How much lean angle have I got?

[Ocean1]

And the lean angle!

Y'know, that might well explain why some of our more well endowed members report more difficulty with LH or RH corners.

You, dude, dress left or right?

[Badjelly]

You, dude, dress left or right?

I lean to the right.

[Mikkel]

Firstly, a lot of modern tyres do indeed have stickier compounds on the sides.
And secondly the sectional profile of most tyres is not a perfect arc, in fact some have a pronounced triangular section. So there is likely to be both a significantly larger contact patch and a higher COF at the designed optimum angle.

First of all - there's only two things that determine the size of the contact patch - tyre profile is not one of them.

To determine the size of your contact patches in square inches you take the weight, in pounds, carried by each tyre in any given circumstance and divide it by the tyre pressure in PSI. It is that simple.

Yes, if the compound varies across the width of the tyre, indeed the coefficient of friction (both kinetic and static) will vary with lean angle. I just said that let's consider it constant in order to determine the impact of lean up the amount of lateral force the tyre can carry.

[Ocean1]

First of all - there's only two things that determine the size of the contact patch - tyre profile is not one of them.

To determine the size of your contact patches in square inches you take the weight, in pounds, carried by each tyre in any given circumstance and divide it by the tyre pressure in PSI. It is that simple.

That would certainly be the case if tyres were completely non-rigid, a completely non-structural pressure barrier.

But they aint.

[Kickaha]

First of all - there's only two things that determine the size of the contact patch - tyre profile is not one of them.

Are you saying for a given rim size the profile of the tyre won't alter how much contact patch there is? eg from a 60 to a 70

[Oldfulla]

Oldfulla - if you really want to know how far you can lean, then you need to take it to and just past the very limits a few times, like Mr Rossi did. Once you've learned what it feels like when you've gone just past the limits, then you don't have to crash so often.
Seriously, if you're not prepared to crash while exploring the limits of your bike and your cornering abilities, then I suggest you stick with being contented with tyres that have no 'chicken' strips (or, as I like to call them, "margins of error").

thanks for the reply.
I dont mind exploring the limits of my bike and tipping off to find them out, it isnt the falling off that worries me so much. its the sudden stop or hitting something hard at the end of the fall. Also I really really dont want to damage my bike, that is the biggest factor that has held me back.
maybe with some more track time in the future and some money I can really push things.

[Mikkel]

That would certainly be the case if tyres were completely non-rigid, a completely non-structural pressure barrier.

But they aint.

Of course - that is indeed the ideal world I am describing. However, it's still a very fair approximation to what you'd see in the real world. Tyre pressure and weight are the two main factors that determine the size of the contact patch.

Are you saying for a given rim size the profile of the tyre won't alter how much contact patch there is? eg from a 60 to a 70

Ideally it wouldn't. I am not saying you wouldn't be able to see a difference between two tyres - real life is incredibly complicated if you start going into detail

If you want to go in detail you have to consider:

Softness of the tyre compound.
Softness of the surface on which the bike is situated.
Temperature.
Humidity.
Topology of the surface on which the bike is situated.
Local variations in the gravitational acceleration due to variations in the composition of the earths mantle.

And the list goes on...

To retain the KISS principle I postulate that tyre pressure and weight supported by the tyre are the two only important factors when determining the size of the contact patch. (But ultimately it doesn't matter - calculating the size and shape of the contact patches for a bike in motion is not currently doable... and let's face it, if the bike isn't moving who gives a fuck anyway?)

[Mental Trousers]

thanks for the reply.
I dont mind exploring the limits of my bike and tipping off to find them out, it isnt the falling off that worries me so much. its the sudden stop or hitting something hard at the end of the fall. Also I really really dont want to damage my bike, that is the biggest factor that has held me back.
maybe with some more track time in the future and some money I can really push things.

Best way to explore the limits of your tyres is to either take it to a track or go find a carpark and start going around in circles. You'll either scrape shit on the ground or find the limits of the tyres.

I think you've guessed by now that you can safely ignore the engineering geeks cos even if you can figure out what they're saying they have conflicting views anyway.

And for the engineering geeks, suspension is less efficient at larger lean angles, a bike can only lean so far so getting the riders weight inside the line of the bike lets you go around corners quicker and the more upright a bike is the less likely a momentary loss of traction is going to spit the rider off.

[90s]

Best way to explore the limits of your tyres is to either take it to a track or go find a carpark and start going around in circles. You'll either scrape shit on the ground or find the limits of the tyres.

+1 Yep. I don't want to remember a big "thump" after someone sliding towards me as I come around a corner because they have been playing skidmark on the public roads trying to find the limits of tyre grip thanks.

There is only one way to find the ultimate limit and that is to push until you crash. But whilst you learn on a track what it feels like, on lumpy tarmac on a public road you might find it is not quite the same at all.

Best way to explore the limits of your tyres is to either take it to a track or go find a carpark and start going around in circles. You'll either scrape shit on the ground or find the limits of the tyres.

I did do that as a teenager (as teenagers do) in a closed school roadway with a roundabout (a nice little track set-up really) at a weekend. The result after leaning and leaning was BANG with me on my bum and the rear wheel of the bike spinning madly and oil & petrol leaking out of it having scraped the mint red plastic work.
Obviously there was some red damage on me too.
I wouldn't recommend it really, esp. as it was Dad's bike.

[Ocean1]

That would certainly be the case if tyres were completely non-rigid, a completely non-structural pressure barrier.

But they aint.

Of course - that is indeed the ideal world I am describing. However, it's still a very fair approximation to what you'd see in the real world. Tyre pressure and weight are the two main factors that determine the size of the contact patch.

Some in the industry seem to have discovered another factor...

"The Storm ST is the first tire to include Avon’s new "Reactive Footprint" technology. This technology marries Avon’s unique variable belt density carcass with Lifetime Profile Engineering to produce a footprint which changes size and shape, depending on the bike’s lean angle, for the full life of the tire.

The result is a contact patch that grows as the bike leans, giving more grip in corners while minimizing wear rates when travelling in a straight line."

Interesting... http://books.google.co.nz/books?id=a...&hl=en#PPP1,M1

[Ocean1]

Best way to explore the limits of your tyres is to either take it to a track or go find a carpark and start going around in circles. You'll either scrape shit on the ground or find the limits of the tyres.

I agree, in fact I believe the only way is to repeatedly crash on a range of surfaces, at different speeds, pressures etc etc.

Not keen eh.

I think you've guessed by now that you can safely ignore the engineering geeks cos even if you can figure out what they're saying they have conflicting views anyway.

And for the engineering geeks, suspension is less efficient at larger lean angles, a bike can only lean so far so getting the riders weight inside the line of the bike lets you go around corners quicker and the more upright a bike is the less likely a momentary loss of traction is going to spit the rider off.

Ignore away dude. The function of discussions like this have little to do with actual riding, it’s about better understanding our wee bit of the world, and sometimes a new way of doing things transpires which really does make a difference in the real world.

Edit: and thanks for the last bit there.

[Mikkel]

Some in the industry seem to have discovered another factor...

"The Storm ST is the first tire to include Avon’s new "Reactive Footprint" technology. This technology marries Avon’s unique variable belt density carcass with Lifetime Profile Engineering to produce a footprint which changes size and shape, depending on the bike’s lean angle, for the full life of the tire.

The result is a contact patch that grows as the bike leans, giving more grip in corners while minimizing wear rates when travelling in a straight line."

Interesting... http://books.google.co.nz/books?id=a...&hl=en#PPP1,M1

Very interesting.

However, it is not the size of the contact patch that determines what friction you have available! That depends only on the normal force and the coefficient of friction.

Generally the size contact patch - but not the shape - is proportional to the amount of normal force (weight on the tyre) and inversely proportional to the tyre pressure.

As the attached image illustrates, the contact patch will change with lean angle - but whether it just changes shape or it actually changes size is a bit hard to tell. As we have established above the softness of the tyre compound may have *some* influence upon the size of the contact patch - so yes if you change the compound across the tyre profile you may observe slight variations of the size of the contact patch depending upon the lean angle.

I won't question that you can design a tyre that will have more grip at lean than in the upright position. However I would argue that it is a matter of variations in the coefficient of friction - not because the contact patch changes.

Also, I'd always be rather skeptic of marketing hype if you want to understand basic principles.

Ignore away dude. The function of discussions like this have little to do with actual riding, it’s about better understanding our wee bit of the world, and sometimes a new way of doing things transpires which really does make a difference in the real world.

Indeed - this discussion doesn't make any difference in how well we ride our bikes. It probably won't have any effect whatsoever - I still find it interesting to discuss such matters though.

Thinking is hard though and some people generally frown upon it. That's ok, we don't force anyone to participate.

[Badjelly]

However, it is not the size of the contact patch that determines what friction you have available! That depends only on the normal force and the coefficient of friction.

So that's it, then. All those wide tyres that people cram onto bikes (and cars) don't make a damn bit of difference. Someone better tell the MotoGP tyre designers.

Rubber tyres are complicated beasts, and their performance is not adequately described by a single number called "coefficient of friction". Having said that, I must admit I don't understand why wider tyres seem to be better, especially since (as you've pointed) they don't necessarily result in a large contact patch than narrow tyres. But it does seem to be true that wider tyres give better performance than narrow ones, within limits.

[Badjelly]

Ignore away dude. The function of discussions like this have little to do with actual riding, it’s about better understanding our wee bit of the world, and sometimes a new way of doing things transpires which really does make a difference in the real world.

Indeed - this discussion doesn't make any difference in how well we ride our bikes. It probably won't have any effect whatsoever - I still find it interesting to discuss such matters though.
Thinking is hard though and some people generally frown upon it. That's ok, we don't force anyone to participate.

Hear hear.

[Mikkel]

So that's it, then. All those wide tyres that people cram onto bikes (and cars) don't make a damn bit of difference. Someone better tell the MotoGP tyre designers.

Rubber tyres are complicated beasts, and their performance is not adequately described by a single number called "coefficient of friction". Having said that, I must admit I don't understand why wider tyres seem to be better, especially since (as you've pointed) they don't necessarily result in a large contact patch than narrow tyres. But it does seem to be true that wider tyres give better performance than narrow ones, within limits.

There are heaps of advantages from using wider tyres. One of the main things is heat dissipation - the same bit of rubber doesn't get "used as much".

Also, stability during high lateral forces.

A wider contact patch also means that you use more of the road surface...

This is especially true for cars. Motorcycles are slightly different of course, but some of the same things are applicable.