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Tyre Size and Horsepower |
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Just can't stay away  
Joined:
2003/8/20 3:55
From Melbourne
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Hi Guys,
Can tyre size affect rear wheel horsepower?
The basis of the question
If you put a car on a Dyno and perform a run and then chage the tyre size up to a larger overall size, will the rear wheel horsepower change.
excluding the very small fraction of a friction increase by the larger tyres.
Cheers Guys,
A link to proof or actual mathmatical proof for a yes or no answer would be appeciated.
Posted on: 2006/8/9 0:56
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Re: Tyre Size and Horsepower |
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No life (a.k.a. DattoMaster)  
Joined:
2004/5/4 8:32
From Canberra
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surely not... or else all the dyno pigs would have custom 10" wheels with low profile tyres.
Posted on: 2006/8/9 2:31
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Re: Tyre Size and Horsepower |
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No life (a.k.a. DattoMaster) 
Joined:
2002/12/2 11:26
From Brisbane
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well on the dyno would it not be the opposite?... because there is a no need for traction because the wheels are turning on the rollers, a heavier larger tyre would actually take more to turn and add wieght, actually taking away from minimal amounts of horsepower...talking about tiny amounts of horsepower.
Posted on: 2006/8/9 2:38
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Re: Tyre Size and Horsepower |
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Moderator  
Joined:
2001/5/3 7:04
From 48 North
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Quote: Can tyre size affect rear wheel horsepower? No, but it certainly affects the overall gearing. Larger-diameter tires will make most cars accelerate more slowly.
Posted on: 2006/8/9 3:08
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Re: Tyre Size and Horsepower |
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No life (a.k.a. DattoMaster) 
Joined:
2002/6/14 7:24
From Sydney
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The horsepower should remain unchanged, however the effective rate of accelleration will change. The larger diameter tyre [increased circumfrence] The effective distance travelled will be longer for 1 revolution. More work would be required to turn the larger diameter tyre at the same rate as a smaller one for one revolution.
I think I got that right. maybe.
Posted on: 2006/8/9 3:24
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Re: Tyre Size and Horsepower |
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Just can't stay away Joined:
2003/8/20 3:55
From Melbourne
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This is my belief that a lager tyer size will use the horsepower for higher top end speed and a smaller tyer size wilol use it for acceleration.
However i am after some way to prove this as it has been an ongoing argument with 2 of my friends that are adament that a larger tyre size will reduce rear wheel horspower.
id like to prove it without going down and putting a car on a dyno. and then changing the tyre size
Posted on: 2006/8/9 3:55
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Re: Tyre Size and Horsepower |
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No life (a.k.a. DattoMaster) 
Joined:
2002/8/6 2:24
From Brisbane, Australia
Group:
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Quote:
Datsun1000 wrote:
Hi Guys,
Can tyre size affect rear wheel horsepower?
The basis of the question
If you put a car on a Dyno and perform a run and then chage the tyre size up to a larger overall size, will the rear wheel horsepower change.
excluding the very small fraction of a friction increase by the larger tyres.
Cheers Guys,
A link to proof or actual mathmatical proof for a yes or no answer would be appeciated.
no, tyre diametre will not affect bhp on a dyno. tyre diametre is just another form of gearing. and gears are torque multipliers. a taller tyre (or gear) will mean less torque (tractive effort) at the wheels, but they will be turning at a proportionately higher speed, so no net change to the power. eg change to a 10% larger tyre will make 10% less torque, but it will be going 10% faster at the same time, so it all balances out. power = torque * speed / a constant
Posted on: 2006/8/9 3:58
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"if you're not on the edge, you're just taking up space"
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Re: Tyre Size and Horsepower |
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Just can't stay away Joined:
2003/8/20 3:55
From Melbourne
Group:
Registered Users
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Quote:
L18_B110 wrote:
Quote:
Datsun1000 wrote:
Hi Guys,
Can tyre size affect rear wheel horsepower?
The basis of the question
If you put a car on a Dyno and perform a run and then chage the tyre size up to a larger overall size, will the rear wheel horsepower change.
excluding the very small fraction of a friction increase by the larger tyres.
Cheers Guys,
A link to proof or actual mathmatical proof for a yes or no answer would be appeciated.
no, tyre diametre will not affect bhp on a dyno. tyre diametre is just another form of gearing. and gears are torque multipliers. a taller tyre (or gear) will mean less torque (tractive effort) at the wheels, but they will be turning at a proportionately higher speed, so no net change to the power. eg change to a 10% larger tyre will make 10% less torque, but it will be going 10% faster at the same time, so it all balances out.
power = torque * speed / a constant
Below is what the retorted with @ says: so your saying that bigger tires need computer adjustment to multiply the torque change? # says: no that is not what is being said @ says: that is exactly what was said "torque multiplier" @ says: you need to change to settings on the dyno to adjust for the change in ratio @ says: so the ratio DOES make a difference @ says: otherise you wouldnt need to tell the computer the difference in gear ratios
Posted on: 2006/8/9 4:16
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Re: Tyre Size and Horsepower |
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No life (a.k.a. DattoMaster) Joined:
2002/8/6 2:24
From Brisbane, Australia
Group:
Registered Users
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@'s a PITA!
the dyno doesn't care what car is on it, or what tyre its got. the dyno simply measures the force seen at the rollers (torque or tractive effort), multiplies that by the roller speed, divides it by a constant (5252 for imperial bhp) and then it has the bhp figure.
no adjustment is needed to the dyno if you change tyre size. eg a 10% larger tyre would produce 10% less torque measured by the roller, but the roller will also be going 10% faster, so the mathematical equation power = torque * rpm / 5252 remains unchanged. The dyno will give the same power output no matter what tyre you put on a car.
Posted on: 2006/8/9 5:14
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"if you're not on the edge, you're just taking up space"
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Re: Tyre Size and Horsepower |
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Just can't stay away Joined:
2003/8/20 3:55
From Melbourne
Group:
Registered Users
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I have been argeing with one of them for an hour now and they still will not admit that tyre size does not effect rear wheel horsepower
Posted on: 2006/8/9 6:22
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