going from 45mm to 38mm rake
 

how much will this change the geometry?

The frame geometry doesn't change because of rack. The frame geometry changes because of axle to crown length.

It will increase the trail, in the steering geometry, of your bike. Your bike will be more stable, and less twitchy/responsive.

http://sheldonbrown.com/gloss_tp-z.html#trail
http://www.phred.org/~josh/bike/trail.html

dramatic change.

why would you mention frame geometry in a question about a fork?

Because that was the only other non-answered question. The OP asked how much a 45mm-38mm = 7mm change in the rake would affect the geometry. You should be asking the OP why they would ask a question to which they already knew the answer if the question was, in fact, about the fork geometry.

:lol:

use your words...

if you mean handling, it will make it turn easier and twitch more, as well as fall over easier at speed. that is if the wheel clears.

Surprisingly it's actually the opposite. Because the contact point of the tire is behind a straight line going down from the headtube, decreasing the rake moves the contact point further back behind that line thereby increasing the trail. This makes the bike more stable (generally) rather than more twitchy.

http://upload.wikimedia.org/wikipedi...TrailDIAG2.jpg

whoops. i was thinking trail.

again, 0 to do with frames.

hell, bringing up stems would've made more sense...

he meant handling. not geometry. use your words, then get over it.

Depending on the fork design, it can slightly change the head tube and seat tube angles, as well as the bottom bracket height. Depends on the axle to crown length and the offset.

The differences are probably negligable though.

you really take offense to my simple interpretation of a question. geez internet wise-guy.

careful, sp00ki has declared this area off-limits. watch yourself.

I put a fork on before with about 38mm rake and my only complaint was the mega toe over lap, not that it will affect your normal riding, but if you're pulling up at a stop light and wanna attempt to do any kind of track standing you may find yourself trying to turn your bars and finding your front wheel hitting your foot, im not great at track standing and always find myself turning the bars back and fourth to maintain balance so it always pissed me off. Other than that I loved the handling with the 38 fork!

http://www.anvilbikes.com/images/1064634020.xls
That link will let you calculate your bike's trail.

http://www.urbanvelo.org/issue3/urbanvelo3_p44-45.html
That link will teach you a little bit about trail and different handling characteristics.

I find that a lower-rake fork on a bike that's not meant for it offers really undesirable handling. So, while this doesn't answer your question, I hope it provides some helpful information.

Why be a jerk?