295/50/15 Rear Tyres on 67 Impala - Impala Tech
Wheels & Tires What fits?

 
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post #1 of 3 (permalink) Old 07-09-2012, 09:16 PM Thread Starter
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295/50/15 Rear Tyres on 67 Impala

G`Day all, My apologies if this has been discussed before, but if it has I sure can`t find it. I`ve also googled til my fingers get sore & cant find any difinitive answers anywhere.
I`ve seen several Impalas at car shows here in Australia, but haven`t been able to speak to the owners, with 295/50/15 rear tyres fitted, so hopefully someone can help.
I have a 1967 4 Door Hardtop, that i`d like to fit 295/50/15 rear tyres to. I`d like to know if any Impala owners can advise the backspacing of their 10" rims and if any modifications were required to make them fit ??
Thanks in advance for any help.
Regards,
Jeremy

67 RHD Australian Delivered 4 Door Hardtop Impala
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post #2 of 3 (permalink) Old 07-09-2012, 10:08 PM
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The reason you can not find a definitive answer is every car is different (unless you have a concours white glove chalk mark correct restoration). Spring sag, cut spring coils, air bags, or air shocks all affect the ride height of your car as you find it when you bought it. This affects not only the up and down position of the wheels in the wheel wells, but their fore and aft distance, as well as any difference in side to side measurements. Trouble is you have no idea what a previous owner has done to your car before you bought it. This results in your ride height being different from the next car "just like yours". It will have different spring rates, and depending upon the condition of the bushings it may not even follow the factory designed movement path.

This is because your wheels do not just go up and down. They are attached to control arms that swing in an arc. In addition to this the side to side position is controlled by a Panhard bar that swings the rear axle in an arc that lies on a plane ninety degrees out from the plane the axle swings in. As it moves up and down the axle first approaches the passenger side's outer fender and then retreats from it moving to the other side of the car.

Wheels: The factory used a neutral centering, or a back spacing equal to half of the wheel width. Custom aftermarket wheels use different back spacing from stock wheels (in fact no two companies sell the same wheel; as each builds a wheel to look different from their competitors in the hope of attracting you to their "look". The proverbial Chrome Reversed look of the fifties was caused by cutting out the center of the wheel and flipping the wheel around (so you had to fill it from the back side of the wheel) and welding it back together again. This was done to get a different offset to make your wheels look deeper and wider than they actually where (unless you bought Magnesium alloy racing wheels there wasn't much available in the late fifties to early sixties as far as aftermarket wheels went).

With the introduction of cheap sand cast aluminum wheels in the mid sixties reversed rims all but disappeared and Magnesium wheels (the reason the term mags was coined) where reserved for race cars only once again. A sand cast wheel could be in any shape and style with offset any where you want them. Aluminum (unlike Magnesium and Titanium) is easy to machine and polish so thousands of different wheel styles shapes and sizes exist now.

Finally tire size in today's market isn't just the width any more (when new, your car took a 7.75x14 inch tire. That was it, they only came in that one size (7.75) and every one was like the next one dimensionally. Today the tire size as well as the ratio of tread to side wall is offered as an option. So your old 7.75 became an E78-14 tire which has morphed into a 205R70-14; but that tire isn't the same size dimensionally as the original 7.75 tire that came on the car that it is supposed to replace. It is just the closest we can get to the original size with today's selection.

Will the biggest tire you want fit. The answer is sure: if you are willing to modify your car (just like all of the previous owners have) to make it fit. Will it fit without rubbing just by sticking it on some unknown size rim I don't know. I always tell people to measure what you have for space and do the math.

Big Dave
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post #3 of 3 (permalink) Old 07-09-2012, 10:14 PM Thread Starter
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Thanks Dave, appreciate all of that, but would still like info from other Impala owners so that I can see if theres a trend with backspacing/modifications required. Cheers.

67 RHD Australian Delivered 4 Door Hardtop Impala
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