Lets talk about Head Tube angles

michael whiteman

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Great picture Jerry. It looks like you head tube angle is greater than DieselTechs. I imagine your bike doesn't turn as quick and requires less concentration to keep it going straight at slow speeds. This is what I'm hoping to obtain. Like I said, I need to change my head tube diameter anyway.
 

Sidewinder Jerry

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Great picture Jerry. It looks like you head tube angle is greater than DieselTechs. I imagine your bike doesn't turn as quick and requires less concentration to keep it going straight at slow speeds. This is what I'm hoping to obtain. Like I said, I need to change my head tube diameter anyway.
Are you a threadless head tube? Was hoping that maybe stem alterations might help you.
 

Cannonball3

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Rake and trail is very important it determines the stability of a bike,the more trail the more stable. I built a recumbent that had a good bit of rake. Turned out to be very unstable. To look at it you would think it easy handling but the trail was less than 1”. I always shoot for around 3”, especially important on a high speed build. Trail is the difference of a straight line thru the head/fork tube and a plumb line thru the axle. Draw them on the floor and measure them. Thats the determining factor in handling.
 

rusty.western.flyer

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@DieselTech hit the nail on the head. It's caster. Just like a shopping cart always turns around and goes forward when pushed backwards - except the "casters" do this with the axle being in front of the turning pivot. Between putting the axle in front of the fork (pivot) and having the head tube angled back, it both keeps the bike in an upright position as well as keeping the wheel straight. It'sd a phenomenon discovered early when we went to safety bikes.

I learnt my lesson on this in 2011. We took the entire sub-frames, drive train, and pedals from an e30 (1988-ish BMW 3) and stuck the whole lot in a 1972 BMW 2002 for the $2011 Grasroots Magazine Challenge (oh and a JY Volvo turbo on the i6, hehe). Well, the lump was entirely too long when using the e30 caster angles, the engine literally stuck 3" out of the front of the grille. We moved the front frame back, but left the strut tops where they were, creating a slightly less favorable caster (basically "straight up"). Since we finished the car midnight before the challenge, we had no time to correct it, but it was the weirdest thing to drive. If you let go of the steering wheel, it would intermediately turn itself to the lock position to whatever side you were favoring. We couldn't even flat tow the stupid thing - imagine competing in a drag race and auto-x with it hahahaha.
 

DieselTech

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Great picture Jerry. It looks like you head tube angle is greater than DieselTechs. I imagine your bike doesn't turn as quick and requires less concentration to keep it going straight at slow speeds. This is what I'm hoping to obtain. Like I said, I need to change my head tube diameter anyway.
How was you planning on welding your head tube back on? Mig, Tig, or stick welder?
 

michael whiteman

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My steering tube does have threads Jerry, but currently I have it half assed into a head tube that is too large. This all needs to be changed. I will rake the new headtube when I weld it on.

Cannonball3 understands the geometry. There are some good videos that explain this very well. Unfortunately for me I have a suspension fork with zero trail so I need to consider the angle a little differently.
 

michael whiteman

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I found the recommended Head Tube Angle on a mountain bike is 62-73 degrees............... Road bike 72-74 degrees.
This confuses me. I would think one would want a mountain bike to turn more quickly than a road bike. For this to happen the steering tube needs to be more vertical but the numbers shown are smaller, not larger.
 

Cannonball3

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I found the recommended Head Tube Angle on a mountain bike is 62-73 degrees............... Road bike 72-74 degrees.
This confuses me. I would think one would want a mountain bike to turn more quickly than a road bike. For this to happen the steering tube needs to be more vertical but the numbers shown are smaller, not larger.
Are they not figures from vertical of the top of the neck. The MTB would be less from vertical than the road bike, right ?
Hence quicker steering for the MTB as its closer to vertical? I checked the R/T on my Honda NC700x rake is 27 degrees trail 4.3” this bike is so stable it hands of easily due to the large trail. Still I was surprised by the small rake figure.
 

michael whiteman

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It appears that Honda measures the rake from the fork to the vertical plane at 27* Bicycles measure from the fork to the horizontal plane. Hence your 27* in bike terminology would be 63* which make perfect sense. Your tremendous trail at over 4 inches is what gives you the stability without all the "flop" experienced with chopper front ends.
 
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