# 21" wheel on a 2007 GSA

Discussion in 'GS Boxers' started by Zpider, Nov 1, 2009.

1. ### GalacticGS1200 GS Rider

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+1

I've had no problems whatsoever running TKC's on my 21" front.
2. ### sabBeen here awhile

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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
3. ### sabBeen here awhile

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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.

sab
4. ### diabolik37Push Dumb C***

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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.
5. ### sabBeen here awhile

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"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
6. ### sabBeen here awhile

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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.
7. ### diabolik37Push Dumb C***

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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....
8. ### sabBeen here awhile

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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.

sab
9. ### slade2Been here awhile

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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.

10. ### Disco DeanLong timer

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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.
11. ### diabolik37Push Dumb C***

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Oh yeah baby, I like it when violent.

I'm glad you got your shit back together..

BTW who's Woody?

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Just to explain the reason i asked in the first place:

I used Wunderlich 21" conversionkit on a 2006 GSA with servobrakes. I recently bought a 2007 GSA without, and Wunderlich says on their webshop and in the cataloque that this should work, with the use of an adapter they sell. Well, asked them for the adapter just to find out that they no longer sell it. Exact answer from them:

"Unfortunately you can not use it, because all systems from 2007 models onwards without power assisted braking, need to order the electronic adapter separately 8180026. But this is no longer available, so you will have problems."

So, i mail them back asking why its still on the webshop and get an answer that the kit wont work at all on a 2007 model and never did. When asking why the webshop and cataloques says different and asking what the adapter was for in the first place they didnt even bother to answer at all. This beeing Wunderlich in Germany since im located in Europe. Wunderlich USA answered that the adapter never worked at all so they never sold any. All in all, it seems like its working fine on my 2007, but i got a whole new perspecitve on the customer support from Wunderlish, or should i say the lack of. Given a choice ill never order a thing from them again...
13. ### diabolik37Push Dumb C***

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I searched the Wunderlich web page (german) but I couldn't find the item N. 8180026. If you can find it and post a pic. I may be able to tell you what it is. In the 2007 GSA you shouldn't need any Gadget to get the ABS to work with a 21" wheel.

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Thats the thing, you cant find it, but its mentioned on the page of the conversionkit, thats why i had to mail them instead of ordering the item directly:

http://www.wunderlich.de/frame.php?...1&lay1=2&lay2=17&lay3=5&lay4=1&prodid=8166240
15. ### diabolik37Push Dumb C***

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My wild guess is that since BMW removed power assisted brake, you don't need the "electronic gadget" anymore. That's why you cannot find it on their web site....
But if your bike has ABS and Traction control then you need to alter the front signal from the pick up to compensate for the bigger slower turning wheel.

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Think you got it backwards here, they say the gadget was for newer bikes without servo assisted brakes, not the older bikes that had it. Would be stupid for Wunderlich to say "dont ever use the 21" kit on a 2007 or newer bike" if they think the adapter is no longer needed.
17. ### diabolik37Push Dumb C***

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From personal experience, when you translate from german to english, sometime is worth it to interpret it the opposite, of what the translation say...
18. ### Treadlessavoiding gravity storms if at all possible

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It's not uncommon for chinese translators to be used, so the translation goes from german to chinese to english.
19. ### sabBeen here awhile

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Woody's the guy who makes the 21" wheels for the GS. He watched this thread, but can't post here as he's a vendor. I did get a few prices from him through -- I can pass the info on if you PM me.

sab
20. ### diabolik37Push Dumb C***

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Thank you for the offer and I'll keep it in mind...

Would that be the same Woody that everyone on here take their spoke wheels to get re-tensioned? For what I've been reading here, he's good...