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toni

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  1. What would be the use or application for this (using the rear brake during acceleration)? CF I don't do this with my CBR on the track but with my CRF on MX track to give more traction on the rear in certain corners...
  2. Hello. Yes, very interesting topic. Nice your explanations racer. I am french spoken, and not a specialist in english but I will try to explain my point of vue. What you are explaining here Big Willy, is ok for a bike not in movement or with little throttle. Effectively, with more preload, you have more rear ride height and your rear shock is working in a softer region because higher linkage ratio and then more rear end movement for a given load. But, if you imagine all the forces who are there when on the throttle, that's not the same results... If with more preload (or more rear ride height) the linkage gives static softer suspension working, the swingarm angle with regard to the ground becomes more important. Then the driving forces at the ground and especially the chain pull are trying to extend the suspension when you accelerate the bike. You have to keep in mind that this 2 forward forces vectors are applied (with their direction, sense and intensity), at the rear wheel axel and they have, with more swingarm angle, more torque with the swingarm pivot. The weight transfert to the rear tries to compress the suspension but the 2 anti squat forces "help" the spring and make the rear suspension stiffer. With a lot of rear ride height, the rear suspension can even rise under acceleration. In the opposite, with little ride heigt, the swingarm is more flat, the 2 anti-squat forces apply then a lower torque with the swingarm pivot, and then the rear height squat a lot under acceleration. This is why the linkage has lower ratio near bottoming out (then more vertical wheel rate) to offset a little the lower action of the 2 anti squat forces. Then with less preload, you get a softer reaction of the resultant of all the forces who interact (weight transfer, chain pull, driving force and spring via his linkage) Note that the chain pull is the more important anti squat force for 2 reasons : 1) the chain pull as +/- 4 time the intensity of the ground driving force (the ratio between the diameters of the rear wheel and the rear sproket) 2) the chain pull has more angle in the opposite direction (forward and downward) of the swingarm (forward and upward), and then more torque with the swingarm pivot (the ground driving force vector is always horizontal forward). PS : my swingarm angle (depending the track) is +/- 10 degree (CBR600RR with Ohlins) because I like to have more grip on the throttle out the corner, then I have to setup with a little more pro-squat That's not easy to explain but I hope that will be comprehensible. I play with this when I am racing my sportbike, that's fun
  3. For that point, I agree with Willy. Yes, you can accelerate with your foot on the rear brake. Then, since the caliper is fixed on the swingarm (not only through a bearing like with the wheel), the rear caliper try, during braking, to lower the swingarm pivot and then compress the shock, even during a acceleration... You have then a little more rear grip due to the little squat rear weight transfer, but less driving force because the brake application. Then you can change for a moment your geometry with the rear brake application...
  4. I am from Belgium and very interested by this subject. I agree with racer. The dominant force who extend the suspension is the chain pull because it is +/- 4 time stronger than the driving force at the rear wheel. What you have to see is that the 2 forward forces vectors are applied (with their direction, sense and intensity) at the rear axel because there is only a bearing between the wheel and the swingarm, and then no torque can be transmitted between the wheel and the swingarm. That is not always easy to imagine but that's the reality. ;-)
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