by Mark Alker
August 8, 2013
We often wonder how mountain bikes might have looked if they’d been designed from ground zero rather than having a junkyard heritage of rescued beach cruisers dictating most things. How large would the wheels and tyres have been? How much suspension would they have had? Actually that’s one question really, as suspension back then was […]
We often wonder how mountain bikes might have looked if they’d been designed from ground zero rather than having a junkyard heritage of rescued beach cruisers dictating most things. How large would the wheels and tyres have been? How much suspension would they have had? Actually that’s one question really, as suspension back then was dictated principally by tyre sizes.
There were plenty of tinkerers in the pioneering days playing around with 650b rims and tyres from European touring bikes, and a few playing with 700c. But the 26in option was quickly served by manufacturers of fat tyres and aluminium rims, so it stuck. We’ll take a stab in the dark now and speculate that the likes of Fisher and Breeze would have gone with Surly’s new 29+ tyres and rims if they’d been available. They’d have been a revelation in the days before fully sprung frames, for going up as well as bombing back down. Thirty-five years later, they still are. One of our test riders, after an hour of thrashing around the woods on the Krampus, said: “If I’d tried this six months ago I wouldn’t have spent three grand on a suspension bike.”
First, we’ll say it again: the Surly Krampus is not just another fat bike. Take a look at their website and you’ll see that the Krampus is listed under ‘Trail’, not ‘Omniterra’. Most fat bikes have rims based on the 26in norm, but wider, plus tyres big enough for floatation to be their principal raison d’etre. They’re great on sand or snow and fun elsewhere, but they’re overkill for most normal trails. The 29+ Krampus wheels, on the other hand, emphasise the advantages of a 29in wheel by running Surly’s own 3in-wide ‘Knard’ tyres, expanding the wheel’s rolling diameter to 31 inches but with a tread that rolls quickly and grips superbly, and with enough air volume to offer very impressive shock absorption. You could buy a Krampus frame and fork for £650 if you have your own ideas about how you’d like to equip it, and if you don’t want Surly’s 50mm ‘Rabbit Hole’ rims you can run conventional 29in wheels. Unlike full-fat bikes, the Krampus doesn’t need a special crankset and hubs. Frame clearance allows for conventional single or double ringed cranks: the limited front mech clearance excludes the use of an inner ring.
- Frame: 4130 chromoly steel
- Fork: 4130 chromoly steel
- Hubs: Surly front, Shimano rear
- Rims Surly Rabbit Hole 29 x 50mm
- Tyres: Surly Knard 29 x 3in
- Chainset: Shimano SLX, Salsa 34t single ring
- Front Mech: Chain guide
- Rear Mech: Shimano SLX 12-36t 10-speed
- Shifters: Shimano SLX
- Brakes: Avid cable disc
- Stem: Gusset
- Bars: Salsa ‘Whammy’ 780mm 11 degree
- Grips: Ribbed
- Seatpost: Kalloy
- Saddle: Velo
- Size Tested: Medium
- Sizes Available: S, M, L, XL
- Weight: 29.4lb (13.2kg) without pedals
It’s obvious that big wheels with knobbly 3in tyres run at the right pressure are going to be absorbent and grippy. The big surprise is that there’s so little drag. This is due to four factors: the shallow angle of attack over bumps and holes, minimum knob squirm in the low profile tread pattern, the surprisingly narrow (about 1.5in) tread print on hard ground and the rolling momentum of the effective 31in wheels once up to speed. Getting tyre pressure right is crucial. We found that about 15psi was perfect for rocky and rooty trails: too much and the rear tyre rebounds too obviously when you’re sat on the saddle, too little and things get squirmy when banking into corners. The Krampus effectively has an uncontrolled two inches of suspension travel at each end, so you tune the tyres to suit your riding style and body weight in the same way you tune air forks and shocks on a full suspension bike. The crucial difference in ride feel is that the tyres absorb the small rocks and roots without the constant geometry rocking that occurs on a bike with chassis suspension. There’s something very pleasing about that.
Because the 3in tyre girth offers such impressive traction and comfort as you bank into corners, this also gives you the confidence to carry speed to a level that would verge on becoming scary on other bikes. So you end up using the brakes less too. This in turn can give you an extra advantage from the rolling momentum that comes with heavier rims and tyres: the tyres and rims on our test bike added nearly a pound per wheel over an average 29in bike. You notice a bit more drag in initial acceleration on hard flat surfaces but you tend to make up for that elsewhere.
The Krampus shows that a relatively low-tech, steel framed, rigid forked bike can be designed to keep up with the high tech opposition on rough trails. Its rack, mudguard and bottle eyelets and the adjustable dropouts emphasise its adaptability and two inches of tyre squish tames bumps without the geometry tiltage of telescopic suspension. Comfort and control, also boosted by the stability of the long wheelbase, is excellent and you barely notice the weight on rougher climbs because rough surfaces are smoothed without obvious speed falter.
The Surly Krampus is both a superb exercise in bike design and an eminently pleasing bike to ride. If you think it might need a suspension fork then you’re not the right rider for it. The 29 x 3in tyres offer enough succour to keep all but the biggest slammers happy, and the way those treads just swallow the roots and stones without the usually bobbing of telescopic suspension is a real joy. The traction makes you want to power into corners instead of slowing. And, in case we haven’t said it enough already, it’s not just another fat bike. Everyone should test ride a Krampus. It’s revealing