• For more information on how to avoid pop-up ads and still support SkiTalk click HERE.

It’s not Stupid

Josh Matta

Skiing the powder
Pass Pulled
Joined
Dec 21, 2015
Posts
4,123
All I said was the COM moves inside the BOS on a bike. It does. Why are you still trying to argue this?

I never talked anything about where the angle happens on a bike its basically our feet, on skis its our hip socket but in both case the COM moves inside the BOS.
 

Rod9301

Making fresh tracks
Skier
Joined
Jan 11, 2016
Posts
2,443
and this is inclination?

View attachment 83673
With the seat up, like on a road bike, all you can do is inclination. Plus there is a lot more traction on the road.

On dirt, less traction, do you have to be more over the contact patch. This way, if the tires wash out, you have s chance to recover

Plus, the seat is down so you have a lot more mobility.
 
Thread Starter
TS
karlo

karlo

Out on the slopes
Inactive
Joined
May 11, 2017
Posts
2,708
Location
NJ
All I said was the COM moves inside the BOS on a bike. It does. Why are you still trying to argue this?

I never talked anything about where the angle happens on a bike its basically our feet, on skis its our hip socket but in both case the COM moves inside the BOS.

I think I see. on the mtn, the base of support are the tires where they meet the ground, right? So, rather than the tires being under our COM, they've gone outside our COM. Put another way, the tires have an arc in the ground. We are inside it
 

Josh Matta

Skiing the powder
Pass Pulled
Joined
Dec 21, 2015
Posts
4,123
yes, which goes back to my first post in this thread.

on both sport the COM has to cross over the BOS and movement is similar. The angulation movements which as @Rod9301 points out is vastly different.
 

geepers

Skiing the powder
Skier
Joined
May 12, 2018
Posts
4,256
Location
Wanaka, New Zealand
The angulation is 180 degrees different.

Really?

Mechanics are different but it sure has some similarities...

Pushbike-Angulation.jpg

Skier-Angulation.jpg


And listening to the commentary on that vid on why the bike guy is doing that - to keep CoG above the bike for more traction... where have we heard that before?

The road bike guys do have a completely different way - they are solving different problems.
Moto-GPBike-Angles.jpg
 

geepers

Skiing the powder
Skier
Joined
May 12, 2018
Posts
4,256
Location
Wanaka, New Zealand
I think I see. on the mtn, the base of support are the tires where they meet the ground, right? So, rather than the tires being under our COM, they've gone outside our COM. Put another way, the tires have an arc in the ground. We are inside it

The 1st 50 seconds of this vid explains the need for inclination. The balancing act applies as much to skiing as it does to bikes.



Angulation is to maintaining grip. On hard surfaces like a road the tires do not cut into the surface so the only thing that matters is friction between the tires and the surface. On surfaces where the contact points (tires/skis) dig in (dirt/snow), angulation provides increased grip. But still require some inclination to balance against the tipping moment.
 

Josh Matta

Skiing the powder
Pass Pulled
Joined
Dec 21, 2015
Posts
4,123
the gyroscopic forces of arelativity heavy spinning extremely fast wheel+tire on the moto are why they have to lean further than their bikes.
 

geepers

Skiing the powder
Skier
Joined
May 12, 2018
Posts
4,256
Location
Wanaka, New Zealand
the gyroscopic forces of arelativity heavy spinning extremely fast wheel+tire on the moto are why they have to lean further than their bikes.

Don't think so - they do it on really slow corners as well.

In decades past the best riders used to keep their bodies in line with the bike. Like Mike Hailwood here who was for a while considered the GOAT.
main1.jpg

The bikes weren't hugely slower (180mph vs 200mph) and the wheel diameters were larger (more angular momemtum).

The big difference is tire grip. Over the years lean angle has increased as the tire compounds improved. Initially the limit was imposed by ground clearance - what scraped 1st. Hard to say who 1st began hanging off the bike increase the corner speed before running out of clearance.. Many people think it was USA rider Kenny Roberts snr however there are photos of earlier riders leaning in for extra ground clearance. Here's John Surtees hanging off the side of a street bike (poor clearance) but that's not the way he rode his GP bikes (with better clearance).
John-Surtees-Getting-His-Knee-Down.jpg

JohnSurteesMVAgusta.jpg



Certainly English rider Paul Smart made people take notice of the technique with his ride at Imola in 1972. Other riders copied and the tires kept getting grippier so the bikes were designed with more and more clearance.

But the tire has to be shaped to provide a good sized contact patch and still fit on the wheel. There's only so far up the side wall that can be gone with a tire that has enough strength for braking and acceleration. Hence the current generations of riders who hang way inside to keep the bikes more upright.

Leaning in isn't the way to overcoming the tire and engine gyroscopes. That vid I posted above has the answer. Counter-steering to move the front tire's contact patch one side of the line of travel of the bike. The bike will then topple the other direction and the rider will reverse the counter steer to stabilize the bike at the required lean angle. The counter-steer may be as little as a pressure applied to the handlebars or a small but noticeable movement. The tilting and re-stabilizing happens quickly however if you've ever had the pleasure of herding a late 1970's large capacity Japanese bike through an S bend at 80mph you'll know the feeling of counter steering.
 

T-Square

Terry
Admin
Moderator
SkiTalk Supporter
Joined
Nov 12, 2015
Posts
7,559
Location
Enfield, NH
Part of a motorcycle racer getting low holding the bike more upright is to help keep more of the tire in contact with the pavement. The tire rests on the pavement and relies on grip to hold it on line. Skis on the other hand dig into the surface of the snow for grip.
 

Seldomski

All words are made up
Skier
Joined
Sep 25, 2017
Posts
3,051
Location
'mericuh
Moving inside like that on a motorbike does a couple things.

1) It moves the center of mass of the system lower and to the inside of the turn. The bike does not need to lean as far over to stay balanced. You do not have to move the entire bike as far, which is a lot more inertia (plus the gyroscopic effects) and therefore slower than simply moving the person. The rider can shift over faster than the bike, so you are more nimble in and out of corners. You might do this with a bicycle if you are going through alternating turns rapidly - like slalom turns. This is not typical, so you don't see it. Plus a human powered bike is much lighter and speeds are much lower, so it's not so important.

2) It puts the rider in a position where it is easier to stay with the bike through continued acceleration. That is, the centrifugal force jams you into the side of the bike. If you sit on top, you have to squeeze with your legs or cling to the bars to stay attached. You need a seat to your side, not underneath you, in a high G turn.

Drawing lines through the bike tires to where the person is located and trying to compare to skiing is a bit of a stretch. The bike weighs a lot more than the person, so the dynamics and what is efficient changes. There could be a squid driving. Or nothing:

 

geepers

Skiing the powder
Skier
Joined
May 12, 2018
Posts
4,256
Location
Wanaka, New Zealand
Moving inside like that on a motorbike does a couple things.

1) It moves the center of mass of the system lower and to the inside of the turn. The bike does not need to lean as far over to stay balanced. You do not have to move the entire bike as far, which is a lot more inertia (plus the gyroscopic effects) and therefore slower than simply moving the person. The rider can shift over faster than the bike, so you are more nimble in and out of corners. You might do this with a bicycle if you are going through alternating turns rapidly - like slalom turns. This is not typical, so you don't see it. Plus a human powered bike is much lighter and speeds are much lower, so it's not so important.

2) It puts the rider in a position where it is easier to stay with the bike through continued acceleration. That is, the centrifugal force jams you into the side of the bike. If you sit on top, you have to squeeze with your legs or cling to the bars to stay attached. You need a seat to your side, not underneath you, in a high G turn.

Drawing lines through the bike tires to where the person is located and trying to compare to skiing is a bit of a stretch. The bike weighs a lot more than the person, so the dynamics and what is efficient changes. There could be a squid driving. Or nothing:


On item 2, racing motorcycles have a seat with a raised resting place for the butt at the back. Resting into that takes a lot of work off the arms when accelerating. Valid point for most street bikes where the seat has no such back stop as that's where the passenger would sit.

The other item worth mentioning is staying low out of the airstream. Quite hard work hanging on to the handle bars in 120 mph winds mid corner.

The vid of the self-controlling bike is interesting. Wonder if they could ever get it to the point of high lean angle, foot rests on the ground cornering?
 

Sponsor

Top