For example would an equivalent 650b bike have say a 1deg steeper head angle than the 26″ version? I expect that larger wheels are more stable, harder to turn and necessitate longer stays and so the head angle would be steepened to accommodate?

I would agree with that but as there seems to be not much difference between 650b and 26 then I should imagine it’s almost the same frames.

No

Well there’s a formula; wheel radius, head angle and fork rake = trail.
so if you want the same trail and you add 25mm to your rim+tyre diameter, fork is same rake, you’d adjust the head angle by close to a degree. But in reality if you can change one aspect you may want to do other things so it’s better to use rake and HA or all 3 to balance a bike out the way you want it. Rule of thumb, no. Usually it’s trial and error plus experience, or copying someone else’s.

no, it’s not a road bike 🙂

Not as such, there are quite a few other factors that come into play ( 65 degree ha on a 29er anyone 😉 )

( 65 degree ha on a 29er anyone )

Sounds like something some of the residents would go for 🙂

Interesting jameso, thanks.

I’ve got a 29er with a 66.5degree head angle.And one with a 72 degree head angle. They both handle fine.

There is a mathematical formula that predicts whether the bike will ‘flop’ or not (i.e. it’s tendancy to just fall over when you contersteer into a corner and stay there untill you turn the bars harder to bring the bike back upright).

There’s also the fact that unlike 26″ forks there are still a lot of different offsets on 29″ forks, so one bike may be designed arround a steep head angle and a short offset, another arround a slack angle and larger offset. Both would give similar handling in a straight line, as the trail is the same, but different in a corner.

Or you could just wack a degree on for each wheel size. IIRC Trek (and therefore presumably everyone) work to a tolerance of +/- 0.5deg between head and seatube angles, so it’s concievable that two identical bikes off the shelf could well be further out than the difference between two designs. (i.e. design is 68deg, one could be 67.5, the other 68.5).

Or you could do what Brant alegedly did with the 456, lie through your teath about the geometry and just post up some numbers people want to hear and vaguely describe what people think the handling characteristics should be.

^ 😆