Let's talk about SX...
By TMX Archives on 12th Jul 07
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 andlaunching the immensely popular 250SX-F and the revolutionaryelectric-start 450SX-F you could forgive KTM for resting on its laurelsa bit for 2008, but the ever progressive firm has been working hard andthe changes across the range, although minor, have once again improvedthe all round performance and reliability of a five bike range - 125SX, 250 SX-F, 250 SX, 450 SX-F and 505 SX-F - that is the mostcomprehensive and competitive on the market.
KTM has even taken the bold and commendable moveto put into mass production the exciting 144 SX model that it hopedwould compete alongside 250F machines in MX2 classes, but thanks to thereluctance of the powers that be in the UK and much of Europe to amendclass structures to give two-stroke machines a more level playingfield, the British market will receive no shipments of the 144 SX andthe closest we in Britain will get to racing it is looking at thepictures in these pages. It is a great shame too as the 144 SX is asuperb motorcycle with huge appeal and was certainly the highlight ofthe test for me personally.
AS previously mentioned, and well known by anyone at the racetrack, KTMput the SX range through a rigorous update for the 2007 line,developing an excellent new chassis and styling as well as giving theentire range serious attention in the engine department, from theformidable 125 SX right up to completely new 450 SX-F.
It really was a big year for the marque andunderstandably after a year of such major changes the list of mods tothe SX range is not as substantial, but the designers at Mattighofenhave been doing their homework and listening to feed-back, however, andthose changes that do appear have succeeded in making the range morerideable and reliable which is a winner on both fronts for customers.
Chassis developments again led the way for 2008with all models receiving revised suspension front and rear, as well asa new bend of Renthal handlebar.
The suspension was actually pioneered this year onthe new 450 SX-F and sees the front units get several internalmodifications including longer springs, a hydro-stop for the cartridge,and revised settings which produce less friction and improveddampening, while the rear shock now features an aluminium body, 10mmlonger, which provides a more progressive stroke and increasedresistance to bottoming.
In the motor departments it is the four-strokesthat ring in the most significant changes with the electric-starting450 SX-F flagship machine benefitting from new crank webs in thecrank-shaft (also shared with the 505 SX-F) which KTM claims increasesinertia weight and results in a smoother power delivery for bettertraction and handling, as well as receiving an additional clutch plateand additional holes in the inner clutch hub for longer durability. Anew 96dBa silencer to meet the 2008 FIM standards is also fitted.
Responsiveness has been the watchword for thephenomenally successful 250 SX-F with the little thumper receiving newvalve springs and exhaust cam timings, a new ignition mapping for thedual curve CDI unit, and larger diameter header pipe all with thepurpose of improving response and power delivery off the bottom-end inparticular.
Again for 2008 KTM remains the only one of the'big five' to continue to develop two-strokes and while the likes ofHonda will wave goodbye to the trusty smoker next year, KTM has ensuredthat its two-stroke machines, the 125 SX in particular, remain thepinnacle of the class with further small developments.
To that end the 125 SX receives new Keystone stylepiston rings to improve power and durability, optimised intake ductsand carburettor settings for a smoother power delivery, and newingniton 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 twodays of intense testing at a superb, and very hot, test facility inOliana, northern Spain recently so read on...
125 SX
ALREADY owner of the strongest motor in the 125ccclass, when KTM made further developments to the 125 SX motor for thisseason's machine it simply put it even further ahead of the pack.
The only downside was that the increased powerfrom the mid-range upwards gave the impression that the bike hadsacrificed a bit off the bottom-end and the power delivery was not assmooth and progressive as it had been in previous years.
For the 2008 incarnation the modifications to theintakes and ignition curve have rectified this and the 125 SX retainsits class leading power but delivers it in a smoother, more progressivemanner that makes it easier to put the power down on the track and aneasier machine to get the best out of for a wider range of abilities.
The bike just seems slightly more responsive andto have a little bit more grunt low down in the range this year andrequires less use of the clutch to keep the bike in the meat of thepower, and as you open the throttle the bike, to me, is noticeablysmoother and more tractable than the '07 model.
Not hugely so, but enough to make a smallimprovement in the bike's rideability and the riders confidence to pushit, 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 thetop-end remains as impressive as ever and when you get bike upright, ina straight line and really signing through the gears the over-rev isreally sensational and you can pull gears for what seems like aneternity.
Significantly contributing to the improvedtractability of the 125 SX also are the updates to the WP suspensionunits which have made a pretty big improvement to the overall handling.
The 450 SX-F had noticeably better suspension thanthe rest of the SX range this season and so it made sense to adoptthese developments across the board for 2008, and the two-stroke modelshave benefited most from this, the 125 SX in particular.
Previously the front end had always felt a littletoo hard and a little vague, especially at speed, and not particularlyin sync with the rear-end, but the new suspension units feel much morebalanced and both ends are noticeably more supple at slower speeds andearly in the stroke which obviously contributes to the tractabilityimprovement. The bike has always cornered fantastically but with thesenew suspension developments it is even better, so job done.
With a superb motor, increased smoothness and nowbetter suspension, the SX 125 pulls even further ahead of the packagain in 2008. It has to be your first choice if you are in the marketfor a 125cc two-stroke.
250 SX
THE 250 SX is the only bike in the range to remainuntouched in the engine department and as such there is nothingdifferent to report from this year's model in terms of its on-trackperformance.
The 250 SX has
traditionally been KTM's bogey bike, the one thatwas a bit fiery and just wasn't quite on a par with the rest, and to anextent this is still true with its fellow class-mate, the 450 SX-Fovershadowing it in terms of performance, but it is now a good 250cctwo-stroke and fans of these bikes will really like the motor.
A lot smoother than older 250SX models, the 2008has a strong yet linear spread of power through the bottom to mid-rangewhile the top end speed of the thing is still staggering, and it revsforever.
The big deciding factor on 250cc two-strokes, andthe area in which the old 250 SX was let down, is the transition fromthe 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 isvery smooth indeed making it a much easier bike to ride and the abilityto get the power down to the ground is improved also.
This has also been boosted by the improvements tothe suspension, notably to the balance of the bike when under load incorners and particularly on front-end stability which one area I stillthought the bike was weak last year.
It just had a tendency to get light and wander onstraights and fast corners which was not particularly confidenceinspiring, but with the new internals to the WP units the front feelsmuch more planted and connected to the bike and handling issignificantly improved by this.
The 250 SX is not the greatest bike in the KTM SXrange still, but it is a very good 250 indeed and riders in the marketfor a new smoker will really like it.
250 SX-F
Two years since its inception the 250 SX-F remainsvirtually unchanged, and with good reason - very little needed changingin the first place.
Very powerful yet incredibly smooth, tractable andtorquey in its delivery, like a small 450 almost, the bike also handledvery well indeed and was in short a great all round package that wasmore than a match for its competition.
As with the rest of the range though, the smallchanges made to the suspension and motor to boost engine responsivenesshave managed to make it that bit better all round.
The new suspension again affords a small butsignificant improvement to the handling of the bike and chassis, interms of a better balance between front and rear units and the abilityto 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 lineunder hard acceleration much better, and in an area where it has laggedslightly behind its Japanese rivals for the past couple of years it isnow more than a match.
I still feel that the motor is the best in itsclass though, and in the one area that it could perhaps have improved abit, its responsiveness, KTM has come up trumps.
The motor has always been supremely strong andsmooth in its power delivery, more so than its competition I think, butunlike its competitors' 250F machines there was a slight delay betweenyou twisting your wrist and the bike responding, especially in slowcorners and landing from jumps.
This has been rectified thanks to the new headerpipe and valve train, and the bike is now razor sharp and responsiveright off a closed throttle making the motor just about as good as Icould 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 thisseason yielded a huge number of developments that benefited the entireSX range but it was on the big thumper that they worked best as apackage and unsuprisingly the bike receives only two enginemodifications and the new bend Renthal 'bars by way of updates.
Because of this the bike remains virtually thesame in terms of ride and performance as the 2007 model. This is not abad thing though as the bike has undoubtedly the smoothest, mostforgiving and useable motor in the class despite being a contender formost powerful also, and manages to appeal to both the average clublevel 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 behonest out on track I couldn't really tell much difference. Because themotor was already so tractable though you can't really hold thisagainst the bike and it certainly does not detract from the overallpackage, it is still stupidly easy to ride.
Just roll on the throttle as hard or as lazily asyou like and the bike manages to find grip and drive, and with the fourspeed gearbox you can virtually just stick in third and ride it like anautomatic if you wanted.
On the subject of the four-speed box, the 450SX-Fwill be the only 450 to run one in '08 and I still feel that this bikeis the only 450 that has managed to make a four-speed box a success inthat you still get three useable gears out of it - second, third,fourth -while retaining an even spread and progression through them, and younever really find yourself wanting more on the track which is wheresome of the Japanese four-speed boxes slipped up in my opinion. Somepeople just are not fans of four-speed but to me if the bike rides thiswell and smoothly out on the track then why change it?
The one downside to the bike for me was the clutchwhich, already significantly heavier than the hydraulic units on therest of the range, feels a bit heavier again for 2008 which is notgreat for rider fatigue and arm pump.
The KTM designers added a ninth clutch plate anddrilled additional holes into the inner clutch hub to improve thedurability of the unit which to its credit it has achieved, but it isat the price of a light action and of all the bikes in the range it wasthis one that took its toll on my forearms faster and more severelythan any other.
I actually think that the new bend on the Renthalbars that all the bikes have may have contributed to this also as Ijust couldn't get on with them personally despite numerous adjustmentsto positioning. It's only a small gripe and I suspect that the majorityof riders will swap them over for a bar to suit their own personalriding style and needs pretty much straight away, but is worth takinginto consideration.
The rest of the chassis performed faultlessly,however, and the suspension units, with a year under their beltalready, really feel very balanced and create superb handling for sucha big bike. The 450 SX-F is undoubtedly one of the sharpest handlingand fastest turning 450's on the market and what really impressed mewith the suspension and handling the most is how well the front-endcopes with choppy stuff now and holds it line at speed.
505 SX-F
AS a very average riding, ten-stone weakling, Ifind myself very surprised saying this next statement, but I absolutelylove the 505 SX-F.
Being imported into the UK in limited numbers atthe request of dealers, the 505 SX-F looks like a 450 and rides likethe 450 in terms of its handling and suspension performance, butsomehow it manages to produce even smoother, more tractable andrideable 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 ifyou are an average level, average fitness rider looking for a newmachine to ride in the 450/ Open class next year you should seriouslygive 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 actuallyonly pumps out 477.5cc but really you don't notice the extra horsepowerover the 450 on the track.
What stands out instantly though is that it iseven smoother off the bottom-end and through the mid-range than the450, and for average riders this is a real bonus.
Instead of being scared of the bike, like I wasexpecting, I found it more enjoyable than the 450 and actually feltmore comfortable pushing on the 505, and my lap times were quicker andI was more aggressive through the corners. After being incredibly waryabout swinging a leg over it initially, by the end of the test youcouldn't keep me off the thing and I had the most fun riding this bikeout of the entire range.
It turns out the 505 is not just for big,moustachioed, mullet-haired Belgians, it's for you and me, averageunfit guys with very average riding skills.
The idea of a motocross bike is to complement therider and inspire confidence in him, and the 505 SX-F does thatincredibly well. It was a great way to round off the test sessions anda 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)
Specification: