Anybody able to take accurate measures of a tyre ?

[Hawk]

I'm using IE for viewing here and I can see the pics fine. 

Very interesting finding Max. 

Hawk

[Napalm Nick]

I've got my IE locked down tighter than rusty nuts. It knows Max's links are dangerous I guess.

[HornetMaX]

Slightly modified the drawing, to show the dunlop and the GPB profile for a tyre with same diameter.

MaX.

[Hawk]

Slightly modified the drawing, to show the dunlop and the GPB profile for a tyre with same diameter.

MaX.

Looks like a big difference to me Max.
If tyre profiles can be altered in the bike physics files it would be good if someone could try this out and see what differences it makes to a bikes handling characteristics?

Hawk.

[HornetMaX]

Looks like a big difference to me Max.
If tyre profiles can be altered in the bike physics files it would be good if someone could try this out and see what differences it makes to a bikes handling characteristics?

At the moment I think it's not possible, the tyre profile is assumed to be round.
How much impact would a different profile have on the handling: hard to say. But as it is a simulator, maybe we should just put a more flexible profile in (maybe as simple as elliptical would already be a big step forward).

Notice however that the tyre "grip" characteristics should be unaffected by the profile, as they are captured in the MF model (which is kind of independent of the tyre profile declared in the tyre's .ini file).

MaX.

[Hawk]

Looks like a big difference to me Max.
If tyre profiles can be altered in the bike physics files it would be good if someone could try this out and see what differences it makes to a bikes handling characteristics?

At the moment I think it's not possible, the tyre profile is assumed to be round.
How much impact would a different profile have on the handling: hard to say. But as it is a simulator, maybe we should just put a more flexible profile in (maybe as simple as elliptical would already be a big step forward).

Notice however that the tyre "grip" characteristics should be unaffected by the profile, as they are captured in the MF model (which is kind of independent of the tyre profile declared in the tyre's .ini file).

MaX.

Personally I would have thought the profile of a motorcycle tyre would have a very large impact on the way a bike handles, especially during cornering manoeuvres and how the bike reacts to changes in direction?

Hawk.

[HornetMaX]

Personally I would have thought the profile of a motorcycle tyre would have a very large impact on the way a bike handles, especially during cornering manoeuvres and how the bike reacts to changes in direction?

In real life yes, of course. But In GPB it may be less so for the handling: don't forget there's the virtual rider in the middle, it could "hide" (or compensate) the differences in handling.

Also, in real life how much "grip" you have from the tyre at a given vertical load, slip angle and lean angle depends (also) on the contact patch size, and that depends on the profile.
But the"grip" characteristic of the tyres in GPB is captured by the MF model: it kind of "includes" the dependency of patch size on tyre profile.
So if you change the profile in GPB without changing the MF model, nothing will change in terms of "grip".

One thing that a different tyre profile can change is how many revs the engine picks up when you lean the bike at different lean angles.

MaX.

[Hawk]

Personally I would have thought the profile of a motorcycle tyre would have a very large impact on the way a bike handles, especially during cornering manoeuvres and how the bike reacts to changes in direction?

In real life yes, of course. But In GPB it may be less so for the handling: don't forget there's the virtual rider in the middle, it could "hide" (or compensate) the differences in handling.

Also, in real life how much "grip" you have from the tyre at a given vertical load, slip angle and lean angle depends (also) on the contact patch size, and that depends on the profile.
But the"grip" characteristic of the tyres in GPB is captured by the MF model: it kind of "includes" the dependency of patch size on tyre profile.
So if you change the profile in GPB without changing the MF model, nothing will change in terms of "grip".

One thing that a different tyre profile can change is how many revs the engine picks up when you lean the bike at different lean angles.

MaX.

What is the MF model Max?

Maybe the differences in tyre profile you have found account for the seemingly slightly(and I do mean only slightly) exaggerated increase in revs as the bike leans over that we hear at this time, and this is what I think Jan is trying to explain too?

Hawk.

[HornetMaX]

What is the MF model Max?

MF = Magic Forumla (silly name, if you ask me).
It's the model that describes the tyre properties in terms of "grip". Also known as Pacejka's model (or Pacejka's Magic Formula, or MF or ...).

Maybe the differences in tyre profile you have found account for the seemingly slightly(and I do mean only slightly) exaggerated increase in revs as the bike leans over that we hear at this time, and this is what I think Jan is trying to explain too?

The fact some seems to say the rev increase when leaning is too big is why I started looking into this.
To be honest we'd need somebody with track experience and good understanding (EdouardB ?) to confirm if the effect is exaggerated or not.
You'll have to go into a turn with constant revs and throttle, looking at your revs before the turns, then leaning significantly keeping the throttle steady and then looking at your revs mid turn.
And don't forget that in GPB you can lean more than what most of us can do ...

Anyway, there's another strange thing: if my interpretation of GPB's tyre size is correct, the 990 has a 225mm wide rear (2*130*sin(60deg)). Now, I can't find 2003 MotoGP data, but 225 seems quite a lot to me ... today's MotoGP seems to be on 190, or at least that's the official message from the tyre maker: it could be more, but 225 ...

MaX.

[BOBR6 84]

Its fine... lets say you are full throttle in 6th gear and you turn into a fast corner.. the revs will hit the roof!!

not too many corners like that so usually you short shift to compensate. or if you are flat out.. roll off the throttle very slightly..

in GPB its the sounds which make it seem unrealistic.. imo.

just my personal opinion..

places like the isle of man point all this out perfectly!

[Hawk]

Its fine... lets say you are full throttle in 6th gear and you turn into a fast corner.. the revs will hit the roof!!

not too many corners like that so usually you short shift to compensate. or if you are flat out.. roll off the throttle very slightly..

in GPB its the sounds which make it seem unrealistic.. imo.

just my personal opinion..

places like the isle of man point all this out perfectly!

Actually Bob, you've probably hit the nail on the head with suggesting it's the bike sounds which make it sound unrealistic. I think you have a genuine point there mate. 

Would still be interesting to test change that tyre profile though. 

Hawk.

[C21]

Anyway, there's another strange thing: if my interpretation of GPB's tyre size is correct, the 990 has a 225mm wide rear (2*130*sin(60deg)). Now, I can't find 2003 MotoGP data, but 225 seems quite a lot to me ... today's MotoGP seems to be on 190, or at least that's the official message from the tyre maker: it could be more, but 225 ...

That´s what it´s still strange to me.
225mm wide tyres were never used in GP or MGP.
They use 190mm-200mm tyres. 190/650R16.5 label of the rear tyre.
Front is 125/600R16.5 label on tyre
(Officially used tyre size in MGP 2010 but still in use)

label on tyre means -> they can differ to what is labeled ;-)

[HornetMaX]

Anyway, there's another strange thing: if my interpretation of GPB's tyre size is correct, the 990 has a 225mm wide rear (2*130*sin(60deg)). Now, I can't find 2003 MotoGP data, but 225 seems quite a lot to me ... today's MotoGP seems to be on 190, or at least that's the official message from the tyre maker: it could be more, but 225 ...

That´s what it´s still strange to me.
225mm wide tyres were never used in GP or MGP.
They use 190mm tyres. 190/650R16.5 is correct label of the rear tyre.

Yeah I know (even if I'm not sure in 2003 they were on 190, but right now they are).

Anyway, the tyre geometry seems to be described by only 3 parameters: total tyre radius, torus radius and the mysterious width. For the 990 they are: 325mm, 130mm and 60.

If 60 is in degrees and describes the half angle of the profile (e.g. the profile is a circular arc of 120 degrees) then I get 225mm tyre width.

If 60 is something else, I'd really like to know what it is

MaX.

[HornetMaX]

Straight from Misano (no, I wasn't there, didn't even watch it on tv, sigh), two pics of MotoGp tyres showing the profile:





MaX.

[Hawk]

Wow! No wonder they are able to touch their elbows on the tarmac these days! Lol.

Have you got a pic of the old classic slick tyre profile to compare Max? I think it would really show the dramatic differences. 

Hawk.