TECH TIP Technical Index
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"Where the Rubber Meets the Road"

Face it, tires are one of the more forgotten pieces of equipment on our VWs. They go through extreme heat on those 100 F days, extreme cold below zero, all kinds of scrubbing, bumping, beating, banging, and everything else that can try its best to tear them apart. Yet tires seemingly are able to hold together under all this (except you-know-who). In this tech tip, I will briefly explain how you can select the right tire for your VW (this can also apply to "those other cars").

First, I will start with general knowledge of tire sizes. In the late 40s and early 50s, VWs had narrow (4-inch, Herschel?) 16 inch rims. From 1952 on all VWs had 15 inch rims, varying from 4 inches to 5.5 inches wide. Busses from the early 70s on had 14 inch rims. The hardest-to-find tires would be for the old 16 inch rims on the early VWs. Fourteen and fifteen inch tires are much more common and widely available.

Now that you know what the basic original tire sizes are, let me go into what the sizes and ratings mean. Early tires were sized using the English system, for lack of a better way of putting it. For example, the old 16 inch tire was a 5.00 x 16 tire, meaning that it was five inches in tread width and 16 inches inner diameter. I do not know what the overall diameter was, but it was probably about 24.5 to 25 inches tall. These tires made for the VW were never given a series number, you know, like 60, 70, or 75 series that we know of today. The fifteen-inch tires started with 5.60-15 size and remained that way to this day if you still kept the bias-ply tire on your car. These tires are 25.5 inches tall. Keep this overall height in mind when you buy any size tire for your VW, as the speedometer cable is driven from the left front rotating assembly. The overall diameter of the tire will vastly affect the accuracy of your speed readout!

What about the radial tires of today? Well, they are given what is called a P-metric sizing system. Lets take a P225-60R16 tire, for example. The "P" stands for passenger tire. The number 225 is the tread width of the tire in millimeters. The number 60 is the ratio of the sidewall-to-treadwidth. In other words, the sidewall height is 60% of the treadwidth. The letter "R" stands for radial. This is also where speed ratings will be given (HR, SR, TR, VR, and ZR); I will explain later. Finally, the number 16 stands for the diameter in inches. I dont know why the industry decided to mix metric and English units. Anyway, suppose you wanted to know the overall diameter of P225-60R16 in inches. Take 225 and divide by 25.4 to get 8.86 inches, which is your tread width. Take the tread width of 8.86 and multiply it by .6 (60%) to get 5.32 inches. Multiply 5.32 times 2 to get 10.64 inches. Add 16 to 10.64 and you get 26.64 inches overall height. Remember, if you want the diameter in inches, you have to convert the width of the tread to inches before you start. Otherwise you will end up with incorrect units. After this, you are on your way to the answer. One inch = 25.4 millimeters. Keep in mind, that whatever width you choose for your VW, use the above formula to come up with the same overall height as the original size tire so your speedometer will read correctly in the end. Play with the above methods on different sized tires and see what you get. The 165R-15 tire that we use today is roughly equivalent to an 80-series tire. With these tires that have no series number, you just have to get out your measuring tape to approximate the overall diameter and back out what the sidewall ratio is from the methods I showed you earlier. Keep in mind that the shorter sidewall will make your ride harsher, even though the overall diameter may be the same. The taller sidewall cushions things better. Take a look at some of those "low-profile" tires and feel the sidewalls and youll know what I mean.

For most VWs, the widest tire you can install without them rubbing on the inner fenders and fender lips is a P205/60R15. This is an inch shorter than original, however, and your speed will not read right unless you have your speedo head recalibrated (that is the only way to have the speed readout corrected if you have to have tires of a different height than original). Any wider and you will have to install wider fenders and wheel spacers.

Most tires we buy for our VWs will have all the speed potential we need. Let me explain the speed ratings, though. Remember HR, SR, TR, VR, and ZR? Respectively, the tire is good up to 110, 115, 125, 149, and 150+ for long sustained speeds. If there is just an "R" then 105 is the sustained limit for safety at that speed. The higher speed rating will also bring increased ride harshness, as the tires have to be built to withstand the speeds for which they are capable.

I know this was a rather quick and dirty explanation of tires, but I hope that it will get you started in your search for the right tire for your VW.

Your VW Maniac andTech Specialist,
- Mike C. -