idea coming!

One thing I forgot to mention that my rim selection will be smoothies!!!
I have alway loved that style rim on these old trucks!

Re: Help Determining wheel size on a C4 IFS & IRS 55.1GMC
 

I clearly am having a hard time learning this system and I am sorry for that!

Re: Help Determining wheel size on a C4 IFS & IRS 55.1GMC
 

Mr48chev

You are running 10" 255's on the rear what size fronts do you run?
Do you run the same size tire and wheel all around?

Re: Help Determining wheel size on a C4 IFS & IRS 55.1GMC
 

I have C4 front and rear suspension and have 16x8s with 4.25 backspace to put under it when paint and assembly is done. Can't find my notes on what tire size to get to work with the speedo in the 700R4. Wasn't much of a side wall bump out. That doesn't help with your C5 front rotors, but steel 8s are real close to frame and rear fender. I've guessed on the front clearance from memory from mockup junkyard 15x7 wheels before disassembly. I ordered the wheels over a year ago after others had said that's about the biggest that will fit. I might have to downsize.

I'ts all a guessing game until the end.

Re: Help Determining wheel size on a C4 IFS & IRS 55.1GMC
 

I ran 14x7 Enkie 32's with 195-60-14 tires on it for years. Staggered wheel size for big and little tires Per Boyd Coddington's concept of having the side walls of the tires have the the same percentage of sidewall to wheel size front and back. His theory being that if you have the same diameter wheels with big tires on the back and little tires on the front like a lot of roadsters have the fronts look funny compared to the rears.

Not a whole lot of difference If I had run 15x7 on the front though.

Re: Help Determining wheel size on a C4 IFS & IRS 55.1GMC
 

After much thought I went ahead and ordered these tools to help me on my journey

Hopefully this will be money well spent!