SkiBike Design Part 1 - by Wayne Richards

Posted: Friday, 15 April 2011 by Mark Kinnon in Labels: ,

One has to think through a little what could constitute a good frame to modify from MTB to Skibike use.
My criteria was:
  • Full long travel suspension
  • Rear clearance for a chairlift to pass over the rear ski
  • Relatively low weight
  • Ground clearance along the side of the rear triangle ( some suspension bikes have lower triangle arms that are part of the mechanism of suspension and have parts lower than the rear wheel centre )
  • Last but not essential, a cheap or older frame no longer being used.
Highly desirable attributes ( and this is only a personal opinion ) were that the pivot point of the rear suspension should be ahead of the feet to transmit body weight to the front ski, most downhill bikes have this and for me equalising the weight onto both skis was quite desirable ( this has to be a late night bar discussion surely ).
The frame we chose gives a 60/40 split. Most XC and Enduro MTB frames with rear pivot seem to give closer to 70 /30 and could be compensated with a long ski / short ski but be careful as the sidecut radius needs to be the same on both skis.
We used 99cm Blade style skis, again second hand for about £ 45.00 on Ebay.

So we hit Ebay and went looking for an older style Y Frame type, eventually locating the frame brand new for less than £ 40.00 delivered, its overly engineered, needs to go on a diet but is simple and will allow quite simply for the rear subframe to be reversed to enable the bike to go into a suitcase.
We exchanged the original cheapo shock for a longer travel unit to match the long travel front forks we had sitting in the garage and it gave almost 150mm of travel front and rear, perfect. The only other thing in the build is the handle bar height, we chose a 75mm stem extension, others use BMX bars. From an initial trial run, keep the stem length as short as possible as the leverage from the bars will overcome the front ski “ edge carve / grip “and cause the front of the bike to tuck under. The consequences of this is the ensuing “ superman “ ejection from the cockpit, when it happens and it will, you will instantly understand what I mean.

Frame - well done eBay less than £40 delivered

On the first prototype ( OK it was a second hand Y frame we paid £ 14.00 delivered ) we cut off all the cable mounts but actually you can use them for mounting all the safety straps and such like. All up with skis, the bikes are less than 10kilos and I would think a sub 8.5 kilos production / purpose built skibike should be pretty achievable.

Mounting the skis is a bit of a conundrum. You can buy WinterX style Ali triangular mounts or make up your own as we did, out of Carbon. We did this for a number of reasons, mainly I feel the ski needs to be able to flex equally along the ski, to be able to carve and more importantly, we wanted a quick release system for getting a ski off as quite a lot of European resorts still run very small “ bubbles “ as lifts, we were not sure we would be able to get a 2.10 metre bike in crossways, take a ski off and no problems.
As it happens the resort we went to had more modern style lifts and simply turning the front ski sideways as you went into the lift worked OK.

Carbon Fibre Ski Mounts
The quick release though is still highly desirable as we discovered, on more than one night we got very “ Mozart and Blist “ on the way home and our Pension was a fair distance from the Apres Ski bars, no problem for us with walking boots, but the skiers amongst us were having none of that long walk business and as there was a taxi rank about 10 very unsteady paces from the bar and only 8 Euros for the taxi spread amongst 8 of us, it was a no brainer. But a 2.1m bike is not goner fit across the boot of a VW Caravelle, one ski off and no probs, that extra work was worth every hour spent.

The design we eventually made is probably a bit too sophisticated with proper “ oil-lite “ bearings, fully O ring protected to stop water and grit getting in, made of Carbon with Ali internals, again for lightness and takes a standard quick release from your mountain bike. They work well and I could perhaps draw up some drawings or have them made in numbers if there was enough requests.

The pegs also are probably more important than what you think. Our originals were simply a reducer from the original bottom bracket size to a pedal size, it works well and is dead cheap, but here is the big but, on harder snow, the steeper the terrain, the more we noticed the inside boot hitting the snow, enough so that on very steep slopes, your inside boots do get clouted quite a bit as the suspension sinks under compression from the G force. We think that a fixed peddle in this situation would either get wiped off over time or could “ unload “ the rear ski, something to ponder and argue over a beer on. Anyway again we took MX

Pegs - more important than you may think

So that’s about it, one thing for certain to build a ski bike is not going to be cheap to get it right, but it was good fun over the winter evenings and very rewarding in the end.

Looking for parts to build a skibike? Or perhaps one ready to ride away? See our Parts For Sale page here.

You can read part 2 of this series here ...