"Back in the Day" people believed that smaller=faster, and manufacturers realized they could brag about the light weight of their tires by making them much smaller than their nominal sizes. Lately there seems to be a trend toward more honest marking of sizes, at least with the Panasonic and Michelins I've installed lately.
I've seen older Conti 27 x 1-1/4" tires that measured just over 25mm on Super Champ Mod 58s (Hardly a narrow rim). New 27 x 1-1/4" Panaracers measured 31.5mm on the same rim.
I had a customer say she had to have "At least 32mm" tires on a bike I was building up for her, when all I could fit, with fenders, were 28s. Then I saw her older bike with "700-32" Specialized Touring tires that measured under 25mm on Matrix rims.
However, now that tire sizes are starting to reflect reality, the relationship between nominal and actual inner tube sizes has become such that if you install them in a similarly labeled tire they get stretched thinner than a condom when inflated. I've been buying 700c x 35-43mm tubes for 28-32mm tires.
At 12/1/2009 03:14 PM -0800, David Boston wrote:
>List-
> I was rooting through old stuff and found some Specialized Turbo
> Infinity/SK4
> tires marked 700x25. I was going to toss them, but decided to do
> a trial mounting
> and see how they would do. Great, as it turns out, but I noticed
> the actual size of
> these 700x25 tires to be smaller than the current day 700x23
> tires I removed, which
> were Conti Grand Prix 3000s. Both measurements, across and off
> the rim, were
> smaller. Why is this? Have the numbers come to represent
> something different?
> They could be mis-sized, but I recall back in the day during the
> introduction of
> skinnier clincher tires that 25c would be the narrowest I would
> want to ride on the
> road, and today I'm riding 23c tires with no consideration. Well,
> I guess because
> they're bigger. So, have tires come to reflect the overall
> cultural obesity situation
> or is there some other "inflationary" cause for this? Anyone
> else notice this in older
> tires? Was this a gradual change or did I miss a tire sizing
> revolution somewhere?
>
>Dave Boston
>Tucson AZ USA
Mark Stonich;
BikeSmith Design & Fabrication
5349 Elliot Ave S. Minneapolis, Minnesota 55417 USA
Ph. (612) 824-2372 http://bikesmithdesign.com
http://mnhpva.org