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Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by DaviesEB, Oct 27, 2012.

  1. DaviesEB

    DaviesEB New Member

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    Joined:
    Sep 20, 2012
    Location:
    Monrovia, Monsterrado, Liberia
    Your Mercedes:
    200/1988/102
    I just bought a second user C 200E W124.
    I was convinced to change the original tires from 185/65 x 15 and put 205/65 x 15.

    I tried applying brakes and the vehicle skidded.

    is it the fault of the change of tire?

    Also i want to change the entire under carriage bushings where can i get these.

    Thanks
    Bright
     
  2. CafeMB

    CafeMB Banned

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    Location:
    Grantham, Lincolnshire
    Your Mercedes:
    Mercedes S320 CDI
    So you've applied the brakes and the vehicle has stopped.... as long as it's done that dont worry.
     
  3. huey

    huey Senior Member

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    Your Mercedes:
    W203 cdi 2004 Estate
    I'm confused you said "you tried" applying the brakes, do you mean that you did apply the the brakes and the vehicle skidded?

    IMO the tyres are too wide for your car. But I would'nt have thought it would affect the braking.
     
  4. OP
    DaviesEB

    DaviesEB New Member

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    Monrovia, Monsterrado, Liberia
    Your Mercedes:
    200/1988/102
    Well very new. Just asking if i can you any tire different tyre size other than185/65 x 15.

    I have a 200E W124.
    Also where can i get undercarriage bushings and AC Compressor for this car to buy.

    Thanks
    Bright
     
  5. CafeMB

    CafeMB Banned

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    Your Mercedes:
    Mercedes S320 CDI
    I dont know if you have someone that supplies parts for Mercedes where you are. You could ask eurocarparts and see if they will ship to you, but it may not be cheap.
     
  6. television

    television Always remembered RIP

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    Location:
    Daventry
    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    By changing the tyre size you have increased the diameter, so your speedometer will be more accurate, if they were new tyres they need to be run in for a few hundred miles to bed down
     
  7. CafeMB

    CafeMB Banned

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    I have no idea how you come to that conclusion
     
  8. huey

    huey Senior Member

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    Your Mercedes:
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    He only changed the width Malcolm, 185 too 205 the diameter is still 15,:)
     
  9. Naraic

    Naraic Moderator

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    Your Mercedes:
    2005 CL500.
    By changing from 185/65 to 205/65, the diameter of the tyre has been increased by 26mm.

    The profile is a % of the width, so if the width is changed and the profile remains the same the tyre grows in diameter.

    I'm not sure why Malc said the speedo would be more accurate...it is a big difference. Though the Alloy Wheels Direct table does list both the 185 and the 205 as standard. If probably depends on which was specified when the car was new.
     
    Last edited: Oct 27, 2012
  10. CafeMB

    CafeMB Banned

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    Would that cause a change to the speedometer reading? I know it would cause more grip as there is more rubber to cause traction.
     
  11. antijam

    antijam Senior Member

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    Your Mercedes:
    2003 SLK320
    The wheel size is the same but the tyre rolling radius is over 4% greater.

    As Malcolm states, his speedo is probably now more accurate since they all tend to over-read.
     
  12. CafeMB

    CafeMB Banned

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    Just out of curiosity, what happens when 17 inch wheels and tyres are fitted then and how does it affect the speedo?
     
  13. Naraic

    Naraic Moderator

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    Yes it would...but not sure by how much, and whether it would be more or less accurate.
     
  14. Naraic

    Naraic Moderator

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    When you fit 17 wheels you then choose a lower profile tyre so that the diameter of the tyre remains the same ( or very close).

    Have a look here:

    http://www.alloywheelsdirect.net/information/fitting_chart/mercedes-benz
     
  15. yorkshire1

    yorkshire1 Senior Member

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    Your Mercedes:
    "98 S202 C250TD Manual hybrid
    speedo

    not sure how the different models read speed but I know my W202 reads from the abs sensors on the front wheels, so regardless of tyre/wheel options the speedo will read true

    regarding the vehicle skidding,it could be that some of the wheels arent braking at all so when the brakes are applied the one/s that are, skid
     
  16. wireman

    wireman Senior Member

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    Your Mercedes:
    nice 201 2.5D 1993 & very nice 129 SL500 1994
    Original spec 195 65 15H
     
  17. antijam

    antijam Senior Member

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    That's a fairly brave assumption!

    ABS sensors do what any form of speedometer sensor does - that is measure (either directly or indirectly) the rotational speed of the wheel. How far the car will travel for one revolution of the wheel (and therefore over a given time interval, how fast it is moving) is dictated by the rolling radius of the tyre.

    This is the combination of the wheel radius and the tyre wall height (with an appropriate compensation for the compression of the tyre under load). With radial tyres the sidewall height is determined by the aspect ratio of the tyre, which is defined as a percentage of the tyre width. e.g. a 185/75 - 15 tyre has a width of 185mm. and a sidewall height of 75% of that - c.139mm. Somewhat perversely the wheel diameter is still specified in inches so in this example the nominal rolling radius of the tyre would be 7.5 inches plus 139mm. Multiply the sum by 2 pi and obtain the rolling circumference of the tyre and therefore how far the car will travel for one rotation of the wheel.

    It is often quite possible to change the wheel and tyre size combination such that the rolling radius remains practically unchanged. for example a change from 16" to 18" wheels could be a change from a 185/75 - 16 tyre to a 205/55 - 18, which differ in rolling radius by only 0.5mm. which is insignificant. Note that the wheel width would probably need to increase also to allow correct fitment of the wider tyre.

    However if the chosen combination of wheel and tyre size produce a rolling radius significantly different from the original this will produce an error in the speedo reading (and also a change in the overall gearing ratios).

    Car manufacturers are allowed a tolerance in speedo reading of 0% to +10%.
    They will tend to aim for the middle of this range since it gives them the widest manufacturing tolerance and therefore minimal scrap, but also because the performance of their car will appear greater if the speedo reading is optimistic.

    Switching to a wheel/tyre combination of greater rolling radius than original will mean that for one revolution of the wheel the car will actually travel slightly further in a fixed time so that what, for example, was previously an optimistcally indicated 60mph actually becomes 60mph.
     
  18. yorkshire1

    yorkshire1 Senior Member

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    Your Mercedes:
    "98 S202 C250TD Manual hybrid
    speedo

    Yes apologies due antijam, I was thinking of my application where the rear tyres are different circumference to fronts and speedo is correct, sorry
     

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