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Old 08-04-2020, 06:36 PM
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Default Tire sizing for 17" on '71 GTO

The local tire shop has a set of low mileage takeoffs that I'm interested in for my .71 GTO. I was just thinking about redlines and painting my calipers red and came across them. They are Continental Extreme (summer tires) with redline sidewalls. Sizing is P285 40 x 17 (rear 26"H x 11.2"w) and P225 45 x 17 (front 25"h x 8.9"w)

I am currently running P255 45 x 17 (26' x 10") and P225 50 x17 ( 25.9" x 8.9").

I've checked out back and see no clearance issues there.

Do you think the smaller front tire will look wrong after I drop the front end 1"?

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Last edited by NeighborsComplaint; 08-04-2020 at 06:42 PM.
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Old 08-04-2020, 07:01 PM
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Bad idea with a stock suspension that positive cambers during braking...

Besides, they are out of scale with the body of that car and look silly..

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Old 08-04-2020, 07:43 PM
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You should have trouble fitting a 285 section width tire in the rear if your wheels are currently centered well enough. It’s only a 5mm increase in section width each side.

The car will come down about half an inch in the front and you’ll notice a bit difference in the tire to fender gab unless the car is lowered pretty significantly.

In regards to the braking standpoint, reducing the overall wheel/tire diameter reduces the instant center but also reduces the contact patch. That means that more braking torque is transmitted to the pavement, but total grip would be reduced if the tire replacement is apples to apples.

Going to a wider rear will change the handling balance slightly.

All of that however probably won’t ever be felt unless you’re driving the car at the limit. The biggest factor would be how you feel about the aesthetic change to the stance and the tire to fender gap.

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Old 08-04-2020, 09:08 PM
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Yeah, the 1" difference in the front tire height is the one that bothers me. That said, every time I look at my current tires, the fronts look taller than the rear to my eye even though they aren't.

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Old 08-05-2020, 01:49 PM
69gtocv 69gtocv is offline
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Quote:
Originally Posted by NeighborsComplaint View Post
Yeah, the 1" difference in the front tire height is the one that bothers me. That said, every time I look at my current tires, the fronts look taller than the rear to my eye even though they aren't.
JMO, but 25" tall front tires are going to look way too short. I ended up with 245/45/18's in front which are 26.7" tall on my 72. I'm lowered one inch and it came out just right.

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Old 08-05-2020, 03:32 PM
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For reference, here's a couple pics of Chevelles with 225/45R17 on the front:




Does look proportionally too small, even with the vehicle lowered. Possible just to purchase the rears, and buy new fronts to match?

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Old 08-05-2020, 04:11 PM
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Quote:
Originally Posted by 69gtocv View Post
JMO, but 25" tall front tires are going to look way too short. I ended up with 245/45/18's in front which are 26.7" tall on my 72. I'm lowered one inch and it came out just right.
Personally, I agree with this. Looks are always going to be subjective, but IMHO the a-body wants a slightly larger diameter wheel with around a 27" tire.

I don't think the GTO is cut as bad, but the Chevelle's wheel wells are cut quite a bit higher in the front than they are in the rear. At least on a Chevelle anyway, you can pretty easily get a staggered size 18/19 combo with a 27/28" overall height for each to look really well. It help get the car sitting a bit better as well, instead of the nose-up look they tend to have. It also hides the fact that the lowest point of the front bumper is several inches higher than the rockers which give the car an "unfinished" look up front.

That is something that due to the style lines on the car isn't as much of an issue on the Pontiac cars. The front valance also slops towards the back of the car which helps finish off that front end better. Pontiac designers knew what they were doing!

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