So I am back to the eternal "is it time for an upgrade?" point in life. I am kind of struggling to get my head around the longer + slacker + steeper trend that all bikes seem to have. When I get off road I'm generally riding disappointingly flat short trails made up of berms and jumps. They are mostly hard pack and dust, with some erosion and roots and barely any rocks. When I am lucky enough to ride the gnarly stuff I have my nomad and one day I might even finish rebuilding my 951. So I don't really see a why on a shoe travel party bike I would want/need these new angles. So help me out...
Going from about 67 in he head tube to 64...am I going to be driving a bus? Or will it retain or even enhance aggressive cornering and lip popping goodness?
I currently rock a 74.9 seat tube angle which at first I felt was way too upright. The seat often got in the way when I was pretending I could throw sick tricks on the jumps. The newer option is offering 76.5 of upright erectile function!
Yours in a confused state of affairs...
Head Angle in isolation is a tricky one to judge. Really need to look at more of an overall picture.
3deg slacker head angle will increase front-centre (distance from BB to front axle) quite a bit, so if your chainstays don't increase a proportional amount your weight distribution on the bike will become more rearward. This is also exaggerated in a change to 29er, as the bigger wheel means a taller fork, which means more stack height, which means for the same reach dimension the bigger wheels have the front-centre grow even more than just the slacker HA suggests. And if you're also 'sizing up' on reach, this effect becomes very pronounced.
If you have a slack-slack HA like 64 degrees and the bike has short-shortish (~425-430mm) chainstays*, it can mean you have to ride a pretty aggressive/forward position if the ground surface is even a little bit loose. Some people like this setup as the bike feels reactive and is easier to loft the front. Others (me) don't like it as it sometimes feels like you have to ride in a permenant push-up position and the front can "push" if you get lazy. It can tend to transfer more of the force from the back wheel through bumpy/rocky terrain too, though aggressive riders can avoid this by just popping the back up over obstacles. Longish-long chainstays* (~440-450mm) generate more front-end traction through corners (particularly on flatter/loose corners as the front wheel is better 'weighted') and offer more stability over bumps/rocks at speed, and also can allow to ride slightly more centrally/upright over bumps (larger 'window' to move your body-weight around in as more input is needed to alter the front/rear balance)
I am very shit at jumping, but longer chainstays are somewhat harder to jump, in that until you're going fast it can make the front feel a little held-down and tend to suit jumps that are more fast and long, rather than short and steep. On the faster jumps the extra stability is a perk though.
IMO, overall I'd look for something around 65deg HA, with medium-sized chainstays. 64deg HA is effective for plowage but goes past anything that could be described as "responsive" or "flickable" (IMO, and prepare for the possibility every following comment will wholeheartedly disagree with this comment), unless paired with quite long chainstays and then the whole bike likely won't feel particularly playful (though will be super capable and fast AF). Super slack/long bikes are sort of victims of their own success in that they're so capable, modest trails can feel quite banal at times.
*I'm basing short/long chainstay feel assessments of a guesstimate of you being around 6' tall?
