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The track of a bicycle back tire [pdf]

tlakoba.w3.uvm.edu

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Re: The track of a bicycle back tire [pdf]

#21

Post by michaelteter »

matsemann wrote: post #6

The math and physics and engineering behind bicycles is so cool. Such a "simple" device, but so many interesting things to dive into. I wrote my thesis on spoke patterns for the wheels [0]. Another cool thing is how the steering of a bicycle works. You don't really turn the way you want to, you actually turn the other way first to initiate so the bike moves from under you, and you then lean the other way to actually…

I have taught several kids to ride bikes. My instructions were very simple: ride, and if the bike starts tipping to one side, turn the handlebars that way.

With humans, that's about all you need to say. You very quickly feel how the lean changes based on the steering input, so righting yourself becomes obvious. And when you inevitably overdo it and end up leaning the opposite way, you turn the bars that new direction. WOBBLE WOBble wobble straight.

Re: The track of a bicycle back tire [pdf]

#22

Post by michaelteter »

navane wrote: post #4
Someone wrote: post #2

FTA: Can we verify the folklore that on a long bike trip the back-tire wear is less than that of the front tire? I’ve never heard that folklore. I thought ‘everybody’ knew back-tires wear out a lot faster because the load on them is higher and because they’re the one being powered. https://www.sheldonbrown.com/tire-rotation.html : “It is common for a front tire to outlast a rear tire by as much as three to one. Rear…

From my experience, front tires only wear of age, not use. Backtires experience (frictional) shear forces, pushing along the earth. This erodes the surface.

And from those glorious big fishtailing skids we do as kids...

Re: The track of a bicycle back tire [pdf]

#23

Post by c0nsumer »

navane wrote: post #4
Someone wrote: post #2

FTA: Can we verify the folklore that on a long bike trip the back-tire wear is less than that of the front tire? I’ve never heard that folklore. I thought ‘everybody’ knew back-tires wear out a lot faster because the load on them is higher and because they’re the one being powered. https://www.sheldonbrown.com/tire-rotation.html : “It is common for a front tire to outlast a rear tire by as much as three to one. Rear…

From my experience, front tires only wear of age, not use. Backtires experience (frictional) shear forces, pushing along the earth. This erodes the surface.

Cornering and braking does wear the front tire, and it is more notable when mountain biking where cornering tends to be more forceful and the tire knobs concentrate forces on more noticeable parts of the tire.

Re: The track of a bicycle back tire [pdf]

#24

Post by fluoridation »

Moru wrote: post #18
Someone wrote: post #2

FTA: Can we verify the folklore that on a long bike trip the back-tire wear is less than that of the front tire? I’ve never heard that folklore. I thought ‘everybody’ knew back-tires wear out a lot faster because the load on them is higher and because they’re the one being powered. https://www.sheldonbrown.com/tire-rotation.html : “It is common for a front tire to outlast a rear tire by as much as three to one. Rear…

It depends on how you use the bike. When I was a kid I used to turn the front wheel left/right to go forward instead of using the pedals. This ofcourse wore out the front tire realy fast :-)

How does that work? I don't see any way that just turning the bars would imprint forward momentum.

Re: The track of a bicycle back tire [pdf]

#25

Post by fluoridation »

InCityDreams wrote: post #5
Someone wrote: post #2

FTA: Can we verify the folklore that on a long bike trip the back-tire wear is less than that of the front tire? I’ve never heard that folklore. I thought ‘everybody’ knew back-tires wear out a lot faster because the load on them is higher and because they’re the one being powered. https://www.sheldonbrown.com/tire-rotation.html : “It is common for a front tire to outlast a rear tire by as much as three to one. Rear…

At €70 a pop, my tyres get rotated front to back, as required. Back wears out much faster.

You're not actually saving anything in the long term, though.

Let's say you start with brand new tires on both wheels. Let's further suppose that you completely wear out your rear tire in 1 year and your front tire in 4 years. If on the first anniversary you rotate and place the new tire in front, you'll need to repeat the procedure after 9 months, and then every 9 months after that. On the 4th anniversary you'll have bought 5 tires: on the 12th, 21st, 30th, 39th, and 48th months. If you simply replace each tire as it wears out without any rotation, on the 4th year you'll have bought 5 tires, 1 to replace the front tire once and 4 to replace the rear tire 4 times.

Re: The track of a bicycle back tire [pdf]

#26

Post by giraffe_lady »

thunderrabbit wrote: post #15
matsemann wrote: post #6

The math and physics and engineering behind bicycles is so cool. Such a "simple" device, but so many interesting things to dive into. I wrote my thesis on spoke patterns for the wheels [0]. Another cool thing is how the steering of a bicycle works. You don't really turn the way you want to, you actually turn the other way first to initiate so the bike moves from under you, and you then lean the other way to actually…

Wow! This explains the trouble I've had trying to ride with the end of my handlebar sliding along a smooth wall near the sidewalk. Thank you!

Also about half the time when you hear about a cyclist dying because they "lost control of the bike" in traffic this is what happened. Car passes slow and too close to give you room to countersteer and you fall into and then under it.

Re: The track of a bicycle back tire [pdf]

#27

Post by giraffe_lady »

michaelteter wrote: post #22
navane wrote: post #4

Earlier quoted context omitted.

From my experience, front tires only wear of age, not use. Backtires experience (frictional) shear forces, pushing along the earth. This erodes the surface.

And from those glorious big fishtailing skids we do as kids...

never stopped being fun this is why fixed gears are still a thriving niche

Re: The track of a bicycle back tire [pdf]

#28

Post by newsclues »

Someone wrote: post #2

FTA: Can we verify the folklore that on a long bike trip the back-tire wear is less than that of the front tire? I’ve never heard that folklore. I thought ‘everybody’ knew back-tires wear out a lot faster because the load on them is higher and because they’re the one being powered. https://www.sheldonbrown.com/tire-rotation.html : “It is common for a front tire to outlast a rear tire by as much as three to one. Rear…

Rear tires do must of your braking. If you hit the front break too hard/fast, you flip over the front tire, hit the rear brake hard/fast and you burn rubber/lose traction.

Re: The track of a bicycle back tire [pdf]

#29

Post by doubled112 »

newsclues wrote: post #28
Someone wrote: post #2

FTA: Can we verify the folklore that on a long bike trip the back-tire wear is less than that of the front tire? I’ve never heard that folklore. I thought ‘everybody’ knew back-tires wear out a lot faster because the load on them is higher and because they’re the one being powered. https://www.sheldonbrown.com/tire-rotation.html : “It is common for a front tire to outlast a rear tire by as much as three to one. Rear…

Rear tires do must of your braking. If you hit the front break too hard/fast, you flip over the front tire, hit the rear brake hard/fast and you burn rubber/lose traction.

I don't even have a rear brake.

Weight is transferred to the front on heavy braking, and if you have proper technique, you will not go over the bars. The front tire does all of the actual stopping.

Re: The track of a bicycle back tire [pdf]

#30

Post by alhirzel »

matsemann wrote: post #6

The math and physics and engineering behind bicycles is so cool. Such a "simple" device, but so many interesting things to dive into. I wrote my thesis on spoke patterns for the wheels [0]. Another cool thing is how the steering of a bicycle works. You don't really turn the way you want to, you actually turn the other way first to initiate so the bike moves from under you, and you then lean the other way to actually…

The way this is described in a control systems framework is that the dynamics are non-minimum phase. A cool high-level video from Mathworks[1] explains in more mathematical detail. Being an experienced rider but having not looked into bicycle models in detail, I think it would make intuitive sense if the dynamics were only NMP for some operating points, particularly very low roll rates at very low roll angles. Or equivalently, the system behaves differently when it's in a banked turn (moderate roll with low roll rates) because gravity is starting to couple into the steering more. There is an angle where the steering switches modes depending on the geometry of the bike, and I think this is why road bikes "feel" "twitcher".

[1]: https://www.youtube.com/watch?v=jGEkmDRsq_M

Edit - also OP, very cool thesis work!

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