Wide tyres - I just don't get it

neeb

Just back from a ride after replacing the 25mm tubular on my front wheel with a 23mm again (which is what I was using until about a year ago). More or less dry roads so a rare outing for the best bike at this time of year. These are Vittoria Corsa tubs and the 23mm is actually only a bit over 22mm actual width, so quite a bit narrower than your average 23mm clincher on a wide rim. My suspicions were confirmed - the ride was sublime, the handling felt sharper and it was just plain faster. I'd been a little disappointed with the 25mm on the first few rides after installing them but had put it down to other factors - wind, fatigue etc. But now I'm sure that my intuition was right - the narrower tyres are just faster and feel better (at least on the front). It didn't feel any less comfortable either, although perhaps that was down to pressure - I'm running the front 23mm at 95psi while I'd been riding the front 25mm at 90psi which is effectively a little higher relative to the tyre width, but not by much (I'm 64kg). In both cases the rear 25mm was at 95psi.

Maybe it's the aero effect? The wheels are Campagnolo Boras with 24.2 outer width so the 23mm tubs (actually about 22.5) are just about perfect given the "at least 5%" rule for how much narower tyres should be than rims. The 25mm Corsas on the other hand are almost exactly the same measured width as the rims when fitted (24.2mm).

I do have experience of "properly" wider tyres (if not mega wide) - I run 25mm clinchers (Corsas again) on another bike which measure practically 27mm when fitted on H plus Son Archetypes. They're fine, but they're not faster. I run them at 85 front and 90 rear. In terms of comfort there's certainly a significant difference over properly bumpy surfaces such as cobbles, pot holes etc, but I don't really notice much difference on rough vs. smooth tarmac. In practice "comfort" just really isn't a factor for me on the roads I ride on, there are some bits that are worse than others and I notice that but it doesn't really impact on my riding experience.

I suppose if I was planning a ride on wet roads that involved a lot of cornering I'd take the bike with the wider clinchers for the extra security of more rubber on the road, and certainly if I was going to ride on cobbles. But for any other situation, based on my experience, I just don't get the wide tyre thing.

What am I missing?

sungod

neeb wrote:

...
What am I missing?

nothing

no amount of marketing hype can change reality, for road, fat tyres on narrower rims will be poor aerodynamically, have higher crr, and can be squirmy in hard cornering

given two tyres of identical construction, but differing widths, at the same pressure, the wider will have lower crr, but the two key things here are identical construction and pressure

it's widely pronounced that wider tyres have lower crr, but the reality will be different depending on construction and pressure

if this site is to be believed (and there're reasons to be critical) https://www.bicyclerollingresistance.com/ the lowest road tyre crr is a skinny tubeless clincher, followed by the 'same' tyre in tubular (using glue and gluing technique both known to be inferior for best crr), followed by the same clincher with tube

on that basis...
tubeless is fastest
tubular next
clincher + tube slowest

of course, these are all skinny, that's because skinny is fastest

cougie

I think you just expected it to be faster. You can't tell me that the aerodynamics of a slightly narrower tyre is noticeable.

neeb

cougie wrote:

I think you just expected it to be faster. You can't tell me that the aerodynamics of a slightly narrower tyre is noticeable.

Well, not the tyre being 2mm narrower in itself but the fact that it's more than 5% narrower than the rim (instead of the same width). It's said that you lose all benefits of aero rims unless the tyre is narrower than the rim.

neeb

neeb wrote:

cougie wrote:

I think you just expected it to be faster. You can't tell me that the aerodynamics of a slightly narrower tyre is noticeable.

Well, not the tyre being 2mm narrower in itself but the fact that it's more than 5% narrower than the rim (instead of the same width). It's said that you lose all benefits of aero rims unless the tyre is narrower than the rim.

That said, I'm a little sceptical - until about 5 years ago all deep section rims were narrower than 23mm tyres and people still seemed to think they got a significant benefit from them.

cycleclinic

tubular tyres dont handle much differently if any on a wide rim compared to a narrow rim.

the effect the OP is probably noticing is aerodynamics. There will be a small difference in power required to sustain a set speed on a narrow rim for a 23mm and 25mm corsa tub (20mm external). On a 27mm wide rims the 25mm tyre will be faster than the 23mm tyre.

On 24mm wide bora's a 23mm wide tyre is perfect aerodynamically. 25mm is a bit too wide and slower.

shirley_basso

I doubt anyone is noticing the aerodynamics of a tyre rim interface.

Tetragrammaton1

Wider tyres can be run at lower pressures than thinner tyres without risking pinch flats ( not including tubs / tubeless, where this doesn’t apply ). Lower pressures = more comfort (usually).

cycleclinic

The OP claims he does though and the aerodynamic gain is the only plausable explanation. Either that or the OP was not actually faster. That is also possible.

Personally I am not faster on 23mm tyres vs 25mm tyres. At high speed though the difference will be more pronounced.

apreading

If you run the 25mm at just about the same pressure then you wont see the benefit. 90/95 for a 25mm at 64kg is mad. I run 80/85 and weigh 100kg at the moment although my fighting weight should be more like 90kg. And I let them run down so usually they are less than that other than when I have just topped them up.

And they really need a matching wider rim. Otherwise you get what is known as the lightbulb effect where the shape is not right.

paulmon

I don't race so I'll take comfort over speed any day of the week and wider tyres at a lower PSI are noticeably more comfortable than narrow tyres with a higher PSI. Run tubeless and you can take those annoying pinch flats out of the equation as well.

pblakeney

PaulMon wrote:

I don't race so I'll take comfort over speed any day of the week and wider tyres at a lower PSI are noticeably more comfortable than narrow tyres with a higher PSI.

That is the answer in a nutshell. No one solution to any issue will suit everyone.
If you want the answer relating to racing then I suggest asking over in Pro Race.

sungod

cougie wrote:

I think you just expected it to be faster. You can't tell me that the aerodynamics of a slightly narrower tyre is noticeable.

in a straight line i doubt i'd notice a difference

but on windy day with changing yaw angle, it's a different matter...

the difference between a veloflex sprinter (nominal 22mm) and a criterium (nominal 23mm) on a lightweight obermayer (20mm width) front wheel is dramatic

with the slightly wider tyre, this wheel 'catches' strongly in crosswinds as yaw angle changes, on a windy day fast twisty descents can be really scary, but with the narrower tyre this doesn't happen, there's no catching as the yaw angle changes, crosswind handling differs little from calm conditions, it's like a completely different wheel

neeb

apreading wrote:

If you run the 25mm at just about the same pressure then you wont see the benefit. 90/95 for a 25mm at 64kg is mad. I run 80/85 and weigh 100kg at the moment although my fighting weight should be more like 90kg. And I let them run down so usually they are less than that other than when I have just topped them up.

And they really need a matching wider rim. Otherwise you get what is known as the lightbulb effect where the shape is not right.

thecycleclinic wrote:

tubular tyres dont handle much differently if any on a wide rim compared to a narrow rim.

the effect the OP is probably noticing is aerodynamics. There will be a small difference in power required to sustain a set speed on a narrow rim for a 23mm and 25mm corsa tub (20mm external). On a 27mm wide rims the 25mm tyre will be faster than the 23mm tyre.

On 24mm wide bora's a 23mm wide tyre is perfect aerodynamically. 25mm is a bit too wide and slower.

Yes, I agree that the only plausible explanation that springs to mind is aerodynanics, and I know about the lightbulb effect and the 23mm being well matched to the 24.2mm Boras (that's why I went back to the narrower size at the front).

The weird thing through is that two or three years back I was running the same 23mm tubs on some Reynolds Thrity Twos (21mm external diameter) and they also both felt and were fast.

I'm very aware of the dangers of subjective judgements but if you ride the same routes regularly (regularly enough to have a big enough mental sample to flatten out the influence of wind and other factors) and have a power meter you get a pretty good feeling for the relationship between power and speed and how that's affected by changes in equipment.

More subjectively, the 23s just seem to accelerate better and feel more lively. I can't explain that but I just find them more fun to ride.

One of many half-baked theories off of the top of my head: the narrower contact patch means the bike moves laterally more easily when riding hard out of the saddle and rocking from side to side. I don't know if the maths would work out to make that faster or slower, but it feels faster.

Maybe it's all down to aero and a 25mm tub on a 27mm rim would feel as fast as a 23 mm tub on a 24.2mm rim. I find it hard to believe it would actually be faster though - the aero advantage should be about the same and the gains from decreased rr with the wider setup would be pretty minimal relatively speaking and would only apply if the tyres were run at the same pressures (in which case the 25s would probably be *less* comfortable).

Incientally, when I look at the current offereings for supposedly aero deep section clinchers I am puzzled. The trend is towards wider, especially as regards the internal bead diameter. But a wide internal diameter such as 19mm (as in the Zipp NSWs) isn't really suited to a 23mm clincher, and will cause a 25mm clincher to have a measured diameter about the same as or possibly even wider than the 27mm maximum diameter of the wheel..

cycleclinic

Not true neeb. Not all 25mm tyres fill out to 27mm on an wide rim.

In fact there is wind tunnel data showing a 23mm conti is faster than the 25mm gp 4000s clincher on a 19mm internal width rim. It's all blindingly obvious aerodynamics.

Many people put tyres too wide on aero rims. On shallow none aero rims fine, go for comfort.

Wide rims are suited to tyres that measure 25mm in real life. Whether that's a 23mm or 25mm tyre depends on the tyre.

First.Aspect

I find my confirmation bias to be completely consistent with any placebo effect I was expecting.

neeb

thecycleclinic wrote:

Not true neeb. Not all 25mm tyres fill out to 27mm on an wide rim.

In fact there is wind tunnel data showing a 23mm conti is faster than the 25mm gp 4000s clincher on a 19mm internal width rim. It's all blindingly obvious aerodynamics.

Many people put tyres too wide on aero rims. On shallow none aero rims fine, go for comfort.

Wide rims are suited to tyres that measure 25mm in real life. Whether that's a 23mm or 25mm tyre depends on the tyre.

Hmm, I don't really disagree with that other than that I was under the impression that 23mm clinchers (labelled as) aren't really designed for internal bead diameters as wide as 19mm and that there are potential safety issues. Obviously a clincher that measures 25mm when fitted would be ideal for a 27mm wide (external) clincher rim.

So what clincher tyre would you fit to the current Zipp NSWs that are 27mm wide and 19mm intermal for maximum aero benefits? Genuinely curious because if I do buy deep section carbon clinchers at some point I will want them to be aero and would probably aim for such a setup (unike with tubs it would be difficult these days to get a clincher tyre that measured 23mm when fitted to a rim that was wider than that).

thegreatdivide

sungod wrote:

the difference between a veloflex sprinter (nominal 22mm) and a criterium (nominal 23mm) on a lightweight obermayer (20mm width) front wheel is dramatic

with the slightly wider tyre, this wheel 'catches' strongly in crosswinds as yaw angle changes, on a windy day fast twisty descents can be really scary, but with the narrower tyre this doesn't happen, there's no catching as the yaw angle changes, crosswind handling differs little from calm conditions, it's like a completely different wheel

To be fair, a Lightweight Obermayer is a wheel with ancient aerodynamic qualities. It's an overpriced, side wind catching vanity purchase that'll send you into ditch every time a bus overtakes.

First.Aspect

thegreatdivide wrote:

sungod wrote:

the difference between a veloflex sprinter (nominal 22mm) and a criterium (nominal 23mm) on a lightweight obermayer (20mm width) front wheel is dramatic

with the slightly wider tyre, this wheel 'catches' strongly in crosswinds as yaw angle changes, on a windy day fast twisty descents can be really scary, but with the narrower tyre this doesn't happen, there's no catching as the yaw angle changes, crosswind handling differs little from calm conditions, it's like a completely different wheel

To be fair, a Lightweight Obermayer is a wheel with ancient aerodynamic qualities. It's an overpriced, side wind catching vanity purchase that'll send you into ditch every time a bus overtakes.

You almost make it sound like youcould afford to own a set.

thegreatdivide

First Aspect wrote:

thegreatdivide wrote:

sungod wrote:

the difference between a veloflex sprinter (nominal 22mm) and a criterium (nominal 23mm) on a lightweight obermayer (20mm width) front wheel is dramatic

with the slightly wider tyre, this wheel 'catches' strongly in crosswinds as yaw angle changes, on a windy day fast twisty descents can be really scary, but with the narrower tyre this doesn't happen, there's no catching as the yaw angle changes, crosswind handling differs little from calm conditions, it's like a completely different wheel

To be fair, a Lightweight Obermayer is a wheel with ancient aerodynamic qualities. It's an overpriced, side wind catching vanity purchase that'll send you into ditch every time a bus overtakes.

You almost make it sound like youcould afford to own a set.

I could think of better things to spend the cash on...like a pair of Gipfelsturms ;-)

meanredspider

The aero advantage of narrower tyres comes from where?

First.Aspect

meanredspider wrote:

The aero advantage of narrower tyres comes from where?

Holmesian deduction, my dear Watson.

meanredspider

First Aspect wrote:

meanredspider wrote:

The aero advantage of narrower tyres comes from where?

Holmesian deduction, my dear Watson.

What: because they are narrow??

svetty

meanredspider wrote:

First Aspect wrote:

meanredspider wrote:

The aero advantage of narrower tyres comes from where?

Holmesian deduction, my dear Watson.

What: because they are narrow??

Partly due to the reduced surface area but mostly because the airflow across the tyre:rim interface is smoother. Not really an issue for shallow rims but relevant when using deeper section 'aero' rims.

sungod

thegreatdivide wrote:

To be fair, a Lightweight Obermayer is a wheel with ancient aerodynamic qualities. It's an overpriced, side wind catching vanity purchase that'll send you into ditch every time a bus overtakes.

if you'd ridden them for years you'd know that with the correct width tyres they don't catch the sidewind any more than other wheels, less in fact than much shallower rims such ambrosio nemesis (though the higher spoke count on those may be a factor there)

in spite of being overtaken by many buses and other large vehicles they show no propensity to send me into ditches, nor off mountain roads, so you are provably wrong there too

obermayers also have great lateral stiffness, astonishing strength, and are light, so very light, no other wheel comes close

but as you are clearly speaking from ignorance, you wouldn't know any of that

sounds more like you are just bitter that you can't afford them

First.Aspect

meanredspider wrote:

First Aspect wrote:

meanredspider wrote:

The aero advantage of narrower tyres comes from where?

Holmesian deduction, my dear Watson.

What: because they are narrow??

Yes I I think that's about it. I'm convinced. I don't even need any evidence.

thegreatdivide

sungod wrote:

thegreatdivide wrote:

To be fair, a Lightweight Obermayer is a wheel with ancient aerodynamic qualities. It's an overpriced, side wind catching vanity purchase that'll send you into ditch every time a bus overtakes.

if you'd ridden them for years you'd know that with the correct width tyres they don't catch the sidewind any more than other wheels, less in fact than much shallower rims such ambrosio nemesis (though the higher spoke count on those may be a factor there)

in spite of being overtaken by many buses and other large vehicles they show no propensity to send me into ditches, nor off mountain roads, so you are provably wrong there too

obermayers also have great lateral stiffness, astonishing strength, and are light, so very light, no other wheel comes close

but as you are clearly speaking from ignorance, you wouldn't know any of that

sounds more like you are just bitter that you can't afford them

EDIT - I actually couldn't give a flying f*ck.

meanredspider

Svetty wrote:

meanredspider wrote:

First Aspect wrote:

meanredspider wrote:

The aero advantage of narrower tyres comes from where?

Holmesian deduction, my dear Watson.

What: because they are narrow??

Partly due to the reduced surface area but mostly because the airflow across the tyre:rim interface is smoother. Not really an issue for shallow rims but relevant when using deeper section 'aero' rims.

The reduced frontal bluff area difference is minuscule as many (most) frames are a broader section than the tyre so the width difference only influences that figure below the BB level - a few square mm. Whether flow is better, worse or the same over the tyre/rim is just a guess without understanding the exact flow pattern for that tyre, wheel and speed combination.

neeb

meanredspider wrote:

The reduced frontal bluff area difference is minuscule as many (most) frames are a broader section than the tyre so the width difference only influences that figure below the BB level - a few square mm..

Hmm, I'm looking at my bike right now and it seems that between a third and a half of the wheel is below the BB level.. And that's not considering the extent to which the aerodynamics of the wheel and frame are separate or otherwise.

meanredspider

neeb wrote:

meanredspider wrote:

The reduced frontal bluff area difference is minuscule as many (most) frames are a broader section than the tyre so the width difference only influences that figure below the BB level - a few square mm..

Hmm, I'm looking at my bike right now and it seems that between a third and a half of the wheel is below the BB level.. And that's not considering the extent to which the aerodynamics of the wheel and frame are separate or otherwise.

If you do the maths, you get about 5cm2 by my reckoning - or, what, a couple of postage stamps?? You’d probably get something similar if your helmet is tipped back slightly or your jersey isn’t fully zipped.

As for shape effects, the wider trailing edge of the front tyre might (who knows) improve airflow transition to the down tube or around the forks...

Honestly, I don’t really care, but personally I doubt any noticeable/measurable difference is down to aero.

First.Aspect

meanredspider wrote:

neeb wrote:

meanredspider wrote:

The reduced frontal bluff area difference is minuscule as many (most) frames are a broader section than the tyre so the width difference only influences that figure below the BB level - a few square mm..

Hmm, I'm looking at my bike right now and it seems that between a third and a half of the wheel is below the BB level.. And that's not considering the extent to which the aerodynamics of the wheel and frame are separate or otherwise.

If you do the maths, you get about 5cm2 by my reckoning - or, what, a couple of postage stamps?? You’d probably get something similar if your helmet is tipped back slightly or your jersey isn’t fully zipped.

As for shape effects, the wider trailing edge of the front tyre might (who knows) improve airflow transition to the down tube or around the forks...

Honestly, I don’t really care, but personally I doubt any noticeable/measurable difference is down to aero.

But narrower tyres feel faster. So do wider tyres, depending on what you were expecting. The thing to do is alternately fit tyres you are told are faster.