your thoughts on fork rake

[bthornt]

Looking for your thoughts on fork rake. Here's the background. I recently purchased a 58 cm Ibis Hakkalugi (the carbon version, cantilever brakes). The purchase did not include a fork. Normally, this frame would ship with an Enve cyclocross fork with a rake of 47.

The frame has a head tube angle of 71.4 degrees. Also I plan on using the bike on the road for long distance riding (thinking centuries) and perhaps also fire roads.

There are many choices. The Easton 90x has 45 degrees of rake, Wound up has 43 and 47 degrees available, Ritchey is (I believe) 45 degrees, and so on.

I appreciate any input, opinions, and the like. If you have any other thoughts on a wise purchase outside of the fork rake question, I would like to hear them.

[Cat3roadracer]

Fork rake confuses me more than the VW TDI thread.

[Kirk Pacenti]

Assuming you're going to buy an off-the-shelf carbon fork and not have something custom made, I would be looking for a fork with 50mm of rake to keep the resulting trail dimension in check.

Cheers,
KP

[HillDancer]

...this frame would ship with an Enve cyclocross fork with a rake of 47.

The frame has a head tube angle of 71.4 degrees...The Easton 90x has 45 degrees of rake, Wound up has 43 and 47 degrees available, Ritchey is (I believe) 45 degrees...
The frame has a head tube angle of X degrees, with a fork of Y offset, and Z axle to crown length. Those dimensions combined with wheel size & tire width (height in reality), will produce a trail distance. If you want to reproduce stock geometry, you would need to match the original fork's axle to crown length plus offset, in addition to intended wheel & tire dimensions. For each 10mm in axle to crown change, head tube angle will be altered about .55 degree. Altering any or all of the fork, tire/wheel, and HTA dimensions will change trail. While trail is only one piece of the handling pie, it is a big tasty piece.

Plugging the known numbers into this calculator (http://yojimg.net/bike/web_tools/trailcalc.php), assuming the tire is 700X23, shows trail of 64mm, and for 700X32 trial of 67mm. You can compare the other forks by entering their offset, and adjusting HTA entries based on their axle to crown length (+ or - .55 degree for each 10mm of difference). Trail numbers above 56-57mm are considered higher than neutral. Some riders prefer high trail, but no one can predict on your behalf how you will like higher trail. I prefer high trail for loose surfaces like unpaved road, but there are those who swear by very low trail numbers for the same conditions. If it were me and pavement was the priority, I would want a fork with 55mm offset with that slack HTA. However, since I'm not aware of a carbon fork with that much rake, I would take as much rake as I could get, along with the shortest A/C dimension.

[bthornt]

Does anyone know the equation to determine trail, given head tube angle, fork rake, and tire width? I think seeing the functional form and the coefficients might be helpful to me in understanding what's going on, although the different pictorial representations are helpful.

It's (almost, I hope) impossible to find a carbon fork with cantilever bosses and a 50 mm (or more) offset. Does anyone know of such a fork?

The research I'm doing in this area makes me wonder why high volume manufacturers offer different frame sizes, with different head tube angles, with forks of the same rake.

I'm sure that if there was a high demand for forks with offset of 50 or more mm, the marketplace would offer them. The move to using wider tires (an oft mentioned topic on this forum) suggests that more riders will be using cyclocross frames or touring frames to accommodate these wider tires, which makes me think that these riders would also want a fork with more offset. Does anyone think that forks with more offset will become more widely available in the future?

[phcollard]

Does anyone know the equation to determine trail, given head tube angle, fork rake, and tire width? I think seeing the functional form and the coefficients might be helpful to me in understanding what's going on, although the different pictorial representations are helpful.

There you go!

http://yojimg.net/bike/web_tools/trailcalc.php

:banana:

[carpediemracing]

Fork rake confuses me more than the VW TDI thread.

:)

[druptight]

I was doing some fork rake digging this morning actually and came across this delightful thread:

http://forums.thepaceline.net/showthread.php?t=97568&highlight=fork+rake

[bobswire]

I was doing some fork rake digging this morning actually and came across this delightful thread:

http://forums.thepaceline.net/showthread.php?t=97568&highlight=fork+rake

THIs!!! Sage advice.

Originally Posted by e-RICHIE
enough with the science atmo. in any given situation, more trail will be more stable (at speed, in a straight line, descending with the wheel facing forward, etc.) but harder to make on the fly negotiations. less trail will steer more nimbly, make life easier getting the front of the bicycle around pesky little obstacles, but harder still to keep the wheel straight ahead in instances when the bicycle is thrown off its line. however, all combinations seem to work when you know your own bicycle and its character. all of this takes in no consideration wrt whether a bicycle fits, or your position is dialed, what the front center is, or what combination of angle and offset yields the particular trail measurement being discussed. how's that for hysterical rhetoric, bro?!

ps

arrange disorder

[HillDancer]

Does anyone know the equation to determine trail, given head tube angle, fork rake, and tire width?...The move to using wider tires (an oft mentioned topic on this forum) suggests that more riders will be using cyclocross frames or touring frames to accommodate these wider tires, which makes me think that these riders would also want a fork with more offset...
One google search for trail equation on your behalf produced this: http://www.kreuzotter.de/english/elenk.htm

Something else to consider, usually wider tire means more volume at lower air pressure. Low tire air pressure plus increased volume increases a dynamic component of trail called pneumatic trail (http://en.wikipedia.org/wiki/Pneumatic_trail). This effect is exacerbated by narrow rims, and mitigated somewhat with proportional width rims. Unfortunately for the OP's application, there are no wide rims for rim brakes. Wide is not 23mm BTW, neither is 25mm, but you take what you can get. For disc brake users there are options for truly wide rims.

[bthornt]

I appreciate all the input. I suppose the real problem is that I can't afford to buy a fork with 43 mm of rake, install it, ride it, then do the same with a fork with 45 mm of rake, then 47 mm of rake, and so on. Especially when these forks are about $500 each.

I'm accustomed to riding road bikes with steep head tube angles in conjunction with forks having rakes of 45 or 43 mm. So, when Kirk Pacenti advised me to get a fork with a rake of 50 mm or more, I was stunned (stressing here that I didn't doubt him). It's just such a departure from the numbers I am used to, and perhaps more important, you can't find forks with that much rake. At least with the other characteristics that I need.

I think I'm just going to bite the bullet and buy an ENVE cyclocross fork with 47 mm of rake, since that's what the manufacturer provides and since I really can't find a fork with more rake than that that also has cantilever bosses.

Thanks to everyone for you help.

[druptight]

I'm accustomed to riding road bikes with steep head tube angles in conjunction with forks having rakes of 45 or 43 mm. So, when Kirk Pacenti advised me to get a fork with a rake of 50 mm or more, I was stunned (stressing here that I didn't doubt him).

If you've got some known numbers of what you're used to riding, angles/rakes/axle to crowns, why don't you calculate the trail that you're used to riding, then calculate the rake/length of the fork you'd need on this frame to create the same trail, and give that your first try?

It would be the most likely way to reproduce the handling characteristics that you're used to dealing with.

[tv_vt]

I appreciate all the input. I suppose the real problem is that I can't afford to buy a fork with 43 mm of trail, install it, ride it, then do the same with a fork with 45 mm of trail, then 47 mm of trail, and so on. Especially when these forks are about $500 each.



I think you're meaning rake when you write trail in that paragraph. Anyway, for a nice stable ride for centuries and fire roads, I'd look for a fork rake that gives you 60-62mm of trail, using the calculator (yojimg.net...) mentioned above. You also plug in the tire size you'll be using and head angle. It's a very useful weblink for calculating this stuff.

T

[christian]

It's a cx bike with a carbon fork. Just get any old fork with 395mm a-c and a 47mm rake. That's what it was designed for.

If you don't want to spring for an Enve, I have a brand new AlphaQ CX20 sitting in a box at home. I actually like that fork better than the Enve.

[tuscanyswe]

Did you mean cx20? or perhaps you got a cs25? if so im intersted but i think just a typo considering the ac you mention.

The cx20 are nice riding forks. I recently sold one cause i cant get my head around the fork legs curving the wrong way visually :/

I got an easton ec90x fork in very good cond with 18cm steerer if that works for the op.

[christian]

Yeah, CX20. Of course.

If I had a CS25.... oooooh!

[tuscanyswe]

Yeah, CX20. Of course.

If I had a CS25.... oooooh!

Yeah they seem to be very hard to come by. I have an ebay search that has given me nothing so far :/

[christian]

I have an ebay search, too, and a Lithuanian hacker who disabled your ebay search.

[tuscanyswe]

I was mostly worried that happycampyer would take notice if one popped up on the bay. Now i have to deal with this lithuanian guy as well. Crap!

[pbarry]

Kirk Pacenti's recommendation of 50mm rake is spot on. Wound Up should be able to build you one with that rake which will result in a mechanical trail of 60mm vs. 63 for the 47mm rake fork. That will still give you more stability for centuries and fire roads, yet be close enough to your road bike trail, which is probably in the mid-50's.