Change forks

[busymate]

Hello,
I would like to change the forks i have on my mountain bike. They are the suspension type but really heavy. I would like to replace them with something lighter. How do i know what im looking for with regard to size and compatibility, when looking at ebay or private adds for forks? are there certain consistent measurements i can take..
Phil.

[xerxes]

Assuming you have a threadless headset. First you need to know the head tube width, is it 1" or 1 1/8"?

Unless you want to change the handling characteristics, you want the same amount of travel, typically 80, 100, 120, 140 or 160mm.

If you are buying used, you'll want to know how long the steerer tube length is, it must be at least as long as your existing one. If it's longer, it's not a problem, you can cut it down.

Be careful if you're buying used, if the forks aren't in good condition and have worn seals etc. they can be expensive to put right.

Even expensive short travel (80 to 100mm travel) XC forks by RockShox, Fox, Marzocchi, Manitou etc. are still pretty heavy, and typically weigh well over 3lbs - more than a lightweight hardtail frame. The weight goes up from there for lower cost forks and more robust, long travel, downhill forks are also heavier.

[busymate]

Ok,
1/ i take head tube width to be the diameter of the tube where the handle bars are / head set..

2/what is the amount of travel? and what do the numbers you refer to mean?

3/ Can you confirm exactly what the steerer tube is? and is that different from the head set tube?

seals will not be a problem, because i just want the standard non suspension type, hopefully they will fit..

Yes the main reason for change is the weight they are ridiculously heavy in comparison with the frame. Plus all this chopping, changing and questions are all part of the learning process really. So after i while i may not remain a complete noob// plus save on cycle repairs for the whole family. So as long as you lot are happy to answer my questions im happy to ask and learn.
regards phil.

[xerxes]

1/ i take head tube width to be the diameter of the tube where the handle bars are / head set.. - Yes.

2/what is the amount of travel? and what do the numbers you refer to mean? - This is the distance the suspension can travel, from fully unloaded to the stop, or the distance the fork can shorten by in order to provide the suspension.

3/ Can you confirm exactly what the steerer tube is? and is that different from the head set tube? - The steerer tube is the one that comes up through the frame, to which you attach the handlebar stem.

seals will not be a problem, because i just want the standard non suspension type, hopefully they will fit.. - In which case, you need to get rigid forks that have roughly the same axle to crown height as your existing suspension forks when loaded, otherwise the handling of the bike will change. Shorter and the steering will be quicker and perhaps too twitchy, longer and it will be slower and lazier.

Axle to crown height would be (B) in this diagram:



© is the rake, and it would be best if that is similar, as that also effects the handling.

[busymate]

superb explanations..
the rake/ the angle at the spindle holder really makes that much difference?

[xerxes]

Tricky one:

http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_geometry

http://www.dclxvi.org/chunk/tech/trail/

http://www.sheldonbrown.com/rinard/forklengths.htm

http://www.phred.org/~josh/bike/trail.html

[busymate]

that lot is going to keep me quiet for a while...
also maybe, i think the noob could be in over his head.
phil