With the recent thread regarding 20" tire size differences, I thought
I'd mention 20" tube sizes, which I have been dealing with.
I wanted to buy some tubes for the tires on my Dahon Speed TR, which has
Schwalbe Marathon Plus 35-406 tires.
There are not a lot of 406 diameter tubes, and even fewer narrow ones,
and even fewer with Schrader valves. QBP doesn't have a narrow 406
Q-Tube with a Schrader valve, only Presta.
I have found the following:
Sunlite (Kenda) 63177 20x1.35-1.50 (37-406)
<
https://www.amazon.com/dp/B000BMT2TC>
Schwalbe AV6 (fits 28-406, 32-406, 35-406, 37-406, 40-406)
<
http://www.schwalbetires.com/node/639>
BikeFriday 984 (20x1.125-1.5" SV (406x32-37))
<
https://store.bikefriday.com/product_info.php?cPath=52&products_id=984>.
I suspect that BikeFriday is reselling Kenda tubes.
Of course no bike shops I've gone to have any. One shop I called said
that they did have the Schwalbe AV6 for $10 each, which is a lot more
than the MSRP of $7.25. So I'm not going out of my way to go to that shop.
Since these tires are inflated to rather high pressure, I don't want to
use larger diameter tubes, plus the next size up probably would not fit
since they are for 1.5"-1.95" tires.
I guess that 406 size tires are too rare for bicycle shops to bother
stocking any tubes. Actually REI had one 406 tube in the back, for wider
406 tires, a Sunlite/Kenda 6307 (20x1.50-1.95 SV).
I read Bicycle Retailer magazine and in just about every issue there is
an LBS owner complaining about web retailers undercutting them. But I'd
have been happy to pay MSRP at an LBS for a tube rather than having to
order it.