Tyre speed rating




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  1. #1
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    Default Tyre speed rating

    Hi all,

    Researching speed ratings as I'm considering AT tyres for my Touareg that have a Q rating (160kmh).

    Wikipedia article about tyre codes describes speed rating as "the maximum speed at which the tire can carry a load corresponding to its Load Index". Page here: https://en.m.wikipedia.org/wiki/Tire_code

    I interpret this as meaning that if your vehicle weighs less than the load index on the tyre, you could increase the speed rating for that tyre on your vehicle.

    The wiki article also refers to a formula on another page but it's in German so I'm not making it out so lekker.

    Anyone with knowledge about this?

  2. #2
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    Default Re: Tyre speed rating

    I don't agree

    The speed rating is more normally considered as:

    the maximum speed a tire can safely sustain for 10 minutes.

    Speed ratings are based on tests in which engineers run the tyre at 6.2 mph steps, in 10 minute increments, until the required speed has been met.

    You cannot drive a Q-rated tyre at 180km/h just because you haven't met the maximum weight. The tyre casing and construction won't be strong enough for the rotational forces.
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  3. #3
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    Default Re: Tyre speed rating

    When I read the SABS codes on this a few years ago it said that the speed rating of the tyre had to be higher than the maximum speed the vehicle was capable of .....

    Johan
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    Default Re: Tyre speed rating

    Quote Originally Posted by J Snyman View Post
    When I read the SABS codes on this a few years ago it said that the speed rating of the tyre had to be higher than the maximum speed the vehicle was capable of .....

    Johan
    Problem is you rarely get AT tyres with speed ratings exceeding H (190km/h)

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    Default Re: Tyre speed rating

    Just inform your insurance company. I've heard some sorry stories with claims being denied due to tires not meeting vehicle specifications. This is for either speed rating or load index.
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  6. #6
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    Default Re: Tyre speed rating

    Quote Originally Posted by JAPster View Post
    Just inform your insurance company. I've heard some sorry stories with claims being denied due to tires not meeting vehicle specifications. This is for either speed rating or load index.
    The problem with fitting tyres with a lower speed/load rating than originally fitted is that your vehicle is not roadworthy anymore .... you can inform your insurance company and they might honor a claim. But in an accident where lives are lost, you can still be held criminally liable.

    In a previous life I worked for a local authority and we had a fleet of Land Cruiser fire fighters. They did a lot of work in mountains and at that stage carried a 1000 L water tank, pumps, hoses, etc, etc - so, basically overloaded. The vehicles were also fitted with heavy duty mud-terrain tyres that also had a fairly low speed rating.

    Then one fine rainy morning one of them came racing into town and could not stop when the robot turned red and collected a number of cars in the process. The insurance did not pay out .....

    You fit inappropriate tyres to your vehicle at your own peril !

    Johan
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    Default Re: Tyre speed rating

    I donít see how they can penalise you for a speed rating lower than originally fitted? It is illegal to drive more than 120 anyway?

    So, in a country with a 120 max, surely it should be above board to have 160-limited tyres? That is a 30% safety margin.
    Dewald

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  9. #8
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    Default Re: Tyre speed rating

    I would spend more time looking at load ratings

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    Default Re: Tyre speed rating

    Quote Originally Posted by Karoo Klong View Post
    Problem is you rarely get AT tyres with speed ratings exceeding H (190km/h)
    190km/h is a T rating. H is 210km/h
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    Default Re: Tyre speed rating

    Quote Originally Posted by DCR View Post
    I donít see how they can penalise you for a speed rating lower than originally fitted? It is illegal to drive more than 120 anyway?

    So, in a country with a 120 max, surely it should be above board to have 160-limited tyres? That is a 30% safety margin.
    You do so at your own peril. Be careful to write a cheque that you cannot cash .....

    Johan
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  12. #11
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    Default Re: Tyre speed rating

    Quote Originally Posted by J Snyman View Post
    You do so at your own peril. Be careful to write a cheque that you cannot cash .....

    Johan
    Audi and VW in particular ar very particular about speed rating or load index. 215/45R16's are easy to come by in a 86 load index as the Polo's have. However the Audi A1 uses the same size but in a 90 load index.
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