Upgrade my $3400 carbon road bike

[warthog1]

I suspect for us non-pros the optimum width is somewhere around 28-30mm, depending on how bad your roads are. But it's quite hard to test well.

That is a more reasonable suggestion.
Jan is advocating significantly wider than that.
There is a far bit of stuff out there about tyre vs wheel width; The Rule of 105 states that the rim must be at least 105% the width of the tire if you have any chance of re-capturing airflow from the tire and controlling it or smoothing it.

https://blog.silca.cc/part-5-tire-press ... rodynamics

I am not feeling a huge difference of 28 vs 23 in ride comfort. It is a bit better but not huge. They do appear to last a bit longer though.
My giant tcr has 27.5 ext wide wheels.
25 on the front for aero (narrower than the wheel)
28 on the back (slightly wider)

Aero is more important than rolling resistance so going no wider on the front. The rear carries the weight and is in dirty air anyway.

[g-boaf]

I suspect for us non-pros the optimum width is somewhere around 28-30mm, depending on how bad your roads are. But it's quite hard to test well.

That is a more reasonable suggestion.
Jan is advocating significantly wider than that.
There is a far bit of stuff out there about tyre vs wheel width; The Rule of 105 states that the rim must be at least 105% the width of the tire if you have any chance of re-capturing airflow from the tire and controlling it or smoothing it.

https://blog.silca.cc/part-5-tire-press ... rodynamics

I am not feeling a huge difference of 28 vs 23 in ride comfort. It is a bit better but not huge. They do appear to last a bit longer though.
My giant tcr has 27.5 ext wide wheels.
25 on the front for aero (narrower than the wheel)
28 on the back (slightly wider)

Aero is more important than rolling resistance so going no wider on the front. The rear carries the weight and is in dirty air anyway.

Nor do I find any big difference in ride comfort with bigger tyres. Where the comfort comes from was the seat post and saddle I had. Together they make a huge difference. The biggest tyres I’ll use are 26mm from S-Works. But even 24mm version of those feels about the same.

[cyclingnolycra]

Here is a bit of a rolling resistance v aerodynamic drag discussion


Notice how rolling resistance starts higher, the two meet around 10mph, and then aerodynamic drag takes off quickly. This is because of the cubic factor of the velocity component of the aerodynamic drag.

https://blog.flocycling.com/aero-wheels ... er-speeds/

An interesting table but it doesn't really help you figure out the ideal tyre width, since the vast majority of that aerodynamic resistance is going to be from your body. The real piece of data that would be useful is simply, what is the difference in watts aero drag at different speeds between an aerodynamically matched wheel and a 25mm vs 28mm vs 30mm etc tyre width?

Jan Heine is arguing the difference is negligible. I just want to know what it is.
Like if the difference between 25 and 28mm at 40kph is only 1W then I'd take 28mm any day to be faster on rougher surfaces, plus more comfort. But if the difference was 5W then I'd probably take the 25mm.

I'm surprised you guys don't find any difference in comfort between 23 and 28mm, are you sure you're not just pumping up the 28mm tyres too much? The difference was unbelievable when I switched. (Unfortunately I couldn't keep the 28's and had to go down to 25mm because I was getting a tiny bit of rub.) I was pumping to about 70psi on 28mm tyres, 100-110 psi for 23mm.

[warthog1]

Wind resistance does not increase in a linear fashion with speed;

It’s true that the faster you go, the more aerodynamic drag consumes your total power. Doubling your speed from 20 to 40 mph creates not double the resistance, but closer to eight times the resistance. But even at relatively slow speeds, the majority of your power goes toward overcoming air resistance, Barry says.

"At speeds near 30 mph, 90 percent of your power goes into overcoming air resistance."
https://www.bicycling.com/skills-tips/a ... n-cycling/

I am no physicist or expert on aerodynamics but do recognise that the faster you go the bigger the proportion of total drag it represents.

Evidenced by the fact that competitive cyclists are not running wider tyres as advocated by Jan.
There is plenty out there about tyres not being wider than the wheel in order to minimise turbulent drag.

What tyre width you should run if high speed is your aim will largely be guided by wheel width

In an email, Zipp lead engineer Josh Poertner said:

In general, a wider tire of (the) same construction will have lower rolling resistance for exactly the reasons (you stated). Ironically, the best description and data on this comes from studies done in Britain in the 1800’s looking to optimize the width and diameter of wheels for locomotives. There is also a lot of great info related to this in “Bicycling Science” from MIT press, as well as Paul Van Valkenberg’s writing on racecar tires.

Generally, though, the decrease in rolling resistance becomes smaller as the tires get bigger. So for example, going from a 19mm to a 20mm may save 1 watt, from a 20mm to a 21mm may save 0.8 watt and from a 23mm to a 25mm may save 0.3 watt. There is great data on this in “Bicycling Science,” using old Avocet Fasgrip tires, which were available from 18-32mm. The 28mm and 32mm were nearly identical, but moving from 18mm to 25mm saved a few watts.

What they are missing is the aerodynamic piece. We have data from the Zipp 303 launch showing the 303 with different width tires (see graph). The figure tells the story of how you can really optimize for tires below a certain (width) number, but eventually the tire really dominates the airflow and ruins everything. In general, our wheels are optimized around 23mm tires, which means that 21mm tires usually run about equal, maybe a fraction of a watt faster, but don’t change the behavior of the wheel. Moving to a 25mm adds drag, but can also change the stall behavior of the wheel. And by the time you are at 27mm, you have something that behaves quite differently.

The question really needs to be in regards to the balance of lower Crr (coefficient of rolling resistance) from the wider tire against the aero penalty. The 303 was designed to be as good as possible with 23mm tires, and as a result, its rim is 28.5mm wide. To behave similarly with the 25mm, it would likely have to be at least 2mm wider. In the graph you see how the 25mm tire has the same curve shape as the 23mm tire on the X45 (code for 303FC clincher). The 27mm tire is on the 285FC (code for 303FC tubular), and you notice that not only is the drag higher, but the curve shape is completely different. In fact, the curve shape looks more like the Easton or Mavic. This is indicative of the rim not being able to clean up the dirty air behind the tire. Ultimately, the offset should be Crr watts vs. Aero watts. In this case you have grams of drag on the left; every nine grams is one watt, so from 23mm to 25mm, you have nearly no penalty up to 10 degrees, and then three-to-six watts at the higher yaw. With the 27mm, you have something like no penalty to five degrees, and then a five-to-eight watt penalty after that.

Ultimately for the Specialized I would say that the 0.2 watt (0.3 to 0.8 watt) of rolling resistance does not overcome the zero-to-six-watt aero penalty.

Last interesting note: we have been working with Jordan Rapp on this since he noticed that his ‘training Firecrest’ wheels with 25’s were ‘twitchy’ compared to his race wheels with 23’s… we thought this might be largely aerodynamic, but the shorter contact patch (you) discuss is actually the culprit; the longer contact patch serves to resist steering input and adds a slight damping effect to steering inputs. By lowering tire pressure to increase contact patch, the effect could be eliminated, even though the aero properties of the wheel remain the same.
https://www.velonews.com/gear/tech-faq- ... ll-faster/

[warthog1]

I have a 25 on the front and 28 on the rear of my TCR.
Yes I have lowered pressures.
Marginally better ride. Not a huge difference compared to 23s.
I was expecting more than I felt.

[cyclingnolycra]

I am no physicist or expert on aerodynamics but do recognise that the faster you go the bigger the proportion of total drag it represents.
In this case you have grams of drag on the left; every nine grams is one watt, so from 23mm to 25mm, you have nearly no penalty up to 10 degrees, and then three-to-six watts at the higher yaw. With the 27mm, you have something like no penalty to five degrees, and then a five-to-eight watt penalty after that.

Ultimately for the Specialized I would say that the 0.2 watt (0.3 to 0.8 watt) of rolling resistance does not overcome the zero-to-six-watt aero penalty.

Last interesting note: we have been working with Jordan Rapp on this since he noticed that his ‘training Firecrest’ wheels with 25’s were ‘twitchy’ compared to his race wheels with 23’s… we thought this might be largely aerodynamic, but the shorter contact patch (you) discuss is actually the culprit; the longer contact patch serves to resist steering input and adds a slight damping effect to steering inputs. By lowering tire pressure to increase contact patch, the effect could be eliminated, even though the aero properties of the wheel remain the same.[/i]
https://www.velonews.com/gear/tech-faq- ... ll-faster/

Hrm Warthog I think you are missing my point - the article you're quoting here seems to be comparing 25 vs 23 on a wheel that is designed for 23's, and says there's a few watts difference depending on the yaw angle.

I'm saying if you have two wheels, one designed for say 23mm tyres, and one designed for 25mm tyres, what is the difference in drag at say 40kph?
It sounds like the guy is saying there something around 0-6 watts difference on average between 23mm and 25mm on a wheelset that is designed for 23mm tyres.
This means the difference between the two wheelsets, one designed for 23mm, and the other designed for 25mm, has got to be a fair bit less than that. Let's call it 0-4 watts. It's up to you whether that's worth having the more uncomfortable tyre, and whether that's worth being slower on for rougher roads.

Funnily enough zipp themselves seem to be moving to wheelsets designed for wider tyres anyway!
There was no mention in the article either about the roughness of the road they were tested on (which was the point of Jan Heine's article on the testing problems of tyres on drums.) Remember that it has been conclusively shown that wider tyres are faster on rougher roads.

Note that I'm not saying that aerodynamics don't matter. They do, and they matter a lot. And they obviously matter more the faster you go. The question is the amount that tyre width affects aerodynamics. It looks like we're all in agreement that the rim width is very important vs the tyre width if you care about aerodynamics.

[MattyK]

If you want to ask Josh yourself, send him a question on the Marginal Gains podcast. (that reminds me, he still owes me a t-shirt). And yes he has analysed road surfaces, it's somewhere on the silca blog. A lot of the foundational stuff in that area was from Tom Anhalt, based on Robert Chung's theories. You can find all these guys at slowtwitch forums if you want.

[warthog1]

I'm saying if you have two wheels, one designed for say 23mm tyres, and one designed for 25mm tyres, what is the difference in drag at say 40kph?
It sounds like the guy is saying there something around 0-6 watts difference on average between 23mm and 25mm on a wheelset that is designed for 23mm tyres.
This means the difference between the two wheelsets, one designed for 23mm, and the other designed for 25mm, has got to be a fair bit less than that. Let's call it 0-4 watts. It's up to you whether that's worth having the more uncomfortable tyre, and whether that's worth being slower on for rougher roads.

Sorry, no I did not gather that you were expecting to be swapping wheels.
This is alot more expensive than swapping tyres.
The point I was making was that tyre needs to be narrower than the wheel.
Thar extract does mention that rolling efficiency improvements are outweighed by aero drag by a significant margin if the tyres are wider than the rim.
I do not know how two different width wheels with tyres matched to the rim compare in terms of speed (and drag).

The difference in comfort between a 23 and 25 is about the same as the improvement in rolling resistance ime.
Next to nothing.

Funnily enough zipp themselves seem to be moving to wheelsets designed for wider tyres anyway!
There was no mention in the article either about the roughness of the road they were tested on (which was the point of Jan Heine's article on the testing problems of tyres on drums.) Remember that it has been conclusively shown that wider tyres are faster on rougher roads.

We are in a thread about upgrading a road bike.
I do not know what roads you are riding on and how rough they are.
Those pieces by Jan are not supported by the aerodynamic reality if he is claiming they are faster.
Perhaps on a mtb, certainly not on a road bike.
As you go faster aerodynamic drag rapidly increases, in contrast to rolling resistance that because it doesn't increase to anywhere near the degree, becomes a far smaller overall proportion of drag as you get faster.
Where speed certainly does count, in competition road cycling, nobody is using tyres anywhere near as wide (35mm+) as Jan is advocating.
Even in the cobbled classics, and I don't come across roads anywhere near that wide, the tyres are nowhere near as wide as Jan is advocating.
I saw Jan's piece as a marketing tool for his Rene Herse tyres and not much more.

Note that I'm not saying that aerodynamics don't matter. They do, and they matter a lot. And they obviously matter more the faster you go. The question is the amount that tyre width affects aerodynamics. It looks like we're all in agreement that the rim width is very important vs the tyre width if you care about aerodynamics.

I suggest aerodynamics are far more important than rolling resistance in terms of speed for road cycling.
I would further suggest Jan's assertion, when taken in terms of road cycling, that 35mm + tyres are faster because of better rolling resistance is not supported by the reality of competitive cycling, which is after all, a contest of speed.