Suspension and cornering forces

[Darkness]

The advantage from climbing over the bike to drag knee, elbow sliders and helmet on the ground is that the combined centre of gravity of the bike and rider moves inboard from the centre line of the bike.
The physics of the corner is based on that combined centre of gravity, so by hanging off the side, the bike is behaving as though it were more banked over than it actually is.
That gives less risk of running off the edge of the tyres.
It’s also giving the suspension more chance to move with bumps: think how the forks and steering react to a bump when leaning at 66 degrees!

[Darkness]

An interesting article.

https://lifeatlean.com/how-to-turn-a-motorcycle/

[Luddite]

Originally Posted by 350TSS

Re the above I am still troubled by the TF diagram. I am not an engineer nor am I a mathematician (O level just 51 years ago).
What caused me to be troubled was the news that Marc Marquez has been recorded as taking a corner with a record 66 degrees of lean and I wondered what the cornering force could be, so I thought I would try to calculate it. Would the force be higher or lower once 45 degrees of lean was passed?
As I thought about it further I was also worried by the statement that the diagram only worked for 45 degrees. One should be able to calculate at 5 degree increments and plot a graph.

I didn't expect to be given homework when I signed up to UKMOC, Rich!

Just to put calculations to Darkness's detailed reply; you can still calculate the various forces involved at different lean angles using trigonometry.



Side 'a' represents the weight of bike and rider
Side 'b' represents the lateral cornering force
Side 'c' represents the resultant force acting on the suspension.

The angle theta represents 90° minus the lean angle.

Using trig:

sin theta = a/c
cos theta = b/c

We know three elements of the triangle:

• 'a' = 1
• The angle between a and b is 90°
• The angle theta is 24° (i.e. 90° - 66°)

So, as sin 24° is 0.4067 then 'c' = 1/sin theta =1/0.4067 = 2.4588

And as cos 24° is 0.9135 then 'b' = c x cos theta = 2.4588 x 0.9135 = 2.2462

So the lateral cornering force = 2.2462g and the effective load on the suspension is 2.4588g.

The simple way to find the cornering force is just to look up the tan of the lean angle i.e. the tan of 66° is 2.246 and this is effectively what this graph shows (again, courtesy of Tony Foale)



I'm just off now for a couple of Anadin

[350TSS]

Thanks guys - I think I now understand

"It’s also giving the suspension more chance to move with bumps: think how the forks and steering react to a bump when leaning at 66 degrees!"
I do not think the suspension works much if at all after 45 degrees - any bump is a vertical deflection of the forks/frame because the fork sliders /rear shock would not slide

[Luddite]

Originally Posted by 350TSS

I do not think the suspension works much if at all after 45 degrees - any bump is a vertical deflection of the forks/frame because the fork sliders /rear shock would not slide

Got some more aspirins handy? Perhaps unsurprisingly this situation is also covered in Tony Foale's book.

Hitting a bump at a 45° lean angle creates two equal forces; one in line with suspension movement and the other at right angles to it. These forces will each be 71% of the vertical bump force.

I don't want to clutter up your excellent thread with esoteric calculations and diagrams, so I've sent you a PM with some more extracts that you can read at your leisure. Just don't blame me if you get a headache!

[Darkness]

Originally Posted by 350TSS

Thanks guys - I think I now understand

"It’s also giving the suspension more chance to move with bumps: think how the forks and steering react to a bump when leaning at 66 degrees!"
I do not think the suspension works much if at all after 45 degrees - any bump is a vertical deflection of the forks/frame because the fork sliders /rear shock would not slide

It is easier to visualise if you think of the vertical axis through the centre of the bike and rider staying vertical as you begin to corner, but the ground tilts beneath you. At 66 degrees of tilt you need pretty huge suspension movement for a small bump if the bike is to stay on line, but that movement reduces a lot in practise if the wheel can kick sideways a little. That’s changing the lean angle though, and there’s a risk of the tyre losing grip as you come off the bump, or as the wheel feels it, someone whips the ground out from underneath it.

Lighter wheels and tyres help massively, as does reduction in unsprung weight, then weight reduction generally.

As the rider can absorb some of the bumps by lifting off the saddle and flexing legs and arms the rider’s weight is less significant, but probably still better to lay off eating all of the pies!

[slob]

Posted to clean up Richard's (350TSS) rebuild thread

...so apologies if it seems to start in the middle of nowhere


and just for good measure this is a quick and educational video on cornering technique
https://www.youtube.com/watch?v=ZJf8qiy-dKM

[Luddite]

As we now have a new dedicated, at Richard's suggestion, I have attached the extracts I sent him earlier, which suspension nerds may find interesting.







I'd also recommend anyone with more than a passing interest in suspension and handling to visit Tony Foale's website https://motochassis.com/

[Darkness]

Thanks Rob.

[Mr Gazza]

Jeez! You guys should get out more!.... The thread I didn't start!

All this maths and conjecture...Just get a tube with a ball in it and gaffer tape it across your tank, but don't look down at it when you're chucking it through some bends. Make a film of it so we can all see.

[slob]

...or in the 21st century, use an app that logs your phone’s accelerometer.

ps I did edit the apparent op to explain, since at creation, my post was the one with the last timestamp, so was at the end of the thread

[Darren69]

You've discussed the theory and all that but for the practical 66 deg is pretty bloody impressive and pushing the laws of physics even a bit too i think!

[Mr Gazza]

Originally Posted by slob

...or in the 21st century, use an app that logs your phone’s accelerometer.

ps I did edit the apparent op to explain, since at creation, my post was the one with the last timestamp, so was at the end of the thread

No worries Rob, I see what you did. Just didn't expect this from a throwaway comment!

...And wow! Phones have accelerometers?? Thinking on, a heavy-ish bead on a piece of cotton sellotaped on a mirror, might do the trick? But still dangerous to try and look at it too much in a bend.

[mickj]

I suspect none of this matters to anyone who has chicken strips on their tyres

[350TSS]

I think this is a bit more than 66 degrees but he did not part company with the bike