DH Home Made - DH4 - Now with Gearbox!

---Matt---

---Matt---

Likes Bikes and Dirt
Now with Alfine 8spd hub HERE


So, here's the latest addition to the family! This is DH MK4 (frame number 9) and it has been a long time coming. While it's not the prettiest bike out there, everything is done for a reason!

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The bike was designed around what I like in a bike as well as my size (187cm). The first ride showed that it's much easier to bunny hop and throw around than my Canfield was. It's also more rearward, so bumps at speed seem to feel less harsh. Pedalling feels extremely positive due to the roller position and the corresponding angle of the rear suspension when at sag. I'm looking forward to getting out on some DH tracks and seeing how it handles.

Everything on it is machined up by us, except for the bottom bracket. Here's the low down:

* 8in rearward travel
* Rising rate suspension ratio
* 65° HA
* 83mm BB shell
* 12x150mm rear axle
* 20mm BB rise
* 425mm chainstay
* 425mm cockpit length
* 597mm effective TT
* 1147mm wheelbase

And the specs:
* Forks: '06 Marzocchi 888 RC2X
* Shock: Fox DHX5
* Wheels: Mavic EX721 on Hadley 20mm/150mm
* Drivetrain: Saint
* Chainguide: MRP chain guide
* Handlebars: Funn Full On handlebars
* Headset: Chris King

And finally some pics
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Comments & questions are welcome
 
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dug8713

Likes Dirt
Awesome work! Looking to eventually put my CAD and TIG skills to work and do a similar project, someday..

Where did you guys source the raw tube from? Also, where did you get the bottom bracket from (as you didn't machine it up)?
 
---Matt---

---Matt---

Likes Bikes and Dirt
SuperSix said:
How many links of chain are you using?
Click to expand...
It's got about 4 more than a standard chain, so around 120 links?

dug8713 said:
Awesome work! Looking to eventually put my CAD and TIG skills to work and do a similar project, someday..

Where did you guys source the raw tube from? Also, where did you get the bottom bracket from (as you didn't machine it up)?
Click to expand...
Yeah, it's definitely worth doing if you have the time and resources.
We get our tubing from http://www.rollcages.com.au They seem to have (or be able to get) a good range of tubing sizes and thicknesses.
I think the BB shell came from http://www.hillbrick.com.au
 
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Mr Kurt

Likes Bikes and Dirt
Bike of the month this! Thats really cool. I like the shock placement, nothing in the way so you can adjust it quickly and easily! Nice geometry too, although a little steep for me. I like it a lot!
 
MB

MB

Intense Australia
Congratulations on a job well done, looks great! I'd be very curious on a ride report, with that pivot so high it would destroy bumps...

Keep us posted on how she goes.
 
Ivan

Ivan

Eats Squid
Mr Kurt said:
Bike of the month this! Thats really cool. I like the shock placement, nothing in the way so you can adjust it quickly and easily! Nice geometry too, although a little steep for me. I like it a lot!
Click to expand...
Because of the high pivot, sag will impact the HA differently to conventional bikes.

This os not aimed at the OP, but the industry should stop talking in static geometry numbers and use geometry at suggested sag instead.

Sent from my HTC Desire using Tapatalk 2
 
bmx

bmx

Likes Bikes and Dirt
You can really appreciate the engineering that goes into making your own downhill frame. Well done.
 
No Skid Marks

No Skid Marks

Blue Mountain Bikes Brooklyn/Lahar/Kowa/PO1NT Raci
Looks great both in the pics and the geo on paper. Slacker head angle would be nice IMO. Can always angle set it.
They get better every time.
Is it clear coated?
Awesome linkage set up. What length shock is that? Did you map the leverage curve on a computer?
Decent ride report please.
BOTM fa shizzle.
 
J

jonozrx

Likes Dirt
That is really, really cool. My first thought was that head angle is a bit steep, but as mentioned above, it might behave differently at sag because of the high pivot point.

I'm finding it hard to visualise the action of the suspension - are you able to post an animation of the suspension moving through its travel?
 
---Matt---

---Matt---

Likes Bikes and Dirt
Thanks for the comments guys!

The head angle comments are interesting... I mentioned that this bike was a long time coming, and since we started designing the bike around 3 years ago it was actually about standard for DH bikes of the time. If you look at the specs of something like the '09 Glory, you'll see the head angle was around 65.5 for the DH0. The Specialized Demo was running a 65/64 head angle, etc etc.
So far I'm happy with it and it's still got a slacker head angle than my previous bike so it'll be a nice change all the same.

We're running the 9.5x3 shock from the Canfield in this frame. Since the Canfield was a 9" bike, I'm waiting on a new 400lbs coil as the 450 is a little firm, but still fine to test the bike out with. And we did map the leverage out on the PC, both in Excel and using linkage. We wanted a linear travel with a rising rate at the end. Our first single pivot bikes had a little trouble with blowing through their travel and relying too heavily on the shock, hence the linkage.

The bike isn't clear coated at the moment. In the pics it was raw, however I've since put something called Lanotec which is a heavy duty liquid lanolin oil on it which is excellent for stopping and reversing rust. It's what I've used on my other frames and they're holding up well with it.

I don't have any images of it moving throughout it's travel but I'm sure someone here has the Linkage application and can throw something together.
 
---Matt---

---Matt---

Likes Bikes and Dirt
So I got up to Mt Buller for the weekend for some trail building and managed to squeeze in a few runs on Sunday. I started out by easing into it by doing a run down Abom into Copperhead, followed by a run down ABOM. By the end of this run I wasn't holding back and was really enjoying the bike.
As with our previous frames, the high pivot eats bumps for breakfast. The slightly firmer than normal rear spring meant I needed to adjust my forks to compensate but there weren't any major issues with being over sprung.
I had no concerns with the head angle and was enjoying the maneuverability through the tighter sections of International and ABOM with the short rear end.
When hitting the wall ride at the bottom of international there was no sign of bottom out, however I only hit it once.

My favourite run of the weekend was down River Spur. Boosting some of those water bars at 60km/hr is great fun, as is drifting around some of the corners early in the track. While I managed to put one nice big flat spot in my back wheel, the bike felt extremely controlled and stable even over the rough stuff and I was thoroughly impressed with how it handled.

This is obviously going to be a biased review, however I feel very strongly that this bike is an improvement in all areas over the Canfield, especially in pedalling efficiency and cornering.

I can't wait to get back up to Buller on Boxing day. The trails are in MINT condition!
 
Nerf Herder

Nerf Herder

Wheel size expert
Nice work ... do you plan to take this anywhere re manufacture ... big step I know ... good luck whatever you do.
 
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