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Offline jm2

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Re: 2009 Mk 1 abs, Should the rear wheel lock up whilst on MOT Roller
« Reply #10 on: 27 June, 2020, 12:58:14 PM »
*Originally Posted by Rick [+]
Thanks JM2, but surely the abs system is trying to prevent a lockup, maximum braking takes place just before a wheel locks, that's where abs braking comes in, by applying cadence type braking many times faster than could ever be achieved manually.
Ah but the abs disengages at very low speed - or you'd never be able to fully stop.
DON'T try it yourself; on a loose gravel surface apply too much rear at moderate speed and abs will work flawlessly and keep everything stable, as you come to a halt the rear will lockup and you may loose it altogether.

Maximum braking effort is achieved just before locking (hence why cadence braking works) and the mot says to lock the wheel.  The trick is to go slowly at the end (just before locking point where the roller detects it has been stopped).
If you can't lock the wheel on the roller (why not) you aren't getting through maximum braking effort.

C-ABS does makes interesting testing figures (especially on the old dials) but doesn't detract from the test - I do believe you are allowed to add the alternate brake in if required for the (lock) test; but these bikes do not need it (5x front pistons are plenty for the test - I seem to remember testing another bike of mine on the rear only front operation and it achieved very good braking effort if really leaned on).

You ought to be able to get the abs working on a road at speed (try 50mph, clutch in, and load the rear brake).
Only do it right - no bodging please.   Keeper of the failed stator list.   John.

Offline Art

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Re: 2009 Mk 1 abs, Should the rear wheel lock up whilst on MOT Roller
« Reply #11 on: 27 June, 2020, 03:14:03 PM »
and the difference in locking the rear wheel on the roller and stopping the bike on tarmac is?

Offline jm2

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Re: 2009 Mk 1 abs, Should the rear wheel lock up whilst on MOT Roller
« Reply #12 on: 28 June, 2020, 10:44:35 AM »
?

The original poster (OP) didn't expect the roller to lock with abs.

- Although I (mis) used my phone to type that reply and it seems I didn't see some (any?) earlier replies.
Only do it right - no bodging please.   Keeper of the failed stator list.   John.

Offline Rick

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Re: 2009 Mk 1 abs, Should the rear wheel lock up whilst on MOT Roller
« Reply #13 on: 28 June, 2020, 12:43:49 PM »
Thanks, Just need feedback from owners who take their abs bike for an MOT and report as to how the rear brake behaves during the roller test, does it lock up ? Presumably this would cause the bike to jump out of the rollers, mine didn't.

Offline Rev Ken

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Re: 2009 Mk 1 abs, Should the rear wheel lock up whilst on MOT Roller
« Reply #14 on: 28 June, 2020, 07:38:12 PM »
*Originally Posted by Rick [+]
Thanks JM2, but surely the abs system is trying to prevent a lockup, maximum braking takes place just before a wheel locks, that's where abs braking comes in, by applying cadence type braking many times faster than could ever be achieved manually.
If you read a little further the manual gives the efficiencies needed and there is no requirement for any wheel to lock.

1.2.2.
'Brake efficiency'
Most motorcycles have 2 brake controls, one operating the front wheel brake and the other the rear wheel brake. One control must achieve an efficiency of at least 30% and the other control 25%.'

Oh and if a wheel does lock it is assumed that it reached the 30% figure.

(When I was in charge of the branch that was responsible for MOT testing there weren't small roller testers available and the usual method was to tie a spring balance to the front forks, get the owner to sit on the bike and apply each brake in turn while ratcheting the bike forward reading the spring balance. Alternatively you could use a ramp and lift one end up gradually with the bike on it - interesting! Oh and it is still legal to use the spring balance method if your authorisation was before the new requirements were introduced. I tested several 'pendulum' testers as used for cars, but they didn't work as on my 400 Superdream I could lift the rear wheel when braking, giving false readings and was considered a little dangerous for some testers.)
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Offline g5guzzi

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Re: 2009 Mk 1 abs, Should the rear wheel lock up whilst on MOT Roller
« Reply #15 on: 28 June, 2020, 09:34:40 PM »
The garage i use on bikes with  linked brake systems take the brake reading
for the front brake effort and the weight of the bike on the front wheel then take the same  readings
 on the rear  then work out if correct brake efficiency has been reached.
Locking the wheel is not essential.

 
Malc

Offline jm2

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Re: 2009 Mk 1 abs, Should the rear wheel lock up whilst on MOT Roller
« Reply #16 on: 30 June, 2020, 05:53:55 PM »
*Originally Posted by Rick [+]
Thanks, Just need feedback from owners who take their abs bike for an MOT and report as to how the rear brake behaves during the roller test, does it lock up ? Presumably this would cause the bike to jump out of the rollers, mine didn't.
Well mine was apply all the way to lock-up - now whether or not that was to get as far as I could and locked was obviously passed that point I can't know. It certainly completed that test element.
Yes, as said earlier, it squirms about !

Sorry Ken, obviously my mot station can't do mental maths or doesn't need to with their testing machine.
- but it begs the question, 30% of what (for the front).  Surely if you've two equally naff brakes it can't pass?
Only do it right - no bodging please.   Keeper of the failed stator list.   John.