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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]

#41

Post by snozolli »

doubled112 wrote: post #29
newsclues wrote: post #28

Earlier quoted context omitted.

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.

The rear brake is very important for initial braking, in order to transfer weight to the front, which allows harder braking without locking up the front tire.

When you initially hit the brakes, your braking potential is split around 50:50. At absolute maximum potential braking force, your rear tire is near lifting, so it's around 100:0.

That said, if you only have one brake, it's better to have it on the front than the rear.

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

#42

Post by kiliantics »

uoaei wrote: post #38
newaccount74 wrote: post #31

Earlier quoted context omitted.

https://biketips.com/calories-burned-biking/ says I burn ~600kcal to ride 20km. 600kcal is ~200g of bread + 20g of butter. Bread costs about 5€/kg, butter costs 2€ / 250g so 600kcal is roughly 1,25€. My car uses about 6l gasoline per 100km, current price is ~1,60€ per liter, so 20km need 1,90€ of gasoline. So if I just eat cheap food riding a bike is cheaper. If I eat at McDonalds, then 600kcal is a hamburger with me…

The costs of sitting idly every time you travel, compared to doing some low-impact cardio over the same distance, for trips shorter than about 3 miles, definitely adds up over the years. The results looks absurd because the math is ignoring a lot of real-world considerations.

There's really no question. Cost of bike maintenance vs car maintenance. Societal cost of road wear due to a huge car vs a tiny bike. Burden on healthcare system, regulation and enforcement for dangerous driving habits. We all pay so much for cars, even when not driving one, when usually a bicycle is perfectly sufficient.

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

#43

Post by wiredfool »

_Wintermute wrote: post #20
wiredfool wrote: post #12

Earlier quoted context omitted.

15K is an overestimate for most bike tires. It might be accurate for ultra hard commuter ones, but my experience is more like 2k miles for a rear (at 700x25c, single racing bike) and 5k for the front. At that point, the rear is a pretty square shape, with thin tread in the center, and starts to have some interesting handling issues. Wider, more supple tires might do better than that, the 26x2.2 rear on my tandem is 2…

2k miles is only 2 months for someone doing decent mileage, but even pros don't train on thin racing tyres.

The 2k figure was from a Michelin lithion 2, which was a decent for the price cheap (15 eur) 700x25 tire. It’s not an event tire. Mainly chosen for its relatively price and predictable performance (1 compound).

The tandem and wider tires are not the cheap ones though, they’re Rene Hearse, roughly 90eur or so. I’d say they’re worth it, but they are about the same price as my last car tires.

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

#44

Post by faeyanpiraat »

kiliantics wrote: post #42
uoaei wrote: post #38

Earlier quoted context omitted.

The costs of sitting idly every time you travel, compared to doing some low-impact cardio over the same distance, for trips shorter than about 3 miles, definitely adds up over the years. The results looks absurd because the math is ignoring a lot of real-world considerations.

There's really no question. Cost of bike maintenance vs car maintenance. Societal cost of road wear due to a huge car vs a tiny bike. Burden on healthcare system, regulation and enforcement for dangerous driving habits. We all pay so much for cars, even when not driving one, when usually a bicycle is perfectly sufficient.

You are also 17× more likely to pay the ultimate price if you travel the exact same amount on a bicycle (according to UK stats).

Edit: Source: https://assets.publishing.service.gov.uk/government/uploads/...

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

#45

Post by itronitron »

michaelteter wrote: post #21
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…

Do the same steering physics apply to riding a bicycle on rollers? That's so much more difficult I wouldn't be surprised if the fundamental steering behavior is changed somehow.

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

#46

Post by uoaei »

faeyanpiraat wrote: post #44
kiliantics wrote: post #42

Earlier quoted context omitted.

There's really no question. Cost of bike maintenance vs car maintenance. Societal cost of road wear due to a huge car vs a tiny bike. Burden on healthcare system, regulation and enforcement for dangerous driving habits. We all pay so much for cars, even when not driving one, when usually a bicycle is perfectly sufficient.

You are also 17× more likely to pay the ultimate price if you travel the exact same amount on a bicycle (according to UK stats). Edit: Source: https://assets.publishing.service.gov.uk/government/uploads/...

Are you making a point? What is it?

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

#47

Post by sritchie »

itronitron wrote: post #45
michaelteter wrote: post #21

Earlier quoted context omitted.

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…

Do the same steering physics apply to riding a bicycle on rollers? That's so much more difficult I wouldn't be surprised if the fundamental steering behavior is changed somehow.

Iirc what makes rollers so tough is that the contact patch is much shorter on the roller than on the road, so the wheel turns more easily. Your reactions need to be that much quicker.

I had a winter of long roller rides (3.5 hours was the longest) and by the time I hit the road again I could ride on the white line with no effort. I think the dynamics are the same, just higher stakes on the rollers!

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

#48

Post by kevin_thibedeau »

alhirzel wrote: post #30
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 equ…

Road bikes are twitchier because they have less trail. Even 25 year old MTBs are twitchy compared to modern equivalents succumbed to the fashion for negative stem lengths and slack head tubes trying to imitate DH bikes.

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

#49

Post by toast0 »

kiliantics wrote: post #42
uoaei wrote: post #38

Earlier quoted context omitted.

The costs of sitting idly every time you travel, compared to doing some low-impact cardio over the same distance, for trips shorter than about 3 miles, definitely adds up over the years. The results looks absurd because the math is ignoring a lot of real-world considerations.

There's really no question. Cost of bike maintenance vs car maintenance. Societal cost of road wear due to a huge car vs a tiny bike. Burden on healthcare system, regulation and enforcement for dangerous driving habits. We all pay so much for cars, even when not driving one, when usually a bicycle is perfectly sufficient.

maintenance and road wear are clear winners for bikes being cheaper.

Healthcare burden, I'm not so sure. Even with the massive difference in usage, street car tracks in Seattle cause a lot more healthcare burden to bikers (and pedestrians) than car drivers. There's certainly a benefit from exercise, but bicycling also has more exposure to injury during use, and not all of them are superficial injuries. Add in things like poor form inducing nerve injuries and it looks even worse.

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

#50

Post by kqr »

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…

This is also why it's impossible to balance a bike without at least a tiny amount of speed. (Even a trackstand that looks completely still uses tiny amounts of forward and backward wiggle to allow the bike to move sideways under the rider.)

The handlebars aren't really used to steer the bike, the way most people think of steering. What they do is shift the bicycle further away from under the rider, which then, due to the bicycles naturally self-stabilising, steer to upright itself.

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