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Build thread: 24" Gu with shortened wheelbase


Target

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I'm planning to build my dream bike, in which things I like about trials bikes are combining: 24" wheels, high bb, comp geo and Hope disc brakes. 

I used to build bikes as light as possible, but this one will be a bit different. I'll try to build this bike with the main accent on stiffness, but still saving weight where possible.

The first parts are already here!

 

Titanium pedal cages made by Racing Line for my Trialtech Jack Carthy pedals. I've bent and broken the original 2-mm alu cages really quickly. These titanium cages should be much more durable, but we'll see.
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Rockman cranks. I love silver cranks because unlike black ones, they still look cool after a few scratches. Always liked the look of the Rockman CNC cranks, and finally got my hands on these. 
I've been using 300-g ultra-light Born cranks for 5 years. They were quite flexible, but held really well until the left one snapped. These 413-g cranks should be stiffer yet not too heavy.
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Trialtech lever blades for Hope Trial Zone. I really love the shape of the blade on Trialtech rim levers that I used before. It seems like they are the only blades on the market that are designed specifically for 1-finger usage. And they are also pretty stiff. So hopefully this will be a significant upgrade for my Hope levers.
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Edited by Target
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New full black Clean Pro 24° stem just arrived! 

I went with a very short stem by today's standards - 125 mm. But I think with the Gu 24" frame and high rise bar that would be fine.

I've used more traditional 150*30 stem before with the Clean 107 mm handlebar rotated forward, and it was too low and too far forward, felt strange even for front wheel moves. Then I tried different bars and stems, and came up with the solution that feels amazing - 127*27 stem with high rise Clean 107 bar rotated a bit more upwards than usual.

The idea is that with 73° head angle frame you need shorter stem than with traditional 72° frame. And having a frame with a short 108 mm head tube, you have to compensate it somehow, for example by rotating the bar slightly upwards, and with adding some spacers.

There is a very significant difference between old Clean Pro 27.8° stem and this new one - new one is 78 (!) g lighter. Hopefully this new one still feels stiff.

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Edited by Target
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Degreased the KMC Z1eHX chain. I prefer to use wax based lubes (such as Squirt Chain Lube) for my chains. It's so good to have a chain that is always clean, doesn't attract dirt and doesn't leave greasy chain marks if you accidentally touch it with your fingers or clothes.

In order to apply a wax lube, you need to completely remove the factory grease first. I put a new chain in a bottle with degreaser, shake it vigorously and let it stay there for a few hours.
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2 hours ago, PLIW said:

What degreaser do you use?

Not sure, just the one with the "Degreaser" label on it from the local store. I don't think that's super important, anything with degreasing properties would work really.

Edited by Target
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Finished painting matte black the Neon Single Wall rims.

These lightweight rims work surprisingly well for me. I've been using the previous pair of Neon rims for 5 years until the front one got bent and the rear one cracked. Pretty reasonable life time for such a low weight and low price, so I bought a new pair.

They seem to be out of production, I managed to find some last items in stock. The front one was available only in golden, hence the repainting.

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6 hours ago, MaderaMark said:

if only I have extra budget for a 24 pure trials, I would love to build one...

24 pure never got it's day in the sun. Just get a mod instead; a world of choices and great disc performance. 24 pures are all tradeoff and no advantages sadly.

 

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On 11/4/2021 at 0:17 AM, Swoofty said:

24 pure never got it's day in the sun. Just get a mod instead; a world of choices and great disc performance. 24 pures are all tradeoff and no advantages sadly.

 

24 for a playbike would be ok for my height. 26 felt too big, handlebars at almost shoulder in rear wheel hop position and I can't squat a lot because of the reach. I am using a 110mm stem from 132mm.

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  • 2 weeks later...

Some new toys have arrived:

Jitsie bashring.
I've used Trialtech Sport Lite, but being the lightest on the market (11 g), it bends too easily. So I went with a slightly heavier option.
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Echo Spanish titanium bottom bracket.
I've been using one for the last five years without any issues, so I bought a new one just to be on the safe side.
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Carbon headset spacers with a matte finish.
For the previous builds, I've used some very lightweight CNC carbon spacers with 1 mm thick wall. And as it turned out, the can snap from trials riding. So these new ones are not CNCed and much thicker.
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  • 2 months later...

It's not that easy to get a 24" pure trials frame these days, especially one with a disc brake mount.
I have been looking for a new Gu frame, but it seems that in the latest batch they ditched a disc brake mount. So I managed to find a slightly used one in a great condition!

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20 hours ago, Canardweb said:

Hurry and build that thing up!

There's no fun in building a bike too fast! So I'm going to enjoy the process a little bit more: creating drawings of some custom parts in brakes, headset, hubs, getting them machined, removing unnecessary parts of the frame, creating decals, making tubeless inserts, removing some anodizing, waiting for titanium bolts from China to arrive...

Edited by Target
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  • 1 month later...

Here's something very unusual for a trials bike - an angled headset. 

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I like the Gu 24" frame, but it's a bit too long with a wheel base 1075 mm. So I have been looking for options to make the wheelbase a bit shorter.

By installing this angled headset, you can adjust headset angle of your frame by +1.6° or -1.6°. The idea is to change the headset angle from 73° to 74.6°, thus making the wheelbase shorter.

The result (measured on a real frame and fork): the wheelbase becomes shorter by 8 mm.

It's not an easy task to find an angled kit compatible with an integrated headset. I've managed to find only one option made by the company "9point8", produced in Canada. It turned out that bearing seats on the Gu frame are not exactly standard, but the Slack-R kit for Specialized bikes fits just fine.

 

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  • 1 month later...

Hmmm. As a wise Tarty Adam once said, you're not holding onto the front axle. 

If the frame feels long, aren't you going to have the opposite effect by running the angle set?

Why not try a backwards facing fork (a la Jeff Anderson) to shorten the WB? It might look a bit special but you aaaaare riding a trials bike (GU no less). :giggle:

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4 hours ago, Ross McArthur said:

Hmmm. As a wise Tarty Adam once said, you're not holding onto the front axle. 

If the frame feels long, aren't you going to have the opposite effect by running the angle set?

For the moves on the rear wheel, that's true, position of the front axle doesn't really matter.
But for the front wheel moves, front axle position does matter.

By changing stem and handlebar, it's easy to adjust "bb to handlebar" distance. So if you find your bike too long, you can install a shorter stem, and that would be enough for pedal ups to rear and other rear wheel moves.
But that wouldn't work, for example, for switches from the front to rear, or for gaps to front. For switches, the distance between the wheel axles matters. And you can't adjust that by changing a stem.

So for me an ideal wheelbase is about 1050-1060. And with the given frame, I'm trying to adjust front wheel position to make wheelbase shorter. And after that, the "bb to handlebar" distance can be easily adjusted using a proper stem/handlebar combo.

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5 hours ago, Ross McArthur said:

Why not try a backwards facing fork (a la Jeff Anderson) to shorten the WB? It might look a bit special but you aaaaare riding a trials bike (GU no less). :giggle:

You mean rotate a normal fork backwards? Or was it some kind of a special fork designed for Jeff?
Interesting, never seen him riding something that looks like a backwards facing fork.

If we're talking about installing a normal fork backwards, the wheelbase would be extremely short, too short (about 1015 with my frame).

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  • 1 month later...

Those Ti cages are awesome, been running mine for a few years now and have help up perfectly, showing very little signs of wear and offering much better grip.

On the topic of headsets, surely you'd be better off with a reach adjust headset (not sure if you cant get them in 1 1/8") if you're looking to shorten the bike a little, as said an angle adjust may reduce your the wheelbase but will increase the reach. Not something you'd want unless you do everything to front wheel?

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On 6/13/2022 at 5:07 PM, craigjames said:

On the topic of headsets, surely you'd be better off with a reach adjust headset (not sure if you cant get them in 1 1/8") if you're looking to shorten the bike a little, as said an angle adjust may reduce your the wheelbase but will increase the reach. Not something you'd want unless you do everything to front wheel?

Interesting, never heard of reach adjust headsets before! I think that increased reach should be just fine in my case since I'm planning to compensate it with a shorter stem. But if my setup doesn't work as I expect, it'd be interesting to play around with a reach adjust headset.

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  • 3 weeks later...

Be careful with reach adjust headsets. Most use external cups, which can increase the height of the headtube. Thus the head angle becomes slacker, and the wheelbase difference becomes negligible...

It is the same for the reach. I saw some people using +8mm reach adjust headset with external cup to replace the integrated (or semi integrated) headset on their enduro or dh bike. The reach is almost unchanged, cause the external cup rises the headtube, shortening the reach...

It is even worse when the head angle is slack (for example on a dh bike) or with a short wheelbase.

So do the maths!

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