Understand Rear Axle Forces in Car Suspensions w/ Instant Center Plot

[jack action]

They normally put a very sticky coating on the track as a traction aid.

That increases the thrust you can put down before spinning, and weight transfer is proportional to thrust, and more weight transfer allows you to get more thrust! Of course you will be able to keep the front wheels off the ground the first few feet in such a case.

There is a little something going on with the initial "push" that digs the tires in, and that something goes away if I angle the arms or tighten rebound to not have that start extension.

That little something is your raised $cg$ that increases your weight transfer and allows for more thrust to be applied, which creates more weight transfer and so on. If you don't allow the rear end to lift (by removing anti-squat or by restraining it with damping), you won't raise the $cg$.

@Tom Rauji ,

I'm not going to go into an endless argument over this like I had with other racers before. My point is not to tell you what you experienced is not real, it is just to give you hints on what to look for.

I have never done an in-depth analysis of dragster launch, especially dynamically, but my knowledge of physics tells me that it is mostly a matter of $cg$ height that can explain all of these differences in hooking the rear tires. I'm telling you that to help you what to look for, not to tell you you are wrong.

Although, it is a dynamic phenomena (the time factor @Ranger Mike talks about), so when you accelerate the body in pitch, it will have to stop eventually and that inertia that needs to be stopped will momentarily overshoot its static resting position (how much the tire deform). But that has nothing to do with the geometry of the suspension design, per say (Although the stiffness of the suspension will influence that). If you have a suspension hitting its travel stops, that is not a smooth transition and it will also upset the weight transfer (again, that damn inertia).

The slick is also a weird beast. Under hard acceleration, a slick actually have a perceived increase in its friction coefficient. I'm not an expert on the matter but, from what I understood, it also have something to do with inertia, when the deformed tire «slaps» the ground.

I'm willing - and would be happy - to have people with better knowledge than me on the subject, telling me I'm wrong about all of that. But I need physics proof, with known theories, rather than people explaining me their feelings about it.

From my study on the subject, the modified typical street car with slicks is a special case where the $cg$ height to wheelbase ratio and weight distribution are just about perfect to be the tipping point where a full weight transfer can be completed. A $cg$ a little bit lower and the front wheel don't leave the ground, a little bit higher and you flip the car. I wouldn't be surprised that we are not even talking in 'inches' of difference. That is why the slightest modification in the body height makes such an impact.

Unless proven otherwise with science, I can't accept that there is any other thing than weight going on, especially when weight can explain everything.

Believe me, instead of looking into magical forces that come from who knows where, examine the $cg$ height, you might find some interesting answers.

 

[Tom Rauji]

I'm not going to go into an endless argument over this like I had with other racers before. My point is not to tell you what you experienced is not real, it is just to give you hints on what to look for.

I have never done an in-depth analysis of dragster launch, especially dynamically, but my knowledge of physics tells me that it is mostly a matter of $cg$ height that can explain all of these differences in hooking the rear tires. I'm telling you that to help you what to look for, not to tell you you are wrong.

Although, it is a dynamic phenomena (the time factor @Ranger Mike talks about), so when you accelerate the body in pitch, it will have to stop eventually and that inertia that needs to be stopped will momentarily overshoot its static resting position (how much the tire deform). But that has nothing to do with the geometry of the suspension design, per say (Although the stiffness of the suspension will influence that). If you have a suspension hitting its travel stops, that is not a smooth transition and it will also upset the weight transfer (again, that damn inertia).

The slick is also a weird beast. Under hard acceleration, a slick actually have a perceived increase in its friction coefficient. I'm not an expert on the matter but, from what I understood, it also have something to do with inertia, when the deformed tire «slaps» the ground.

I'm willing - and would be happy - to have people with better knowledge than me on the subject, telling me I'm wrong about all of that. But I need physics proof, with known theories, rather than people explaining me their feelings about it.

From my study on the subject, the modified typical street car with slicks is a special case where the $cg$ height to wheelbase ratio and weight distribution are just about perfect to be the tipping point where a full weight transfer can be completed. A $cg$ a little bit lower and the front wheel don't leave the ground, a little bit higher and you flip the car. I wouldn't be surprised that we are not even talking in 'inches' of difference. That is why the slightest modification in the body height makes such an impact.

Unless proven otherwise with science, I can't accept that there is any other thing than weight going on, especially when weight can explain everything.

Believe me, instead of looking into magical forces that come from who knows where, examine the $cg$ height, you might find some interesting answers.

OK, thanks for your time. I guess we have reached the limit.