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Thread: Tyre Tread Depths...

  1. #1
    spoons
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    Default Tyre Tread Depths...

    Was chatting last night about tyre tread depths... wondered what your thoughts were..

    Generally new tyres have 8mm of tread. I've noticed a huge drop in tyre performance once it gets to 3mm of tread. My mates seem to agree.

    So I wondered if you could generally apply this logic when it comes to fast road driving... :-

    8mm = 100% (available grip for the tyre)
    7mm = 80%
    6mm = 60%
    5mm = 40%
    4mm = 20%
    3mm = Need to Replace

    I'm not talking about the sort of driving around town, or to the shops and back. This would be for fast road driving & high speed cornering etc.

    Maybe the science behind it all is completely different, but just wondered wether the performance decline of a tyre is linear

  2. #2
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    I just had my front tyres replaced - they were down to somewhere between 2.5 and 3mm and I was noticing that their performance was dropping off especially on cornering.

    It seemed a wise move with winter approaching. I did a bit of Googling and found people saying that it's best to replace them when there's somewhere between 2 and 3mm of tread left -opinions varied as usual.

    Note that this is driving at 'normal' speeds.

    All set for the winter rain and snow with plenty of tread to clear the water...


  3. #3
    Regular Member Penfold101's Avatar
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    That's what all the tyre sites recommend - try looking at e-tyres for a nice video featuring VBH showing it all...

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    Regular Member m8internet's Avatar
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    Quote Originally Posted by spoons View Post
    8mm = 100% (available grip for the tyre)
    7mm = 80%
    6mm = 60%
    5mm = 40%
    4mm = 20%
    3mm = Need to Replace
    In terms of wear for available grip AND braking it is more like this :
    8mm = 99%
    7mm = 100%
    6mm = 100%
    5mm = 90%
    4mm = 75%
    3mm = 65%
    2mm = 50%
    1.6mm = 40%

    That is assuming at a constant 70mph on a dry road
    If there is standing water of 1mm then take the above and divide by 2
    As you can see on a wet surface the performance drops very rapidly from 3mm at 33% to 1.6mm 20%, and it is this drop the increases the braking distance

    Finally, you need to calculate the composite tread of all four tyres, and this gives the real %
    This is one reason why many people put new tyres on the rear as the average tread will be at least 65%

    Another factor is the brake wear
    New brakes can stop you in half the distance that worns brake can
    Compare :
    8mm tyres and new brakes
    1.6mm tyres and worn brakes

  5. #5
    Regular Member rushy's Avatar
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    Its all down to heat. The deeper the tread the more the tread blocks will move creating heat, as you know spoons from your little monitors the more heat in the tyre the greater the grip. The smaller the tread depth the less heat can be generated by movement of the rubber so less grip. Again this would all be on a dry road at the same surface temperature. This is why in cold dry weather tyre performance is so very poor with low tread levels. You could generate the heat with hard stopping and cornering but lets keep that for the track

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    VIP-Member Johnsdutton's Avatar
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    Normal day to day use change at 3mm. I remember seeing a Feature on Top Gear (or something similar) many years ago, about tread depth and grip. They reckoned that maximum grip an a dry road was acheived at around 2mm, but remember that was in almost ideal conditions. I certainly would never try it on our roads.
    3.2 v6 Signum and loving it

    http://www.freewebs.com/johnsdutton/

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    Regular Member barkzz's Avatar
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    My fronts had worn to 2mm and although perfect in the dry, they were obviously a nightmare in the wet. Twitchy front end, and on the odd occassion begining of front end slide/aqua plane at low speed.

    Also bear in mind that the lower the tread depth available, the greater the stopping distance under heavy braking

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