Lean angle

[Dendrob]

never really put much thought into it myself

Ha ha. Just got that (it's early).

[freeridenick]

Thanks guys for the input.

What are your thoughts on the other part of my op? How a tyre of a certain width demands a certain lean angle and yet the front and rear tyres are substantially different widths. What is happening here?

I don't think they need different lean angles, the fact they're different widths means they need different profiles to track properly at the same lean angle.

The reason the front doesn't scrub to the edges is that most folks, me included, aren't as happy on the brakes as they are on the power. To get the front scrubbed the tyre needs to be squashed into the tarmac when the bike's leant over. Which means braking hard and turning hard.

As soon as the weight comes off the front the profile recovers and the edges lose contact, which happens more when you get on the power. So at max lean, unless you're carrying loads of corner speed, the there's not enough weight on the front to get the edges in contact. The rear squashes when the power comes in and gets closer to the tarmac on edit.

Tyre type makes a huge difference with softer sidewalls on sticky tyres making it easier to get the edges dug in.

[Dendrob]

Thanks guys for the input.

What are your thoughts on the other part of my op? How a tyre of a certain width demands a certain lean angle and yet the front and rear tyres are substantially different widths. What is happening here?

I don't think they need different lean angles, the fact they're different widths means they need different profiles to track properly at the same lean angle.

The reason the front doesn't scrub to the edges is that most folks, me included, aren't as happy on the brakes as they are on the power. To get the front scrubbed the tyre needs to be squashed into the tarmac when the bike's leant over. Which means braking hard and turning hard.

As soon as the weight comes off the front the profile recovers and the edges lose contact, which happens more when you get on the power. So at max lean, unless you're carrying loads of corner speed, the there's not enough weight on the front to get the edges in contact. The rear squashes when the power comes in and gets closer to the tarmac on edit.

Tyre type makes a huge difference with softer sidewalls on sticky tyres making it easier to get the edges dug in.

Brilliant reply. I'm grateful you passed that knowledge on. It makes a lot of sense and answers the bulk of my question. It certainly explains personal things. I love the twisties, I ride for the twisties, but I'm an old school smoothie so I am very light on the brakes. As bikes have got more powerful I have learned to trail brake a lot deeper into corners than I ever used to, but nowhere near as much as a track rider I guess.

If you care to expand on the differing tyre width thing I'm all ears.

Thanks.

[freeridenick]

Hard to describe what I'm thinking with the tyre width thing but if both were the same profile (radius) the rear would never get near the edges.

Try taking a ball and mark a point. Put that ball down so the point is at the bottom and roll it to one side to 45 degrees and mark it so you can see where the contract point is. Now roll it to 90 degrees and see what happens to the second mark - it loses contact.

If you apply this to a bike. If both were the same size there'd be no problem with contact but we want bikes that are fast turning stable and have loads of grip. Same size tyres don't achieve that. The front tyre is narrower to make it turn more easily, the rear is wider for more grip. If the smaller front had the same radius as the rear it would lose contact as with the ball above. So it has a smaller radius to make sure it stays in contact as the rear gets closer to its edge.

At least it makes sense to me.

[Dendrob]

Hard to describe what I'm thinking with the tyre width thing but if both were the same profile (radius) the rear would never get near the edges.

.....

Yip that seems to be true. Almost. It's complicated though, by the fact that there's a pivot between them in the form of the steering head. And even more complicated because the damn thing is set at an angle (the rake). How does that impact upon what you've put forward?

[Dendrob]

.... If both were the same size there'd be no problem with contact but we want bikes that are fast turning stable and have loads of grip. Same size tyres don't achieve that. The front tyre is narrower to make it turn more easily, the rear is wider for more grip. If the smaller front had the same radius as the rear it would lose contact as with the ball above. So it has a smaller radius to make sure it stays in contact as the rear gets closer to its edge.

At least it makes sense to me.

Yes, I can see what you're saying. It makes a lot of sense! Maybe what I've just said above amends it slightly, but broadly I bet you're right.

[popkat]

Here's an example the old Michelin pilot power tyres would reach the edges front and rear at about the same time, a Pirelli Diablo you will struggle even on track to get right to the very edge of the front. It's all about the profile the manufacturer chooses for their tyre, Pub bragging means many will go for the one that gets closer to the edge but is it as good ?, on the road maybe it's fine but on the track not so good as you may run out of front tyre earlier than you'd like, it's much harder to save the front if it goes.

Contact patch.. when you reach the edge of the tyre that is just the edge of the contact patch, you still have a good area of tyre on the tarmac, imagine a long oval and that's your contact patch, this changes with different tyre profiles and makes of tyre, a 190/55 has a larger contact patch than a 190/50 the profile is steeper so there's more rubber available at the edges. Now when your rear tyre gets to the edge you still have lean left, if your front tyre isn't there yet that's good as you have plenty left, if your front is there at the same time as the rear the more you lean the less rubber in contact with the road as you lean more, not so good.. So forget pub bragging rights and have a front tyre that grips well and keeps plenty on the road, the rear is easier to handle if it slides a little.


.

[Dendrob]

Here's an example the old Michelin pilot power tyres would reach the edges front and rear at about the same time, a Pirelli Diablo you will struggle even on track to get right to the very edge of the front. It's all about the profile the manufacturer chooses for their tyre, Pub bragging means many will go for the one that gets closer to the edge but is it as good ?, on the road maybe it's fine but on the track not so good as you may run out of front tyre earlier than you'd like, it's much harder to save the front if it goes.

Contact patch.. when you reach the edge of the tyre that is just the edge of the contact patch, you still have a good area of tyre on the tarmac, imagine a long oval and that's your contact patch, this changes with different tyre profiles and makes of tyre, a 190/55 has a larger contact patch than a 190/50 the profile is steeper so there's more rubber available at the edges. Now when your rear tyre gets to the edge you still have lean left, if your front tyre isn't there yet that's good as you have plenty left, if your front is there at the same time as the rear the more you lean the less rubber in contact with the road as you lean more, not so good.. So forget pub bragging rights and have a front tyre that grips well and keeps plenty on the road, the rear is easier to handle if it slides a little.


.

The bt45's I ran on my old Beemer have an aspect ratio much nearer parity than modern profiles. They looked skinny as hell but you could carry a fair bit of corner speed. What you say about how the "steeper" radius of the profile helps provide a decent contact makes sense. Might go towards explaining how the skinny looking tyre sticks.

[freeridenick]

Hard to describe what I'm thinking with the tyre width thing but if both were the same profile (radius) the rear would never get near the edges.

.....

Yip that seems to be true. Almost. It's complicated though, by the fact that there's a pivot between them in the form of the steering head. And even more complicated because the damn thing is set at an angle (the rake). How does that impact upon what you've put forward?

I don't know really but I don't think the rake has much impact. The tyre is circular and the lean angle would always be perpendicular to the road surface.

The steering pivot would make a difference but I think that's into the realms of maths I'm not comfortable with - too many factors. At some point front and rear tyres could well be at different lean angles relative to each other but I don't think it's enough to leave different chicken stripes.

I think Popkat's pretty much nailed it.

[Dendrob]

Hard to describe what I'm thinking with the tyre width thing but if both were the same profile (radius) the rear would never get near the edges.

.....

Yip that seems to be true. Almost. It's complicated though, by the fact that there's a pivot between them in the form of the steering head. And even more complicated because the damn thing is set at an angle (the rake). How does that impact upon what you've put forward?

I don't know really but I don't think the rake has much impact. The tyre is circular and the lean angle would always be perpendicular to the road surface.

The steering pivot would make a difference but I think that's into the realms of maths I'm not comfortable with - too many factors. At some point front and rear tyres could well be at different lean angles relative to each other but I don't think it's enough to leave different chicken stripes.

I think Popkat's pretty much nailed it.

I think he probably has. I'm glad I put the post up as I've learnt along the way.

To think about the rake angle effect imagine the extremes. 0 degrees rake and 90 degrees rake.

[Stormin Ben]

Don't forget that in a corner the rear tyre also has to cope with the application of power as well as cornering force.
This extra load causes the tyre to distort more which also contributed to the amount of chicken strip.

This is borne out (maybe) by the fact that on track, where I was leading the front tyre up with pretty hard braking whilst leant over, the tyre was scrubbed right to the edge and nicely bobbled too

[Dendrob]

Don't forget that in a corner the rear tyre also has to cope with the application of power as well as cornering force.
This extra load causes the tyre to distort more which also contributed to the amount of chicken strip.

This is borne out (maybe) by the fact that on track, where I was leading the front tyre up with pretty hard braking whilst leant over, the tyre was scrubbed right to the edge and nicely bobbled too

True. I think that was pretty much freeridenick's point too.

Then there's load transfer. I like accelerating but I don't brake heavily at all. That would also go towards explaining perhaps why I have scrubbing to the edge on the rear but not the front.

Thanks for your input. It's all helping to build up a reasonable picture of what probably happens. Cheers.