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R1250RT Front Wheel on a GSA

I’m trying to determine if a 17 inch front wheel from a BMW R1250RT will fit on a R1250GSA without modification to the wheel or motorcycle.  I’ve read conflicting opinions on this and would like to hear from someone who has first hand experience.  

FlyingMonkeys has reacted to this post.
Kevin - Team Pterodactyl's Montana Outpost Silver City, Montana

I did it on my 2008 R1200GSA with a similar vintage RT wheel, but not sure about doing it with a 1250.  Will investigate and report back.

FlyingMonkeys has reacted to this post.

OK, here's what I found out.

The front axle, wheel spacer, shaft seals and wheel bearings for the GSA and the RT all have the same part numbers.  That tells you then that the front wheels are interchangeable, will mount up, and will spin between the forks.

Next, will the tire rub?  Probably not.  Though the RT tire is wider it's gonna have more clearance under the fender (called the lower front wheel cover in BMW-speak) because it's a 17 not a 19.  You probably won't know for sure, though, until you mount it and, even then, you could look at different tire options that might give you more clearance.  On my 2008, I could fit a 130/70-17 but not a 130/80-17.  You can also take your belt sander to the fender to make it "shape" it to your needs.

Next, the ABS ring.  The rings have the same part number for both bikes so it looks like that's a no-brainer.

So now we come down to the real issue -- what about the brakes?  The RT brake rotor is 320mm in diameter, and the GSA rotor is 305mm so that's a no-go.  Or is it?  Are the rotors swappable?  To check this out, (I'm assuming that you don't actually have a RT wheel sitting around)  you'd need to get your hands on a RT rotor and see if the mounting tabs match up with the mounting tabs on the GSA rotor.  (On my 2008, they did -- I used a RT wheel and I mounted my GSA rotors to that wheel.)

Short of actually buying a RT rotor (about $120 on eBay), you could go to the local BMW dealer and ask permission to measure the distance between the mounting tabs on the front wheel of a R1250RT in the showroom.  If the tabs have the same spacing as your GSA, then the rotors are swappable.

Lastly, will the GS calipers fit inside the smaller wheel?  Here's where it gets interesting.  Since the RT rotors are bigger than the GSA, and we already know that RT calipers fit OK inside the RT wheel, doesn't it make sense that the GS calipers -- which must be mounted lower on the forks to fit the smaller GS rotors -- should fit? So it's probably gonna come down to the spokes on the RT cast wheel and are they gonna clear the GS calipers or not?  On my 2008 swap, I could spin the wheel but the spokes rubbed the calipers.  I was able to fix the issue by removing about 2mm of metal from the caliper body at the spot where there was contact. That gave me 1mm of clearance.

Your best plan might be to go on eBay and start shopping for a used RT wheel. There's one on there now for $525 shipped.  Then mount it up and find out for sure.  If it's a no go, sell the used wheel on eBay and, even if you sell it for a loss, it was a worthy experiment.

SwampFox, Kevin and FlyingMonkeys have reacted to this post.

Thank you Drone for your excellent analysis of the idea. I found a thread on ADVRIDER that discusses the swap in detail.  There are more issues with making the swap than I am willing to tackle at the moment.  The was a company in Europe that made an adapter for the swap and it still required some grinding on the calipers.  That company is no longer active.  

DRONE, MGV8 and FlyingMonkeys have reacted to this post.
Kevin - Team Pterodactyl's Montana Outpost Silver City, Montana