Wheels / Tires: How to: Measuring GT Hawk wheel wells for BIG tires

[studebaker-R2-4-me]

I've been pondering buying some big tires for my GT Hawk in preparation for this year assault on the Pure Stocks, but I've been worried whether 235/70R15 redlines would fit, even after one member said that he runs these big tires under his R4 Hawk.

I been scouring the internet on the best way to measure the wheel wells to be able to fit the biggest tire under my car. What I came up with is making a jig out of some scrap 2x4's I had laying around.

The first task was to measure the backspace of the FoMoCo Crown Victoria rims I purchased today at the local scrap yard for $25/piece. I managed to find 4 of them. My lucky day.



Backspace is measured from the mounting surface back to the edge of the rim. These Crown Victoria rims are 4 1/4" backspace. I also measured from the mounting surface to the front edge of the rim. The Crown Victoria rims are 3 3/4". Offset is the distance the mounting face is off the centre of the rim. This is important to set up the wooden jig.

Next in line is measure the front disc rotor's hub. The stock rotor's hub is 2 1/4" Divide this number in half to get the centre of the hub. This is important to minus the 1 1/8" from the radius of the big tire you want to install. The BF Goodrich 235/70R15 tire is 28" in diameter... 14" radius. Tread width was 7" and Section width was 9.5". Cut all wooden pieces to these lenghts.

With the specs of the tire you want go with you can now set up the jig. So the first wooden stick I cut was 12 7/8" long (14" - 1 1/8") and two others 7" and 9.5" for tread and section width.



The wooden jig represents the tread width, section width, and radius of the tire with consideration for offset (not backspace) of the rim. When you place the jig up against the hub you are able to rotate the rotor with the jig to see any interferences that the tire would have. The 235/70R15 was just to close the the frame rail for my comfort zone so I made another jig to represent a 225/70R15 tire from the spec off the Coker site.

Dimentions for the 225/70R15 BF Goodrich Redline's off the Coker site are 27.4" diameter 6.7" Tread and 9" sectional width.

With the new jig made and tried out, I was happy with the clearances and ordered my tires today.



The picture doesn't show the clearances too well but there is a good 1.5" to the frame rail and about an inch to the "mud pan".



I tried using the Chrysler Cordoba rims that were on my Hawk but the offset was way different than the Ford rims on my Lark, causing alot of interference, hence going out and getting the FoMoCo rims and bead blasting them this afternoon. I guess tomorrow I will be going to buy some Wimbleton White Code M dupicolor and spray my new wheels.

I should have my new tires by next week.

Allen

[doug]

Thought you had to run stock tires in the PSMDR.

[Pat Dilling]

Here are the tire rules from the PSMCDR web page:

"You are allowed to run tires one size over stock, with G70s being the largest size allowed for cars with 70-series tires, and G60s the largest allowed for cars that came with 60-series tires. All four tires must be the same size. No 60-series tires will be allowed unless they were originally available for the car's year and model. 60-series tires must be run on 15-inch rims as they were originally. Cars built before the introduction of 70-series Polyglas or Wide Ovals are allowed to upgrade to 70-series of appropriate size. Factory wheels only. Wheels must be correct in size, offset, and style for the car's make, model, and year. All four wheels must be the same size and offset."

[53 stude mod]

I don't know about the spacing you are looking for but what a great idea you came up with. The closest set up I saw was maybe
100.00 or more. I am impressed.............53 stude mod

[PackardV8]

225/70R15 BF Goodrich Redline's

Yes, larger than 6.70s
No, wouldn't call 'em BIG
Maybe, keeping in context, 245/50-16" and 245/45-17 will fit with the correct offset. Some who can tolerate the occasional rub have run even larger.

Bottom line, the Ford wheels and the 225 radials tires aren't rule-book legal for PSMCDR, but those here who've run it say they don't always enforce to the small print.

jack vines