chris_uk
Premium Member
Registered: 8th Jul 03
User status: Offline
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can someone please explain to me how the rolling roads work..
i know they measure it from the wheels and then convert it to at the fly bhp, but i dont know how it does it.
there are some people on the forum where i went to get mine done and they all are saying its at the wheels bhp, obviously its not because my car made 143.. and thats 1bhp under standard at the fly..
just because the guy at the place said its deffinatly measured at the wheels.. 
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chris_uk
Premium Member
Registered: 8th Jul 03
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does no1 know?
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thegsi
Member
Registered: 3rd Feb 07
Location: Kidderminster Drives: Evo (you can't afford one)
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I believe they get a wheel power reading as its the most accurate then convert it to a rough engine power figure. They take into consideration average loss from engine and transmission then get a round figure.
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thegsi
Member
Registered: 3rd Feb 07
Location: Kidderminster Drives: Evo (you can't afford one)
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and if you think your figure is inaccurate remember some rollers give generous readings, some not so generous. However all claim to be accurate.
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luke85
Member
Registered: 26th Nov 07
Location: Chesterfield
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Obviously all rolling roads measure it at the wheels unless your on an engine dyno, Almost all rolling roads will quote you the "estimate" at flywheel power because it looks more impressive but it depends how they arrived at that figure. Some RR places over estimate transmission losses some underestimate them in my opinion
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chris_uk
Premium Member
Registered: 8th Jul 03
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i dont think my readings are out i think they are spot on..
BUT i think/know they are at the fly estimations not at the wheels.
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Fonz
Premium Member
Registered: 12th May 06
Location: Newbury, Berks
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u2u DaveA
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harrisp
Member
Registered: 15th Dec 07
Location: Derbyshire
User status: Offline
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It was on top gear, they measure it at the wheels but then by letting the car run down on the dyno allows them to calculate transmisson loss and then working out the power at the fly.
Correct me if I'm wrong.
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T5POL
Member
Registered: 22nd Mar 01
Location: Fife
User status: Offline
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They run the car on the rollers, at peak rpm, put the car in neutral. The 'Coast down' loss is then added to the 'at the wheels' bhp to give a flywheel figure. Not particularly accurate.
In my opinion you should only treat Rolling Roads as a tool to aid with tuning. If you stick with the same rollers all the time and as you mod your car, you can see how much of a difference, if any, a particular mod makes, referring back to the reference Bhp obtained on your first visit to the same rolling road.
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chris_uk
Premium Member
Registered: 8th Jul 03
User status: Offline
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well im going to go to a rr in leeds who are going to test the car propperly, give it enough air to breath as it was starved of air at top revs..
maybe do to the fact the air intake is at the back on mine not the front where the radiator is..
then i will see what they say and ill be getting my mods done there aswell.
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T5POL
Member
Registered: 22nd Mar 01
Location: Fife
User status: Offline
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quote:
Originally posted by chris_uk
well im going to go to a rr in leeds who are going to test the car properly...
To test an engine properly it has to be run on an engine dynamometer, in most cases, if not all, out of the subframe and out of the car itself.
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T5POL
Member
Registered: 22nd Mar 01
Location: Fife
User status: Offline
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On another note, I have found Dastek Rollers to give a reasonably accurate flywheel figure. Is there one near you??
[Edited on 01-05-2008 by T5POL]
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broster
Premium Member
Registered: 6th Dec 02
Location: Drives: E39
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a rolling road is nothing more than a strain gauge, it measures the turning force, or Torque at the wheels, or at the hub depending how it is mounted.
as the car is run on the dyno the retarder twists on its mounting, due to the cars torque, this then causes the strain gauge to give off a different reading, the rolling road machine usues this output to give a wheel figure.
to calculate the flywheel figure (which IMO is a better way of giving a figure but i wont get into that as many many internet experts will say im wrong) the car is left to run down to idle again, the computer then works out what the losses are due to the resistance in the run down period, then you have your flywheel figure.
a rolling road is onl yas accurate as the calibration, all this my rolling road is more accurate than your is crap IMO, a maha rolling road, a dyno dynamics rolling road, a mustang rolling road may cost £100,000 with software, but if they arn't calibrated properly then the reading wont be as accurate.
however its always good to remember that a rolling road is a tuning tool, to compare the gains given so using one rolling road to do before and after runs will always say what power the car has gained or lost
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chris_uk
Premium Member
Registered: 8th Jul 03
User status: Offline
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----- Original Message -----
From: Chris Redman
To:
Sent: Wednesday, April 30, 2008 9:14 PM
Subject: BHP Results.
Hi, I attended the www.vauxonline.co.uk session you guys had at the weekend, a couple of people are under the impression that the results are shown as 'at the wheel' bhp, obviously this is not the case.
Can you just confirm for me that the readings were taken from the wheels but actually indicate the 'at the fly' bhp reading.
kind regards
chris (vx220)
From: .co.uk
To: .com
Subject: Re: BHP Results.
Date: Thu, 1 May 2008 10:22:33 +0100
All bhp readings were at the wheels kind regards mick
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whitter45
Member
Registered: 15th Nov 02
Location: Norton
User status: Offline
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so your car has 143 BHP at the wheels
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John
Member
Registered: 30th Jun 03
User status: Offline
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You haven't got any engine mods apart from the enlarged throttle body have you?
Maybe you bought a turbo and haven't realised 
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chris_uk
Premium Member
Registered: 8th Jul 03
User status: Offline
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yes apparently i have 143bhp at the wheels..
i know this to be bollox.. there is no way a ported and polished TB with 2.5" airfeed would do anything like that!
well i wont be reccomending that place.
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John
Member
Registered: 30th Jun 03
User status: Offline
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I love how most forums swear by these places that blatently over-read instead of the ones that give them more realistic lower figures.
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Dave A
USER UNDER INVESTIGATION - DO NOT TRADE
Registered: 10th Dec 03
Location: County Durham
User status: Offline
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come to me, my dyno under-reads according to most saxo/106/corsa XE owners.
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chris_uk
Premium Member
Registered: 8th Jul 03
User status: Offline
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im quite sure that its 143 at the fly, i have no reason to doubt it..
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