Tire mounting question

dafischer · 10-10-2006, 07:16 PM

In a rare workplace automotive discussion today, my boss (a 911 owner) was mentioning the bad ride characteristics a friend of his was having with a 914, and how he'd pointed out to the guy that his tires had been mounted wrong.

"Wrong direction?" " Nope, heavy side of the tire mounted in the wrong place". I hadn't ever heard this, and he proceeded to explain that the heavy side of the tire was marked with a dot, and needed to be mounted with the dot in a specific position on the wheel. I did some research tonight and found out about "match mounting" which was described as the high spot on a modern high performance tires was marked with a dot which was to be matched with a corresponding dot or sticker on the wheel, which indicated the wheel's low spot. This helps eliminate the need for excessive wheel weights. News to me.

Anyway, since I doubt a 30+ year old refinished Fuchs would have a mark for match mounting, is this a crucial step in the balancing process, would it make a noticeable difference in ride & feel, and where would the dot go in absence of a reference mark on the wheel?

Anyone with knowledge or experience?

Zeke · 10-10-2006, 07:40 PM

You're close. Wheels shouldn't have any low spots, they should run true. Then older steel wheels found on many cars might be out of round and you can match the tire's OOR to the opposite of the wheel.

That doesn't correspond to the dot, always. The valve stem throws a wheel out of balance before any correction can be made. By mounting the heavy spot (the overlap in the manufacturing process) opposite the valve stem, you can cheat the weight box by a few grams.

BTW, the "overlap" is not what it used to be. At one time, tire molds were filled by hand with layers of fabric and one could see the overlap on the sidewall. Not anymore. The process is a lot more exacting. Nevertheless, a new tire will not necessarily be balanced, or perfectly uniform in its casing thickness. This weight in the casing can start to move away from the center of the wheel at high speeds. This can cause an out-of-round condition that doesn't show up static.

There's a lot to this subject, but tires are better than ever and most competent tire mechanics can mount an balance tires very well nowadays. The dot is one of things left over from a bygone era, but there's still some validity to the process.

hcoles · 10-10-2006, 07:53 PM

I thought the dot was to be lined up with the valve stem....which I thought meant the dot was the light spot on the tire...to line up with the heavy spot on the wheel...to cheat the weight a bit or possibly require fewer weights...
I think with modern tires this is probably not a big issue..a few extra grams in a spot shouldn't matter as long as the whole assembly is balanced and there are no "hard" spots in the tires or out of round in tire or wheel.

hcoles · 10-10-2006, 07:57 PM

Here is a cut and paste from googling the subject

Now to seat the bead. This either requires a lot of air or some ingenuity. First find the yellow dot on the sidewall of the new tire. This dot signifies the light spot on the tire. Place this dot at the valve stem. You may have to relocate this dot several times to get the ideal spot for it. The object of this exercise is to use as little weight as possible when balancing the assembly.

real550A · real550A's Garage

That's what the Yokohama rep told me, also. Match the dot to the valve stem.