zondag 31 maart 2013

First things first, the front wheel.


I have been pondering about what R 1200 GS to get ... One like the the 2007 I had before, a slightly newer one, or the new and improved water cooled R 1200 GS LC. I didn't even know if I'd go for the regular 1200 GS or the Adventure!

When I talked to my friend Berrt about riding a GS or GS Adventure off road he said that the difference between the two is fenominal ... in the way that a GS Adventure is 3 times more difficult to handle in sand than the GS. This difference can be partially compensated by using a 21 inch front wheel, he said. I had seen that the wunderful people at Wunderlich.de had a 21 inch conversion in their catalog, but the price tag of € 1500 did not help much. Berrt however told me that it was possible to build your own for approximately € 700. It should fit in the original fork without modification and even the ABS should still be in working order as long as the brakes are not of the power assisted kind, so if you have ABS, the all bikes of model year 2007 and later should be OK, if you don't have ABS, I do not see why this could fail (no guarantees though). So, even before I have a 1200 GS, I decided do a 21" front wheel conversion on it.


Let's build my own 21 inch front wheel.

Ingredients

  • 1200 GS hub for a spoked wheel
  • 21 inch R 100 GS rim
  • 21 inch R 100 GS spokes
  • 1200 GS hub nipples and grub screws
  • A healthy dose of elbow grease

Tools

  • T-40 key for the spoke nipples
  • Allen key 2 mm for the spoke nipple grub screw

Hub

As I did not have a 1200 GS yet, let alone a spoked wheel for it, I decided to get one from the recycling industry. I found an injured front wheel with a near perfect hub for a fair price.

Perfect hub with imperfect rim

The previous owner obviously did something to the wheel that the rim was not prepared for. Lets hope nothing serious happened to the person!  I'll have the BMW dealership replace the bearings, cos they might have been damaged in the mishap!

When I got this wheel in the mail I just had to take it apart immediately. All the spoke nipples came off easily, that was a relief! The nipples will be reused when spoking the wheel.


Rim

After a bit of searching and bidding, I got meself a nice, straight and shiny rim on eBay.
I decided to not order the spokes from BMW (chromed steel), but order Stainless Steel spokes from Haan Wheels.



What is wrong in this picture?

As I wanted to have black rims, I tried to find out if a chrome rim can be powder coated. Unfortunately, that is not possible unless the chrome is removed from the rim first. The powder coat does not stick to the chrome well enough! I found a powder coater who claims to have a good process to remove the chrome, apply an epoxy bonding layer and give the rim a beautiful black coat!

Powder coated rim, new stainless steel spokes
and a hub with new bearings


Assembly

With all the ingredients in my possession, it is time to get spokin'.
It took me about an hour to put the spokes in and tighten the nipples by hand. This is where I found out that each nipple had a tiny little allen screw/bolt (called a grub screw) in the head to secure the nipple.


Assembled wheel

The next step was to think of a rig where I could see if the wheel was true (straight and centered). I could have built a rig, but I had a rig standing in the garage ... 'cos in the mean time I bought meself a GS.


Rim in fork as a rig to work in
sorry about the light

After maybe 4 hours of tensioning and releasing the spokes, I think I have a pretty straight wheel. I read somewhere that BMW accepts a tolerance of 1.7 mm on spoked wheels, I believe this wheel now has a bounce and wiggle of less than 1 mm. I made the mistake of wanting it even better, which made things only worse ... so I had to start from the beginning ... twice.

Now I had to insert all 40 little allen screws that go inside the nipples. These screws go inside the head of the Torx nipple.

Now it was time to get some rubber on the wheel. I ordered a Heidenau K60 21 - 90/90 tire for the front wheel (and a K60 Scout for the rear) and now that they were on the wheels it was time to see if all would fit.

Yep it fits!
With enough space between wheel and mud guard

When I first put the complete wheel in the bike, I noticed that the space between the tire and the mud guard was enough ... for normal use. I did not modify the mud guard in any way! I can imagine however that when riding this combination through dirt and loose rocks, the space can become clogged and I'd ruin my mud guard at the very least. It might be worth looking into solutions to raise the mud guard a bit.

All I needed to do now was to build the brake discs onto the wheel. And we are done!

And we are done!
Center stand is barely tall enough for this wheel.

Hints & Tips

Valve stem

Beware that the valve stem for the new 21" rim is not a very popular size. The hole in the rim is 8 mm, and that was smaller than the tire-guy had on stock. I had to get my own at the BMW dealership.

Brake disks

For the model year 2008, BMW revised the way the brake disks were mounted on the hub. They used different bolts of similar length and they used different mounting rings.

In 2010 BMW started using longer bolts ...

Nipples

If I do it again, I would probably order new Stainless Steel nipples (with grubs). This can be done at Motorworks BMW Motorcycle Specialists or at any other shop that has 'em.
This time I re-used the original 1200 GS nipples and grubs, but one can see the difference between the color of the spokes and the nipples.

Spokes

The original R 100 GS spokes do fit, but it leaves just a tiny bit too little room for the grub. I would order the spokes 1 mm shorter than the original ... to allow the grubs to disappear into the nipple completely.

Tensioning the spokes

Don't be too demanding about the 'true-ness' of the wheel. After the first time I tensioned the spokes, I still thought that 1 mm of wobble was too much. However, trying to fix that made the wobble only worse. So I loosened all spokes and tried again. First iteration was OK, improving failed again. The third time I was wise enough to be content with 'almost right' and on the road the wobble is not noticable.

Mud guard

The distance between the new Heidenau tire and the mud guard is some 12 to 13 mm (half an inch). I believe that for normal road use this is enough. But you don't build a 21 inch wheel for road use, do you? I am afraid that when dirt and rocks get jammed between the two, the mud guard may loose the fight. I have not tried to find a solution for this, but Wunderlich sells a bracket and mud guard that are especially made for the 1200 GS and their 21 inch wheel ... but that would cost some 800 Euro's (or 2050 € including the 21 inch wheel).


Tire

In some countries or states it is forbidden to use tires on your motorcycle that have a lower speed and/or load rating than 'what the bike is originally fitted with' (or something). As the front wheel of the GS is usually fitted with a 59V (59 for 243 kg, V for 240 KM/h), I tried to find a 21 inch tire with the same rating. I could not find one. I only found 21 inch tires with a 54 weight rating (212 kg). Well, I did find the Dunlop GEOMAX MX51 FA TT with a weight load of 57, but that is a true dirt / off road tire, not for road use.
Maybe next time I try the ContiEscape ... that tire is slightly less offroad than the TKC80 and the K60, but has a 54H rating (210 KM/h, the fastest 21 inch dual sports tire that I could find)



Test ride in some easy grassy, sandy terrain

Center stand and side stand

Now that I have temporarily mounted my standard wheels again, I must say that it is noticeably easier to put the bike upright from the side stand. Also when the bike is on the center stand (with the 21" wheel), oftentimes both wheels touch the ground when the ground is not perfectly flat.
You might wanna do something about that ... perhaps use the stand(s) from the GS Adventure.

Conclusion

It was a lot of fun building this wheel. For approximately 600 Euro (700 US Dollars), lots of time browsing the internet (mostly eBay) and perhaps 8 to 10 hours of actual work, I have built myself a wheel.

Wunderlich offers a 21 inch front wheel for the 1200 GS, for 1400 Euro (1500 for the black version), so I saved myself a bundle.

I learned that by replacing the hub in a R 100 GS wheel, I could do a 21" wheel conversion for the BMW R 1200 GS. Everything fits and everything still works (if installed).
I learned that spoking a cross spoked wheel is just as hard (or easy) as spoking a wheel for a racing bicycle. I did that years ago.

As the distance between the rim and the hub is different from the original 1200 GS wheel, and the rim is not as wide, the angle between the spokes and the hub are not the same as in when the original 19 inch rim was used. I expected to notice this, but I did not. Everything fit beautifully!

On a test ride, I found a patch of grass / sand / dirt where I could test ABS and ASC without too much risk and they work like a charm! After half an hour or so, a warning light comes up 'saying' that the RDC is not working, but that is only logical when the wheels are not fitted with the sensors.

6 opmerkingen:

  1. Is it possible to calibrate the speed sensor to match the larger 21 inch wheel?

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  2. The speed sensor is not on the front wheel, it is in the cardan / drive shaft.
    Everything works, ABS, ASC, speed indicator is not affected.
    Regards,
    Wouter

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    Reacties
    1. That is even better!

      Have you found a solution for the mud guard clearance yet, without spending a small fortune on a new (raised) fork clamp?

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    2. Yes I have!
      My BMW service person (the one with the dirty fingers), told me that it is possible to raise the fork clamp itself!!
      The distance between the new rubber and the mud guard is more than 1 cm (more than 0.4 inch), so perhaps you can try to raise the clamp 0.5 cm (0.2 inch). It does affect the height of the Paralever, and thusly the length of the travel of the suspension, and the ride height.
      This mechanic did this on his bike that he uses to do Rally's with.
      I have sold the 1200 GS and purchased a 1200 GS Adventure LC. Still thinking if I'd go for the 21 inch wheel on that bike.

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