- Chumba Racing EVO
- £1,300 frame only
- 6in travel all-mountain beastie
Chumba Racing has been around since 1993, having been founded by Ted Tanouye. It’s got a lot of history in gravity racing, having had various National and World Champions on its books. The company is based (and does all of its manufacturing in) Southern California, while Sorted Cycles bring the frames into the UK.
The new EVO (which apparently has to be capitalised, although we don’t know what, if anything, it stands for) is Chumba’s all-mountain frame. Chumba certainly isn’t shy of making big claims for it: “The stiffest, strongest, well-balanced, and best-handling bike on the market today,” says its website.
All dimensions based on M/L frame with spec as in photos
- Effective top tube length (TT) 23.5in
- Seat tube, centre to top (ST) 18.5in
- Chainstay (CS) 17.25in
- Wheelbase (WB) 43.5in
- Bottom bracket height 14.75in
- Head angle 68°
- Seat angle Anything between 61° and 72° depending on how you choose to measure it – see text for a fuller explanation
In these times of hydroformed this, forged that and monococque the other, a full-suspension frame made out of round tubes welded together is something of a novelty. Which isn’t to say that the Chumba isn’t innovative – the construction methods may be vaguely traditional, but the shape that they construct is pretty out-there.
The EVO’s profile is a classic example of form following function. Chumba’s Force Channeling Centralization suspension design demands that certain bits – the shock, the rocker, the various pivots – are located in certain places. Once you’ve put in the other unmovable bits (bottom bracket, head tube, rear axle etc) and joined all the dots while allowing sufficient clearance for the moving parts to move, this is the shape you end up with.
While we’re on the subject of FCC, here’s what Chumba says about it: “A unique, proprietary suspension system that uses torque conversion devices attached to a gusseted force channeling area. By strategically placing such devices on an area of the bicycle designed to bear loads – rather than weaker structural elements of the bicycle such as the seat tube – impact- and brake-induced forces are not only isolated, but channeled and centralized.”
What we think that means is that the rocker arm that links the seatstays and the shock pivots off the downtube rather than the more usual seat tube so that the suspension loads end up in the middle of the bike. To get a sensible suspension geometry, the rocker pivot has to be somewhere that downtubes don’t normally go, hence the EVO’s heavily-cranked tube. It’s actually two tubes welded together, with a hefty gusset to spread the loads. A useful side-effect of the downtube’s shape is better-than-usual clearance for fork adjusters on single-crown forks.
To avoid the top of the seatstays punching their way through the seat tube at the limit of compression, the seat tube is also a two-piece construction. The bit that the seat post fits into leans back at a crazy-looking angle, while the bottom section to the bottom bracket is getting on for vertical. This arrangement has a number of interesting consequences. For a start, you can’t use a conventional clamp-on front derailleur as the angle of the tube is well outside the range for which derailleurs are designed. Fortunately Shimano’s E-type plate-mounting mechs are there for just this kind of thing.
More dramatic is the effect of seat height on effective geometry. Because the bit of tube that the seat post mounts in doesn’t aim directly at the bottom bracket, the concept of a “seat angle” becomes something of a movable feast. The actual angle of the seat post is about 61°, while the effective seat angle of the frame – the angle of a line between the BB axle and the seat clamp – is a more conventional 72°. Which means that you’ll get a 72° seat angle with your seat right down but the higher it goes, the slacker it’ll get. With the seat at our pedalling height, a line from the BB axle to the top of the seat post sat at around 67°. Which is very slack indeed.
Certainly no complaints about the actual construction – it’s all tidily done and there are some very smart details. The seatstay yoke has a stiffening rib across its width, and that width is considerable, giving plenty of mud room. There’s also plenty of space at the chainstays, but only once the tyre is in place – anything bigger than about a 2.35in will probably have to be put in the frame deflated and then pumped up in situ as there’s a narrow bit just behind the chainstay yoke.
Other little details include the cut-away dropouts to minimise mech clatter and the “inside-out” swingarm pivot at the bottom bracket (the tabs on the BB run outside the swingarm rather than the more usual inside). There’s a lot of metal in it, though – even with an air shock you’re looking at 4.1kg (9lb) for the bare frame.
UK distributor Sorted just sells EVO frames, so we chucked our usual big-bike parts at this one – a Saint groupset, Syncros bar and stem, a random seatpost that happened to fit and a new Magura Wotan fork up front. The twin-braced, Maxle-equpped fork packs 160mm of travel – Chumba recommends 150mm of travel, but the Wotan is quite short for it’s stroke. The EVO is one of the few bikes for which the manufacturer actively (and strongly) recommends a fork with a lock-down or travel adjust feature. The Wotan’s lock-down drops the travel to a handy 120mm. The complete bike weighed a not-insubstantial 36lb (although quite a lot of that is in the old DX pedals…).
There’s a couple of points to note if you’re planning to build one of these up. First is that you’ll need a seatpost with a big range of available seat angles – the seat tube arrangement means that many posts will prevent you from getting the saddle level. You’ll also need an E-type front derailleur (the kind that mounts to a BB-mounted plate and is secured by a boss on the seat tube). If you’re planning to run a twin-ring-and-bashguard setup with a chain device, you’ll need to choose one that lets you mount the actual mech to it – with the mech sitting behind the drive-side BB cup, there’s nowhere to put the inner plate of a chain device.
Climbing aboard the EVO is a somewhat unfamiliar experience. For a start, it’s very high off the ground. The stated BB height is 14.25in, but with the Wotan fork and tallish Schwalbe tyres the test bike was nudging 15. It settles to the realms of normality with some weight on it, but at first you feel like you need a stepladder.
Second, you end up a long way back. While the seat angle isn’t anything like as slack as it looks, it’s still very relaxed and gets more so the higher you put the seat up. If you’re tall you find yourself perched above the rear wheel – if you think you can’t wheelie, try one of these. That makes for plenty of grip at the back but a somewhat wayward front end on climbs – it’s no accident that Chumba recommends a fork with a lock-down feature. With some shuffling and elbow-bending you can keep it on line, but you do have to work at it. A lock-down makes things a whole lot easier.
In fact, with the right fork (and the Magura Wotan we ran worked well for this) you may find that the best approach with the EVO is to ride it locked down most of the time and just open it up for the steeps. The Wotan loses 40mm of travel in lock-down mode, which is enough to steepen the bike up considerably but leaves a useful 120mm of travel still to go. The Chumba’s generous bottom bracket height means that you won’t end up dragging your pedals along the trail even with the front end dropped an inch and a half or so.
Leaving aside any issues of keeping it going in the right direction, the EVO pedals surprisingly well. With the linkage delivering a very up-and-down axle path for most of the stroke and no detectable pedal feedback, we were expecting it to be rather plungy. But even with all the DHX shock’s ProPedal damping would off it’s entirely acceptable. And with small-bump sensitivity to spare, adding ProPedal makes it better without compromising the suspension performance.
When you stand up, of course, the position of the seat becomes largely irrelevant, and the seat tube arrangement means that if you drop the seat it shifts forwards out of the way. That gives you a lot of freedom to move around on the bike, in particular to get over the bars to help the front end bite. Once you get into it, it’s a whole lot of fun – the high BB means that you can pedal through nearly everything, but it manages not to feel topply and nervous even though you’re a long way up. With a bit of familiarisation the EVO will deliver a level of agility that belies its heft, but it remains confident at speed and over drops and jumps.
A lot of that is down to the sheer solidity of the frame. Obviously there’s quite a lot of metal in it, but it’s cleverly distributed. The wide stance of the back end and hefty tubing all contribute to the planted feel. One thing’s for sure, you can always rely on the wheels being where you put them. Mind your legs, though – even test riders with pipecleaners for lower limbs tended to brush them on the stays.
Positives: Super-solid, good fun, agile yet stable, pedals well, plenty of mud room, sensible price
Negatives: Idiosyncratic geometry, limited seatpost choice, E-type front mech, needs work to get the best out of it, heavy, wide back end
Chumba’s EVO is an interesting proposition. It’s pitched as an all-mountain bike, but the weight and geometry seems to put it at the freeridey end of that particular spectrum, near to things like Specialized’s SX Trail. That said, it doesn’t mind being pedalled and with judicious component choices you could get it to an acceptable all-day weight. The unusual geometry means that you’ll have to think carefully about the spec if you want something trail-capable, though. You may not be the first to the top of the hills but if you’re not first to the bottom then it won’t be the bike’s fault. It has its niggles, but the price is pretty good. And if you think that the EVO looks like it might be a bit too much bike, have a look at the shorter-travel (and lighter) VF-1.