Actual HP at the wheels not crankshaft
04-04-2005, 04:10 PM
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All major manufacturers utilize net or rear wheel horse power today. It will vary form car to car, dyno to dyno, altitude and weather though.
04-05-2005, 01:04 PM
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Originally Posted by pennetta' date='Apr 4 2005, 06:10 PM
All major manufacturers utilize net or rear wheel horse power today. It will vary form car to car, dyno to dyno, altitude and weather though.
[snapback]111124[/snapback]
All major manufacturers use crank horsepower, NOT rear wheel horsepower. Crankshaft HP is the horsepower measured at the crankshaft with the engine alone sitting on a stand on the dyno. Rear wheel HP is measured by putting the rear wheels of the car on rollers, and measuring the torque at a given rpm.
Rear wheel HP will be 15% or so lower with a manual transmission or SMG, around 20% lower with a steptronic. The difference between crankshaft HP and rear wheel HP is due to losses in the drivetrain. These numbers are well documented, with BMW being much better than most at converting crankshaft HP to rear wheel HP.
Rear wheel hp of a 545 should be around 275 HP or so, and yes, it will vary significantly with conditions.
04-05-2005, 01:21 PM
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Originally Posted by pennetta' date='Apr 5 2005, 12:10 AM
All major manufacturers utilize net or rear wheel horse power today. It will vary form car to car, dyno to dyno, altitude and weather though.
[snapback]111124[/snapback]
What manufacturers don't have to do is guestimate engine power and torque using transmission losses combined with dyno figures, as you have to if you want to get a vague idea of your engine power from a rolling road. They of course have the luxury of engine test beds to get the figures...
04-05-2005, 06:19 PM
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Originally Posted by wolverine' date='Apr 5 2005, 04:04 PM
[quote name='pennetta' date='Apr 4 2005, 06:10 PM']All major manufacturers utilize net or rear wheel horse power today. It will vary form car to car, dyno to dyno, altitude and weather though.
[snapback]111124[/snapback]
All major manufacturers use crank horsepower, NOT rear wheel horsepower. Crankshaft HP is the horsepower measured at the crankshaft with the engine alone sitting on a stand on the dyno. Rear wheel HP is measured by putting the rear wheels of the car on rollers, and measuring the torque at a given rpm.
Rear wheel HP will be 15% or so lower with a manual transmission or SMG, around 20% lower with a steptronic. The difference between crankshaft HP and rear wheel HP is due to losses in the drivetrain. These numbers are well documented, with BMW being much better than most at converting crankshaft HP to rear wheel HP.
Rear wheel hp of a 545 should be around 275 HP or so, and yes, it will vary significantly with conditions.
[snapback]111550[/snapback]
[/quote]Does the weight of the wheel and tires effect HP. If so, would run flats add weight and reduce horse power at the wheels?
Thanks.
04-05-2005, 06:40 PM
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Originally Posted by Guest' date='Apr 5 2005, 08:19 PM
[quote name='wolverine' date='Apr 5 2005, 04:04 PM'][quote name='pennetta' date='Apr 4 2005, 06:10 PM']All major manufacturers utilize net or rear wheel horse power today. It will vary form car to car, dyno to dyno, altitude and weather though.
[snapback]111124[/snapback]
All major manufacturers use crank horsepower, NOT rear wheel horsepower. Crankshaft HP is the horsepower measured at the crankshaft with the engine alone sitting on a stand on the dyno. Rear wheel HP is measured by putting the rear wheels of the car on rollers, and measuring the torque at a given rpm.
Rear wheel HP will be 15% or so lower with a manual transmission or SMG, around 20% lower with a steptronic. The difference between crankshaft HP and rear wheel HP is due to losses in the drivetrain. These numbers are well documented, with BMW being much better than most at converting crankshaft HP to rear wheel HP.
Rear wheel hp of a 545 should be around 275 HP or so, and yes, it will vary significantly with conditions.
[snapback]111550[/snapback]
[/quote]Does the weight of the wheel and tires effect HP. If so, would run flats add weight and reduce horse power at the wheels?
Thanks.
[snapback]111690[/snapback]
[/quote]Forgot to log in. That was me above.
04-05-2005, 08:15 PM
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Originally Posted by Guest' date='Apr 5 2005, 08:19 PM
[quote name='wolverine' date='Apr 5 2005, 04:04 PM'][quote name='pennetta' date='Apr 4 2005, 06:10 PM']All major manufacturers utilize net or rear wheel horse power today. It will vary form car to car, dyno to dyno, altitude and weather though.
[snapback]111124[/snapback]
All major manufacturers use crank horsepower, NOT rear wheel horsepower. Crankshaft HP is the horsepower measured at the crankshaft with the engine alone sitting on a stand on the dyno. Rear wheel HP is measured by putting the rear wheels of the car on rollers, and measuring the torque at a given rpm.
Rear wheel HP will be 15% or so lower with a manual transmission or SMG, around 20% lower with a steptronic. The difference between crankshaft HP and rear wheel HP is due to losses in the drivetrain. These numbers are well documented, with BMW being much better than most at converting crankshaft HP to rear wheel HP.
Rear wheel hp of a 545 should be around 275 HP or so, and yes, it will vary significantly with conditions.
[snapback]111550[/snapback]
[/quote]Does the weight of the wheel and tires effect HP. If so, would run flats add weight and reduce horse power at the wheels?
Thanks.
[snapback]111690[/snapback]
[/quote]Absolutely - minimizing the rotational inertia of the wheels and tires is one of the most important things in 'tuning' a car for maximum performance. If you have heavy wheels and tires, you will show lower outputs on a rwhp dyno test, and on top of that you have a heavier car! Going to lightweight wheels and tires is probably the best single thing you can do to improve acelleration and overall performance.
04-05-2005, 09:28 PM
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Originally Posted by wolverine' date='Apr 5 2005, 01:04 PM
Huh?? I agree with everything but the first sentence.?
All major manufacturers use crank horsepower, NOT rear wheel horsepower.? Crankshaft HP is the horsepower measured at the crankshaft with the engine alone sitting on a stand on the dyno.? Rear wheel HP is measured by putting the rear wheels of the car on rollers, and measuring the torque at a given rpm.?
Rear wheel HP will be 15% or so lower with a manual transmission or SMG, around 20% lower with a steptronic.? The difference between crankshaft HP and rear wheel HP is due to losses in the drivetrain.? These numbers are well documented, with BMW being much better than most at converting crankshaft HP to rear wheel HP.?
Rear wheel hp of a 545 should be around 275 HP or so, and yes, it will vary significantly with conditions.
All major manufacturers use crank horsepower, NOT rear wheel horsepower.? Crankshaft HP is the horsepower measured at the crankshaft with the engine alone sitting on a stand on the dyno.? Rear wheel HP is measured by putting the rear wheels of the car on rollers, and measuring the torque at a given rpm.?
Rear wheel HP will be 15% or so lower with a manual transmission or SMG, around 20% lower with a steptronic.? The difference between crankshaft HP and rear wheel HP is due to losses in the drivetrain.? These numbers are well documented, with BMW being much better than most at converting crankshaft HP to rear wheel HP.?
Rear wheel hp of a 545 should be around 275 HP or so, and yes, it will vary significantly with conditions.
[snapback]111550[/snapback]
04-05-2005, 11:32 PM
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Originally Posted by Hormazd' date='Apr 6 2005, 05:28 AM
However I was led to believe that BMW has always published their rear wheel numbers and not flywheel numbers like other manufacturers, thus explaining why your 545i hauls a$$.? Am I wrong?
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