Let's Discuss Head Tube Angle

[Carbon_Dude]

I've seen some recent discussions in other threads about head tube angle and thought it would be productive to have a separate thread for this topic.

For me, head tube angle is one of the most noticeable characteristics of frame geometry.  I have an IP-057 hard tail which for me has very good, well balanced, geometry and an IP-036 which, even though it has a longer wheelbase than the IP-057 feels shorter due in part to the head tube angle.  I recently rode a Giant Trance that for me, had too slack of a head tube angle.

For comparison purposes here are a list of bikes I have ridden in the last year or so:

IP-036 29er HT angle = 71 deg (100mm fork).  Nimble but feels like it has a shorter wheelbase than
IP-057 29er HT angle = 69.5 deg (100mm fork).  Good balance between being nimble but also stable.

Scott Scale HT angle = 69.5 deg (100mm fork).  Rides very similar to my IP-057
Scott Spark HT angle = 70.1 (100mm fork).  Rides very similar to my IP-036

Giant XTC Advanced 27.5 = 69.5 deg (100mm fork).  Good balance, nice bike if I wanted a 27.5 wheel size.
Giant Anthem X Advanced 29er = 71 deg (100mm fork).  Nice bike, similar feel to my IP-057.
Giant Trance (27.5)  HT = 67 deg (140mm fork).  Probably a great downhill bike but too slack or stretched out for the XC/trail riding that I do.  Just not the geometry I prefer, the bike felt like it would roll over anything but was slow feeling.

I've also ridden a Santa Cruz which felt more like the Giant Trance but I need to go back and check which model it was.

[carbonazza]

The Lefty on my 256 is 10mm off from the AC distance defined on the geometry.
Making it in theory steeper than it should.

I'm still not convinced of the effects of small variations in the chainstay, the offset of the fork, the angle of the head tube/seat tube, etc. 
Even if Cannondale market all this massively on their FSi for instance.

However if a brake lever is just few mm lower on one side, the seat is a hair lower, etc. after a fall for instance, I notice it immediately.
Like if someone change, even slightly, the position of your car seat or driving wheel.
So small things matter apparently.

The problem, is that it's very difficult to isolate a change like the head tube angle and be sure of its effect.
Testing the same bike with different fork length could be a good test, even if the whole frame angle change.

[RS VR6]

I have a Pivot that originally came with a 140mm fork. I swapped to a 150mm...and to run a taper fork...I had to use an external lower cup to accommodate the larger lower bearing. That lower bearing is 12mm tall.

I know that I won't know the true change in height without measuring the a-to-c of the forks...but I'm just guesstimating a 20mm increase in the front end. 20mm's will roungly slacken the HTA by 1 degree. I can't tell the difference in handling.

Sometimes I swear that a lot of what you feel on a bike is more perceived than anything else...especially flex.

[RS VR6]

So here is something I've been for wondering for while on geometry.

How do these Chinese manufacturers decide their geometries? The big brand guys have their designers come up with a design...make prototypes...and have their pro riders test them and provide feedback.

I've seen some pretty odd geometries on some Chinese carbon frames. Some don't even provide geo numbers. One of the first things I did was measure my frame to see that if it is consistent with the numbers that were given.

This was another reason it took me so long to decide on a Chiner frame. I had no idea where these geo numbers were coming from.

The 256 looks close to a Open 1.0...but it wasn't 100%. The HTA is different. There is a reason why Open did their HTA at 72 degrees. Wouldn't a random change throw off the handling of the bike to what Open intended or would you not know any better since you've never ridden an Open?

Do any of the guys from the trading companies truly ride bikes? I mean really ride as a roadie or mountain biker. I would think that the engineers and designers at Specialized or Cannondale are all cycling enthusiasts. Even the guys/gals that work at bike shops...they all love bikes...or else they wouldn't be working there. I worked for a bike shop and then a local bike builder over the course of a year...for crap pay just to see what its like to be on the "inside".

Maybe I'm just rambling...

[Carbon_Dude]

Both of my Chiner frames have geometry nearly identical to Scott bikes so I think they just copy existing brand name frames.

[Digi]

I was holding out on a frame choice for a while because I couldn't find anything with a steep head tube and a short chain stay.  I started off with a FR-211(IP-033) but decided the 450mm chain stay was too long and moved to an IP-256SL.  There is the Orion 29er but the standover height seemed a bit high.