Technical > Wheels, Tyres and Brakes

Tire Width and Inner Rim Width

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mickeg:
This is a topic that I have had a few arguments with others on, I won't go into details on the past arguments.  Just posting a short note here because Lennard Zinn recently wrote a short bit on this topic too.

I have often cited a table with recommended tire widths for rim widths on the website published by the late Sheldon Brown, table is at the bottom of the page at:
https://www.sheldonbrown.com/tire_sizing.html

I used that table when I built up my Thorn Sherpa.  I planned to use that bike with tires that ranged from 40 to 50mm.  I chose a rim with an inner width of 21mm for that bike, as that rim width matched my plans for tire widths.

Andra 30 is often mentioned on this forum.  On that table the Andra 30 rim with a 19mm inner width should be used with tires in the range of 28 to 44mm width.

Lennard Zinn in his column dated November 2, 2021 briefly mentioned tire width and rim width, pasted from that column:  "A general guideline is to take the inner rim width and multiply by 1.25 for the minimum tire size and by 2.5 for the maximum tire width. So, a 22mm inner rim width should not have less than a 27mm-width tire on it, and no bigger than a 55mm tire."

Source for above:  https://www.velonews.com/news/technical-faq-tire-size-and-rolling-resistance/

Based on that rule of thumb from Zinn, a rim with a 19mm inner width should then be used with tires in the range of 24 to 48mm.  That is a range that is slightly wider than the range on the table from the Sheldon Brown website, for this rim width the Zinn cited formula gives a range that is wider by 4 mm on both upper and lower tire widths than the table published by Sheldon Brown.

Zinn mentions that some use tires outside of that range, but I won't elaborate here, review the article if you want more detail.

John Saxby:
Thanks, George, useful info. 👍

JohnR:
My Mercury was fitted with Thorn rims https://www.sjscycles.co.uk/rims-tape/32-thorn-275-650b-584-disc-rim-black/ (19mm internal width) and 50mm tyres which is a slightly above the Zinn recommendation and I've got a pair of 57mm Schwalbe G-One Allrounds which I was planning to fit when the winter roads turn mucky. There's some relevant discussion at https://bicycles.stackexchange.com/questions/52587/what-is-the-maximum-tire-or-minimum-tire-width-i-can-fit-on-my-bicycle which suggests that, since the rims are hooked, then the maximum multiple of tyre width to rim width can be more than 2.5.

mickeg:
You already have the tires, you already have the rims.  I think you should try the tires and see how they work for you.  For riding around near home on an unladen bike I run 45 psi in the rear, 35 psi in the front on 57mm wide tires on the Andra 30 rims.  Works fine at those pressures.  Touring I run higher pressures.

In my case there were times that for better traction, I wanted to drop the tire pressure but that became impractical on rims that were too narrow for those tires.  I found that I needed to run higher pressure than I wanted to keep the tire from being too squirmy on a narrow rim. 

Why did I order such a narrow rim?  The problem in my case was that Thorn pushed the Andra 30 as the best expedition rim.  And their brochure for the Nomad Mk II at the time was suggesting tires that included a 2.15 and a 2.25 tire.  Thorn had a good reputation, so I did not feel it necessary to look at whether or not there would be incompatabilities.  I simply accepted that the Andra 30 was sized right for those tire widths I would be running, so I did not research the specifications like rim widths.  And when I got them, I was quite disappointed.  When I asked why they were saying this rim would work with those tires, they simply cited Ryde advertising literature that said it would be great all the way up to 57mm. 

I had paid a fortune for the CSS rims, and to return them would have meant a very expensive shipping charge from USA to UK.  So, I went ahead and used them.  And it was later that I decided that it was a mistake. 

Then much later I tried to figure out how much it would cost to buy Andra 40 rims with CSS, that was when I learned that CSS was no longer on Ryde website, CSS rims had been discontinued. 

So, at least for now, I decided to keep the Andra 30 rims, they work with the 57mm tires at the pressures I cited above on an unladen bike, I use higher pressures when touring.  And the main reason that I kept them is that I value the CSS rims.  It is rare when I want to drop the pressure lower than the pressures that I cited, so it is rare that these rims do not meet my needs.  But it is those rare times when I get very frustrated.

martinf:

--- Quote from: mickeg on November 07, 2021, 06:45:01 pm ---For riding around near home on an unladen bike I run 45 psi in the rear, 35 psi in the front on 57mm wide tires on the Andra 30 rims.  Works fine at those pressures.  Touring I run higher pressures.

--- End quote ---

I run at 35 psi in the rear, 30 psi in the front on 50 mm wide tires on the Andra 30 rims for light loads. 45 rear, 40 front for maximum load. If I let the pressure drop much below 30 psi I notice squirming.

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