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Referring from the question, specifically, what is the closest modern wheel size for my old 32-630 ( 27 x 1 ¼ ) wheels. It's hard to find rims and tires for that size now a days. I'm looking for the closest size in terms of wheel diameter. It should not go any bigger but close to exact size or smaller. I'm also converting my bike with disc brake, so rim size won't be any issue with rim brakes.

I have read this guide and mostly I found closest to mine is the 700C or 622mm ISO version for road bikes.

https://bike.bikegremlin.com/285/bicycle-tyre-dimensions/

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    700c/ISO 622 is it. See sheldonbrown.com/tire-sizing.html – Argenti Apparatus Aug 12 at 13:31
  • See also the answers to this question: bicycles.stackexchange.com/questions/63517/… – Ross Aug 12 at 17:19
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    700c is no doubt the closest, but your brakes may not be able to handle the difference. – Daniel R Hicks Aug 13 at 12:03
  • @DanielRHicks I will convert my bike to have disc brake so rim size won't be any issue. I have already discuss this is different question. – WashichawbachaW Aug 13 at 12:58
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    @DanielRHicks, hosses you mean or hose mount/guide? I'll be modifying my bike to be compatible with modern components. Everything from disc brake mount, hose, drop-out clearance, etc. that most modern component would fit. No worries, I know what I'm doing. I'm an experience welder myself. – WashichawbachaW Aug 13 at 13:33
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For your red bike, I'd suggest 622 mm wheels (the "700c" size") which is 8mm smaller diameter than your existing wheels.

Its your choice if you want to go for a "road 700c" or a "MTB 29 inch" wheel, which will be governed by the clearance between stays and between fork tines for the tyre. Both have the same rim diameter, but will be available in different rim widths (where the tyre lies) A wider tyre will sit better in a wider rim.

Given your earlier statements, I'd go with road bike 700c wheels, with gum-wall or tan side-wall tyres to maintain the historic look. A wider tyre would also look more original than a narrow, so 28mm as a minimum, and 35mm~38mm would be great.

enter image description here

Not a product rec, just an example.

Other considerations:

  • With disk brakes, you can run a pair of 650b wheels with larger rubber on them, if that is of interest.
  • Rim profile will be important too - you ideally want some box-section rims for the look, not deeper-section rims. This will be very hard to find in a MTB wheel and somewhat hard to find in a pre-built road wheel. So you may have to build your own wheels with older style rims onto disk-based hubs.
  • Rim material - Your red bike would have had distinctive steel rims which are a shiny chrome, or a rusty steel. A more modern bike would have alloy rims, which have a dull grey patina clearly visible on the brake track and no rust. Since you're not using the brake track, it may be worth either polishing the alloy rim to a mirror finish, or exploring some kind of spray-on chrome finish for the brake track.
  • Its going to be impossible to hide the disk brake rotors, so you might choose to distract by fitting items like a gutted bottle dynamo housing, and an old school front headlamp (which could have modern LED inside.) You might even hang a set of vinyl pannier bags off a front rack, but that all adds frontal area and increasing drag.
  • Another option is build the mounts for common 140mm rotors, but to fit an interposer adapter and run a tiny 120mm rotor, which would have a "side area" of 113 cm^2 vs 153 cm^2 for a 140mm rotor. Also look for a rotor that has more cooling slots so its less to see. You could even fit plastic spoke protectors on either side of the front wheel to help hide the brake rotor from the right-hand side, though that would also look weird.
  • I've just replaced my 29er tires 2.1" with 622/38 so going slimmer has no effect on width issues. I will say it was a proper hassle getting the bead to sit though. – Dan K Aug 15 at 5:19
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    @Criggie I've checked on 650B wheels and it may look awesome on my bike with skinwall tires on it. My current setup looks so thin and skinwall tire and aluminum rim doesn't look too appealing. I'm planning to replace it with 650B chrome rims with fatter skinwall tire from your suggestion. Regardless of hubs, I like a really silent freehub like Onyx but it's not available in my country, so I settled on XTR instead. I'm also, opting for 140mm rotor for that is the lightest available in our area. I'm currently running 2.4W dynamo fronthub with lamp on the side. – WashichawbachaW Aug 15 at 11:40
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    Strangely my "road 700C" (touring) rims are wider than my "MTB 29er" rims. The former were sold with 35mm tyres, the latter with 2.1" (53mm) – Chris H Aug 16 at 15:35
  • @ChrisH interesting - how old are they? Are either specified as tubeless-ready ? – Criggie Aug 17 at 1:20
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    @Criggie both about 2 years. The (cheap) MTB definitely wasn't tubeless ready. I've just had to Google the rims on the tourer and they're not tubeless ready either - but they are also marketed for MTBs, at least in the 32 hole version – Chris H Aug 17 at 6:46
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After measuring the outside diameter of my ETRTO 630 sized rim and tire with a modern ETRTO-622 sized tyre, (ie a "700c") I notice they have a slight difference which my fork and frame can tolerate.

The 622 rim is 8 mm smaller diameter (4mm smaller radius) than a 630 rim and is a good fit. So therefore I will go with a more modern 700c wheelset.

Thank you for those who have comment and helped me decide better.

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