DH Out of the shed: Galah DH3 (6inch)

[Benj]

Our third dual susser, finally complete! (after a couple of months of Sundays)

design:
This bike was designed to a be a more playful DH bike along the lines of a Bottle rocket.

We are trying out a few new ideas with this one, both in terms of manufacturing & bike design.

The use of a linkage is the most obvious new direction.
The advantage of using a linkage is that it gives you much greater freedom in shock positioning & allows for tailored shock rates.
This leverage ratio on this bike moves from a fairly linear rate in the first half of the travel and ramps up in the second half (from memory it gains about 100lb equivalent spring rate by bottom out)

geometry:

cockpit (reach/horizontal distance between the BB & top of head tube):
420mm (16.5 inch)
chain stay :
420mm (16.5 inch) (@ 33% sag) -it's rearward so it's about 390-400mm static
Head angle:
~66.5
(sposed to be 66 but it pulled a little in welding -must set & tack more carefully next time)

spec:

forks: 08 talas 36 RC2
shock: DHX5 air
wheels: hope pro 2/mavic 721
brakes: avid elixir
deraileur: saint
shifter: XT
cassette: XT
cranks: SLX
pedals: fun soljam
bars: fun full on
stem: gusset
headset: FSA pig pro
seat: charge
post: tioga

thanks:
Matt -for all the help & enthusiasm


more general info & links here:
http://www.rotorburn.com/forums/sho...rburn.com/forums/showthread.php?t=77133[url/]

 

[.Alex.]

we need bigger photos but from what i can see looks amazing

 

[---Matt---]

This bike is siiiick! Had a quick ride as well this arvo and can't fault it!

Here's the bigger versions of the ones above along with a couple of my own

 

[Danoz]

they look interesting and great..........would love a ride report when you've had a decent ride!

 

[evObda2]

Can see a strong Canfield influence there..
I think the bike looks great.. very balanced. You've done well.

 

[brutasauras]

High pivot = rearward axle path, Great job good to see home made bikes pushing designs in the right direction not just relying on custom valved shocks to make up for the reduction in time the shock has to react to bumps due to the forward motion of the axle path of most production bikes. And by the look at the height of the pivot the axle path wouldn`t be far off matching the path of the front wheel?. Do you do your own tig welding and if so do you find it hard welding the tubes?

 

[xc_machine]

How stiff is the rear?

Damn good effort mate. Damn good.

 

[---Matt---]

The rear is really good in terms of stiffness. No noticable flex at all.

From the short ride we did yesterday, the linkage seems to be doing its job perfectly. It feels extremely supple over small bumps but still takes big hits well too. Our last frames felt good, but having the linear ratio made the bikes feel a little industrial and like a bit of a pogo stick. This one ramps up nicely towards the end of the travel and feels more professional.
The axle path is fully rearward throughout the travel and passes through the angle of the forks at sag.

The frame is TIG welded. I'll let Russ explain since he did the welding.

 

[Benj]

And by the look at the height of the pivot the axle path wouldn`t be far off matching the path of the front wheel?. Do you do your own tig welding and if so do you find it hard welding the tubes?

spot on: the axle path is 66 deg at sag (matching the forks) -I actually use this contraint and the swing arm length to define the height of the pivot (others start with the height of the pivot which doesn't make much sense to me)
-matching the fork angle means that the wheel base doesn't change much
-66 degrees also provides a very effective drive angle for a concentric roller (the other advantage of a high pivot that not many people mention is that with the right angle (and a roller that is approximately concentric to the pivot) you can make a bike that pedals really positively, without any pedal feedback.

I tig myself: It certainly is a challenge -rewarding when it comes out right and generally very frustrating in the fiddly bits -I'm always learning...and sometimes improving.
I have great admiration for those taiwanese chaps turning out three hundred buck beaters!

 

[Menzies]

Interesting Rigs man, the Suspension Set up makes the bike all the more interesting, nice.

 

[brutasauras]

What sort of tig do you guys use i know you only use dc with cromo but do you use a foot pedal. I am very keen on giving this a go but tig welding is the one skill that i lack. and it is not every day you run into a frame builder in aus.

 

[---Matt---]

For anyone interested, here's some build pics...

Making the jockey wheel


Main pivot cup, ISCG tab, bearing spacers, main axle, linkage bearing and rocker frame mount


Mitreing the swingarm tubes


Downtube gusset ready to be welded


Finishing off the swingarm


Frame almost complete

 

[Benj]

What sort of tig do you guys use i know you only use dc with cromo but do you use a foot pedal. I am very keen on giving this a go but tig welding is the one skill that i lack. and it is not every day you run into a frame builder in aus.

I didn't have any of the skills or tools required when I decided to start making bikes....so I went to night school at tafe.
Tafe is the only way to go unless you already have access to a full workshop & someone that knows how to use it.


I use a lincoln invertech v205t but all you really need is a DC machine with high frequency start.
I've thought about getting a pedal because the amount of heat required varies as you move around each tube but it's certainly not necessary. You'll find that you have more than enough variables to get your head around without the added complication.

 

[camtb]

I think you should make me one
haha
but seriously, sick design, any chance of you going into production?

 

[starship303]

Looks great, quite a neat design. Any chance of seeing a video of the suspension working? Interested to see its 66 degree rearward travel and linkage in action.

Can't wait for the next Galah installment, though i'd imagine you'd want to enjoy this one for a while before playing with the tig & jig again.

Keep up the awesome work!

*

 

[French Fries]

Can i say..... FREAKING AWESOME!!

Thats amazingly well put togeather bike for something that was build at home!!

D

 

[Benj]

ride report

I hadn't been to Maldon for Downhill before and having heard a bunch of positive reports, a trip out there has was long overdue. Testing the new bike seemed like a perfect excuse.

Maldon's Mt Tarrengower has a great little set of tracks with good variety and mix of flow and challenge. As a bonus the shuttle has to be the quickest and easiest in the state.



It took me a couple of runs get back into the flow, not having ridden DH for a while, but after afew surprises early on (hidden rock gardens are a cute little feature) it didn't take long to get up to speed.



The geometry fit well from the start, giving the sensation of being well centred on the bike -it would be a medium/large frame (I'm 6'2).
With the shorter forks I found it very easy to get my weight over the front in corners, enjoyning the minor rear wheel drift through turns as the rear is unweighted.

The rear end is super short when static and, despite the rearward travel, still short at sag (for a DH bike). This works really well with the rearward travel because unlike Matt's canfeild or the first dually we made, it's easy to unweight the front and lift into a manual -very handy for the extra rough sections or for lifting over logs.

Being lighter than my previous DH bikes and with the capacity to shift weight effortlessly, this bike is also easy to bunnyhop. Of course there is always the extra preparation when jumping a dually as you compress the suspension, but with this bike I am able to get a useful loft without feeling the strain of lifting a big dead weight.

The pedalling efficiency of the high pivot and concentric roller drive has been proven on our previous bikes and is shining again on this one: I took it for a spin at lillydale BMX track the other night and though it's no 4x-er, it certanly didn't embarass itself.



The shorter travel is certainly noticable when compared to a full-on DH rig , particularly when combined with the geometry designed for agility. However, the suspension action is wonderfully plush and (due to the linkage progression) bottomless, so that I didn't feel like I was lacking the extra.
The front end is longer, the head angle slacker and the bottom bracket lower than the previous dually (Matt's 'play bike') and this gives it sufficient stability and space to make it much more capable of high speed DH plow.
In the flat out & rough sections a big bike will always be quicker but in the tight stuff that makes up a big proportion of Victorian tracks, the 'little' bike has a definate edge.



I really am trying to find the weaknesses in this bike and the potential improvements for the next one but so far havent any to report.

It's nimble enough to be playful, stable enough to plow, it jumps and pedals beautifully, it's reasonably light (could always be lighter) and the mass is low down in the frame. It's plush and bottomless and access to the shock adjustments is better than previous bikes. I reckon the aesthetics are alright too.



Thanks to the guys at Maldon for building a wicked set of trails (thanks also to the tolerant ranger)

 

[Xmetal]

It's one of those bikes that is truly unique, no other words can describe it.

You've done yourself proud, Ben.

 

[Case king]

That bike is sick. love the way the linkage works.
Sick photos of the building process...really interesting.

any chance your going to race it?
whats the suspension like under brakes?

 

[Bodin]

I wish I had the $$ to help you blokes quit your day jobs and do this full time - brilliant work. I'd love a bike like that. I'll be looking you up if I ever win the lotto.