Rim size for 28mm tyres

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benedwards
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Joined: 8 Dec 2022, 3:58pm

Rim size for 28mm tyres

Post by benedwards »

Hi, I need to get new a front wheel for my Audax, as it's for general use I think 28mm tires are the ones to go for.

Looking at https://www.cyclist.co.uk/in-depth/1025 ... -rim-width for 28mm tire it seems "Even for dedicated racers, 28mm is close to becoming the new normal. To accommodate these wider tires it's a good idea to look for an internal rim width of around 18-23mm."

someone in the house had a spare wheel but it has a 35mm tire on it and seems to be about 25mm wide so I think that's not appropriate. The weel I took of it seems about 20mm.

Image

But what are the pros/cons of the smaller (18mm) vs the bigger (23mm).

Also am I measuring properly (see image).
Jdsk
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Re: Rim size for 28mm tyres

Post by Jdsk »

Welcome.

The image isn't showing.

Jonathan
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andrew_s
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Re: Rim size for 28mm tyres

Post by andrew_s »

I've used 28 mm tyres since about 1995. I used to use MA2 & Open Pro (15 mm internal), and now use Exal LX17 (17 mm)
Add about 6 mm for the external width.
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Cugel
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Re: Rim size for 28mm tyres

Post by Cugel »

benedwards wrote: 8 Dec 2022, 4:10pm Hi, I need to get new a front wheel for my Audax, as it's for general use I think 28mm tires are the ones to go for.

Looking at https://www.cyclist.co.uk/in-depth/1025 ... -rim-width for 28mm tire it seems "Even for dedicated racers, 28mm is close to becoming the new normal. To accommodate these wider tires it's a good idea to look for an internal rim width of around 18-23mm."

someone in the house had a spare wheel but it has a 35mm tire on it and seems to be about 25mm wide so I think that's not appropriate. The weel I took of it seems about 20mm.

Image

But what are the pros/cons of the smaller (18mm) vs the bigger (23mm).

Also am I measuring properly (see image).
First, when considering rims for width notice that the inner rim width and the outer rim width are two different things. Tyres are usually recommended to match the inner rim width.

Most wheel rims have figures somewhere on them that give the wheel diameter and inner rim width. For example "622 X 20" is a 700C or 29" diameter wheel (the three numbers 622, 700C and 29" all mean the same size) and the "20" is the inner width of the rim in millimetres.

28mm wide tyres are usually at that size on 15-17mm inner rim widths. As the inner rim width increases, the actual width of the tyre on that rim, when the tyre is blown up, increases. For example, the ladywife has 28mm Continental tyres on a wheelset that's 622 X 20 and the tyres actually measure 31.5mm wide on those rims when blown up.

28mm tyres will run just fine on any rim between 15mm and 25mm inner width. All that happens is that the actual tyre width changes slightly. Generally speaking, a wider tyre (from a wider inner rim width) is going to more comfortable as you can use it, for your weight, with less pressure than if it was on a narrower inner rim width.

There is an ideal interface for tyres and rims that makes them the most aerodynamic. 28mm tyres on rim widths of 19mm can be "ideal". But there are many other factors involved besides the match of tyre width to rim width that affect aerodynamics so unless you're a top class racer wanting an extra 5 watts less resistance from your wheel/tyre combination at 40kph, no need to worry about getting this ideal match.

Personally I would match 28mm wide tyres with an inner rim width of between 20 - 24mm. This will increase the width of the tyre to more than 28mm and give the ability to have a lower pressure in them, giving more comfort and better road grip. The aerodynamic penalty of these wider tyres is trivial for all riders except racing types. But 28mm wide tyres will work perfectly well on wheels with narrower inner rim widths, down to 15mm.

Cugel
“Practical men who believe themselves to be quite exempt from any intellectual influence are usually the slaves of some defunct economist”.
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mattsccm
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Re: Rim size for 28mm tyres

Post by mattsccm »

As above. I would say that you have a good 10mm range of internal rim width. I happily run 25mm on 20mm rims. I did fit a 23 for the hell of it and it was great. Didn't keep it as I didn't have a matching pair!
Bear in mind that all recomendations from manufacturers will be cautious and conservative, if for no other reason than to cover their rear end. (Aero optimums may also apply). As with sell by dates they are best regarded with some scepticism.
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squeaker
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Re: Rim size for 28mm tyres

Post by squeaker »

"42"
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Chris Jeggo
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Re: Rim size for 28mm tyres

Post by Chris Jeggo »

According to a Chris Juden web page in the technical area of an old CTC web site, long since vanished in a CUK website revamp (dumbing down?), the ideal relationship between tyre width and internal width of rim section is about 1.8 to 1, but any tyre from 1.4 to 2.2 times should fit.
pwa
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Re: Rim size for 28mm tyres

Post by pwa »

And you need to be sure that 28mm tyres will leave enough space under your mudguards (if you have them) and brakes (if you have calliper rim brakes). If the clearance is too small you will find it soon clogs up with mud from winter lanes. On my own Audax bike I had to settle for supple 25mm tyres to keep enough clearance.
axel_knutt
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Re: Rim size for 28mm tyres

Post by axel_knutt »

From Schwalbe:
Tyre width.png
“I'm not upset that you lied to me, I'm upset that from now on I can't believe you.”
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benedwards
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Joined: 8 Dec 2022, 3:58pm

Re: Rim size for 28mm tyres

Post by benedwards »

I know this was a while ago but realized I did not thank everybody for their great advice. I ended up getting a new weel. Thanks.
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andrew_s
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Re: Rim size for 28mm tyres

Post by andrew_s »

Cugel wrote: 8 Dec 2022, 7:24pmThis will increase the width of the tyre to more than 28mm and give the ability to have a lower pressure in them, giving more comfort and better road grip.
Not necessarily.
As far as being able to reduce pressure is concerned, what matters is not the tyre width, but the height of the tyre above the rim.

An inflated tyre is circular in cross section.
If you take a narrow rim that contacts the tyre at 5 o'clock and 7 o'clock, very little of the tyre cross section is within the rim.
If you take a wide rim that contacts the tyre at 4 o'clock and 8 o'clock, much more of the tyre cross section is within the rim.

The length of the cross section circumference between the two contact points is the same for any given model & size of tyre, so the diameter of the cross section is necessarily larger for the wider rim.

The question is whether the height you gain from the increased diameter is more than the height you lose through having more of the cross section within the rim, or less.
This is less than obvious without resorting to pencil diagrams and a calculator, but the limiting cases (6 & 6 o'clock vs 3 & 9) give the same height, so rim width may well make no difference to the lowest usable pressure.
Carlton green
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Re: Rim size for 28mm tyres

Post by Carlton green »

As a general observation, which supports later comments in the thread rather than answers the OP, I’ve ended up using the widest rims (about 19mm) that I could find commonly available for my tyres - plus also run in my frames - and noticed both a more enjoyable ride (seems to cope better with all surfaces) and wheels that much better stay in true. To an extent each of us find our own way forward based on our own experiences; I don’t cover as many miles as some other forum members but slightly wider rims have definitely served me best - a few mm can make a very useful difference - and if given the option I wouldn’t use wheels with narrow rims ‘cause they’re more trouble than they’re worth.

As a start point on any topic I’ve found CJ’s comments to be very helpful. Many years back he had an article (Tired and Emotional, IIRC) about tyre width and rim width in the CTC mag - I still have have a copy of it somewhere.
Don’t fret, it’s OK to: ride a simple old bike; ride slowly, walk, rest and admire the view; ride off-road; ride in your raincoat; ride by yourself; ride in the dark; and ride one hundred yards or one hundred miles. Your bike and your choices to suit you.
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