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  1. #11
    Join Date
    Mar 2005
    Location
    Northampton
    Posts
    1,104
    Quote Originally Posted by scepticwoody View Post
    Hi,
    I think it is easier to re - set the speedo. Use the tyres which you want - do the calcs and reset the speedo dip switches.

    sceptic
    There aren't any dip switches, and last time I sent it off it was away for months !
    David (AKA Firestarter29)

    Lead, follow, or get out of the way.

  2. #12
    Join Date
    Mar 2005
    Location
    Northampton
    Posts
    1,104
    Quote Originally Posted by BomberG View Post
    Dave
    Try this online tyre size calculator by Spiyda. If you change your profile from 60 to 70 it shows a 7% reduction in wheel 'rotations per mile'.

    https://www.spiyda.com/magento/index...yre-calculator

    Graham
    That's a useful piece of kit, cheers Graham.
    David (AKA Firestarter29)

    Lead, follow, or get out of the way.

  3. #13
    Join Date
    Dec 2004
    Location
    Staines Middlesex / Abu Dhabi
    Age
    65
    Posts
    1,083
    Quote Originally Posted by Firestarter29 View Post
    The time has come to change tyres, the Bild tyre survey listed on another post was very helpful, I think I'll be going for the Continental premium contact 6 which performed well. Preferably I'd like something with white lettering on the side but getting these with a decent performance is tricky I'm not going down the Avon route as I'm not convinced they are the best tyres, they are costly, and they start off with relatively shallow tread depth.

    The question I have is what speed rating ? V and above or W and above ? (It's a 4.6 Rv8 ).

    The other Question is slightly different: The speedo under-reads by 5-6%, so if you travel 100 miles on the stanav, the odometer registers 106. This is a pain when following tulip style route maps etc. Would taking the rear profile up from 60 to 65 (or 70) correct the error ? They are 235 60 R15.
    My opinion - Tyres are same like seat belts, seem expensive but when you need them to work in an emergency no price is too high !
    In my opinion tyre choice would need to be a minimum of rating for the cars performance, I thought it was part of the MOT that under rated tyres were a failure ??
    If "enthusiastic" driving or track days are on the agenda then get higher rated tyres, even if you do not achieve the speed they are rated to they will still be better tyres ( albeit more expensive)
    The point made about speedo under reading - that's an IVA failure isn't it ? - Allowed to be travelling slower than the speedo shows - but certainly not allowed for you to be travelling faster than the speedo indicates. Which brings me to a question - how does the odometer know the correct distance travelled if the speedo is reading incorrectly.
    Surely the odometer only indicates what the internal gauge calculates from the speed input ? or am I missing the point here ? I understand that the speedo is running slow but the odometer is either correct or reading high - how can that be ?
    Chris Lutman -427SC Coupe / MG Tojeiro "LOY" replica

  4. #14
    Join Date
    Feb 2007
    Location
    West Sussex
    Posts
    8,880
    Quote Originally Posted by Firestarter29 View Post
    There aren't any dip switches, and last time I sent it off it was away for months !
    try Richfield Speedograph - far better than (Non)Speedycables, and can sort out most gauge problems....quickly!
    http://www.speedograph-richfield.com...t_repairs.html
    Crendon Chassis No.49
    Huddart FE428 + toploader

    Not listed in the Shelby Register.

  5. #15
    Join Date
    Mar 2005
    Location
    Northampton
    Posts
    1,104
    Thanks everyone for the advice, an alternative to Speedy Cables is certainly a consideration, although it is some years since I used SC in fairness to them. As for IVA, my car is pre-IVA, and it's possible that the tyre profiles have been changed prior to me buying it 11 years ago.

    After many hours of very dull research, I chose a tyre only to find it wasn't available in a 15" so I've gone for Goodyear Efficient Grip 205 60V R15 on the fronts, £146 for the pair (fitted) which seem to give the best balance of wet/dry braking, feedback, handling and customer satisfaction. I'll do the rears later in the year, or possibly next year - when I work out which profile I need. The car is now booked into Northampton Motorsport to get the geometry looked at.
    David (AKA Firestarter29)

    Lead, follow, or get out of the way.

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