A probably pointless discussion about watts/effort and bikes

[ripvanrando]

OP did ask about randonneuring and ultra endurance racing, not merely gravel.

He also asked if Jan was full of crap. I'll just say, go to any 24 hour race on pavement and see how many 42 or 48 mm wide tires there are in the top finishers or go to PBP and see how many of the Premieres are on fat "rando" tires. None. Zippo

Discussion about road tires for long distance hardly seems irrelevant given OP's second post.

[marciero]

Originally Posted by txsurfer

That is another factor Im working on. At what point do I want to give up speed for comfort, mileage or time wise?

The weather on the ETS was horrendous and my BMC Monstercross disc ate it up and was comfortable to the finish. In dry weather, I wonder if I could have hammered the 280 out on my Bowman Pilgrim's (road +) on 32-35c gravel tires. It would have been fast and potentially bone jarring, but less time in the saddle.

Not just a question of comfort for its own sake. For many riders, a more compliant tire may improve speed in terms of overall time on a long event, but as an indirect effect that results from being able to perform better for longer duration, rather than the tire being faster. This can be a subtle effect resulting from reduced fatigue rather than pronounced difference in comfort that you notice. As far as anecdotal evidence, there seems to be plenty of it-as much as for narrow tire advocates. My guess is that, if true, this type of effect would be very different for high vs low wattage riders. Assuming similar rider weight for simplicity, a high wattage rider will have more weight supported by pedal pressure than at saddle and hands. I noticed this effect myself years ago - that I get more fatigued on slow rides. So what the top finishers are using may or may not be relevant for a given rider. I dont know if one might be able to get the same effect with suspension elsewhere on the bike such as seatpost or stem.

[marciero]

Originally Posted by ripvanrando

It depends on speed and the road surface. On normal asphalt roads at higher speeds, the difference is massive. At 30 mph, I have measured a large difference between a 23 mm and 25 mm. Not miniscule at all.

As I've said, I've found your experience compelling. But I am dubious of claims like this because the difference of 2mm is likely to be small. You say "measured", so is this based on times over a given course with both tires rather than a math model for power using rolling resistance and aero coeff?

[ripvanrando]

Originally Posted by marciero

As I've said, I've found your experience compelling. But I am dubious of claims like this because the difference of 2mm is likely to be small. You say "measured", so is this based on times over a given course with both tires rather than a math model for power using rolling resistance and aero coeff?

Chung method. Multiple measurements. Same kit, same power meter, on the same days.

If a rim is say 24 mm wide and you put a 25 mm that balloons to 26 mm, this is not going to be trivial at speed. At 15-20 mph, 2 mm is trivial.

You can search for wind tunnel results if you don't believe me. I do not know if the Pros carefully match tires to front rims, but I suspect they do and I would not be surprised to see 22 or 23 mm tires on the front wheel for time trials. My fastest front tire is a 22 mm Supersonic, it is much faster than a 25 mm GP5000 at 45-50 km/h

Edit:

Here is some testing done by Tom A. from at the Specialized wind tunnel. A 22 mm tire vs 26mm vs 28 mm on the same rim changed the Cda by 0.0015 and 0.0025 m^2, respectively. At 45 km/h, the 28 mm tire would take an additional 30 watts approx. vs the 22 mm front tired wheel. I did not see that big of an effect on my wheels....more in line with the following. Two other places to look would be Hambini and his friends at Flo. Both claim to have done wind tunnel tests and both have published comparisons of different width of tires. At 20 mph, an improper fit costs 2-4 watts per both Hambini and flo and 10-15 watts at 30 mph per Hambini (Flo only shows results at lower speeds).

http://bikeblather.blogspot.com/2016/

[spoonrobot]

Originally Posted by txsurfer

That is another factor Im working on. At what point do I want to give up speed for comfort, mileage or time wise?

The weather on the ETS was horrendous and my BMC Monstercross disc ate it up and was comfortable to the finish. In dry weather, I wonder if I could have hammered the 280 out on my Bowman Pilgrim's (road +) on 32-35c gravel tires. It would have been fast and potentially bone jarring, but less time in the saddle.

The calculus is fun, wondering what would have been faster. For the courses around here, at my weight, I can't race on anything less than 40mm or I end up pinch flatting a lot, if I boost the pressure, getting big punctures. Several years ago when I was about 5 kilos lighter I was on 35s with no issues. There are enough smooth sections to tempt me every year but I just know I'm not skilled/lucky enough to make it on smaller tires.

Having the upper body strength to handle the narrower tires is another thing often underrated. I let hand and arm strength languish my first couple years on the road and really paid for it when I started back on gravel.

It's definitely worth experimenting. I've seen more than one guy show up to a race with 28s stuffed in his road frame and crush everyone else on our gravel bikes. Part of it was luck (and being lighter weight), but a big part was skill.

The responses/irrelevant concepts in this thread are whack... ask a cyclocross rider (pro or otherwise... heck I'd think even a beginner) about how much more important tire pressure is than 5-8mm of width, if you don't want to take my word for it.

A difference of 5-8mm can be 30%+ more air volume in the tire. A 33mm tire vs. a 40mm has a much narrower band of fast/comfortable/ideal traction. Tire pressure can only go so far, there's no reason to look at one variable in isolation for this exercise.

For me; 5mm difference was the cause of pinch flatting, and coming in down 15+ minutes over a 3 hour race. Then the next race, getting a huge rock cut, losing the pack and coming in down 5 minutes over a three hour race. Moved from 37s to 42s and won the field sprint for 5th in the third race.

It's not possible to affect a 35mm tire as compliant and comfortable as a 50mm tire using pressure, for most gravel. As well it's not possible to make a 50mm tire as fast and aero as a 35mm tire for road, and some gravel.

[Tandem Rider]

Originally Posted by txsurfer

That is another factor Im working on. At what point do I want to give up speed for comfort, mileage or time wise?

The weather on the ETS was horrendous and my BMC Monstercross disc ate it up and was comfortable to the finish. In dry weather, I wonder if I could have hammered the 280 out on my Bowman Pilgrim's (road +) on 32-35c gravel tires. It would have been fast and potentially bone jarring, but less time in the saddle.

It's horses for courses, assuming you are in it to win it. I have won a dry Midwest gravel race on 28mm Gatorskins, I have also won a wet race on 32mm smooth CX tires. I moved out to OR and neither of the above tires work, even for training rides, on the gravel/dirt roads here. It's all about looking at the conditions the day of the race, knowing your own abilities, and making a judgement call at that point.

[rain dogs]

Originally Posted by ripvanrando

Cda by 0.0015 and 0.0025 m^2, respectively. At 45 km/h, the 28 mm tire would take an additional 30 watts approx. vs the 22 mm front tired wheel. I did not see that big of an effect on my wheels....more in line with the following.

Total threaddrift, but can you give more insight into your calculations?

0.0015 m^2 at 36kmph by my calcuations = 1watt. @ 45kmph it's 2 watts.

I find it hard to believe today's Tour de France pros would be using 28's vs the old school 22's if it was costing them 30ish watts. That's about what some riders would hope to gain with oxygen vector doping.

[ripvanrando]

Originally Posted by rain dogs

Total threaddrift, but can you give more insight into your calculations?

0.0015 m^2 at 36kmph by my calcuations = 1watt. @ 45kmph it's 2 watts.

I find it hard to believe today's Tour de France pros would be using 28's vs the old school 22's if it was costing them 30ish watts. That's about what some riders would hope to gain with oxygen vector doping.

How do you figure 1 watt to 2 watts? You think pros are TT on 28 mm tires??

CdA of 0.195 takes about 275 watts for 45 km/h whereas 0.215 m^2 takes about 305 watts. The Cda figure came off the chart. Like I said, I have different wheels and saw a smaller differential at 30 mph and my CdA is a little lower.


Air density Rho (kg/m3) = 1.22601
Crr = 0.004
Rider and bike = 170 lbs

If you look at the previously linked blogpost by Tom A., it shows 5 watts differential at 35 km/h between a 22 and 28 mm tire. It takes a little more work but similar estimations can be seen by Hambini and Flo.

https://www.hambini.com/testing-to-f...icycle-wheels/

https://blog.flocycling.com/aero-whe...-study-part-1/

[rain dogs]

Originally Posted by ripvanrando

You think pros are TT on 28 mm tires??

I don't 'think' pros are riding 28's on their road bikes and some on the TT bikes I know they are, because I know who is mounting the tires on the teams and the tires they are using.

Nobody is using 22's on any bike at any time. First google search for "proof" (admitedly not 28's) but Julien Alaphilippes TT shiv is with 26mm.
I'm not going to take the time to scour the internet for bike reviews of TT bikes. Bu by your calculations he'd be losing what? 20watts with a 26 vs a 22?

https://www.cyclingnews.com/features...works-shiv-tt/

No one is handing away anything close to 30 watts like that. They wouldn't hand away 5 watts like that.

0.215-0.195 is not 0.0015. It's 0.02 or about 13x the amount. You're miscalculating by a decimal place. If your CdA of .195 is taking 275 Watts and you add 0.0015 - that's 0.1965 and 277 Watts or 3 (not 30) extra Watts. Using your numbers,

[marciero]

I read the Hambini post. Or tried to as his description gives only the vaguest indication of what was actually done.
My guess is that they used road data in lieu of wind tunnel data but wanted to use methods of analysis similar to those used in the wind tunnel. That has to be what “equivalent” refers to. But no detail and no guidance and have to guess how we might interpret the axis labels on the graphs as he does not define “equivalent…” Without any of this it is very hard to get past the first graph which looks like noise-in fact he states that it is- that would surely mask any small effects, as these almost certainly would be. Maybe some detail is in the video, which I did not watch. Still, the post should be self-contained, or at least reference the video.

But setting all that aside, and giving whoever did this analysis the benefit of the doubt, consider the graphs of drag vs tire width (Which are very misleading as the x-axis is not at y=0 in either the 30kph or the 50kph). At 30kph with a 2 mm increase in tire width on the Enve wheels the difference in power is about 1/10 of 1%. In other words no difference. With the Shimano wheels the biggest difference is 2.7% increase. Again, even if that is significant we are talking small effects. Not insignificant, but small. This is for the 30kph. The 50kph results are similar- no difference or on the order of 2%.


Going to the bike blather blog-on part 3 he has Crr improvement more than making up for the CdA penalty of the wider tires, with “cominbined” wattage lowest for the wider tires. What am I missing here?

[sitzmark]

Best reference I can give with specific variables "controlled" is the flattest (road) route I ride: All carbon bikes but different build weights.

Course: 18.5 miles, 1,060 vert gain, similar kit (lycra)

Bike 1 (road): Parlee Z5sl 14lb bike - 700x23 conti gp5000, P1 pedals, Zipp404, 50/34x11/28.

Moving time: 1:01:23
Wind: 12.5 WNW
Avg Speed: 18.0 mph
Avg Power: 224 watts
Relative Effort: 83%


Bike 2 ("gravel"): Parlee Chibacco LE, 17lb bike, 700x38 spec Pathfinder Pro, same P1 pedals, Zipp303 tubeless, 46/34X11/32

Moving Time: 1:01:52
Wind: 10.7 SSW
Avg Speed: 17.9mph
Avg Power: 214watts
Relative Effort: 79%

Fastest historical on that route is 21.0 mph average. 296 avg watts. Wind unknown. Bike 3 - Parlee Z1, same P1 pedals, 50/34x11/23, 700x23 conti 4000 Zipp404 Years ago when I was younger and fitter.