Tire size observations and a question

[NHAero]

Conti GP5000 (not tubeless) on two bikes.
700x25 on 22mm ID carbon rims, measures 28.25mm at 80 psi
700x32 on 15mm ID (I think) Mavic Open CD rims, measures 30.0mm at 60 psi

Seems like rim ID makes a big difference.

The 700x32 tires are on my 1972 Bob Jackson. I have about 4mm clearance at the round-oval-round chainstays, so don't feel I could go larger. My question is that IIRC I started out in 1972 with 27x1-1/4 inch tires, I think they were called Schwinn Le Tour. Given that the 27" wheels are 4mm taller, it's hard to see how i would've fit the 1-1/4" tires in.

Photo (by Sheldon Brown) is from summer 1972 shortly after receiving the bike. The tires look like they could be 1-1/4" (32mm), no?

[ColonelJLloyd]

ID of the rim makes a big difference as you've illustrated with your two examples.

Nearly all of the 27" x 1 1/4" tires I've ever used measured less than 32mm and many less than 30mm. The word "nominal" is good to remember in regard to stated tire sizes.

[Louis]

Originally Posted by NHAero

Photo (by Sheldon Brown) is from summer 1972 shortly after receiving the bike.

Cool

Feel free to admit it - I bet some part of your motivation in starting this thread was to give you an excuse to post that picture!

[oceanview]

Depends on rim width as it can stretch out tires. Best to check measured width after installing.

[Dave]

Tire width is based on a specific internal width or IW rim. 19mm or 21mm is common. A 28mm tire on a 25mm IW rim will measure about 31mm and a 30 may measure 33. Wider rims make for wider tires.

[Ralph]

Rode a lot of miles on Schwinn 27X1 1/4 LeTours in 73 on P 15 (touring) Paramount. Schwinn advertised these tires as rolling better than most tubulars of that time. Good tires as I remember. Would be great on a Bob Jackson of that era.

[NHAero]

Originally Posted by Ralph

Rode a lot of miles on Schwinn 27X1 1/4 LeTours in 73 on P 15 (touring) Paramount. Schwinn advertised these tires as rolling better than most tubulars of that time. Good tires as I remember. Would be great on a Bob Jackson of that era.

Did those tires measure out to a true 1-1/4” or were they smaller, if you can recall?

[2metalhips]

Jorts FTW!

[redir]

Can't really help you with the tires but that's you in the pic on the same bike? Freakin' awesome!

[fignon's barber]

There were bikes back then?

[NHAero]

Originally Posted by fignon's barber

There were bikes back then?

Yes, they came with a pair of cut-offs

[Mark McM]

Originally Posted by fignon's barber

There were bikes back then?

This is a slightly different topic but - although today the bicycle is considered such a rudimentary transportation device, it is surprising that the bicycle first appeared so late in history. By the time the first bicycle appeared, locomotives had been in use for decades and the transcontinental railroad was already under construction; steam powered ships were already sailing the globe; steam powered dirigibles had already taken flight; and steam carriages were already in use on the roads. (A Transatlantic cable had also already been laid by then, enabling instantaneous communication between continents.) And then in 1864, the bicycle finally emerged.

[Nomadmax]

I've always said; asking how wide a particular tire will be without listing the ID of the rim is the same as asking "How long is a piece of string?".

[reuben]

Originally Posted by NHAero

Yes, they came with a pair of cut-offs

POTD.

[Ralph]

Originally Posted by NHAero

Did those tires measure out to a true 1-1/4” or were they smaller, if you can recall?

They were on wide rims. Weinman I believe. Tire were at least 1 1/4". Had a raised up strip of rubber down the middle.