Go Back  Bike Forums > Bike Forums > Framebuilders
Reload this Page >

Which fork do I need

Notices
Framebuilders Thinking about a custom frame? Lugged vs Fillet Brazed. Different Frame materials? Newvex or Pacenti Lugs? why get a custom Road, Mountain, or Track Frame? Got a question about framebuilding? Lets discuss framebuilding at it's finest.

Which fork do I need

Old 12-14-20, 01:21 PM
  #1  
jpc6000
Newbie
Thread Starter
 
jpc6000's Avatar
 
Join Date: Jan 2018
Posts: 1
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Which fork do I need

I want to buy an new aluminium bike frame. When I find an interesting frame, mostly their are no information what the height of the suspension fork is need for the frame. Can I measures myself? They write that I can use fork 80/120 suspension. (450mm / 520mm axle to crown height) Is this true? Or only with an XC frame?

XC frame is good for fast e-bike on road?
jpc6000 is offline  
Old 12-14-20, 02:04 PM
  #2  
unterhausen
Randomhead
 
Join Date: Aug 2008
Location: Happy Valley, Pennsylvania
Posts: 20,869
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked 875 Times in 653 Posts
If you are going to buy a mountain bike frame, then an XC frame is the one you want. A DH frame has much more relaxed geometry.

I think I would try to find an older XC frame for road ebike use.

If the manufacturer tells you 80/120mm suspension fork, I think I would believe them. But that's quite a range of forks.
unterhausen is offline  
Old 12-14-20, 09:54 PM
  #3  
Andrew R Stewart 
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 14,328

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Raleigh Pro, Trek Cycle Cross, Mongoose tomac ATB, GT Bravado ATB, JCP Folder

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2692 Post(s)
Liked 866 Times in 632 Posts
I have found the willingness to be "flexible" in resulting geometries in the MtB world somewhat odd. But then since the suspension forks are a constantly changing A-C dimension (during a ride) I guess this lack of concern about steering geometry (compared to the road world) kind of makes sense, if they can't nail down what the geometry is then why even bring specifics up? (That said with an amount of tongue in cheek). Andy
__________________
AndrewRStewart
Andrew R Stewart is offline  
Old 12-15-20, 07:08 PM
  #4  
unterhausen
Randomhead
 
Join Date: Aug 2008
Location: Happy Valley, Pennsylvania
Posts: 20,869
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked 875 Times in 653 Posts
People who design mountain bikes usually look at the sagged geometry. Or at least that's my understanding. So they are thinking of a particular fork length. 80/120 A-C must not really mean what it looks like it means. 120 sags to 90, I think. Maybe someone that knows mtb geometry a little better can comment
unterhausen is offline  
Old 12-16-20, 02:55 AM
  #5  
guy153
Senior Member
 
Join Date: Dec 2019
Posts: 510
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 181 Post(s)
Liked 99 Times in 81 Posts
Originally Posted by unterhausen View Post
People who design mountain bikes usually look at the sagged geometry. Or at least that's my understanding. So they are thinking of a particular fork length. 80/120 A-C must not really mean what it looks like it means. 120 sags to 90, I think. Maybe someone that knows mtb geometry a little better can comment
When I made a hard-tail it seemed like everyone else was assuming 25% fork drop in their numbers. Citation needed, I can't remember where I found this.

I measured the fork fully extended at 555. It was a 140mm travel fork so I subtracted 25% of 140 from that so designed the frame on the assumption the fork was 520mm long. It worked out pretty good. The head angle at 25% drop was 65 degrees. I also estimated what it would be at full compression and can't remember the number but I think it was about 71. I wanted to know it wouldn't go outside the range of what one might consider reasonable (I guess 74 max).

I don't know what you do for full-suss. Would be fun to try and make one of those one day but need to get my head around how to design the rear geometry.
guy153 is offline  
Old 12-16-20, 10:25 AM
  #6  
unterhausen
Randomhead
 
Join Date: Aug 2008
Location: Happy Valley, Pennsylvania
Posts: 20,869
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked 875 Times in 653 Posts
I have always heard 25%, that's where I got 90mm from. So whatever the un-sagged A-C is minus 30mm
That's fairly close to 80, so I'm not sure if that's not what 120/80 means.
unterhausen is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.