26, 650B or 29er? Prototype Chiru RMK Mountain Bike is All of the Above
South African French brand, isn’t the first to consider changing parts to convert a frame to work with multiple wheel sizes. Intense is doing it officially, we’ve hacked a Norco and riders everywhere are doing it in their garages.
Chiru, however, may be the first brand to build an entirely new model around the concept and take frame and rider size into consideration.
The RMK (Race Morpho Koncept) is a full suspension mountain bike that converts between 26″ and 27.5″ wheel sizes on the small frame, and 27.5″ and 29er for the medium and large. Travel is 75mm in the rear with an 80mm to 100mm to 110mm recommended fork travel as frame sizes go up. They’re big into marathon racing there and these travel increments suit the terrain and riders the RMK is aimed at.
The idea came about from one of their shorter female racers. She raced the 29er for a bit and liked the benefits but felt the smaller wheels allowed for a bike that fit her better. That got founder Pierre thinking, and the solution was a series of frames that can work with appropriate wheels sizes.
It’s handled by swapping dropouts and using a Cane Creek AngleSet to change the necessary parameters -wheelbase, chainstay length and geometry- for whichever wheel size you’re using. Before you knock it, we’ll say this: The Intense Carbine with 650B wheels conversion rides just fine because they accounted for geometry and BB drop changes, too. For purists, this might be anathema, but if it works, it works, and we’re withholding judgement until we can throw a leg over one.
The RMK uses flex chainstays rather than a pivot to keep it at a target weight of 1,500g for frame and shock. These are prototypes, so actual weight isn’t final, and the dropouts, rockers and even frame will be quite a bit more refined.
The AngleSet lets you adjust head angle to suit trail conditions. On the RMK, it serves a second purpose, too, fixing wheelbase and front center to match the chosen wheel size.
Pierre pointed out that it would also let you experiment with mixed wheel sizes, putting a larger wheel on the front if conditions suit such things, or just dialing everything in to work for you.
Depending on fork selection, you might new two of the sitting around. Many forks will work with both 26″ and 27.5″, but the jump from 27.5″ to 29er probably calls for wheel size specific forks.
Price will be around €2,300 (frameset) and custom graphic and paint color options start at €200. That includes two sets of dropouts and the AngleSet. Complete bikes will ship with two wheelsets. Should be available in February.