I don't climb, I walk
Thinking about upgrading the fork on my 08 mkiii comp. What size, length and diameter steerer are necessary? Thanks, Joe
The 08 MKIII uses a 44mm "internal" headset, aka "Zerostack" headset. The zero stack headset that came with that bike is designed for use with a 1 1/8in dia. steer tube, which is the most common size steerer.
Regarding length, just use a tape measure and measure from the bottom of the your head tube (the part of the frame that the steerer goes through) up to about 3" past the top of the head tube. This length (length of the your head tube plus ~3", which I think is about 7" total) is about the correct length of steerer for that bike. If you like a high stem mount than maybe 4 or 5 inches past the top of the head tube, so a total of 8" or 9" but that's getting pretty long. You can always cut the steerer down to a short length if it's too long.
Also, when you switch forks, there will be a little metal ring pressed onto the steerer of your old fork, it will be at the very base of the steerer. You need to transfer that ring over to your new fork steerer. It is a press fit so you may want to have a bike shop do the transfer for you.
Originally Posted by JTK37