KTM Enduro Model … With an Air Fork?
A couple of weeks ago, when KTM released their all-new WESS special edition model 350EXC-F – a bike that pays homage to KTM’s success in the WESS Enduro World Championship – it prompted a lot of social media discussion about the fact this enduro model was fitted with WP’s air-sprung AER fork (along with a bunch of other special components, that is).
But is this WESS-edition 350EXC-F KTM’s first enduro model to be fitted with WP’s AER air fork? From a production bike point of view, yes. But it’s not the first time a 350EXC-F has been fitted with an air fork. Back in late 2016 – to get an insight into the relative feel, performance and adjustability of air-sprung and coil-spring forks – we rounded up three 2017-model KTM 350s, and put WP’s new 48mm AER (air-sprung) and Xplor (coil-sprung) forks head-to-head in a variety of terrain.
This content was first published in the Nov-Dec 2016 issue (#59) of Transmoto Dirt Bike Magazine, and it made for some fascinating insights…
Because your front wheel is the first thing to come in contact with any obstacle, the fork it’s attached to plays a critical role in a bike’s steering, handling and overall performance. While it’s possible to ‘ride around’ an under-performing engine, shock absorber or brakes, it’s near impossible to push a dirt bike hard unless its fork has a compliant and predictable action. Put simply, the way your fork reacts to bumps sets the tone for the entire bike’s ride, and that directly affects the speed, safety and comfort of the rider onboard.
Given that KTM has introduced two new WP forks for 2017 – the 48mm ‘AER’ air-sprung fork on its motocross (and four-stoke cross-country) models, and the 48mm ‘Xplor’ coil-sprung fork on its enduro models, we figured a back-to-back comparison between the two was in order; a test that would shed some light on the forks’ comparative performance and versatility, and give us sense of whether an air fork is likely to soon find its way onto KTM’s enduro range.
To bring this comparo alive, we joined forces with the guys from Australia’s number-one KTM dealer, KTM Newcastle, and pitted three 2017-model KTM 350s – a 350SX-F motocrosser, a 350EXC-F enduro model, and a hybrid 350XC cross-country machine – against each other in the bush and around a motocross track. In addition to generating feedback about each fork’s performance across a variety of terrain, we also address the scepticism that continues to surround air forks in a bid to quarantine fact from fiction.
TEST TRACKS & TEST RIDERS
To get a well-rounded feel for the differences between WP’s 2017-spec air (AER) and coil (Xplor) forks, we tested the three KTM 350s at two very different tracks. The first was the Gunns Gully-based Transmoto 6-Hour, whose 15km loop included rootinfested singletrack, snotty rock gardens and flowing grasstrack. The other was Lakes Motocross track, an undulating hardpack circuit with lots of hard downhill braking zones that put a premium on front-end feel and fork performance. And to ensure we had a good cross-section of rider weight and abilities, our test pilots were: Pro rider, Brock McLeary (65kg); B-grade Vet, Shane Place (75kg); and fast-as-f#@k Vet, Greg Timmins (97kg).
KTM’s THREE 350s – SETTINGS SNAPSHOT
Here’s what stood out about each of the three 2017-model KTM 350s we used in this comparo, and the optimal settings our three test riders found for them…
THE MXER 350SX-F:
- Unless you’re a 100kg+ rider, the manual’s recommended 154psi for the bike AER fork will feel way too firm, no matter how big the jumps on the rack are. Irrespective of rider weight, lower pressures in the fork produce a much better front-to-rear chassis balance.
- Our 97kg tester settled on 144psi, finding that it created a much more balanced chassis, but added a few clicks of compression damping on the motocross track to ensure the fork didn’t ride down in the firmer part of its stroke. Our Pro-level 65kg rider (who admits he’s always preferred a softer set-up) settled on 132-134psi, saying the lower pressure gave him much better front-end feel, traction and an ability to hold or change lines better through turns – all without blowing through the stroke during downhill braking bumps or jump landings.
- Our 75kg intermediate-level tester found his favoured setting was around 138psi, combined with 23 clicks out (standard is 17 out) of compression damping.
THE ‘HYBRID’ 350XC-F
- On the bush loop and motocross track, all three testers found this bike – which uses a combination of the MX and enduro model components – a great all-rounder. It retains the punch of the MX-spec engine, while its suspension (AER air fork and linkage-assisted shock absorber) happily handles the rough stuff.
- With plusher compression damping settings in its AER air fork (relative to the SX-F), the XC-F has a more forgiving ride over snotty trail obstacles. Similarly, the bike’s softer shock settings creates great drive on the hardpack MX track and over square-edged trail bumps, but it still resists bottoming over MX track jumps pretty damn well.
- Even with its softer valving, the recommended 142psi for the XC-F’s air fork is a good base setting for MX, but too firm for off-road use. We found that 132-135psi gives it a much more compliant ride over the roots and rocks you find on an average trail loop, without compromising chassis balance and bottoming resistance for most trail situations. At those lower, trail-oriented pressures, however, the fork bottomed too easily around the MX track.
THE ENDURO BIKE 350EXC-F
- The all-new Xplor fork and shock give the 2017 EXC-F a really well balanced chassis, which makes for a confidence-inspiring ride when you’re pushing hard in tight, tree-lined terrain. Compared to its predecessor, the Xplor fork is just as sensitive over small bumps, and yet it offers significantly more damping progression and bottoming resistance for big hits or accidental flat landings. And while this new fork does tend to ride lower in its stroke when pushed hard on the MX track, it still manages to ‘catch’ the compression toward the end of the stroke and offers really good bottoming resistance.
- The softer suspension settings allow the bike to settle and squat into turns, and this produces great feel, predictability and drive where traction is at a premium. And the no-linkage PDS shock is particularly good at hugging the ground over a series of small, square-edged bumps at lower speeds. As you’d expect, however, this comes at the expense of bottoming resistance on the motocross track.
- The bike’s DDS (Damped Diaphragm Steel) clutch creates a noticeably lighter pull at the lever, and a gentler modulation that actually helps the rear wheel find traction over chattery bumps and slick hardpack.
- With lower engine compression ratio and lighter valve springs (to suit the 1000rpm lower rev limit), the enduro machine has noticeably less engine braking. That made the bike easier to ride fluidly through singletrack, snotty terrain and, interestingly, on the slippery sections of the MX track.
THE BIG QUESTION: 350EXC-F WITH AER AIR FORK
NOTE: As the AER fork is approximately 20mm longer than EXC-F’s Xplor fork, we ran the air fork about 15mm up through the triple clamps on the enduro machine (which is where it hit the handlebars) to best replicate the EXC-F’s chassis geometry (see pic, right).
- With the much lighter AER fork fitted, the bike’s steering (even at walking pace in the pits) felt noticeably lighter. In tight and technical terrain, this made the entire bike feel lighter and more nimble.
- Running the air pressures they’d felt most comfortable with in the AER fork, all three testers reported that the AER air fork held up in its stroke better than the Xplor fork, and offered a more progressive feel through its stroke. For the two heavier testers, in particular, that translated into more confidence through braking bumps and during turn-in, and a more stable chassis (mainly due to less of a hobby-horse effect).
- On hard downhill braking, the AER fork is able to sit up in its stroke better, and this gives the entire chassis a more composed, stable feel. By comparison, the Xplor fork tends to ride down in firmer part of its stroke. That said, its hydrostop design still delivers remarkably good control in the last third of the stroke and excellent resistance to bottoming.
A-GRADE VET: GREG TIMMINS (43, 97KG, 178CM)
“I own a 2017 450SX-F, so this exercise was really interesting for me. I’ve quickly become a convert to air forks. I’m a heavier guy, so I love the range of adjustment they give you, though it does take a while to work out a good balance between air pressure and clicker settings. And it’s worth noting that the recommended pressure in KTM’s manual is way high. While the enduro bike’s Xplor fork obviously works well in the bush – and its chassis is well balanced – both fork and shock were very soft for my weight, and I had no way of changing that without handing the bike over to a suspension tuner. Around the MX track, the Xplor fork rode way too low in its stroke for me, but it did have surprisingly good bottoming resistance. When we fitted the air fork to the EXC-F (with the 144psi I like in it), the enduro bike was a heap more fun to ride because it was more stable and predictable everywhere. The fork’s action was progressive and it resisted bottoming well. The only downside with the air fork is that you need to check it before each ride. I’ve got accustomed to doing that when I check tyre pressures, but I’ve actually found the pressure in the fork barely changes.”
B-GRADE VET: SHANE PLACE (42, 75KG, 170CM)
“To me, the best things about the air fork are its progression and its adjustability; the way you can change settings at no cost to suit different track types and conditions, and rider weight and ability. It encourages you to experiment, which helps you understand how your bike responds to different settings. With all that adjustment on offer, you can find a happy medium between an acceptable firmness in the initial part of the stroke, while still having a plush ride over small bumps and good bottoming resistance. At the air pressure I needed to prevent it bottoming (around 138psi), I did have to give up some of that initial plushness relative to the Xplor fork, but not a lot. To its credit, the Xplor does resist bottoming really well, but I think it would benefit from some added spring preload to help prevent it from falling through the mid-stroke in the hands of a heavier, faster rider. Once you get the AER air fork’s settings right for you, I reckon it has a more progressive and predictable action throughout the entire stroke. I know most off-road guys remain sceptical about air forks, but I think they’ll have to embrace them before long. They offer so many benefits, and no downsides that I can see (aside from the minor inconvenience of the rebound clicker being on the bottom of the fork leg.”
PRO: BROCK McLEARY (19, 65KG, 174CM)
“I was amazed how even a 5psi change to the pressure in the air fork could have such a large impact on how the entire bike rode – its chassis balance, braking stability, and the way it’d turn in and then squat in turns. And on the hardpack MX track, that made a massive difference to the bike’s traction – at both ends – and my confidence to push the thing. Similarly, just two compression clicks on the AER made a really noticeable difference. I actually felt that the AER and Xplor forks had a pretty similar action, but at the 132psi I found I liked in the AER fork (mainly to help it squat and keep my cornerspeed up), it didn’t initially have as much bottoming resistance as the Xplor fork. But after winding some compression clickers back into the air fork, I found a really good setting that made it better than the Xplor everywhere. For me, this test really reinforced how much tunability an air fork puts back into the rider’s hands. It’s going to mean more trial and error to get the thing set-up right for different tracks and conditions, but that also gives you a better understanding of your bike. To me, enduro bikes need to be super-versatile, and the AER air-sprung fork fits that description to an absolute T.”
KTM’s WP FORKS – EVOLUTION OF THE SPECIES
- 1998 – The first of the new-era KTMs arrived with a no-linkage PDS shock absorber on the rear-end and a 43mm open-cartridge WP fork up front.
- 2003 – KTM’s enduro models were all fitted with the upgraded 48mm open-cartridge WP fork. This same open-cartridge fork – albeit with updated componentry and revised settings – was used right up to the 2016 enduro range.
- 2017 – KTM surprised everybody by revealing an all-new WP ‘XPlor’ fork (and shock absorber) across their entire enduro range. The Xplor fork uses an open-cartridge design with compression and rebound functions split between the fork legs – both of which have coil springs, a new ‘hydro-stop’ hydraulic bottoming system, and tool-free star-clickers in the fork caps. Initially considered a bold move (because the existing PDS shock and open-cartridge fork had been refined into a hard-to-fault package), the Xplor fork and shock soon proved to have broader operating range. That made the 2017 bikes more user-friendly and versatile across a broader variety of terrain and rider weight/ability.
- 2007 – KTM’s motocross models moved from the 48mm open-cartridge fork to a 48mm closed-cartridge fork.
- 2015 – The bikes sold in the American and Australian markets were fitted with WP’s 4CS (4 Chamber System) 48mm fork, while the KTMs in Europe retained the WP 48mm closed-cartridge fork. With the benefit of hindsight, KTM would probably acknowledge the 4CS move was driven more by marketing concerns than performance. After all, the 4CS was specifically designed with added stanchion flex to create the sort of supple, compliant ride suited to enduro bikes, not MXers.
- 2016 – The USA/Australia-spec bikes retained the WP 4CS fork, while the bikes sold in Europe were fitted with WP’s all-new 48mm AER air-sprung fork. Why the discrepancy between markets? Well, as KTM’s Joachim Sauer conceded, “WP did not have the capacity to produce the AER air fork for our entire worldwide production of 2016 year-models, so the bikes we sent to the USA and Australia retained the 4CS for another year.”
- 2017 – Worldwide, KTM’s MX (and four-stroke cross-country) models were fitted with WP’s 48mm AER air-sprung fork. Compared with the AER fork used on the European bikes in 2016, the 2017-spec AER fork gets revised flex characteristics in the outer stanchion (this helps inner and outer tubes bend in greater harmony for reduced stiction), and an upgraded upper triple clamp to suit.