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Old 01-15-07, 12:00 AM   #1
zaddpac
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What do you want in an extreme downhill bike?

Hey everyone. I am a college engineering student looking to design the best extreme downhill bike that I can. If you can give me suggestions as to what is most important to you in a bike that would be great. Also, if you have any innovative ideas that you would like to pass along I would be happy to listen. This is your chance to have a say in the downhill bikes that you want to ride so make the most of it and I will be sure to use your suggestions! Thanks.
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Old 01-15-07, 06:00 AM   #2
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First off please don't call them EXTREME DH bikes sorry just wanted to get that off my chest.

I want something that is built strong but not excessively heavy, around 19kg when fully built I would be happy with. Look at the Morewood Izimu for light strong bikes but they do get a tiny bit of lateral flex in the swingarm, which is not too uncommon in singlepivot bikes. This could be fixed with a swing link such as in the Cannondale Judge.

I want something that will last a fair while but not need heaps of service, this is where non super complex linkages come in, an Orange 222 from 2002 can still be working in next to new condition now with minimal maintenance all because of the simple singlepivot design. However the new Yeti 303, which should last a long time needs lots of maintenance due to complex rail system (very often you need to put oil in the oil nipple on the carts, for best ride do it before you go out for a ride that day). However it is possible to get reliability by making them well, I see Santa Cruz V10's in the old style frame still kicking very hard and they have a complex linkage.

A frame that will allow a little bit of tweaking by the user (ie bolts that raise or lower BB or change the travel from X to X) but don't go stupid, don't use this as an excuse to underdesign your bike. It should be like on the Specialized Bighit, you had two settings for the two different travel modes. I thought that systtem was great.

I want a bike with a slightly rearward axle path so it doesn't get hooked on the edge of bumps and I want the pedal stroke to not be too effected by suspension movements. Something like a high pivot single pivot is very nice to ride but they need a chain pulley slightly above the pivot point in order to prevent pedal feedback. Try to make it efficient to pedal but that can be masked with new shock technology, also I want a eising rate suspension system, this way it will absorb low impact small bumps but won't bottom out easy on a hard hit.

Now to the geometry.....
Travel: Around the magic 7.5-8.75 inch mark

Head Angle: 64.5 degrees with an 8 inch fork- Like a low front end aswell to help cornering

Top Tube (or virtual top tube) of arounf 570mm (I like a nice tight cockpit)

Wheelbase: 1190mm This is probably upper part of normal length, the longer the more stable at speed

BB Height: I can't give a value as different values for other parts of bike make this different, but i like a nice low bike as they rail corners liek it's no-ones business

Chainstays: 450mm make them short-middle length in order to make bike more flickable and turn friendly and manual friendly

Probably want 1.5 headtube aswell as that is becoming more standard


In summary, make a biek that is middle weight so it can be strong and STIFF, not a super travel bike like an M3 or V10, non hooking suspension, simple design so either something like a 224 or Judge but if you can make iot reliable I don't mind if you go crazy like the Demo GT's iDrive or Mongooses Freedrive or use a VPP like Santa Cruz and Intense.

Look at the Lahar Mk9 and the MorewoodIzimu, both of these bikes have very goo characteristics (you will never be able to make a bike like the Lahar with the stuff you have but look at the angles)

Last edited by Hopper; 01-15-07 at 08:22 AM.
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Old 01-15-07, 07:29 AM   #3
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It should be made out of concrete. Because concrete is heavy and when riding downhill you have gravity helping you. But make sure it is reinforced concrete. Anything else would be just silly. Also, no pedals or drivetrain is necessary. And a seatbelt would be good.
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Old 01-15-07, 08:08 AM   #4
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junk yard has a good point
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Old 01-15-07, 08:14 AM   #5
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i also think two kickstands. so you can balance the bike to the left or the right, depending on the situation. but, they need to be EXTREME kickstands.
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Old 01-15-07, 08:23 AM   #6
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Ummmmm what was the point of your post Junkyard? The guy is asking a serious question for proper work and if you want to be a dick about then don't write anything and keep your comments to yourself.

I'm going to make give a basic version of what I want. Low centre of gravity, lowish BB, raked head angle (around 64.5), low front end, seat tube should also be pretty raked, mid to long wheelbase with a short chainstay. Also not overbuilt and not going to get hooked up in bumps. Also a better rider may also help me........
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Old 01-15-07, 08:38 AM   #7
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if you want to be a dick about ...
No name calling please.
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Old 01-15-07, 09:00 AM   #8
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Hey chelboed nice contribution to the thread (I know I'm being hypocritical as this post has no immediate help to thi thread but hopefully it will get more serious answers). If someone starts a thread purely asking advice and straight away someone makes fun of them, in my opinion they are being a dick. This guy is new and wants our help, it is obvious that Junkyard knows nothing about what he wants in a DH bike probably due to lack of experience BUT he wants to show he is a big player on teh int3w3bs so makes stupid jokes to show how big he is.

Sorry I shouldn't call him a dick, that is insulting to men everywhere, he is trying to lower the value of a thread that is of no bearing to him. As for you trying to defend his actions...... maybe you should stop trying to get moderator status, stop defending him, stop further insulting this guy through secondary means and add something of value to this thread.

*Gets off soap box* ahhh feels good to do that
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Old 01-15-07, 09:15 AM   #9
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Ok, this has been settled nicely, just cease with it.

Also Junkyard, if you have nothing useful to contribute in a thread do not post at all in it. What you put down there can get a person seriously hurt or killed.

For me:
low bottom bracket height

a slacker geometry

150mm rear spacing

a design that is easy to maintain.

a common shock stroke and eye to eye so that any shock can be run
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Old 01-15-07, 09:28 AM   #10
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I don't know anything about DH bikes, but I would like to see your results!
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Old 01-15-07, 10:06 AM   #11
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Ummmmm what was the point of your post Junkyard?
my point was to be a dick.
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Old 01-15-07, 10:14 AM   #12
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just wondering why people are attacking junkyard while, at other times, certain individuals appear to be given free reign. is this because some people can take nice photos?
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Old 01-15-07, 10:16 AM   #13
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just wondering why people are attacking junkyard while, at other times, certain individuals appear to be given free reign. is this because some people can take nice photos?
maybe i should get a camera.
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Old 01-15-07, 10:23 AM   #14
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Ok, this has been settled nicely, just cease with it.

Also Junkyard, if you have nothing useful to contribute in a thread do not post at all in it. What you put down there can get a person seriously hurt or killed.

For me:
low bottom bracket height

a slacker geometry

150mm rear spacing

a design that is easy to maintain.

a common shock stroke and eye to eye so that any shock can be run
hurt or killed?
this guy is an engineering student, he should ask an engineering professor not an internet bike forum.
It's not like you're posting specs from a ****ing 4 link patent.
here's my idea, test the piss out of the welds you make before you put a human on it. presumably you can get access to some machinery at your school for this, if not, don't build a ****ing downhill bike.
BTW, putting a homeless person on it does not count as "testing"
and if you're not selling it go look at all the patents that specialized and ellsworth have, I doubt they'll come after you for infringing.
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Old 01-15-07, 10:31 AM   #15
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Quote:
Originally Posted by Hopper
Ummmmm what was the point of your post Junkyard? The guy is asking a serious question for proper work and if you want to be a dick about then don't write anything and keep your comments to yourself.

I'm going to make give a basic version of what I want. Low centre of gravity, lowish BB, raked head angle (around 64.5), low front end, seat tube should also be pretty raked, mid to long wheelbase with a short chainstay. Also not overbuilt and not going to get hooked up in bumps. Also a better rider may also help me........
a) I agree with both points

b) A little variation on your preferred build. Some downhillers like a long chainstay for stability at high speeds.
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Old 01-15-07, 10:31 AM   #16
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Quote:
Originally Posted by magic8ball
hurt or killed?
this guy is an engineering student, he should ask an engineering professor not an internet bike forum.
It's not like you're posting specs from a ****ing 4 link patent.
here's my idea, test the piss out of the welds you make before you put a human on it. presumably you can get access to some machinery at your school for this, if not, don't build a ****ing downhill bike.
BTW, putting a homeless person on it does not count as "testing"
and if you're not selling it go look at all the patents that specialized and ellsworth have, I doubt they'll come after you for infringing.
besides, he was looking for EXTREME. a concrete bike with two kickstands is SUPER EXTREME.
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Old 01-15-07, 10:34 AM   #17
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Quote:
Originally Posted by mx_599
just wondering why people are attacking junkyard while, at other times, certain individuals appear to be given free reign. is this because some people can take nice photos?
I am pretty sure I remember lots of people attacking the dick you are referring to. It just got to the point where he ignored the comment and just became a bigger dick.
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Old 01-15-07, 10:38 AM   #18
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Quote:
Originally Posted by junkyard
a concrete bike with two kickstands is SUPER EXTREME.
I concur..
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Old 01-15-07, 10:54 AM   #19
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A lot of the ideas thrown about already exist in something I can already get. Hopper, thanks for giving the OP a very thoughful reply.

If I were to spec my 'ideal' "extreme downhill" (whatever that means) bike, it would have:
  • High bottome bracket (for clearance)
  • Low center of gravity (all of the suspension/linkage/whatever weight concentrated low in the frame)
  • 12" of travel front and rear but still very pedalable (hey, I'm talking ideal here)
  • Changeable axle path by moving pivot bolts (rearward for courses with a lot of square-edged hits; more vertical path when that's not needed)
  • 64 degree or slacker head angle
  • Longish swingarm (like the original Rotecs) that concetrates cockpit center to where the front end can be weighted on bermless corners (like a motocrosss bike)
  • Gearbox drivetrain; but I don't want the box to be a stressed-member part of the frame (like the V-Boxx protos I've seen)
  • No seat tube/seatpost; but a long, narrow seat that I can slide way up on to weight the front
  • Oh, and still as close to 40# as it can get (yeah, right!)

Brooklyn actually made a TMX prototype once that was very similar to this, except it was like a 50#+ bike. I'm looking, I guess, for an RM125 that pedals
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Old 01-15-07, 11:09 AM   #20
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I'm looking, I guess, for an RM125 that pedals


you kill me...you're the best!
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Old 01-15-07, 12:02 PM   #21
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Look, jerk. No one likes when some wise-ass shows up talking about their concrete bike ideas. Keep it up, and I'll impale you with a Wii controller.

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Old 01-15-07, 12:03 PM   #22
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I would like to thank everyone who took time to answer my questions and I will be sure to use all of your suggestions (excluding the concrete bike idea). Also, I am sorry to anyone who decided that my forum was a waste of time and I should just go "ask an engineering professor." This is some preliminary research in order to design a bike that the people would like, and therefore, a professor who does not ride would not know how to answer my questions as well as people who do ride can.
Thanks again to those who answered honestly and with good intentions. To those who just wanted to poke fun at my forum post, you should think about why you are picking on a person online instead of actually doing something productive.
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Old 01-15-07, 12:15 PM   #23
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"something productive"... such a subjective statement. why would you assume that i'm not doing "something productive"? because of a couple posts on your engineering project?

i know exactly why i did it. i was in a bad mood and it made me feel better. how's that for "something productive"?
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Old 01-15-07, 12:37 PM   #24
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Well no one can accuse you of dishonesty haha
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Old 01-15-07, 01:01 PM   #25
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"something productive"... such a subjective statement. why would you assume that i'm not doing "something productive"? because of a couple posts on your engineering project?

i know exactly why i did it. i was in a bad mood and it made me feel better. how's that for "something productive"?
is your avatar the scene where he is comparing business cards? hahahaah
i need to rent that again. i need some body care tips from the opening scene.
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