Anyone have any problems running a 120mm fork on a bike designed for 100mm? I want a bit more travel on my Anthem but don’t know if the increased leverage on the frame would be troublesome.
Many thanks
Tim
Pure Mountains

depends on the frame and the fork as some forks have a longer longer axle to crown for the same amount of travel. although my hardtail was really designed for a 120mm fork i’ve been running a 150mm fork (marzocchi so the axle to crown length is greater than other forks) without any problems. one of the fs bikes i had also was designed for 130mm up front and i ran a 150mm fork with no issues (again another marzocchi with a long axle to crown length). regarding frames – a strong frame such as one designed for AM/FR/DH will be able to handle the extra load bearing stresses placed on the head tube by a longer fork, but frames designed for cross country wont be able to handle the extra stress. your anthem frame is well engineered so i think you should be ok, albeit the head angle will become slacker so during climbing the steering will tend to wander a bit more but it will descend better and be more stable at high speed. onceyou’ve fitted the new fork you may need to re position the bars, brake levers and shifters. you may also need to readjust your saddle angle/position and may need to change to a shorter stem.

Quite of a few of the Loco Racing endurance team ran 120mm forks on their Anthems the last few years as it made them more stable and decend better.
Both Sids and Fox 120’s.
Nobody had any issues with the frames and covered thousands of miles with quite a few podiums 😉 so they weren’t hanging around either 😀

I have 120mm forks on my anthem I think its quite common.
I am going to drop them to 100mm though as I currently have 3 120mm bikes.

Andy

Yep, yep and yep. Well documented 120mm forks on Anthems, remember to adjust your setup for the 10mm extra height, I.e. saddle forward, and dipped, drop a spacer on the steerer, and adjust your body position on climbs.

You’ll barely notice it really on climbing 🙂

Surely the increase in overall fork length going from a 100 – 120mm travel fork is fairly small. The force exerted on the head tube will depend on the overall length of the fork from the bottom headset bearing to the tyre contact patch. Maybe around 800mm? So even fork 40mm longer is only around 5% of the overall fork/wheel length.

I’d say the increase or decrease with different fork lengths is far less than the variation with rider weights. So unless you are a heavy rider absolutely nothing to worry about as far as leverage on the frame.

But then I’m not an engineer so others may know different.

irc – you’re probably right there, in truth its probably a combination of what we both said. it probably also makes more of a difference on a hardtail than a full sus frame…

just as a reference – the marzocchi 66rc fork i have is currently set at 150mm – fork lenght is 572mm
the new marzocchi 55cr if set up for 150mm travel has a fork length of 536mm
so i think it can make a difference.. 😀

Thanks for posing this question as it s exactly what I have in mind for mine.

Thanks everyone. Very helpful and encouraging.
Tim
Pure Mountains