Im going all out with my next build. Im going to make a rigid 69er fixed geared mountain bike and Ive been looking through as many vendor catalogs and reading my Paterek manual (from 1985) to figure out what combination of head tube angle, axle to crown measurment, and offset, will give the most proper handling. Im starting with a frame for 26in wheels and a 70 degree head tube angle. With a bigger wheel this will make the bike ride like it has ape hangers and the wheel falling to one side and the other as I turn. But since im using a rigid fork, I dont have a boss blocking my wheel and I can go to a smaller axle to crown length. Does any one have any info to help
Here's a basic steering calculator. http://www.kreuzotter.de/english/elenk.htm
The steering-trail is much of what gives the steering feel of having stable handling but floppy at low speed or quick handling but twitchy at high speed. Weight distribution also makes a difference, with greater steering-trail the rider should be positioned more rearward over the back wheel using a slacker seat tube angle to reduce the weight on the front and heaviness in steering feel at low speeds.
Greater steering-trail is typically used for downhill oriented bikes for higher speeds and/or steeper drops, while shorter steering-trail for slow climbing easy balance and tight trail or quick XC or DS race handling. All mountain design is to blend easy climbing with slow to moderate downhill speeds over rough trail, and balance the two with steep seat angles and moderately longer steering trail than XC race and climbing oriented.
Use the calculator to compare known good feeling bike’s seat tube angle and wheel base with what you are designing.
Can you go 30-40mm shorter on the fork?
Else, get as short as you can, and make sure it's got a bit more offset.