The Bicycling Thread

[wildbears]

"The force of rolling resistance does not change at higher speeds. However, because there is a lot more heat being produced at higher speeds, the cyclist uses more power (energy per second) to work against rolling resistance."

https://www.sciencelearn.org.nz/reso...ing-resistance

[wildbears]

The Tour de France has 8,000 meters more climbing this year than last for a total of 56,000 meters.

[wildbears]

That's like going up Mt. Everest 5 times from sea level.

[955i]

The Tour is shaping up to be something special. I wish Jumbo would have sent Roglic. They have all their eggs in one basket now, even though Vennigo is in fine form. Stuff (and wrecks) happens!

[wildbears]

The repeated, long, and steep climbs will thin the front groups.

[955i]

The GC time gaps are likely to be the largest we have seen in quite a few years.

[wildbears]

[wildbears]

Berto 15% Tire Drop Rule



How to measure tire drop with a micrometer from side to side versus rim to floor.

Approximately equal to adding 15% of the tire width/diameter to the width to get 15% vertical squish.

For a measured 26.9 mm wide tire (without the rider on the bike), decreasing the vertical height by 15% results in increasing the horizontal width by 15% or to 30.6 mm with the rider on board.

Guestimation:

26.9/2 = 13.45
15% of 13.45 = 2.02
13,45 - 2.02 = 11.43
13.45 + 2.02 = 15.47
15.47 x 2 = 30.93 or ~ 31 mm target width for 15% squish.

Calculated results using math formulas (see below)::

15.3 x 2 = 30.6 mm.

The correction factor for guesstimation versus calculation is 30.93 - 30.6 = 0.335 or about 1%.

So multiply the measured tire width without-rider by 14% and add that to the tire width (without-rider) to get the approximate tire width with-rider and 15% squish.

Pics below are from an on-line ellipse circumference calculator. The first shows the results from a circle as with no-rider. The second solves for "a" with 15% squish with the "b" axis 15% smaller (the "b" axis in the first pic minus 15%).

The circumference, "C", stays constant with or without squish.

The solution in the second pic calculations is based on guesstimating the "a" value in order to have approximately equal circumferences for both calculations.

[wildbears]

Route of the Hiawatha....

[wildbears]

Wheel Flop Versus Cow Flop...

https://cyclingindependent.com/the-a...nd-wheel-flop/

[wildbears]

Heresy And Current Tire Parameters Thinking: Rolling Resistance Versus Comfort

Here's the starting point that espouses current findings and general thinking....'

??????

Reference: https://blog.flocycling.com/aero-whe...-for-cyclists/

So, using the above information, it follows that the high pressure tire will result in more vibration being transmitted through the wheels to the rider. And the vibration is perceived as a "rough" ride and "uncomfortable".

This applies to pavement with smaller imperfections as opposed to large imperfections such as open-expansion joints that allow the wheel to significantly drop into the gap.

The latter results in a jarring ride as opposed to one with vibrations.

And perhaps the "jarring" is increased by lower tire pressures.

Here's the hypothesis.

All other things being equal, a lower tire pressure results in a smaller functional tire diameter. The smaller diameter allows the wheel to drop further and harder into the expansion joint gap as it rolls off of the leading edge of the gap. And, dropping further, the angle it strikes the trailing edge is at an angle closer to that of the head tube angle. (Note that this effect may be partially mitigated by faster velocity.)

This results in the fork (front suspension) being less able to absorb the impact and isolate it from the rider.

If true, this suggests that lower tire pressure for a given tire size, other parameters being equal, results is a smoother ride over smaller pavement imperfections but may increase jaring from larger pavement defects.

Opposing this effect is the ability of the tire with lower pressure to better absorb the impact shock. I'm not sure what a graph would look like comparing pressure and impact shock transmitted to the rider. There would likely be a recognizable nadir at the transition point.

Additionally, forward velocity affects how far the tire can drop and the impact force. Less drop with higher speeds but greater impact for a given angle.

Note that previous studies found with very smooth pavement, higher tire pressures are more effective.

[955i]

I warched a good GCN video a year or so ago that drew force vectors onto the illustration. Some of them were exactly the wrong way, not just up and down. It was this video that finally convinced me to try much lower pressures.
! weigh 195 and am now running 90 psi.in 700c x 25. Twenty years ago it was 120 psi in a 23. When I first started using a 25 I still inflated to 11,
The tires "feel slower" subjectively, but I'm not convinced they are. I am sure, however, that the ride is nicer and more comfortable.

[wildbears]

I was trying to remember how we put air in our tires when we were kids. I mainly remember going to the filling station to use the air pump there. The main concern was to not blow the tire apart with too much pressure. We must have had a hand pump for our basketballs at the time, though, and no pressure guage.

[wildbears]

Anecdotal results today and yesterday comparing high speed downhills over rough pavement. The steel road bike with 28Cs and 85 psi was less jarring than the aluminum gravel bike with 37Cs and 35 psi.
???

[wildbears]

Downtown Columbus, OH, from the bike trail....

[wildbears]

A steep downhill cobblestone alley near home....



Test the brakes before entering.

[955i]

Ah, the Paterberg! Or is this the Oude Kwaremont! LOL

[wildbears]

At speed, a rough downhill pavement can cause the tires to bounce and lose contact. Braking becomes sketchy.

Different mechanism for the ABS issue while trying to brake on off-road downhills but similar results.

[wildbears]

[wildbears]

So the pros take ice baths after a race.

I wonder if a cold shower could help us amateurs after a hard ride?

[955i]

I don't know, but yesterday after push mowing in 101 heat, I took a shower with no hot water mixed in. Felt good.

[wildbears]

[wildbears]

Is the risk of pinch flats proportional to the tire to rim width ratio?

Does more tire per rim act to protect the innertube?

Note that this is usually not a problem when running higher pressures. But what if you want low pressures?

Do wider tires allow the "pinch" to occur at a more obtuse angle? Or for there to be more give in the innertube?

[955i]

Man, I have NO idea. I would think multiple factors interfere with arriving with a straight mathematical answer. Tire sidewall strength and construction.as well as compound toughness would make experimentation tough.

[wildbears]

Freewheel Wobble?

Just noticed this with an 8 speed Shimano freewheel/hub and cassette. Very slight but noticeable when there is no tension on the chain. The latter occurs with the bike turned upside down and resting on the saddle and the brake hoods.

Apparently this is not uncommon for Shimano cassettes and does not cause a problem, neither excessive wear or shifting problems.

See: https://bikeryou.com/should-rear-cassette-wobble/