How is 'at the wheels' different to 'at the crank' BHP?

DaveU · 05-03-2004, 20:43

Reading through VWVortex (as you do) they are quite fussy when people quote BHP as to if they mean 'at the wheels' or 'at the crank'. Now i've heards people say "it's got nnn bhp - and that's at the wheels as well!"

So what is the different and in what context would you use each?

I take it at the wheels is a lower figure and when we get dyno's done they normally quote at the crank figures?

So what's that all about then?

Mark · 05-03-2004, 21:04

the transmission (inlcuding clutch, gearbox, tyres) all have a drag associatted to them.

Rolling roads measure the wheel horse power & calculate the flywheel bhp by means of a roll down

you can make your whp look better by pumping up your tyres... so it's a bit of bollicks really.

ninja_alex · 05-03-2004, 21:06

Crank BHP is true engine power where as 'at the wheels BHP' is the true value of the car after the %age has been lost through transmission and drive. This is generally about 30-40BHP.

Steve vRS · 05-03-2004, 21:12

Quote:

Originally Posted by ninja_alex

Crank BHP is true engine power where as 'at the wheels BHP' is the true value of the car after the %age has been lost through transmission and drive. This is generally about 30-40BHP.

I think on a FWD car, the transmission losses are about 10%. On my old Scoob it was closer to 25% due to the 4wd system.

Steve

daver · 06-03-2004, 01:24

Quote:

Originally Posted by Steve vRS

I think on a FWD car, the transmission losses are about 10%. On my old Scoob it was closer to 25% due to the 4wd system.

Steve

I have been told that Scoobs lose around 100BHP through the transmission losses? possibly expalains a few Scoob refugees takin up vRS's ( not to mention the Fuel costs)

Steve vRS · 06-03-2004, 08:12

Quote:

Originally Posted by daver

I have been told that Scoobs lose around 100BHP through the transmission losses? possibly expalains a few Scoob refugees takin up vRS's ( not to mention the Fuel costs)

Bollox.

It will lose 100bhp if ti was a 500hp car.

Steve

daver · 07-03-2004, 01:02

Quote:

Originally Posted by Steve vRS

Bollox.

It will lose 100bhp if ti was a 500hp car.

Steve

Steve,

No disrespect but I think you will find that a Scoob with 248 Bhp at the flywheel will give around the 160bhp at the flywheel mark, the tendancy of the mass 'max power' brigade to quote a percentage loss regardless of power is.......Mmmmm how did you put it? "Bollox" a car is a machine and like any other machine converts energy ( basic physics) as a result the drive train will generate a certain amount of power loss through heat generated by friction, turning the various gears against each other and transferring the power through differnt plains. if a vehicle loses 88 to 95 BHP at 248, the losses at 500BHP are not likely to be significantly more, certainly when expressed as a percentage of the higher power output I think that you will find them signifcantly less! The scoobs transmission saps power like no tomorrow, hence the fuel consumption of even standard scoobs are lousy to say the least. go have a look on scoobynet, do a search on drivetrain losses, 88-95BHP is the norm, not far from 100 i queried, explains why on a rolling or in gear 'fight' the vrs skud will see off all but the seriously modded scoobs!
Anyone care to comment?????

andy_ccr · 07-03-2004, 13:53

My Focus was rolling roaded tested at approx 135bhp at the 'crank' by Power Engineering in Uxbridge. Relative wheel power came out at something around the 105bhp mark, so there was quite a loss. As just another point, my Focus had been rolling roaded at a least 3 different tuners and with only '135' bhp, I've had different figures from 118 to 135, lucily at least two tuners have seen approx 135 more than once.... I tend not to believe most of these bhp figures given in magazines though !

One thing to notice that in American they ofen quite WHP rather than our 'traditional' BHP.. One thing I can never understand is this 'stupid' metric kWh stuff for engine powers.

All I can say for true BHP try a 4 litre V8 BMW M5 with '400bhp' and torque to match. When that starts jumping around on the 'rollers' you know thats serious power !!! Or try a Ford F150 Lightening for real 'power' figures.

Just to finish, I find that my vRS 'appears' SO much faster than my Focus (180-190bhp turbo charged compared with 'somewhere around' 130bhp). Even though we are talking less that 50bhp difference.

DaveU · 07-03-2004, 14:10

Quote:

Originally Posted by andy_ccr

All I can say for true BHP try a 4 litre V8 BMW M5 with '400bhp' and torque to match. When that starts jumping around on the 'rollers' you know thats serious power !!! Or try a Ford F150 Lightening for real 'power' figures.

4 litres is for wimps

***DGW*** · 07-03-2004, 19:44

Quote:

Originally Posted by DaveU

4 litres is for gaylords!

UNoHoo will not be amused when he sees that comment, Dave!

**delcac** · 07-03-2004, 19:52

Quote:

Originally Posted by DGW

UNoHoo will not be amused when he sees that comment, Dave!

What's wrong with being a gaylord?

DaveU · 07-03-2004, 19:54

Denis - I don't know what you are talking about...

Nigel26 · 08-03-2004, 14:44

i found the norm was around 20bhp loss through transmission on nearly all the FWD cars that ran on the RSC RR days we held, over the years there were days at Aldons & Hi-Tech (midlands), Nobles (chesterfield) and EP Motorsport (stoke).

Alot of the the rollers measured BHP at the wheels and calculated the flywheel / crank figures as said above, only Nobles simulated road drag and measured the flywheel figures more accurately.

I would agree that a $WD car would have a bigger loss than a FWD but i would agree that it would be as high as 90-100bhp. i just cant see the cars being competative enough with such massive losses through the drive train, and if they were i'd hope to think the manufacturers would be doing something to solve it.

DaveU · 08-03-2004, 15:31

So in summary:

'At the crank' is the normal and true bhp figures talked about - eg the Octy vRS has 180 bhp at the crank

'At the wheels' / flywheel bhp is the figure after losses due to transmission / drag

So while a chipped 4x4 and a chipped Octy might have the same 230ish bhp at the crank, in reality the at the wheels figures would be much lower for the 4x4 due to transmission losses etc and it would therefore be slower.
That all makes perfect sense now!

SkodiRS · 08-03-2004, 15:43

Quote:

Originally Posted by DaveU

So in summary:

'At the crank' is the normal and true bhp figures talked about - eg the Octy vRS has 180 bhp at the crank

'At the wheels' / flywheel bhp is the figure after losses due to transmission / drag

So while a chipped 4x4 and a chipped Octy might have the same 230ish bhp at the crank, in reality the at the wheels figures would be much lower for the 4x4 due to transmission losses etc and it would therefore be slower.
That all makes perfect sense now!

4X4 might not be slower as although there are transmission losses it's lower gearing may make it a little quicker off the line.

***DGW*** · 08-03-2004, 16:08

Quote:

Originally Posted by DaveU

So while a chipped 4x4 and a chipped Octy might have the same 230ish bhp at the crank, in reality the at the wheels figures would be much lower for the 4x4 due to transmission losses etc

Only true when in 4WD mode.....which is when a 2WD car in the same circumstances would be struggling to put any power down on the road.
QED.

Looking at a few Jabba plots, typical figures for dissipate power (ie engine power minus wheel power) for the vRS were 27.5bhp, 27.4bhp, and 23.0bhp - and for the 4X4 were 55.5bhp (Fabpreza) and 46.7bhp (DGW).

RallyMarshal · 10-03-2004, 15:32

Any figure from a rolling road that gives flywheel values is pie in the sky as none of them can accurately calculate the flywheel figure as they dont know the transmission losses for that car. However a good rolling road (ie not a max power brigade RR) will guestimnate the flywheel figure. Even doing power runs in different gears affects the transmission losses - and the losses the RR has itself through higher wheel speeds etc.

TBH, its the wheels figure thats the most accurate important anyway as thats where you need the power to be.

Paul..

Tavia4x4 · 10-03-2004, 16:09

Of course 2wd boys will love to quote their low transmission losses, but you can't calculate the power loss on a wet road....

(stands back, waiting for bite.....

)

redbaron · 10-03-2004, 16:34

Quote:

Originally Posted by Tavia4x4

Of course 2wd boys will love to quote their low transmission losses, but you can't calculate the power loss on a wet road....

(stands back, waiting for bite.....

)

no need to bite.. i just have sympathy for the deluded.

05-03-2004, 20:43	#1
DaveU VIP Join Date: Nov 2002 Location: South, then East a little bit. Posts: 2,455 Thanks: 0 Thanked 0 Times in 0 Posts	How is 'at the wheels' different to 'at the crank' BHP? Reading through VWVortex (as you do) they are quite fussy when people quote BHP as to if they mean 'at the wheels' or 'at the crank'. Now i've heards people say "it's got nnn bhp - and that's at the wheels as well!" So what is the different and in what context would you use each? I take it at the wheels is a lower figure and when we get dyno's done they normally quote at the crank figures? So what's that all about then? __________________ Dave Dave's new runaround ^ The Beast: 2001-2007 (now re-homed). 5 1/2 years of frightening the living daylights out of other road users and ashaming various high end cars.

05-03-2004, 21:04	#2
Mark Briskodian Join Date: Oct 2002 Posts: 90 Thanks: 0 Thanked 0 Times in 0 Posts	the transmission (inlcuding clutch, gearbox, tyres) all have a drag associatted to them. Rolling roads measure the wheel horse power & calculate the flywheel bhp by means of a roll down you can make your whp look better by pumping up your tyres... so it's a bit of bollicks really. __________________ www.SEATCupra.net

05-03-2004, 21:06	#3
ninja_alex Old Skool Fan Join Date: Jan 2004 Location: Bucks Posts: 509 Thanks: 0 Thanked 20 Times in 20 Posts	BHP figures Crank BHP is true engine power where as 'at the wheels BHP' is the true value of the car after the %age has been lost through transmission and drive. This is generally about 30-40BHP.

07-03-2004, 13:53	#8
andy_ccr Briskodian Join Date: Aug 2003 Location: Essex Posts: 407 Thanks: 0 Thanked 0 Times in 0 Posts	My Focus was rolling roaded tested at approx 135bhp at the 'crank' by Power Engineering in Uxbridge. Relative wheel power came out at something around the 105bhp mark, so there was quite a loss. As just another point, my Focus had been rolling roaded at a least 3 different tuners and with only '135' bhp, I've had different figures from 118 to 135, lucily at least two tuners have seen approx 135 more than once.... I tend not to believe most of these bhp figures given in magazines though ! One thing to notice that in American they ofen quite WHP rather than our 'traditional' BHP.. One thing I can never understand is this 'stupid' metric kWh stuff for engine powers. All I can say for true BHP try a 4 litre V8 BMW M5 with '400bhp' and torque to match. When that starts jumping around on the 'rollers' you know thats serious power !!! Or try a Ford F150 Lightening for real 'power' figures. Just to finish, I find that my vRS 'appears' SO much faster than my Focus (180-190bhp turbo charged compared with 'somewhere around' 130bhp). Even though we are talking less that 50bhp difference. __________________ Black '53' Octy vRS - 18inch RS4 in Graphite Grey - Colour coded front grill - Samco TIP - Carbonio filter - OBD Remap by Mike @ Impossible Performance Forge FMIC SuperSprint cat back exhaust. Coming soon - Rear ARB, better suspension, better brakes.... Damn that bloody Nurburgring ! Coming before the end of Jan 2007 - Audi A4 Cabriolet - Ebony Black- 18inch RS4 Wheels - Red Knappa leather

07-03-2004, 19:54	#12
DaveU VIP Join Date: Nov 2002 Location: South, then East a little bit. Posts: 2,455 Thanks: 0 Thanked 0 Times in 0 Posts	Denis - I don't know what you are talking about... __________________ Dave Dave's new runaround ^ The Beast: 2001-2007 (now re-homed). 5 1/2 years of frightening the living daylights out of other road users and ashaming various high end cars.

08-03-2004, 14:44	#13
Nigel26 Briskodian Join Date: Nov 2003 Location: Walsall, West Midlands Posts: 2,298 Thanks: 0 Thanked 0 Times in 0 Posts	i found the norm was around 20bhp loss through transmission on nearly all the FWD cars that ran on the RSC RR days we held, over the years there were days at Aldons & Hi-Tech (midlands), Nobles (chesterfield) and EP Motorsport (stoke). Alot of the the rollers measured BHP at the wheels and calculated the flywheel / crank figures as said above, only Nobles simulated road drag and measured the flywheel figures more accurately. I would agree that a $WD car would have a bigger loss than a FWD but i would agree that it would be as high as 90-100bhp. i just cant see the cars being competative enough with such massive losses through the drive train, and if they were i'd hope to think the manufacturers would be doing something to solve it. __________________ Sea Grey Mondeo Titanium X

08-03-2004, 15:31	#14
DaveU VIP Join Date: Nov 2002 Location: South, then East a little bit. Posts: 2,455 Thanks: 0 Thanked 0 Times in 0 Posts	So in summary: 'At the crank' is the normal and true bhp figures talked about - eg the Octy vRS has 180 bhp at the crank 'At the wheels' / flywheel bhp is the figure after losses due to transmission / drag So while a chipped 4x4 and a chipped Octy might have the same 230ish bhp at the crank, in reality the at the wheels figures would be much lower for the 4x4 due to transmission losses etc and it would therefore be slower. That all makes perfect sense now! __________________ Dave Dave's new runaround ^ The Beast: 2001-2007 (now re-homed). 5 1/2 years of frightening the living daylights out of other road users and ashaming various high end cars.

10-03-2004, 15:32	#17
RallyMarshal Briskodian Join Date: Nov 2002 Location: Mansfield, Notts. Posts: 189 Thanks: 0 Thanked 0 Times in 0 Posts	Any figure from a rolling road that gives flywheel values is pie in the sky as none of them can accurately calculate the flywheel figure as they dont know the transmission losses for that car. However a good rolling road (ie not a max power brigade RR) will guestimnate the flywheel figure. Even doing power runs in different gears affects the transmission losses - and the losses the RR has itself through higher wheel speeds etc. TBH, its the wheels figure thats the most accurate important anyway as thats where you need the power to be. Paul.. __________________ paul@rallymarshal.co.uk Just back from Barbados See www.teamrallymarshal.co.uk for details

10-03-2004, 16:09	#18
Tavia4x4 Briskodian Join Date: Oct 2002 Location: J5 M61 Posts: 5,294 Thanks: 0 Thanked 0 Times in 0 Posts	Of course 2wd boys will love to quote their low transmission losses, but you can't calculate the power loss on a wet road.... (stands back, waiting for bite..... ) __________________ Ian __________________ Nice to be important, but more important to be nice...

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How is 'at the wheels' different to 'at the crank' BHP?

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