Suzuki released specs and details today on its ’05 RM lineup, including the all-new, aluminum framed RM-Z450 MXer. The RM125, RM250, and RM-Z250 all receive updates for ’05, as well.
The RM-Z450 (pictured above) uses a twin-spar aluminum frame built using a variety of techniques – the steering head, main spars, and front engine mount bracket are forged, while the rear shock mounts are extruded and the down tubes combine extruded and pressed sections. The aluminum swingarm and rear suspension linkage are described as “similar to the RM250″, as are the Showa forks. The bike also comes off the showroom floor with Renthal aluminum bars – the only full size RM to come so equipped.
The RM-Z450 motor was designed with an “emphasis on broad power delivery”, and is an oversquare (95.5mm bore x 62.8mm stroke) design with dual overhead cams actuating titanium valves through a shim-under-bucket valvetrain design. A forged aluminum piston is used. The engine inhales through a Keihin FCR40 carb (with hot start and digital TPS) and exhales by way of a titanium headpipe and aluminum muffler. In addition to using an automatic decompression system similar to that of the RM-Z250, the motor uses a “semi-dry-sump lubrication system” which Suzuki calls “Suzuki Advanced Sump System (SASS)”. The SASS uses separate chambers for crankshaft and transmission oil, with the transmission used as the oil sump. This permits “lower crankshaft placement for reduced engine height and lower center of gravity”. The lubrication system also features “Suzuki Active Vent System”, which uses a “one-way reed valve system between crankshaft and transmission to reduce crank chamber pressure”. The motor turns its sprocket through a four-speed transmission, which Suzuki apparently chose for “weight reduction and compact engine size”. The RM-Z450 will retail for $6,499 when it hits dealers later this summer.
Suzuki’s RM125 two-stroke receives an updated version of last year’s motor, featuring revisions to the cylinder head, exhaust power valve, crankshaft, and carburetor. The RM125’s chassis has revised ergonomics with a different footpeg position, as well as an updated swingarm and refined components and valving for the forks and shock. Other minor updates include redesigned rear brake caliper and new aluminum handlebars.
The RM250 two-stroke is updated for ’05 as well. The motor has received a host of revisions, with changes to the cases, cylinder head, intake and exhaust ports, power valve, and crankshaft. The chassis receives an updated swingarm, new titanium footpegs, and revised components and valving for the forks and shock.
Perhaps the most-needed revisions come on the RM-Z250 four-stroke – larger radiators (17.8% bigger) and a redesigned oil filter cover to allow the filter to be changed without draining the coolant. The smaller RM-Z also gets modified intake and exhaust ports, and the transmission has shot-peened 3rd and 4th gears for improved reliability.