transmission losses on a rolling road
Discussion
whats the widely accepted figure here?is it a percentage or is it an actual bhp figure?i realise that all rolling roads will be slightly different,but the actual losses at all of them must be similar musnt they?.my inexperienced and unscientific brain says you should use a certain amount of bhp through the transmission no matter how much you change the output of the engine ie i should loose 40bhp on my griff for example weather its producing 200 bhp or 300bhp.so whats the right way of calculating it,i presume there are different allowances for fwd,rwd and 4wd? cheers,mike.
Losses will vary with transmission type and engine power. For a TVR or similar RWD a rough rule of thumb is 15 bhp +10%. So 250 bhp at the crank will read about 210 bhp at the wheels. Different rule of thumb for FWD and 4WD though.
This is all my own idea, not to be relied on etc.....
This is all my own idea, not to be relied on etc.....
If it's a hub-dyno, the losses for a 2wd car should be no more than 10%. 4wd, probably 15-18%, but don't hold me to that.
If it's a "real" rolling road (i.e. rollers under the tyres), then the losses are greater, more in the region of 15-20% for 2wd, 25-30% for 4wd.
It really does vary from road to road. In addition, the calibration of some roads is terrible. The final consideration is making sure the r-r uses 4th gear AND uses the correct final drive ration in their calculations.
If you want my opinion, there's little point in just getting a headline number from a r-road, unless it's to compare against another car of the same type which has also been on the r-road that day (i.e. a shootout). There's just too many variables.
What they are very useful for is measuring the effectiveness of modifications and tuning tweaks, but then the time on the road can become expensive...
If it's a "real" rolling road (i.e. rollers under the tyres), then the losses are greater, more in the region of 15-20% for 2wd, 25-30% for 4wd.
It really does vary from road to road. In addition, the calibration of some roads is terrible. The final consideration is making sure the r-r uses 4th gear AND uses the correct final drive ration in their calculations.
If you want my opinion, there's little point in just getting a headline number from a r-road, unless it's to compare against another car of the same type which has also been on the r-road that day (i.e. a shootout). There's just too many variables.
What they are very useful for is measuring the effectiveness of modifications and tuning tweaks, but then the time on the road can become expensive...
Munter said:I think it was ages ago when someone sent me the link to his explanation of power and torque.
How did you find his site jeremyc?
Many of his technical white papers are informative, no-nonsense discussions of issues that frequently come up here on PH.
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