Have a question about weight transfer

[260DET]

My post got messed with, I'm sure it was not deliberate

 

Torque reaction can manifest itself in different ways and can occur when the car is already in motion, just look at a top fueller in action for an extreme example.

[johnc]

Ack! Sorry! I thought I was editing my own post. I'll fix it.

[kamikaZeS30]

If you accept that anti-squat and pro-squat exist, then it should be pretty easy to figure that there is a middle point where you have neither pro nor anti-squat, and that's what a Z has. It will still squat, but it squats due to weight transfer.

 

Okay, I think I understand a little bit better, now. I'm not trying to be argumentative, I am trying to pose questions in such a way that I might get an answer that I can learn from.

 

So, the S30's suspension (looking at the "side-aspect") favors a slightly forward CG to counter-act squat, or is all of this isolated to simply the angles in the rear-suspension?

[JMortensen]

Angles in the rear suspension determine pro or anti-squat. You could try to affect the total amount of weight transfer by moving weight to the front or rear. Again, not dealing with drag racers, but most road racers like 50/50 or more tail heavy weight distributions as that extra weight to the rear gives better braking allowing the rear brakes to be used more, and better traction on corner exit.

[WizardBlack]

Might I ask something? In regards to the suspension movement from lots of torque. Does it not depend on the vehicle? Motorcycles will completely extend the suspension when you accelerate hard enough. I guess you could say that's the extreme opposite argument to help understand the nature of suspension. I thought one school of thought, as stated here, it to tune the suspension movement (squat/anti-squat) to what you use the car for and where the static load was, etc. I've seen street, erm drag, racers tune their old school cars to actually rise up in the rear when doing burnouts like a bike will. I would presume because they will end up losing enough front end weight as it is (trying to avoid wheelies). Road racers will tune the squat to allow a controlled transfer of weight under relatively lower amounts of acceleration to transfer tire load to the rear in corners so they don't burn out the front tires.

[johnc]

Might I ask something? In regards to the suspension movement from lots of torque. Does it not depend on the vehicle? ...Road racers will tune the squat to allow a controlled transfer of weight under relatively lower amounts of acceleration to transfer tire load to the rear in corners so they don't burn out the front tires.

 

As you said, it depends on the vehicle and usage. A FWD road racer surely doesn't want any squat under acceleration and in general most road racers want very little, if any squat. The process of "squatting" slows down the vehicle's response. It takes X amount of time for the rear suspension to compress and the front suspension to extend. As that is happening the sprung mass is not really accelerating much in the direction desired.

[tube80z]

I would presume because they will end up losing enough front end weight as it is (trying to avoid wheelies). Road racers will tune the squat to allow a controlled transfer of weight under relatively lower amounts of acceleration to transfer tire load to the rear in corners so they don't burn out the front tires.

 

John's reply has a lot of good info. Maybe this will help too.

 

The suspension movement really has little to nothing to do with the overall weight transfer. That's a function of CG height and wheelbase. But where it will make a lot of difference is on how the car is used. Using a RWD road race car as an example you may want it to squat when coming out of a corner. When the rear suspension drops the RC generally lowers, which would shift some of the roll stiffness forward. This would allow the rear tires to have more longitudinal traction if they are not fully utilized and help the car come of the corner harder. For a FWD car you might want to try the opposite of this.

 

The other thing to keep in mind is the geometric changes cause load to transfer much quicker than spring/shock/arb changes. These can have an effect on a car over a longer run where they may heat up or overheat a tire by working it too hard. And an example where we may want to use a lot of antisquat is on a car that needs to keep a certain ride height (underbody aero). In this case the aero is more important than the mechanical traction.

 

In a lot of the newer books and publications they are not looking at a single axle as much and talking about pitch centers. It's kind of the same thing but looking at what happens the car overall.

 

Hope this helps,

Cary

[johnc]

Aerodynamics have become so important in the professional level of motorsports that race engineers look at the aero needs first and mechanical grip needs second. If you get the aero right, the mechanical grip almost takes care of itself. What we discuss and do here regarding mechanical grip on our 40+ year old cars is kind of a dying art. At some point in the near future we will be looked upon the same as the old British mechanics who worked with Whitworth tools, mechanical shocks, kingpins, and sliding pillars.