Not a single one of the current fuel-injected 250Fs—or the carbureted Yamaha, for that matter—keep the power percolating as high into the rpm range as the TM MX250FI |
The stigma of sluggish, Euro-style understeer is broken by the TM MX250FI.
Q: WHERE HAS TM BEEN FOR THE LAST FIVE YEARS?
A: TM is not a big brand and you can forgive most American motocrossers if they have never seen one. For the last five years, TM has had importer troubles in the USA (in fact, up until recently the United Sattes importer was in Canada). No big deal because, at their height, TM only sold a couple hundred bikes a year in the USA. To rectify this, TM and Pete Vetrano, who was their American importer during their best years, came to terms for Vetrano to take over TM Motorcycles USA. Vetrano is a respected motorcycle executive and racer—and he immediately put the Italian brand back on the map for American motocross racers.
Q: WHAT IS THE BORE AND STROKE?
A: The bore and stroke is 77mm x 53.6mm, which is identical to the YZ250F, KX250F and RM-Z250.
Q: HOW DOES THE POWER OF THE TM MX250FI COMPARE TO ITS COMPETITORS?
A: Very favorably, unless you try to lug it. We know that modern 250Fs are capable of spinning really high rpm, but no one seems to be taking full advantage of the high rpm range that four-strokes can live in—until now. Not one of the current fuel-injected 250Fs—or the carbureted Yamaha, for that matter—keep the power percolating as high into the rpm range as the TM. Every MXA test rider liked the wide-open powerband on the race track. It wasn’t all that easy to ride at low rpm, so we instituted a no-fly rule for any rpm below 7500.
The best way to go fast on the TM MX250 is to go-for-broke.
Q: HOW DID THE TWO-POSITION IGNITION SWITCH WORK?
A: The MX250FI has a two-map selector switch on the handlebars. On Map 1, the bike was slower revving and less responsive. On Map 2, the bike ran freer and was less apt to bog. One downside of the TM 250cc powerplant was engine braking. It felt like a built motor and was wound up tight, which meant that it wound down tight.
Q: WHAT'S THE BEST WAY TO RIDE THE MX250FI?
A: Rev it out. The TM 250FI worked best the sooner it got into the upper midrange. This is where the engine gets down to business. As the 250FI climbs into the upper reaches, it hangs on its power. This allowed MXA test riders to wait as long as they wanted to before shifting.
The downside of the high-rpm powerband was that there were situations where test riders couldn’t keep it percolating and had to come down into the lower rev ranges. In that case, every test rider kept his trigger finger on the clutch to avoid the bog.
With a high-tech finger follower valve train the MX250FI is not a Japanese clone.
Q: WHAT'S COOL ABOUT THE ITALIAN-BUILT TN MX250FI ENGINE?
A: Unlike the Japanese-built 250 four-strokes, which are cam-over-bucket engines (or in the case of the CRF250 a forked rocker arm), the TM MX250FI engine’s cams actuate finger followers. Many engine designers believe that finger followers are superior to both rocker arms and the bucket-over-shim configuration. Finger-followers are small levers, much like miniature rocker arms, that allow for smaller cam lobes. When properly designed, they provide a quicker valve opening and a straighter push on the valve. With this borrowed MotoGP technology, the cam lobes do not need to be super steep, so the valve springs can be lighter. All of KTM’s four-stroke motocross engines use finger-followers.
Q: HOW IS THE GEARING?
A: The stock 13/51 gearing was very well mated to the high-rpm powerband.
TM uses a downdraft design and proprietary parts in their fuel injection system.
Q: HOW DID THE FUEL INJECTION WORK?
A: The 250FI and 450FI share the same TM-built 44mm throttle body. What’s unique about TM’s fuel injection is that instead of just making a throttle body that was a direct replacement for the old carburetor, TM cast a new cylinder head to accept a downdraft design that placed the throttle body above the intake tracts. This position required a unique extension to the airbox to get the air boot high enough. Our only issue with the MX250FI’s fuel injection was that the bike was hard to start (and in typical four-stroke fashion, it would resist starting for one test rider, but fire up in one kick for another). Eventually we used this sequence to improve the starting:
(1) We pushed in the choke lever (hot or cold).
(2) We never touched the throttle.
(3) We raised our leg as high as possible and kicked all the way through to the bottom of the stroke. TM advises against short, swift strokes because it can load up the engine.
(4) There is an idle adjustment knob on the left side of the bike. We set the idle at a relatively high 2500 rpm.(2) We never touched the throttle.
(3) We raised our leg as high as possible and kicked all the way through to the bottom of the stroke. TM advises against short, swift strokes because it can load up the engine.
Q: WHAT WAS OUR BEST FORK SETTING?
A: The 50mm Marzocchi Twin Chamber forks are overkill for a 250 four-stroke. Showa forks are 47mm, and Kayaba and WP forks are 48mm. The fork caps are designed to be removed with a pin spanner, and underneath a small rubber plug is a Schraeder-style air valve to release air buildup.
For hardcore racing, we recommend this fork setup on the 2011 TM MX250FI:
Spring rate: 0.43 kg/mm
Oil height: 300cc
Compression: 23 clicks out
Rebound: 14 clicks out
Fork leg height: 5mm up
Notes: The MX450FI and the MX250FI both have the exact same forks, spring rates and damping. Smaller 250F riders will need softer fork springs.
Oil height: 300cc
Compression: 23 clicks out
Rebound: 14 clicks out
Fork leg height: 5mm up
Notes: The MX450FI and the MX250FI both have the exact same forks, spring rates and damping. Smaller 250F riders will need softer fork springs.
Marzocchi supplies the Shiver forks for both the TM 450 and 250. In fact the 250 uses the exact same fork springs...we think that most small riders will need softer fork springs.
Q: WHAT WAS OUR BEST SHOCK SETTING?
A: In Europe, the TM MX250/450FIs come with Sachs shocks. No disrespect to Sachs, but American consumers are lucky to get Swedish-built Ohlins 46 PRC shocks.
For hard-core racing, we recommend this shock setup for the 2011 TM MX250FI:
Spring rate: 5.2 kg/mm
Race sag: 100mm
Hi-compression: 1-1/2 turns out
Lo-compression: 17 clicks
Rebound: 16 clicks out
Notes: Ohlins’ newest shock is the TTX, which features the CSC valve. The TM spec’ed shock is just the basic Ohlins from before the TTX.
Race sag: 100mm
Hi-compression: 1-1/2 turns out
Lo-compression: 17 clicks
Rebound: 16 clicks out
Notes: Ohlins’ newest shock is the TTX, which features the CSC valve. The TM spec’ed shock is just the basic Ohlins from before the TTX.
For a 250cc four-stroke the TM MX250FI is a big bike.
Q: HOW DOES THE TM MX250FI HANDLE?
A: Pretty well—although for a 250 four-stroke it is tall feeling. One thing we know for sure is that the stigma of sluggish, Euro-style understeer is broken. The TM 250FI is better balanced and lighter feeling in the corners than its 450FI brother. With most of the Japanese bikes going to more aggressive geometry, the more neutral characteristics of the TM MX250FI make it feel like a stable platform to operate from. Still, riding at race pace, the Michelin Starcross tires and the need to keep the revs up put more demand on the chassis than a low-to-mid engine would have.
TM specs quality parts, not just in the stuff you can see, but deep inside the engine (which comes stock with copper beryllium valve seats).
Q: WHAT DID WE HATE?
A: The hate list:
(1) Height. Even 6-foot-2 testers noticed that the bike was tall. It’s not quite as bad sitting back in the pocket of the seat, but we would definitely like a flatter gas tank area.
(2) Triple clamps. The CNC design seems rigid. The bar mounts are fixed to the top clamp. There’s no adjustability and no vibration absorption.
(3) Grips. We haven’t seen Domino grips in a few years...and we wish we could have gone longer.
(4) Low-rpm bog. It didn’t happen often, but when it did, it was a big surprise. The power felt like it was there—and then vanished.
(5) Bolts. We are intrigued by the thought process that spec’ed the plethora of Allen bolts on the plastic parts and the incredible number of bolts holding the rear sprocket on.
Q: WHAT DID WE LIKE?
A: The like list:
(1) Components. Unlike the typical bike, which comes from a variety of anonymous suppliers, TMs use Brembo, Takasago, Nissin, Ohlins, Marzocchi, Braking, Reikon and HGS components. And there are lots of handmade CNC-machined parts on a TM.
(2) Brakes. The 270mm Brembo front brake is about as big and powerful as you would ever want on a 250 four-stroke. This thing could stop a charging rhino.
(3) Hubs. TM’s hubs are works of art. They are billet-machined aluminum, highly polished, spool-style hubs that are laced to blue anodized Takasago Excel rims.
(4) Valve seats. The valve seats on the TM MX450FI and MX250FI are copper beryllium. These valve seats would cost $500 to put into a red, yellow, green, blue or orange cylinder head.
You can almost see yourself in the shiny finish of the TM hubs.
Q: WHAT DO WE REALLY THINK?
A: Past TMs have been beautifully crafted but flawed machines. Previous TMs bristled with works-like parts, but had Italian handling. Additionally, they had awesome powerbands, but soft suspension. This year, the 2011 TM MX250FI is less of an art project and much more of a competitive race bike. For more info on TM Motorcycles go to www.tmmotorcyclesusa.com
