Since 60mm presta valve Michelin AirComp Latex tubes in 20s are so hard to find, what would be your best estimate as the best combo:
20mm Vittoria Corsa Evo CX with high quality butyl tube, shove in 23 latex aircomp, or 23mm ProRace2 with 23mm latex tube. All FRONT wheel, clincher, on a Hed Jet 90?
I stick with 23 for the rear for comfort and since the “aero” tire is less important.
Thanks - looking for every last watt 
…
Since 60mm presta valve Michelin AirComp Latex tubes in 20s are so hard to find, what would be your best estimate as the best combo:
20mm Vittoria Corsa Evo CX with high quality butyl tube, shove in 23 latex aircomp, or 23mm ProRace2 with 23mm latex tube. All FRONT wheel, clincher, on a Hed Jet 90?
I stick with 23 for the rear for comfort and since the “aero” tire is less important.
Thanks - looking for every last watt …
I’m not Tom but I will be sleeping in a Holiday Inn Friday night (:-). The Vred tubes in the following link have removable valve cores - personnally verified for the 60 mm valve and promised by the vendor for the 40 mm:
http://www.dotbike.com/ProductsP2584.aspx
Shipping is a bit steep but they are available and test out equivalent to the Michelin 18/20’s with respect to Crr.
Since 60mm presta valve Michelin AirComp Latex tubes in 20s are so hard to find, what would be your best estimate as the best combo:
20mm Vittoria Corsa Evo CX with high quality butyl tube, shove in 23 latex aircomp, or 23mm ProRace2 with 23mm latex tube. All FRONT wheel, clincher, on a Hed Jet 90?
I stick with 23 for the rear for comfort and since the “aero” tire is less important.
Thanks - looking for every last watt …
What Al said (AFM)…or, just get the short valve 18/20 michelins and throw on one of these:
http://www.biketiresdirect.com/...ctdetail.asp?p=QUPVE
That’s what I do (i.e. both of the above). Hope that helps 
I use the exact same extension - love it! But, it won’t quite work with the std 43mm presta valves in my Hed 90’s. I realize the “math” works, but reality …
Also, why does Michelin have a 20 and 23 mm version and the Vred is a one size fits all (18-25)? I realize that natural latex expands a ton, but would this make the Air Comp tube possibly more puncture resistant? I can’t imagine how thin that tube must be inflated in a 25mm tire!
Even so, at what point does matching the rim profile (say 21-22mm most are designed for - seems less on my Heds than on my 404s) to save “aero watts” outweigh “hysteresis watts” of butyl vs. latex. THIS I have not seen …
I use the exact same extension - love it! But, it won’t quite work with the std 43mm presta valves in my Hed 90’s. I realize the “math” works, but reality …
Also, why does Michelin have a 20 and 23 mm version and the Vred is a one size fits all (18-25)? I realize that natural latex expands a ton, but would this make the Air Comp tube possibly more puncture resistant? I can’t imagine how thin that tube must be inflated in a 25mm tire!
Even so, at what point does matching the rim profile (say 21-22mm most are designed for - seems less on my Heds than on my 404s) to save “aero watts” outweigh “hysteresis watts” of butyl vs. latex. THIS I have not seen …
I don’t know why Michelin makes the 2 sizes…it seems like with the claimed ability of latex to be stretched ~900x before damaging that the Vred approach (one size fits all) would be the best route…who knows?
The difference in Crr between a 21-22mm wide tire and a 23-24 size tire will be a lot less than the additional aero drag at race (TT or Tri) speeds due to tire to rim mismatch, or just plain increased frontal area. However, if your events are stuff like brevets and the like, where your average speeds are lower, I’d go for the slightly wider tire that rolls better since the aero drag force is much less at the lower speeds.
YMMV
Thanks! That is about what I was thinking. Still not sure if I “should” use a 23mm Michelin tube in a 20mm tire, but I’m not sure why not.
Brevets? Yeah, one of my local roadie buddies just finished Paris-Brest-Paris (his 3rd time I think). Super stud. Was 55 hours once. Always leaves with the 80 hour crowd. I’d say his avg speed is still close to 20 mph! Todd Williams if you care to look him up! I don’t know what is holding him back for a solo RAM attempt - but I know he is thinking about it.
Thanks! That is about what I was thinking. Still not sure if I “should” use a 23mm Michelin tube in a 20mm tire, but I’m not sure why not.
Brevets? Yeah, one of my local roadie buddies just finished Paris-Brest-Paris (his 3rd time I think). Super stud. Was 55 hours once. Always leaves with the 80 hour crowd. I’d say his avg speed is still close to 20 mph! Todd Williams if you care to look him up! I don’t know what is holding him back for a solo RAM attempt - but I know he is thinking about it.
I’d use a 20 tube in a 23 tire, but NOT a 23 tube in a 20 tire. Just too much tube to stuff in there…IIRC, I think Jens tried doing this way back before I pointed out to him that there’s a narrower tube. It’s a pain just trying to put the 23 tube in a 23 tire…I can’t imagine how it would be to try to stuff one into a 20. You’re just ASKING for a pinched tube on install.
Rod, what race are you getting ready for?
Some new latex tube data just posted on BTR Performance Forum.