Tyre Markings on New Tyres

[melmose]

Hi,

i originally placed this query in one of the above pinned/sticky threads http://www.wheels-inmotion.co.uk/forum/ind...p?showtopic=165 and as i haven`t had an answer,thought it may be best doing a seperate post.Hope that`s ok?

 

 

The dots on the sidewall typically denote unformity and weight. It's impossible to manufacture a tyre which is perfectly balanced and perfectly manufactured in the belts. As a result, all tyres have a point on the tread which is lighter than the rest of the tyre - a thin spot if you like. It's fractional - you'd never notice it unless you used tyre manufacturing equipment to find it, but its there. When the tyre is manufactured, this point is found and a coloured dot is put on the sidewall of the tyre corresponding to the light spot. Typically this is a yellow dot (although some manufacturers use different colours just to confuse us) and is known as the weight mark. Typically the yellow dot should end up aligned to the valve stem on your wheel and tyre combo. This is because you can help minimize the amount of weight needed to balance the tyre and wheel combo by mounting the tire so that its light point is matched up with the wheel's heavy balance point. Every wheel has a valve stem which cannot be moved so that is considered to be the heavy balance point for the wheel.

As well as not being able to manufacture perfectly weighted tyres, it's also nearly impossible to make a tyre which is perfectly circular. By perfectly circular, I mean down to some nauseating number of decimal places. Again, you'd be hard pushed to actually be able to tell that a tyre wasn't round without specialist equipment. Every tyre has a high and a low spot, the difference of which is called radial runout. Using sophisticated computer analysis, tyre manufacturers spin each tyre and look for the 'wobble' in the tyre at certain RPMs. It's all about harmonic frequency (you know - the frequency at which something vibrates, like the Tacoma Narrows bridge collapse). Where the first harmonic curve from the tyre wobble hits its high point, that's where the tyre's high spot is. Manufacturers typically mark this point with a red dot on the tyre sidewall, although again, some tyres have no marks, and others use different colours. This is called the uniformity mark. Correspondingly, most wheel rims are also not 100% circular, and will have a notch or a dimple stamped into the wheel rim somewhere indicating their low point. It makes sense then, that the high point of the tyre should be matched with the low point of the wheel rim to balance out the radial runout.

 

Very interesting and helpful,but as usual nothing is straight forward for me!

On my new set of tyres,i have a red dot on 3 tyres and a yellow dot on one-which is the tyre that`s pulling,so may be able to do something about that one.

However, i cannot find a notch on any of my steel wheel rims to match up to the red dots!

In this situation what do you recommend?

 

Also,if you can find all the dots,like in your illustration, when you line one of the dots up to either the valve or the rim notch,surely one is going to be lined up correctly and the other not?

Do you compromise in this case and what is the best compromise?

Cheers

Mel

[Tony]

The information in the thread is years old, tyre and wheel manufacturing has progressed in leaps and bounds over the last decade.

 

Modern tyres have such a small tolerance for lateral of material runout the markings nowadays are more or less redundant. The only car i can recal on steel wheels with a "H" Heavy mark stamped on them is the Rolls Royce Silver Shadow.

 

By preference i asked the team to align the tyres heavy mark with the wheels valve simply because logic suggests this area on the wheel would be light?

 

Point for the thread "tyres and their markings" is the existing problem where new tyres can make the car pull to one side.

[melmose]

The information in the thread is years old, tyre and wheel manufacturing has progressed in leaps and bounds over the last decade.

 

Modern tyres have such a small tolerance for lateral of material runout the markings nowadays are more or less redundant. The only car i can recal on steel wheels with a "H" Heavy mark stamped on them is the Rolls Royce Silver Shadow.

 

By preference i asked the team to align the tyres heavy mark with the wheels valve simply because logic suggests this area on the wheel would be light?

 

Point for the thread "tyres and their markings" is the existing problem where new tyres can make the car pull to one side.

 

Thanks for the clarification Tony!