Tires

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

	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.
	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:

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.
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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