Yak Attack and Stage Racing. What bike?

© The penny farthing by Peter Jackson. Lookandlearn.com 

I'm often asked by potential racer's what bike I consider most suitable for Yak Attack.

Hardtail or full-suspension? Aluminium, carbon, titanium? etc.

So I thought I'd give a few thoughts on the matter.

First of all, if you are thinking about taking on The Yak Attack then just do it.

Anyone can do it. It is considered extreme and that is a fair tag but it's not so extreme that it's unattainable for most people. If I can do it so can anyone else.

You will need to have a reasonable level of fitness and bike handling skills but you certainly don't need to be anywhere near elite level to take part in, and enjoy, the adventure. The most important ingredient to finishing Yak Attack is grit.

Let's be honest here, it's more about the rider than the bike. The best riders will still win despite the machine. For anyone else comfort and survival are the primary motivators. However there are some performance advantages to be gained for everyone with prudent bike and component selection.

1. Buy the best that you can afford.
2. Any bike is better than no bike at all.

Frame material choice: There really isn't much of a contest going on here.
It's all about carbon or titanium. Aluminium is crap, the ride characteristics on a hardtail are harsh and you will get a sore bum very quickly on the rough and rugged Nepali trails; Unless it is your only choice then aluminium is best saved for smoother trails or full-suspension bikes.
Materials like carbon and titanium offer more absorption and a smoother ride.
I haven't personally ridden a titanium framed bike in Nepal so I can't draw an accurate comparison but quite a few riders have, including Race Director Phil Evans.
Carbon, in my experience, is fantastic. I'm certain, given anecdotal evidence, that titanium is equally so.
A good quality carbon frame is lighter, absorbent, accelerates quickly, and won't transfer the cold through to your fingers on the Thorong La hike-a-bike.

For Yak Attack 2012 I used an Aluminium Hardtail. I won't do that again.

Hardtail or full-suspension?
This is something that divides opinion quite a lot. There are advocates and opinions for both.
With Yak Attack in particular it's a trade-off situation, a lesser of two-evils, depending on your personal standpoint.
The climbing efficiency of a hardtail is indisputable for the 15000m of ascent, however the comfort, and additional grip, of a full-suspension is also indisputable given the harshness of Nepal's myriad rock-armoured trails. The mechanical simplicity of a hardtail over full-suspension is another factor to consider.
The weight advantage of a hardtail is less important these days; the increased push through of jeep roads has reduced the hike-a-bike to just Thorong La.
Decisions, decisions.

For 2013 & 2014 I used a 26" hardtail based around a Kona Kula Watt carbon frame with 120mm of travel. Great bike :)

Suspension travel.
100mm is sufficient to get the job done (front and rear). I'm quite an aggressive rider so I prefer 120mm up front.
There is no benefit from going any longer than 120mm; the steep climbs and minimal technical sections nullify the need for any more.

The wheel-size debate.
26", 27.5", or 29"?
These days 26" bikes are pretty much dead in the water. Fantastic advantages for descending but the roll-over and smoothness of bigger wheels has ended the debate in racing situations.
Most of the Nepali racers are small and so they tend to ride 27.5" now, thus far this hasn't proven to be a disadvantage over 29". Nepal National Champion Ajay Pandit Chhetri has won the last two editions on 27.5".
The nature of the trails in Nepal lend themselves to big wheeled bikes and I'd go 29" if you have the option available. Bolt-thru axles have also added greatly to the stiffness and efficiency of modern bikes making the 29er a no-brainer.
The recent advent of boost axle technology also gives the option of much stiffer wheeled 29ers should you want that.

Stan's Arch EX rims on Hope Pro2 EVO hubs, built by Moonglu.

Tyre choices also vary considerably.
The trails are rocky, rolling efficiency doesn't need to be a massive consideration, and pinch-flats can be numerous. Race weight tyres won't survive for very long. A tubeless-ready tyre with a robust sidewall is a necessity in my opinion.
The trails are generally dry, but mud, snow, and river crossings, will be encountered; a middle-of-the-road tread pattern will be most beneficial.
I like the big volume Maxxis Ardent 29x2.25" LUST, absolutely bombproof, the bigger volume tyres also add a bit of comfort. I'm considering switching to Maxxis Ardent Race or Maxxis Aspen for this year to save some weight on my paltry airline baggage allowance.
Maxxis Crossmark and Schwalbe Racing Ralph are very popular choices for many.
As with most things tyre choice is very personal. If in doubt sacrifice a bit of weight and go for something robust.

Drivetrain - 1x or 2x?
There's probably not much in it with the wide ranging cassettes available now.
Most people will still be running 2x10, and those granny-ring gears are quite nice when it gets super steep. The difficulty when running 1x will be choosing which size chainring to use. 30t, 32t, 34t? I'll tell you more after this years edition, where I'll be running 1x10 for the first time. I have an 11/42t cassette and my standard 34t chainring. I'm also taking a 30t chainring too and I'll be experimenting with it beforehand. Watch this space. 
Current 1x11 and 1x12 set-ups shouldn't be an issue for a suitably fit rider.

Carbon handlebars and seatposts, notwithstanding the obvious weight advantage, will also give a much more comfortable ride feel. If you only have an aluminium frame available then these will definitely be worth investing in. The Easton EC90 seatpost is a superb option if you can afford it, as are the Easton Haven bars and Renthal Carbon Fatbars.

Pedal choice is another personal preference but the efficiency and climbing benefits of SPD's far outweigh flat pedals. There isn't much in the way of technical descending, where flat pedals might offer an advantage. That said, however, on a couple of the stages where snow may be encountered then flat pedals and hiking boots can make life on and off the bike much easier.

Conclusion? 29" Carbon hardtail or a very light full-suspension bike with 120mm of travel.
Lightweight XC race bikes will just about survive the brutality of ten days hard racing but personally I'd worry less about saving a few hundred grams here and there and go for a more robust,  trail-ready, carbon hardtail at Yak Attack every time.

For what it's worth my current bike build is based around:
Pivot LES 29er carbon frame with a 142x12mm rear end and Fox Factory Performance FIT 120mm Fork - 15mm bolt-thru.
Moonglu built 29" Stans Arch EX rims and Hope Pro2 EVO Hubs.
Hope 165mm Crank (1x) and 34t chainring with bashguard.
Shimano 10spd XTR rear shifter and XT Shadow+ rear derailleur.
Sunrace 11-42t rear cassette.
Shimano XTR hydraulic disc brakes with 203mm (front) and 180mm (rear) discs. I have gone for bigger discs to help with cooling on the very long descents.
Rockshox Reverb dropper seat post (because I like it, and I'm not trying to win).
Fizik Gobi XM k:ium saddle.
Raceface Turbine 60mm stem.
Renthal 780mm Carbon Fatbar handlebars with a 10mm rise.
ODI Ruffian Lock-on Grips.
Shimano XT SPD pedals/DMR Vault flat pedals.
Maxxis Ardent 29x2.25 LUST tyres.

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