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Tires

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195/60HR15 on 5.5 in. rims next to 165HR15 on 4.5 in. rims


The standard tire for 1965-1969 912s were 165R15 on 4.5 in. steel rims. 5.5 in. steel rims appeared in 1968. 1969 had some other factory options including 185VR15 on 6 in. rims and 185HR14 on 5.5 in. rims.

I upgraded to fatter tires this week using some 5.5 in. steel rims picked up at Parts Heaven last week.

Forged Fuchs alloys were optional starting in 1967. We considered getting Fuchs, but have decided to wait.

Tire Rubbing



020428-1028 I selected 195/60HR15 tires for font and back. However, the fronts rub on the shields for the shocks. This rubbing only occurs when the car is on the ground - they rotate freely when on jacks and the shock is extended. As a result I did not notice the problem at first.
020428-1026 There are a couple of solutions for the problem. Narrower tires for the front (185/60HR15) or spacers that move the tires out from the shock struts come to mind. For now I have removed the shields, substituting large galvanized steel washers for the mounting shoulder at the top of the shield.


Tire Pressures



This table shows factory standard and optional wheels and tires that were available on various 912 cars.

 Wheel Size Tire Size Tire Pressure
 4.5JX15 165HR15 29psi 32psi
 5.5JX15 165HR15 29psi 35psi
 6JX15 185VR15 32psi 35psi
 5.5JX14 185HR14 32psi 35psi


The wheels are stamped with sizes and dates.

Fuchs Alloys



The forged aluminum alloy Fuchs wheel was the only alloy available for many years on Porsches. It first appeared in 1967 standard on the 911S and optional on other models in a 4.5 in. x 15 size. It went to 5.5 in. in 1968 and some 6 in. x 15 were available in 1969. There was a 5.5 in. x 14 variant in 1969.

The 6 x 15 was offered in two versions distinguished by differing offset and the step-down which allows tire mounting. The earlier one has more offset and a step-down further from the outer rim edge. Tires should be mounted from the back of the rim on this rim. Mounting is difficult on these and high performance tires are particularly hard because of extra reinforcement in the head and sidewall.

In 1972 a new design was introduced with less offset.

There were several variants of center hub sizes leading to differences in cap sizes.

Yokohama Avid H4 Tires



The tires are asymmetrical. There is an arrow on the tire indicating the correct rotation direction. Be sure to check after they are mounted that all four wheels rotate in the direction of the arrow.

Features of this tire:
  • Extra strong Honeycomb Carbon Technology
  • 20 V-Groove for maximum water drainage
  • Unidirectional tread design for optimal wet handling ability
  • Solid center rib for increased high-speed handling and stability
  • 45,000-Mile Limited Tread-wear Warranty


Yokohama Factory specifications:

 Tire Size 195/60R15 87H
 UTOG 360AA
 Rim Width Measured (in.) 6
 Rim Width Approximate (in.) 5.5-7.0
 Inflated Dimensions Overall Width (in.) 7.8
 Inflated Dimensions Overall Diameter (in.) 24.3
 Tread Width (in.) 6.2
 Loaded Dimension Tread Depth (1/32 in.) 10
 Loaded Dimension Static Radius (in.) 11.6
 Rev/Mile 855
 Max Load @ Cold Inflation Pressure (lbs@psi) 1190@35


The table is from the Yokohama web site.

Comparison of the Old and New Rim/Tire Combination



   165HR15 195/60HR15
 Max Width 6 3/8 in. 7 7/8 in.
 Offset (1) 1.7 in. 1.6 in.
 Rev/Mile (2) 827 855


Notes:
  1. Position of the inside mounting surface compared to the center line of the tire. There is only 1/8 in. difference the the tire centerline on the two wheels. This based on measurements off the mounted tires, old and new.
  2. There is a 3.4% difference in revolutions per mile with the new tires, the new ones being lower profile and smaller diameter. I would expect this difference to be seen with an equivalent change in the speedometer accuracy, bring it closer to being correct. With the old tires, 70 mph indicated was 75 mph actual. Now 70 mph indicated is 71 mph indicated.
Last modified: Wed, 20 Mar 2002

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