Lean Angle and Contact Patch

[DucDave]

Read something interesting today. Pretty obvious but not what most people believe.

The fact is, the greater the lean angle the GREATER the contact patch. (Up to the point when you run out of tire....)

Most folks, (myself included), operate on the assumption that we hang off to keep the bike more upright which increases contact patch. Not so. The reason we try and keep the bike more upright is to reduce the side loading forces. The reason that we can't grap gobs of throttle in full lean, even though thats when we have the LARGEST contact patch, is because we are using that patch for lateral traction...

I found this interesting....
...Keith Code's article in this months Motorcyclist has more...

[Kurlon]

Another random data point: According to Sava tires, you get more traction as you decrease your contact patch, as you increase the point loading. Sava actually tells you to UP the pressure in the rain, or for cold tracks, to decrease your contact patch and up the point loading (their words) and I'll be damned if it doesn't work. Playing with Dunlops on concrete it appears they respond similarly.

[cdovego]

Another random data point: According to Sava tires, you get more traction as you decrease your contact patch, as you increase the point loading. Sava actually tells you to UP the pressure in the rain, or for cold tracks, to decrease your contact patch and up the point loading (their words) and I'll be damned if it doesn't work. Playing with Dunlops on concrete it appears they respond similarly.

+1 I've found that higher air pressure on the street in the rain provides better traction.

[Paul_E_D]

We all raise air pressure for the rain. My sources tell me it's really just the keep the sipe open. Too little pressure and they fold closed

[DucDave]

...also, i believe that a slightly 'narrower' footprint contributes to a better avoidance of hydroplaning...

[Currently]

Same thing in snow ... put 50 psi in your snow tires and go try the difference.

Learned that from an old timer when called me ignorant for reducing air pressure in my tires to get unstuck ... he was right.

[a13x]

I avoid Keith Code's ramblings like the plague.

[DucDave]

I avoid Keith Code's ramblings like the plague.

....for those who already know everything he, (or anyone else), might have to contribute, that's understandable

for me, I'm willing to listen to anyone that has proven to know more than me...and that's a pretty broad freeking group! (I even listen to you Alex!)

[a13x]

bwahah I wish! I ask more questions about riding than you could imagine. Constant work in progress man, constant!

I just avoid Keith Code's particular brand of riding advice......

[The Snowman]

Wow, all this is good to know, since the Si has 45 series sport tires and I'll need to use them for the snow.

Should be interesting.

On the bike front, the information above will be particularly helpful when I finally do a wet track day. I lucked out this past week, riding on nothing but dry pavement.

[union]

Read something interesting today. Pretty obvious but not what most people believe.

The fact is, the greater the lean angle the GREATER the contact patch. (Up to the point when you run out of tire....)

Most folks, (myself included), operate on the assumption that we hang off to keep the bike more upright which increases contact patch. Not so. The reason we try and keep the bike more upright is to reduce the side loading forces. The reason that we can't grap gobs of throttle in full lean, even though thats when we have the LARGEST contact patch, is because we are using that patch for lateral traction...

I found this interesting....
...Keith Code's article in this months Motorcyclist has more...

Makes sense about the contact patch. I cant imagine it getting smaller until youre over the edge of the tire.

I did learn the hard way what happens when youre leaned over, accelerating and trying to turn at the same time. It wasnt that much fun.

[TTD]

you get more traction as you decrease your contact patch, as you increase the point loading.

Yes, I can understand that if you apply 300 pounds of pressure on a 1 inch contact patch, that means 300psi. If the contact patch is 4 square inches, then it is only 75psi. (I think it works this way, right?)

But .... I'd question this statement as it relates to bikes.

One reason you "settle" the front end before braking hard is to get the front tire to squat... thus putting more rubber on the ground before you load it.

I'd be interested to see real world tests or data on this?

[LiononaLeash]

(nerd mode engage)

Thinking in principle way back when...


Holding power does not change with surface area with respect to non deforming, non-adhering surfaces coming together with the same force(think baby smooth and flat stone blocks).

But, holding power does change with surface area when adhering surfaces get pressed together with the same force(up to an ultimate point, of course). The more sticky area, the better it holds(Think double sided tape).


"Settling" the front is basically increasing the force that presses the surfaces together to increase the holding power, even if you didn't get any increase in contact area(which we do anyway), you will get more holding power in both cases of sticky and non-sticky surfaces. But, we all know that stone tires don't grip as well as the rubber ones.

I can't quote the source of this information other than physics class... a long time ago!

(nerd mode disengage)

[Paul_E_D]

Ya, don't go pumping your DOTs up to 50 lbs. You'l have a tiny contact patch and NO traction! So much for that one...

[Kurlon]

One reason you "settle" the front end before braking hard is to get the front tire to squat... thus putting more rubber on the ground before you load it.

Or it could be to preload the suspension so it's primed to act should the front slip? : )

[Paul_E_D]

I would think force would be more important than contact patch area in this equation, no?

[The Crashing Tomato]

Kinda what Kurlon said but a bit more violent ...

[LiononaLeash]

I would think force would be more important than contact patch area in this equation, no?

Yeah, that's true for the non-adhering and non-deforming surfaces being forced together. If the surfaces are not sticky, then the contacting force is more important(to a limit). When they are sticky, surface area accounts for a lot of holding power. Obviously with tires, both force and area account for holding adhesion(perhaps more area allows more force to be applied before things deform beyond what's practical?). I guess its kinda hard to determine which one in a specific case adds more friction. The factors for total adhesion are always changing when we ride I suppose.

Some limits for example, might be if you have too little surface area, the rim starts to smoosh and cut through the tire as more and more force is applied(you get deformation of the materials and the maths gets weird really fast, don't ask me... I aint that smart hehe). I know you couldn't bring a truck to a stop very quickly with 1 square inch of rubber on the road, no matter how hard you press that little piece of rubber to the pavement. Both force and area have to play into the total available adhesion.

I generally don't think like this when I ride my bike hehe. my head hurts.

[Ken C]

From my understanding:

Contact patch size does not change significantly with lean angle. The same area of contact will be very similar between, say, 20 degrees of lean and 35 degrees of lean, as long as you don't run to the edge of the tire (which you start to at 40 degrees or so). Of course this all depends on the actual tire's construction and profile.

It's true that the "coeficient of friction" is greater with a smaller contact patch, but as Lion says, too small an area will tear and overheat, reducing grip.

Load is what increases grip, not increased contact area, although under hard braking a larger contact patch prevents overheating of the rubber.

Side forces do not change when you hang off the bike, even though the bike is more upright. You still need the same side force to get around the corner. The only thing that reduces side force is speed or turn radius.

However, the force and friction from rolling on the smaller diameter part of the tire is reduced a bit when you keep the bike more upright. (Camber thrust)

So, the reason to hang off is to: 1.keep hard parts from dragging 2. keep the bike upright so that you keep the contact area as far away from the edge as possible to prevent "running off the edge" 3. reduce the drag that occurs when you ask the tires to roll on the smaller outside part of the tire 4. to use body weight to influence control.

[Jaynnus]

This is why I love Ken....a plethora of information formatted/presented in a way that a physics dummy like me can understand.

[Karaya One]

From my understanding:

Contact patch size does not change significantly with lean angle.

Depends on the SHAPE of the casing. This is how 16.5" and now 16" race tires evolved. You will see a change in how the tire reacts to lean angle changes as it tries to conform to the pavement.

That is where the C3M race tires show how they work.

There are three C's involved - casing, compound and construction. Each one of these has a direct effect on how the tire works, reacts, slip-angle, etc.

[Ken C]

From my understanding:
Of course this all depends on the actual tire's construction and profile.

Like I said.

[Nazo]

Ken,
Want a job as a my chief racing engineer next season? lol.
This is the knowledge and insight I need to put it all together out there.
Reading advanced books that use a lot of physics can sometimes have me contradicting myself in what I think I need to do on the track.

So much to still learn.......

[Daytona440]

This is why I love Ken....a plethora of information formatted/presented in a way that a physics dummy like me can understand.

I thought it was cause he's DEAD SEXY!?!?

[Karaya One]

Like I said.

If you say so....