2013 Chiru 26-650b-29er full suspension mountain bike prototype changes wheel size to fit the rider

Chiru, a 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.

2013 Chiru 26-650b-29er full suspension mountain bike prototype changes wheel size to fit the rider

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.

2013 Chiru 26-650b-29er full suspension mountain bike prototype changes wheel size to fit the rider

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.

2013 Chiru 26-650b-29er full suspension mountain bike prototype changes wheel size to fit the rider

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.

2013 Chiru 26-650b-29er full suspension mountain bike prototype changes wheel size to fit the rider

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.


  1. This has been happening in the recumbent sphere for a while. The Spanish MetaBikes (no relation to US Meta Bikes) supports several different wheel sizes: 24″, 26″, 700c, 29″. The frame even supports mixed wheel sizes, like a 20″ front/26″ rear.


    They use a brake bridge to accommodate the different wheel sizes, with changes in front fork depending on size and whether or not you want disc brakes.

    And the frameset is only $1700.

    The MetaBikes frame has been around since at least 2006.

    Of course, some things can be taken to extremes… https://sphotos-b.xx.fbcdn.net/hphotos-ash3/s720x720/538435_10150673896654843_1074945913_n.jpg

  2. I have an Enduro and used to have a spare heavy duty wheel set (including DH tires) for park days.

    But even that did not work well. There were always a lot of tedious details that made the swap not worth it in the end. I sold the wheels.

    This bike has many details that will make the wheel size changes take a lot of time & not be a “swap”. But some riders may be into taking an afternoon to swap.

    Still, the concept potentially runs into the zone of “jack of all trades, master of none”

    Very smart thinking to get it all to fit on one bike tho!


  3. I imagine there was a D’oh moment when someone realized the chain was cutting into the chainstays when in the smallest cogs. Hopefully this is rapid proto and not from a finished mold. I love the look of the front triangle, could live without the bulky dropouts.

  4. Steve M, bullseye!
    and the other issue is those flexstays that flexes not only up and down, but twisting too.
    I’ve had a scalpel, torsionally weakest frame ever.

  5. All – yes, forgot to mention: both of the frames on display were rapid prototypes. While the sag with a rider on it would add space between the frame ad chain, Pierre admitted it was an early version and put togetherainly to show the concept in time for the show. Many things will change prior to production, and he may actually launch the concept with a hardtail first.

  6. Uhm… How can they have a post mount rear caliper with swappable dropouts? Seems like they have a ton more work to do just to make it work.

    Congrats on the poor concept with even worse execution!

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