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 Rollimg resistance ...?

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john bass

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Number of posts : 1712
Age : 88
Localisation : Bensberg, Germany
Registration date : 2006-12-06

PostSubject: Rollimg resistance ...?   Sun Nov 20, 2011 6:12 am

My mentioning fairings and using "Coasting Down" tests to determine a coeficient of drag for each make of fairing had me thinking that its not a bad idea in the trying to get the best out of a racing Bantam would be to make sure the optimum LEAST ROLLING RESISTANCE has been obtained/achieved ...

Since we are good mechanics we immediately assume that the brake pads/linings are are not rubbing and dragging -- but being `good...´ we do check to make sure:--

The main contributors to Rolling Resistance are wheel bearings and the tyre deformation processes which occur between the tire patch and road surface which are surely affected by tyre-pressure and temperature.

My previous suggestion of a speed trap was really, way out of date because all that is needed is a Hall Sensor Pick UP, attached to the swinging arm, reading & counting the gaps on the rear sprocket (as the teeth rotate past the sensing eye...) which are stored against real time. This records the lapsing time and number of rotations of the rear wheel from the moment of snicking into neutral and allowing the bike to slow down from a selected max speed to stop -- again this should be all done on the level road -- and could be done at relatively low speed because Rolling Resistance is a linear relationship to road speed and as such can be interpolated/extrapolated....
To prove the difference tyre-pressure makes, a run with lower-than-`normal´
and another run with higher-than-`normal´ pressures are made and compared with with the NORM -- remembering that the temperature will have an effect....




No! On the other hand if this gets Bantam racers sensitive about their tyres I will probably have created a "must have new tyres" syndrome and added another expensive item to "Low Cost Racing"...!!??
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Derek

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PostSubject: Re: Rollimg resistance ...?   Sun Nov 20, 2011 8:23 am

Hi john actually it does not need to be on a flat! surface, "does' it".

as long as you compare bikes on the same surface. ! but from memory with a gradiant the force of gravity and angle of gradiaent and the bike weight are taken into the equasion, again as long as two bikes are compared, then a comparison can be made.

I think !.

Regards:- Derek
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john bass

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PostSubject: right Derek!   Mon Nov 21, 2011 12:01 am

Right Derek!
No, of course not -- it could be a downhill section where you don´t even start the engine -- just let the bike (with rider, of course!) run down-hill onto the flat and come to a stop -- with the Hall sensor reading wheel revs (could be from front wheel´s, brake disc) against real-time base... you see the whole picture of accelerating to max downhill speed and then deceleration to stop and it could be good for making comprisons and verifying benefit of weight reduction etc... etc... ....***

Of course! Linear motion & rolling resistance are weight-effected. Weight effective when you think of how much quicker it´ll be going down-hill. Tyre distortion comes from total weight and weight distribution change on acceleration and braking -- which, now I think of it, could be included in this Coasting-Down testing.

The more I think about this Coast-Down test the more I like it -- doesn´t need to upset people by noise either!

To get a real understanding of this:- just a silly test at home is to push the bike
with very low tyre pressures across the garage floor and then with high pressures
but I am telling what is known to everyone already...


To think that the last time I did such a Coast-Down test, it was with a 70ton HGV .... we did it on the flat, of course -- at a well-known testing ground!!

*** I am sure, a lot of `Natural´ artisans reading this know by feel without going to all this bother as to whether their Rolling-Resistance is acceptable or not!! and will tell us so!! why not!!

Cheers!
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Derek

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PostSubject: Re: Rollimg resistance ...?   Mon Nov 21, 2011 12:49 am

yes John I would be interested in doing this as I feel there is a lot to this frictional losses

I like this subject, I will see if we can find a suitable road as the bike is not running only free wheeling, I may have a section of road not far from my house, we have a small him then a flat section about two to 3 miles country roads I will ask a local authority first, about it in the interests of science "see if we would infringes any law's.

will let you know "I will call them tomorrow.

see if i would be covered under "none motorised or effectivley like a cyclist".

not sure we would come under the none licence laws.


regards Derek
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john bass

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PostSubject: Yes Derek!   Mon Nov 21, 2011 5:19 am

You have got me going Derek, on this costing-downhill-test -- see what else you could compare:-

It doesn´t matter about the slope angle-of-dangle because a Hall Effect sensor reads the gaps on a toothed-disc attached to the back or front wheel and that number against real-time is all you are interested in:- those two signals tell you all you need to know, speed data, acceleration and max speed achieved against real time.

Wheelbearings loaded with bike + rider weight. Remove the rear chain and keep it in your pocket*** whilst freewheeling downhill.

Tyre pressure differences.

Tyre tread profile -- although cold -- nmightn´t tell much.

With all other things equal you could have the just the gearbox oil being tested for its drag -- must be high because one statement I read the gearbox transmision efficiency was a mere 88%. Further part of this would be in 3 parts. Removal of spark plug and freewheel downhill driving the non-working engine with each of the 3 gears engaged which would give an idea of engine and gearbox losses in each gear -- remembering that this is COLD engine/gearbox and no compression resistance ...

You can probably think of more things to include in the testing.

Could be a fun exercise with surprising results. Could be callede "Non-destructive, non-polluting testing..." and maybe get a sponsor to provide assisstance on the day.

*** any Cockneys close by might nick it!

Dunno! Never heard of Coast Down testing done on a hill -- maybe you make it a FIRST!

Cheers!
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PostSubject: Driver Dynamometer??   Mon Nov 21, 2011 5:44 am

It is a long time since I was into this and I ask in as much humility as I am capable of -- if any of you dyno users have come across the Driver dyno?

It is, of course, a very expensive equipment that was first set up by McLaren in the late 60´s to replicate a GP circuit on the dyno by driving the engine as well as absorbing the engine power and must have undergone a lot development itself in 4 decades...

OK! unless this has been done before, I am wondering if just a normal electric motor of suitable power was attached to an engine on a dyno was made to drive the engine whether just measuring the volts and and amps the electric motor is using (to driver the engine at given speeds) would give an accurate indication of engine Friction Losses? I am not enough up on electrics to know whether the electric moter efficiency comes into this ... all I can see at the moment is that measuring the volts & amps tells the wattage used at that instant but that the electric motor´s efficiency would have to be known to be able to assess the engine losses accurately?

I see it as the dyno-engine-electric motor attached in line witzh dog clutches between each. Engine taken up to full load and at its max running temperatures
is shut off, disconnected from the dyno and connected to the electric motor which then takes it up to its full load speed when the Watts are measured. Repeats at
lower full-load engine speeds and with say five readings a good indication of engine friction curve versus speed could be obtained.

Maybe only comparative tests of different (radial and tangential pressure) piston rings would show by this -- but might it be worthwhile....??


Hmmmm!???

Postscript:
One hour later: -- PS -- Sorry! just had a thought -- if the volts & amps are measured when the electric motor runs free the watts (amps X volts) when "motoring" the dead engine will be the amount indicated minus the free-running watts which will be the engine friction or Losses in Watts --- won´t it??

Cheers!
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PostSubject: Second Thoughts...??   Tue Nov 22, 2011 12:20 am

Warning! Derek, even if you are dead-engine coasting down hill, in the Brum area, someone´s sure to call the police...!!??

When visiting my Sister at Bloxwich I have taken walks along by the local canal and seen notices saying, "Riding motorcycles on this public land is prohibited. Offenders will be fined a minimum of 2,000 pounds..."
Words to that effect! So even if you are dead-engine coasting you´d be breaking the law _- and someone is bound to shop you...

The Hi-Tec way to measure engine friction -- losses -- would be to use a Torque Tube suitably instrumented, installed between an electric motor and the test-engine. Torque measurement used to be by strain-guages but there´s one which has an electronic-eye at each end of the tube looking straight at each other. With applied torque the twist on the tube is seen as a shift from zero -- eye-to-eye --, which is calibrated through conditioning eqipment and the amounts amplified to send direct readings of torque-required-to-rotate crankshaft (at given speed) onto the VDU/monitor screen. Instant graph curve as well... I guess!!

So, I visualise the ideal for measuring Engine Losses would be to couple the crankshaft to an engine-test dyno (by chain and dog-clutch) off to one side and have the Torque-Tube directly connected to the crankshaft -- again using a dog-clutch so that as the engine is brought up to a given power output with temperatures up to normal operating level the engine is shut down, decoupled from the dyno and then `motored´ by the electric motor up to that particular speed to then record the torque required to run at those higher temperatures at that given speed.

Anyone in your area capable of the instrumentation and installation, Derek?
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