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Thread: Tyre pressures

  1. #1
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    Tyre pressures

    Evening everyone,

    Not long had my first cobra and wondering what tyre pressures other drivers use for road use, I have a Dax de-dion with Toyo proxes TR
    Front 235/40 zr 18s
    Rear 295/35 zr18s
    Any advice appreciated.

  2. #2
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    It varies a lot from car to car some run them as low as 18 psi but others as much as 24 psi it is all about trying what suits you best as I suspect how well the cars geometry is set up will have a bearing on it as well. I would say put the front at 20 psi and the rear at 22 psi and go from there. I run mine with the front at 22 psi and the rear at 24 psi but I do have 16" wheels if that makes a difference.
    Martin

    351W 416.7 HP and 466.8 ft-lbs

    Running Mega Squirt and Edis 8


  3. #3
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    From what I've seen, many owners run their tyre pressures too low and use the tyres as their suspension. If the ride is too firm, they tend to reduce the tyre pressure rather than adjusting their shock absorbers.
    The correct pressures for these cars should, in most cases, be in the 25-30 psi range, but it's easy to check using a digital thermometer. After a decent run, check the tyre temperature at three points across the tread i.e. outside edge, centre and inside edge. If the edges are warmer than the centre, the pressure is too low and vice versa.

    Paul

  4. #4
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    Hi Terry,
    I would go with 20-22. I think that's also what Dax recommend from memory.
    BTW you a have PM from me. (Notifications top right of the screen).
    Kev Davies
    South Wales Area Rep. UKCC Membership Secretary
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  5. #5
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    The previous owner of my Dax told me that he'd contacted Dunlop or one of the other tyre manufacturers who suggested that below 20psi there is an increased risk of the tyre bead shifting off the wheel rim on exuberant cornering. I'm sure they included a bit of a safety margin in their advice. Personally I run low- to mid- 20s and maybe put a couple more pounds in if I'm doing a longer run on a motorway.
    There is a document on the net somewhere which suggests marking the tread and shoulder of the tyre with chalk. Go for a spirited run out and see how much of the chalk is rubbed off at different tyre pressures. The idea being you want all the tread and none of the shoulder to be used. As you'll imagine, this could take a few hours and I can't say I have the desire to do this.
    Russ.
    Joint Area Rep - East Midlands Region
    1984 DAX Cobra
    Rover 3.5 V8 with Holley carburetor.

  6. #6
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    I run 25 front (235/60R15) and 28 rear (295/50R15). This was recommended by the kit manufacturer. Prior to this, I really hadn't given the matter much concern and ran 32 psi all around. Reducing the pressure eliminated the odd chirp when shifting gears.

    Quote Originally Posted by FatBoy View Post
    The correct pressures for these cars should, in most cases, be in the 25-30 psi range, but it's easy to check using a digital thermometer. After a decent run, check the tyre temperature at three points across the tread i.e. outside edge, centre and inside edge. If the edges are warmer than the centre, the pressure is too low and vice versa.

    Paul
    Coincidentally, I was just reading about checking tire temps and here's a little bit more to add: The center measurement should be the average of the two outer measurements. Above average means too much inflation and below, not enough.

    The reason for this averaging is to allow for temperature differences across the tread caused by the wheel camber.

    John

    “A prudent person profits from personal experience, a wise one from the experience of others.”

  7. #7
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    Quote Originally Posted by Russ-Notts View Post
    There is a document on the net somewhere which suggests marking the tread and shoulder of the tyre with chalk. Go for a spirited run out and see how much of the chalk is rubbed off at different tyre pressures. The idea being you want all the tread and none of the shoulder to be used. As you'll imagine, this could take a few hours and I can't say I have the desire to do this.
    If you have some chalk and a load of time to kill...

    Russ
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    Joint Area Rep - East Midlands Region
    1984 DAX Cobra
    Rover 3.5 V8 with Holley carburetor.

  8. #8
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    Quote Originally Posted by Eggbert View Post
    Coincidentally, I was just reading about checking tire temps and here's a little bit more to add: The center measurement should be the average of the two outer measurements. Above average means too much inflation and below, not enough.

    The reason for this averaging is to allow for temperature differences across the tread caused by the wheel camber.
    That's correct. I wrote a fully explanation on another thread somewhere that basically said the same.

    Paul

  9. #9
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    Front 22 , whilst rear 24. Makes up slightly for the hard ride

  10. #10
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    Quote Originally Posted by Eggbert View Post
    I run 25 front (235/60R15) and 28 rear (295/50R15). This was recommended by the kit manufacturer. Prior to this, I really hadn't given the matter much concern and ran 32 psi all around. Reducing the pressure eliminated the odd chirp when shifting gears.



    Coincidentally, I was just reading about checking tire temps and here's a little bit more to add: The center measurement should be the average of the two outer measurements. Above average means too much inflation and below, not enough.

    The reason for this averaging is to allow for temperature differences across the tread caused by the wheel camber.

    with the Dax camber comp front and the De Deon rear they run very litle camber none on the rear so the difference in temp from iner to outer will be very close if running on a straight road , i would say 22 front 24 rear as a starting point
    camber compensation and anti roll. http://xcsdesigns.co.uk/

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