Here we go...bicyclerollingresistance.com finally tests the Compass Bon Jon Pass

[ripvanrando]

Originally Posted by endosch2

Jan, I would be curious why you don't state your case on slowtwitch. That seems to be the place where all of the engineers discuss this topic and there seems to be a high level of expertise. I think you would provide a valuable contribution there with all of your data.

I know that the tri people are usually concerned with the combination of aero and crr data but they all do the crazy math to combine both.

I don't see why people on this forum would overly obsess about crr data when aero resistance is not a concern for the brevet crowd.

Also can you provide me a link (I have not been around this forum in a while) for where you have done the statistical real world study on why drum testing is so bad?

Do you mean CdA?

Rolling resistance (Crr) is always important but especially so at most Rando speeds but once you hit 15 mph, aerodynamic losses are approximately 2/3 of the total drags and at 20 mph, they represent 75% of the losses. 15-20 mph would be typical rando speeds; thus, aerodynamics are not unimportant even if nobody obsesses about them.

[andrewsuzuki]

Originally Posted by Jan Heine

Tom is a great guy, but he tests on even smaller rollers - the ones used for training, so the effect of the convex roller is huge. That is why he finds higher pressures working better.

On real roads, the suspension losses always are considerable. We've tested four different tires at pressures up to 180 psi – on very smooth asphalt – and even in this best-case scenario, there is no linear relationship between pressure and performance... These are real-road tests under very carefully controlled conditions, with excellent repeatability (we test each setup three times) and a rigorous statistical analysis to make sure we are seeing real results and not noise in the data.

But...on the Silca article I linked they carry out real-world tests and they match up quite well with roller tests if I'm not mistaken -- decreasing losses until the breakpoint, which is quite high. Tom has also carried out real-world tests. Were their tests flawed?

I want to believe that suspension losses dominate across the block, because who doesn't want to run lower pressures? But speed is very important to my use case (ultraendurance) as well.

I found a page referencing your Aug 2009 BQ suspension loss test results:
http://biketechreview.com/forum/1-ge...-in-human-body
Which indeed seems to support your side...so what are the others missing? Or is it possible your test was flawed?

[commonguy001]

I have put a ton of miles on Marathon Supremes and a good number on Compass tires and wouldn't ever say the Supreme feels as fast as Compass do but I'm only using my butt dyno. My Marathon Supremes are also not the latest version so it's probably not a fair comparison.
I've only flatted with the Compass a couple of times but I also am very attentive to what I'm riding through with them as they're not nearly as robust as the Marathons.
I've only flatted once with the Marathons and it was a pretty stout piece of wire that made it through the casing. I've also ridden those Marathons through pretty much every conceivable road hazard and never worry about destroying the tire as they pretty much laugh at glass and everything else they've gone through.


What that test does have me thinking about - retiring my Supremes which are a little long in the tooth for a set of those Almotion tires for my commuter.

[Jan Heine]

Originally Posted by rain dogs

However, the 'real' world includes other factors commented on by bicyclerollingresistance.com and many others. Can you comment on the findings of:

- punture resistance (which is the harshest criticism in the review I read)
- durability (if i'm doing a 2000km, or 3000km, or 4000km loaded tour how many tires am I going to have to bring?)
- tubeless performance (is the bead holding well on those tires?)

The needle puncture resistance test isn't used much any longer. It's a static test that assumes you stop on the object. In the real world, rolling over a sharp object is a dynamic process, and many factors influence whether a sharp object punctures the tire. Most important is tire pressure: Lower pressure let’s the tire deform around the sharp object, rather than being flicking it up so it can puncture the tire.

However, there is little doubt that high-performance tires, including Compass tires, are not as puncture-resistant as stiff, belted tires like a Schwalbe Marathon. However, especially the wider Compass tires still have more than enough puncture resistance for most riders – but if you ride through glass or steel wires from exploded car tires a lot, then you might choose different tires!

Longevity depends on tire width, because you spread the wear over a larger contact patch. With a 35 mm Compass tire, an average rider can expect at least 4800 km (3000 miles). I get about 8000 km (5000 miles) out of my 42s...

Tubeless performance mostly depends on the rim. .If the rim is to the correct diameter, these tires work great tubeless. That is how all the gravel racers ride them. If the rim is slightly undersize (and unfortunately, many are, because rim tolerances haven't caught up to the requirements of tubeless), then it's harder to seat a supple tire than a stiff one. There is an illustrated how-to guide in the current Bicycle Quarterly on setting up a tire tubeless with a floor pump.

Hope that answers most of your questions...

Jan Heine
Founder
Compass Cycles
www.compasscycle.com

[Jan Heine]

Here is our data about performance and pressure. As you can see, we didn't find any evidence of a 'break point' in our studies. As with all real-world data, there is some noise, but the statistical analysis indicates that the lower performance of the supple CX tires at medium-high pressures is real. The testing was on brand-new, very smooth asphalt, so a best-case scenario for high pressures, and yet the resistance didn't go down as pressures went up. The supple tires are as fast at 80 psi as at 130 psi!


The odd speed of 27.87 km/h is due to the regression analysis that correlates speed with power in these runs. We got similar results in our roll-down tests, so we've confirmed this with two different methodologies - power meter and rolldown. I am very confident in these results, since they were done with many different tires under carefully controlled conditions.

In the real world, as a long-distance rider, I also have found that I roll faster with less effort on wider tires at lower pressures. My fastest PBP time (49:59 hours) was on 32 mm tires, my fastest 600 km brevets (22:48 and 23:12 hours) were on 42s.

Jan Heine
Founder
Compass Cycles
www.compasscycle.com

Originally Posted by andrewsuzuki

But...on the Silca article I linked they carry out real-world tests and they match up quite well with roller tests if I'm not mistaken -- decreasing losses until the breakpoint, which is quite high. Tom has also carried out real-world tests. Were their tests flawed?

I want to believe that suspension losses dominate across the block, because who doesn't want to run lower pressures? But speed is very important to my use case (ultraendurance) as well.

I found a page referencing your Aug 2009 BQ suspension loss test results:
http://biketechreview.com/forum/1-ge...-in-human-body
Which indeed seems to support your side...so what are the others missing? Or is it possible your test was flawed?

[endosch2]

Originally Posted by ripvanrando

Do you mean CdA?

Rolling resistance (Crr) is always important but especially so at most Rando speeds but once you hit 15 mph, aerodynamic losses are approximately 2/3 of the total drags and at 20 mph, they represent 75% of the losses. 15-20 mph would be typical rando speeds; thus, aerodynamics are not unimportant even if nobody obsesses about them.

Actually I did mean Crr or rolling resistance. I just wonder why someone might care about a 10-15 watts of rolling resistance if you have a huge handle bar bag acting as a wind block out front and a big seat bag, loose clothing, hairy legs, etc. All of those things add more drag than a difference in tires.

[ripvanrando]

Originally Posted by endosch2

Actually I did mean Crr or rolling resistance. I just wonder why someone might care about a 10-15 watts of rolling resistance if you have a huge handle bar bag acting as a wind block out front and a big seat bag, loose clothing, hairy legs, etc. All of those things add more drag than a difference in tires.

Dunno

I shave

No bag unless 1200km

Assos T-Cento and S7 jersey

Conti gP4000Sii 28mm with Latex tubes (much faster than Compass)

60mm rims

Cervelo S3 or other similar fast frame

Specialized Evade helmet

I care about 15 watts and this is about what the Bon Jons cost. $80 plus $14.50 for shipping is trivial but the weak casing is a huge issue for me.

Your categorization of randonneurs is how some dress-up but not the fast riders.

[Mark McM]

Originally Posted by andrewsuzuki

It's actually on the same article you linked

Ah, spotted it. It's buried a bit in the article.

I think of it like if you have a 17mm rim and the tire's already far beyond 95% of the rim width, what happens if you increase the tire by 2mm.

The 1 Watt per 2mm of width is only for low yaw angles. At moderate yaw angles, the difference in drag can become much greater - and that is primarily due to the disparity between tire and rim width, rather than tire width alone (see the graph in the article).

[Mark McM]

Originally Posted by Jan Heine

Here is our data about performance and pressure. As you can see, we didn't find any evidence of a 'break point' in our studies. As with all real-world data, there is some noise, but the statistical analysis indicates that the lower performance of the supple CX tires at medium-high pressures is real. The testing was on brand-new, very smooth asphalt, so a best-case scenario for high pressures, and yet the resistance didn't go down as pressures went up. The supple tires are as fast at 80 psi as at 130 psi!

Are you sure your data doesn't show the 'break point'? for all three tires in your test, as the pressure is increased, there is a an inflection point where the rolling resistance changes from decreasing to increasing - and for two of the tires, the increase is dramatic. The inflection points I'm referring to are at 6.5 bar for the Rubino, 5.5 bar for the CX tubular, and 6.0 bar for the CX clincher. If this is not the 'break point' that Anhalt and Poertner refered to, what is it?

[andrewsuzuki]

Originally Posted by Mark McM

The 1 Watt per 2mm of width is only for low yaw angles. At moderate yaw angles, the difference in drag can become much greater - and that is primarily due to the disparity between tire and rim width, rather than tire width alone (see the graph in the article).

That's with a Zipp 404 though...this is all conjecture but in this realm of 35mm+ tires the the disparity between tire and [typically shallow] rim is already so far gone that it's not worth thinking about flow characteristics at higher degrees of yaw (until even wider road rims appear). And 80% of riding is done below 10deg of yaw on average. So the rule of thumb is more about the effect of increasing frontal area of the tire, assuming it even scales beyond the 23-38mm road tire range.

[ripvanrando]

Originally Posted by Mark McM

The 1 Watt per 2mm of width is only for low yaw angles. At moderate yaw angles, the difference in drag can become much greater - and that is primarily due to the disparity between tire and rim width, rather than tire width alone (see the graph in the article).

Good point. The wind tunnel chart can be edited in the attached. Shows the point exactly.

At 17.5 degrees of yaw, the difference between the 23mm and 25mm GP4Ksii is almost 10 (ten) watts at racing speeds but at more realistic speeds and yaws, 23 to 25 mm would only be 1-2 watts increase but probably a wash considering improved rolling resistance of 25mm. Aero loss of 35mm tire? Not small. I doubt few others have done the Chung method and controlled rolldown tests.

http://flocycling.blogspot.com/2016/...ire-study.html

[Jan Heine]

Originally Posted by Mark McM

If this is not the 'break point' that Anhalt and Poertner refered to, what is it?

You are right – I had disregarded the lower end of the pressure spectrum, because the tires wobbled so much (due to low pressure) that they were almost unrideable in the test runs below the 'break point.' That means that the break point for supple tires like the CX Corsa is so low that as long as you inflate your tires high enough that they are rideable, you don't give up any speed. (I am glad we could reconcile our data with Joshua Poertner's.)

In the end, it seems that we all agree that drum tests show a continuous decrease in rolling resistance with higher pressures, but in the real world, pressure doesn't affect speed in a meaningful way – at least for supple high-performance tires. Less supple tires have a higher break point, and they may benefit a bit from higher pressures – witness the break point for the Rubino at 6.5 bar –*but they'll always be slower than the supple tires.

Of course, the road surface will affect your break point, too. On a rough surface, the break point will be much lower - in cyclocross, you ride your tires at such low pressure that they are almost unrideable on the few paved sections. So if you were to ride a short out-and-back time trial on a uniform road surface, it might be tempting to optimize your tire pressures for that road surface – on our very smooth asphalt, you'd want to run the CX tubulars at 5.5 bar or the CX clinchers at 6 bar. However, on most rides, you encounter so many slightly different surfaces that there probably is no 'optimum' pressure.

Jan Heine
Founder
Compass Cycles
www.compasscycle.com

[benb]

The more interesting take aways from this for me are the puncture notes I guess.

I've been semi-scared to try these as I was on a group ride where someone had a horrific time with these tires. It was a road ride, no gravel or anything that would have been a torture test for a tire, and the rider with the Bon Jons flatted so much the entire group's tube supply came into concern. It was absolutely ridiculous. It was winter weather, and the group showed a really strong and great concern for the rider who was in trouble but the tires were really scary. Literally everyone in the group had taken a turn inspecting the tires looking for a hidden sharp object that was causing the repeated flats by the end of the ride. This was a group of really seasoned riders and no one could figure it out.

According to these tests the Bon Jon Pass tires have thinner tread than all but the most crazy "race day" road clinchers, that seems odd for a gravel tire. (E.x. the Specialized Turbo Cotton is slightly thicker.)

I have a set of Panaracer Gravel King 32c tires on my "gravel bike", they're a good tire but for our local definition of "gravel" they aren't terribly great. They're a good "bad road" tire for me, but the traction just isn't there for cornering off pavement.

One other thing I notice about these tests is he's testing the tire to a 42.5kg load. If you're like me and you take Jan's tire pressure chart as a religious thing you're going to have the front tire pretty low. And these tests show more rolling resistance at the lower pressures. But for the front tire the load is not likely to be 40kg+ for most of us.

I'm relatively large for a rider who is in shape & I have a tank like gravel/touring bike and I still don't exceed 40kg load on the front tire.

[rain dogs]

Originally Posted by Jan Heine

You are right – I had disregarded the lower end of the pressure spectrum, because the tires wobbled so much (due to low pressure) that they were almost unrideable in the test runs below the 'break point.' That means that the break point for supple tires like the CX Corsa is so low that as long as you inflate your tires high enough that they are rideable, you don't give up any speed. (I am glad we could reconcile our data with Joshua Poertner's.)

Can you comment on what "low pressure" is in your mind. I know that varies on volume (larger volume, lower pressure) but when we had a subscription to BQ, you've written and seemingly endorsed regularly riding at pressure close to the sidewalls collapsing in corners???

I've ridden CX Corsa's at ~55 / 60 psi (in a 23c) and although it's slow, it's hardly collpasing or wobbly. Think of post-flat, after pumping a mini-pump 36,000 times you get to like 55psi. You can ride (albeit slightly sluggishly) a full ride like that. 70psi would be/is completely rideable. I normally ride at about 80/85 front back .... weigh 68kg.

I never though of that as low pressure.... just normal pressure for a light guy who didn't want to lose his fillings. When I read how you write about low pressure you seem to imply that the lowest possible is best - but I read, insanely low.... like just more than bottoming out, or collapsing in corners low. Am I mis-reading/interpreting? And how does the above data support that?

On the flip-side, does anyone in their right mind pump their tires up to 130psi for a regular ride?

[Jan Heine]

[QUOTE=benb;2341007Literally everyone in the group had taken a turn inspecting the tires looking for a hidden sharp object that was causing the repeated flats by the end of the ride.[/QUOTE]

When you get multiple punctures, and never find the 'offending' object, then it's still in the tire, and will give you punctures until it's removed. That can happen with any tire... That happened to me during a 600 km brevet (way back before we made Compass tires), where a tiny piece of steel wire was buried in the tread. You couldn't feel it from the outside, nor the inside, but with the rider's weight on the bike, it nibbled away at the tube until I got another flat – every 90 km exactly! Finally, after the third flat, at 1 a.m., we checked super-carefully and found the wire. Digging it out with a pocket knife took another five minutes!

However, there is little doubt that high-performance tires, including Compass tires, are not as puncture-resistant as stiff, belted tires like a Schwalbe Marathon. The question is how much puncture resistance you need, and how much performance and comfort you want to give up to achieve it. Especially the wider Compass tires still have more than enough puncture resistance for most riders – but if you ride through glass or steel wires from exploded car tires a lot, then you might choose different tires –*and give up some speed and comfort in return for extra puncture resistance. The extreme are foam-filled tires as you see on the rideshare bikes in Seattle. We tested those, and it was almost impossible to maintain the test speed of 28 km/h, as the bike required 50% more energy than with our fastest tires!

Jan Heine
Founder
Compass Cycles
www.compasscycle.com