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Offline B2

  • Slowest Ferrari Owner

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I didn't think this happened very often unless there is a tyre failure.

Ah Ok,  Just asked because I remembered when racing that at events they would put a dab of paint on head nuts carbi screws etc as well as on the edge of the rim and tyre.  This was to ensure no one tampered with their engine or changed tyres etc.

I always noticed at the end of racing that the tyre had rotated around the rim.  Just thought that may happen with a car as well.  Perhaps I should do a test myself just to check.  :thumbsup:



Offline mondi

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Probably teaching Granny to suck eggs but some one may find this interesting.

Quote
Porsche designs and manufacturers some of the highest performance cars in the world (with the exception of the butt-ugly Cayenne). All this design and performance is worth nothing if you put cheap Korean tyres on your Porsche though, and because of that prospect, Porsche introduced the N rating or N specification system. In order for a manufacturer to be an OE (original equipment) supplier of tyres for Porsches, they must work with the Porsche engineers at the development and testing stage. They concentrate on supreme dry-weather handling but they also spend a considerable amount of time working on wet-weather handling. Porsches are typically very tail-heavy because of the position of the engine relative to the rear wheels, and with traction control off, it's extremely easy to spin one in the wet. Because of this, Porsche specify a set of wet-grip properties which is way above and beyond the requirements of any other car manufacturer.
OE tyres for Porsches must successfully pass lab tests to prove that they would be capable of adequately supporting a Porsche at top speed on a German Autobahn. Once the lab tests are done, they must go on to track and race tests where prototypes are evaluated by Porsche engineers for their high-speed durability, uniformity and serviceability. If they pass all the tests, Porsche give the manufacturer the go-ahead to put the car tyres into production and then they can proudly claim they are an N-rated Porsche OEM (Original Equipment Modifier).
The N-ratings go from 0 (zero) to 4, marked as N-0, N-1 etc. This N-rating, stamped into a tyre sidewall, clearly identifies these tyres as having gone through all the nauseating R&D and testing required by Porsche as described above. The number designates the revision of the design. So for a totally new design, the first approved version of it will be N-0. When the design is improved in some way, it will be re-rated as an N-1. If the design changes completely so as to become a totally new tyre, it will be re-rated at N-0.
If you've got a Porsche, then you ought to be aware that as well as using N-rated tyres, you ought to use matching tyres all around because many Porsches have different sizes tyres front and rear. So for example if you have a Porsche with N-3 rated tyres and the rear ones need replacing but the model has been discontinued, you should not get N-0's and put them on the back leaving the old N-3's on the front. You should replace all of them with the newer-designed re-rated N-0 tyres. But then you own a Porsche so you can certainly afford four new tyres....
One final point. You may go into a tyre warehouse and find two tyres with all identical markings, sizes and speed ratings, but one set has an N-rating. Despite everything else being the same, the non-N-rated tyres have not been certified for use on a Porsche. You can buy them, and you can put them on your car, but if you stuff it into the armco at 150mph, Porsche will just look at you and with a very teutonic expression ask why you didn't use N-rated tyres.



Offline mondi

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the yellow dot is quite clear, and so is the red one opposite!!!!

but the dots don't always mean for mounting alignment... they can be production references..

AND, I can't really see the tyre brand name on that one anyway  :tilt:

Some tyres have red dots, blue dots, green dots  AND yellow dots, all at different places around the tyre..... then what?

....

Quote
When you're looking for new tyres, you'll often see some coloured dots on the tyre sidewall, and bands of colour in the tread. These are all here for a reason, but it's more for the tyre fitter than for your benefit.
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 garage 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 tyre 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. (Trivia side note : wheels also have light and heavy spots. Typically the heaviest spot on the wheel is found during manufacture and the valve stem is then located diametrically opposite that point to help balance the wheel out).
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.

What if both dots are present?
Generally speaking, if you get a tyre with both a red and a yellow dot on it, it should be mounted according to the red dot - ie. the uniformity mark should line up with the dimple on the wheel rim, and the yellow mark should be ignored.



Offline Aircon

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....


boy am i going to give my next tyre fitter a headache!

I love my car. Buy your own



Offline mondi

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Offline B2

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Just some more unless info.   :tilt:

I think I should have a go then on testing the tyre rotation on a car.  Technically it makes sense. Would be good to test in practise.



Offline dkabab

i just spent the last 20 minutes in the pouring rain changing the missus tyre. she decided to take the 'off road' route entering the petrol station and drove up the curb.... side wall is split :doh:



Offline AshSimmonds

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We've had a few discussions which began on something specific which ended up one general tyres/wheels/etc with a fair bit of depth. 

Do we need a tyre/wheel section, or technical in general?  I'm sort of thinking tech in general is too general as it will more apply to each marque, but a general wheel/tyre section might be fruitful.


eg.

http://aussieexotics.com/forum/cars/dunlop-dzo2-t2234.0.html
http://aussieexotics.com/forum/cars/honeycomb-airless-tyres-tyre-of-the-future-t2782.0.html
http://aussieexotics.com/forum/porsche/tyres-for-996-carrera-t4384.0.html

I'm sure there's a bunch more...



Offline mondi

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Do we need a tyre/wheel section, or technical in general?  I'm sort of thinking tech in general is too general as it will more apply to each marque, but a general wheel/tyre section might be fruitful.



How about a general Tech area, which could include a restoration "progress report" thingy if anyone is interested in posting their projects, and if it gets big enough, break it up into Marques????



Offline Ferrari Fissatore

  • Soap Dodger

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yes Brett

Tyres can and do rotate on the wheels, in heavy duty applications. BUT, it has no affect on alignment, only balance.

We don't bother blancing wheels on the race cars. Once in a while we get a vibration, but so infrequently, that it's never a problem. Plus, we get so many bits of hot rubber stuck to the inside of the rims, that balancing is pointless anyway.

ABS equipped cars do this more than non abs, due to the shock loads.

On the race cars, with slicks, obviously, the tyres always rotate.... it's impossible to say how many times, but often as the mark I put on can be half way round from point of fitment. And the driver style makes a difference too.

Good work detective mondi....

the coloured dots are points of interest, but there is not enough clarity, consistency, significance or effect in practice to worry too much about it  :thumbsup:

and peepee..... surely Carl will fit your next tyres?

he's got a headache already, after his weekend!



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