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There is no formula - it depends on the power losses in the transmission and between the tyres and rollers. The most popular solution is to use a coast down test in which the rollers drive the transmission to assess the power absorbed. Different engine/gearbox layouts have different power losses depending on how may gears the drive goes through, straight cut or not, and whether there are bevel or hypoid gears along the line. To give you an idea few straight cut gearboxes are more than 93% efficient. It is easy to drop into the low to mid 80's for the whole driveline before accounting for tyre losses. The will probably give you a loss of over 20%, so to gorss up you need to multiply by about 1.25. hope this is of osme help.
its different for all vehicles..
depends on the gearbox design, wheel size, tyres, etc probably wheel weight.
the rolling roads do it i think by doing a run down.. they drive your car hard foot to the floor, let off after thepower run and leave it to coast down itself and it somehow works out and guestimates the power loss, adds this onto the measured ATW figure and thus gives you the guestimated fly figure.
as far as i know there isnt any exact figures but ive read
a FWD car should be around 18-20% ish..
4wd cars loose something stupid like 30 or more%
some 4wd systems are very innefficient.
depends on the gearbox design, wheel size, tyres, etc probably wheel weight.
the rolling roads do it i think by doing a run down.. they drive your car hard foot to the floor, let off after thepower run and leave it to coast down itself and it somehow works out and guestimates the power loss, adds this onto the measured ATW figure and thus gives you the guestimated fly figure.
as far as i know there isnt any exact figures but ive read
a FWD car should be around 18-20% ish..
4wd cars loose something stupid like 30 or more%
some 4wd systems are very innefficient.
Nafoff
ClioSport Club Member
yeah i wondered this dan....
any news on your motor mate?
any news on your motor mate?
Nafoff
ClioSport Club Member
ah so it wasen't the head then...thank god...
nice to meet you again bud
nice to meet you again bud
Megane Trophy
I always thought that after the run down test, the computer then applies an equation from those results to equate the transmission loss
then works out the estimated flywheel figure
the only way you can do it is by looking at your rolling road printout
it should really say somewhere the transmission loss and then the flywheel power or you may have to work that out
then works out the estimated flywheel figure
the only way you can do it is by looking at your rolling road printout
it should really say somewhere the transmission loss and then the flywheel power or you may have to work that out
Megane Trophy
on my corsa for example that made 168bhp at the flywheel and had a transmission loss of 27% if i remember correct so the at the wheel power was just over 120 bhp
Megane Trophy
well im sure thats what it made, was over 18 months ago now!
on a 20 year old engine as well!
Yes everyone says about rolling roads being taken with a pinch of salt
but who has the 1k needed to take the engine out the car and out on a proper dyno.
They rolling road map cars with aftermarket management and gains are seen with them, so as long as its a decent rolling road then there shouldnt be as many innacuracies.
In an ideal world we would all use a test bed but that isnt affordable for 99% of us, so a power run at an established place such a BBT who map cars etc is the best way!
on a 20 year old engine as well!
Yes everyone says about rolling roads being taken with a pinch of salt
but who has the 1k needed to take the engine out the car and out on a proper dyno.
They rolling road map cars with aftermarket management and gains are seen with them, so as long as its a decent rolling road then there shouldnt be as many innacuracies.
In an ideal world we would all use a test bed but that isnt affordable for 99% of us, so a power run at an established place such a BBT who map cars etc is the best way!
Nafoff
ClioSport Club Member
so what are we saying then...for 2wd and for 4wd...
Confusing!
At Janspeed yesterday I got 144.54 atw and this was fairly average for 172 Cups iirc, therefore if it does have a genuine 170bhp then a 15% loss would be absolutely spot on, if it was up towards 20% I'd be looking at 180bhp, which on a completely standard car with 18k on it would be a bit unlikely!
I don't think there was a single 182 which got close to a 10bhp raise over a 172. Some 182s prior to their first 12k service were seeing low 140s, which by the same 15% is around 165bhp, a huge drop from the claimed figures but perfectly understandable considering how most people talk about their cars seriously loosening up once it was many more miles on it. It will be interesting to see how some higher mileage 182s get on in the future, hopefully if my theory is correct they should improve considerably once 20k+ is passed.
At Janspeed yesterday I got 144.54 atw and this was fairly average for 172 Cups iirc, therefore if it does have a genuine 170bhp then a 15% loss would be absolutely spot on, if it was up towards 20% I'd be looking at 180bhp, which on a completely standard car with 18k on it would be a bit unlikely!
I don't think there was a single 182 which got close to a 10bhp raise over a 172. Some 182s prior to their first 12k service were seeing low 140s, which by the same 15% is around 165bhp, a huge drop from the claimed figures but perfectly understandable considering how most people talk about their cars seriously loosening up once it was many more miles on it. It will be interesting to see how some higher mileage 182s get on in the future, hopefully if my theory is correct they should improve considerably once 20k+ is passed.
