Reduce nose dive under heavy braking
 

Hi guys need a bit of help here,

During autox events whenever I do heavy braking I notice that the rear end gets very loose and unstable. Since I have installed coilovers it has gotten better but I still would like to reduce nose dive and increase stability if possible.

I understand that one way to fix this problem is to up my front spring rate but I really don't want want stiffer springs up front. 750lb is already rough at times, lots of potholes where I live. Is there another way to gain stability by adjusting ride height,toe or reducing rear spring rates?

Here is my setup incase this helps:

custom valved konis with 750lb springs up front and 600lb (might be too stiff) springs in the rear.
-1.9 degrees camber front and -1.7 degrees camber rear
0 toe front 0.16 rear
Car is corner balanced and has a ride height of 27" in front and 27" 3/16 rear

Just wondering, but can't you stiffen up or adjust the front struts to be stiffer?

Single or double adjust Koni's? Also what brake pads front and rear are you running?

fwiw I run 1100 lb springs front and 900 lb rear on mine with custom valved 2-way AST shocks.

Good point I have my konis on .5 turn from full stiff front and 1 turn from full stiff rear.

Its SA Koni yellows revalved by proparts usa. The shocks can handle higher rates but the car is my DD. I have EBC redstuff front and rear with stock rotors.

You will need double-adjustable dampers with individual adjustment. Increasing compression damping reduces brake dive to a point. While brake dive is one thing, there is a possibility that the rear brake pads are a bit too aggressive initial bite creating a slight instability during heavy braking.

Also, some suspension designs incorporate an anti-dive geometry. Has the car been lowered by a substantial amount?

The car is 27 inches from the ground in the front and 27 and 3/16th in the rear. I don't think its the brake pads since its was squirrely when I had stock pads. The car is much more improved this year with SA colivers and the drop vs stock but I still feel like there's more stability to be had under hard braking.

Could some of the instability under braking be caused by toe loss when the rear end is unloaded?

I'm unsure about those ride height numbers since I don't have a point of reference.

Rear toe out gain is also a possibility. If there is a considerable amount of rear-steering is built into the suspension design, rear would toe out during a hard braking. However, this is only at an autox; can you adjust your driving style to take advantage of it? I don't race my 370Z, but many years ago when I autoxed my '95 Eagle Talon TSi AWD, I gained a habit of trail braking because the car would rotate under hard-braking.

One other thing, if the instability was indeed due to the rear wheel steering, see if more toe in in the rear could be dialed in.

stock height is 27.89 and 27.99 so my drop is very mild. If toe is my problem I can definitely go and get some more dialed in. At the moment I only have about 1/8th toe in with me in the car. I can try trail braking if that is what it will take to keep the rear end from wagging around.

The number one thing I would say is to adjust your driving style to not require so much braking. Braking scrubs off speed. Find a way to keep more speed requiring less braking.

I found this article. I might try some of the tips.My rear damping was up a bit high.

Handling Guide | RACING ON THE CHEAP

Instability under hard braking: car wants to spin
• Excessive rear brake bias
• Insufficient rear droop travel
• Wildly uneven corner weights
• Excessive rear damper rebound force
• Unbalanced ride/roll resistance – too much at rear
• Insufficient rear camber (usually in combination with one or more of
the above)

A tad more rear toe, softening the rear shocks, and more importantly, is the is happening in straight lines, or trail braking??

Tracy Ramsey

When I mentioned trail braking, I meant to say that I changed my driving and used that feature to my advantage. In my current car that's RWD, I can't use trail braking; it just doesn't work in an autox, might work when I want to slide around, but it induces major, sometime unrecoverable, power oversteer. I use a small amount of throttle to maintain a more steady cornering speed.

It's hard for me to say what you could use that instability for without being there. A very brief application of trail braking might work in your case as long as throttle is applied gradually afterward. Watch for the weight shift and start from there. You might or might not be comfortable with a tiny slide for a quicker rotation purpose. What tires do you run?

This car does funny things with rear toe out try a touch rear toe in. Your spring rates are not the reason (most likely) you are having braking problems. Probably your pads. Most people prefer a little less aggressive pad in the rear.

OEM anti-sway bars?

A few things to try:

1) 1/16-1/8 total toe-in in the rear.

2) Disconnect one side of the rear sway bar at your next autox event.

3) For at least one run go full soft on the rear shocks and full stiff (or close to it) on the front shocks.

While none of these will do much for the nose dive issue, both of these should "tighten" the car up and help stabalize the rear end.

Thanks for all of the replies lots of good info here. One thing I want to clear up first is that I do have 1/8th toe in, actually I have 0.16 so a little more than 1/8th. My previous statement about toe out was that maybe as the rear is unloading the reduction of toe-in is causing me some grief.

Suggestions that I will try at this weekends event are:
Setting the rear shocks to full soft
Disconnecting the rear bar ( if i can borrow a jack while at the event)
Upping my front damper stiffness to reduce nose dive

If none of the above helps I will get my alignment checked and make sure that nothing got out of whack.

As for the nose dive, I guess I will have to learn to live with it. I don't want heavier springs up front as roads are really rough here and I can't find a set of 2 way coils that don't cost 3k+.