Motorcycles in motion have some of the most complicated physics of any vehicle, especially when suspension design is taken into account. The whole 'the bike wants to tighten the radius when the throttle is opened' isn't necessarily wrong, but it's definitely not the complete story. Most sportbikes have quite a bit of antisquat geometry built into the rear suspension linkage that will drive the front tire into the ground and extend the rear shock when throttle is applied. The obvious other forces in action during throttle application is chain pull which acts in the opposite direction of the antisquat in addition to weight transfer rearward. Ultimately of course the rear squats under acceleration and weight is transfered away from the front axle causing a reduction in friction and therefore making it impossible for the radius to become tighter when throttle is applied given all other factors remain equal.
It's complicated. The ycrs guys say keep it simple, forget about swingarm angles etc have in mind that more mph results in a wider radius,so maintenance throttle (steady r) untill you can see your exit and truly accelerate, giving away lean angle simultaneously. Keep it simple, keep it safe. Trying to "steer on the gas" might lead to painful highsides.
Doesn't the rear raise under acceleration? They seem to on the dyno anyway. I've also noticed it on TV when watching SBK. When they are exiting some corners the rear raises a bit and the bike starts to wheelie.
And what happens when you throw an alternative / non fork front end into the mix ? That's another can of worms, should add to the page count.
Yes it does, but the force of the chain pull is greater than the force of the antisquat of rear suspension and therefore ultimately the bike does shift weight rearward, not forward.
The front end actually doesn't play a roll under throttle input, so regardless of it being a coil over shock in the front, or a traditional inverted (or non) fork tube setup, the chain pull and antisquat geometry of the rear of the bike is what determines how the weight is transferred rearward.
https://global.yamaha-motor.com/about/technology/urbanlegend/#no02 I think there is a split second when you open the throttle before the bike gains any meaningful speed to widen your radius that geometry can be more advantageous to turning. But as the bike gains mph, the bike can do nothing but increase the radius for a given lean angle. The rear extending does not eliminate weight transferring from acceleration. In some cases it could increase it due to change in cog height.
Any telemetry guys to tell us what "usually" happens when a sportbike is accelerating? Does the rear squat in any case or is it just our perception ?
Pretty sure it depends on swingarm angle and the height of CG and getting this just right is that ever elusive hunt for corner exit traction. The question of what happens as you add speed probably needs to be divided into small speed additions where geometry might be relevant and larger speed additions where basic speed, lean angle and radius are all that matters. This is the basic YCRS r=mph per above posts. I think this is the main principle at work and the minor speed changes and geometry impacts are secondary.
Alberto naska's video posted above shows his telemetry and the rear extending. His channel has some awesome stuff, imo. A lot of fluff too.
around 9:40 Ducati test rider Alessandro Valia on the advantages of cf wheels regarding mid-corner throttle opening: "reduction of the tendency to close the throttle line. what I'm talking about is the mid-cornering phase , when you begin to accelerate and the bike tends to tighten the line on its own" the above were mentioned during the Panigale V4 SP's presentation at the "Physics & Motion interactive and didactive laboratory" , dedicated to students and enthusiasts who want to understand how the laws of physics influence the dynamics of motorcycling.