Tire Size on 4 1/2x 15 Wheels

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Pierre Ducroit
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Re: Tire Size on 4 1/2x 15 Wheels

#16 Post by Pierre Ducroit »

I apologise to get in these post with a question.What would be the difference on having 16 wheels in a 1956 356A,would it alter something like spedommeter acuuracy?what more problems should i excpect?or any benefeats?
thanks for your advise.

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Re: Tire Size on 4 1/2x 15 Wheels

#17 Post by Edwin Ek »

Pierre, are you asking about Porsche supplied 16" x 3.25" early rims or aftermarket rims?

The circumference of the tire determines the accuracy of the speedometer and odometer. If you keep the same circumference (same overall height of the rim tire combination), the accuracy is unaffected.

Keeping the same overall height and switching from a 15" rim to a 16" rim means that the height of the sidewall must shrink by half an inch. That shorter sidewall means less rubber so harsher ride and crisper handling.

If you are talking about original 16" x 3.25" rims, you use some very skinny tires. That's not good for handing or braking. Plus, you don't have many choices for tires, let alone good tires.
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Pierre Ducroit
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Re: Tire Size on 4 1/2x 15 Wheels

#18 Post by Pierre Ducroit »

than you very much for the explanation.

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Jules Dielen
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Re: Tire Size on 4 1/2x 15 Wheels

#19 Post by Jules Dielen »

16 inch wheels also require tubes. Not very safe.
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Re: Tire Size on 4 1/2x 15 Wheels

#20 Post by Dwayne Deese »

Mr Jones wrote
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Re: Tire Size on 4 1/2x 15 Wheels
#3 Post Thu Nov 16, 2017 9:43 pm

Bob, your speedometer is going to read high because of the smaller rolling radius of the 175 x 65 tire. A 185 x 65 will get you closer to the original tire diameter of the 165 x 80 x 15and the correct rolling radius plus your handling may be better because of the small increase in footprint.

I found pictures of the 165 15 SR Michelin on 4 1/2 rims
Does any one have a photo of the 185 65 for stance comparison?
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Re: Tire Size on 4 1/2x 15 Wheels

#21 Post by Al Zim »

We are headed to the Hill Country Rallye in March in a 1957 356A with 16 inch wheels. These wheels are custom made and you can mount a set of significant tires on them. AFTER YOU HAVE THEM MADE: DO NOT USE CHEAP "AMAZON TIRES" If the tread comes off the tire! plan on some expensive down time to repair the damage.
Last edited by Al Zim on Wed Feb 21, 2024 12:46 pm, edited 1 time in total.
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Re: Tire Size on 4 1/2x 15 Wheels

#22 Post by Jules Dielen »

Also before you mount any tire, cheap, good, bad, ugly, put your freshly 'made' rims on a balancer. I had some of mine restored at a recommended shop in Cali and 3 out of 4 were so out of round they were turned into (very pricey) hose reels.
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Re: Tire Size on 4 1/2x 15 Wheels

#23 Post by Al Zim »

DETERMINING IF THE RIM IS CORRECTLY ASSEMBLED: This can be done on a Road Force machine. Unfortunately road force cannot evaluate the tires that you will be using on your car. Their construction is too flexible. al
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