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So I've been ignoring the wider rim revolution on road bikes as it didn't seem relevant to me at the time but now I'm playing catch up as bought a new bike with wider rims.
The rims are DT R460s, which are 2mm wider internally than my usual Fulcrum Racing 3s. The tyres are obviously now 2mm wider also.
First impressions were that for the same tyre pressure the ride was more chattery, although I can't really compare to the other road bike as it has fancy skinny stays and a carbon seat post.
Can I get away with lower pressures? Does a wider rim make the sidewalls sit squarer and therefore make the tyre less supple?
Ta
I'd say it gives you more support at lower pressures, so you can get better rollover. But that only applies to MTB experience never tried it on road.
I think it's to do with casing tension isn't it? Same tyre construction at the same pressure but a larger section means the casing tension is higher, so the tyre is less supple. Drop the pressure to get the casing tension back to where it was? I could be barking up the wrong tree here.
What pressures are you running at the moment? I'm running 75PSi at my hefty 63kg (plus Christmas), could probably actually go slightly lower
I had a similar rim-width change on my main road bike/ I didn't notice any obvious extra 'chatter' but I did drop the pressure from 85psi to 75psi with no apparent extra drag. Managed to convince myself that the cornering feels better at lower pressure. Maybe it is.
80psi at 85kg! I laugh at your paltry 63kg...
Not 100% sure I understand the science of casing tension, I usually think in terms of pressure x internal surface area = 'hardness'. The rim might have got wider but the actual internal surface area of the tyre hasn't changed, therefore the force applied to the inside of the tyre hasn't changed, therefore the tension in the carcass would remain the same?
A few millimeters may seem insignificant on paper, but the effect those wider rims had on performance and ride quality was eye opening. Broadening the base of the rim not only effectively widens the tire, but it also changes its profile to one that’s shaped more like a “U” than a “C”. As a result, you not only get more air volume for the same tire size, but also less casing deformation under load at at a given inflation pressure, and a larger-radius curvature on the tread cap.
https://cyclingtips.com/2016/11/the-new-normal-the-thinking-behind-wide-road-wheels/
Decent article but doesn't explicitly mention tyre pressures...
Carcass tension increases with internal pressure but also decreases with the tyre's curvature. So you need more pressure in skinny tyres to get the same carcass tension because they are more curved*. Wider rims reduce this curvature so you get more carcass tension for the same pressure and tyre.
*from bead to bead, not around the whole wheel or to put it another way, tension increases with increasing radius of curvature
Wider rims give a similar profile for a narrower tyre. That 23c on 15mm becomes. 25c on 17mm. Albeit with the same volume hence it has a different profile to 25c on a 15mm rim. To be perfectly honest, I don’t think I really notice a difference. My 25c Pavea on 15mm open pro rims have a U profile but a perfect fit. 23c Corsa on 17mm carbon deep sections have a much rounder profile, in fact the 25c have a significant aero deficit. I have 23 on the front and 25c on the back of most of my race wheels now.
For me volume determines pressure so I drop the psi by about 5 on wider rims. I’m 69 kg and run at about 85-95 unless circuit racing when it is higher. I have yet to properly test the 21c on the HED3s.
23c on 15mm becomes. 25c on 17mm. Albeit with the same volume
Has the volume not increased though? I thought that the rim was an arc of the "circle" made up of rim and tyre. Increase the size of that arc by 2mm and the circumference of the circle increases by 2mm too. Increase the circumference and the volume increases too.