There are ways to solve for Crr but you need to be pretty careful about data collection in order to get good estimates because Crr is relatively "smaller" than CdA. The overall rule is this: the smaller the effect you're trying to find, the more careful you need to be in testing. A consequence of that is that it's easy to spot the difference between hands on hoods and hands in drops but if you're trying to spot the difference between two different front brakes you need to be pretty careful.

Crr is multiplied by weight, so what you're estimating is the overall average Crr for both front and rear tires. So don't double it.

If all you're doing is "Is A better than B?" then, yeah, you don't really need to get an exact estimate on Crr. If, however, you want to use this to know "*how much* better is A than B?" then you'll want to get a good estimate of Crr.

Perhaps, but the oddity is that if I stop for a couple of minutes to change something and then re-start another test, I don't always get higher drag for the second set of tests. So after a while I just gave up and added some sacrificial laps at the start. It also gave me a chance to practice my line through corners and settle into a position and remember that I was going to take of selfie of exactly what I was wearing and to make a note to avoid that pothole.

Do you think it could be due to heat in the tires?

Maybe they get up to temp after some time rolling and become more supple relative to the beginning of a run.

Interesting, just a thought but it might just be the flexing of the tire body frees it up and makes it more supple, sort of like something such as maybe leather or blue jeans after they are washed (I know totally different things, just trying to generate ideas) where you move it a bit and it becomes more supple but when left to sit it changes back to being in a less supple state. I am not a materials scientist but I have seen materials that when they sit for a while the suppleness changes (ie they become more stiff) but once they are flexed they return to that supple nature. It takes time though for the change back and forth and might be exacerbated by temperatures and humidity?

Anyhow if it is rather random maybe that is just one of those unknowns.

That is a ridiculous idea.

We need to all chip in and getting Robert one of these

http://www.izzeracing.com/...nitoring-system.html

In motorsports people check with physical probes (say after a pit stop). I’d be tempted to use either one that connects to a multimeter or a kitchen meat thermometer probe or infrared (like Thermapen).

They measure the outside temperature of the tire ?

At least on a drum CRR test-rig the surface temperature of a bicycle tire heats up fast in about 30 to 60 sec upon loading, but not more than 5K above room temperature. After fast heat up surface temperature is almost constant. During the heat up I can not observe a significant change of CRR (i.e. any potential change has to be below about 3%).

I guess environment temperature and road temperature play a bigger role for the tire temperature than the heat from the rolling losses.

The devices probe beyond the surface with a needle, sometimes after scraping off the very melted rubber.

https://m.youtube.com/watch?v=Blcij45sLus

However, since bicycle tire temps are closer to ambient temps and not super high like race tires , the need to probe into the (very thin) rubber is probably not necessary or useful.

My experience on small drum roller testing is quite different.

I can detect the lowering Crr effects of increasing tire temperature lasting over quite a few minutes in the power trace of a roller test. That's how I ended up with my testing protocol of first doing a 5 minute tire "warm-up" at a higher wheel speed, followed by a 4 minute test run (at a slightly lower wheel speed), where the average wheel speed and average power is taken from the last 2 minutes of that run. Even then, depending on the tire (e.g thick casing or tread) I'll still see a slight downward power drift from the start to the end of the 4 minute test run.

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http://bikeblather.blogspot.com/

I’m not sure what the standards are for crr testing, but the temperature change should depend on load and velocity even though the crr value itself is considered to be independent of these parameters.

So even though one could in theory find crr with a light load and low velocities, the temperature deltas to the “steady state” value would change, which ultimately (apparently) may have some small effect on crr.

All of that is correct, but from an engineering standpoint, there are ways to "work around" those variables. In the end, it's really about making sure the tires are tested in an equilibrium state for the conditions. That way, the results can be better applied to race conditions (or field testing).

What I've found is that for both drum testing and field testing, the tire temperature closely tracks the ambient air temperature near the tire/wheel. Considering the quite large convective heat transfer effects on the tire of even just spinning a wheel in the air, this observation is expected. Knowing this, quite a long time ago I ran a series of drum tests over a wide range of ambient temperatures, and then calculated an approximate temperature compensation for Crr vs. ambient temperature. Applying that compensation (1.36% per degree C, see http://bikeblather.blogspot.com/...ollers-chartand.html) to the drum testing data dramatically improved the repeatability of the results for the same tire across test sessions (I now "normalize" the results to predicted Crr at 20C ambient.)

I also "baked" this temperature compensation into my personal VE spreadsheet, where there too it has greatly improved the repeatability across test runs at varying temps.

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http://bikeblather.blogspot.com/

Or, just a set of these: https://www.sks-germany.com/en/products/airspy-sv/

(BTW, I just picked up a set of these for myself...haven't played with them yet, though)

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http://bikeblather.blogspot.com/

Or, just a 20 year old bottle of armagnac.

My drum has a diameter of 0.9m and is made of wood to be closer to a wooden indoor track. A test run is from 55kmh down to 25kmh in 7 steps. Every step is first 3min almost unloaded (around 1N, tire just touching the drum in order to get the moment to spin the wheel). Than 3min with load (between 300 and 500N) for warm up (I do it just for protocolary reasons, experience tells that it wouldn't be necessary) followed by 5min actual test run and unloading.

Tire surface temperature increases with speed and load and with crr, but up to now it was never more than 5K above room temperature. After around 100 7 steps test runs I could never observe a variation of crr during the usual 8min with load.

This makes sense, but the large drum and its smoothness probably reduces the contact patch deflection and the amount of heat that remains in the tire versus heating the wooden drum.

On actual roads, the asphalt can be much hotter than ambient air, along with causing larger displacements and slipping on the contact patch.

Again, not suggesting these are giant points, just bringing them up for discussion. I agree with Tom A. that convection somewhat compensates for velocity in a manner that may be modeled away, when moderate ambient temps are close to ground temps, but I think there is, plausibly, a decent effect of hot road surfaces.

If all you want is the bottle, I might be able to make that happen :)

I did a bunch of rides outside with an IR thermometer, and I compared tire temp to the temp of a small plastic piece that was shaded, located at ~axle level on the bike. Even in bright sunshine, tire temp and the temp of the test piece were nearly identical when taking a temp reading immediately upon stopping the bike. It was those observations that made me confident in just using a Crr temperature compensation based on ambient temps.

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http://bikeblather.blogspot.com/

What about this: https://www.tubolito.com/tech/

Tom maybe you, Josh or others can comment on a statement from the paper on rolling resistance estimation:
https://journals.sagepub.com/...177/0954407018802733
"Tyre hysteretic loss has been the main essential issue in numerical prediction of rolling resistance. In other words, the rolling resistance force is a measure of the hysteretic losses. In all of the popular numerical methods used for this reason, the time histories of strains must be approximated to calculate the hysteretic loss and rolling resistance during one revolution. These methods are classified based on the technique by which strain cycles are approximated during the cycle."
as you have so well noted as has Josh, hysteresis is the main reason for rolling resistance break point. In the above they mention time histories of strains. Would this have any impact on initial VE trials? This is outside my scope so I am interested in a hysteresis for dummies explanation. Does this mean that there is a time domain change in hysteresis that requires knowing what happened before to predict the effect?

Those have a pretty large resolution (+/- 3 psi) for the purpose...I think he'd enjoy the armagnac more ;-)

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http://bikeblather.blogspot.com/

No...when they talk about "time history of strains", they're basically describing the process by which one would quantify/calculate the hysteresis of a material.

And, I think you might be misunderstanding the "breakpoint" concept. In the total bike+rider system, at pressures below the breakpoint pressure for the conditions/use, the majority of losses are due to hysteresis in the tire carcass (i.e. due to flexing of the tire material in response to movement AND to surface irregularities). Good tires with low hysteresis properties end up returning most of that flexing input to the road surface in the trailing half of the contact patch. That's why pneumatic tires work so well.

However, the tire is containing an air spring (which has quite low hysteresis) which makes up a big part of the "suspension" (i.e. nearly all of the spring rate) and if that air spring is inflated to too high of a spring rate (too stiff for the conditions/use) then the energy imparted into that tire by the surface irregularities isn't used to flex the tire as much, and more of it is transmitted through the tire and into the rest of the system, where it can be dissipated in the "squishy bits" of the rider.

Does that make sense?

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http://bikeblather.blogspot.com/

Thanks Tom, what I read from the quote is to be able to model rolling resistance of a tire they needed to take into account the material characteristics. Now I assume that because this is a model for automotive tires it may be more important than in bicycle tires for exactly the reasons you state, that the material hysteresis is not significant to the over all effect of the bike rider system. thanks for the explanation.

Im not sure if this has popped up in previous pages but I occasionally get a noticeable drift that makes some tests useless. It usually ends with position B almost always being faster than A. I know the easy answer is to go ABBA but I usually save those for recovery weeks.

Does temperature effect the VE calculation or possibly my Quarq numbers? Here is an example where the temp dropped more than what is likely (Starts at 34 before stabilizing at 28) - https://www.strava.com/activities/4682092261. I also went out today on an endurance ride and noticed the temp started around 61 and dropped until it stabilized at 52. The actual temperature was 60. The funny thing is that I dual recorded using a Garmin 520 and a Wahoo Bolt and both had the same temp drop. Full disclosure - I rode with GPS on both but even still the cda drift is pretty significant. I would have to move the density slider from 1.22 to 1.16 to get the start and end to show similar numbers.