MZ/MuZ Riders

I'm not sure, but it might require a longer swingarm to accomodate the larger size wheel, and because of that, the wheel would also be further back meaning the rear mud-guard might need to be changed or angled in a way so that the wheel does not hit the mudguard. This will also require a longer chain too, of course. 2 links more. So.. A bit of work required I think.
The rear hub system is the same though.

Can I ask, why would doing this modification fail the MOT?

one of my bikes has a 16 inch rear tire .. here in the USA the selection of 16 inch tires is very poor and the 18 inch fronts are all to wide
makes it a pain at new tire time
dave

UK mot's only really check the safety of a motorcycle, and don't really do red tape like "this rear wheel should be x size for this one year". If you had a later 251, it would have the much larger/longer plastic mudguard. I think you might be able to get away with the centre stand. Possibly...



When it comes to my MOT's, they are shall we say... just a 30 minute chat about motorcycles



I also think the 251 is a bit small for me too (I have a 1990 metal rear mudguard too!). The steering is more direct certainly and sure this can be nice in the city, the 250 though is a nice longer bike that somehow seems to hold more confidence with me. The seating position all seems the same, and although I feel like I am sitting 'in' the bike on the 251 owing to the way the tank is shaped, I do feel more bolt upright almost whereas the 250 seems lower.

On my ETZ125 I converted it to 18" rear wheel by lacing an ETZ250 rim onto the ETZ125 hub. The fit was then straight forward but to make a nice job of it I moved the swing arm cross piece forward buy an inch, this works well and looks like a factory finish.

The reason for the 18" rear wheel is to give the bike a higher ride & seat height as I'm just over 6' 2"

Hi

If it`s any help many years ago i converted a Supa 5 for off road use.
I had my local MZ/Jawa/CZ dealer replace the original rear 16" rim with an 18" one from a CZ 250 and fitted a 4.00 x 18 trials tyre, i don`t recall any clearance problems.

Cheers

That's exactly what I did, but I used a slightly bigger section of box steel rather than the original piece of tube, I'm guessing at about 40mm x 25mm, placed a piece of large studding through the pivot end and the same at the other end to keep everything in place. Cut, ground and then welded, gave it a little tweak in the vice and then painted it.

I always wondered whether that extra hole at the back of each side of the swingarm was to change shock angle?

What kind of effect does it give?