SX-Y Thing!

20 September 2022

I’m feeling thankful. Blissful times have returned to KR HQ. We’ve had a 250 two-stroke in to test, for the first time since, well, forever. The bike in question is KTM’s 250 SX - without the F bit. A good old-fashioned motocross two-stroke; a real MX bike. Some of you older riders will already have joy in your hearts at the very thought. Minds wistfully going back to the heydays of pre-mix, castor oil, av-gas and the glorious sound and smells of a crisp two-stroke on the pipe. My heart warms simply tapping this out.

THE PERFECT CAPACITY
Seriously, it’s a 250 MX engine; the best all-round two-stroke motocross engines ever made. Forget any romantic notions you may have of the two-stroke 500s, truth be told, they were pigs of things. Sure, they were amazing fun on the right track, but mostly they were hard work and punished mistakes, often brutally, when conditions didn’t suit. Likewise, the awesome 125 engine, but for different reasons...with a usable powerband about the width of a skinny kid’s wrist, they were a real challenge to ride fast too. Fall off the pipe for a fleeting moment and you’d lose two places in an instant. 

The 250 motocross engine had it all – post introduction of power valves that is. Amazing low-end torque and thrust into the mid-range, followed by a searing top end. To say the power delivery was linear would be something of a stretch... and some were anything but – but despite some having significant power band effect, most were still quite manageable.

In essence, 250s are very fast and largely fail safe for the rider. Of course, younger riders might disagree, perhaps finding them a bit of a handful. But then their riding education is sadly lacking, having been spoilt by the current super smooth four-strokes, unfortunately making them very ‘soft’. I hear that some brands of the latest 250 four-strokes even come with hand cream, a hairnet for the man bun and some Vaseline for the pimples. Am I right? Please send all complaints in writing...

TIME-PROVEN FORMULA
Now, let’s stop taking the proverbial, put the nonsense aside and get to the 2021 KTM 250SX and truth reveal. I’ve seldom ridden two-strokes in the last 20 years and truly love my KTM 500 EXC four-stroke, but I was instantly at home on the 250SX. It took me right back to my two-stroke days; it felt so right, so light, quick and very familiar. So much so that later I compared spec sheets between the 2021 KTM 250SX with a 1989 Honda CR250R – the standout model of the time. And guess what? Not that much has changed. The same 249cc, identical 72mm stroke and 66.4mm bore, the same 96kg dry weight, similar power output of around 41hp, a similar sized 7.5 litre fuel tank. Both have Kokusan ignitions. The list goes on.

The only real engine changes are the move to a nicely light, hydraulically actuated Brembo clutch and the addition of a balancer shaft (that certainly means the modern bike has the barest hint of vibration compared to the old smokers). Even the chassis are alike with double cradle chrome-molly frames, USD forks and a rising-rate linkage rear end. 

CHASSIS 
However, obviously, the new ergonomics are miles ahead and suspension action is unbelievably good compared to the 33-year-old Honda. The much flatter riding position is brilliant, although seat comfort has gone backwards... oh well. 

The two huge improvements in suspension action are plushness and bottom-out resistance. Early USD forks were as supple as a brick and the shocks were kind of harsh... then they bottomed out. The KTM SX glides over square-edged holes that would have the Honda head-shaking the bars out of your hands, and nicely absorbs massive jumps and landings that would most likely have seen you on a wee trip to A&E back in the day. No question, hugely better suspension action all-round. 

Both ends have WP XACT units with 48mm USD forks giving 310mm travel and the single shock delivering 300mm wheel travel. Interestingly, the old CR had 320mm travel out back and around 300mm at the front. 

Both old and new machines turn extraordinarily well. The KTM has a slightly steeper (sharper turning) 63.9 steering head angle than the CR, but the KTM balances that out with a lower rear end and longer forks. The overall result is they both turn superbly, but the KTM is more stable. 

There’s no question the 250 SX has a vastly superior front brake. The 260mm front disc on the KTM is 20mm larger, offering much greater stopping power and also better feel. It is excellent out of the box. The rear brakes are about equal in strength,, but the old CR might have a very slight edge in feel if my memory bank serve me correctly. The small 220mm KTM rear disc brake has never been a stand out, but definitely gets the job done well enough. 

POWER DELIVERY
The KTM has a wonderful power delivery. The 250SX is strong everywhere, smooth and responsive, has excellent torque and is easy to ride. It pulls super well and surprisingly smoothly into the mid-range where it comes on the pipe very powerfully. It then has a very manageable progression to a decent top end. The top end is not comparable to a four-stroke revs wise but it’s still strong. For this type of engine, it’s very linear and easy to ride. It really is truly impressive. 

CRACKING RACE BIKE
Overall, this is a wonderful race bike. One that’s totally competitive even in the modern world on a cc basis and superior to four-strokes in some conditions. I must say here that the bike was not entirely standard; it is Damon Neild’s personal race bike and has some modifications mainly aimed at bullet-proofing it for cross-country racing. So, many thanks to Damon for the test ride, it was a genuine pleasure!

SECOND OPINION
Ever since KTM moved to the TPI technology on the EXC range there has always been the memory of how good a two-stroke with a carburettor was. Was this just nostalgia, remembering all the good times and none of the bad? Perhaps, but, nevertheless, I was eager to twist the throttle on the new 250SX!

Damon Nield (the bike’s owner) has thrown the aftermarket parts catalogue at this bike, but one part that caught my eye was the Two Stroke Performance high compression head. The first thing I should’ve done after seeing this mod was tighten up my belt a couple of clicks because, paired with the JW seat cover, it had you looking like you’d borrowed MC Hammer’s pants. 

The FMF powercore silencer gives it a raspy, crisp sound that just made me want to rev it. However, the TSP head meant that with the increase in power I could also run a taller gear to take full advantage of the low end power; smoothing out the power hit. The engine is surprisingly torquey; making getting traction and drive easy. Being a motocross bike it has very little flywheel effect, meaning it’s easy to stall, which then just makes me realise how spoiled I’ve become on enduro bikes with electric start.

The suspension package that comes stock feels pretty good – with decent big bump absorption, which is great on open farmland riding. Having spent such a long time on KTMs I know exactly what the Brembo front brakes feel like, and hopping on this bike I noticed something was a bit different. This turned out to be the 270mm Moto Master front brake disc, which is bigger than standard. The difference is noticeable, with stronger braking power, but almost bordering on grabby compared to the stock brake, which are quite progressive, but require a lot more input. That said, a bike with this much acceleration needs good anchors.

The 250SX is the complete package I think, with plenty of power, good cornering and handling straight out the box as well as its lightweight feel; making it hard to beat. It also leads to it being a very versatile bike as Damon has shown by using it on the MX track, as well as in the bush. And, yes, for XC-style riding I still think the carb is the way to go, especially one set up as crisp as this bike. TOM BUXTON

IT’S MY BIKE
I often get asked why I ride an SX over an XC or EXC. There are a handful of reasons; mainly power, weight, versatility and fun-factor.

I’ve ridden two-strokes pretty much my whole life and really enjoy them. Most people think the SX is a bit much for off road events, but I enjoy the aggressive power and it plays into my often ‘overly aggressive’ riding style for the bush, and somehow how I make it work (most of the time anyway).

I’m not going to pretend that it isn’t a bit of a handful at times, and hard work, but with how light the SX is, I can really use that to my advantage and put the bike where I want; man-handling it, to get out of a bad situation. 

I love that it’s so versatile. I am able to enjoy all types of riding; MX, XC, enduro, and trail rides. I can ride a national level MX, then do a Dirt Guide XC the next weekend with just a few clicker adjustments. This isn’t something you do with many bikes.

Then there’s that fun factor. The enjoyment of ripping a 250 two-stroke on a freshly prepped track is something that just can’t be beaten. And it sounds pretty bloody good at the same time. DAMON NIELD

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