This is an 'in progress posting' as I work through issues with a fork swap. WHAT I'M DOING: So Ive decided to get cracking on the 05 YZ250F fork conversion. These are 48mm Kayaba (KYB) forks, with adjustable rebound & compression damping. They will replace the standard 91 R100GS Marzocchi 41mm conventional forks, which have no provision for external adjustment. I bought these forks in a rolling chassis 12 mths ago. Ive recovered my money from the other parts I sold, so this is a free upgrade, at least from a basic component perspective. Quite apart from the other Unholy Union writeups, for inspiration I've also looked at these other threads. Yamaha Forks on a BMW F650 Dakar To Those Who Have Put Modern Forks... KTM lc4 forks on my gspd Whilst it would have been nice to go all KTM with the HPMGuy triples, I just did not have the available cash when it mattered. The KYB forks are an economic alternative. WHY I HAVE DONE THIS: The BMW forks are adequate, but not adjustable without disassembly. They are not very tuneable, albeit that Gold Valves can be installed to partially improve damping performance. Gold valves aside, they are very much 80's technology. The front end from the BMW weighs a tonne, especially the front wheel. Given I dont use tubeless tyres (I do single & 4WD tracks, with low pressures) I cant see the advantage of retaining these. A flat in the boonies will be a major pain. My bike isnt concours, has already done 206k kms (129k miles) & is heading towards being a bitza, so Im not losing any value as an immaculate example of the breed. The conversion will fit what I want from the bike more. Watch any video & you'll see I'm not an aggressive rider. Part of this is concern re suspension compliance & weight. The swap is an easy weight saving & should improve the ride comfort for the bike, and give me some other options later with the bike in terms of ride height. Originally I was going to do this conversion after HPN style frame bracing. Ive not gotten' around to this yet, & given I have the forks just sitting there.... STEERING STEM LENGTH & OFFSET: Standard offset on the BMW R100 GS is 38mm. On the YZ250F triples 25mm. The axle offset I measure as 40mm for the standard forks, 34mm for the YZF forks. So there will be some difference in steering. I'm not running a fairing, use a Baja Designs 8" light, & also have an HPN tank, so can accommodate bigger fork legs with no clearance or fitting issues. I will need to do something to modify the steering stops on the YZ250F triples. These hit the BMW frame braces rather than the designated stop on the headstock. The length of the YZF steering stem is too long for the BMW headstock, & is in an hourglass shape, which limits shortening options. The overall length of the stem needed to be kept consistent with the stock Yamaha stem, given the forks also have a couple of tapers that the stem needs to work with. The brown stain on the stem is where the Yamaha bearings sit in the YZ250F headstock. The Yamaha bearings are both the same outside diameter as the BMW bearings, but the bottom bearing uses a larger inside diameter. The bearing cup giving the reference nos is pictured. The top bearing has the same I/D is the same as the BMW bearing (ref 320/28 J). FORK SPECIFICATIONS: BMW stock springs are said to be circa 0.47-0.48kg/mm. I'm currently running 12.5w & 10w fork oils. Fork travel is 225mm. Standard, YZ250F KYB fork comes with 43.5kg/mm springs. The forks have come with a 0.41kg/mm spring installed. YZF fork oil is 2.5w standard, & stock free spring length is 470mm. Fork travel is 300mm. The forks are externally adjustable for compression & rebound damping. WHEEL: Im not particularly a fan of the BMW wheel set, which is tubeless great on road, but IMHO a bugger if you get a flat elsewhere, and aren't running a tubeless road oriented tyre. They are also damned heavy (albeit strong as a strong thing). Given this I want to keep the Yamaha DID wheel & rim. Axle sizes are 25 mm BMW, & 20mm Yamaha. BRAKES: The YZ250F brake rotors are 250mm, compared to the BMW's 280mm. I want to retain the standard GS 13mm mastercylinder, partially because I don't want to swap out the switchgear, & throttle housing. The YZ250F uses an 11mm mastercylinder, & Nissin 2x27 mm calipers.