Target Posted February 9, 2023 Report Share Posted February 9, 2023 Idea I wanted to try a front disc brake on my Gu 24", so I installed a Crewkerz 26" disc fork. But I've faced an unexpected issue. The Gu is long for a 24" bike, and I always thought it would be way cooler if it was shorter. But it turned out that it's even longer with the new fork: the wheelbase I measured was a massive 1081 mm. That's more than some 26" bikes have, and that was way too much for my dream bike. So I started thinking of ways to shorten the wheelbase. Fork with small offset One way to shorten the wheelbase could be to get a fork with less offset. I found out that the offset of the Extention carbon fork is only 20 mm (compared to 35 mm for Crewkerz), so I ordered it. The only downside was the height of the fork - 415 mm, which is 10-15 mm more than usual, and this extra height actually makes the wheelbase longer than it would be with the same offset and standard height. Angled headset There's also a thing that's widely used on mountain bikes to play with the geometry and make the head angle slightly slacker - the angled headset. I've only found one compatible with the integrated tapered headset found on Gu - 9point8 Slack-R 1.6°. I planned to install it backwards to make the head angle steeper (74.6° instead of 73°), therefore making the wheelbase shorter. There was also a similar drawback as with the fork - extra height has the opposite effect on the wheelbase. Front end height The taller fork and angled headset add a total of about 40 mm to the distance from the stem to the front axle. I've compensated for this using a lower stem and rotating the bar forwards (downwards actually compared to my previous setup). After a few experiments with different bar positions, it now feels exactly the same as on my previous Gu (one with a normal fork and headset) relative to BB and rear axle, only the front axle position feels different. Wheelbase with upgrades: expectations and reality According to my calculations, installation of the angled headset would shorten the wheelbase by 8 mm, and the Extention fork would shorten the WB by 12 mm (compared to the Crewkerz fork). So in total the wheelbase should be 20 mm shorter. In reality: the wheelbase of the complete bike turned out to be 1060 mm, which is 21 mm shorter than with a standard headset and the Crewkerz fork. So the reality matched the expectations. I'm really happy with the result! Now the bike feels exactly as I wanted it to. But it's a shame that most trial frames don't come in different wheelbases. The BB rise is +85 mm (10 mm higher than in a standard setup because of the extra height of a fork and a lower headset cup). Disc brakes I really like how controllable, quiet and powerful good disc brakes feel on a trials bike. The only major drawback for me is the spoke/rotor flex - the main reason why 26" comp bikes don't use disc brakes. In this build I've tried to reduce the flex as much as possible. I've deliberately used the straight-pull spokes instead of butted spokes. The front hub has large flanges (both left and right) to perform well under torsional loads. The front wheel has 32 spokes instead of the usual (on comp bikes) 28 spokes. I believe that trials brake rotors should have arms in both directions in order to handle forward and reverse loads, so I've chosen the symmetric Hope TZ V2 rotors. The dropouts on my frame were not parallel to each other, that's probably the reason why even after facing the rear brake mount (using the Hope for IS mounts) the pads were not parallel to the rotor. Since a dedicated tool for facing failed in my case, I decided to use a file, and spent 7 evenings trying to face the mount manually. The result turned out to be really good, the rear brake feels very solid and controllable, noticeably better than on a previous non-faced frame. Brake levers The Trialtech lever blades are specifically designed for single finger use, and they feel really great! I suspect my brakes now feel more powerful with these blades not only because they are slightly longer, but also because they are really ergonomic. I was tired of reaching out for the allen key every time I wanted to adjust the lever, so I designed and ordered some custom made adjusters so I can adjust the brake without tools. Front 15 mm through-axle This is something standard on modern mountain bikes, but very unusual on trials comp bikes (Clean bikes have 12 mm front through-axles, and Crewkerz have 9 mm front through-axles). The obvious advantages are increased stiffness and easier wheel installation (no rotor rubbing when you reinstall the wheel because the placement with the through-axle is more precise). The only disadvantage is the weight, the axle alone weighs 72 g. Stem The attempts to commit front wheel moves with the modern technique usually left bruises on my chest from the stem bolts, so I tried to find something more chest-friendly for a new bike. This clamp found on the Clean Pro stem is much better. The only drawback is that it doesn't hold the handlebar tight enough, and I had issues with the bar rotating forward under load. This was only solved by adding some texture to the contact surface of the stem and the handlebar with hundreds of dots of superglue (completely dry before assembly). The standard bolts on the clamp were a bit too long, and they were steel, so I ordered black titanium bolts for the stem, saving 13 g in total. The headset cap bolt is aluminium. Pedals and cranks Racing Line titanium pedal cages feel grippier than aluminium ones, and shouldn't wear down, bend and lose grip as fast as aluminium cages. Removed black anodizing from the BB spacers to match the cranks! Weight: 8.00 kg To be honest, I'm a little bit surprised about the weight. On the one hand, I built a temporary version of a full disc 24" Gu with alu fork some time ago, and its weight was 7.65. For the current build, with a carbon fork, lightweight rims and tyres, some fancy titanium parts I was expecting something around 7.5 kg. On the other hand, my aim was to make a stiffer bike than before. And an angled headset, 15 mm front axle and straight spokes definitely add some weight. Riding impressions It turned out to be the most fun bike to ride I've built in a long time (even though it's the heaviest one)! The front end feels really stiff (thanks to the massive carbon fork legs and crown, tapered steerer tube and 15 mm axle). The shorter wheelbase makes the bike more playful and helps with the switches. Two disc brakes allow me to try more different things and tricks, making riding more interesting. Spec: Frame and Fork - Frame: Gu 24" - Fork: Extention Carbon disc, 15 mm through-axle Front wheel - Rim: Neon Single 35 mm - Tyre: Schwalbe Rocket Ron 2.1 - Hub: Progress Endurance 15 mm 32h Rear wheel - Rim: Neon Single 47 mm - Tyre: Schwalbe Fat Albert Rear 2.4 - Hub: Jitsie Race Disc 135 - Nipples (front + rear): Sapim Alu - Spokes (front + rear): Sapim Leader 2.0 Brakes - Front and rear: Hope Trial Zone, 180 mm Hope V2 rotors, Jitsie pads, Trialtech lever blades, custom adjustment screws Drivetrain - Cranks: Rockman 160 mm - Freewheel: Jitsie 108.9 - Chain: KMC Z1EHX - Rear sprocket: Jitsie alu 14T - Pedals: Trialtech Carthy with Racing Line titanium cages - Bottom bracket: Echo Urban Ti Steering - Stem: Clean Pro 125 mm x 24° with ti bolts - Handlebar: Clean Carbon K1.2 690 mm (107 mm rise) - Headset: Echo tapered & 9point8 Slack-R 1.6° angled headset Geo: Wheelbase: 1060 mm BB rise: +85 Chainstay length: 368 mm Headset angle (taking the angled headset in account): 74.5° Weight: 8.00 kg Some photos of the building process Chainstay protector glued to the frame Fork choice Painting the Neon Single rims matte black Some custom parts: - An adapter to fit a sloped stem onto the Extention fork - Washers for the rear Jitsie hub to use it without snailcams - Adjustment screws for Hope TZ levers Preventing the bashring from spinning 3 Quote Link to comment Share on other sites More sharing options...
La Bourde Posted February 9, 2023 Report Share Posted February 9, 2023 Amazing effort! I like also that you detail your components choices. Wish you a lot of fun on this bike. Quote Link to comment Share on other sites More sharing options...
craigjames Posted February 10, 2023 Report Share Posted February 10, 2023 Bike looks awesome, apart from the forks Have you tried it with the current headset and the Crewkerz forks for comparison? Quote Link to comment Share on other sites More sharing options...
Target Posted February 10, 2023 Author Report Share Posted February 10, 2023 (edited) 3 hours ago, craigjames said: Bike looks awesome, apart from the forks Have you tried it with the current headset and the Crewkerz forks for comparison? I'm not a big fan of the look of the Extention fork too. Purely from aesthetic point of view, I'd prefer the Crewkerz one with straight thinner legs. But functionally, I'm 100% satisfied with the Extention fork. Those bulky forms make it really stiff. And it does the job of shortening the wheelbase. So I just accept the look as it is. Partially, it's a matter of getting used to. BMX racing carbon forks or 90's Monty's forks also look controversial, if you got used to the look of today's trials bikes. I haven't tried the Crewkerz fork. The wheelbase should be about 1072 mm if I install it (12 mm more than now), which is noticeably longer and a little bit too much, based on my experience with other forks and headsets. But it would be interesting to compare these two forks in terms of stiffness and flex, I'm curious if one can tell a difference between them. Edited February 10, 2023 by Target 1 Quote Link to comment Share on other sites More sharing options...
Ross McArthur Posted February 10, 2023 Report Share Posted February 10, 2023 Amazing effort dude. Bike looks great! I will admit, as much as I enjoyed my Echo 24 DD, the distance between the wheels (not to be confused with wheel base) did feel massive. If I could ride one again, id run an Inspired element fork to bring the wheels closer together. Would love to see a few clips of you riding it? Quote Link to comment Share on other sites More sharing options...
Target Posted February 11, 2023 Author Report Share Posted February 11, 2023 22 hours ago, Ross McArthur said: Would love to see a few clips of you riding it? Definitely, at some point when I get used to the new geo and do something worth filming Quote Link to comment Share on other sites More sharing options...
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