25mm tyres

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mig
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Re: 25mm tyres

Postby mig » 23 Feb 2018, 9:10am

foxyrider wrote:25? I consider my 23's wide, I used to use 20's, sadly they seem to have stopped making them and the pair I have on wheels are dead, sniff.

I've been using 23's all winter, its not the tyres that are causing any discomfort but the crap state of the roads! Mind you, I have been riding them flat, well @ 80psi.

A lot of this width stuff Is to do with aerodynamics - problem is most people don't actually consider the rim width they have before spouting all the techno babble - the tyre should be the same width as the rim to work aero dynamically which in turn will affect Micks 'roll out' data.


i read a review of the latest racing wheels idea in the comic a few weeks ago. usual ridiculous babble about this and that with the added comment that a pattern on the rim was an echo of shark's skin (or whale or something) which made that more hydro-dynamic. er...okay...so your new £3k+ wheels are good a cutting through water?

ehhh when i were a lad...

elPedro666
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Re: 25mm tyres

Postby elPedro666 » 23 Feb 2018, 9:23am

foxyrider wrote:25? I consider my 23's wide, I used to use 20's, sadly they seem to have stopped making them and the pair I have on wheels are dead, sniff.

I've been using 23's all winter, its not the tyres that are causing any discomfort but the crap state of the roads! Mind you, I have been riding them flat, well @ 80psi.

A lot of this width stuff Is to do with aerodynamics - problem is most people don't actually consider the rim width they have before spouting all the techno babble - the tyre should be the same width as the rim to work aero dynamically which in turn will affect Micks 'roll out' data.
PlanetX did have a stack of 19-20mm tyres going dirt cheap (like 80-90% off kinda cheap!), not looked for a little while though...

I'm a trendy consumer. Just look at my stupid phone.

Leeflatz
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Re: 25mm tyres

Postby Leeflatz » 23 Feb 2018, 12:01pm

I think tyres used to go down to 18mm
They were for hardcore racers and we're tubular, glued to the rim
There was a chance they could come off when cornering
Never tried 'em
Too nutter, bonkers for me.
Thanks for all your replies.

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Re: 25mm tyres

Postby elPedro666 » 23 Feb 2018, 12:40pm

I did used to race track* on 19mm clinchers - the gunshot noise echoing around the concrete velodrome when one crept off the rim at 150psi isn't something you forget quickly! Fortunately it was parked up and I was on my 'cross bike at the time

*also my only road bike at the time

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fastpedaller
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Re: 25mm tyres

Postby fastpedaller » 23 Feb 2018, 1:14pm

ISTR vredestein used to sell 17mm clincher tyres.

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foxyrider
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Re: 25mm tyres

Postby foxyrider » 23 Feb 2018, 1:33pm

Leeflatz wrote:I think tyres used to go down to 18mm
They were for hardcore racers and we're tubular, glued to the rim
There was a chance they could come off when cornering
Never tried 'em
Too nutter, bonkers for me.
Thanks for all your replies.


The pro's still use tubulars and I still have one (old) race bike with tubs. Yes they were narrow but i've never had one roll, if they are fitted and stuck on properly it's no more likely than a clincher to leave the rim. Used to use them for all my riding but there again most 'racers' used to - the problem has always been punctures and the need to carry a full tyre as spare.
Convention? what's that then?
Airnimal Chameleon touring, Orbit Pro hack, Orbit Photon audax, Focus Mares AX tour, Peugeot Carbon sportive, Owen Blower vintage race - all running Tulio's finest!

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Mick F
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Re: 25mm tyres

Postby Mick F » 23 Feb 2018, 1:59pm

When I first went to 700c, my tyres were listed in Imperial widths and less than an inch ............. or that's the way I remember them.
Vittoria (somethings) and Wolber(?) Armadillos.
Mick F. Cornwall

Brucey
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Re: 25mm tyres

Postby Brucey » 23 Feb 2018, 4:03pm

mig wrote: i read a review of the latest racing wheels idea in the comic a few weeks ago. usual ridiculous babble about this and that with the added comment that a pattern on the rim was an echo of shark's skin (or whale or something) which made that more hydro-dynamic. er...okay...so your new £3k+ wheels are good a cutting through water?

ehhh when i were a lad...


There is indeed a lot of technobabble and outright BS in the world of bike magazines. I have not bought a bike magazine for about a decade. About five years ago I picked up one to leaf through whilst waiting for a train and just spending a couple of minutes reading bits of it reduced me to alternate fits of apoplexy and laughing out loud. A load of nonsensical hackneyed drivel for the most part.

Regarding the science, there is an effect that it may be possible to exploit to make a marginal gain. The main phenomenon is that when an object is either 'blunt' or presented into the airflow unfavourably, the flow tends to detach on the lee side and this creates more drag. However if the boundary layer is made turbulent (under conditions where it would otherwise be laminar) then it tends to adhere better and the onset of flow detachment is delayed somewhat. Note that if the flow was going to stay attached anyway, there is a small penalty for turning the boundary layer flow turbulent; this creates a little bit more drag, all the time. But if it prevents flow detachment even for 10% of the time, there will likely be a net gain overall. There is also a second effect whereby the skin drag is reduced (all over) if certain textures are employed. This effect (widely exploited in nature) is less well understood by fluid dynamicists.

Examples where this kind of effect is used practically include;

- reducing the stall speed of light aircraft; Flow detachment is synonymous with 'stalling' in aircraft wings when flying at low speed. Quite a few models of light aircraft have been retrofitted with 'turbulators' just aft of the fattest part of the chord section near the wing root; this can delay the onset of a stall by 5-10 knots in some cases, and in some cases the stall is less abrupt too, which all means that the plane is safer and easier to fly.

- golf balls; the dimpled surface causes the boundary layer flow to be turbulent, the flow remains better attached, the ball sees less drag, and flies further than if it were not dimpled. Golf balls used to be made smooth at one time; golfers soon noticed that worn balls (with rough surfaces) usually flew further than new (smooth) ones.

- shark skins; these are made of tiny bones called 'denticles'. Their shape is convoluted and mysterious; it is thought to possess the flow detachment properties created by dimples. In addition the shape is thought to modify/control the boundary layer flow in such a way that skin friction is reduced even if the flow is not just about to detach.

-use of 'riblets' on aircraft and wind turbine blades. About 15 years ago 3M made some tape that could be applied to the outside skin of an aircraft and this was trialled on long-haul aircraft crossing the pacific. There was a small but significant fuel saving, however the surface tended to stop working if it became dirty. There is a summary of the work to 2002 here
http://inter.action.free.fr/faq/riblets.pdf

More recently research has looked at wind turbine efficiency http://web.archive.org/web/20150226044952/http://m-selig.ae.illinois.edu:80/pubs/SareenDetersHenrySelig-2011-AIAA-2011-558-WindTurbineAirfoilsRiblets.pdf again showing an effect but one that isn't well understood, or always of benefit, even.

Regarding bike wheels, it is questionable if the Reynolds number is in the right range to do any good. It is also questionable whether the flow over the wheel rim would be susceptible to being controlled in this fashion (the wheel is turning, and except for the very front of the front wheel, the flow is already 'mucky' anyway). Doubtless one could devise a test (probably not representative of real conditions) that appears to show a drag reduction using dimples, in an attempt to flog your new rims. Whether it is likely to make any real difference or not is quite another matter.... :roll:

cheers
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Gattonero
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Re: 25mm tyres

Postby Gattonero » 25 Feb 2018, 10:36am

Leeflatz wrote:Is there honestly that much difference between 25mm and 23mm tyres?
Been using 23s for years in all weather's, even on tracks and canal bank, no problem.
On these tracks you can manage as long as you don't sit on the bike like a sack of spuds.
Just wondering.
Does 2 mm make that much difference?
Bemused by all the debate I keep coming across.


I am stubborn on 23mm tyres on classic 20mm rims.
All the recent trend and fashion or road bikes with massive tyres just makes me think if millions of cyclists have been fools so far? :wink:

I do use 25mm on my commuter, because I may need more air volume, but not expecting miracles from them
It is by riding a bicycle that you learn the contours of a country best,
since you have to sweat up the hills and coast down them.
Thus you remember them as they actually are...

mig
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Re: 25mm tyres

Postby mig » 25 Feb 2018, 9:58pm

Brucey wrote:
mig wrote: i read a review of the latest racing wheels idea in the comic a few weeks ago. usual ridiculous babble about this and that with the added comment that a pattern on the rim was an echo of shark's skin (or whale or something) which made that more hydro-dynamic. er...okay...so your new £3k+ wheels are good a cutting through water?

ehhh when i were a lad...


There is indeed a lot of technobabble and outright BS in the world of bike magazines. I have not bought a bike magazine for about a decade. About five years ago I picked up one to leaf through whilst waiting for a train and just spending a couple of minutes reading bits of it reduced me to alternate fits of apoplexy and laughing out loud. A load of nonsensical hackneyed drivel for the most part.

Regarding the science, there is an effect that it may be possible to exploit to make a marginal gain. The main phenomenon is that when an object is either 'blunt' or presented into the airflow unfavourably, the flow tends to detach on the lee side and this creates more drag. However if the boundary layer is made turbulent (under conditions where it would otherwise be laminar) then it tends to adhere better and the onset of flow detachment is delayed somewhat. Note that if the flow was going to stay attached anyway, there is a small penalty for turning the boundary layer flow turbulent; this creates a little bit more drag, all the time. But if it prevents flow detachment even for 10% of the time, there will likely be a net gain overall. There is also a second effect whereby the skin drag is reduced (all over) if certain textures are employed. This effect (widely exploited in nature) is less well understood by fluid dynamicists.

Examples where this kind of effect is used practically include;

- reducing the stall speed of light aircraft; Flow detachment is synonymous with 'stalling' in aircraft wings when flying at low speed. Quite a few models of light aircraft have been retrofitted with 'turbulators' just aft of the fattest part of the chord section near the wing root; this can delay the onset of a stall by 5-10 knots in some cases, and in some cases the stall is less abrupt too, which all means that the plane is safer and easier to fly.

- golf balls; the dimpled surface causes the boundary layer flow to be turbulent, the flow remains better attached, the ball sees less drag, and flies further than if it were not dimpled. Golf balls used to be made smooth at one time; golfers soon noticed that worn balls (with rough surfaces) usually flew further than new (smooth) ones.

- shark skins; these are made of tiny bones called 'denticles'. Their shape is convoluted and mysterious; it is thought to possess the flow detachment properties created by dimples. In addition the shape is thought to modify/control the boundary layer flow in such a way that skin friction is reduced even if the flow is not just about to detach.

-use of 'riblets' on aircraft and wind turbine blades. About 15 years ago 3M made some tape that could be applied to the outside skin of an aircraft and this was trialled on long-haul aircraft crossing the pacific. There was a small but significant fuel saving, however the surface tended to stop working if it became dirty. There is a summary of the work to 2002 here
http://inter.action.free.fr/faq/riblets.pdf

More recently research has looked at wind turbine efficiency http://web.archive.org/web/20150226044952/http://m-selig.ae.illinois.edu:80/pubs/SareenDetersHenrySelig-2011-AIAA-2011-558-WindTurbineAirfoilsRiblets.pdf again showing an effect but one that isn't well understood, or always of benefit, even.

Regarding bike wheels, it is questionable if the Reynolds number is in the right range to do any good. It is also questionable whether the flow over the wheel rim would be susceptible to being controlled in this fashion (the wheel is turning, and except for the very front of the front wheel, the flow is already 'mucky' anyway). Doubtless one could devise a test (probably not representative of real conditions) that appears to show a drag reduction using dimples, in an attempt to flog your new rims. Whether it is likely to make any real difference or not is quite another matter.... :roll:

cheers


yeah i mainly follow the science but i'm just a tad tired of the hype that has come into bikes in the past ten years or so, the way that 'advances' are marketed. would rather the magazines cover more real world elements of bikes rather than waffle on about niche wheels or power meters.

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NATURAL ANKLING
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Re: 25mm tyres

Postby NATURAL ANKLING » 3 Mar 2018, 7:44pm

Hi,
Mick F wrote:When I first went to 700c, my tyres were listed in Imperial widths and less than an inch ............. or that's the way I remember them.
Vittoria (somethings) and Wolber(?) Armadillos.

25's less than an inch :)
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mullinsm
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Re: 25mm tyres

Postby mullinsm » 8 Mar 2018, 8:35am

In my experience, nothing effects the performance of a bike more than the weight of the wheels and smaller tyres will weigh less than larger tyres of the same make and model.

elPedro666
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Re: 25mm tyres

Postby elPedro666 » 8 Mar 2018, 9:28am

mullinsm wrote:In my experience, nothing effects the performance of a bike more than the weight of the wheels and smaller tyres will weigh less than larger tyres of the same make and model.
Under acceleration from low speed wheel weight is key, and I'm also a great lover of lightweight wheels, but as soon as you're rolling it's nearly all about wind resistance and to a lesser extent rolling resistance. At a reasonably steady pace (ie. not sprinting between hairpins or endless traffic lights) the reduced rolling resistance of a 25mm should easily outperform the tiny weight saving of a 23mm. In terms of 'feel' though, the more chattery ride of the 23mm may well give the opposite indication.

Goes without saying that we're talking about fractions here though I think.

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Brucey
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Re: 25mm tyres

Postby Brucey » 8 Mar 2018, 10:05am

the thing is that the Crr is almost always compared at the same tyre pressure and yet it is not likely that different tyres will be run at the same pressure. The spring rate of the tyre defines in large part how the tyre feels on ordinary tarmac, and to a first approximation that spring rate remains roughly constant if [pressure x tyre width] = fixed value.

In other words a 23mm tyre ought to be inflated to ~25/23 x the pressure of a 25mm tyre. On a smooth surface the Crr might be about the same (within 0.5W or so) and the way the tyre rolls will mostly feel the same too, because the spring rate is about the same. It is only on rougher surfaces with discrete bumps that the tyre will feel much different, and that will mostly happen if you roll over bumps that are narrow enough that they occupy most of the contact patch in a 23mm tyre vs not most of the contact patch of a 25mm tyre.

This is all hair-splitting stuff TBH; it might matter in racing (and they will be using rims and tyres that are well matched as an aero package BTW) but if you stick on 25s instead of 23s and expect things to be a lot different on normal wheels (with conventional ~20mm wide rims) then prepare for a disappointment; probably you will go slower (if you intend to ride at 20mph average or more) because the aero drag is larger, but you might be fractionally more comfy doing it if you choose your tyre pressures carefully. The type of tyre is far more important than a footling 2mm width difference.

If you want a slightly cynical overview of this, I'd argue that 23mm tyres still make sense for folk that weigh ~70kg (or that are skilled and/or ride carefully), but that the demographic of people that want to buy road bikes today is heavily skewed towards relatively unskilled heavier people that 'want to ride what the pros ride'. In simple terms 25mm tyres and 28mm tyres will better take the extra load and the clumsy use (on rotten roads) that bikes like that sold into those hands will see. It makes for much less 90kg novice customer disappointment if you can sell them something 'like the pros use' which is more likely to survive intact.

cheers
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mullinsm
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Re: 25mm tyres

Postby mullinsm » 8 Mar 2018, 12:11pm

I understand the science says that rolling resistance improves with bigger tyres on rough roads, but my experience doesn't support the theory. I have a carbon bike with Mavic wheels and 23mm tyres and when I swap them for 25mm tyres, it is noticeably and measurably slower and that is on minor roads in North Norfolk which aren't smooth by any stretch of the imagination.

I have ridden bikes of similar weight with 25mm and 28mm tyres on and the 28mm is noticeably and measurably slower but is significantly more comfortable.

I have a 700c touring bike with 32mm tyres that weighs 15kg and a 26" tourer with 50mm tyres that weighs exactly the same and the 26" is noticeably and measurably slower by as much as 10% or more.

The common factor is the weight of the wheels and on a long tour, I don't spend too much time accelerating as it's mostly grinding out the miles.

Quad erat demonstrandum.......