65mm travel anD rigid offset

Get all your technical information about electric bikes here.
Post Reply
tomjasz
1.21 GW
1.21 GW
Posts: 3831
Joined: Mar 29, 2014 1:45 pm
Location: Out riding, MN USA
Contact:

65mm travel anD rigid offset

Post by tomjasz » Jan 02, 2018 2:07 am

The OEM fork for the frame i bought had 65mm of travel. When converting to a rigid fork, how does that translate to proper, or closest offset?
Thanks Justin_le we're here thanks to you. All the best to the mods for their tireless work keeping it on an even keel.

User avatar
amberwolf
100 GW
100 GW
Posts: 25052
Joined: Aug 17, 2009 6:43 am
Location: Phoenix, AZ, USA, Earth, Sol, Local Bubble, Orion Arm, Milky Way, Local Group
Contact:

Re: 65mm travel anD rigid offset

Post by amberwolf » Jan 02, 2018 1:54 pm

If you mean fork length to give the same headtube/steerer angle so the handling is the same, you'd want to measure the suspension fork length while it's compressed with your weight on the bike saddle (takes two people or setting up a jig with a marker on the crown and a board on the wall, and a bit of math).

THen get a fork with the same length from crown race to dropouts, and the bike will have the same angles so would "ride" the same.

Then measure the dropouts' offset from the steering tube and get a fork with the same offset, and it should handle the same there, too, giving the same trail.


This page may explain why these things change handling better than I can:
https://www.sheldonbrown.com/rinard/forklengths.htm

tomjasz
1.21 GW
1.21 GW
Posts: 3831
Joined: Mar 29, 2014 1:45 pm
Location: Out riding, MN USA
Contact:

Re: 65mm travel anD rigid offset

Post by tomjasz » Jan 02, 2018 6:19 pm

Thanks, not possible since it's a bare frame and I don't have the original fork.

Searching 2009 data,
Travel 63mm
SAG in % 15% - 20%
SAG in mm 9mm - 13mm
Thanks Justin_le we're here thanks to you. All the best to the mods for their tireless work keeping it on an even keel.

tomjasz
1.21 GW
1.21 GW
Posts: 3831
Joined: Mar 29, 2014 1:45 pm
Location: Out riding, MN USA
Contact:

Re: 65mm travel anD rigid offset

Post by tomjasz » Jan 03, 2018 5:45 pm

Original fork,

Spinner Enroute AC 26" Hybrid Bike Suspension Fork Coil 63mm Black *USED*
If you are looking for a fork with amazing results that doesn't hurt the wallet the Spinner Enroute AC fork is for you. Made with a steel steerer tube and 63mm of travel, this is a great choice for hybrid bike riders.

Preload adjustment
Bike Type: Hybrid
Wheel Size: 26"
Steerer Diameter: 1-1/8"
Steerer Length: 265mm
Brake Compatibility: Post or Disc
Travel: 63mm
Adjustments: Preload
Stanchion diameter: 25.4mm
Dropouts: 9mm
Inner Hub Spacing: 100mm
Color: Black
Weight: 2160g
Thanks Justin_le we're here thanks to you. All the best to the mods for their tireless work keeping it on an even keel.

User avatar
Chalo
100 GW
100 GW
Posts: 6657
Joined: Apr 29, 2009 11:29 pm
Location: Austin, Texas

Re: 65mm travel anD rigid offset

Post by Chalo » Jan 03, 2018 6:16 pm

There's no single answer for that. It's "whatever offset gives you the desired amount of trail". Trail is a function of head angle, wheel diameter, and fork offset.

The amount of trail you're looking for varies by riding style, typical speed, and amount of load carried on the front wheel. For a very fast bike, you want more trail. For a bike that carries lots of weight on the front, you want less trail. But you can't go much wrong shooting for about 2 inches of trail.

What kind of bike are you retrofitting with a new fork?

With MTB suspension forks, you don't really get to choose from among different fork offset values. They're all going to be right around 44mm. It isn't always right for the job, but it's what you get. If you can find a rigid fork with a little more offset, you might like the handling better.

The shorter the fork is from axle to crown, the less steering trail you'll have with the same fork offset.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

User avatar
Lenk42602
10 kW
10 kW
Posts: 884
Joined: Oct 04, 2007 1:03 pm
Location: Pittsburgh

Re: 65mm travel anD rigid offset

Post by Lenk42602 » Jan 03, 2018 11:00 pm

good info in rake/trail/head tube angle interplay

scroll down to the "rake and trail 101"

http://www.chopperhandbook.com/rake.htm

tomjasz
1.21 GW
1.21 GW
Posts: 3831
Joined: Mar 29, 2014 1:45 pm
Location: Out riding, MN USA
Contact:

Re: 65mm travel anD rigid offset

Post by tomjasz » Jan 04, 2018 12:38 am

Chalo wrote:
Jan 03, 2018 6:16 pm
There's no single answer for that. It's "whatever offset gives you the desired amount of trail". Trail is a function of head angle, wheel diameter, and fork offset.

The amount of trail you're looking for varies by riding style, typical speed, and amount of load carried on the front wheel. For a very fast bike, you want more trail. For a bike that carries lots of weight on the front, you want less trail. But you can't go much wrong shooting for about 2 inches of trail.

What kind of bike are you retrofitting with a new fork?

With MTB suspension forks, you don't really get to choose from among different fork offset values. They're all going to be right around 44mm. It isn't always right for the job, but it's what you get. If you can find a rigid fork with a little more offset, you might like the handling better.

The shorter the fork is from axle to crown, the less steering trail you'll have with the same fork offset.
https://www.google.com/search?q=marin+s ... n3ZHsZdOHM:

I want to get as close to the upright position of my Trek Pure, Townie, or KHSto use on front.

Thanks
Last edited by tomjasz on Jan 04, 2018 12:45 am, edited 1 time in total.
Thanks Justin_le we're here thanks to you. All the best to the mods for their tireless work keeping it on an even keel.

tomjasz
1.21 GW
1.21 GW
Posts: 3831
Joined: Mar 29, 2014 1:45 pm
Location: Out riding, MN USA
Contact:

Re: 65mm travel anD rigid offset

Post by tomjasz » Jan 04, 2018 12:39 am

Sorry the changed method of posting pictures is almost as difficult as a PM! Confusing.
Thanks Justin_le we're here thanks to you. All the best to the mods for their tireless work keeping it on an even keel.

tomjasz
1.21 GW
1.21 GW
Posts: 3831
Joined: Mar 29, 2014 1:45 pm
Location: Out riding, MN USA
Contact:

Re: 65mm travel anD rigid offset

Post by tomjasz » Jan 04, 2018 12:46 am

Lenk42602 wrote:
Jan 03, 2018 11:00 pm
good info in rake/trail/head tube angle interplay

scroll down to the "rake and trail 101"

http://www.chopperhandbook.com/rake.htm
Thank you.
Thanks Justin_le we're here thanks to you. All the best to the mods for their tireless work keeping it on an even keel.

User avatar
Chalo
100 GW
100 GW
Posts: 6657
Joined: Apr 29, 2009 11:29 pm
Location: Austin, Texas

Re: 65mm travel anD rigid offset

Post by Chalo » Jan 04, 2018 4:12 am

tomjasz wrote:
Jan 04, 2018 12:46 am
Lenk42602 wrote:
Jan 03, 2018 11:00 pm
good info in rake/trail/head tube angle interplay

scroll down to the "rake and trail 101"

http://www.chopperhandbook.com/rake.htm
Thank you.
Careful! Motorcycle guys say "rake" when they mean head angle, and bicycle guys say "rake" when they mean fork offset. You have to translate.

For what it's worth, I think the best thing for you would be a super long fork, like a 29+ fork, but with extra generous offset, like 60mm. Tough luck finding one of those.

Short of that, try a fork without any suspension correction (not more than 400mm axle to crown), with more than 45mm offset, if you can find one. A framebuilder may be able to add offset to the steel fork of your choosing.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

tomjasz
1.21 GW
1.21 GW
Posts: 3831
Joined: Mar 29, 2014 1:45 pm
Location: Out riding, MN USA
Contact:

Re: 65mm travel anD rigid offset

Post by tomjasz » Jan 11, 2018 10:22 pm

More data, Spinner EnRoute AC, 63mm with Preload Adjustment, crown to axle 420mm, pitch 107. Some specs call it a 40mm travel, others, same year a 63mm travel. What should the axle to crown length be corrected? All i find for corrected are for 100mm travel correction.
Attachments
F7BAD9FA-D0C8-407A-B015-C7C67A564C4D.jpeg
Thanks Justin_le we're here thanks to you. All the best to the mods for their tireless work keeping it on an even keel.

Post Reply