I’m a bit of a Womble when it comes to bike parts I’ve upgraded from and have enough in the shed to build up a second 29er. Going to go Hardtail as I’ve been offered a really good deal on a 2019 orange clockwork evo 29 frame. My spare forks are 160mm pikes with a TF coil conversion in them so I can’t drop the travel. I know that this will knock approximately 2 degrees off the 67 degree head angle (clockwork evo is designed around a 120mm fork). I’m fine with that and not too fussed about it raising the bb a bit but does anyone know roughly how much it will slacken the seat tube angle by? The frame isn’t the longest so I’d rather not be slamming the seat all the way forward. I know the general rule of thumb is -0.5deg off the HA for every 10mm increase in fork length but I’ve never heard a similar formula for seat angle. I just want to be able to ride it up hill without popping involuntary wheelies all the time.

The geometry calc I always use…
https://bikegeo.muha.cc/
Bung the figures in there and have a play

Is the frame designed to be strong enough for forks that long?

I know the general rule of thumb is -0.5deg off the HA for every 10mm increase in fork length but I’ve never heard a similar formula for seat angle.

It’ll be exactly the same change.

Unless (as per Kelvin’s post) your head tube snaps off 🙂

Given that your HA and SA are very much linked, I’m sure you can do the maths…… until your headtube snaps off as above 😉

The extra stress from 40 mm long forks won’t snap your head tube off if you’re just riding along. It’ll be less than a 10% increase in stress. However, if you put burly forks on a lightweight XC frame and bash down rough descents, jump silly things, etc, then you will probably break the frame. You would also break it if you did that with 120 mm forks. It’s how you ride it that will break it.

Leverage of longer forks is not significant – they are compressed at highest impacts for instance.

It’s the anticipated style of riding that matters.

Thanks guys, the head tube won’t snap off from a longer fork. The bike won’t be getting hard use, I’ve got a big bike for that (but even on that, I’m no where near rad or heavy enough to be ripping off head tubes) . It’s going to be a budget mile muncher, I’m just using the parts I’ve got lying around the shed.

I’ll just suck it and see, it it’s horrible to climb on then I’ll put the forks up for swaps I guess.

I had a Transition Bandit which was designed around 140mm forks I tried it with 160mm forks it descended well but was a terrible climber so went back to 140mm forks so 160mm on a bike designed around 120mm travel would be a very poor climber I would of thought.

I run a Kona Kula (sold with 100 mm forks) with 130 mm Fox 32s, It climbs just fine.