Rolling Road Question

[mark28G60 0]

Does it make a difference what size wheels you run on your car for a rolling road session or do they input this info in the pc.

Had my bike on a rolling road and i know he never checked wheel size but what about cars???

 

Thx

 

Mark :evil:

[dr_mat 0]

The at the wheel figure will be accurate (ish), no matter what size wheels you have. Of course, the transmission losses vary based on wheel size/weight, and most operators will key this in for the predicted "at the crank" figures, but most RR results we've seen have listed hopelessly optimistic at the crank figures, and perfectly reasonable at the wheel figures...

[Henny 0]

with dr_Mat here... 8)

 

When I had my chip written, the rollers would have been programmed for the wheel radius to make it all accurate, but the controller was damaged which is why I still don't know what power my engine puts out (when it's running... :roll: )

[Roger Blassberg 0]

Does anyone have a view on what are sensible losses for transmission, ancilliaries (with and without a/c compressor running), tyre rolling resistance etc on a standard VR?

 

Thanks in anticipation.

 

Best wishes

 

RB

[Mike Edwards 0]

40bhp?

[dr_mat 0]

The suggested figures I've seen are around 10% of engine power + 10bhp fixed losses (this is for a normal front wheel drive manual boxed car).

So for a completely standard VR6, 190 bhp less 10 % (19), less 10 bhp gives 161 bhp at the wheels. I suppose the air con pump (if it's running) might cost another 2-3 bhp...

[olly elworthy 0]

I think ATW figures are what should be used for comparison and conversation as these have not been fettled and all are on equal ground, + the ATW figure is what is actually pushing your car along,,,, 8)

[jedi-knight83 0]

mark28G60, does this mean you coming to the east anglia rr meet??

 

the wheels will be fine as has been said but thats a pretty low bumper..... may need to come off to fit on the rollers????

[davidwort 0]

I think ATW figures are what should be used for comparison and conversation as these have not been fettled and all are on equal ground, + the ATW figure is what is actually pushing your car along,,,, 8)

 

As it's only ATW torque that is actually measured on the rollers, does anyone know how accurate ATW bhp figures are, i.e. are there any particular problems calculating this, seems like a simple rpm associated sum to me, but then I failed my maths and physics A level miserably :-)

 

David.

[dr_mat 0]

Yeah, power = revs* torque / 5225 rpm. (I think.)

 

The roller actually just measures it's rotational speed, not acceleration force (torque) or power. The acceleration force applied by the wheels (which can be translated directly into torque) is calculated by plotting the CHANGE in roller speed, and using the known mass and drag of the rollers themselves. The power plot is then a simple case of applying the above formula to the torque plot.

 

The ATW figure is as accurate as the calibration that was done on the road. Since it's only a simple "roller speed" measuring tool, all the clever scaling should remain pretty constant and it shouldn't really drift out of calibration much.

[jedi-knight83 0]

end of the day these road are not 100% acurate.....but when you have lots of cars all on the same rr then you can get an acurate picture of whos there on that day is putting down more power and then you can always compare the printout to other rr days you attend

[Henny 0]

the best roads are those which you calibrate to the car's gearbox before you do a power run... these test the resistance through the gearbox to give a much more accurate Engine BHP and Torque figure... The Dubsport road is one of this style, however it's reasonably well known that people weren't happy with the lower figures that they got after a run on this properly set up road so the installers were called back in to "re-calibrate" the road and it now gives "more consistant" figures for BHP@crank... :roll:

 

IMHO the best places to get a rolling road session done are those which don't normally do shoot-out style sessions and only have the road installed to set up the fuelling on a car properly... these guys don't give a damn what BHP figures they get, only that the figures they DO get are accurate so they can set up the car properly... ;) 8)

 

(199.6BHP@wheels during mapping session was the final figure I got on such a road... )

[Kevin Bacon 5]

What's that Henny, I can't read your tiny subscripts...... :lol:

[Henny 0]

I can...

[mark28G60 0]

mark28G60, does this mean you coming to the east anglia rr meet??

 

the wheels will be fine as has been said but thats a pretty low bumper..... may need to come off to fit on the rollers????

 

Jedi,

 

I do intend on coming to the meet, taken the bumper off is not a problem im just worried about putting nice split rim 18's onto a rolling road and not getting a true reading of what the engine is capable, otherwise i need to get some 16's on my car.

 

Mark :evil:

[dr_mat 0]

What's the point of changing the wheels just for a rolling road? If that's not how the car is when it's actually used on the road, it's a meaningless figure! IMHO.

Anyway, the only way to get a figure for what the engine is capable of is to stick it on an engine dyno.

[jedi-knight83 0]

yeah just run with the 18's... the place does all kind of cars and they know what there doing so im sure they'll get the best figure for your car

 

i'll put your name on the list :wink:

[mark28G60 0]

What's the point of changing the wheels just for a rolling road? If that's not how the car is when it's actually used on the road, it's a meaningless figure! IMHO.

Anyway, the only way to get a figure for what the engine is capable of is to stick it on an engine dyno.

 

The reason for changing is i might be changing the style of the car a little which involves smaller wheels im just thinking at the moment what to change them to.

 

Mark :evil:

[corradostorm 0]

The Witham RR is an engine builders so i guess the RR is good.

 

One car we had on there last year showed about 10BHP more on the Stealth RR a few weeks later and i've heard that the Stealth RR may 'slightly'over state the BHP.

 

For reference my standard 2.9 showed 194.5BHP but more importantly 145BHP at the wheels. Torque was 195.

[dr_mat 0]

corradostorm: Don't you think that those that work using the RR day to day just reverse the "customer uplift"? I think so. I'm sure Vince at Stealth knows their road is up on reality, but he knows how much it's over by, so he can compensate in his head...

Your 145bhp at the wheels is down on standard, as is my 151bhp. Funny how we both have reported "@crank" figures well over the book "standard" figure tho.. Also funny your torque figure is no less than 15lbft over the book figure!!

[corradostorm 0]

corradostorm: Don't you think that those that work using the RR day to day just reverse the "customer uplift"? I think so. I'm sure Vince at Stealth knows their road is up on reality, but he knows how much it's over by, so he can compensate in his head...

Your 145bhp at the wheels is down on standard, as is my 151bhp. Funny how we both have reported "@crank" figures well over the book "standard" figure tho.. Also funny your torque figure is no less than 15lbft over the book figure!!

 

The problem is that, as you say, no two RR's are the same and therefore there is no way to really compare like for like. 145 on one could easily be 151 on another. I agree that torque figure looks way off.

 

Guess the only answer is the have everyone on the CF attend a RR day together. Now that would be a meet.

 

In all truth, i'm not to bothered with the power figures as the car is still a dream to drive and thats all that matters.

[corradostorm 0]

If your interested, these are the figures that RR put out that morning:

 

Name Car Flywheel BHP Wheel BHP Torque LbFt

Jamie Corrado Storm VR6 2.9 194.8 @ 5728rpm 145 @ 5728rpm 194.7 @ 4342rpm

Glenn Vento VR6 2.8 183.3 - 174.8

Russ Golf VR6 2.8 183.3 @ 5980rpm 130 174.3

Tom Golf VR6 2.8 Highline 181.2 - -

Graham Golf VR6 2.8 Highline 180.2 @ 5879rpm 135 @ 5879rpm 175.7 @ 4427rpm

Justin Golf VR6 2.8 Highline 176.2 @ 5763rpm 128 @ 5763rpm 174.5 @ 4459rpm

[dr_mat 0]

In all truth, i'm not to bothered with the power figures as the car is still a dream to drive and thats all that matters.

 

Agreed. :)

[mark28G60 0]

In all truth, i'm not to bothered with the power figures as the car is still a dream to drive and thats all that matters.

 

Agreed. :)

 

Id agree with that, wierd this, i only went to look at having my on a rolling road in colchester earlier this week and the people i went to said that with my G60 id be best to wait for a nice damp moist morning then run it down and for £25 + vat he could normally do it most mornings.

 

Looking forward to CF day now am in anticipation.

 

Mark :evil:

[jedi-knight83 0]

agreed with the driving bit too 8)

 

im sure no one expects 100% realistic figues but its all just for a bit of fun and an excuse to meet really and if the figures do look half sensible then hey its a bonus... plus if there are a number of cars its good to compare figures etc.

 

im looking forward to it aswell to be honest... not done a rr day in the corrado yet :)