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Discussion Starter · #1 ·
Ok, who can give a lesson on Head Tube Angles for some of us novices?I'm building a bike with a 71 deg HT.I can't seem to get it to handle like I want.I checked all the angles on my other bikes,.,72,73.I know alot of other factors are relevant,but any rules of thumb?Stem length ect?
 

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The head angle on your current bike is a degree "sharper" than on your previous bikes, so it will handle a bit more quickly generally speaking. Is this what you're experiencing? As I've read 29er manufacturers use the steeper HA to help combat the longer wheelbase normally associated w/ going to a 29er from a 26er to make it feel not so sluggish. ON a normal 26" wheeled MTB a 71 HA would be twicthy as heck and found mainly on race specific bikes.
 

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LyNx said:
The head angle on your current bike is a degree "sharper" than on your previous bikes, so it will handle a bit more quickly generally speaking.
Er...he's going from a 72/73 setup to his current bike which is a 71, might want to break out that geometry book you've obviously been neglecting...;)
 

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Harmonius Wrench
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Examining the "whole" enchilada

Thanks for the recommendo, gitzit!

Anytime you want to define the handling of the front end of your bike, it's best not to get any more simplistic than looking at head angle/offset/trail issues. In reality, there is even more than that, but most don't want to get into it deeper because it makes their heads hurt! :p
 

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did 72-73 HA make you want a 71?

29erPilot said:
Ok, who can give a lesson on Head Tube Angles for some of us novices?I'm building a bike with a 71 deg HT.I can't seem to get it to handle like I want.I checked all the angles on my other bikes,.,72,73.I know alot of other factors are relevant,but any rules of thumb?Stem length ect?
And what/how do you want the bikes handling to improve?

frame geometry differences between the bikes?

Im using a FS frame with a 71HA reba 100mm and a spec resolution and really like the bikes handling..
 

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Discussion Starter · #7 ·
my prior bikes are Gunnar Ruffian/Km Fork 110 stem
Voodoo KM Fork 100mm stem
KM/KM Fork 100 mm stem
Fisher Reba 80mm/ 100 mm stem

current bike Redline Flight Redline Fork 100 mm stem

All of my bikes have been set up with basically the same components The MC just seems very twitchy when I get out of the saddle.It just feels like the front end is up to high.I'm running a flat bar with -5 deg stem.If I run no stack it gets better,I'm just wondering how far I should be dropping the bar?Is this because the bike is able to run a Suspension fork? What would happen if I put a shorter fork on it?This would also mess up the Geometry?
 

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The usual angles that are referred to in frame design are the head-tube (or fork) angle and the seat-tube angle. These angles are usually measured with reference to the horizontal. The typical range is from 68 to 75 degrees.
Quoted from Sheldon Brown's Site:
In general, bicycles with shallower, "slack", "relaxed" angles (lower numbers) tend to be more stable and comfortable. Bicycles with steeper, more upright angles (higher numbers) tend to be manuverable, but less comfortable on rough surfaces. Shallower frames tend to have longer wheel bases than more upright frames; bicycles with shallower head angles normally have more fork rake. All of these factors contribute to the riding characteristics cited.
 

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Harmonius Wrench
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All of my bikes have been set up with basically the same components
How about top tube lengths? I checked trail figures for a few of these bikes you mentioned and they vary too. It's more than just your components. I say this because you seem to be indicating you believe stem length and height is to blame???

The MC just seems very twitchy when I get out of the saddle.It just feels like the front end is up to high.
You feel this during slow speed, out of the saddle climbing/manouvering, or just whenever you get out of the saddle? If it's during slower speeds, could it be wheel flop? The feeling that the bars want to fall to one side or the other.

I'm running a flat bar with -5 deg stem.If I run no stack it gets better,I'm just wondering how far I should be dropping the bar?
This just tells me you're getting more weight on the front wheel and perhaps keeping it planted where you want it to go. You could have your stem at any height, but if you try riding no handed and you have a bit of trouble with the front wheel wanting to steer one way or the other, especially at slower speeds, this could indicate a bit of wheel flop.....maybe....it's just hard to say.

Is this because the bike is able to run a Suspension fork?
No. All the forks you have mentioned are either a suspension fork, or corrected for suspension, as are all the frames you mentioned.

What would happen if I put a shorter fork on it?This would also mess up the Geometry?
Well, that depends on what you mean by "mess up". It certainly will steepen both the head and seat tube angles, lower your bottom bracket height, and the final out come would eventually be determined by what offset the fork had.

By the way, the Flight Monocog 29"er has a trail of 76.2mm and a Karate Monkey has a trail figure of 73.6mm. This essentially means that the KM should be more prone to being twitchy than your Redline. Not much, but a little bit, and some folks can tell. This is what is leading me to the wheel flop idea, which happens when trail numbers get higher. I've got a Raleigh XXIX+G with a trail figure in the 80's and it really has a heavy handle bar going slow in corners. Wheel flops way more than my KM, or any other 29"er I have ridden. The good news is, you can get used to it. Humans are really adaptable, and in the end, it's just a bike.

Good luck!
 

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Ooops, my bad

Shouldn't try to do stuff like this when you've just come in from a pretty good, hard ride and are trying to get some food into your system.

Either case the 71 HA would make the bike feel more sluggish.

2xPneu said:
Er...he's going from a 72/73 setup to his current bike which is a 71, might want to break out that geometry book you've obviously been neglecting...;)
 
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