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Old 11-02-2009, 10:33 PM   #16
RudyBoy
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Quote:
Have you ever ridden a GS with a 21" front wheel on the dirt?
If you have you should have noticed a big improvement in the handling particularly in sand or mud.

I presume that this thread about the bigger wheel was because Zpider wanted to use the bigger wheel off road
Maybe I'm just enamored with the newness of my GSA, or maybe it was the more sophisticated suspension, but during a recent side-by-side comparison ride featuring my 650 Dakar (21") vs GSA, I/we found the GSA handled rough, rutted jeep roads way better than the Dakar! It would be interesting to do a similar comparison ride with two GSA's, one with OEM wheels and one with a 21".
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Old 11-03-2009, 05:04 AM   #17
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Originally Posted by sab
But how would the computer know they are locking up? It would sense one wheel turning slower than the other. I wonder if the fix is a ring plate w/ a different number/spacing of holes to compensate for the increase in wheel diameter?

Seems to me that would trick the computer into thinking all was well...
The ABS doesn't compare wheels, it just use a magnetic pick up (hall sensor) as a reader to see if the wheels are spinning (pretty much the same way an old mechanical computer mouse work but with infrared), but the principle is identical.

So it doesn't matter how many hole the ring plate has or in the case of the back wheel, how many teeth the crown has, it will only check that there is a constant on/off from the hall sensor, so it knows the wheels are spinning. There is no need to trick the computer to think anything. As long the wheels are spinning his job is to check NOT to count.

The traction control does the Counting and Comparing between wheels (the front using the ABS ring, the back using the speed sensor again).
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Old 11-03-2009, 06:00 AM   #18
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I've got a 21" wheel from Woody's on my 2006 GS with servo assist ABS. I just used the ABS ring from my original 19" wheel. The ABS works just fine - no problems at all either onroad or offroad.

As far as handling, don't notice much of a difference at all on the road - a little slower in turning in twisties, but you get used to it pretty quick.

Offroad, the handling is much improved - the 21" just runs over obstacles much easier, and easier to ride in sandy conditions. In my view, it was well worth the cost to swtich to a 21", but I ride an awful lot of offroad!
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Old 11-03-2009, 09:32 AM   #19
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MY take is that the 21" TKC is much more squared off than smaller sizes and that adversely affects the tires' ability to lean/corner. So a question for those running a 21. What front tire are you using / have you used?
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Old 11-03-2009, 02:55 PM   #20
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Running the 21'' TKC 90/90 getting good wear out of them and the handle well on both tar and dirt, except if its wet on road you need to be a little careful.
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Old 11-03-2009, 08:45 PM   #21
GalacticGS
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Originally Posted by SYDADVGS
Running the 21'' TKC 90/90 getting good wear out of them and the handle well on both tar and dirt, except if its wet on road you need to be a little careful.
+1

I've had no problems whatsoever running TKC's on my 21" front.
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Old 11-03-2009, 10:36 PM   #22
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Quote:
Originally Posted by diabolik37
The ABS doesn't compare wheels, it just use a magnetic pick up (hall sensor) as a reader to see if the wheels are spinning (pretty much the same way an old mechanical computer mouse work but with infrared), but the principle is identical.

So it doesn't matter how many hole the ring plate has or in the case of the back wheel, how many teeth the crown has, it will only check that there is a constant on/off from the hall sensor, so it knows the wheels are spinning. There is no need to trick the computer to think anything. As long the wheels are spinning his job is to check NOT to count.

The traction control does the Counting and Comparing between wheels (the front using the ABS ring, the back using the speed sensor again).
So why doesn't the bike release the brakes when they're "locked up" at a red light? Seems there needs to be a little more happening than what you've described.

There also needs to be some element of "counting" involved...meaning that it needs to determine more than just on/off, it needs some sense of speed. Again, sitting at a traffic light would just be a prolonged "off" between a couple of "ons" or vice versa.

This is just rational speculation on my part and I reserve the right to be corrected by someone who actually knows how this works (which certainly may be you, diabolik37).

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Old 11-03-2009, 10:57 PM   #23
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"The frequency of this sinusoidal current is a direct measure of the rotating speed of the wheel and is processed as such by the control unit."

The frequency mentioned is that of the slots passing over the sensor.

http://www.largiader.com/abs/abs2.html

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Old 11-04-2009, 05:02 AM   #24
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Quote:
Originally Posted by sab
So why doesn't the bike release the brakes when they're "locked up" at a red light? Seems there needs to be a little more happening than what you've described.

There also needs to be some element of "counting" involved...meaning that it needs to determine more than just on/off, it needs some sense of speed. Again, sitting at a traffic light would just be a prolonged "off" between a couple of "ons" or vice versa.

This is just rational speculation on my part and I reserve the right to be corrected by someone who actually knows how this works (which certainly may be you, diabolik37).

sab

The reason why you ABS doesn't release the brake when the bike is stationary is because one of the If/Then statement criteria is not met.

The ABS know that you are not moving because that information is past from the computer reading 0 speed.

If that is what you mean by counting, then yes there is some counting but not done by the ABS unit

Quote:
Originally Posted by sab
"The frequency of this sinusoidal current is a direct measure of the rotating speed of the wheel and is processed as such by the control unit."

The frequency mentioned is that of the slots passing over the sensor."

sab
Yes and translate by the ABS as on/off or 0/1. So in this case the frequency is processed as "how often", not as "how many". It may be a fine line but an ABS when working is comparing, not counting the frequency. Traction control on the other hand has to count and compare to perform.

My point is that within limits you can have different wheels size without compromising ABS performance.
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Old 11-04-2009, 09:24 AM   #25
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Quote:
Originally Posted by diabolik37
The reason why you ABS doesn't release the brake when the bike is stationary is because one of the If/Then statement criteria is not met.

The ABS know that you are not moving because that information is past from the computer reading 0 speed.

If that is what you mean by counting, then yes there is some counting but not done by the ABS unit



Yes and translate by the ABS as on/off or 0/1. So in this case the frequency is processed as "how often", not as "how many". It may be a fine line but an ABS when working is comparing, not counting the frequency. Traction control on the other hand has to count and compare to perform.

My point is that within limits you can have different wheels size without compromising ABS performance.
"How often" is the same as "how many", but with "how often" you're just dealing with an unspecified period of time. A different number/spacing of holes on the wheel would change the frequency.

I'm pretty sure you're just making this shit up as you go.

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Old 11-04-2009, 09:47 AM   #26
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Originally Posted by diabolik37
My point is that within limits you can have different wheels size without compromising ABS performance.
Agreed on this point, there has to be a tolerance for variations in wheel diameter... No idea if a 21" wheel falls within this tolerance.
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Old 11-04-2009, 12:19 PM   #27
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Originally Posted by sab
"How often" is the same as "how many", but with "how often" you're just dealing with an unspecified period of time. A different number/spacing of holes on the wheel would change the frequency.

I'm pretty sure you're just making this shit up as you go.

sab
Do you react this way every time you fail to understand something?

You can look up this shit anywhere you want.

Good luck....

PS

Nothing to do with tolerance. It has to do with how many times per second the ABS can check the frequency....

Good luck again....
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Old 11-04-2009, 12:45 PM   #28
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Originally Posted by diabolik37
Do you react this way every time you fail to understand something?

You can look up this shit anywhere you want.

Good luck....

PS

Nothing to do with tolerance. It has to do with how many times per second the ABS can check the frequency....

Good luck again....
I typically react more violently. I kept it pretty cool here. :) Woody says no ABS change required, so my speculation about what one would change if it was required is moot.

I still think my speculative solution for a hypothetical situation was spot on.

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Old 11-04-2009, 12:45 PM   #29
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My understanding of how abs works is that it look at the rate of deacceration.
If the wheel slows down to rapidly the abs kicks in and reduces brake pressure.

Slade2

slade2 screwed with this post 11-06-2009 at 04:24 PM
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Old 11-04-2009, 01:03 PM   #30
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Just a quick note here... that seems to be overlooked.

Most cars have pretty sophisticated systems of ABS and traction control. Much more with traction control.

But we are talking bikes.

A Moto-GP bike measures many parameters - including but not restricted to - front fork travel, rear ride height, throttle position, AND RPM plus the relationship between the front end and the back - as well as the sudden shift in speed of the rear wheel. They also have lean angle sensors to reduce wheel spin at greater lean angles. Thus the very difficult prospect of setting up a MotoGP bike and how come one rider might get it so very right and another not.

You can get some of this technology on the newer race ready Ducati's - some very few new kit bikes.

While I do not know for sure - you cannot get this technology on our BMW's.

The ABS is simple and not relative to front or back - it just works by noticing when the wheel stops spinning - period. Then reduces the brakes to let it spin.... Any size of front or rear wheel will not change this. It will however change your indicated speed and odometer (of course).

This is from BMW's website archive when they introduced the ASC - so sorry guys - it looks like it won't be affected by a different size wheel...

In its basic principles, the system and its various functions are quite straight forward: The ABS wheel sensors determine the speed at which the wheels are turning. Registering any sudden change in the difference in speed front-to-rear, the electronic control unit is able to detect any risk of the rear wheel spinning, engine management responding immediately by intervening in the ignition angle to take back engine power. Should this not be sufficient, that is should a greater reduction of engine power be required, fuel injection will be cancelled out for a certain time.

This kind of control and management is fast and sensitive, with any effects on riding comfort and dynamics being virtually negligible, claims BMW.


The traction control on our BMW's measures only only measures a sudden spike in rotation from the wheel, based on a pre-set parameter. The wunderlich rings only fixed the speed differential and didn't fix anything else because it didn't need to.

Think about it - our front and rear tires can change circumference by .25 to .5 of an inch or more from normal wear - tire inflation - heat - and running speed - I have had rear tires grow under speed by more than 3/4 of an inch and this is normal in some circumstances and with some tires. Add into that the change in circumference in lean angles between the front and back -- the back changing much less than the front... and you need many more measurements to accommodate this comparative analysis you guys are talking about.

I am sorry but I think BMW traction control systems (ASC) are a little more - dare I say - pedestrian than that.

D.
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