19mm internal rims and 25mm tyres?

[Bianchi Boy]

I am considering getting some rims with 19mm internal width and using them with 25mm tyres. Will this work or are the tyres too narrow for the rims?

Thanks in advance.

BB

Sent from my H8216 using Tapatalk

[mcshroom]

I've done it before without any issues. My combination was a Michelin Pro4 Endurance on a Mavic A319 front wheel so I could use my tourer's dynamo wheel for audaxing. The Pro4 was pretty wide compared to some 25mm tyres though.

[zigzag]

definitely not too narrow. fwiw, i've been using 25mm tyres (gp4000s2) on 21mm rims - they come up 28.7mm wide. on the same rims -  i also use s-works turbo 28mm which measure 30.3mm.

[wajcgac]

I had a set of wheels built by Dave at DCRwheels using Kinlin XR31T rims that have an internal width of 19mm.

One of his comments when discussing rim/tyre options was

'I think that 25c is going to be a nicer option for you, it offers better grip and comfort.  However you can definitely run 23/25/28s without any issue on these rims'

.

I've been running 23mm tyres on them (was concerned about frame clearance) for nearly 10,000km with no issue. Not sure whether this is true of all 19mm rims though or just the ones I have.

[BFC]

No problem. Be sensible about choice of tube - if the 25mm nominal tyre is coming out at 28mm width when fitted make sure the tube is OK up to the larger effective size or it will be prone to failure around the valve stem.

[Bianchi Boy]

Thanks for the reassurance. Think I will be going for a kinlin.

BB

[Oxford_Guy]

At the other end of the scale, will 25mm tyres (true 25mm in this case - Veloflex Masters), be okay on 15mm internal width rims (Mavic Open Pro)?

[zigzag]

At the other end of the scale, will 25mm tyres (true 25mm in this case - Veloflex Masters), be okay on 15mm internal width rims (Mavic Open Pro)?

they'll be fine, but sub-optimal from aerodynamic point of view as wider tyre will be causing more turbulence around the rim. for road cycling tyre sidewall should be similar size as the rim (external). the drag is lowest when the rim is slightly wider than the tyre.
however, mavic open pros are not aero rims, so i assume speed is not important so any tyre in the range of 23...32 will be fine.

[Genosse Brymbo]

At the other end of the scale, will 25mm tyres (true 25mm in this case - Veloflex Masters), be okay on 15mm internal width rims (Mavic Open Pro)?

they'll be fine, but sub-optimal from aerodynamic point of view as wider tyre will be causing more turbulence around the rim. for road cycling tyre sidewall should be similar size as the rim (external). the drag is lowest when the rim is slightly wider than the tyre.
however, mavic open pros are not aero rims, so i assume speed is not important so any tyre in the range of 23...32 will be fine.

I've been running Michelin Pro4 Endurance 25mm on Open Pro rims for the last 4 years with no problem.  Gutted to read that the combination is not aero; I could have improved my PBP2015 time 

[Oxford_Guy]

At the other end of the scale, will 25mm tyres (true 25mm in this case - Veloflex Masters), be okay on 15mm internal width rims (Mavic Open Pro)?

they'll be fine, but sub-optimal from aerodynamic point of view as wider tyre will be causing more turbulence around the rim. for road cycling tyre sidewall should be similar size as the rim (external). the drag is lowest when the rim is slightly wider than the tyre.
however, mavic open pros are not aero rims, so i assume speed is not important so any tyre in the range of 23...32 will be fine.

Well I won't be doing any actual racing, just want to be able to keep up on the faster club rides. The frame will be steel (Reynolds 853), so am already handicapping myself!

Having said that - any other rims worth considering, that wouldn't look out of place on a Mercian Strada Speciale? Need to be 32 hole, as want to use my Campagnolo Chorus hubs with them.

[Oxford_Guy]

It looks like the Sonnet Road Bike is by default equipped with Open Pro rims and 25mm Veloflex Masters - you can see in the photos here: https://www.sonnet.cc/road-bike

They Masters don't look too bulb-like on those rims.

[Brucey]

Etrto say you can fit up to 32mm to a 15C rim



but that you shouldn't put a 25mm tyre on a 19C rim.  In fact you cannot have any of Zig-zag's aero fitments according to etrto….

 BTW some tyres tend to blow off the rim if they are fitted to a rim that is wider than recommended.  Note that the above chart applies to hook-bead rims only; straight sided rims have a much narrower range of recommended tyre fitments.

FWIW I think the best rim/tyre combination (from a tyre security and handling perspective) is usually the second or third smallest size tyre for any given rim recommended in the chart above. Needless to say your wheels with fat tyres need to have a substantially lower drag coefficient to be as aero as tyres that are simply narrow, because wide tyres are, er, wide. 

Note also that most of the 'evidence' about aero wheels is in fact unrepresentative of real world conditions in two main respects

1) the wheels are often not turning when tested and
2) the wheels are only tested in steady state conditions.

On the latter point; in the real world conditions around the front wheel are hardly ever steady state; no-one rides in a straight enough line for that and in addition real winds are gusty/turbulent, not steady.

All of which means that the real benefits of aero wheels are often a small fraction of those touted by those who would sell them to you and a much simpler approach (eg smaller frontal area) may work just as well in terms of aero drag.

cheers

[Oxford_Guy]

Etrto say you can fit up to 32mm to a 15C rim

Sure, but just because you can, doesn't meant that it's ideal...

FWIW I think the best rim/tyre combination (from a tyre security and handling perspective) is usually the second or third smallest size tyre for any given rim recommended in the chart above. Needless to say your wheels with fat tyres need to have a substantially lower drag coefficient to be as aero as tyres that are simply narrow, because wide tyres are, er, wide. 

Note also that most of the 'evidence' about aero wheels is in fact unrepresentative of real world conditions in two main respects

1) the wheels are often not turning when tested and
2) the wheels are only tested in steady state conditions.

On the latter point; in the real world conditions around the front wheel are hardly ever steady state; no-one rides in a straight enough line for that and in addition real winds are gusty/turbulent, not steady.

All of which means that the real benefits of aero wheels are often a small fraction of those touted by those who would sell them to you and a much simpler approach (eg smaller frontal area) may work just as well in terms of aero drag.

Also (though the difference may be minor) - thin, non-aero wheels (if made from the same material), such as Open Pros, can be made lighter than wider/aero wheels

[zigzag]

In fact you cannot have any of Zig-zag's aero fitments according to etrto….

 BTW some tyres tend to blow off the rim if they are fitted to a rim that is wider than recommended.

not sure why would the tyre blow off if it pops nice and tight onto the rim. in the photo below - rim internal 18.5mm, external 27mm. tyre marked as 23mm (way out of etrto guidelines) measures 25.7mm wide. at 80-85psi they ride amazing.
maybe there are tyre/rim combos prone to blowing off, but i'm not convinced until i see it in real life - it could be bad installation among other reasons.



p.s. i always inflate the tyres to the max (120+ psi) to make sure they are seated properly, then let some air out for the actual riding.

[Oxford_Guy]

In fact you cannot have any of Zig-zag's aero fitments according to etrto….

 BTW some tyres tend to blow off the rim if they are fitted to a rim that is wider than recommended.

not sure why would the tyre blow off if it pops nice and tight onto the rim. in the photo below - rim internal 18.5mm, external 27mm. tyre marked as 23mm (way out of etrto guidelines) measures 25.7mm wide. at 80-85psi they ride amazing.
maybe there are tyre/rim combos prone to blowing off, but i'm not convinced until i see it in real life - it could be bad installation among other reasons.

Are those GP4000s or GP5000s? If the former, they're well-known for being oversize: "On a 17C rim, at an air pressure of 100 psi, all versions of the GP4000S II measure about 2 - 3 mm wider than the specified size. ": https://www.bicyclerollingresistance.com/specials/conti-gp4000s-ii-23-25-28

Which may partially account for being able to seat a 23mm tyre on those rims

[Brucey]

I suspect that one reason the narrow tyre/wide rim combination is not recommended is that this fitment changes the bias angle in the carcass from that intended and this in turn affects the loads seen by  the beads (*). Another is that if the tyre is retained by a hook bead ( yes in tubed tyres, less so in tubeless) then the hooks only get to work if the tyre is pressed against them; if the tyre is narrow and the rim is wide, there is less force on the hooks and therefore less benefit from the hook beads.

(*) there is a simple but elegant method which compares the hoop stresses vs the longitudinal stresses in a pressurised cylinder (short length of tyre) and therefore enables the 'ideal bias angle' to be calculated. In practice tyres deviate from this a little, eg most tubs have a bias angle that causes the tyre to tighten slightly onto the rim when inflated. But deviations further than a certain amount will cause the loads in the tyre structure to be abnormal.

However in this world of non-standardised tubeless fitments there are combinations that ought not to work but do, and others which ought to work but don't. Only today I was looking at some stan's rims and it was obvious that the lips were less then 5mm high (rather than ~6.5mm)  above a tapered bead seat, i.e. the bead was meant to stretch to fit the rim, something not all tyres will happily do....

Practical problems with the wide rim/narrow tyre fitment include that, during hard cornering on a bumpy/dirty road, the rim edge can clonk against the road surface. This does little for the rim, and less for traction....

FWIW my gripe with the other combination (wide tyre/narrow rim) is that the range of tyre pressures that is acceptable can be  very narrow; at low pressures the tyre isn't well stabilised laterally and tends to flop around. This means that if you are running fatter tyres for reasons of comfort, some of that advantage is likely to be lost if you are sensitive to this lateral movement.  Having said that I've run rear tyres of nominal 35mm width (actual 32mm once fitted on a narrow rim) on 13-15C rims and they have been OK provided they are kept well inflated. At the front the same combination felt too 'floppy' at pressures that were good for comfort. On a wider rim the same tyres felt OK over a wider range of pressures.

cheers

[mattc]

but that you shouldn't put a 25mm tyre on a 19C rim.  In fact you cannot have any of Zig-zag's aero fitments according to etrto….

I believe Mavic use the same chart on their site.

I've seen a lot of recent bike reviews where the rims seem to be wider than the etrto/mavic/schwalbe figures. Which would be worrying, if I planned to use such wheels.
(!)

[Brucey]

I dunno how to square that circle either. Maybe it is a fad, maybe it is real progress. Hard to say....

cheers

[mzjo]

Practical problems with the wide rim/narrow tyre fitment include that, during hard cornering on a bumpy/dirty road, the rim edge can clonk against the road surface. This does little for the rim, and less for traction....

cheers

Been there, done that! Only front wheel available had an old Alesa rim  perhaps 22mm wide (non-hook, IIRC), only tyre 23mm (might have been rigid bead, ICRTW). It lasted the afternoon's club ride but did not fill me with confidence at all. And yes there is a serious risk of touching the rim onto the road when cornering, even gently!

The CTC did have a pair of formulae with coefficients for the widest and narrowest rim given a nominal tyre width. One was for the recommended rim width and the other was for max possible rim width usable in normal conditions (what you can get away with!). I can't think where I saw them, possibly linked on another forum, but they gave an absolute max width of 21.5mm for a 32mm tyre. (I was looking at possible mtb rims for the 32mm tyres of the 650B Confrérie at the time).

[suffolkngood]

Retro is very conservative. 25mm tyres do work on 19mm internal width rims but I don't think fitting such tyres to wider rims makes sense. The crown of the tyre is too flat on wider rims and the tyre squares off sooner. Handling should be affected. Squared off tyres are less aero if you care about such things. Also the side walls are more exposed to damage.

21mm internal Trim's are really for 32mm tyres or wider.

Tyre manufacturers make there tyres to meet ertro guidelines. You can step out side a bit but the more you fo the more the tyre under performs.