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

A million and one variables - front center, HTA, fork offset

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.

A million and one variables - front center, HTA, fork offset

Old 12-12-23, 04:11 AM
  #26  
Senior Member
 
Join Date: Dec 2019
Posts: 954
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 321 Post(s)
Liked 263 Times in 212 Posts
There's a lot to be said for 26" on a touring bike anyway. Easier to get parts when riding across the Hindu Kush. The opposite is probably true of 650b. It also makes much more sense than 700c if using quite fat tyres, which make up the diameter. Huge wheels are very popular these days (29ers etc.) which is probably why I view them with suspicion.
guy153 is offline  
Likes For guy153:
Old 12-12-23, 09:15 AM
  #27  
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 18,056

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Mongoose Tomac ATB, GT Bravado ATB, JCP Folder, Stewart 650B ATB

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4195 Post(s)
Liked 3,837 Times in 2,295 Posts
When I was just beginning to learn frame building the shop's owner had a GF who was also making her own frame (my kind of woman!) for her around the world tour. besides the frame bit I was curious about the rest of her planning (being a sort of tourer myself). She was going to run 26x13/8 (590) wheels and steel cottered cranks. Initially I was surprised at this. Why not the usual 27x11/4 tires and "good" alloy cotterless cranks. She said finding repair parts (this being in 1978) of the grade I had assumed on would be unlikely but any village blacksmith could handle cotters and steel and that 590 tires were vastly more common in the third world.

I was impressed with her planning and willingness to not focus on the bike as being the reason to tour. A real good lesson for me early on. Andy
__________________
AndrewRStewart
Andrew R Stewart is offline  
Likes For Andrew R Stewart:
Old 01-01-24, 07:34 PM
  #28  
Junior Member
Thread Starter
 
Join Date: May 2021
Location: New Hampshire
Posts: 81

Bikes: 1986 Schwinn Voyageur, SWB home-built recumbent and a couple other uninteresting ones.

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 32 Post(s)
Liked 47 Times in 26 Posts
Just to close this off - after lots of consideration of wheels, tires, angles and offset from the above discussion - I have decided to aim for a 559 wheels with up to a 55mm tire (I'm thinking about giving the Rat Trap Pass Kool-Aid a sip), with the deciding factor being that I already have a set of nice 559s from a MTB which doesn't get ridden. But, in my search - I also discovered that there are some canti's which have enough adjustment to reach both 559 and 584 and/or add a removable boss, so I can change my mind (see: LHT 650b Brakes).

So this means that I need my FC to be at least 600mm to get to a zero toe-overlap. To get to this place I can use an HTA of 71.5 and rake of 50, for a trail of 62. This is definitely within the scatter plot where my sampling of touring bikes seem to fall.

Thanks for all the input.
dschad is offline  
Old 01-02-24, 01:53 PM
  #29  
Randomhead
 
Join Date: Aug 2008
Location: Happy Valley, Pennsylvania
Posts: 24,386
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked 3,687 Times in 2,510 Posts
If you are going with a custom fork, I think 50cm rake is a bit tight for a bike like that. YMMV, and YCRA (you can ride anything)
unterhausen is offline  
Old 01-03-24, 08:03 AM
  #30  
Junior Member
Thread Starter
 
Join Date: May 2021
Location: New Hampshire
Posts: 81

Bikes: 1986 Schwinn Voyageur, SWB home-built recumbent and a couple other uninteresting ones.

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 32 Post(s)
Liked 47 Times in 26 Posts
Originally Posted by unterhausen
If you are going with a custom fork, I think 50cm rake is a bit tight for a bike like that. YMMV, and YCRA (you can ride anything)
Indeed we shall see - it looks the numbers are working out, but I must admit that rake is one of my escape parameters. If things get too tight I will embrace that "low trail" philosophy until reality comports with what my design says it should.
dschad is offline  
Old 01-03-24, 01:58 PM
  #31  
Randomhead
 
Join Date: Aug 2008
Location: Happy Valley, Pennsylvania
Posts: 24,386
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked 3,687 Times in 2,510 Posts
It really depends on if you are ever going to put a front load on it. If not, it really doesn't matter. Except your geometry is going to be a little annoying while standing on hills.

Your proposed head angle makes it so a 55mm rake fork would be mid-trail, I think. If you look at production bikes, they definitely lean towards high trail. It makes sense, most production bikes don't get ridden, and most of the ones that do get ridden are ridden without a front load. People don't like steering they have to get used to, and low trail takes a bit of adaptation. Unladen high trail bikes do not. So production bikes are made to feel stable during a 10 minute test ride.
I have a bike with 73mm hta and 55mm rake, and it takes me approximately one hill to get used to the steering if I have been riding something higher trail. The one with 73hta and 65mm rake takes two hills to get used to, but since it always has a front randonneur bag on it, it feels perfectly normal all the time. Even if the bag is mostly empty.
unterhausen is offline  
Old 01-03-24, 03:08 PM
  #32  
Junior Member
Thread Starter
 
Join Date: May 2021
Location: New Hampshire
Posts: 81

Bikes: 1986 Schwinn Voyageur, SWB home-built recumbent and a couple other uninteresting ones.

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 32 Post(s)
Liked 47 Times in 26 Posts
Originally Posted by unterhausen
It really depends on if you are ever going to put a front load on it. If not, it really doesn't matter. Except your geometry is going to be a little annoying while standing on hills.

Your proposed head angle makes it so a 55mm rake fork would be mid-trail, I think. If you look at production bikes, they definitely lean towards high trail. It makes sense, most production bikes don't get ridden, and most of the ones that do get ridden are ridden without a front load. People don't like steering they have to get used to, and low trail takes a bit of adaptation. Unladen high trail bikes do not. So production bikes are made to feel stable during a 10 minute test ride.
I have a bike with 73mm hta and 55mm rake, and it takes me approximately one hill to get used to the steering if I have been riding something higher trail. The one with 73hta and 65mm rake takes two hills to get used to, but since it always has a front randonneur bag on it, it feels perfectly normal all the time. Even if the bag is mostly empty.
You just had to open up that can again....

The trail of my design should be around 59 (HTA 71.5, 559 x 2.0, 50mm rake). I was surprised to discover that my Voyaguer was 62, as that seemed a bit low relative to the other touring bikes I was seeing. I also found that the Fuji S10S (a darling of the 650b/low trail conversions) shipped with a trail of 40 (HTA73, 27", 65mm rake), with the 650b conversion going to 33mm and being "fixed" with a bag (this sounds like your second bike from above?).

At this point, I sort of gave up worrying about it at this point, as it seems to put "low trail" at around 30mm, "standard touring trail" around 67, and I have no idea about high-trail. So my thinking was that 8mm +/- (20% towards low trail) won't be something I can detect, or register enough to complain to the builder about.

I always found the bag idea confusing, as it doesn't sound like big loads (lunch and a patch kit), as you suggested. So is 2# really changing behaviour that much? It seems like fit items - handle bar reach, slope of the terrain, would move that way more (i.e. a 200# rider shifting 1% by changing posture would offset that).

But, I do agree that in the end one can adapt very quickly and happily. Sort of like toe clips - after a flop or two it is completely second nature, even under panic situations.
dschad is offline  
Old 01-04-24, 12:25 PM
  #33  
Randomhead
 
Join Date: Aug 2008
Location: Happy Valley, Pennsylvania
Posts: 24,386
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked 3,687 Times in 2,510 Posts
Don't get me started on the reach effects of reach on handling. You are in Unterhausen's law of cognitive bias territory.
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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.