T/C Rod Relocation - Front of suspension?

[Wheeler]

Anyone have experience with relocating the T/C rods so they mount in front of the front LCA on a S30. I ask for two reasons:

 

1) This is what is done on the 240SX's and I believe on the zx

 

2) Most importantly because it seems that (and describing it here will be hard) during braking with the stock S30 T/C location, as the front suspension compresses, and the LCA is loaded rearward (in reaction to brake force), and as the T/C is pushed on (compression) that the T/C rod would, depending on whether its intial angle was above or below horizontal, either cause additional drive during brakeing or front end jacking (raise the front end).

 

By relocating the T/C rod forward of the front suspension, brakeing forces would then to pull (tension) on the T/C arm rather than push (compression) on it. This pulling force during braking would then act to center the T/C in a horiznotal position and therefore the front suspension and assist in limiting dive under braking.

 

I'm sure this would improve / reduce dive under hard brakeing I'm just not sure how much.

[JMortensen]

Dive/anti dive depends on the angle of the rod. If the rod is forward of the crossmember and angles down to the control arm, then the suspension will have "pro-dive". If it angles up to the control arm, then you'll have anti-dive.

 

Likewise in the stock location angling down from the mount to the control arm gives anti-dive and angling up gives pro-dive.

 

You can certainly relocate the rods, but the steering is going to be in the way. You could probably adapt a ZX steering setup in to fix that problem, but the question is: is it really worth all that hassle. You can change the mounting points and also just run stiffer springs to reduce dive as well, so changing all of the front suspension seems like a lot of work. One big advantage of a rear mounted rack is that adjusting in Ackermann is much easier.

 

You might check my sticky thread on TC rod pivot relocation. If you did what you're talking about you'd basically be into everything I was into, plus a bit more with completely switching the steering rack to the other side. Lots of work.

[datsunscom]

Funny, the 510 has forward runing T/C rods and I moved mine to the S30 style of rearward facing - because the 240Z has a front rack and adapting it to the 510 involved making the T/C's rearward facing. All other factors being the same it is unlikely you'll feel any difference by simply having the T/C's run forward instead of rearward. As Jmortensen said, the *angle* of the T/C rod will make far more difference than weather it's forward or rearward facing.

[Wheeler]

Might have to agree to disagree on this one.... The way I look at it, in simple terms is; imagine a rod pined on one end. Now if you push horizontally on the oposite end, toward the pined joint, the rod, depending in the initial angle realative to the line of action of the input force, will rotate either up or down. Now take the same rod and pull horizontally on it, regardless of its initial position it will center (move to a horizontal position).

 

Now all that said the benefit of this tendency may be small in relation to the other forces at work on the suspension during acceleration and brakeing.

[JMortensen]

Might have to agree to disagree on this one.... The way I look at it, in simple terms is; imagine a rod pined on one end. Now if you push horizontally on the oposite end, toward the pined joint, the rod, depending in the initial angle realative to the line of action of the input force, will rotate either up or down. Now take the same rod and pull horizontally on it, regardless of its initial position it will center (move to a horizontal position).

You're absolutely right about this.

 

The problem is you haven't factored in the angle of the rod BEFORE you step on the brakes. If the rod is angled down from the front of the car to the control arm, then as you step on the brakes that will try to pull the arm level like you said, which will cause nose dive on the car. If you have the angle the other way stepping on the brakes will attempt to lift the car (irrespective to the weight transfer and all the other BS, but just looking at the TC rod here) which gives anti-dive.

 

The other thing going on is like you say, the arm wants to be straight back, so it actually tends to reduce the suspension's ability to travel at all. Same think with the trailing arm rear suspension. If you could theoretically reduce the sprung weight of the vehicle to say 20 lbs and you were to step on the brakes the suspension would go to that straight back position in the front and the rear and wouldn't move from there, or would hardly move. This is a problem with some mountain bike frame designs and is more noticeable there because the sprung weight isn't enough to overcome the braking force.

[johnc]

You're mistaken in assuming the TC rod is acting as an independent link in the front suspension. Its not. The TC rod acts as one of the arms of a lower a-arm. Think of a line connecting the LCA pivot and the TC rod pivot as the base of a triangular a-arm. The LCA and the TC rod itself are the other two sides of that triangular a-arm. The fore/aft angle of that base line on the triangle determines dive behavior, as Jon said above.