Darksiding a GS850G

I've been looking seriously at this for my GS850 and did the following;
Got a 15" wheel from a Suzuki Cavalcade, which will fit with a bit of bearing molishment (possibly available off the shelf, but might need a carrier/sleeve machined), and have a Nankang 135r15 to go on that, when it's ready. I reckon that will all fit nicely and should comfortably retain some clearance in the swingarm. The overall rolling radius of that is slightly smaller than the 130/90-17, but is very close to the factory original size of 4.50-17.
Shortly after buying that, I acquired a shaft-drive 16" rim from a GS1100GK, which will fit more-or-less straight into my bike, and kept it aside for future use, in the possible event of finding a suitable tyre.
Recently I discovered that Heidenau are making a 5r16 tyre that should fit that rim and still fit in the swingarm space.
They're available here...
http://www.tyreleader.co.uk/car-tyres/heidenau/p29/5r16-74p-95654
Of the two, I'm likely to fit the Heidenau first, as the wheel will go straight in - only need a disc for that, buy the tyre and good to go.

Well, ain't that a sod.
I found a disc for that 16" wheel, was about to buy the Heidenau tyre shortly, went over to that site and they're all sold out.
I suspect Heidenau make a limited number of them for the classic car market and probably make them in batches, so it might be a while before they appear again. If they don't show up for a while, I'm just going to proceed with the 15" Cavalcade rim and have a disc made for that locally.
The other possibility is to simply fit a x-ply or bias 16" as a stop-gap and see how it goes.

Finally got things sorted out.
At the start of the year I found a sidecar rim that had been made to allow a car tyre on an outfit. Quite an expensive item, back in the day.
Snapped that up as soon as I saw it. It's basically a GS850 or GS1000G hub that's been shorn of its original wheel and then welded into a car alloy wheel casting.
Nothing quite as crude as that, as the casting looks like it's been made for this job, but the wheel section looks a bit familiar, as I'm fairly sure I've seen these wheels back sometime in the 80s, when they were used as car rims.
Anway, fitted the Nankang CX668 135r15 to it and of course, it being a car rim, there was no trouble trying to seat it.
One thing I noticed was the previous owner had been a bit lax in lubing the drive splines, as they were half worn, enough to make me fit a new-ish replacement. A set of new bearings to be on the safe side, and good to go. The wheel needed no balancing, either.
Fitted the wheel to the bike a couple of days ago, and it's ready for use.

Well, after a few hundred miles I'm very happy with the way it runs and tracks the road, but the only downside is the effect on the overall gearing.
I'm not too comfortable sitting at a cruise speed of 70 and the engine is running at 6000rpm - and especially if I want to wind it on a bit and sit at 85 to 90, which is normal on the local motorway, I'd be thrashing the poor old beast.
So... I've just pulled the trigger on a 175/75-16 Firestone Vanhawk II tyre which will be with me next week. The pics on Firestone's website don't show it that well, but from other sources I see it has a nicely rounded shoulder, which will help.
I have a 16" wheel from the GS1100L model and I know the tyre will fit that and also fit into the width of the swingarm. Only slight difficulty will be having to shift the wheel along to the right on the axle and maintain full mesh on the drive splines. I've planned on how to do it easily enough and still leave the bike capable of easily taking the standard wheel again if it has to.

https://www.firestone.eu/en/van/vanhawk-2/

Update:
Turned out the Firestone Vanhawk tyre was too big for the available space and frankly, even if it fitted in there, would have probably been dodgy as hell on the narrow 16" rim.
I acquired a Michelin 155r15 for the custom rim and found there's an interference problem with the left-hand swingarm, so replaced that with a 143r15 which clears it nicely.
I'll re-visit the issue of the 155 next year when the workshop warms up a bit.
I'll have to make spacers for the rear hub and move the wheel over to the right by about 6mm or so, then I can use the 155 safely.