GSB's Whyte PRST-4 build
- Thread starter GSB
- Start date
Absolutely right about form over function, time has shown that the reported advantages of the design don't seem to have been warranted by the enourmous amount of re-engineering that was required to actually do it, but then the same is true of the entire bike.02gf74":2i5nmyfe said:
That said, after a few years of development they're now very different wheels. The first generation wheels I had were utter garbage. Flexy, rattly, creaky and supplied with chocolate freehubs. The 2nd gen wheels I have in 26" are much much better, arguably the wheel that they should have launched in the first place. These 650b 3rd gens are much improved regarding stiffness, probably due to the greater cross section and width of the rim. They're easily as stiff as the hope wheels on my other bike, and these are an inch and a half bigger, so I don't think stiffness is the biggest problem with them anymore. These weigh in at 1650g a set, which is about 180g more than a set of Mavics at the same price point. Not heavy, but the new technology certainly hasn't realised any weight savings over traditional wheel design, leaving the looks of the things being the only real advantage of note. If I were a real wieght weenie I'd probably worry about those extra grams, but I think I'll live. I haven't even put a carbon seatpost on it yet and the whole bike only weighs 26.8lbs, which for a nearly 20 year old full suspension bike wearing wheels and tyres that are to big for it is pretty respectable.
kneeslider
Retro Newbie
Loving the 27.5in conversion, those wheels look great. Can you let me see a detail pic of how you have managed to get a 27.5in wheel into the front end?
I rather fancy having a go myself!
I rather fancy having a go myself!
Re:
I can't send pictures, as I left the bikes at my in-laws after the weekend, but I can tell you how it was done.
First was replacing the steering bolt. Whyte uses a cap head bolt with a very prominent head on it, I replaced this with a normal hex head bolt. To sneak a couple of extra mm of clearance I machined the head down a little and gave it a domed profile. I used a lathe, but you could easily do the same thing by spinning the bolt in a drill and shaping the head on a file.
Second was the big gripper bobbins. The front bobbins have a 9mm hole to accept the standard quick release wheel axles. I drilled these to 10mm (same as rear bobbins) and then used shim steel cut into 4 0.25mm thick semi-circular shims to close one side of the hole down by 1mm. This effectively offsets the axle centreline by 0.5mm from the centreline of the bobbins. Line the two bobbins up relative to one another to maintain alignment.
Lastly, I put 0.5mm shims into the big gripper cutouts on the fork legs.
Total result was to push the axle down and forward from the crown by 1.0mm, which is enough to run the 2.0" tyres without rubbing. There's next to no mud clearance space, but I don't ride in mud anyway, and wanted sonething that would roll super fast on the sort of gravel trails I normally use. If I need to get really dirty then the 26" wheel will drop straight back in.
The only issue I have left to resolve is the slight interference between the tyre and the lower shock bushing at full compression. With normal fox bushings there's no problem, but with the modified (and much bigger) Whyte ball bearing based bushing there's a slight rub when the shock bottoms out. I might just live with it, or I might revert to the fox bushing instead. More concerning to me though is why I'm bottoming out, which appears to be pie related.
All this aggro can of course be avoided by a) fitting a smaller tyre
Or b) sticking with a 26" front wheel.
I only did it to see if it could be done, there's no competitive edge being sought and I had no performance gains in mind, but having acquired the wheels it seemed like it was worth trying. Having tried and failed with 2.25" and 2.1" tyres these 2.0" tyres were going on whether they fitted or not, but next time I change I'll fit narrower rubber. A 1.9" would probably be perfect.
Was it worth it? Well, it rolls really nicely, It looks pretty unique, and it seems to fit my 6'3" frame rather better. Plus, I can go back to 26" in about 20 seconds, so yes, it was a fun little project and it'll probably stay as a 650b for the time being.
I can't send pictures, as I left the bikes at my in-laws after the weekend, but I can tell you how it was done.
First was replacing the steering bolt. Whyte uses a cap head bolt with a very prominent head on it, I replaced this with a normal hex head bolt. To sneak a couple of extra mm of clearance I machined the head down a little and gave it a domed profile. I used a lathe, but you could easily do the same thing by spinning the bolt in a drill and shaping the head on a file.
Second was the big gripper bobbins. The front bobbins have a 9mm hole to accept the standard quick release wheel axles. I drilled these to 10mm (same as rear bobbins) and then used shim steel cut into 4 0.25mm thick semi-circular shims to close one side of the hole down by 1mm. This effectively offsets the axle centreline by 0.5mm from the centreline of the bobbins. Line the two bobbins up relative to one another to maintain alignment.
Lastly, I put 0.5mm shims into the big gripper cutouts on the fork legs.
Total result was to push the axle down and forward from the crown by 1.0mm, which is enough to run the 2.0" tyres without rubbing. There's next to no mud clearance space, but I don't ride in mud anyway, and wanted sonething that would roll super fast on the sort of gravel trails I normally use. If I need to get really dirty then the 26" wheel will drop straight back in.
The only issue I have left to resolve is the slight interference between the tyre and the lower shock bushing at full compression. With normal fox bushings there's no problem, but with the modified (and much bigger) Whyte ball bearing based bushing there's a slight rub when the shock bottoms out. I might just live with it, or I might revert to the fox bushing instead. More concerning to me though is why I'm bottoming out, which appears to be pie related.
All this aggro can of course be avoided by a) fitting a smaller tyre
Or b) sticking with a 26" front wheel.
I only did it to see if it could be done, there's no competitive edge being sought and I had no performance gains in mind, but having acquired the wheels it seemed like it was worth trying. Having tried and failed with 2.25" and 2.1" tyres these 2.0" tyres were going on whether they fitted or not, but next time I change I'll fit narrower rubber. A 1.9" would probably be perfect.
Was it worth it? Well, it rolls really nicely, It looks pretty unique, and it seems to fit my 6'3" frame rather better. Plus, I can go back to 26" in about 20 seconds, so yes, it was a fun little project and it'll probably stay as a 650b for the time being.
Re:
Looks like an earlier frame, but it's very original (originality seems to be a bit of a 'thing' here!). The only non standard item appears to be the saddle. It also has the V brake mounts on the swingarm and fork which is a rare addition. Most '4's don't have these.
Treat it to a full strip, a complete set of bearings, a new headset and a pair of new shocks and it'll be superb.
Looks like an earlier frame, but it's very original (originality seems to be a bit of a 'thing' here!). The only non standard item appears to be the saddle. It also has the V brake mounts on the swingarm and fork which is a rare addition. Most '4's don't have these.
Treat it to a full strip, a complete set of bearings, a new headset and a pair of new shocks and it'll be superb.
Duxuk
Retro Guru
I've had a JW4 for a couple of years. I bought a new old stock JW4 in 2005 and loved it but decided to make a new start in 2011 when the bushes were shot. This was a mistake which I instantly regretted one I'd ridden a telescopic forked replacement. I have loved the newer JW and for some reason felt compelled to buy a PRST4 frame, shocks, rear wheel and seat post from Ebay for £165. Built up now and I've road tested it. The day after I acquired the frame my wife's brother, Gary, came round. He'd bought a PRST1 for £850. It had been assembled but never had the pedals fitted!
The advice to set the shock pressures at bodyweight (rear) and 75% of that (front) is spot on. Lower pressures will leave you with a bucking nightmare. I don't think Gary will ever ride his PRST1 off road. I'll maintain the family honour by thrashing my 2. I have never managed to match my PBs set on my first JW4 and next year will do some tests to see if a modern FS trail bike is as fast on a local man made circuit of a "red" grade.
The advice to set the shock pressures at bodyweight (rear) and 75% of that (front) is spot on. Lower pressures will leave you with a bucking nightmare. I don't think Gary will ever ride his PRST1 off road. I'll maintain the family honour by thrashing my 2. I have never managed to match my PBs set on my first JW4 and next year will do some tests to see if a modern FS trail bike is as fast on a local man made circuit of a "red" grade.
fotorat1
Retro Guru
HI GSB
Only just read this thread- very useful- whats the update on sourcing a spherical on a budget..ie dimensions so I can Mail order one..
I picked up my 1st JW2 at christmas and have been riding daily thinking my front shock was clunking and only discovered, this week, a silly amount of play in the spherical.
I still have a massive rubber queen on but with the coil shock - its never going to bottom out - I had some fun on an original 02 shock up front which ramped up and the rubber queen destroyed my front crud guard.
I still have the original coil on the front - but its damping dial doesnt do much so I will see if I can do an oil change on it.
In the rear I have a Manitou Metal - which is very comfy - I wouldn't want to try and do a 20mile off round trip on this bike but for mooching around at low speed its great.
I am fed up with getting punctures in the rear wheel - so I have a pair of stans Alpines + Vertical protection (which should be a bit skinner than the RQ's) coming for it any day now....
Then in January I picked another one up which was 98% original + bigger frame
I need to do an uptodate photo as it has its slr rear wheel in now and a chain! I also have a DT swiss XR shock on it ways to me - i might try it in the front..
I have also fitted a 90mm Specialized comp set stem which means the stem can almost sit on the headset - but I now have a dilema - to cut the steerer tube or not- I am inclined to leave and fit the stem at the top with flat bars!
Only just read this thread- very useful- whats the update on sourcing a spherical on a budget..ie dimensions so I can Mail order one..
I picked up my 1st JW2 at christmas and have been riding daily thinking my front shock was clunking and only discovered, this week, a silly amount of play in the spherical.
I still have a massive rubber queen on but with the coil shock - its never going to bottom out - I had some fun on an original 02 shock up front which ramped up and the rubber queen destroyed my front crud guard.
I still have the original coil on the front - but its damping dial doesnt do much so I will see if I can do an oil change on it.
In the rear I have a Manitou Metal - which is very comfy - I wouldn't want to try and do a 20mile off round trip on this bike but for mooching around at low speed its great.
I am fed up with getting punctures in the rear wheel - so I have a pair of stans Alpines + Vertical protection (which should be a bit skinner than the RQ's) coming for it any day now....
Then in January I picked another one up which was 98% original + bigger frame
I need to do an uptodate photo as it has its slr rear wheel in now and a chain! I also have a DT swiss XR shock on it ways to me - i might try it in the front..
I have also fitted a 90mm Specialized comp set stem which means the stem can almost sit on the headset - but I now have a dilema - to cut the steerer tube or not- I am inclined to leave and fit the stem at the top with flat bars!
