mtbvfr

Hi Folks,

This is the first time I am considering doing something like this. I've read through some of the pertinent threads.

I'm looking for some advice regarding Rigid Fork selection to replace the current 100mm Suspension Fork for Touring purposes using a Lowrider rack.

I have been using the free version of BikeCAD but it doesn't recalculate the Head Angle for a change in the Axle to Crown (A-C) and Rake (Offset) for a Fork. However, a previous thread, in this forum, suggests that a change in A-C of 10mm effects a change of 0.5°. I also noticed that the BB Height wasn't being recalculated neither.

The Frame parameters I used are the following for the 100mm Suspension fork at rest.

BB Height: 295mm
Chain Stay Length: 425mm
Effective Top Tube: 594mm

So, for the Fork Parameters I unchecked Suspension and then I altered the A-C (AC) and Rake (R) values and the Head Angle values and Seat Angle values accordingly. For the Wheel, I chose Standard 26 x 2.125/2.2" and then selected Custom and changed the Width to 53mm. The tyre diameter of 670mm appears to be a very close match to the Conti Race King 2.2" that I have inflated to 20PSI with the following results.


Current Fork - 100mm Suspension - At rest
Steerer: 265mm
AC: 480mm, R: 38mm, Head Angle: 71°, Seat Angle: 73°
Calculated Trail: 75mm


Current Fork - 100mm Suspension - allowing for 25mm Sag
AC: 455mm, R: 38mm
Head Angle: 72.25° (BikeCAD used 72.3°), Seat Angle: 74.25° (BikeCAD 74.3°)
Calculated Trail: 67mm


Salsa CroMoto Grande 29er 80mm Suspension Corrected
AC: 468mm, R: 45mm
Head Angle: 71.6°, Seat Angle: 73.6°
Calculated Trail: 64mm
Need a Rack to Suit


Salsa Firestarter
AC: 483mm, R: 45mm
Head Angle: 70.85° (BikeCAD used 70.9°), Seat Angle: 72.85° (BikeCAD used 72.9°)
Calculated Trail: 69mm
This fork would raise the BB slightly. I can't say how much exactly, maybe a 1mm ?, because BikeCAD didn't recalculate this value when changing the Angles and Fork parameters.


Surly Krampus
AC: 483mm, R: 47mm, Head Angle: 70.85° (BikeCAD used 70.9°), Seat Angle: 72.85°
Calculated Trail: 67mm
Ditto for the BB height.

I like that the Salsas have stainless steel fork dropouts.


The Firestarter offers the most Trail. Could/Should I cut the Steerer Tube down to 240mm or 245mm to allow for most of the Sag that would occur for the Suspension fork? I have a 5° stem that can be flipped to make the handlebar higher if I feel the need to.

I'm looking for the bike to be as stable as possible as I'm still recovering from a Dislocated Shoulder and wish to reduce any risk of a fall due to an unstable bike. So, I am hoping those of you with MUCH more experience in bike geometry, both technical and seat of the pants, than me could recommend the most stable option.

Of course, my preferred solution would be to have made a custom Lowrider rack that could be mounted to V-brake bosses and use either P-clamps at the bottom of a Suspension fork, where there is a "ledge" at the front where the fork leg morphs into the Dropout Plate, or the integrated Eyelet of a Rigid fork so that I could use the rack on either my suspension fork or the rigid fork of my old 26" Mountain Bike which also has rack mounts in the middle of the fork legs. Because the external widths of the forks are different, the supporting Arch that loops over the top of the wheel would need to be adjustable for width. Instead of a Curved arch, the Arch would have to be made flat to allow one tube to slide within another to allow a small bolt to be inserted through both tubes and secured by a nyloc nut. Anybody here that can do that?

Thanks, MTB.