Transmission loss 4x4
10-08-2009, 01:42 PM
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10-08-2009, 03:04 PM
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as a general rule of thumb in uni we were told toassume approx 85% efficient for FWD 75% efficient for RWD and then 50% for 4wd due to the extra diff and shafts etc.
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10-08-2009, 03:12 PM
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40 - 50% seemed waaaaaaaaaay high to me as I thought it was more like 25% max so did a quick search and found this article on pumaracing.com. I've read some good articles on there so I've posted an extract here and the link to the full write up is at the bottom.
The average front wheel drive road car with between 100 and 200 bhp loses about 15% of the engine bhp as transmission losses.
The average rear wheel drive road car with between 100 and 200 bhp loses about 17% of the engine bhp as transmission losses.
The 2% increase in losses over front wheel drive is because the differential has to turn the drive through 90 degrees at the back axle which soaks up a bit more of the engine's power. Copyright David Baker and Puma Race Engines
4wd cars will have higher losses because of the extra differentials and other power transmission components. The tyre and main gearbox losses will be the same though. Correlating the performance of vehicles with the both 4wd and 2wd options (Audi's and the Sierra Cosworth are examples) shows 4wd transmission losses to be about 5% higher than rwd. 22% seems to be a good average.
What each individual car loses is an unknown - it will depend on tyre sizes and pressure, suspension angles and other things, but it shouldn't be far from the figures above. For sure though, no 2wd car in the world, unless it has flat tyres and a gearbox full of sand, loses anything like 30% of the engine's power in the transmission and tyres as many rolling road operators would try to have you believe. In general though it is fair to say that low powered cars have higher % losses than high powered cars. This is because some of the frictional losses are independent of engine power and so represent a bigger drain on a small engine. For example, a 60 bhp Fiesta will have around 14 to 15 bhp total transmission and tyre loss (25%) whereas a 90 bhp XR2 will only have about 17 to 18 bhp loss (20%) - a smaller % obviously. By the time you get to RWD cars with engines in the 300 to 500+ bhp range, losses can eventually drop to as little as 12% to 14% or so.
http://www.pumaracing.co.uk/POWER3.htm
The average front wheel drive road car with between 100 and 200 bhp loses about 15% of the engine bhp as transmission losses.
The average rear wheel drive road car with between 100 and 200 bhp loses about 17% of the engine bhp as transmission losses.
The 2% increase in losses over front wheel drive is because the differential has to turn the drive through 90 degrees at the back axle which soaks up a bit more of the engine's power. Copyright David Baker and Puma Race Engines
4wd cars will have higher losses because of the extra differentials and other power transmission components. The tyre and main gearbox losses will be the same though. Correlating the performance of vehicles with the both 4wd and 2wd options (Audi's and the Sierra Cosworth are examples) shows 4wd transmission losses to be about 5% higher than rwd. 22% seems to be a good average.
What each individual car loses is an unknown - it will depend on tyre sizes and pressure, suspension angles and other things, but it shouldn't be far from the figures above. For sure though, no 2wd car in the world, unless it has flat tyres and a gearbox full of sand, loses anything like 30% of the engine's power in the transmission and tyres as many rolling road operators would try to have you believe. In general though it is fair to say that low powered cars have higher % losses than high powered cars. This is because some of the frictional losses are independent of engine power and so represent a bigger drain on a small engine. For example, a 60 bhp Fiesta will have around 14 to 15 bhp total transmission and tyre loss (25%) whereas a 90 bhp XR2 will only have about 17 to 18 bhp loss (20%) - a smaller % obviously. By the time you get to RWD cars with engines in the 300 to 500+ bhp range, losses can eventually drop to as little as 12% to 14% or so.
http://www.pumaracing.co.uk/POWER3.htm
Last edited by Northern Bloke; 10-08-2009 at 03:14 PM.
10-08-2009, 03:20 PM
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Yeah, it's a good site that one Pete
As you say though 50% is maaad, that means my 4x4 is running about 100bhp at the wheels
As you say though 50% is maaad, that means my 4x4 is running about 100bhp at the wheels
Last edited by Northern Bloke; 10-08-2009 at 03:23 PM.
10-08-2009, 05:18 PM
#16
I had done 2 rolling road sessions in the past with my cossie 4x4 and when calculating the figures, both saw about 40% transmission loss.
I also thought it was very high, that's why I ask. This friday I am doing a new session so I can compare it again.
I also thought it was very high, that's why I ask. This friday I am doing a new session so I can compare it again.
22-08-2009, 05:03 PM
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Sounds a bit over dramatic and not sure about the 4WD number, for for the others that makes sense more or less.
Last edited by canst; 22-08-2009 at 05:06 PM.
22-08-2009, 06:30 PM
#24
Who ACTUALY has compared their engine BHP on a dyno to the power in the car? IE run it in a dyno cell (TUV approved 
), then on a proper set of rollers such as Dyno Dynamics?
50% or even 40% losses
The rule of thumb / fudge factor / generally accepted figure on the MLR for Evo transmission is 24%, and I bet most Cossie 4*4 trasmission losses are similar.
Most guys on the MLR now only quote the ATW (at the wheels) figure, as the bhp at the fly varies so much with the different operators and rolling roads.
At the wheels is the most important real world figure. Mine on DD rollers is 437bhp, sounds low for a GT35 running 2 bar boost, but that's all hitting the ground, unlike half the dream figures people are quoting if they are using a 50% conversion rate Does that make mine 655 bhp, cool 
), then on a proper set of rollers such as Dyno Dynamics?50% or even 40% losses
The rule of thumb / fudge factor / generally accepted figure on the MLR for Evo transmission is 24%, and I bet most Cossie 4*4 trasmission losses are similar.
Most guys on the MLR now only quote the ATW (at the wheels) figure, as the bhp at the fly varies so much with the different operators and rolling roads.
At the wheels is the most important real world figure. Mine on DD rollers is 437bhp, sounds low for a GT35 running 2 bar boost, but that's all hitting the ground, unlike half the dream figures people are quoting if they are using a 50% conversion rate
Does that make mine 655 bhp, cool
22-08-2009, 06:36 PM
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I have known st220's to test at 5-10bhp more at the wheels than 330i (e46)'s.
Even though (officially) the 330 has about 5bhp more at the flywheel.
This makes me think that the losses are about 5% worse for RWD. Even so the 330 would still get from 0-60 faster thanks to grip.
Even though (officially) the 330 has about 5bhp more at the flywheel.
This makes me think that the losses are about 5% worse for RWD. Even so the 330 would still get from 0-60 faster thanks to grip.
22-08-2009, 08:48 PM
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Who ACTUALY has compared their engine BHP on a dyno to the power in the car? IE run it in a dyno cell (TUV approved ), then on a proper set of rollers such as Dyno Dynamics?
50% or even 40% losses
The rule of thumb / fudge factor / generally accepted figure on the MLR for Evo transmission is 24%, and I bet most Cossie 4*4 trasmission losses are similar.
Most guys on the MLR now only quote the ATW (at the wheels) figure, as the bhp at the fly varies so much with the different operators and rolling roads.
At the wheels is the most important real world figure. Mine on DD rollers is 437bhp, sounds low for a GT35 running 2 bar boost, but that's all hitting the ground, unlike half the dream figures people are quoting if they are using a 50% conversion rate Does that make mine 655 bhp, cool
), then on a proper set of rollers such as Dyno Dynamics?50% or even 40% losses
The rule of thumb / fudge factor / generally accepted figure on the MLR for Evo transmission is 24%, and I bet most Cossie 4*4 trasmission losses are similar.
Most guys on the MLR now only quote the ATW (at the wheels) figure, as the bhp at the fly varies so much with the different operators and rolling roads.
At the wheels is the most important real world figure. Mine on DD rollers is 437bhp, sounds low for a GT35 running 2 bar boost, but that's all hitting the ground, unlike half the dream figures people are quoting if they are using a 50% conversion rate
Does that make mine 655 bhp, cool
22-08-2009, 09:31 PM
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forgot about this thread, as i said we were told to assume that, i didnt say it was a true reflection tho did i! 
i would say that it was prob 90 - 85 and 75 efficeint (fwd, rwd 4x4) to be honest as if it was that much loss through the drive train you would be seriously questioning why it would loose so much, well i would! lol
i would say that it was prob 90 - 85 and 75 efficeint (fwd, rwd 4x4) to be honest as if it was that much loss through the drive train you would be seriously questioning why it would loose so much, well i would! lol
22-08-2009, 10:00 PM
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been saying this on other threads lately..our rollers calculate 17 18% on 2wd cossys and 20 22% on 4wd...i know of two other maha rollers and every car weve done back to back have been within a couple of hp of eachother...as for si b car that would equate to 550 bhp on our rollers..cheers danny
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