21 inch front wheel conversion

This is something I've been thinking about for a while, initially I was going to do it on my 1150 Adventure but I sold that last year before I found a donor rim at the right price. So now it's going to be for a 1200 Adventure.

My plan was to use a 21inch rim from an R100GS as it has the same 40 hole spoke pattern as the 1100/1150/1200 models. That way I could use the existing hub and brake discs and run a tubeless front tyre.

Eventually I found a complete R100GS PD wheel on Ebay and when it arrived it looked like this :- [/IMG]

The whole wheel was in very nice condition with no scratches, dings or flat-spots. [/IMG]


I already had a spare front wheel from a 2008 Adventure that had had been off-roaded and the rim was a bit worse for wear. So, the first job was to break both wheels down to rims and hubs. I knew this would be a bitch of a job as I've replaced a few broken spokes on my previous 1150. The spokes corrode into the rim and are VERY difficult to remove. It took me 3 1/2 hours for each wheel but out of a total of 80 spokes, I only had to cut one. The rest all came out with mole-grips and a hammer.

I then did a trial assembly using the 1200 hub with the 100 rim and spokes (which were the perfect length.) [/IMG]

Now I was happy that it would all fit together, I pulled it apart again. The hub went off for powder coating and I took the rim to be anodised satin black to match the back wheel. Despite being assured by the anodising firm that all would be well, it was a complete disaster. Anodising accelerates corrosion and all the invisible pits and scratches on the rim showed up horribly. They stripped it off again and didn't charge me but I had a hell of a time getting the rim back to a presentable state. It took me 10 hours of polishing It does look nice when finished though.[/IMG]

I went to collect the hub from the powder coaters and found that they'd done it a horrible shade of grey instead of the silver it should have been. They did it right the second time around but I had to wait another 2 weeks for it.

When I eventually got it back I fitted new wheel bearings, top-quality items instead of the cheap Polish ones that BMW fit as OE.[/IMG]

I'd bought a complete set of stainless steel spokes, made by the same manufacturer as the original BMW spokes, new nipples and grub-screws.
Next job was to assemble it all again.

I really like doing this bit, it's very satisfying seeing a wheel come together and it's not difficult. (that bit comes next )

A BMW wheel has 40 spokes which are all exactly the same. There are 4 different spoke positions, 2 on each side of the rim.

First step is to lay the hub and rim on a flat surface, making sure that the direction arrows on hub and rim correspond. Then, insert a spoke into any one of the holes in bottom of the rim (circled in red) and it will point towards the holes at the top of the hub. You now have a choice of 10 holes and you may have to rotate the hub slightly so that one of them lines up with the spoke. You will not be more than 18 degrees out so just pick the nearest hole and screw the nipple on a few turns. [/IMG]

That's the hardest bit of lacing the wheel done, picking which hole to go for first. All the rest are obvious, you cannot get them in the wrong hole, here's the second spoke in place. [/IMG]

Fit the nipples as you go, just a few turns and you must use oil with stainless steel spokes. I put the nipples and grub-screws in a tub of ACF 50.
When finished the first side should look like this. [/IMG]

Flip the wheel over and fit the spokes into the other side, job done. [/IMG]


Well, it's not completely done yet because the wheel needs truing by tensioning the spokes. This is the difficult part. Really difficult. If you live near a canal you shouldn't attempt this bit, nor if you own a gun.

I've no pictures for this bit but it's a fairly straightforward set-up. I used a length of M16 threaded bar through the wheel bearings and locked in place with a couple of M16 nuts. The threaded bar then rests in a pair of vee blocks, this allows the wheel to rotate freely on its bearings. Then you spin the wheel by hand and adjust the spokes so that :-
1. The rim and hub are concentric.
2. The rim and hub have the correct offset. This should be the same at each side but the two 1200 wheels I checked were both 2mm out, so it's not super critical. (I built this wheel to less than 1mm diffence)
3. The rim must run true.

When all 3 of the above are correct, the spokes need to be finally tensioned so that they all sound the same when 'ringing' them by tapping them with a small spanner or similar.

On a normal spoked wheel, 1-3 above are fairly easy to achieve.

On the BMW cross-spoke wheel it's almost bloody impossible

You have to go VERY slowly, using only your fingers to increase tension on the spokes. When it all goes wrong you MUST slacken ALL the spokes and start again. And again and again and again.........
When (if) you finally get it all correct you can tension the spokes firstly by using an extension bar between your fingers and then by using a ratchet but you must do each spoke by only a few degrees at a time. Work around the wheel, do one set of 10 spokes then do 10 on the other side of the rim. Then come back to the first side, do the other 10 then back to the other side and do the final 10. Then repeat until they're all about the same tension. All the time you need to keep checking 1-3 above. Finally adjust them by 'ringing' until they all sound similar. Then check 1-3 above again. If all's well, you can fit the grub-screws. Then you get pissed
It took me 3 days to get it right. Probably 12-15 hours in total, that's why most wheel-builders won't touch them with a barge-pole. BMW dealers will sell you all the parts but they won't do the job either. I believe BMW build these wheels in a jig and that's the way I would do it if I ever did another.
Still, all turned out well in the end, here is the finished wheel wearing a nice new TKC80.[/IMG]

Here's a comparison with a standard 1200 19 inch front wheel fitted with a nearly new Tourance. [/IMG]

Fitted to the bike. I know the discs aren't on but it seems to 'lighten' the whole look of the front end. Sidestand lean is unaffected. [/IMG]

Centre-stand clearance is adequate and the effort required in putting on and off the stand is unchanged. [/IMG]

The back wheel still spins freely when on the centre-stand (there is daylight under there )[/IMG]

However, there is insufficient clearance on the front mudguard so it needs modifying or replacing. [/IMG]

Do you have ESA and tyre pressure monitoring on your bike? I'm concerned by the decreased distance from wheel to shock on the ESA bikes vs non-ESA.

Wrt tyre pressure monitoring- unlikely that the monitoring valve would fit in the narrower 21" rim. Any experience in this regard?

Just recently converted to a 21" tubeless crossspoke front on my 1200GS - should have done this years ago. This conversion should be evolution, rather than revolution for the 1200GS - BMW, this is what we in SA need. Lacing the wheel is a test of patience and attention to detail, I can assure you... My 1200 has no ESA, nor Tyre sensor, so cannot be of any first hand help here. I suspect that the thinner (lowererd) inside channel that accomodates the bead when chaning the tyre, on this 1.85" rim may be a bit narrow to seat the tyre pressure sensor unit, but I am guessing here. Maybe a picture of one in a rim, from the tyre side, with the tyre removed can help - Any takers? In any event, the valve hole in the rim is 8mm, whilst I think the tyre sensor requires a 14 or so mm hole. This potentially leaves a 14mm hole with no horizontal "meat" left next to the hole on the upright side of centre channel - hope this makes sense. I suspect the clearance to the wheel from the bottom of the ESA sensor will be suffcient when bottoming out the suspesion, but it will surely foul the mudgurad in the riased position, above the tripple clamp. Will be interesting to see if someone with ESA has done this convertion. I am subscribed.

Well done Mr6. Ive always wanted to have a go at spoking these wheels in order to exploit rich bmw owners with messy wheels..

Think the 21" in the pic taken from the side looks a bit 'comical' though. Penny farthing comes to mind.

Den said:

.............

Think the 21" in the pic taken from the side looks a bit 'comical' though. Penny farthing comes to mind.

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I reckon a knobbly on the back will balance it out better

I'm dead impressed No6. Bet you cant wait to try it out in anger

Andres

Mr No6, You seem to know what your doing when it comes to wheelbuilding.
As I mentioned a post or two ago, Ive toyed with the idea of doing bmw wheels because very few people do them.
I know its tricky, and potentially dangerous, but so are a lot of things. and I'm not bad at most things.

I designed a jig for initial assembly years ago, but Ive lost my doodles it so ive done it again.
If you can decipher it, do you think it would work efficiently for initial (fairly accurate) assembly.

Sorry for the late reply, I've only just seen these posts....

Caprilian said:

Do you have ESA and tyre pressure monitoring on your bike? I'm concerned by the decreased distance from wheel to shock on the ESA bikes vs non-ESA.

Wrt tyre pressure monitoring- unlikely that the monitoring valve would fit in the narrower 21" rim. Any experience in this regard?

Click to expand...

I do have ESA but the tyre is within the original mudguard so no issues there.

I don't have tyre pressure monitoring so I don't know if the sensor will fit into the 21" wheel well.

Fred400 said:

Just recently converted to a 21" tubeless crossspoke front on my 1200GS - should have done this years ago. This conversion should be evolution, rather than revolution for the 1200GS.......

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I don't understand why BMW haven't done it, they already have all the parts

Outtomunch said:

I reckon a knobbly on the back will balance it out better

I'm dead impressed No6. Bet you cant wait to try it out in anger

Andres

Click to expand...

Yeah, I reckon a knobbly will make it look a lot better

Den said:

Mr No6, You seem to know what your doing when it comes to wheelbuilding.
As I mentioned a post or two ago, Ive toyed with the idea of doing bmw wheels because very few people do them.
I know its tricky, and potentially dangerous, but so are a lot of things. and I'm not bad at most things.

I designed a jig for initial assembly years ago, but Ive lost my doodles it so ive done it again.
If you can decipher it, do you think it would work efficiently for initial (fairly accurate) assembly.

Click to expand...

Hi Den, I'm no expert wheelbuilder, I've done about a dozen so far but only one cross spoke! The only danger is to your sanity, these are weird things to work with.

Your set-up looks a little complex to me. If I was building a jig I'd just have a flat plate to give the correct offset and with the hub and rim positively located to ensure concentricity. The spokes should then be able to be tensioned without any movement between the rim and hub. (in theory!) Runout and concentricity can then be checked with a front wheel mounted on it's own bearings and spindle. Rear wheels don't have bearings so obviously some form of bearing support is required.

The wheel can be laced up very easily without any form of jig, it's the initial tensioning of the spokes that causes problems.

Den said:

Well done Mr6. Ive always wanted to have a go at spoking these wheels in order to exploit rich bmw owners with messy wheels...

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There's definitely a market for this, there are a hell of a lot of GS's out there!

However, the hardest part is dismantling the wheels in the first place, the spokes are a right bastard to get out.

Hello to everybody, and first sorry for my english, I'm from Spain (barcelona), and this message is for "number 6".

I have a BMW R100GS, and now is in reconstruction, because i buy it in bad state, my principal problem is the front hub wheel is broken, and I see you buy a complete wheel on ebay, and only use the ring of 21". My question is, it´s posible you sell me the front hub???

If you like to contact with me or response, this is my mail:

[email protected]

I espect your answer, Thanks in advance¡¡¡

Sorry for enter in the forum with this method...

Hola emilio, I have sent you an email.

1150gs front wheel mod.

Sweet tap dancing Christ somebody please help me.

I've just bought an 1150 gs after a bit of time out of biking and discovered an anomilie. The front wheel is from a K100..
It's a 100/90/18 (56H) rather than a 110/80/R19 (59H or V).

The guy I bought it from says it's ok; the tyre dealer that I spoke to (because rear on legal min.) says it might not be.

Plenty of posts exist about spec'ing up to 21 but what about spec'ing down (?) to 18?

Is this dangerous?

Btw if this is , apologies - I'm new to forums!

GoodcashGone? said:

Plenty of posts exist about spec'ing up to 21 but what about spec'ing down (?) to 18?

Is this dangerous?

Btw if this is , apologies - I'm new to forums!

Click to expand...

Wouldn't be dangerous, the bike will just turn in a bit quicker

Timolgra said:

Wouldn't be dangerous, the bike will just turn in a bit quicker

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Cheers!

I'll stop over-reacting now!

I have a couple of off road wheels for 1150 including 21" if anyone interested....

Tim dont worry I'm still keeping yours, I just had a wheel frenzy when i was keen on off roading the lardy GS

So hopefully this will work and there are some pics.







Rim is a new Akront or equivalent 2.25 heavy duty, spokes are heavy duty too. Bearings are good but are what was on the wheel when I split it (1150 circa 2004). Discs are good but not mint, and I did away with the floating bolts and they are directly mounted.

If I take the tyre and discs off I'd take £200 which is what it cost me. £240 with the discs, £280 with tyre, tube, and discs.

Plus either carriage at cost or whatever we can work out on getting it to you.

21" wheel

Hi is this still for sale?

Yep, and I'm hoping to be up at Adv Bike Warehouse later in month....

I have 2 x 21" wheels covering both ABS types and of course non ABS. I'll PM you my mobile....

Ah - I cant PM you. email me mike at rtsw dot co dot uk if you like.