pinchvalve
pinchvalve MegaDork
10/25/19 9:48 a.m.

I am looking to maximize tire width in STH for next year. The plan is to see how much I can squeeze under a Fiesta within STH rules. If I order custom wheels, how do I measure for them?  I am thinking about ordering one tire to use as a mockup perhaps? Or borrowing some end-of-season cast offs? Or using measurements of tires from TR and mocking something up out of cardboard? Anyone ever done this?

z31maniac
z31maniac MegaDork
10/25/19 10:12 a.m.

Take the current wheel size and offset. Measure inboard and outboard clearance, don't forget to turn the wheels to lock, then some simple math will get you pretty close. 

pinchvalve
pinchvalve MegaDork
10/25/19 10:18 a.m.

Damn, I was hoping you wouldn't use the M word.

RevRico
RevRico PowerDork
10/25/19 10:19 a.m.

Paging MKE to the white courtesy phone. 

Maybe dig through that wicked Ferrari build thread of his. I know it's huge, but he just got custom wheels made.

79rex
79rex Reader
10/25/19 7:57 p.m.

Unfortunately theres no way around not using math when trying to size custom wheels.  I fabed a test wheel when I fiited my 15x10s on my neon.  Rolled the diameter with thin sheet metal, then tacked to more sheet metal with my bolt pattern.  Tack it at a certain back spacing, check it.  Either cut tacks and repeat at a different backspacing, or order wheel if clearance is sufficient.

ProDarwin
ProDarwin UltimaDork
10/25/19 10:07 p.m.
z31maniac said:

Take the current wheel size and offset. Measure inboard and outboard clearance, don't forget to turn the wheels to lock, then some simple math will get you pretty close. 

Also don't forget to account for alignment settings.

Strut and fender clearance are usually not too difficult to measure. 

Clearance for full compression travel can be difficult without taking the springs off the car.

Clearance for the control arms can be difficult to measure without creating a 'barrel' as suggested above.

Curtis
Curtis GRM+ Memberand UltimaDork
10/26/19 1:05 p.m.

Someone here made me a CAD of some wheel bolt patterns which I'm going to cut into a piece of plate steel with some bolt-on arms  In the arms I'll weld some 3/8" nuts and get some 3/8" allthread cut in lengths that represent common tire widths.

Slide the arm out to match the radius of the tire, thread in the corresponding allthread that represents the tire width, and adjust it in and out.  Then I can droop and compress the suspension and turn the wheels to make sure I have clearance.

Then it's just a matter of measuring the inside length of the allthread versus the outside and subtract.  Bingo.  Offset.

stuart in mn
stuart in mn MegaDork
10/26/19 4:41 p.m.

Most wheel manufacturers have information available on how to measure for wheels.  Here's one example: https://www.americanracing.com/wheel-measure-guide/

Ranger50
Ranger50 UltimaDork
10/26/19 4:50 p.m.

Get one of those wheel/rim simulators from summit/jegs. Provided you have a 4 or 5 lug pattern...

iceracer
iceracer UltimaDork
10/26/19 9:19 p.m.

Negative camber can reduce the inside clearance.

tire diameter is easy to figure or you can do it the old fashioned way with a long tape measure

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