650B or not to B.
nerdy wheelsize? Marketing spin? or the size a mountain bike wheel should be!

We've been playing with the idea of a 650B wheeled frame for a while now, but couldn't decide if it was marketing BS or common sense so we asked Tim Green to make our minds up. Read on and find out...

Now here's something to think about.. potential. And not the kind to to be collected just by anoraks! Theres been a point made by Kingdom, about the bike design in particular, being the product of chance, which evolved into the best it can be at any given time with the technology available,  this is this one part of the design that hasn't changed, everything else has from the early days. Wheel size is something that, whenever i've seen it brought up it has met controversy, but just the same as everything else was, wide bars should have been thought of years ago, but they pushed in as soon as the curious started to try them, ending up on most bikes especially in the trail and more extreme market getting hefty bars. Point is, wheel size has seen more scepticism than most, but that's mainly due to the fact that it is a big change, it would be a big step to try it, as a new frame is needed, so it has to be proved and properly tested to most before it is accepted as the way forward. Should sound a familiar concept though - exactly how suspension was received when it first came through. That took years to make proper sense though, whereas 650 wheels are the finished product, no evolution in design is needed.
 
It's the 650B wheel size that mountain bikes would use, out of the 4 different sizes out there. These different rim sizes exist to provide the 650c tyre diameter, with each of the 4 sizes representing a different width (and therefore depth) tyre. To have a 2" wide tyre, the rim size is 584mm - 650B.
 
This does sound like a biased argument i'm putting through, but there is reason, so here's the good and the bad;

Good:
The main point the advantage would come in to play for the largest part of the market - the average trail rider, is comfort and stability. It's a proven fact - the bigger the diameter, the easier it rolls over bumps and obstacles. On the face of it the 25mm increase in diameter of 650B doesn't sound like it would make enough of a difference to be worth the effort, but if you've ever ridden a 29" wheel, the increase in the ease it rolls over bumps, and the smoother ride this creates is massive. The difference of 650 is half that of 29", but the increase in smoothness is exactly proportional, still a big, worthy difference. This extra inch would also make the bike more secure over ruts and rocks - the larger the diameter the less likely it it to hook an edge on the rut/rock, as it just rolls over it.

The area though, that is likely to be the first interested in 650 is the xc race market. The massive plus it holds is in the rolling speed it maintains. The same as 700c road bikes and 29" bikes, 650 would carry speed in the same manner. Speed is maintained easier and more efficiently, less effort on the part of the rider is required to maintain a speed. This is one of those rare cases where the bike makes the difference to the speed of a rider, 650 would make any rider faster, on simple, untechnical terrain such as the open sections and hard surfaced paths. This difference in speed would be less notable on technical terrain where the rider is pushing themselves to the limits of the comfort zone, as the extra speed available would only make a difference if they could further their comfort zone.

• There is one benefit of 650 that would help increase confidence in ability in one area though, and that is cornering, the main area pretty much everyone can improve in. The advantage comes in the larger footprint the tyre has, giving increased grip, and allowing riders to push harder and carry more speed through turns.
  
  These characteristics of 650 would be felt by all riders, some more notable than others, and some more relevant than others. But there is definate benefits to everone with this.
  
  
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  Jeremiah Bishop's Cannondale Scalpel 650-6er
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  The downsides then;
  

• The first is weight; it's a fact that bigger rims, longer spokes, more rubber and the fact that bigger forks, frames and wheels will need more reinforcement in order to maintain strength and stiffness will add weight to the overall bike. This extra weight is not massive though, the front 650 wheel on an xc race bike weighed about 100g more than a 26” set up. Interestingly that bike had just the front wheel at 650, benefiting from the smoother ride and faster rolling, the significant part of this set-up was that it used a standard lefty fork, something that is very popular, it only needed one 10mm spacer adding to provide the clearance. Back to the weight, as that was a race light set – up, the average bike would look at about a 3-400g increase in weight, not much as the increased rolling speed does offset most of this, though less so up hills.
  
  Manoeuvrability is another point that will provide the  main cause of doubt within riders, bigger wheels are in theory detrimental to a bikes agility, producing a larger turning circle and higher front end for example. This can be minimised through adapting the geometry of the frame, as opposed to just making a standard one bigger, the bottom bracket would stay at the standard height, but the wheelbase would grow to give the clearance needed, not excessively though, as chainstay length for example could stay almost the same, if a little mud clearance was lost. The head tube and cockpit set-up could easily be set up to minimise the front ends increase in height.
  
  That big point then, the availability of parts, specifically forks. It’s been shown that a standard lefty will work with a minor adjustment, so it is definitely in the realm of possibility for a lot of racers. Normal two legged forks cannot be modified for this though. But there is a surprising amount of choice and parts available.
• A lot is listed here: http://mtbpath.com/riders/forums/display_topic/id_283/650b-Specific-Frames-Forks-and-Wheelsets/
  
  The point here is that every part needed would be relatively easy for a customer to source, through the internet or local shop special orders. This makes it just as easy to build up a custom 650 bike as it is a custom standard bike. The one downside of lack of choice, though it is constantly getting broader, especially with the big names like Stans, Schwalbe, and Kenda getting involved.
  

To me, the benefits far outweigh these issues, especially as choice of parts is only going to increase.

That is pretty much it as far as an outline of this concept goes, and I’ve persuaded myself that this is going to become a big thing in mountain biking! It does also cross over to practically every type of riding, with trials and dirt jumping being the exceptions, as they are always going to want the most agile bikes possible.





Ti 650b-26″ Full Susser Lefty Mountain Bike

 

We invite you to post your comments and thoughts below and watch this space as I think Tim might just send us in a 650B ti-frame design soon.....and your input could help shape the future...