Tyre ply cord angle versus rim width

[Samuel D]

Are bias-ply tyres as used on bicycles designed for a particular rim width?

[LittleWheelsandBig]

Don't know for sure myself but what prompted this question?

[Samuel D]

Just the observation that road rims have generally increased in width recently, albeit not all of them. So we have a situation where a single tyre, e.g. a 25 mm Veloflex Master, is used on a fair spread of rim widths (~13 mm to ~20 mm internal width). Is this ideal?

I accept that even if it’s not ideal, it may not matter very much. I’m just trying to better understand how tyres work.

[Brucey]

this is a pet idea of mine;  being that there is a 'perfect' bias angle, (for which the tyre designer was aiming for) and that when the tyre is mounted on different width rims, the bias angle will vary away from that slightly, and maybe the tyre will not behave the same way any more.

Possible changes in the way the tyre works include

1) that the width of the inflated tyre will vary differently with inflation pressure

2) that the security of the tyre (i.e. the loading in the beads required to retain it) will vary with pressure in a different way

3) that the way the carcass deforms in the contact patch will vary, and with it, the rolling resistance.

Against whatever changes there are in the tyre, there will be other effects which may (say) make the tyre (when mounted on a wider rim) work more like a wider tyre on a narrow rim, i.e. perhaps with lower rolling resistance.

BTW the way the tyre transfers the wheel load to the rim is also something to think of.  To my mind there are only two ways this can happen

a) the angle that the sidewall meets the rim is different in the contact patch

b) some cords near the contact patch actually become slacker, so don't exert the same force on the rim any more.

TBH I don't know what the true answer is; again not all tyres may work in quite the same way.

cheers

[zigzag]

while the tyre would feel different on narrow and wide rim, it would be because of different volume and shape, and not because of a particular way that the casing is made. i presume manufacturers optimise the layup based on average rim width so that the tyres work alright in the whole range.