adding longer forks to old hardtail frame

swod1

Just wondering will adding 120mm forks to an old hardtail frame that I'm building up as a light travel xc bike alter the handling/geometry to make it un ride able?

The frame used to run 100mm forks but I've some nice 120mm air forks that I want to use on it.

I'm thinking once you set the sag on the forks there shouldn't be any real difference as the stance of the bike would be similar to 100mm travel?

Why I'm wondering is that I may need to add one of those bottom headset cups to take a tapered fork which will add another 10mm to the head tube.

does the headset need to be 44mm to use those headset cups, going to double check the size of this once I'm home later as it could make or break the build I'm thinking.

Anything else I need to check, got loads of parts for a bike so thought I'd build something up.

buddy_club

It wont make it unrideable, and you are correct that once sagged the change will be small. Head angle will be slightly slacker, BB slightly higher. Will probably void the warranty - but on an old frame i doubt the warranty is still in place.

To run the tapered steerer with an external bottom cup headset you will have to make sure you have 44mm ID head tube.

swod1

buddy_club wrote:

It wont make it unrideable, and you are correct that once sagged the change will be small. Head angle will be slightly slacker, BB slightly higher. Will probably void the warranty - but on an old frame i doubt the warranty is still in place.

To run the tapered steerer with an external bottom cup headset you will have to make sure you have 44mm ID head tube.

the frame is from a trek bike I bought back in 2014 but ended up stripping down to upgrade and the parts are now on my nukeproof mega tr.

I'm sure the head tube is 44mm currently has a semi integrated headset fitted will double check if not are there any other options for using a tapered fork?

.blitz

As you say, unless you run your spring pressure sky high some of that extra 20 mm will be used up in sag. Calculated out, if you add 10 mm to the fork's stroke your head and seat angles will be a bit less than 0.5 degree slacker and your bottom bracket will rise about 3.5 mm. A slacker head angle will calm the bike's handling slightly and moving your saddle forward by 5 mm or so will correct for the change in the seat tube angle.

Having said that and having done exactly the same thing myself I would not recommend it. If you're the kind of person who notices small changes in bar position or saddle position or crank length or tyre pressures, your short travel XC bike will feel like something Orange County Choppers have made. Although it will be better downhill, the peculiarly tipped-back riding position will be a drag on the flat and uphill you'll be climbing all over the bars in an effort to keep the front down.

You'll get used to it of course but be aware the extra travel *does* make a difference.

HTH

02gf74

2014 is not old. 1994 is.

apreading

Plenty of people have done it in the past. It was very common on specialized bikes a few years back, which often came with 80mm travel forks - many, many people switched them out for 100mm, even 120mm although the latter voided the warranty. My son says that his Hardrock is much better with 100mm forks than it was before with 80mm - much better for descending.

It wont be as good for climbing though. 20mm is not alot though so the difference wont be huge.

The Giant anthem for example used to come with 100mm by default but then Giant themselves launched the Anthem SX which was the same bike but with 120mm forks.

swod1

yeah, don't think it will be a problem to be honest. Just hope I can use the old frame with these spare tapered forks.

forgot to measure the headset tube, if this is smaller than 44mm then it will be a waste of time