[Jack21]

Paul, you're not hijacking the thread. Backspacing is an important consideration, but it depends on what you're using for a front and rear suspension and brakes.

With a CR, assuming you're using the MII front or aftermarket derivative, and a mid 80's 8.8 diff, my backspacing was 4" front for the 8" wheels, and 5" rear for the 9 1/2" wheels. With a different suspension, you have to measure it, and baseline your backspacing on the original factory wheel.

And you might want to get Don Scott's opinion on this also.

My brakes were installed already and were setup for 15" wheels. I can upgrade to bigger brakes with the 17's. Anyway, fronts are 11" Grenada rotors with '66 Mustang GT, 4 piston calipers. They are newly minted copies of the Kelsey-Hayes calipers from Stainless Steel Brakes. Rears and master cylinder are off '87-'89 Tbird Turbo Coupe from Ford Racing Mustang rear disk brake conversion. Rotors are 10" with single piston caliper.

Backspacing - front. The stock CR wheels were 15 x 8, used a 235 tire, and had a 4" backspacing. It fit fine, so I copied it to the 17".

Backspacing - rear. Going from an 8" to a 9 1/2" wheel was a tight call. I was tempted to split the backspacing like the fronts, and use 4 3/4". For insurance, it's easier to shim a wheel out, than in, so I went with 5" backspacing.

The 17" tires are a lot smaller than their 15" counterparts! There is no sidewall bulge like the 15's. You have a lot more fenderwell clearance. The overall height is the same, about 25 1/2". But these guys are all tread, and perfectly flat! The car looks "All Business", like a Porche, or M class Beemer, not like a '60's hot rod.

They don't break loose and spin like the 15's either if you get tires with the "AA" traction rating. No smoke, all go. My 275's are almost a foot wide.

One more thing. Wide tire - light car = hockey puck on a wet road. Totally untrue with these 17's. They're designed for wet roads (just not ice and snow). On the way to DVSFIII in '02, it was rain and thunderstorms through the twisty, winding roads of Western PA, and WVA. Car tracked straight and true, passing trucks, keeping speed 75 - 85 all the way.

So good luck with your wheel and tire upgrade.