An MC21 Gull-Arm can be made to work, but it's not quite as simple as just throwing it in there. Many years ago I actually met a guy while out on a ride with a SEED R5K fitted with a Gull-Arm. He was stopped in a layby as I rode past, so I did a quick U-turn and went back for a chat! (Irrelevant, but thought I'd share, as I've actually seen it in person!😉)

If I recall correctly, he was still running the MC18 18" wheel, but as I say, it was a long time ago, so may be mistaken. I just seem to recall the wheel looked rally big in the Gull-Arm.

However, I can tell you that an MC21 wheel will fit an R5/6K with little (possibly no) modification, but again, it's not quite that simple. Obviously the rolling radius of the 150/60-18 and 150/60-17 is quite different, and not that long ago someone posted about trying to fiddle around with various link plates to try and correct the geometry/ride-height. Bear in mind the MC18 already sits low at the back (corrected with HRC F3 link plates), so fitting a 17" rear wheel will make it "squat" even worse! Also, suspension geometry isn't just a case of jacking it back up to the desired height, and it's way too easy to screw up the rising rate... but that's way beyond my level of understanding.

I'm afraid it really is a case of "you're gonna have to try it", and find out... and let us know how you get on, please! But yes, the MC21 rear-end will mate to an '89 MC18, just be prepared to do some faffing about to get it to work. Remember to pay particularly close attention to the chain run.

Oh, don't forget the R5/6K has a torque-arm for the rear caliper too, so you will need the MC21 caliper hangar (which is captive to the swingarm).

The MC21 tank won't fit. You could probably make it fit, if you really wanted to, but it would look very odd!
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Andy.
NSR-WORLD.COM

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