# How to calculate rigid fork replacement for suspension one?

Let's say I am reading spec for 29er with suspension fork and I would like to calculate replacement parameters for rigid one. Calculation is needed because I don't want to change geometry after replacement -- so the rigid fork should feel (in sense of geometry) as locked in neutral position suspension fork.

How to do the calculation, what parameters are important? Example:

"Custom SR Suntour XCT 29, w/ custom Multi-Circuit Damping, alloy lowers, coil/MCU spring, Hi-Ten 28mm stanchions, 1-1/8" steerer, hydraulic lockout w/ preload adjust, disc mount, 100mm travel"

(text from Specialized Rockhopper 29).

Background 1: I want to do calculations before I buy the bike to avoid situation, that I am buying popular bike but there is no rigid fork replacement (or it is very hard to get).

Background 2: In reality I wanted to buy fitness bike (100% rigid, disc brakes, 700C) and mount wider tires (2"). After some query it appears that all fitness bikes (like Trek 7.2 FX, Cube Hyde, etc) have so little space that you can fit 1.75" tire max (Kross Seto). I found only single bike so far with frame for wider tires (Sulry Ogre), but it is out of reach for me (Poland). So I see no other option as do more expensive replacement -- instead of buying fixed fork bike and replacing tires, buying 29er and replacing fork.

• This seems all a bit weird - if you want a fitness bike, why do you want 2" tires? Also, why not pick up an old rigid mountain bike (like an 80's or 90's rockhopper) and use 26" wheels and put a 2 inch tire on that, if you want 2 inch tires for some reason? Mar 10, 2015 at 12:47
• I have seen this calculation done with a hacksaw Mar 10, 2015 at 13:18
• @Batman, it is like asking why do you want black bicycle, when white are available. My personal preference is 700C wheels plus 2" tires (I already have 26" bike with 2.35" tires). Mar 10, 2015 at 14:12
• @PeteH Really? Please explain how you measure with a hacksaw? Or how this a hacksaw is a solution to the problem? Mar 11, 2015 at 0:25