[Realtom]

I recently bought a used 2005 GS but the owner, being a little short and used to Harley's, fitted the the bike with K1200S wheels (in black). Looks very cool but the downside is that I have to change to sticky, sport bike tires that are limited to the pavement and will wear out more quickly. And, the speedometer reads about 5 mph too fast and the engine is turning higher rpm's

The previous owner had to have the center and side stands modified to make this change as well as some slight machining of the wheels for track accuracy.

My questions are:

1. Is anyone interested in talking trade?
2. Are there longer lasting sport bike tires that I could fit on this hybrid bike.

Realtom

 

[Scotty]

I would think you could fit a GS tire on the rear rim because the K1200s and R1200GS both run a 17" rear rim. (according to the info I found on the web) The K1200S runs a 190/50 17 The R1200GS runs a 150/70 17. I don't Know if the rims are the same width, that would change the curve of the tire cross section, not always a big deal. But, to give you something to go on when you search for the right combo, forgive me if this is something you already know, the way tire sizes work is:
150/70 17
The first number (150) is the width of the tire, measured across the tread 150mm.
The second number (70) is the aspect ratio, the hight of the tire, think of it as the distance from the rim to the ground. This is calculated as a percentage. 70% of 150mm = 105mm.
The third number (17) is the diameter of the wheel the tire fits on, in inches.
So, the aspect ratio of the tire on a K1200S is 95mm, on a R1200GS it's 105mm. You may be able to find front and rear dual sport tires that fit your rims and work on your bike, without getting new rims. At the very least, you could find a little taller rear and fix the speedo issue.
Hope this helps a little

 

[Realtom]

Reply

Good info. The mod has lowered the bike quite a bit and it has a Sargent seat which also helps. I am 6' 0" and my legs are bent when at rest. Weird feeling on this big a bike.

Realtom

 

[Scotty]

Opinion

If you are going to ride any dirt, you really do want to get a 19" or 21" wheel and appropriate tire on the front. Otherwise, potholes and ruts will beat the crud out of you. I think I would want the correct size tire on the rear as well. Don't want my engine screaming like I'm doing 120 mph, unless I get to do 120 mph.
That said, can we see a pic? I am really curious.

 

[Nick V]

K1200S wheels (in black).
Looks very cool but the downside is that I have to change to sticky, sport bike tires that are limited to the pavement and will wear out more quickly. And, the speedometer reads about 5 mph too fast and the engine is turning higher rpm's

The engine won't turn higher RPMs - both the R-GS and K-S rear wheels are 17" diameter.
Rolling circumference MIGHT be an issue if there is a big variance in terms of tyre profile, but it won't be overly huge.
Having said that, if you want a slight reduction in cruising RPMs, why not try a 190/55-17 rear? Slightly taller profile.

The previous owner had to have the center and side stands modified to make this change as well as some slight machining of the wheels for track accuracy.

That's weird. My bike also uses a K1200S rear wheel. I've noticed no skewed tracking that would indicate too much 'meat' on the wheel hub for this application. There were no mods to my sidestand or centre stand, and there have been no tyre-clearance issues.
Having said that, I'm currently running a 180/55-17 rear tyre (as you rightly point out, the K1200S uses a 190/50-17 as standard).

Are there longer lasting sport bike tires that I could fit on this hybrid bike.

Anything billed as an 'everyday' or 'commuting' tyre will do fine.
I run a 110/80-19 Bridgestone Battlewing (to be replaced by a Michelin Pilot Road 3 Trail when it wears out) on the front, and a 180/55-17 Pilot Road 3 on the rear.
The one thing I can say about the wide rear wheel conversion - the turning stability is incredible. My old GSA (on wire wheels) used to get a bit flustered when I hacked it really hard around twisty roads. This thing? It just laps it up.

I would think you could fit a GS tire on the rear rim because the K1200s and R1200GS both run a 17" rear rim. (according to the info I found on the web) The K1200S runs a 190/50 17 The R1200GS runs a 150/70 17.

Trust me when I say that is NOT a good idea.
Modern bike tyres are each designed for rims of very specific width, and the tolerance for rim-width errors is about half an inch either way.
Any more than that, you're going to get flaky handling.

I don't Know if the rims are the same width, that would change the curve of the tire cross section, not always a big deal.

The standard GS rear rims (wire and alloy) are about 4" wide. The K1200S rear is 6".
Two inches variance in width is HUGE. Put it this way - if someone showed me a 150/70-17 tyre mounted on a K1200S rear rim, and offered me a ride, I'd politely refuse.

At the very least, you could find a little taller rear and fix the speedo issue.

Have a chat with your local dealer. I'm told there are software tweaks available to tune your speedo accuracy, especially in cases where wheel diameters have increased or decreased.

 

[Scotty]

Good info Nick V, I didn't realize the rims were so different in width. I can see how that could be a bad idea. Have not heard anything from realtom in a while, I hope he got it sorted.

 

[Nick V]

Good info Nick V, I didn't realize the rims were so different in width. I can see how that could be a bad idea. Have not heard anything from realtom in a while, I hope he got it sorted.

Me too!...
Tyre/rim basics aren't too difficult, but they're so easy to get wrong if one doesn't know the principles behind them.
Having said that, a great deal of motorcycle engineering is about fashion. If enough people see it on an open-class MX bike or MotoGP racer, and go ***WOW!!!!***, you can bet your last pfennig that it'll be on next year's bikes - even if 99% of road riders would never know the difference once they're on board.

In 1995, it was 16" front wheels (Honda RC45). In 1998, it was underseat exhausts (Ducati 916 and BMW R1100S). By 2000, it was radial front brakes (as seen now on the latest R1200GS). A short time ago, it was 190/55-17 rear tyres... it never ends.

The upshot is that there are ever newer and more drool-worthy ways to spend your disposable income.