Rigid Fork size advice

chris_bass

Hi

I am considering changing the fork on my old MTB to somethign a bit lighter to make it more suitable for commuting in the winter when my road bike will try and kill my on the icy roads!!

it is a GT Aggresor XC1 2009 20" model, i can only find a link to the 18" but i the fork will be the same:
http://www.halfords.com/webapp/wcs/stores/servlet/product_storeId_10001_catalogId_10151_productId_512553_langId_-1_categoryId_165499

I want to put one of these one it:
http://www.carboncycles.cc/?s=0&t=2&c=43&

but what size would i need? either the 42.5 or the 44.5?

i'm leaning towards the 42.5 because i want it to be a bit less upright but would this cause anyu problems?

i really dont know anything about this so any help would be great, thanks.

rubbernekker

This number is the distance from the fork dropout to the top of the crown.

You can simply measure your existing for to get the answer to which one you should choose.

It's not a good idea to try to change this distance if you don't know what the effect will be-ie Alter the steering characteristics. There are far better ways to drop your position, not the bikes.

chris_bass

thanks for the reply!

i have two questions though (i did warn you i know nothing about this!!) what is the fork drop out and what is the crown?! sorry, i really am a novice at this!

i wont go for the shorter one then (unless it is the right size), i might go for a flat bar instead of riser bar handle bar and maybe drop it down a bit!

davewalsh

The drop outs are the part of the fork where the wheel is mounted. There are 3 common MTB sizes, 9mm quick release and 15mm and 20mm bolt-through. IF your fork is the same as the one in the link, it's a 15mm bolt through.
Here's your first problem, the forks you're looking at are 9mm QR, so your existing front wheel will not fit, therefore you'd need to change the wheel as well, unless you can find a set of forks with 15mm drop-outs.

The crown is the peice of the fork which joins the 2 fork legs to the steerer tube (the part which goes through the frame). The axle to crown measurement is from the centre of the axle to the top of the crown (the point where the steerer enters).

As for geometry, I would definately go for the 44.5cm fork on your frame.
A 120mm fork is approx 49cm axle to crown. Knock of 3.5cm for sag, that leaves 45.5cm to give you your original geometry. Therefore running a 44.5 would just steepen it slightly. Steepen it too much and you risk making the front end twitchy at speed.