With my luverly new Mojo HD 140 soon to arrive (next week maybe!), I’m now pondering what to do with my front end. Have a shiny BOS Deville fork awaiting it’s rightful home, travel on this is 160mm.

Obviously the Mojo is setup for 140mm up front to match the 140mm out back, and I can get the Devilles reduced to do this, but what’s the likely result if I leave ’em at 160mm? Headangle with a 140mm fork is 68°, would this get steeper or slacker (slacker, right?)?

HA depends on the A to C of both forks rather than the actual travel.

If both forks have the same A to C then no change

if it’s different roughly 1 deg slacker HA with every 10mm longer

Is that 68 degrees sagged or not? If it isn’t, then the head angle will probably be 68 with 160mm forks sagged, but it obviously depends on personal preference.

I wouldn’t change the travel.
The frame isn’t intended to use a 140 fork, iirc the 68 ha is derived from a 150 fork, presumably Fox 32’s.
Obviously as Orangista says, the a-c is the important figure, so you need to compare the a-c of Fox32’s @150 to the Devilles .
I’ve got Rev 150’s on mine, which are a touch longer than the Fox’s, (I’m guessing 67 ha), and it handles great, albeit with a real low bb- which has it’s plusses and minuses- I certainly wouldn’t want to use a shorter fork.

Only reason I havent got 160’s is because of the weight, but if I could have afforded the Bos’s I probably would have given those a go.

Coolio then, will find out the A2C of both, most likely shall stay at 160mm… can always adjust the HA a touch with my fancy Angleset if need be! I didn’t twig that Ibis spec’d a 150mm for for the HD140, good to know 🙂

With similar travel front and rear the sagged and unsagged head angles will be almost identical. A longer fork will slacken things off slightly.

Just been looking at this myself. As said above, the important measurement is axle to crown which is measured un-sagged. If you look at the detailed specs of your frame it should say somewhere what the axle to crown measurement is to give 68%. General view is 10mm extra = 1 deg extra which could make the bike feel like a dog.

RS Pike 140 A to C = 518mm
RS Rev 150 = 529mm
Fox 36 Float/Talas = 545mm
RS Lyric = 545mm

So in theory if your frame was designed around a Pike/Rev 140 and you used a Float it would decrease the head angle by almost 3 deg.

With the right length fork it will handle, with the wrong length fork will make it handle crap.

Just try it first.

b r – Member

“With the right length fork it will handle, with the wrong length fork will make it handle crap.”

Aye, but right length can be a range, there’s plenty of bikes out there that work well at different fork lengths.

Shame the BOS height change is permanent.

i thought it was 1 degree = 25mm ?

With the right length fork it will handle, with the wrong length fork will make it handle crap.

If that was true then you’d only be able to make a bike handle well with rigid forks, cos they’re the only ones that have a static length. They work fine with all sorts of lengths, lots of factors in play.

If that was true then you’d only be able to make a bike handle well with rigid forks, cos they’re the only ones that have a static length

Not true. Manufacturers specify a particular length and travel of fork because they have spent huge amounts of time arriving at the right geometry that gives the bike the characteristics they want through the largest possible set of riding circumstances.

There is definitely a range, but an extra 30-40mm in A to C would totally change the bike, and probably invalidate the warranty

“Characteristics THEY want.”
Some people might prefer it different?

i thought it was 1 degree = 25mm ?

same here. I usually work on 10mm = 0.5°

Yup I was along the lines of 25mm is roughly equal to 0.75deg unsagged