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Discussion Starter #1
have a 68 gto that I put on the year one 17 inch cast wheels. I replaced 14 inch rally ii's. I'm running 245 45 17's on the new wheels. I know the aluminum wheels have more weight, but I have experienced a significant performance loss with the new wheels compared to the rallys. Does the unsprung weight difference really affect performance that much? Someone mentioned the difference in circumferencemay be affectiing the axle ratio, does that follow? I have a 3:55 posi out back. I love the looks and the ride is fine, but in terms of wheelspinning and fun, the car now seems like a dud. Granted the 17's put more rubber on the road, and the old radial TA's were old and probably hardened with age, but i'm not happy with the performance. Anyone else have those wheels and can give me some feedback?

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Your tires are ~80 2/3 inches, stock was a G78-14 which is ~85 inches. So yes, you have essentially have a 0.95 overdrive on your car.

As for rotating weight, well opinions on that are all over the place. Take your pick. Any poor handling you experience probably is coming from your modern, square profile tires or worn out suspension components.
 

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Also, changing the size of you wheels doesn't affect tractive force. Your contact patch for a shorter, wider tire is probably smaller than stock. Tire height, if carcass/wheel flex can be controlled, is preferable to width.
 
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