[Rear Suspension And Gas]

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...

 

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...

[Ride Height]

Interesting topic. Very nicely explained Racer.

I remember reading some time ago that riders were unwinding the preload on the rear spring to attempt to get a "softer" ride.

Now this combined with rising rate linkages in fact made the suspension "harder" because the swingarm was now in the region where a lot more force was required to compress the spring.

In other words, more preload can = softer ride (softer meaning compliant).

Always best to get the right springs for the job and set the sag properly. (insert smiley here)

 

 

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

[Rear Suspension And Gas]

Of course, applying rear brake in a deceleration mode will add more weight to the front as evidenced by nose dive, but we're talking applying rear brake under power.

To simplify, if you had a piece of rubber in your hand or sandpaper or timber and your ubbed them across a concrete surface, would friction be greater if you applied more weight to these? Same applies to tyres. Would you have any grip on the rear tyre when it is skipping across the tarmac because you are heavy on the front brakes?

 

I agree that braking into a corner can place extra stress on available front wheel traction as evidenced many times watching GP's. That is not to say that there is not more traction available due to weight transfer, more a case of simply overbraking/locking front wheel or just going beyond the limit of available traction.

 

You are correct when you say that the rear brake will bring the front down cresting a hill, as would deceleration. The point I'm making is to apply the rear brake WHILE accelerating.

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...

[Rear Suspension And Gas]

To whom it may concern:

 

Once you accept or grok that chain pull is always working to extend the suspension, raise the rear of the bike and/or pull the swingarm down, the next realization is that the forward motion of the rear wheel is also trying to push itself under the bike (ultimately lifting the front wheel) which also works to extend the suspension, raise the rear and/or pull the swingarm down.

 

So, there are actually two "component force vectors" being applied to the swingarm to create one "composite" force vector. At that point, the question becomes, which component is dominant or stronger, ie. which is more responsible for the fact that the rear of the bike raises up under acceleration? Chain pull acting to pull the swingarm down? Or the forward force of the rear wheel trying to push itself under the bike?

 

And then, just how dominant is that component? Are they relatively close or is one WAY stronger than the other? And does that relationship remain consistent across the acceleration curve?

 

racer

 

 

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. ;-)