Geometry parameter and motorcycle ridability

Good morning, this is my first post in this forum, but I read it a lot.
Sadly, I don't speak french, and google translate don't help me because of really strange translation of some world.
I register anyway because I see lots of expert people here.
I'm trying to understand how the parameter of the geometry improve the driving behaviour.
I'm not sure the old says "big trail = stability, low trail = agility" is correct, because I rode bike with low trail that is not really agile (1999 Yamaha R6) compared to a bike with higher trail, but really more agile (2007 Honda CBR600RR).
So, I'm sure there's more.
I know that change suspension, chassis and almost all the other parts, but if you look at these two bikes, the geometry looks really similar, the behaviour it's really different.
So, why? what makes the Honda easier to be ridden fast? Maybe is not the geometry, but the "secret" is on the center of gravity?


Thank you

Voilà c' est fait .

Bonjour, c'est mon premier post sur ce forum, mais je le lis beaucoup.
Malheureusement, je ne parle pas français, et Google Translate ne m'aide pas à cause d'une traduction vraiment étrange de certains mondes.
Je m'inscris quand même car je vois beaucoup de gens experts ici.
J'essaie de comprendre comment le paramètre de la géométrie améliore le comportement de conduite.
Je ne suis pas sûr que le vieux dicton "grande traînée = stabilité, faible traînée = agilité" soit correct, car j'ai roulé sur une moto avec une faible traînée qui n'est pas vraiment agile (Yamaha R6 de 1999) par rapport à une moto avec une traînée plus élevée, mais vraiment plus agile (Honda CBR600RR de 2007).
Donc, je suis sûr qu'il y en a plus.
Je sais que cela change la suspension, le châssis et presque toutes les autres pièces, mais si vous regardez ces deux motos, la géométrie semble vraiment similaire, le comportement est vraiment différent.
Alors, pourquoi ? Qu'est-ce qui rend la Honda plus facile à conduire vite ? Ce n'est peut-être pas la géométrie, mais le "secret" est sur le centre de gravité ?

Merci

Good morning Pironman, the old saying ‘big trail = stability, low trail = agility’ is broadly correct. But the centre of gravity position also plays a role. ‘High and Forward’ promotes agility.
The inertia around the steering head axis of front wheel plus front suspension also plays a role: the lower the inertia, the better the feedback to the rider. And finally the rotating inertia: a light wheel with a small diameter also helps.
I share your experiences with Google Translate: the results can sometimes give you wonderful new ideas, but if you want reliable translations, you're better off using DeepL.com translator, which is miles better.

Or write in Italian... (Bonjour et bienvenue, pironman.)

For the front part, There is often confusion between trail and steering angle, both have an action. You may have the same trail with a différent angle.
Are the data always true in technical descriptions ?

Frits Overmars a écrit:

Good morning Pironman, the old saying ‘big trail = stability, low trail = agility’ is broadly correct. But the centre of gravity position also plays a role. ‘High and Forward’ promotes agility.

I didn't know that. I could try to measure the position of the CoG of both these bike, I have it at home.

Frits Overmars a écrit:

The inertia around the steering head axis of front wheel plus front suspension also plays a role: the lower the inertia, the better the feedback to the rider.

I read times ago that is better to have a low inertia of the steering "system", but I didn't know that this also improve feedback, interesting.
I read it in the blog of Peter Williams, I found really interesting what he says, for example he think that a nearly unstable setup is better for racing. Maybe because a bike that is unstable is also more responsive.

Adco a écrit:

Are the data always true in technical descriptions ?

That's true! I'm based to data, and these data says:
- Yamaha 24° rake 81 mm trail
- Honda 23.55° rake 98 mm trail

Wheelbase almost the same, 1375 for the Honda and 1380 for the Yamaha. But I didn't measure these values.
If you look only at these, you could think that the honda is more stable, the yamaha more agile. But it's not!
Honda look more stable AND more agile.

And what's the wheight on each front wheel, in static and dynamic situation?
Quel est le poids ou la charge sur chacune des roues ( Yam et Honda) en statique et dynamique?
Nota: je suis assez surpris de la chasse de la CBR 600 à 98mm, Honda aime bien souvent la valeur de 89 mm, mais bon, pourquoi pas.
Comme le rappelait souvent Pépé, la chasse est un produit entre valeur géométrique et charge.
Nota: Il me semble que sur les vieilles R6 ils montaient souvent un pneu AV en taille 120/60/17 alors que le standard est 120/70/17, la hauteur en 60% semble complètement abandonnée, il doit y avoir une raison, non?
Dan