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Automotive Torque and wheel size of a car

  1. Dec 9, 2014 #1
    So lets assume I have 100 Nm at the wheel of a car, with a wheel size of 25 in diameter

    If I put wheels that are 24 in diameter, so 4% smaller, what exactly will change ? Will I have 4% more torque ?
  2. jcsd
  3. Dec 9, 2014 #2

    You'll have exactly the same amount of torque. Something will change at the contact patch through.
  4. Dec 10, 2014 #3
    Isnt there some formula that might be applied here ? ... F = T*r ? Doesnt a change in wheel size of a car act like a gear change ?
  5. Dec 10, 2014 #4
    Ohhh...its F=T/r ... I get it now.
  6. Dec 11, 2014 #5
    If F is the ground force on the wheel then T- F.r = IG
  7. Dec 17, 2014 #6
    Also your rpm changes. The circumference (pi*D) is less on the smaller diameter.
  8. Dec 23, 2014 #7
    no you won't have more torque .. torque is a function of gear ratios at wheel torque = engine torque*gear ratios*differential ratio
    So when you are considering change in tyre dimensions assume it constant. so for changing wheel selection following things will occur.
    in this case your tractive force will increase..
    tractive effort= Torque/tyre radius (dynamic rolling radius)
    say you have 100Nm of torque which is constant
    now you used 25inch tyre= radius=0.3175m
    so tractive effort = 100/.3175=314N

    Now you used 24inch dia tyre=radius=.3048m
    so tractive effort = 328.08N

    so basically your tractive effort increases which can help you to climb gradients..
    you can calculate percentages.
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