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· Destroyer of Worlds
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Discussion Starter · #1 ·
At least some of us have wondered why we lean against the turn, while motorcycle riders and street riders often do exactly the opposite. I found this youtube video that explains it really well. It references primarily motorcyclists, but everything the guy says is applicable to mountain bikes.

 

· Wanna ride bikes?
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Skimmed the video, but motorcycles have smooth tires used on a smooth/predictable surface. They also have stationary foot pegs.

MTB tires have more aggressive knobs on the edges and you have to lean the bike more to get them to dig in so you have grip. You're also on a very inconsistent/unpredictable surface. You're also going to have your outside foot down in most corners which keeps your weight centered as the bike leans more.

Then there's the difference in weight of bike vs. motorcycle...

Counter-steering to initiate a turn may be the only similarity in my mind.
 

· Rides all the bikes!
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Blocked from work, but probably the Fort9 video.

In which case, it has the motorcycle internet world in a tizzy.

(Personally, I haven't seen the video as I don't like the guy much, and I already understand cornering dynamics)
 

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I actually don't think this, or any of the internet explains are correct. But good news everyone, I have the answer you are looking for:

We need to separate bike lean (angle of bike), vs Center of Mass lean (bike and rider).

Bike lean:
  • we need to lean the bike to decrease the steering angle (how much you turn the bars). The tighter the turn and the faster the speeds, the more we need to lean the bike to decrease steering angle.
  • Why? Turning the front tire takes away traction for gripping through the turn. For people that drive track, if your car is understeering, you know that you need to slowly open up your steering while slowing down to help your front tires regain traction.
  • Try this: off your bike, roll it and then turn it purely by steering angle without any lean. What happens? Your front tire starts to scrub, or the bike wants to OTB.
Center of Mass lean:
  • No layman's explanation for this one. Vector of force from gravity and centrifugal through the CoM must point to the the contact spot between tire and surface. Only way for this to happen is for the CoM to lean inward. CoM is a combination of bike and rider, the amount of influence depends on bike vs rider weight.

Okay, so bike lean vs rider lean?
  • Depends on the grip level, the radius, and the Gs. Nothing to do with the "style of riding" really.
  • Superbike: Big radius, so bike stands up. High G, so CoM needs to be inside > the rider goes in to put the weight in.
  • Dirtbike, and Cops on Harleys (like in the video): TIGHT radius, so bike needs to lean lots. Low G (slow speeds, or loose surface), so CoM needs to stay up > rider stays up to keep the weight from being too far in, counterbalancing the bike to some extent.
  • MTB: TIGHT turns, so bike leans. Low G because of loose surfaces, so CoM needs to stay up > rider stays up.

Nice.
 

· since 4/10/2009
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Blocked from work, but probably the Fort9 video.

In which case, it has the motorcycle internet world in a tizzy.

(Personally, I haven't seen the video as I don't like the guy much, and I already understand cornering dynamics)
It is that vid. While I didn't care for the guy's delivery, I didn't see anything in there that was worth raising a fuss about. True, I don't know squat about motorcycles, so I don't really care how it applies there.

With bicycles, there are times you counter-lean, and times you don't. Depends what you're doing which method you use, but the objective is the same - achieving traction while attempting to balance the main forces that affect it.
 

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Different styles of leaning depends on the type of bike, contact patch and tire. Cornering lugs on dirt bikes have the most grip, so leaning the bike further to get that part of the tire to grip makes sense. MotoGp bike, the edge of the tire has less grip, so you want to hang off and use as much of the center as possible. Supermoto slide the bikes in corners, so they want to use the edge in corners they square off, but hang off the bike on faster corners, like motogp.

He is wrong on why MotoGp riders put their outside leg out when they slide. They are putting their weight on their inside knee to get the bike back upright
 

· Wanna ride bikes?
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With bicycles, there are times you counter-lean, and times you don't. Depends what you're doing which method you use, but the objective is the same - achieving traction while attempting to balance the main forces that affect it.
That's true, for some reason when someone posts a video like this my brain goes strait to cornering at speed but there ARE times that you need to do the exact opposite from what you "normally" do. For instance a very slow speed off-camber switchback where you keep your body weight way to the inside while pushing the bike away from you to the outside and more upright.
 

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Not to mention, surprisingly, physicists still don't know exactly why a bike will stay vertical while in motion with no rider on it.



And my favorite, if maybe not directly related it's hilarious.

 

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I can't say I've ever consciously counter-leaned on a mtn bike, I think speeds are too low anyway.
 

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On my BMW GSA800 I lean into the turn on the street and counter lean in dirt for the most part. But understand what he is talking about.

I have a sport bike along with my adventure bike but sadly they hardly get ridden much these days because mtb is awesome.
 
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