Results 1 to 6 of 6
  1. #1
    mtbr member
    Reputation:
    Join Date
    Apr 2014
    Posts
    77

    Tandem fork rake and steering geometry

    Learning the intricacies of bicycle geometry can be a lifetime endeavor. I've read a little on the 'net about tandem geometry, and I have some experience, owning several tandems myself.

    My first is an '88 Fisher Team tandem built by Santana, and the head angle is 72.5 with 2" of rake. This gives less trail than a standard bike would have, and for me, easy steering and technical agility. That's my starting point.

    My second tandem, a '96 700C Cannondale, has a 73.5 head angle and 2.1" of rake. Same thing: more rake, less trail, neutral steering.

    I recently bought this tandem, a rarer than rare '98 Manitou. There's more about it in the Vintage Tandem thread in the VRC forum.

    Tandem fork rake and steering geometry-20140614_193205_zpsc12174b1.jpg

    This bike has a 72 head angle and a Manitou X-Vert fork. I looked up the X-Vert rake, and it's only 1 5/8" (unless this one is special - I don't think so). And this bike handles like it. Steering is heavy, climbing is difficult (wobbly) with any stoker movement, and despite it being a cool bike (and great descender), I'm not happy. At first I thought the weird feeling was just because it's tall, but I suspect the small fork rake.

    Someone might say, "Get a new fork". Yeah...it's difficult. VRC is my thing, and... the fork is custom painted to match the frame. The fork action is awesome - Barcalounger for sure. A nice new fork might cost nearly what the bike did, so I hesitate to throw too much money into an older rig, as cool as it may be.

    Does anyone here have any opinions about geometry, like "Less rake is OK, must be something else", or maybe I can lower the fork crowns a little, or can one find new triple clamps for such a thing that would allow more rake? The headset is 1 1/4", so there's almost room for some adjustable head angle headset, though I think most of those are 1.5".

    I'd enjoy hearing what the experts think.

  2. #2
    PMK
    PMK is offline
    mtbr member
    Reputation: PMK's Avatar
    Join Date
    Oct 2004
    Posts
    2,564
    I saw the bike a week or more in the VRC forum...yes rare.

    As for the frame and front geometry, before I could even consider an answer I need to ask, how much front travel, and how much rear travel? Plus how much sag are you setup with?

    Also, when you got the head tube angles, was that from published data or measured?

    PK
    Reps! We don't need no stickin' reps!

  3. #3
    mtbr member
    Reputation:
    Join Date
    Apr 2014
    Posts
    77
    Quote Originally Posted by PMK View Post
    I saw the bike a week or more in the VRC forum...yes rare.

    As for the frame and front geometry, before I could even consider an answer I need to ask, how much front travel, and how much rear travel? Plus how much sag are you setup with?
    Thank you. I'm such a retrogrouch I didn't play much with the suspension. I believe the travel is 5.5" front, 4.5" rear, and maybe an inch of sag all around.
    Also, when you got the head tube angles, was that from published data or measured?

    PK
    Published actually. I can measure the head tube angle, but I'm sure that's right, 72. I will check it though. Maybe I should make sure there's less sag in the rear than in the front. We don't want it sinking into 68 parallel like my Ibis Bow-ti does.

  4. #4
    PMK
    PMK is offline
    mtbr member
    Reputation: PMK's Avatar
    Join Date
    Oct 2004
    Posts
    2,564
    Never came to terms on the few IBIS Szabos I rode, setting up their Fox Alps rear shocks.

    What is the dimensions of the rear shock, fully extended then fully compressed?

    That bike will definitely need the rear suspension to work and move freely. Riding the bike with an overinflated rear shock or stuck rear shock will destroy the rear end of the bike. Manitous are not known to be a strong construction.

    When you deflate the shock, and better yet remove one shock bolt, see if the rear end moves freely. Slowly inflate the ALps shock and ensure it moves smoothly with only a few PSI being added.

    I recently rebuilt and ALps 5 from a Y bike. It had been rebuilt by a company that does not know or work on these shocks. Suffice to say it was bound up if it had not dumped all the fluid from them installing the wrong seals, the shock would have ruined the frame.

    Check the rear, it's easy and we can sort out proper rear sag. After that, it should be easy to get the front dialed in which should sort out some of the handling concerns.

    BTW, I doubt you will want the often published 20% or 25% or 30% rear sag on this machine. Those numbers seldom worked on old school stuff.

    PK
    Reps! We don't need no stickin' reps!

  5. #5
    mtbr member
    Reputation: switchbacktrog's Avatar
    Join Date
    May 2013
    Posts
    99
    This thread is about my experiences with fork rake on an ECdM. I'm currently running at about 69.5 degrees.

    http://forums.mtbr.com/tandem-mounta...ry-925544.html

    I'm not sure if you can get an adjustable head angle insert to fit a 1 1/4". You may be able to get one made though

  6. #6
    mtbr member
    Reputation: XC Mike's Avatar
    Join Date
    Sep 2004
    Posts
    596
    Wow that is Sweet!!!
    I always wanted a HT Manitou
    I had the first batch of the Manitou forks that Doug built before Answer started making them All Hand Made parts...
    Had them on a Merlin back in the day

Similar Threads

  1. RST 801-7 fork rake and length?
    By cadiremar in forum Shocks and Suspension
    Replies: 4
    Last Post: 12-27-2014, 02:49 AM
  2. Replies: 3
    Last Post: 04-24-2012, 08:28 AM
  3. Specialized fork rake
    By Fred Smedley in forum Vintage, Retro, Classic
    Replies: 3
    Last Post: 04-22-2012, 03:06 PM
  4. Replies: 12
    Last Post: 11-19-2011, 02:19 AM
  5. Axle to Crown Length, Fork rake, and Hardtail Geometry
    By Dlevy05 in forum General Discussion
    Replies: 5
    Last Post: 03-29-2011, 08:06 PM

Members who have read this thread: 0

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

THE SITE

ABOUT MTBR

VISIT US AT

mtbr.com and the ConsumerReview Network are business units of Invenda Corporation

(C) Copyright 1996-2018. All Rights Reserved.