Wet/dry traction comparisons

[CookMySock]

anecdotally, I heard (one of) the pilot powers is the only tyre that will wheelie in the wet.

Michelin is been the uber elite road tyre since ages ago. We were putting them on our performance citroens (digressive suspension!) thirty years ago - any other tyre felt like meatballs. It was funny pulling out and passing V8's with our 2.2 litre cars mid-corner - them to blow us off on the straights, and we toast them again in the bendies - never to be seen again.

Michelin FTW!

Steve

[Sketchy_Racer]

Ok putting it in a racing situation, I only lost 3 seconds a lap when it was pissing wet than when it was dry around manfeild on the 250. There is more grip than many would believe in the wet.

Wet - http://motorsport.sportimage.co.nz/m...geViewsIndex=1
Dry - http://motorsport.sportimage.co.nz/m...g2_itemId=9817

Not a huge amount of difference really!

[beyond]

Ok putting it in a racing situation, I only lost 3 seconds a lap when it was pissing wet than when it was dry around manfeild on the 250. There is more grip than many would believe in the wet.

Wet - http://motorsport.sportimage.co.nz/m...geViewsIndex=1
Dry - http://motorsport.sportimage.co.nz/m...g2_itemId=9817

Not a huge amount of difference really!

That's pretty bloody good actually
Won't find me getting my 1400 over like that in the wet.

[FROSTY:Me]

Don't do a lot of rocket science myself.
What I do know is the 125gp guys use double thickness knee scrapers when wet racing. That limits the dangle angle

[Badjelly]

But I can't see how just lean-angle alone dictates maximum parameters. Sure, speed must also become a factor at some point?

This is the sort of question for which you can either have a simple, but approximate, answer or a more exact, but much more complicated answer.

The simple answer (the only one I know) can be obtained if you make a few assumptions/approximations:

• Road is level.
• Rider keeps his/her centre of gravity in the plane of the bike.
• Ignore "gyroscopic" forces, i.e. those required to change the direction of the axis of rotation. I think this should be OK except for really tight corners.
• Assume constant speed and constant turning radius, i.e. consider that you've "settled in" to the corner.
• Tyres are pretty narrow, so the contact patch is in the plane of the bike. (I think this might be the approximation that falls down first.)

Then the lean angle is given by a simple formula

tan(angle) = (lateral acceleration)/(gravity)

where "tan" stands for the mathematical tangent function.

You want proof? Geez, you don't ask for much do you? Go ask a real engineer like ocean1. It's simple trigonometry and I'm sure there are diagrams showing the balance of forces on the WWW somewhere.

This means that if you're going round a corner with a lateral acceleration of 1 g, then your lean angle will have to be 45 deg. Or conversely, if you're going round a corner leaning the bike at 45 deg (no leaning off the bike, mind you) then your acceleration will be 1 g. For 0.5 g, the lean angle is 26.6 deg (not 22.5 deg, because the tangent function isn't a straight line).

How does speed come into this? Well, for a corner of a given radius, the faster you go, the higher the lateral acceleration required to hold your line, so the more you have to lean. Or for a given speed, if you want to tighten your line you have to lean more. But speed as such doesn't enter into the formula.

I said this was simple but approximate. How approximate? Like I said, the assumption that the tyre contact patch is in the plane of the bike isn't very good at high lean angles on a modern bike with wide tyres. And neither is the assumption that the rider keeps his CoG in the plane of the bike. Still when you see Casey Stoner going round a corner leaning at (what?) 60 deg and hanging off the inside, you'd have to think he's achieving lateral accelerations somewhat more than 1.0 g. Which is pretty amazing to mere mortals like me, though not impressive compared with a single seater racing car which, due to its downforce, can corner at 3 g or something.

What angles do I corner at? I have no idea, but my chicken strips suggest I seldom get beyond 30 deg.

[Badjelly]

It's simple trigonometry and I'm sure there are diagrams showing the balance of forces on the WWW somewhere.

You'd think so, wouldn't you?

I finally found one on this page

http://tripatlas.com/Bicycle_and_motorcycle_dynamics

See the section on "TURNING", about halfway down.

The circle thingy towards the top, left-hand corner is the centre of mass of the bike+rider. The point in the middle of the graph is the centre of the tyre contact patch. Unfortunately, just to confuse you, the angle, theta, they've indicated is 90 deg minus what people usually call the lean angle.

[vgcspares]

Course in amongst all the trigonometry there's also the coefficient of friction to consider (loads bigger for soft sticky tires)

[Badjelly]

Course in amongst all the trigonometry there's also the coefficient of friction to consider (loads bigger for soft sticky tires)

The way the coefficient of friction fits in (according to the simple, approximate view of things) is that it determines your maximum lateral acceleration and therefore it determines the maximum lean angle you can support before you start to slide out.

So what do you think is the coefficient of friction of a soft sticky tyre? I'd guess 1.2 or 1.3. I'd be very surprised if even a MotoGP qualifying tyre could get anywhere near 1.5.

[dpex]

I've done about 80Ks today, slowly scrubbing in the front Pilot Power. Despite my lack of significant experience I can say I can feel a significant difference in handling. Can't wait to get the back one on and scrubbed.

[racefactory]

Ok putting it in a racing situation, I only lost 3 seconds a lap when it was pissing wet than when it was dry around manfeild on the 250. There is more grip than many would believe in the wet.

Wet - http://motorsport.sportimage.co.nz/m...geViewsIndex=1
Dry - http://motorsport.sportimage.co.nz/m...g2_itemId=9817

Not a huge amount of difference really!

Wow some excellent posts here!!! Really enjoyed the read.

sketchy racer.. that's awesome... i guess it's not about how far you can lean in the wet (on a road bike clearances) but more about how much extra force you can put through the tyre while cranked over (acceleration and braking in turn) before it starts to slide as the coefficient is lowered.

[Flip]

Did an advanced riding skills course in the wet and some of the sports bikes were doing stoppies no problems on the wet track. My bike not do stoppies, do good bulldozer. The thing I picked up is there is heaps more grip than I expected but the effect of diesel or other crap on the road is a lot more noticeable. Also the bike locks up and skids quicker-easier by which I mean there was less notice it was going to happen and it was harder to release and re-apply the brakes. Before you ask yes a harley rider went on a skills course. Good reading the data.

[cowpoos]

My thoughts on this is that you guys are all reading to much info which isn't really going to compensate for lack of skill/experience. You just need to start doing miles in the wet.

You just can't rely on a mathmatical figure you read. its much more a case of having good feel for your bike in the wet. using comon sense to where you place your wheels,where you look. setting your speed correctly for the corners. relaxing...never rely on what someone tells you,or something you have read.

I heard (one of) the pilot powers is the only tyre that will wheelie in the wet.

nah you can do a wheelie on any tyre in the wet...I've done them on screwed slicks in the wet.
And rolling stoppies on a dirtbike on wet paddocks in the pissing rain.

Having good feel...knowing your bike well...having a couple of clues...you can create grip over and above what other people can find or believe they can find.

[sharky]

Well put Cowpoos. - I don't think people will be whipping out their protractors and calculators mid-corner in the pissing rain doing 100km/h+. Gaining wet weather riding experience is what is required.

[slofox]

What angles do I corner at? I have no idea, but my chicken strips suggest I seldom get beyond 30 deg.

Errrrmmmmmmmm.....yeah me too probably...

[ferriswheel]

It all depends on your breed of tyre
If got mates with Perelles n they havnt pushed there bikes hard enough on the wet to notice much difference
where as I have Bridge Stone Battlemax's on my bike and it scares the shit outa me in the wet
It feels like I have about 20 maybe 25% of grip in the wet verses dry