Tire Size on 4 1/2x 15 Wheels

[Bob DiCorpo]

Could someone tell me if there could be any problems using tires that are size 175/65R/15 on a 356B coupe with 4 1/2x 15 standard wheels? Thank you, Bob

[Doug McDonnell]

Those should work depending on ride height,previuos body work, If a problem will probably be in the rear.But I don't think you are going big enough to cause a problem. Lots of discussion in the permanent tire sticky at the top of main discussion page. 24 pages of comments in fact.

[David Jones]

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.

Standard tire size for 1963 Porsche 356 C/1600 SC Coupe:
(in case of different tires in front and rear the dimensional data are valid for driving or rear wheels)
Standard tire size:165 R 15
Tire width (mm):165
Tire sidewall factor:82
Rim size (in):15
Total wheel diameter (mm / in):
652 / 25.7
Tire air pressure (cold):
Front:230 kPa / 33 psi / 2.3 atm / 2.3 bar
Rear:230 kPa / 33 psi / 2.3 atm / 2.3 bar
I do not agree with these tire pressures. I like a differential of 3 to 5 psig. Lower on the front.

https://www.tacomaworld.com/tirecalc?wi ... 65&rim2=15

[Bob DiCorpo]

Thank you Doug and David. I'll also look into the 185. Bob

[Al Zim]

We have used the Michelin 185/65X15 tire successfully on the 4.5 inch rim. I have found that if you are ordering from Tire Rack tell them you have a 912 with 5.5 inch wheels. This alleviates all their fears about fitment. al zim

[Edwin Ek]

185-70 tires have almost exactly the same rolling radius as original, so no error with the speedometer or odometer.

185 x 0.7 = 129.5
165 x 0.78 = 128.7

Difference in sidewall height is 0.8 mm per sidewall, or 1.6 mm overall (top and bottom together) difference in diameter. Keeping the same sidewall height means ride comfort is unchanged.

[Erik Thomas]

I have no idea why folks install the 185-70 tires. To me, the 165 tires look original, and do not suffer as much deformation with the swing axles. Who drives a 356 on the street such that 165 width tires are not sufficient? I road race with the VSCCA on 165x15 Blockley radials. Never felt that there was an issue with tires. The issue is the nut behind the wheel.

[Erik Thomas]

Bob: Sorry if I seemed to harsh on your choice of tires. I meant to say that around my 356, the problem was usually the nut behind the wheel, as in myself. My apology for being a clod.

Blockley lists 4 1/2 inches as the minimum width for the 165 tire, and 5" for the 185. (they do not make a 175) Generally, Blockley's are designed for narrower rims than a lot of other tires.

[Bob DiCorpo]

Hi Eric,
Your advice was very much appreciated. I actually went to the Blockley Tyre website to look at their tires. I had never heard of them before. The tires are actually for a friend of mine's car, which is currently in my garage. He just purchased it from a seller here on the East Coast and I'm trying to do a bit of preparation work on it over the winter, as he and his wife will be picking it up in the spring and driving it back to Las Vegas, where they live.
I personally have Michelin 165/15 SR's on my car. He's trying to find a tire that is a bit less expensive, but not of real poor quality. BTW, we're all nuts when we're behind the wheel of our 356's. Thanks, Bob

[David Jones]

Bob, you can buy a set of 185 x 65 x 15 tires from Amazon. My pick would be this one https://www.amazon.com/Kumho-Solus-TA31 ... +65r15+88h
Another option but more money would be these folks. I understand shipping is not as much as would be expected.
https://www.longstonetyres.co.uk/classi ... e/356.html
I do not think the Blockley tires would be a good choice for the street as the compounds made for vintage racing are not going to last long for street use.

[Albert Tiedemann]

In the March 1965 issue of Panorama there is a table relating tire size to odometer error and to the calibration standard for Porsche speedometers in revolutions/mile. Important then for the Rally enthusiast. There is also a float level gauge for the Zenith Carburetor that is/was a precursor to the one offered by Precision Matters cited therein. The tires on the silver car on the cover were Michelin X 165mm x 15inch at 800 rev/mile.

[Edwin Ek]

Hi Eric,
Your advice was very much appreciated. I actually went to the Blockley Tyre website to look at their tires. I had never heard of them before. The tires are actually for a friend of mine's car, which is currently in my garage. He just purchased it from a seller here on the East Coast and I'm trying to do a bit of preparation work on it over the winter, as he and his wife will be picking it up in the spring and driving it back to Las Vegas, where they live.
I personally have Michelin 165/15 SR's on my car. He's trying to find a tire that is a bit less expensive, but not of real poor quality. BTW, we're all nuts when we're behind the wheel of our 356's. Thanks, Bob

Bob, Vredestein Sprint Classics are a great tire. Very, very popular with this crowd, and a little cheaper than Michelins. HR-rated also. Not that our cars need the higher speed rating, but a higher-rated tire runs cooler at all speeds, which is a good thing.

[Bob DiCorpo]

Thanks everyone. Lots of good choices. I'll have my friend read all these posts in order to make a good decision for himself. Bob

[Erik Thomas]

Bob:

I do not agree at all that the Blockley tires are just for racing. While they seem fine at the track, they have been on my 356 B coupe since 2012, and about 2500 miles a year on the road x 6 = 15K miles. They still look new. These have a tread pattern similar to the old Dunlop radials of the period. While they are not cheap tires, you get what you pay for.

Erik

[John Lindstrom]

Steal some 5.5's and put these on https://www.toyotires.com/tire/pattern/ ... tion-tires