help with changing to a new rake/crown-axle measurement for my custom frame
#1
Newbie
Thread Starter
Join Date: Jan 2009
Posts: 4
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
help with changing to a new rake/crown-axle measurement for my custom frame
I have a custom frame that was designed around a form (Easton EC90SLX 43mm rake 360mm AC measurement) and I'm looking to swap over to an ENVE 2.0 with a AC measurement of 367 and various rake options. I'm leaning toward 43 or 40. I understand the implications of changing rake when all things are equal, but given the AC crown measurement is 7mm longer on the ENVE, how will this change the dynamic? Seems like it will slacken out the bike if I go with the same rake, so it might make it even more appealing to go with a 40mm rake to balance out the extra length. Am I thinking about this correctly? Also, will 7mm of additional fork length make a noticeable front height difference with an equivalent rake?
#2
Voice of the Industry
Join Date: May 2007
Posts: 12,572
Mentioned: 19 Post(s)
Tagged: 0 Thread(s)
Quoted: 1188 Post(s)
Likes: 0
Liked 8 Times
in
8 Posts
What I suggest is either plot it on graph paper, or find a primitive 2D CAD program. Basically you will elevating the head tube by 7mm which will fractionally slacken the HTA and slow the steering down. So directionally to compensate you would seek less fork rake to reduce castor and speed the steering back up.
If you are adept at trig, you can calculate this...or plot it and analyze the fork rake you seek with a taller fork...net wash maybe only a deg of rake reduction but you would need to calculate it.
It also depends directionally which way you want to take the steering of the bike. For example I ride a Roubaix which natively has a slack hta and more fork rake and I love the rock solid handling. Your preference maybe for a quicker handling bike.
Good luck with your custom.
If you are adept at trig, you can calculate this...or plot it and analyze the fork rake you seek with a taller fork...net wash maybe only a deg of rake reduction but you would need to calculate it.
It also depends directionally which way you want to take the steering of the bike. For example I ride a Roubaix which natively has a slack hta and more fork rake and I love the rock solid handling. Your preference maybe for a quicker handling bike.
Good luck with your custom.
#3
Should Be More Popular
Join Date: Dec 2007
Location: Malvern, PA (20 miles West of Philly)
Posts: 43,049
Bikes: 1986 Alpine (steel road bike), 2009 Ti Habenero, 2013 Specialized Roubaix
Mentioned: 560 Post(s)
Tagged: 2 Thread(s)
Quoted: 22596 Post(s)
Liked 8,925 Times
in
4,158 Posts
#4
Senior Member
Join Date: Jan 2011
Posts: 208
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 13 Post(s)
Likes: 0
Liked 2 Times
in
2 Posts
You want more rake to offset the increased trail caused by lifting the headtube (slackening the HTA) . ENVE fork with 45mm rake will likely have similar geometry to the Easton fork with 43 mm rake. With the Enve fork you will be lengtening the wheelbase also. You can use https://www.bikecad.ca/ to plug in all the numbers and see the actual differences.
#5
Voice of the Industry
Join Date: May 2007
Posts: 12,572
Mentioned: 19 Post(s)
Tagged: 0 Thread(s)
Quoted: 1188 Post(s)
Likes: 0
Liked 8 Times
in
8 Posts
You want more rake to offset the increased trail caused by lifting the headtube (slackening the HTA) . ENVE fork with 45mm rake will likely have similar geometry to the Easton fork with 43 mm rake. With the Enve fork you will be lengtening the wheelbase also. You can use https://www.bikecad.ca/ to plug in all the numbers and see the actual differences.
Also, thanks for the link for bike cad.
#6
Senior Member
The increase in wheelbase is minimal, compared to the change in the HTA. Here's a link to an explanation.
https://www.sheldonbrown.com/rinard/forklengths.htm
If you put the change of HTA into the formula for trail, you need 3mm more fork offset. The trail formula is R/tanH - (rake/sinH).
https://www.sheldonbrown.com/rinard/forklengths.htm
If you put the change of HTA into the formula for trail, you need 3mm more fork offset. The trail formula is R/tanH - (rake/sinH).
#7
Newbie
Thread Starter
Join Date: Jan 2009
Posts: 4
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
Thanks for all the guidance guys. I was actually able to track down the original CAD, and it turns out there is a discrepancy in the measurements. The frame was actually designed around a 367mm AC fork, but according to what I'm seeing, the Easton is 360. So interestingly enough, I've been riding a bike that's "out of spec".
All that said, I'm going to use the advice everyone provided to sketch out the differences that I can anticipate.
All that said, I'm going to use the advice everyone provided to sketch out the differences that I can anticipate.
Thread
Thread Starter
Forum
Replies
Last Post
Daspydyr
Bicycle Mechanics
5
12-11-09 06:57 PM