Hi jags,
You're welcome to contact me through my email with any questions and particulars wrt your wheels as you get closer to building them. Are you going to build them yourself, or have them done? If you're going it alone and are a first-timer, I can heartily recommend Robert Wright's little book on the subject. It may not still be in print, but is often available on eBay here in the States. If you need a copy, let me know and I'll keep my eyes open.
As to your Sherpa, I think the wheel change will transform the bike as you desire. Yes, the frame will still be on the heavy-duty side, but the wheels will be so much easier and quicker to accelerate and I believe the lighter, narrower tires will contribute further to the feel you desire. They will ride harsher, of course, but that is to be expected, and the carbon fork will offset that. This is a terrific example of how every single Thorn is unique in some way from all its brethren. Yours will be ideally suited for your needs and use, jags, and that much more beautiful for being truly personalized. Yes, it is a bit counter to the usual orientation for the frame, but really, who cares? If it works better for you, then it is the best choice of all.
As to the specifics of the wheel build, I think you're right on track. I've used hubs by Phil Wood (no relation) since 1978, and have always been very happy with them. Mine are all of the older style and freewheel-specific, but from everything I've seen, the newer cassette versions are true to the proud heritage of the company. Their FSA (field-serviceable axle) design is a terrific idea, and makes possible user replacement of the sealed-cartridge bearings wherever you happen to be...including alongside a dirt goat path in the remotest of locales. Stop, grab a 5mm allen, swap the bearings, and you've got a new pair of hubs for all intents and purposes. Phil's customer service is generally outstanding, even after he left the company. I have over 35,000 miles on one set of hubs and more than 28,000 on another, and they are still as nice as the day I installed them. Three of my bikes have Phil bottom brackets, and I managed to find and fit a pair of Phil platform pedals to my father's bike some years ago. To reassure you about their customer support, these were used pedals, and one fractured through the spindle due to a flaw in the billet. All it took was mailing them to Phil Wood & Co. and I received them back repaired, in a week, with a letter of apology from their head of customer service.
<nods> Yes, Phil cassette rear, Phil front, and the Velocity Synergys are a good combo. You have the option of an offset rear or conventional. I used to build wheels professionally, back in the day. If it were me, I would lean toward three cross, 15g spokes with the pulling spokes originating on the inside of the hub flanges. DT make top-notch spokes, but in recent years, I have leaned toward Wheelsmith (Asahi), as I prefer their Duristan nipple treatment; it seems to be a much longer-lasting finish than DTs, and I like the Wheelsmith bend and head-flanging treatment a bit better from a builder's standpoint. I thnk the threads are rolled a little cleaner, and the nipples seem to have a bit less friction when tightened in the rim ferrules at high tension. In truth, it probably doesn't make a whit of difference in use and I think you'd be happy with either.
The wheels you are planning aren't too far off what I've used successfully for many years on just about everything, though mine were 700C. My favorites use Phil hubs, Mavic MA2 rims, and 36, 15g 3x DT spokes. They're the ones with 35,000 miles on them, and they've hauled me and 50lbs of gear back and forth across Oregon's Cascade Mountains on gravel and dirt as well as done good service on 400k rando rides on pavement. Yours will be stronger with a 26" rim, but likely no less responsive. Be careful with tires, though, and try to get a cross-section measurement on a mounted and inflated example of the type you seek before you buy. Especially in the narrower sizes, so many tires are labeled optimistically and may well be narrower than stated. I'd suggest something that is truly slick at the tread and around 32-35mm in actual width for your project. Yes, you'll have to keep them well-inflated and yes, they'll ride harshly, but the overall combination will surely *feel* quicker, I'd judge. If I may suggest...keep the original fork and spares in case you ever again wish to set the bike up for a touring orientation. One can't really see the future, and if you've already got the bits 'n' bobs, it doesn't hurt to store them in the shed, "just in case". It would also be nice if, say, you wished to try the bike on Begian cobbles with wider tires. Keeping the old parts essentially gives you two Sherpas -- a go-fast and a go-soft. Sounds like a terrifically fun project, and I look forward to photos of the progress and result, jags. Good on ya!
Thanks for the fellclub invite, jags; after seeing the club site, I do believe I will plunk down my check for £7; it looks like a good one. Fine-looking group of folks and what appears to be a lot of fun at meets and rallies. I envy you the forthcoming Ireland end-to-end; what a wonderful trip ahead for you! I'll bet you can't wait till May. Of course, we will all pester you for piccies and reports on your return; I now you'll have a wonderful time and wish you the best. Ah, lovely Ireland! Some of my relatives on one side come from around Sligo Bay and the others near the River Shannon. Still others settled near Belfast. The rest of the family heritage runs toward Scotch, German, French and Dutch.
Best,
Dan.
