[rocwandrer]

Ok, I pretty much know what I think I like in MTB geometry at this point, but the snow bike might be a bit different...

Top of my ponderings is the fork. I think I'll be running a 70.5 degree head angle. I don't want the bike wandering all over the place at low speed on technical winter singletrack. I also don't want a twitchy bike at the moderate (~20-25 mph tops, probably) top speeds it will see (ice and twitchy don't play well together).

I'm thinking I want to rake the fork out quite a bit more than is typical of production endomorph-capable snow bike forks. This has me worried. Why does the typical fat bike run so much trail? I figure trail on the low end of normal will be livable at speeds of 5-25 mph or so, and minimal trail will reduce the thrust wobble that happens in very low speed maneuvering around obstacles on the local (highly technical, even in winter when the snow isn't very deep) singletrack. I also wonder if there isn't some pneumatic trail at speed due to the drag on the big, low pressure tire that will help more at high speeds than it hurts at low speeds....

Thoughts?

 

[pvd]

I am mearly speculating and it sounds like you have much more experience riding snow than I. I have ridden snow and ice a bit, but not in a while and never by choice.

Here's my take...

I think that you would want the fork to have a minimum of offset (not maximum) to increase the arc or the wheel during turns. With a larger trail, the wheel motion is smoothed out in a turn allowing the tire to gently track in the snow. A small amount of trail will act more of a pivot than an arc, breaking the wheel free on the loose or slipery surface.

Again, pure specutlation.

 

[coconinocycles]

sand is the same way - it greatly increases the contact patch, moving it more towards you. also, i think your speed estimate is greatly exagerated. snow is some slow going. lots of walking, too........cheers, building nordic sit-ski chairs today, steve.

 

[perttime]

You can get 20mph, going down the hill on a really nice packed trail. You'll probably spend a lot more time well below, than above, 10 mph.

 

[Schmucker]

You can really fly across frozen over lakes.

 

[rocwandrer]

What did I say to get us so hung up on speeds....? I've been riding bikes on snow and ice for almost 20 years now. It is possible under some conditions (like riding with the wind on a frozen lake) to spin out an 11-44 gear. I was just giving some typical speeds. My last ride in the woods near my house was picking through half frozen puddles with roots in them, snow drifts, over partially downed logs, through rock fields, between trees that are only 2 feet apart, etc at between 0 and 10 mph. I want the bike to feel right at home in that sort of riding. The miles will probably be even split between that sort of riding and plodding along on deep snow partially packed by snowmobiles.

So, one recommendation for tons of trail, my thoughts the opposite. Maybe I should build two forks.....

 

[pvd]

So, one recommendation for tons of trail, my thoughts the opposite. Maybe I should build two forks.....

That would be a perfect test of what is best. Make sure that the head angle remains consistant. Let us know the results.

 

[Schmitty]

Anyone remember those Fisher fork drop outs from waaay back that had three different axle positions? I' m talking when Murray was king...

 

[Schmucker]

Walt's first fork had adjustable rake.

 

[SuspectDevice]

Steve,
Post up the Sit-Ski chairs... Would be interested to see your take on them. I spent Friday night waxing 15 of them and thinking about how to improve the handling of them while maintaining stability....

as far as snow bike... Yeah, I'd build with tons of trail. I'd like to picture a Spooky Snowbike as having the geo numbers from our CX bike scaled to fit 4" tires....

 

[TortugaTonta]

Are you talking about somethin like this?