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Chasing Your Tail

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Road Cycling “It is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them. Thus you remember them as they actually are, while in a motor car only a high hill impresses you, and you have no such accurate remembrance of country you have driven through as you gain by riding a bicycle.” -- Ernest Hemingway

Chasing Your Tail

Old 09-11-19, 07:06 AM
  #1  
spinconn
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Chasing Your Tail

This will be of no practical value to anyone but I am curious. I have a route that includes several small and tight traffic circles usually empty of traffic. They are tight radius and I am trying to figure out the fastest way around.

Not being vested with mathematical prowess I have tried trial and error, going around wide enough that I can pedal continuously, going around tight as possible and not pedaling at all since I have to stand on the outside pedal, and mixing it up by entering tight and going out half way through to pedal a little and going tight again.

Having no computer to help I am going by feel and cannot tell which is faster. Going around multiple times gets even more interesting.

Any ideas?
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Old 09-11-19, 07:11 AM
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Spoonrobot 
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When track racers compete in the Flying 200 they start at the outside of the track, build up speed and move down as close as possible to the inside about halfway through. Velodromes aren’t a circle but, something to think about.
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Old 09-11-19, 07:28 AM
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You can pedal thru many corners by keeping the bike more upright and leaning your body over center toward the apex.
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Old 09-11-19, 07:59 AM
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Depends on how much of the "circle" you have to go through. Fastest line will almost always be the biggest radius through any corner.
This translates roughly to start wide, head to the inside and exit wide. Look up racing line and apex for more info, but much of that relates to auto racing.
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Old 09-11-19, 12:08 PM
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woodcraft
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Often, you can pedal at greater lean than you think you can.

IME, taking the most inside line, which is the shortest, is faster.

This shows up riding with a group- around a sweeping turn, taking the center line vs the fog line

can put you 3 or 5 bike lengths ahead for the same effort.

The dynamics on a tight roundabout are somewhat different, but the inside line is still much shorter.

Try counting it off "one one thousand..." and see.
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Old 09-11-19, 12:34 PM
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Originally Posted by mvnsnd View Post
Depends on how much of the "circle" you have to go through. Fastest line will almost always be the biggest radius through any corner.
This translates roughly to start wide, head to the inside and exit wide. Look up racing line and apex for more info, but much of that relates to auto racing.
This. The fastest line is almost always the one with the highest exit speed.
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Old 09-11-19, 10:02 PM
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woodcraft
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Originally Posted by mvnsnd View Post
Depends on how much of the "circle" you have to go through. Fastest line will almost always be the biggest radius through any corner.
This translates roughly to start wide, head to the inside and exit wide. Look up racing line and apex for more info, but much of that relates to auto racing.


If that were the case for cycling, you'd see it at the velodrome- swing wide, head to the inside, exit wide- on every turn,

but you don't.


A rough calculation of 11m inside circle, and 30m outside; traveling 3/4 around so say 60%; shortest line vs wide approach & exit equals approximately the distance of a middle line.

The wide approach/exit travels ~9m further, about 30%. Since the entry speed is the same, the exit speed would have to very different to overcome 5+bike lengths.

[end techno rant]
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Old 09-11-19, 10:30 PM
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Originally Posted by woodcraft View Post
If that were the case for cycling, you'd see it at the velodrome- swing wide, head to the inside, exit wide- on every turn,

but you don't.


A rough calculation of 11m inside circle, and 30m outside; traveling 3/4 around so say 60%; shortest line vs wide approach & exit equals approximately the distance of a middle line.

The wide approach/exit travels ~9m further, about 30%. Since the entry speed is the same, the exit speed would have to very different to overcome 5+bike lengths.

[end techno rant]
So true.....if you never have to slow down.
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Old 09-12-19, 05:00 AM
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Originally Posted by Jack Tone View Post
So true.....if you never have to slow down.
And/Or if the corners are highly banked.
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Old 09-12-19, 06:13 AM
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asgelle
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Originally Posted by woodcraft View Post
If that were the case for cycling, you'd see it at the velodrome...
Have you ever seen a velodrome? (apologies to Shaun Wallace)
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Old 09-12-19, 07:33 AM
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realistically how much time are you looking to save? I would just stick with road rules & be where drivers expect you to be. what is it about ppl that make them want to take rotaries or traffic circles as fast as possible? got any pics, vids or coordinates so we would know more about what your asking about?

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Old 09-12-19, 07:36 AM
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Bikes don't have to apex every corner in a velodrome because they're simply not going fast enough to overcome available grip. Motorcycles and cars are absolutely going fast enough. If they had unlimited grip, they would drive the shortest inside line because it covers less overall distance.

I have a roughly square lap I ride inside the parking lots at our defunct airport. Because mine is square, I am apexing every corner, but choosing the entrance and exit angles is where the fun is. I've tried sticking to the inside as close as possible, but I can feel and see the speed losses due to wheel scrub from taking the corners too sharply. If I enter or exit a corner too wide, I can feel the extra time required to cover the added distance. Getting it just right feels amazing.

So going in a circle, you want the tightest line on which you can pedal continually, without scrubbing speed off of the tires.
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Old 09-12-19, 12:19 PM
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Bunny hop the parts of the road furniture that you can, that's the obvious answer!

https://www.youtube.com/results?sear...hop+roundabout
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Old 09-14-19, 04:03 AM
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RShantz
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Originally Posted by drisotope View Post
bikes don't have to apex every corner in a velodrome because they're simply not going fast enough to overcome available grip. motorcycles and cars are absolutely going fast enough. If they had unlimited grip, they would drive the shortest inside line because it covers less overall distance.

I have a roughly square lap i ride inside the parking lots at our defunct airport. Because mine is square, i am apexing every corner, but choosing the entrance and exit angles is where the fun is. I've tried sticking to the inside as close as possible, but i can feel and see the speed losses due to wheel scrub from taking the corners too sharply. If i enter or exit a corner too wide, i can feel the extra time required to cover the added distance. Getting it just right feels amazing.

So going in a circle, you want the tightest line on which you can pedal continually, without scrubbing speed off of the tires.
exactly
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Old 09-14-19, 08:57 AM
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Originally Posted by RShantz View Post
exactly


"bikes don't have to apex every corner in a traffic circle because they're simply not going fast enough to overcome available grip."

FIFY
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