Narrow vs wide tyres - Bring data

[BenCousins]

One thing I don't really understand yet is that some people say "yeah with a smaller tire just drop pressure to get the right comfort level".

But BRR is showing that smaller tires suffer a big rolling resistance hit when you drop the pressure?

Below the table from BBR comparing the different versions of the GP5K. If you drop the 25mm GP5 from 6.5 bar to 4.0 bar you lose 2.8watts per tire. For 2 tires that is 5.6watts in additional RR.

So what is the logic here?

Tire GP 5000 S TR GP 5000 S TR GP 5000 S TR GP 5000 S TR
Tire size 25-622 28-622 30-622 32-622
Sealant 20 ml 22 ml 24 ml 26 ml
Rolling Resistance
109 psi / 7.5 bar 8.8 Watts - - -
Rolling Resistance
102 psi / 7.0 bar 9.2 Watts - - -
Rolling Resistance
94 psi / 6.5 bar 9.6 Watts 9.2 Watts - -
Rolling Resistance
87 psi / 6.0 bar 10.0 Watts 9.6 Watts - -
Rolling Resistance
80 psi / 5.5 bar 10.4 Watts 9.9 Watts - -
Rolling Resistance
73 psi / 5.0 bar 11.0 Watts 10.3 Watts 9.8 Watts 9.4 Watts
Rolling Resistance
65 psi / 4.5 bar 11.7 Watts 10.8 Watts 10.3 Watts 9.8 Watts
Rolling Resistance
58 psi / 4.0 bar 12.4 Watts 11.3 Watts 10.8 Watts 10.2 Watts
Rolling Resistance
51 psi / 3.5 bar - - 11.4 Watts 10.8 Watts

At the same perceived comfort level BRR find no RR difference between widths.

[BenCousins]

It's pretty simple. It appears if want it, you can trade <1w of Aero-RR or at least be within the margin of error to run a lower PSI with a wider tire. That might get you more comfort, it will get you better resistance to punctures and tubeless performance. Also likely better real world grip. For some of us, going from a handful of flats a year to zero is a game changer. Maybe for others wide tires across really broken pavement or being able to ride a 20-30 miles of gravel on a 100 mile ride is a game changer

So wider tires are slower but more comfortable and (maybe have lower puncture probability). This is exactly the argument people like me are making. We ride narrrower (for me 25 front, 28 rear, both at 80PSI w/latex) because we care more about speed than comfort or punctures. Having said that, on this setup I've had zero punctures in about 12k km. I do however 100% avoid riding shit roads unless it's a competition.

Again on grip - I gurantee that 99.9% of the people 'upgrading' to wider tires for more grip are not even at 50% of the grip limit of thier narrow tires. Even in relatively high end amateur races and super fast group rides I'm surrounded by people going incredibly slowly and riding incredibly upright in corners compared to what their tires can take. The single easiest way to move up groups is to brake later and less on corners.

Are disc brakes or electronic shifting a conspiracy too? (this is rhetorical, you can create a new thread if you think they are)

It's rhetorical, but of course the push to sell both of those upgrades to people who aren't competing or attempting extreme endurance or dnagerous rides is more marketing than supplying a need. Most people on road bikes have way way way more tech than they need and many upgrade way more often than they need to. I would say 50% of people on drop bar road bikes don't need a drop bar road bike. Of course the bike industry leans on the social aspect of riding and exploits human psychology around fashion/keeping up with the joneses/extravagant displays of wealth.

[Nereth]

One thing I don't really understand yet is that some people say "yeah with a smaller tire just drop pressure to get the right comfort level".

But BRR is showing that smaller tires suffer a big rolling resistance hit when you drop the pressure?

Below the table from BBR comparing the different versions of the GP5K. If you drop the 25mm GP5 from 6.5 bar to 4.0 bar you lose 2.8watts per tire. For 2 tires that is 5.6watts in additional RR.

So what is the logic here?

Tire GP 5000 S TR GP 5000 S TR GP 5000 S TR GP 5000 S TR
Tire size 25-622 28-622 30-622 32-622
Sealant 20 ml 22 ml 24 ml 26 ml
Rolling Resistance
109 psi / 7.5 bar 8.8 Watts - - -
Rolling Resistance
102 psi / 7.0 bar 9.2 Watts - - -
Rolling Resistance
94 psi / 6.5 bar 9.6 Watts 9.2 Watts - -
Rolling Resistance
87 psi / 6.0 bar 10.0 Watts 9.6 Watts - -
Rolling Resistance
80 psi / 5.5 bar 10.4 Watts 9.9 Watts - -
Rolling Resistance
73 psi / 5.0 bar 11.0 Watts 10.3 Watts 9.8 Watts 9.4 Watts
Rolling Resistance
65 psi / 4.5 bar 11.7 Watts 10.8 Watts 10.3 Watts 9.8 Watts
Rolling Resistance
58 psi / 4.0 bar 12.4 Watts 11.3 Watts 10.8 Watts 10.2 Watts
Rolling Resistance
51 psi / 3.5 bar - - 11.4 Watts 10.8 Watts

This is important - you just looked at a 1.5 bar drop. But you only need to drop about 6psi (0.4 bar) for equal comfort (depending on starting pressure).

Further, in my original posts on this thread, we're not talking about doing this on both tyres. Just the front where aero is more important, loads are lesser, and the arms suspend more of the weight. The rear can have the wider tyre.

[warthog101]

I ditched the 25 f on my Reynolds AR60s for a 28 based on this thread.
No negatives that I have noted. It is still a touch more comfy and you would expect marginally more grip. Not a huge difference though.
The ARs are designed for a 28 I believe but for some reason came with 25s at each end when I bought the bike. The rear came off immediately.

[mbrider]

I dont specifically have data to provide, but there is a ton of info out there BRR and interestingly a recent rolling resistance test (I think bikeradar published the results) found that Pirelli was top dog and their protocol used a drum with bumps on it.

Couple of things I think that have not been talked about - I think the comfort part now is important in regards to tires because of the switch from rim brake to disc brake (and wider tires do provide more comfort). Some might not remember but even the bike manu said that they had to reinforce / build up the forks and frames to handle the forces due to disc brakes. This means that they took compliance away from the frameset.
I have a NeilPryde Bura SL and have had many other bikes (been riding for ~ 30 years now) bikes that are carbon, aluminum, steel etc. I had both a Cervelo S3 rim brake (the last one before the disc brake one) and the NP Bura SL at the same time. Both set up with ~ 25mm tubs and the NP Bura SL is and was by far the most comfortable bike I have ever ridden.

Disc brake bikes have their place dont get me wrong. I am going to eventually get a disc brake bike, and I think that for the vast majority of bike riders they are the best option. If you happen to be a larger / heavier rider, disc brakes are the way to go. Better braking no matter the conditions and you can use any tube tire that you want without fear of heat transfer to the rim tire system. I've had a blowout on a wet descent and my clincher rim brake aluminum rim immediately on wet pavement. One of the scariest moments of my life. Would not want anyone to experience that.

But I am pretty sure that high quality tubulars are just as fast as the latest and greatest new tires (within a handfull of watts for both front and rear tires). Tubulars solve the problem of air pressure. You can go as low as you want. And you can pump them up high too. It would seem to me that RR is dependent upon tube or lack of tube, suppleness of tire carcass and rubber compound. And it is always a balancing game. There are tubulars that I will not use as a rear tire (Vittoria Corsa Speed for example) because it is more delicate and Im sure is easier to puncture. I would argue that if you are going to run rim brakes you should run tubular. By far the safest option. And as far as gluing and roadside flat fix seems on par or maybe even a little better than tubeless. The other advantage of tubular is that they are generally very close to the stated size. So a 25mm tub on a 26mm wide at the brake track rim will be around the 105% rule for stability in regard to aero. I think the 105% rule is about stability and making sure you can ride a deep / fast wheel without being blown off of the road. The fastest set up I have ever ridden was a Zipp 808 firecrest set up with the Zipp tub in 21mm. The 808 firecrest was 25.7mm or so wide at the brake track. It was so fast that it would give the sensation you were accelerating / found a new gear above 25mph. No other combo has given this kind of sensation. It was also extremely dangerous. that much exposed rim (about 4.5mm total) made leaning the bike really scary. And I hit just the right pothole that totally dented the rim. But man it was fast and fairly stable too.

I think Specialized took advantage of these factors back when they launched the Tarmac SL7. The aero on that bike while good was not exceptional. The wheels are what made it competitive against more aero bikes. The Roval Rapide with the 35mm outer rim width paired with the turbo cotton tires and latex tubes were as fast as any rim brake aero wheel. And might have had a slight edge in terms of rolling resistance. If you run a tire that blows up to a 29mm measured width that is ~ 6mm of exposed rim - quite aero and these wheels are known to be very stable. These wheels are also very fast due to the spoke count and lacing pattern. BTW one of the common complaints about the turbo cotton tires is that they flat easy. That is that balancing act I am talking about. They are very supple and fast and comfortable but also flat easy.

It will be interesting to see how much faster I am on descents with a disc brake bike. I am guessing the added braking and the added traction will give disc brake bike the advantage. But it will be interesting to see. For now my rim brake bike and tubs do not seem to be holding me back. But then again I dont race anymore so perhaps I am not pushing at the same level.

[macwatt]

No data to show just a observation I use Roval Rapide CLX 1 (21mm int) and have previously used Specialized Turbo Cottons and Michelin Power Cup clinchers both 28mm which measured pretty much identical to GP5000 30mm which are currently in use.

This maybe a stupid question but Silca's tyre pressure calculator asks for measured width but excludes actual tyre size. Would the increased height of the larger 30mm tyre not increase the volume of the tyre even though the measured width of the three tyres are all over 30mm which is the main variable for calculating tyre pressure.

[youngs_modulus]

The nominal tire size is irrelevant to volume. Inflated bicycle tire casings are almost exactly circular in cross-section; variations in measured height are overwhelmingly due to different tread thicknesses/profiles.

This is counterintuitive to many people because they're reasoning by analogy from modern car and motorcycle tires, which do not have circular cross-sections. However, those are steel-belted radials.

The steel belt isn't there for puncture protection (as is commonly assumed). It's there primarily to add torsional stiffness and to help enforce a non-circular casing cross section. Bias-ply tires (including all bicycle tires) are much, much stiffer than radials in torsion and thus don't require a steel belt.

[warthog101]

Cbfed

[warthog101]

cbfed

[EtoDemerzel]

This thread is the Terryology of bicycle tires. You remember posting in it, being interested, but now pop in once in a while just to see how far people move the goalposts and reminisce on when scientists vs flat earthers was a thing...

[rhs2z]

https://www.cyclingnews.com/news/we-alw ... t-records/

Interesting, I didn't think track racers went with the super high pressure anymore

[DHG01]

The closest I have seen is Josh@Silca stating that losses are going to be different when standing-climbing. And that this is something Silca began studying in order to optimize for specific events like Everlasting, which was becoming really popular during the pandemic. The key Use Case assumptions for Everesting are that +80% will be climbing, remainder descending. Rider preference will dictate seated vs standing ratio. Weight distribution will be based on the gradient for the chosen Everest segment. Based on these assumptions, the rear tire needs to be pumped accordingly (usually higher than recommended, based on trig).

Another interesting use case is Hill Sprints, where most riders will torque the bike at maximal effort, and the rear tire will see higher loads than what you'd get rolling steady-state at 0% grade while seated at tempo.

Takeaway is use case and context matters when optimizing. Luckily I think most folks in this thread are agreed this is an optimization problem, and the first of many devils that get us tangled up is the nuance required to clearly spec out and define the scenario.

It's been nearly 4 years since Josh hinted they were looking into losses in dynamic scenarios, which I believe is what you mean by vertical deflection normalized data. My guess is they have more data now, but they're not publicizing it to maintain competitive advantage with the teams they are working with. Like when they first discovered wider is faster (need to dig up link on Silca's history).

IME, it seems to take 1 to 6 years for the bleeding edge R&D discoveries to hit mainstream. Sometimes even for WT pro teams.

This is exactly what I was asking about a few pages back. And it probably applies to sprints also.

Interesting- thank you.



For standing climbing, the rear tire load takes on a sinusoidal shape where the tire will actually see peak load that is higher than what it would be during seated climbing AND the tire sees additional lateral forces that allow for additional scrubbing losses. For this, the pressure should ideally be higher still by at least a few % but hard to really model without knowing your exact style and loads. In general, rolling losses will be a good bit higher for standing climbing than seated climbing, and this can be partially offset with higher front and rear pressures

[Nereth]

You're also probably better suspended while standing. So less hysteresis-in-the-rider to offset with lower tyre pressures.

[maxim809]

Going off topic to say it is absolutely okay to have differences in viewpoints.

One of WW's many purposes is to serve as a platform for folks to exchange ideas, experiences, and knowledge. Seeing people bring counterpoints that may not jive well with you personally, is a necessary and natural part of this process. Not everything will be correct, and this is also expected (reminder: we're on the internet). The hope is someone with energy will step in to help adjust what's misaligned.

So I ask everyone to be respectful. No ad hominem. It would be a sad day when WW turns into a gigantic echo chamber. That would either mean all the world's bike questions have been solved and there's nothing to discuss, or we're stuck frozen in time just agreeing with each other while the rest of the bike world progresses forward. So try to think of it this way when there is disagreement. Don't take things personally, and don't take it out personally on others.

My next post will be back to bikes, and more useful. Hopefully.

[maxim809]

Regarding tubulars, they are slower than clinchers and tubeless for Road application... unfortunately.

SuperDave (industry member on this forum) gave a hint without giving the full answer when TrainerRoad Jonathan asked what's the limit with internal width of wheels and tires when it comes to optimization.

"We know that clinchers have less rolling resistance. We know that clincher tires can be molded into an aerodynamic shape, where you can't mold the shape of a tubular tire. So to make the fastest wheel we made it a clincher, tubeless compatible. And designed to run a width that accommodated what size of tires people wanted to race on."

Timestamp @ 43:57 in video at bottom. Note this video is nearly 6 years old, meaning Spesh knew about this much earlier. All tunnels have independently arrived at the same observation.

To explain this simply, shapes influence the Drag Coefficient (Cd). Lower number is better. We can take this unitless (Cd) and multiply it by the cross section Area (A) of a rider, a piece of equipment, or a bike & rider system to get CdA.

The specific issue with tubulars is they are round. Bad shape for aero. Moreover, R&D is nearly all focused on tubeless, and it has all but halted for tubulars. All the new compounds and aero treads are going to clincher/tubeless. There is no tubular offering for Continental Aero 111's with Sailing Effect treads.

There are perhaps a few niche applications where tubulars could have advantages that heavily prioritize weight and maybe safety. More often than not, the fastest everyday clincher/tubeless will perform better than the fastest tubular.






Timestamp: 43:57