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Wide tyres - I just don't get it

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Posts

  • neebneeb Posts: 4,315
    neeb 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.
    Nope, I expected wider tyres to feel faster when I first fitted them and they quite distinctly didn’t. They were expensive tubs too, so I had plenty investment in wanting them to feel faster (not to mention be faster, which they weren’t either).
  • neeb wrote:
    neeb 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.
    Nope, I expected wider tyres to feel faster when I first fitted them and they quite distinctly didn’t. They were expensive tubs too, so I had plenty investment in wanting them to feel faster (not to mention be faster, which they weren’t either).
    did you take any actual measurements though? Speed, for example.
  • svettysvetty Posts: 1,904
    svetty 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.

    This guy is an aerodynamics engineer with Airbus - he probably knows a little bit about these things - not as much as you though clearly :roll:

    https://www.hambini.com/blog/post/bicyc ... s-fastest/
    FFS! Harden up and grow a pair :D
  • neebneeb Posts: 4,315
    neeb wrote:
    neeb 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.
    Nope, I expected wider tyres to feel faster when I first fitted them and they quite distinctly didn’t. They were expensive tubs too, so I had plenty investment in wanting them to feel faster (not to mention be faster, which they weren’t either).
    did you take any actual measurements though? Speed, for example.
    Yes - I have multiple average speeds and average power figures for a couple of 30-40 mile routes - not controlled conditions obviously and doubtless not enough repetitions to be statistically robust given the other significant variables (basically wind and 2 or 3 traffic lights), but strongly indicative.
  • apreadingapreading Posts: 4,532
    If you are just looking at aerodynamics, you are only looking at one of many factors though.

    Obviously the smaller frontal area the better aerodynamics, only a fool would suggest otherwise.

    But comfort and rolling resistance also contribute to speed and/or energy conservation. See here for more than I can be bothered to type:

    https://road.cc/content/feature/182519- ... ider-tyres

    Wider rims are being made to support the move to wider tyres, not the other way around, and the move is based on the holistic appraisal of a variety of factors, of which aero is only one.
  • First.AspectFirst.Aspect Posts: 3,589
    edited November 2018
    ...
  • neeb wrote:
    neeb wrote:
    neeb 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.
    Nope, I expected wider tyres to feel faster when I first fitted them and they quite distinctly didn’t. They were expensive tubs too, so I had plenty investment in wanting them to feel faster (not to mention be faster, which they weren’t either).
    did you take any actual measurements though? Speed, for example.
    Yes - I have multiple average speeds and average power figures for a couple of 30-40 mile routes - not controlled conditions obviously and doubtless not enough repetitions to be statistically robust given the other significant variables (basically wind and 2 or 3 traffic lights), but strongly indicative.
    strongly indicative eh? On a good day in the summer I'm about 5 to 7% faster on the same bike over the same route than on a bad day. How much faster are you on 23c tyres than 25's exactly, because I'm sure as hell buying a set of your 23c tyres if you can really tell the difference over that much scatter in your data.
  • neeb wrote:
    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?

    How do you know you are faster with the narrower tire? In other words, what is your approach to measure it?
  • zefszefs Posts: 484
    About comfort, I tested today between my bikes back to back.

    Bike 1: Race geometry - 17c internal with 25mm tires (26mm actual) -> Hutchinson Performance Tubeless
    Bike 2: Endurance geometry - 19c internal with 25mm tires (28mm actual) -> GP4000sii with butyl tubes

    Bike 1 was more comfortable at same psi (80 - 90) despite Bike 2 being an endurance Giant Defy which is supposed to be more forgiving. I think tire casing plays a big role, GP4000sii is known as a more stiff/harsh tire.

    That said for simple tarmac I think 25mm tires are still optimal.
  • zefs wrote:
    About comfort, I tested today between my bikes back to back.

    Bike 1: Race geometry - 17c internal with 25mm tires (26mm actual) -> Hutchinson Performance Tubeless
    Bike 2: Endurance geometry - 19c internal with 25mm tires (28mm actual) -> GP4000sii with butyl tubes

    Bike 1 was more comfortable at same psi (80 - 90) despite Bike 2 being an endurance Giant Defy which is supposed to be more forgiving. I think tire casing plays a big role, GP4000sii is known as a more stiff/harsh tire.

    That said for simple tarmac I think 25mm tires are still optimal.
    So you changed 4 variable there. Tyre brand, bike, inner tube, internal width. #gcndoesscience
  • de_sistide_sisti Posts: 1,176
    sungod wrote:
    neeb wrote:
    ...
    What am I missing?
    nothing

    have higher crr, ......

    lower crr, .....

    have lower crr, ......

    for best crr), .....

    :D
    Can you explain what crr is?
  • zefszefs Posts: 484
    zefs wrote:
    About comfort, I tested today between my bikes back to back.

    Bike 1: Race geometry - 17c internal with 25mm tires (26mm actual) -> Hutchinson Performance Tubeless
    Bike 2: Endurance geometry - 19c internal with 25mm tires (28mm actual) -> GP4000sii with butyl tubes

    Bike 1 was more comfortable at same psi (80 - 90) despite Bike 2 being an endurance Giant Defy which is supposed to be more forgiving. I think tire casing plays a big role, GP4000sii is known as a more stiff/harsh tire.

    That said for simple tarmac I think 25mm tires are still optimal.
    So you changed 4 variable there. Tyre brand, bike, inner tube, internal width. #gcndoesscience

    Well, I've tested them on the same bike as well (25 vs 28 with same air volume). Wider tires were only more comfortable and had better handling. Great choice if you are not chasing numbers/racing but they were slower.
  • neebneeb Posts: 4,315
    neeb wrote:
    neeb wrote:
    did you take any actual measurements though? Speed, for example.
    Yes - I have multiple average speeds and average power figures for a couple of 30-40 mile routes - not controlled conditions obviously and doubtless not enough repetitions to be statistically robust given the other significant variables (basically wind and 2 or 3 traffic lights), but strongly indicative.
    strongly indicative eh? On a good day in the summer I'm about 5 to 7% faster on the same bike over the same route than on a bad day. How much faster are you on 23c tyres than 25's exactly, because I'm sure as hell buying a set of your 23c tyres if you can really tell the difference over that much scatter in your data.
    Yes, I'm faster in summer too and on different days as a result of fatigue, effort etc, but the powermeter largely factors that out.

    If I ride exactly the same route in the same clothing at the same average power (which I fairly often do) there's a pretty consistent relationship between average power and average speed. Because there are a couple of routes I ride a lot in summer on weekday evenings I pretty much know the extent to which the reltionship between power and speed varies, and the variation can mostly be explained by wind and traffic conditions. I nearly always look at wind speed and direction before going out because it affects my choice of route. The net result of all this is that I'm pretty sensitive to any other factors affecting my speed. If I nearly always average between 19.7 and 20.7 mph for an average power of 210-215 watts on a particular 35 mile route and suddenly find I'm averaging between 19.2 and 20.2 mph instead for the same power I will notice that over the course of a week or two.

    (as an interesting aside - I used to believe that I was faster at the height of summer just because of increased fitness and perhaps better clothing-related aerodynamics. Then I realised that I have a habit of always going out as late as possible in the evening after getting back from work, while still allowing time to get back just before sunset. So I would consistently leave about two hours before sunset. Of course the later I left the lighter the traffic would be, the less I would have to stop or slow down getting in and out of town, and the higher my average speed would be - as well as to a lesser extent my average power, because that's always affected a bit too by stopping and starting. So there was a pretty good relationship between average speed and proximity to the summer solstice...).
  • cyclecliniccycleclinic Posts: 6,863
    Neeb on those 27mm wide Zipps I would fit 23mm conti GP4000sII they would site at 26mm wide. The safety issues come with some narrow open tubulars on wide rims. The safety concerns are over blown. I would be dead already if they were not.
    http://www.thecycleclinic.co.uk -wheel building and other stuff.
  • cyclecliniccycleclinic Posts: 6,863
    The difference in drag by using a narrow tyre is quite measureable. Here is just one set of data from hambini's blog.
    What it clearly show is the difference in drag between a narrow and wide tyre is not just down to the width of the tyre but also the width difference between the tyre and rim. the difference may not be huge but if your buying aero wheels it is shame to squander half the gain by fitting a wide tyre.

    tyrewidthdrag30.png
    http://www.thecycleclinic.co.uk -wheel building and other stuff.
  • The difference in drag by using a narrow tyre is quite measureable. Here is just one set of data from hambini's blog.
    What it clearly show is the difference in drag between a narrow and wide tyre is not just down to the width of the tyre but also the width difference between the tyre and rim. the difference may not be huge but if your buying aero wheels it is shame to squander half the gain by fitting a wide tyre.

    tyrewidthdrag30.png

    Gotta love a bit of pseudoscience

    The entire Enve data set is something like 183W +/- 1W

    He’s used a charting technique that hides how small the difference is. I’d like to see that data with the confidence intervals plotted too. The accuracy of the PM must account for more than the difference let alone the other MSA influences.

    I haven’t read the blog (I’m on a phone in Shanghai right now) so I can’t comment on the Shimano data set differences.
    ROAD < Scott Foil HMX Di2, Volagi Liscio Di2, Jamis Renegade Elite Di2, Cube Reaction Race > ROUGH
  • pblakeneypblakeney Posts: 11,302
    zefs wrote:
    Well, I've tested them on the same bike as well (25 vs 28 with same air volume). Wider tires were only more comfortable and had better handling. Great choice if you are not chasing numbers/racing but they were slower.
    I wonder at what distance comfort means less fatigue and the speed crosses over.
    The above may be fact, or fiction, I may be serious, I may be jesting.
    I am not sure. You have no chance.
    veronese68 wrote:
    PB is the most sensible person on here.
  • To see / feel the difference fully, keep everything except the pressures and widths the same. As your tyres get wider, you can run lower pressures without pinch flatting, and therefore increase your comfort ( in theory).
  • From https://janheine.wordpress.com/2018/01/ ... re-slower/


    The faster we ride, the higher the frequency at which our bike vibrates, because our tyres encounter road irregularities at a higher speed. However, narrower tyres also increase the frequency of the vibrations they transmit. Basically, a bike with narrow tyres feels faster even though it may actually be slower. Inflating your tyres harder is a simple way of tricking your brain into feeling that you are going faster
  • neeb wrote:
    neeb wrote:
    neeb wrote:
    did you take any actual measurements though? Speed, for example.
    Yes - I have multiple average speeds and average power figures for a couple of 30-40 mile routes - not controlled conditions obviously and doubtless not enough repetitions to be statistically robust given the other significant variables (basically wind and 2 or 3 traffic lights), but strongly indicative.
    strongly indicative eh? On a good day in the summer I'm about 5 to 7% faster on the same bike over the same route than on a bad day. How much faster are you on 23c tyres than 25's exactly, because I'm sure as hell buying a set of your 23c tyres if you can really tell the difference over that much scatter in your data.
    Yes, I'm faster in summer too and on different days as a result of fatigue, effort etc, but the powermeter largely factors that out.

    If I ride exactly the same route in the same clothing at the same average power (which I fairly often do) there's a pretty consistent relationship between average power and average speed. Because there are a couple of routes I ride a lot in summer on weekday evenings I pretty much know the extent to which the reltionship between power and speed varies, and the variation can mostly be explained by wind and traffic conditions. I nearly always look at wind speed and direction before going out because it affects my choice of route. The net result of all this is that I'm pretty sensitive to any other factors affecting my speed. If I nearly always average between 19.7 and 20.7 mph for an average power of 210-215 watts on a particular 35 mile route and suddenly find I'm averaging between 19.2 and 20.2 mph instead for the same power I will notice that over the course of a week or two.

    (as an interesting aside - I used to believe that I was faster at the height of summer just because of increased fitness and perhaps better clothing-related aerodynamics. Then I realised that I have a habit of always going out as late as possible in the evening after getting back from work, while still allowing time to get back just before sunset. So I would consistently leave about two hours before sunset. Of course the later I left the lighter the traffic would be, the less I would have to stop or slow down getting in and out of town, and the higher my average speed would be - as well as to a lesser extent my average power, because that's always affected a bit too by stopping and starting. So there was a pretty good relationship between average speed and proximity to the summer solstice...).
    So, if you average 19.7 on your 23's, you are on a bad day, whereas if you average 19.7 on your 25's you are going like a train, and your tyres are holding you back - except a week or so either side of the summer solstice?
  • w00dsterw00dster Posts: 878
    First Aspect, did you read something I didn't in Neeb's last post? I certainly didn't think he was saying what you summarised. His last paragraph has nothing to do with tyres and is just a personal anecdote relating to his increased average speed over summer, not fitness related or tyre related, but he attributed it to the roads having less traffic.
    You may not agree with his personal findings of narrow tyres (23mm) being faster than 25mm tyres. Obviously its pretty much impossible for Neeb to scientifically prove why his average power is lower when using 23mm tyres but his average speed is higher.
    I also prefer 23mm tyres for racing on. Some do, some don't, I can't categorically state they are faster, but based on a large number of rides I can make a judgement based on my own data and perception. Scientifically it could well be wrong. I find that 32mm tyres are still pretty quick, but I've got no scientific way to say that while they are still good, very comfortable, I find them a touch slower than my 23's. It can only be observational. I ride a couple of routes regularly and have a good idea for what my average power and average speed should be depending on weather conditions. If I was half a mile an hour slower I'd probably notice it and be curious as to what difference caused it.
    Like a lot of people on here I've raced using 28mm tyres, during the early spring season crits, the circuits can still be wet, cold, odd leaves lying about, so I prefer to use 28mm tyres (Vittoria Corsa G+ in my case). I would say that in outright speed they are possibly a tad slower than the 23mm lightweight race tyres (23mm Vittoria Corsa Speed and Conti Supersonics). I'd also it would be measurable, but at the same time, given wet conditions I'd probably be faster on 28mm Corsa's due to increased confidence in braking and cornering speeds. In the dry I would expect it to be the reverse.
    Now that's impossible to scientifically prove that on my bike, with my wheels, my riding position, my clothing, that the 23mm tyres are faster. I also can't scientifically prove that the 28mm tyres are infact better in the wet. I just have to use my own history and observations to make a conclusion.
  • Everyone is entitled to personal choice. I am merely ridiculing some of the justifications. I am as fussy as the next guy but I am not deluded enough to think I can actually measure a difference. So yes I read what he said and I summarised its technical content. It really was that absurd.
  • neebneeb Posts: 4,315
    Everyone is entitled to personal choice. I am merely ridiculing some of the justifications. I am as fussy as the next guy but I am not deluded enough to think I can actually measure a difference. So yes I read what he said and I summarised its technical content. It really was that absurd.
    First Aspect - no, it’s you who is being absurd - either absurdly obtuse or absurdly obstreperous, but I’m pretty sure it’s the latter..

    Obviously I’m not claiming that I’ve reliably established a difference in speed attributable to tyre width, I’m describing patterns of observation that lead me to suspect such a difference (for me at least, in my particular circumstances).

    Of course in your penultimate comment you were just being silly in implying that I would assume anything from a single observation of about the effect of tyre width. I’m talking about pattern recognition in a complex system based on many observations where most of the significant variables are known to a reasonable degree of accuracy - something the human brain has evolved to be pretty good at.

    If I go out one day with different tyres and my speed is a little lower relative to power I’m not going to read anything into that. If I do it for two weeks and it remains consistently lower, and then switch back and it’s consistently higher again, I might start to. Especially if I’ve considered and ruled out most of the other likely explanations. The longer I continue to observe such a difference in a wide range of different circumstances the more likely it is to exist.
  • Why am I being absurd?
  • bobonesbobones Posts: 1,023
    Why am I being absurd?
    You tell us.
  • neebneeb Posts: 4,315
    Why am I being absurd?
    You’re choosing to misinterpret what I’m saying for no constructive reason.
  • bobones wrote:
    Why am I being absurd?
    You tell us.
    It's not as though I overanalysed and data, made broad assumptions, arbitrarily discounted variables, mistook precision and accuracy, asserted that 95 and 90 were the same or made a correlation between the precession of the earth's axis and athletic performance, is it? That really would be absurd.
  • neeb wrote:
    Why am I being absurd?
    You’re choosing to misinterpret what I’m saying for no constructive reason.
    The point is that I am not misinterpreting it, you are. But what do I know about science or engineering.
  • neebneeb Posts: 4,315
    bobones wrote:
    Why am I being absurd?
    You tell us.
    It's not as though I overanalysed and data, made broad assumptions, arbitrarily discounted variables, mistook precision and accuracy, asserted that 95 and 90 were the same or made a correlation between the precession of the earth's axis and athletic performance, is it? That really would be absurd.
    See above.
  • neebneeb Posts: 4,315
    neeb wrote:
    Why am I being absurd?
    You’re choosing to misinterpret what I’m saying for no constructive reason.
    The point is that I am not misinterpreting it, you are. But what do I know about science or engineering.
    If you knew about science you’d know that the first stage in the process is informal observation, hypothesis generation and generally throwing ideas about in a constructive environment that encourages imaginative speculation. That’s what real scientists do. Formal testing comes afterwards. I can’t speak for engineers.
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