sigh..... really i told them how they should be fitted!

[adam_r]

well. i purchased a pair of tyres online and went to my local pro tyre (near work) to get them fitted.

 

I was specific on how they where to fit them in relation to the coloured dots on the side walls of the tyre / the valve.

 

did they listen ???

 

 

not bad to be honest but i was asked Why i had informed them to fit them like that and then

I even got asked why my tyres had coloured bands on the tread!!!

HA

[Rich]

Are you taking them back to do again?

 

The last time I bought tyres off the internet I was sent a pair with the coloured band on the same side, meaning they could make the car drift...luckily they didn't.

[Tony]

The reason for the dots...

............................

 

First, if the tire has a red dot, ignore the yellow dot. Then, if you have a steel wheel, look for the low point dimple on the wheel, and mount the tire with the red dot next to the low point dimple.

If the wheel is aluminium, or if it's steel, but has no low point dimple, mount the tire with the red dot next to the valve stem.

And if the tire has only a yellow dot?

Regardless of the type of wheel, if there is no red dot, mount the tire with the yellow dot next to the valve stem.

Why do it that way?

We'll start with the yellow dot, because it's easier to explain. The yellow dot indicates the overall light static balance point of the tire. In other words, it's as though the tire is a bit lighter in the area where the yellow dot is located.

How does that relate to the wheel?

On an aluminium wheel, the valve stem marks the heavy point of the wheel. So, you're matching the light point of the tire with the heavy point of the wheel, because that's likely to give the best initial balance.

Why is an aluminium wheel heavier at the valve stem location?

While steel wheels are forged, aluminium wheels are machined. For that reason, aluminium wheels are very uniform in their overall balance.

And, if you look at an aluminium wheel, you notice that where a hole has been cut into the wheel, an identical size and shape hole is cut at a location 180 degrees opposite it.

The result is that even with all their cut outs and holes, aluminium wheels are still very uniform in balance. Except for one place.

Where's that?

Where the valve stem is located. At that spot, the manufacturer has to bore a hole through the wheel for the stem, removing metal from the wheel.

That hole is about 9.7 mm in diameter and the aluminium at that point is usually about 7.6 mm thick. If we do the math, knowing that aluminium weighs about 2.64 grams per cubic centimetre, we find that the aluminium removed to make the hole weighs about 0.52 ounces.

So wouldn't that make the wheel lighter at that point?

If you didn't replace the aluminium you drilled out. But you do. Into that hole, you mount a valve stem. And one of the most popular valve stems, including its securing nut and rubber grommet, weighs about 1.7 ounces.

So, when the valve stem is mounted, the wheel is about 1.2 ounces heavier at the valve stem location, making it the heavy point of the aluminium wheel. When you mount the tire with the yellow dot (the light point) next to the valve stem (the heavy point), you are at least partially balancing out the assembly.

The same is true on steel wheels, so match the yellow dot to the valve stem on those.

OK, that makes sense for the yellow dot, but what about the red dot?

The red dot is much more complicated than the yellow dot. It indicates the "radial force variation first harmonic maximum." That's a mouthful, of course, but it's a way of indicating where the centrifugal force tending to pull the rotating tire away from the wheel is greatest.

Another way of looking at it is that in a sense, if the tire were out of round, the red dot would more or less correspond to the "high point" or place where radial runout forces are greatest.

Why not just measure the runout of the tire?

The radial force variation measurement is much more accurate in predicting tire behaviour. In fact, the red dot often isn't located exactly at the "high point." Instead, it accurately marks where the runout-like force is greatest.

But, if you think of it as marking the tyer's "effective" high point, it becomes pretty obvious why you'd match the red dot with the steel wheel "low point" dimple. It's as though the tire is a bit "thicker" (from wheel to tread) in the red dot area.

And, since the dimple marks the low point on the steel wheel, you might say the wheel is a bit "thinner" (from axle to flange edge) where the dimple is.
So, it makes sense to match the red dot to the wheel dimple.

And on aluminium wheels?

At the red dot location, the tire is trying to pull away from the centre of the axle a little bit, as a result of higher centrifugal force.
As in our last example, it's as though the tire is a bit "thicker" near the red dot, which has the effect of pushing the wheel and axle upward as the red dot gets to 6 o'clock.

Meanwhile, the fact that the wheel is a bit heavier at the valve stem location generates a centrifugal force effect trying to pull the axle downward as the valve stem gets to 6 o'clock.

Those forces tend to counteract each other.

And the final result?

Matching the dots is no substitute for balancing tire and wheel assemblies. What it does, however, is give you the best start, so you are more likely to use less total weight to bring an assembly into balance.

[MLAM]

Thanks for the detailed post above Tony,

 

In regards to the red dot, should the valve on an alloy wheel be placed OPPOSITE side of the red dot?

 

What about if the tyre only has a red dot?

[adam_r]

as i understand it.. the Red dot should be nearest the valve.. not the opposite side of the wheel...

 

that is unless the alloy wheel has a low point marker on it.

[Tony]

Correct.....