The Pro's & Con's of changing Fork Travel on a MTB

[Clinton - theCOW]

I gather most bikes/frames are designed around a certain geometry for XC/Trail/DH etc.

 

Trying to keep my girlfriends bike's (Spark 35 - 26") fork travel the same with a better fork since she's happy with the 120mm travel but due to it's age, it's working out to be a real challenge. She's pretty light on the existing fork, don't think she even uses 80mm of travel.

 

What are the effects of putting a 100mm travel fork on the bike?

 

The things i've worked out would change:

• BB would drop minimally (doubt there'll be any noticable difference)
  
• Headtube angle will increase (more responsive)
  
• I'd need to work out how to keep the bar height and reach the same, since i gather it would drop by about 20mm.
  

 

Anything i'm missing here that i should be thinking of covering before making the change?

 

I'm assuming as well with such a small change, there shouldn't be any huge stresses on the frame or mounting points etc due to the headtube angle change?

 

Any advice would be appreciated.

[Capricorn]

bikes tend ot have a max fork travel rating as opposed to a minimum. So you are golden there wrt frame stresses and similar concerns. Also nailed the effects of decreasing the travel on BB height and HA.

if you want to keep the bar height the same, get a bar with 20mm rise if the steerer is too short. If there's still sufficient steer left, add spacers and use current bar.

 

Bit of a pity you not getting a fork with travel adjust. Better to have and not need than to need and bla blah...

Edited June 6, 2013 by Capricorn

[MrJacques]

What is the new fork you want to put on the bike? Some reba's (and maybe other rockshox and fox?) have a spacer you can take out to increase travel from 100mm to 120mm, so you might be lucky and buy a 100mm fork and take out the spacer and not have to make other changes.

[Clinton - theCOW]

Capi - the lil Mrs loves the technical stuff but ain't into big rocky sections yet & i'm a weight weenie. Steerer is un-cut so i can play with that to keep her at the same height, don't need her getting any faster, i need to keep up with her & not get dropped

 

Got a 2011 SID, looked at the SRAM website and it's pretty easy, just need to get oil etc which isn't a bad thing cos it doesn't seem like servicing a fork is that difficult & i prefer to know what's been done. I've been told tho that since 2009, most Reba & SID can be adjusted but if you look at the YouTube Video on the SID 2011, they mention 2 different chassis options, round the 14sec mark, hence my reluctance to open the fork right now.

http://www.youtube.com/watch?v=jX6DYNCrYjs

 

I'm going to see if she likes the shorter travel, if not, i'll open it up and check if we can extend. Failing that, back to the Reba SL where she's happy

[RockCoach]

You say steering will become more response. She might find that twitchy.

But one thing for sure - she will be more nervous going downhills.

[DR ◣◢]

You say steering will become more response. She might find that twitchy.

But one thing for sure - she will be more nervous going downhills.

 

Exactly. Rather take your time and get another 120mm fork.

 

As for her not using more than 80mm travel... Setup the sag, compression and rebound properly and her ride experience will also change.

[Clinton - theCOW]

You say steering will become more response. She might find that twitchy.

But one thing for sure - she will be more nervous going downhills.

 

The twitchyness shouldn't be that bad, stem is 100mm & running negative (if Neg is more horizontal than pitched) so almost 110mm stem.

 

From all the geometry research i've done, the Spark geometry should still be more "relaxed" than my Ghost and the Anthem (thought i'd check Giant's Geo), so she should be fine.

 

As a light weight, even with the + & - air pressures at 50psi (- marginally less), she doesn't use the fork that much.

 

Sag & setup also done on the rear and she seldomly uses even 80% of that.

 

I'd like to think she's just a well balanced rider and distributes her (little bit) of weight well