Retrobike Forum Index

It is currently Sun May 26, 2019 11:17 am

* Login   * Register * Search  * FAQ



Post new topic Reply to topic  [ 6 posts ] 
Author Message
PostPosted: Thu May 09, 2019 11:04 am 
Devout Dirtbag
User avatar

Joined: Tue Jun 24, 2014 1:13 pm
Posts: 133
Location: London
Hi all,

I'm helping out my dad in trying to identify the size of the rims of his old Bianchi touring bike (purchased in 1965, I believe).
The outside diameter of the rim is 645mm, which would suggest it's a 700A size (642mm).

Something he said that I find interesting but I can't completely understand is that tyres are 27 and that 28 tyre don't fit because they are too small.
I know the nominal size of tyre does not reflect the actual measurement but I don't fully get what he meant, also because I have never heard of 28 tyres...

Any help?

Thanks


Top
 Profile  
 
PostPosted: Thu May 09, 2019 11:55 am 
Old School Grand Master

Joined: Mon Feb 11, 2008 9:42 am
Posts: 3366
IIRC 28" tyres are 700c.


Top
 Profile  
 
 Post subject: Re:
PostPosted: Thu May 09, 2019 3:42 pm 
Old School Hero
User avatar

Joined: Wed Oct 21, 2009 1:51 pm
Posts: 202
Location: Kingston
The easiest way is to read the number off the side of an existing tyre that fits the rim!

Failing that, look inside the rim and it will probably have a hook bead to hold the tyre on - not always with older rims. Below the hook bead there will be a flat edge - at the bottom of the flat edge will be the well of the rim. The circle made by the bottom of that flat edge is the bead seat, diameter of which is the ETRTO size.

I've got a 700c Mavic rim here - the outside diameter is 632 mm and the depth of the rim to the bead seat is about 5 mm. Subtracting the depth (x2) from the outside diameter gives 622, which is the ETRTO size for 700c.

I have a 27" road rim here too, the outside diameter of which is 641 mm. ETRTO size for 27" is 630.

I don't know anything about Italian touring bikes, but most Italian road bikes I've seen have either tubulars (which Italians called 28", but are the same size when it comes to setting brake blocks etc. as 700c clinchers), or 700c clinchers.

Some continental manufacturers put 27" wheels on bikes exported to Britain or the US, so your Dad's Bianchi could well have 27 inch wheels.

I suspect what he means by 28 not fitting because it's too small is that 700c doesn't fit, because it's smaller than 27".

28" is obviously smaller than 27" :facepalm:


Top
 Profile  
 
 Post subject: Re:
PostPosted: Thu May 09, 2019 5:07 pm 
Devout Dirtbag
User avatar

Joined: Tue Jun 24, 2014 1:13 pm
Posts: 133
Location: London
Thanks for the explanation!

From what you say, it might be a 27'', with 2mm deeper rims, assuming the 645mm measurement is accurate.

I will ask my dad to measure the depth of the rim


Top
 Profile  
 
 Post subject: Re:
PostPosted: Fri May 10, 2019 9:21 am 
Retro Guru

Joined: Sun Aug 22, 2010 7:07 pm
Posts: 1577
Location: Cotswolds
Here in the UK 1960s we had either tubular tyres or wired-on. The latter had an inextensible wire bead. Nominally 27 x 1 1/4 inch diameter, the important measurement was the rim diameter which supported the wire bead, which was 27 - 2 1/2 inches = 24 1/2 inches.

Any other size would have been virtually unobtainable.

Keith


Top
 Profile  
 
 Post subject: Re:
PostPosted: Mon May 20, 2019 6:07 pm 
Dirt Disciple

Joined: Sun Sep 20, 2015 7:28 pm
Posts: 17
Hi always found this page to be helpful http://sheldonbrown.com/tire-sizing.html


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 6 posts ] 

All times are UTC [ DST ]


Who is online

Users browsing this forum: Markone, Midlife and 15 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  

About Us

Follow Retrobike

Other cool stuff

All content © 2005-2015 Retrobike unless otherwise stated.
Cookies Policy.
bikedeals - the best bike deals in one place
FatCOGS - Fat Chance Owner's Group

Powered by phpBB® Forum Software © phpBB Group