Rpm changing by the angle of the bike?

[EdouardB]

Look at this video with this in mind, it's so noticeable when he changes direction left/right. Also, I want to add that the fact that their RPM drop so much at the entry of the turn despite leaning the bike over means they are really, REALLY braking hard.
https://www.youtube.com/watch?v=WELoKmv0DCo

[HornetMaX]

I was asking because the calculated value for for GPB tires (990 bike) is huge: 20% smaller tire radius @ 60 degrees lean ! That's a lot of extra RPMs ...

It could be because GPB assumes a circular tire profile while in reality the profile could be flatter (flatter than a perfect circle I mean).

MaX.

[EdouardB]

First of all, while the profile of a slick tyre (or even a supersport DOT race tyre) is a lot pointier than a street tyre, it s not completely round. It's very round at the top, and the tyre goes flatter at the edges, to provide a lot of contact patch, like this (asymmetrical compounds FTW lol):
http://media.crash.net/original/340268.jpg

Second of all, they reach the edge of the tyre through tyre deformation and not through pure lean angle. What I mean is that the circumference you should consider is about 2 cm away from the absolute edge of the tyre. The tyre will be deformed and the edge will be on the ground as well in real life. See what I mean? Besides, on some tyre profiles, I've seen national level racers with a 2/3 mm chicken strip on the front tyre (the rear deforms more so usually no strip). The profiles are that extreme. With no tyre deformation we would probably have chicken strips.

You could say "OK Ed, but since the tyre compresses it reduces the radius right?" And you would be right, but it also happens in a straight line so I m ignoring that since we're looking for a ratio here.

You could also say "OK ed, but the edge of the tyre is still on the ground, it inflicts rotation on the wheel, so why are we taking the circumference 2cm away from the edge?" Well, you can have the same reasoning for the beginning of the contact patch towards the center of the tyre, so you take the middle of the contact patch. About 2cm way from the edge. Yay

Having said all that, after these corrections, I would not be surprised if the ratio is still 12 to 15% on a motogp bike, it sounds pretty normal, it's really noticeable and is part of riding on racetrack (in magny cours for example some riders change their lines to lean less so that they don't reach the limiter in 6th!)

[EdouardB]

You should see what I mean on this picture more easily
http://images.motorcycle-usa.com/PhotoGallerys/valentino-rossi-motogp-assen-20.jpg

You can really see it on the front tyre, and it's the same in the rear.

Is piboso reading this by the way? This is important stuff haha.

[HornetMaX]

Thanks EdB

If I just measure the 1st picture, the ratio between the outer diameter and the central one is roughly 0.76, so even more than what I have in GPB.

Tire deformation is taken care of somewhere else but I see what you mean, it has an impact on the loaded radius, hence enters the computations we're discussing here.
As Piboso already has the notion of loaded radius (also dependent on the tire rotation speed), it should be possible for him to consider this (if it's impact is significant on the radius change).

MaX.

[EdouardB]

Instead of doing the ratio between the middle and the absolute edge, try using the middle of the flat side on the right part of the tyre (his tyre has worn out in a flat surface on the right). You'll get more than 0,76, that's what I meant!

[EdouardB]

I'm guessing (I haven't measured, I'm not on my computer) that you will obtain about 10 to 15%, which is what we observe at the track ( Iit can be 2k rpm on a 600 easily)

[EdouardB]

I just measured on an onboard video I did with the 600: my speed on the dashboard goes from 195 to 218 when leaning over (so about 12%) and that's just at about 40° (it's not a big corner). We can expect more than 15% at 60° lean easily! Probably around 18

[HornetMaX]

OK, all seems to indicate that 20% at 60deg is not out of the ballpark.

I just realized that I can modify my plugin to show side by side the speedo speed and the real bike speed (as if it was measured by a GPS).
Can't work on it right now (and tonight the silly italian team plays against the even sillier english team), but that should show what GPB is doing right now and, probably more interestingly, what GPB will do in beta5 after Piboso has fixed this.

Will show what I find.

MaX.

[HornetMaX]

Well, at the moment I see no change at all: the speedo speed and the "GPS" speed (speed of the COG) are identical.
So I'd say there's no radius change due to lean at the moment in GPB (which in fact was already pretty clear as there's no RPM increase).

MaX.

[BOBR6 84]

Not many people seem to be excited by this..

I cant wait for this to be applied!!

I think it will have a big effect on the bike handling.. But even if it doesnt it will still make the gpbikes experience more emersive..

Flicking the bike right to left vice versa will be awesome with the suround sound pumped up

[Alby46]

me too