Wednesday, 22 February 2012

Rolling Resistance Rig

Rolling Resistance Rig 

I have borrowed the idea for a RR test rig from the authors of The World's Most Fuel Efficient Vehicle.
Theirs looks a bit swisher than mine but the principle is the same.
The whole rig weighs about 60kg which is approximately half the weight of a fully loaded Quattro. The wheels are bolted directly to the axle with no bearings.
To do a test, I pull the pole down to touch the ground and then let it go.
I time it until it stops and average over four runs. Two tests in one direction and two in the opposite direction. 
The Rig is being modelled by Steve who interests include, fashion, foreign travel and fast bikes.
The tests I have done so far are not that scientific, as I need a more accurate means of measuring a stop point for each test.
I may try and fit a mercury switch or some other kind of level switch.
The tests have also been done on the smooth factory floor at Portaprompt and should be verified on a number of different oad surfaces.
All tyres are 16” ETRTO 349mm
                                                            Pressure              Width                    Time to Stop
New Greenspeed Scorcher                                 100                         39                           71.9s 
Part worn Old Yellow Brompton                          100                         34.5                        61.3s
Part Worn Kojak                                                  140                         30.5                        55.7
Part Worn Kojak                                                  120                         30.5                        51.9
New Marathon                                                     100                         33                           46.9s
Near new Kojak                                                   100                         30.5                        46.8s
Near new Marathon Plus                                     100                         33                           45.8s
New Stelvio                                                          100                         28                           43s  ##  
New Brompton Green Kevlar                               100                         35                           38.1s
##   Estimate based on only having one tyre. 

I have ordered some more Greenspeed Scorchers for the BHPC races this season, on the strength of these initial results.
There are a couple of drawbacks with the Scorchers, as their greater width may cause extra aero drag and less lock.
Latex tubes do seem to help but unfortunately, I only had some very old Moulton ones that only survived a couple of runs.
My next trick is to try and go tubeless. I watched Stan’s Video over the weekend and will try and have a go later this week.
It has always been suggested that Kevlar does horrible things to tyre RR and my initial tests on the Brompton tyres seem to support this.
We used the original Brompton tyres on our first Greenpower car to great effect. It is a shame they are no longer available.
Another interesting thing is that the Marathon Plus tyres don’t seem to be that bad compared with the Kojaks.
I mentioned this in my Quattro part III write-up. When I switched from Kojaks to MPs on the ROAM trip, I didn’t notice a huge difference in performance.

I must emphasise that these tests need doing again on a more realistic surface and with more accurate timing, which I will try and do soon.

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