Let’s talk about SX...
Published: 12th July 2007
Author: Ben Johnson
A YEAR after it pulled out all the stops to deliver not only a new 450cc model in the shape of the 450 SX-F, the second brand new four-stroke delivered by KTM in as many years, but also a complete and radical re-design of the chassis’ of the entire SX motocross range, refinements, rather than radical developments dominate the five bike 2008 SX model range which will hit the Austrian manufacturer’s UK dealer showrooms right about the time you read this test.
After two consecutive years developing and launching the immensely popular 250SX-F and the revolutionary electric-start 450SX-F you could forgive KTM for resting on its laurels a bit for 2008, but the ever progressive firm has been working hard and the changes across the range, although minor, have once again improved the all round performance and reliability of a five bike range - 125 SX, 250 SX-F, 250 SX, 450 SX-F and 505 SX-F - that is the most comprehensive and competitive on the market.
KTM has even taken the bold and commendable move
to put into mass production the exciting 144 SX model that it hoped
would compete alongside 250F machines in MX2 classes, but thanks to the
reluctance of the powers that be in the UK and much of Europe to amend
class structures to give two-stroke machines a more level playing
field, the British market will receive no shipments of the 144 SX and
the closest we in Britain will get to racing it is looking at the
pictures in these pages. It is a great shame too as the 144 SX is a
superb motorcycle with huge appeal and was certainly the highlight of
the test for me personally.
AS previously mentioned, and well known by anyone at the racetrack, KTM
put the SX range through a rigorous update for the 2007 line,
developing an excellent new chassis and styling as well as giving the
entire range serious attention in the engine department, from the
formidable 125 SX right up to completely new 450 SX-F.
It really was a big year for the marque and understandably after a year of such major changes the list of mods to the SX range is not as substantial, but the designers at Mattighofen have been doing their homework and listening to feed-back, however, and those changes that do appear have succeeded in making the range more rideable and reliable which is a winner on both fronts for customers.
Chassis developments again led the way for 2008 with all models receiving revised suspension front and rear, as well as a new bend of Renthal handlebar.
The suspension was actually pioneered this year on the new 450 SX-F and sees the front units get several internal modifications including longer springs, a hydro-stop for the cartridge, and revised settings which produce less friction and improved dampening, while the rear shock now features an aluminium body, 10mm longer, which provides a more progressive stroke and increased resistance to bottoming.
In the motor departments it is the four-strokes that ring in the most significant changes with the electric-starting 450 SX-F flagship machine benefitting from new crank webs in the crank-shaft (also shared with the 505 SX-F) which KTM claims increases inertia weight and results in a smoother power delivery for better traction and handling, as well as receiving an additional clutch plate and additional holes in the inner clutch hub for longer durability. A new 96dBa silencer to meet the 2008 FIM standards is also fitted.
Responsiveness has been the watchword for the phenomenally successful 250 SX-F with the little thumper receiving new valve springs and exhaust cam timings, a new ignition mapping for the dual curve CDI unit, and larger diameter header pipe all with the purpose of improving response and power delivery off the bottom-end in particular.
Again for 2008 KTM remains the only one of the 'big five' to continue to develop two-strokes and while the likes of Honda will wave goodbye to the trusty smoker next year, KTM has ensured that its two-stroke machines, the 125 SX in particular, remain the pinnacle of the class with further small developments.
To that end the 125 SX receives new Keystone style piston rings to improve power and durability, optimised intake ducts and carburettor settings for a smoother power delivery, and new ingniton curve for further smoothening of the motor.
The big question though is do KTM's claims actually stack-up when you get the bikes out on the track?
T+MX News were lucky enough to find out over two days of intense testing at a superb, and very hot, test facility in Oliana, northern Spain recently so read on...
125 SX
ALREADY owner of the strongest motor in the 125cc class, when KTM made further developments to the 125 SX motor for this season’s machine it simply put it even further ahead of the pack.
The only downside was that the increased power from the mid-range upwards gave the impression that the bike had sacrificed a bit off the bottom-end and the power delivery was not as smooth and progressive as it had been in previous years.
For the 2008 incarnation the modifications to the intakes and ignition curve have rectified this and the 125 SX retains its class leading power but delivers it in a smoother, more progressive manner that makes it easier to put the power down on the track and an easier machine to get the best out of for a wider range of abilities.
The bike just seems slightly more responsive and to have a little bit more grunt low down in the range this year and requires less use of the clutch to keep the bike in the meat of the power, and as you open the throttle the bike, to me, is noticeably smoother and more tractable than the ’07 model.
Not hugely so, but enough to make a small improvement in the bike’s rideability and the riders confidence to push it, get on the throttle and still find grip which on the loose, hard-packed test track was impressive. >>>
The progression up through the mid-range to the top-end remains as impressive as ever and when you get bike upright, in a straight line and really signing through the gears the over-rev is really sensational and you can pull gears for what seems like an eternity.
Significantly contributing to the improved tractability of the 125 SX also are the updates to the WP suspension units which have made a pretty big improvement to the overall handling.
The 450 SX-F had noticeably better suspension than the rest of the SX range this season and so it made sense to adopt these developments across the board for 2008, and the two-stroke models have benefited most from this, the 125 SX in particular.
Previously the front end had always felt a little too hard and a little vague, especially at speed, and not particularly in sync with the rear-end, but the new suspension units feel much more balanced and both ends are noticeably more supple at slower speeds and early in the stroke which obviously contributes to the tractability improvement. The bike has always cornered fantastically but with these new suspension developments it is even better, so job done.
With a superb motor, increased smoothness and now better suspension, the SX 125 pulls even further ahead of the pack again in 2008. It has to be your first choice if you are in the market for a 125cc two-stroke.
250 SX
THE 250 SX is the only bike in the range to remain untouched in the engine department and as such there is nothing different to report from this year’s model in terms of its on-track performance.
The 250 SX has
traditionally been KTM’s bogey bike, the one that was a bit fiery and just wasn’t quite on a par with the rest, and to an extent this is still true with its fellow class-mate, the 450 SX-F overshadowing it in terms of performance, but it is now a good 250cc two-stroke and fans of these bikes will really like the motor.
A lot smoother than older 250SX models, the 2008 has a strong yet linear spread of power through the bottom to mid-range while the top end speed of the thing is still staggering, and it revs forever.
The big deciding factor on 250cc two-strokes, and the area in which the old 250 SX was let down, is the transition from the low to mid-range. If it is too fiery and the bike is hard to ride, but KTM has sorted this out on the 2008 250 SX and the transition is very smooth indeed making it a much easier bike to ride and the ability to get the power down to the ground is improved also.
This has also been boosted by the improvements to the suspension, notably to the balance of the bike when under load in corners and particularly on front-end stability which one area I still thought the bike was weak last year.
It just had a tendency to get light and wander on straights and fast corners which was not particularly confidence inspiring, but with the new internals to the WP units the front feels much more planted and connected to the bike and handling is significantly improved by this.
The 250 SX is not the greatest bike in the KTM SX range still, but it is a very good 250 indeed and riders in the market for a new smoker will really like it.
250 SX-F
Two years since its inception the 250 SX-F remains virtually unchanged, and with good reason - very little needed changing in the first place.
Very powerful yet incredibly smooth, tractable and torquey in its delivery, like a small 450 almost, the bike also handled very well indeed and was in short a great all round package that was more than a match for its competition.
As with the rest of the range though, the small changes made to the suspension and motor to boost engine responsiveness have managed to make it that bit better all round.
The new suspension again affords a small but significant improvement to the handling of the bike and chassis, in terms of a better balance between front and rear units and the ability to absorb square-edged kickers and choppy braking bumps in particular.
It just soaks everything up better than before, sits better in corners, especially loose sweepers, and holds the line under hard acceleration much better, and in an area where it has lagged slightly behind its Japanese rivals for the past couple of years it is now more than a match.
I still feel that the motor is the best in its class though, and in the one area that it could perhaps have improved a bit, its responsiveness, KTM has come up trumps.
The motor has always been supremely strong and smooth in its power delivery, more so than its competition I think, but unlike its competitors’ 250F machines there was a slight delay between you twisting your wrist and the bike responding, especially in slow corners and landing from jumps.
This has been rectified thanks to the new header pipe and valve train, and the bike is now razor sharp and responsive right off a closed throttle making the motor just about as good as I could imagine. It really does not have any weak spots.
Team it with the already sweet chassis and improved suspension and the 250 SX-F is a formidable package.
450 SX-F
The development of the new 450 SX-F for this season yielded a huge number of developments that benefited the entire SX range but it was on the big thumper that they worked best as a package and unsuprisingly the bike receives only two engine modifications and the new bend Renthal 'bars by way of updates.
Because of this the bike remains virtually the same in terms of ride and performance as the 2007 model. This is not a bad thing though as the bike has undoubtedly the smoothest, most forgiving and useable motor in the class despite being a contender for most powerful also, and manages to appeal to both the average club level 450 rider and Expert level pilots in equal measure. I really, really love the power delivery and spread the bike produces.
The addition of the new crank webs, KTM claims, further increases the smoothness and traction from the motor, but to be honest out on track I couldn't really tell much difference. Because the motor was already so tractable though you can't really hold this against the bike and it certainly does not detract from the overall package, it is still stupidly easy to ride.
Just roll on the throttle as hard or as lazily as you like and the bike manages to find grip and drive, and with the four speed gearbox you can virtually just stick in third and ride it like an automatic if you wanted.
On the subject of the four-speed box, the 450SX-F will be the only 450 to run one in '08 and I still feel that this bike is the only 450 that has managed to make a four-speed box a success in that you still get three useable gears out of it - second, third, fourth - while retaining an even spread and progression through them, and you never really find yourself wanting more on the track which is where some of the Japanese four-speed boxes slipped up in my opinion. Some people just are not fans of four-speed but to me if the bike rides this well and smoothly out on the track then why change it?
The one downside to the bike for me was the clutch which, already significantly heavier than the hydraulic units on the rest of the range, feels a bit heavier again for 2008 which is not great for rider fatigue and arm pump.
The KTM designers added a ninth clutch plate and drilled additional holes into the inner clutch hub to improve the durability of the unit which to its credit it has achieved, but it is at the price of a light action and of all the bikes in the range it was this one that took its toll on my forearms faster and more severely than any other.
I actually think that the new bend on the Renthal bars that all the bikes have may have contributed to this also as I just couldn't get on with them personally despite numerous adjustments to positioning. It's only a small gripe and I suspect that the majority of riders will swap them over for a bar to suit their own personal riding style and needs pretty much straight away, but is worth taking into consideration.
The rest of the chassis performed faultlessly, however, and the suspension units, with a year under their belt already, really feel very balanced and create superb handling for such a big bike. The 450 SX-F is undoubtedly one of the sharpest handling and fastest turning 450's on the market and what really impressed me with the suspension and handling the most is how well the front-end copes with choppy stuff now and holds it line at speed.
505 SX-F
AS a very average riding, ten-stone weakling, I find myself very surprised saying this next statement, but I absolutely love the 505 SX-F.
Being imported into the UK in limited numbers at the request of dealers, the 505 SX-F looks like a 450 and rides like the 450 in terms of its handling and suspension performance, but somehow it manages to produce even smoother, more tractable and rideable power than its smaller sibling.
It's incredible, and I don't think I have thrown a leg over a bike that is easier to ride in my life, which is in complete contrast to what I was expecting, and for me if you are an average level, average fitness rider looking for a new machine to ride in the 450/ Open class next year you should seriously give thought to
the 505 SX-F because there is a very strong chance you will find it a more forgiving and rewarding ride than the 450.
Not a true 505cc machine, the 505 SX-F actually only pumps out 477.5cc but really you don't notice the extra horsepower over the 450 on the track.
What stands out instantly though is that it is even smoother off the bottom-end and through the mid-range than the 450, and for average riders this is a real bonus.
Instead of being scared of the bike, like I was expecting, I found it more enjoyable than the 450 and actually felt more comfortable pushing on the 505, and my lap times were quicker and I was more aggressive through the corners. After being incredibly wary about swinging a leg over it initially, by the end of the test you couldn't keep me off the thing and I had the most fun riding this bike out of the entire range.
It turns out the 505 is not just for big, moustachioed, mullet-haired Belgians, it's for you and me, average unfit guys with very average riding skills.
The idea of a motocross bike is to complement the rider and inspire confidence in him, and the 505 SX-F does that incredibly well. It was a great way to round off the test sessions and a great book-end to another superb SX range from KTM.
2008 Model KTM 125SX
ENGINE
Type: Single cylinder two-stroke
Displacement: 124.8cc
Bore x stroke: 54/ 54.5mm
Carburetor: Keihin PWK 39
Cooling: Liquid cooled
Starter: Kick-starter
Transmission: Six-speed
Primary Ratio: 23 : 73
Final Drive: 13 : 50
Clutch: Wet multi-disc clutch, operated hydraulically
Ignition: Kokusan digital magneto CDI
CHASSIS
Frame: Central double-cradle-type, 25 CrMo4
Subframe: Aluminium 7020
Handlebar: Renthal, Aluminium 28/22mm
SUSPENSION
Front: WP USD, 48mm
Rear: WP PDS shock absorber
Travel Front/ Rear: 300/ 335mm
Brakes Front/ Rear: Disc brakes 260/ 220mm
Rims Front/ Rear: Excel 1,60 x 21"/ 2,15 x 19"
Tyres Front/ Rear: 80/100-21"/ 100/90-19"
Main Silencer: Aluminium
Steering Head Angle: 63°
Wheelbase: 1471mm
Ground Clearance: 390mm
Seat Height: 925mm
Fuel Capacity: 7.5 litres
Weight: 90.8kg (Without fuel)
2008 Model KTM 250SX
ENGINE
Type: Single cylinder two-stroke
Displacement: 249cc
Bore x Stroke: 66.4/ 72mm
Carburetor: Keihin PWK 36SAG
Cooling: Liquid Cooling
Starter: kick-starter
Transmission: Five-speed
Primary Ratio: 26:76
Final Drive: 13:48
Clutch: Wet multi-disc clutch, operated hydraulically
Ignition: Kokusan digital magneto CDI
CHASSIS
Frame: Central double-cradle-type 25 CrMo4
Subframe: Aluminium 7020
Handlebar: Renthal, Aluminium 28/22 mm
SUSPENSION
Front: WP USD, 48mm
Rear: WP PDS shock absorber
Travel Front/ Rear: 300/ 335mm
Brakes Front/ Wheel: Disc Brakes, 260/ 220mm
Wheels Front/ Rear: Excel, 1,60 x 21"/ 2,15 x 19"
Tyres Front/ Rear: 80/100-21"/ 110/90-19"
Main Silencer: Aluminium
Steering Head Angle: 63.5°
Wheelbase: 1475mm
Ground Clearance: 385mm
Seat Height: 925mm
Fuel Capacity: 7.5 litres
Weight: 95.4kg (Without Fuel)
2008 Model KTM 250 SX-F
ENGINE
Type: Single cylinder, DOHC four-stroke
Displacement: 248.6cc
Bore x Stroke: 76/ 55mm
Compression Ratio: 12.8:1
Carburetor: Keihin FCR-MX 39
Cooling: Liquid
Starter: kick-starter
Transmission: Six-speed
Primary Ratio: 22:68
Final Drive: 13:48
Clutch: Wet multi-disc clutch, operated hydraulically
Ignition: Kokusan digital magneto CDI
CHASSIS
Frame: Central double-cradle-type 25 CrMo4
Subframe: Aluminium 7020
Handlebar: Renthal, aluminium 28/22mm
SUSPENSION
Front: WP USD. 48mm
Rear: WP PDS shock absorber
Travel Front/ Rear: 300/ 335mm
Brakes Front/ Rear: Disc brakes, 260/ 220mm
Wheels Front/ Rear: Excel, 1,60 x 21"/ 2,15 x 19"
Tyres Front/ Rear: 80/100-21"/ 100/90-19"
Main Silencer: Aluminium
Steering Head Angle: 63.5°
Wheelbase: 1475mm
Ground Clearance: 380mm
Seat Height: 925mm
Fuel Capacity: 7.2 Litres
Weight: 98kg (Without Fuel)
2008 Model KTM 450 SX-F
ENGINE
Type: Single cylinder DOHC four-stroke
Displacement: 449.3cc
Bore x Stroke: 97/ 60.8mm
Compression Ratio: 12.5:1
Carburetor: Keihin FCR-MX 41
Cooling: Liquid
Starter: Electric
Tranmission: Four-speed
Primary Ratio: 29:74
Final Drive: 14:52
Clutch: Wet multi-disc clutch, operated hydraulically
Ignition: Kokusan digital DC CDI
CHASSIS
Frame: Central double-cradle-type 25 CrMo4
Subframe: Aluminium 7020
Handlebar: Renthal, aluminium 28/22mm
SUSPENSION
Front: WP USD, 48mm
Rear: WP PDS shock absorber
Travel Front/ Rear: 300/ 335mm
Brakes Front/ Rear: Disc brakes, 260/ 220mm
Wheels Front/ Rear: Excel, 1,60 x 21"/ 2,15 x 19"
Tyres Front/ Rear: 80/100-21"/ 110/90-19"
Silencer: Aluminium
Steering Head Angle: 63.5°
Wheelbase: 1475mm
Ground Clearance: 380mm
Seat Height: 925mm
Furel Capacity: 8.2 litre
Weight: 104.6kg (Without Fuel)
2008 Model KTM 505 SX-F
ENGINE
Type: Single cylinder DOHC four-stroke
Displacement: 477.5 cc
Bore x Stroke: 100/ 60.8mm
Compression Ratio: 12.5:1
Carburetor: Keihin FCR-MX 41
Cooling: Liquid
Starter: Electric
Transmission: Four-speed
Primary Ratio: 29:74
Final Drive: 14:52
Clutch: Wet multi-disc clutch, operated hydraulically
Ignition: Kokusan digital DC CDI
CHASSIS
Frame: Central double-cradle-type 25 CrMo4
Subframe: Aluminium 7020
Handlebar: Renthal, aluminium, 28/22mm
SUSPENSION
Front: WP USD, 48mm
Rear: WP PDS shock absorber
Travel Front/ Rear: 300/ 335mm
Brakes Front/ Rear: Disc brakes, 260/ 220mm
Wheels Front/ Rear: Excel, 1,60 x 21"/ 2,15 x 19"
Tyres Front/ Rear: 80/100-21"/ 110/90-19"
Silencer: Aluminium
Steering Head Angle: 63.5°
Wheelbase: 1475 mm
Ground Clearance: 380mm
Seat Height: 925mm
Fuel Capacity: 8.2 litres
Weight: 104.6kg (Without Fuel)