Bicycle Mechanics - 28mm is 28mm, right?

Because of sidewall deterioration, I just replaced a 700Cx28 Specialized Armadillo Turbo tyre with a Continental Ultra 2000 700Cx28. The latter is very noticeably narrower than the former, and measures just under 25mm across.

This is not really a complaint or a question, simply an observation. It could be a problem if someone ordered an Armadillo 700Cx28 and then found it was too wide for his/her frame to accommodate.

It is also interesting that Continental Ultra 2000s are now blackwalled, instead of gumwalled.

I am very fond of panaracers, but find that their numbers seem to be inaccurate. their 32s look more like 28s, and so on. but perhaps that is due to them using a fairly oval-shaped profile to their tires.

Tire sizes are like women's shoe and dress sizes, they are a relative guide only.
One companies 25 is anothers 23 etc. 10% variance is reasonable. Steve

Sch is right, none of the tire sizes correspond with different manufactures, which I think there should be some mandatory law that says they should. I was barely able to get a 28 Armadillo on the rear of my bike; I had to deflate the tire and then press the tire flat against the seat tube to squeeze it off. Even now with the Armadillo 26 on the rear, I still have to deflate the tire...but I had to do that with 20's and 23's anyway! The geometry on my bike is very tight.

I think Panaracer tend to be pretty on the nail, size-wise. I recently bought some Specialized Roll X Pro 2.0 for my bike and they were massive - I had to send them back because of chainstay clearance issues. I bought some Panaracer Cinder 1.95 tyres and they fit perfectly. The Specializeds were more like 2.2/2.3 size :( .

They sell smaller tires under larger designations(ie it says 28 but measures 25) so the can brag about howmuch lighter their tire is than the competitions. At one point this had gotten quite ridiculous with 20s being sold as 25s and so they went back to accurate nominal sizes, but it seems things have started to come full circle. :(

http://www.etrto.org/

http://www.iso.ch/iso/en/stdsdevelopment/tc/tclist/TechnicalCommitteeDetailPage.TechnicalCommitteeDetail?COMMID=1302

to which there is an attempt to standardize the problem.

But yes the Conti 28mm tires are narrower but taller than other "28mm". I think Conti is basing it on volume and thinks the narrow tire provides less rolling resistance but the taller tire will provide more pinch-flat-protection thus acting like the older 28mm tire...

Oh well..

[QUOTE=prestonjb
But yes the Conti 28mm tires are narrower but taller than other "28mm". I think Conti is basing it on volume and thinks the narrow tire provides less rolling resistance but the taller tire will provide more pinch-flat-protection thus acting like the older 28mm tire...

Oh well..[/QUOTE]
Pinch flats I have no idea but rolling resistance would be increased over a short wide tire. Of course construction, max pressure, and wind drag also have a big effect but based on shape alone it would have more rolling drag.

I think Panaracer tend to be pretty on the nail, size-wise.

It depends highly on which model. I have Category Elites listed at 23mm that measure 21mm and Paselas listed at 28mm that measure 25mm. I also have a few pairs of various Stradius models listed at 23mm and they all measure 23mm.

Even in the same model, sometimes...

I have Continental Top Touring 2000 700x32 which are 29 mm wide... and 700x37 which are 36.5 mm wide.

John E,
You have hit on my main objection to the Armadillos in road sizes. They not only seem wider than other tires of the same nominal width, but the tread area seems wide and flat. Maybe it's just my imagination, but they just seem to have more rolling resistance. Now I do like the Specialized Infinity Armadillos which come in slightly wider sizes 32,35,38. I run a 32 front and 35 rear on my primary commuter. Pumped up to 100 psi their rounder profile actually seems to have lower rolling resistance than the 28 mm smooth Armadillos due to a narrow raised strip of tread along the center. Again, maybe just my imagination.