I know there's a massive lack of standardization out there in wheel/tire sizings, specs, etc. -- but if one were to limit oneself to the "26+ inch" sort of range, there seem to be three basic categories:  a) "559," or "26 inch,"  b) "650," and c) "700"
 
The "559/26inch" appears to be common to both MTBs and recumbents, at least in my experience.  However, obviously RANS and other manufacturers continue to come out with either "650c" or "700" versions -- and there seem to be a VERY limited range of tires available for the "650" spec.  But if you design for a 650, you can't necessarily change to a 700 due to frame fit, brakes, etc.  Yet there is a much wider range of tire widths (up to ~40mm) available for 700!
 
So given this, what's the advantage of going with 650 over 700 on a new bike design?  Or vice versa?  Is a reason for 650 at least in part to reduce the "heel strike" issue slightly, to reduce the fork extension required on a LWB?  Is the acceleration difference of a 650 that significant over a 700?

In my experience, which isn't much, 650 and 559 (26") tires make many bikes like highracers beyond the reach of many casual users due to stop/start seat height. The larger 700 (same diameter but smaller then the new 29er) wheel may present heal strike issues, or crank strikes but from what I have seen on dual bikes they push the seat up a bit too cutting even more people from using them.
 
I'd think with a long reach caliper you could fit a 559 wheel/tire on a 650 bike without much problem? Sort of like fitting a 700c tire on a an old 27" wheeled bike. Now finding a narrow 559 rim is a bit of a pain.
 

Don't forget 650B (584).  I have at least one bike for every wheel size mentioned below.   650c become vogue again in the 90's due to a triathlon fad with smaller wheels and to a smaller extent the need to fit shorter women.  If not for that peformance recumbents would have likely stayed with something else.  26" / 559 in performance sizes are only around because of bents I believe though (maybe junior racers).  I think thanks to Bacchetta, and other Hi -Racers 650c has been given a  new lease on life.  For somebody short like me the 650b size makes a lot of sense on a DF, but the available rims and tires are oriented towards touring, because that was the traditional use, first in France, and later adopted in Japan.  I think we're going to be good in the future though, because unlike cars - bikes are going to become increasingly important and more universally used.  I think we'll see all sizes stocked and available for a long time, especially the more utilitarian types.
 
 
so 26"+
 
559 (26" MTB) lots of stuff
570 (650c) much better selection than there used to be thanks to Performance Recumbents and women specific bikes
584 (660b) much better selection than there used to be thanks to MTB, and Randonneuring
622 (700c + 29" MTB) lots of stuff
 
stuff not mentioned 650a, 26x1 and 3/8, 27"  all still available.
 
There are so many more tires available in every category than there were just 25 years ago its not even funny.
 
Take Care,
Nelson.
 
 
Take Care,
Nelson.

26x1 on a bent especially a bacchetta or rans should be a 559 I think.. 650 usually say 650x25 but I have seen them listed online as 26x1.
Tis why it is very important to get the 3 digit number and not just the inches. I bought some 20" tubes and they were the wrong 20". They were 451 instead of 406, or maybe they were 419 ugh   Most all tires will have a 5 digit number with a - in it with 3 numbers on one side and 2 numbers on the other such as 50-406 which are much current tires or 37-406 which were my old tires I'm too heavy for according to the company.
 
Lot of tires sizes listed over here though many you are going to have a hard time finding much if any selection in.
http://www.sheldonbrown.com/tire-sizing.html
 
There was a time that terry made bikes with 700c back and a 24" front wheel, or perhaps they still do for really small sizes. To avoid problems on really small framed bicycles for women because there was severe toe strike. I remember reading how there were some mens bike that used 650c for the front for lower aero losses and a 700 in the back for more power or a bigger gear or some such.  If i remember correctly you now have to use the same size wheels front and rear in the big bike racing association so they cut that practice out.

If the tires you have been riding say 559 it is almost certain you have 559 rims and need 559 replacement tires. If they were 650 rims they'd probably be harder to get on then marathon plus tires on a mavic 319 rim (Tire diameter on the small side and rim diameter on the large side) if you could get them on at all.
 
The primo comet racer 26x1 is a 559 tire. I don't think Primo makes a tire in 650.  

Quote from kingjason on Jun 15^th, 2009, 10:50pm:

I think it came from the fact that a normal 559 tire and a normal 650c tire are both around or equal to 26" because the 559 tire was traditionally a fatter mtb tire and a 650c was a 23mm speed tire. At least that is what some old crazy guy once told me.
If people would just get off inches it would be alot less confusing.

One reason I'm asking this is from a "bike versatility" standpoint.  When I had the Proto XStream, I tried to change the rear (650) tire from a 23mm to a 28mm, and there wasn't enough frame clearance -- it rubbed against the back end of the main frame tube.  This prompted an immediate discussion with Randy, and he did a "running change" on the frame design to increase the clearance to accept wider tires.  
 
However, I think the widest tire you can even obtain in 650 is the 28mm, and I'm not sure if you can retrofit the brakes and fit a 700 on the back or not on the production XStream -- granted, you would lose additional recline angle due to reduced seatback clearance, again.  But, given the ~65:35 (or worse) weight distribution on bikes like the SXP, V3, and XStream, it just seems like having the ability to have tires wider than 28mm on the back makes good sense.
 
I've read various things about how 650 was brought out to help shorter riders and women -- but why are recumbent companies designing for 650s while not leaving room for an easy change to 700s?  Granted, I'm sure there are issues like brake tabs, etc. involved that I don't know the specifics of.

I think the delta between 622 and 571 is big enough that designing a bike with the option for either is difficult.  However,
622 <-> 584 is doable (I've done it on the Lemond, and now my Davidson.  571 <-> 559 is also close enough to run both and I do it on the Corsa, and Strada.  Now why you choose the smaller wheels is likely due to trying to fit more folks than just going with 622 would have allowed.  
 
I think Bacchetta made a good decision to go with the 650c / 571 wheels with the option to mount 26" / 559 for utility riding.  However on my 2006 Corsa the tolerances are so tight that there are 23c tires I couldn't run without modifying the brake bridge (ie filing).  At least that is better on the newer models, as I think they can run up to 28mm.  
 
All that said, on a LWB where one's reach to the ground is lower naturally I would think there are less reasons not to just go with the 700c / 622 or 26" / 559 size and be done with it.
 
Take Care,
Nelson.