Rolling roads (daft question alert!)
05 November 2009, 09:31 AM
#1
Rolling roads (daft question alert!)
Hi guys, going on a rr this coming saturday, a dyno dynamics at Ajec Racing in gloucestershire. Since I went on a rr last time I have gone up from 17" to 18" wheels (heavier as well as larger) and bigger brake discs on the front. I'm just wondering what effect this could have on the figures, would the extra weight (unsprung I think...) have a negative effect on the power? Do they take the wheel diameter into account on a rr like they do with a delta dash? Anyone been on Powerstations (maha?) rollers and a dyno dynamics, what differences were there??
Cheers
Iain
Cheers
Iain
05 November 2009, 10:07 AM
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Example from my experience. Evo 9 on Bosch rolling road, which accounts for driveline losses (we all know that isn't 100% correct, but anyway).
Peak loss with 245/40 18" Kumho roal-legal slicks (much like Toyo R888) - around 112 bhp
Peak loss with 225/45 17" some usual everyday tires - 58 bhp
Peak loss with 245/40 18" Kumho roal-legal slicks (much like Toyo R888) - around 112 bhp
Peak loss with 225/45 17" some usual everyday tires - 58 bhp
05 November 2009, 11:46 AM
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Blue Dragon, was it meant for me? Rolling circumference is one thing, but then there is rolling resistance which is strongly affecting car's acceleration and therefore - rolling road measures. What my example is showing is rolling resistance vastly differs between different width and compound tyres.
Last edited by moro; 05 November 2009 at 11:50 AM.
05 November 2009, 11:50 AM
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Iain
A rolling road company, should do a cost down run, where they let the vehicle slow down and measure the losses from the transmission/tyres etc. This is then added back to the measured amount to calculate the BHP at the flywheel.
As I understand it, without the above being done, you can get a theoretical increase in flywheel bhp by pumping up the tyres, as this reduces the rolling resistence.
Pete
A rolling road company, should do a cost down run, where they let the vehicle slow down and measure the losses from the transmission/tyres etc. This is then added back to the measured amount to calculate the BHP at the flywheel.
As I understand it, without the above being done, you can get a theoretical increase in flywheel bhp by pumping up the tyres, as this reduces the rolling resistence.
Pete
05 November 2009, 02:20 PM
#7
My main question really is about the weight, will the extra unsprung weight have an effect on performance?
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05 November 2009, 02:22 PM
#8
Iain
A rolling road company, should do a cost down run, where they let the vehicle slow down and measure the losses from the transmission/tyres etc. This is then added back to the measured amount to calculate the BHP at the flywheel.
As I understand it, without the above being done, you can get a theoretical increase in flywheel bhp by pumping up the tyres, as this reduces the rolling resistence.
Pete
A rolling road company, should do a cost down run, where they let the vehicle slow down and measure the losses from the transmission/tyres etc. This is then added back to the measured amount to calculate the BHP at the flywheel.
As I understand it, without the above being done, you can get a theoretical increase in flywheel bhp by pumping up the tyres, as this reduces the rolling resistence.
Pete
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