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Thread: Big wheel wagon

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    Bodger

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    Big wheel wagon

    The trend of late is to fit larger diameter wheels but what does this do to Acceleration
    Is the weight of these larger wheels a disadvantage.

    Is the larger reciprocating diameter and tyre assembly slowing the acceleration of the vehicle down as I can see the wheels an extension of the flywheel
    so a car fitted with 13" from factory then gets fitted with 14" or 15" maybe there is no noticeable difference
    but what if 17",or 18" wheels are fitted and the gearing remained the same would the car accelerate at the same speed?

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    Re: Big wheel wagon

    its not acceleration that is the biggest problem,the gyroscopic effects on the handling is,but if its only used for posing along the high street it wont matter.
    if fitting larger diameter wheels get the lightest possible same for tyres as the are at the outer edge of the flywheel

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    Re: Big wheel wagon

    Thank you Turbospud
    Not for posing
    I'm just trying to ascertain the best possible sinarieo performance wise, a lot of cars are changed from what is standard with out truly knowing the reason as to why and no measure is made before or after to determine the outcome weather it be a net gain or loss
    Will the lightest wheel possible in 15" still have more centrifugal force than the lightest 13" or 14"

    Or should the availability of a better tyre choice in the 15" rim be the deciding factor

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    Mechanic beeRS's Avatar

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    Re: Big wheel wagon

    Assuming that you use a lower profile tyre with a larger wheel and keep the overall diameter more-or-less the same, you should have a negligible change to acceleration. If the diameter changes the gearing changes and this would have an affect.

    If the difference in weight between a 15" alloy wheel and tyre compared to a 13" wheel and tyre is, say, 5kg per wheel, this will change your overall weight by 20kg. Even in a lightweight car of 850kg, this is a difference of less than 2.5%. Yes - it will make a difference, but its very small. With regards to centrifugal force (I think you mean 'moment of inertia' here) for the rotating masses, again - it would be negligible.

    Where the wheel weight really does matter, is with handling. Wheel and tyre weight is unsprung, and has to do all the up/down movement. Larger unsprung weight can negatively affects handling.

    As Turbospud said, the real reason most fit larger wheels is for posing. However, there can be good reasons for fitting larger wheels, such as to accommodate larger diameter brake discs, or better tyre choice.

    Sure, you can get lighter wheels to compensate for larger diameters, eg. forged alloys, flow formed alloys, or (if you win the lottery) carbon fibre wheels.

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  7. #5
    Pit Crew Decade Plus User jpblue's Avatar
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    Re: Big wheel wagon

    wheel size is like everything else on a car a compromise between looks, economy and performance.
    I run 15x9 on the Mk1 originally fitted with 13's or probably 12's.
    the 15's give a bigger tyre patch than 13s fitted with same width tyres (however I run 225/50's) I can get a bigger selection of race tyres in 15 at better prices and availability than in 13. 13's and 14's wont fit over the front brakes.
    The wheels and tyres fill the arches properly. What minor loss in unsprung weight, offset against heavier springs and bigger dampers, is made up for in braking performance and cornering grip. As a race only car I don't suffer from many major mid corner undulations so the mass isn't moving up and down as bad as a road car!
    Click image for larger version Name:	WP_20160917_17_50_03_ reduced.jpg Views:	54 Size:	116.4 KB ID:	81463

    JP

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  9. #6
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    Re: Big wheel wagon

    Quote Originally Posted by profit View Post
    Thank you Turbospud
    Not for posing
    I'm just trying to ascertain the best possible sinarieo performance wise, a lot of cars are changed from what is standard with out truly knowing the reason as to why and no measure is made before or after to determine the outcome weather it be a net gain or loss
    Will the lightest wheel possible in 15" still have more centrifugal force than the lightest 13" or 14"

    Or should the availability of a better tyre choice in the 15" rim be the deciding factor
    the reason i use 15in wheels is to get bigger brakes in,you will not repeatedly stop a 500 bhp mk2 on brakes that fit under 13in wheels,yea canny beat the laws o pysics as scotty used to say
    to reduce the gyro effects you would want bigger wheels and tyres to be the lighest possible,

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    Bodger

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    Re: Big wheel wagon

    Thanks Lads
    all very valid points, great to discuss

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    Re: Big wheel wagon

    also if you fit wheels which are a larger rolling radius,lowering it back to the original ride height will give unwanted geometry changes

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