Anti-dive shocks - What are the options?

[island911]

...for the T-bar 911's..

I love the active (PASM) system on the newer stuff. So, I'm thinking along the lines of an active system, rather than the pitched A-arms of the turbos.

Thoughts? Suggestions?

[gtc]

I suppose you could use a shock with an inertia valve, but I have not seen one for a 911 yet.
They are common now for offroad vehicles. I wonder if there is some reason we don't see them on cars.

[island911]

Because God and Ferry died in 1973?

Seriously, thanks, and I'm pretty sure I saw something like that on an auto-x car.. . ..Motorcycles have had them for quite some time as they really improve braking performance.

[winders]

Originally Posted by island911

...Motorcycles have had them for quite some time as they really improve braking performanve.

What motorcycles? Not road race motorcycles. The forks you find on road race motorcycles (MotoGP, WSB, AMA Superbike, etc.) today don't have anti-dive. Anti-dive systems were tried in the 80's and 90's on race bikes but were abandoned.

Why? Because they made braking worse because ant-dive transferred the load faster which could cause the brakes to lock faster and the tire to lose grip sooner. Dive is now "controlled" with geometry, spring rates, and fork valving.

The 930 front end geometry provides a modest amount of ant-dive compared to a regular 911. If you want to control dive, I would do it with stiffer torsion bars, different valving on the shocks, or a combination of the two. You aren't driving a Cadillac....

Scott

[Flieger]

I think the strict definition of anti-dive would not allow for a damper to contribute to it. The brake torque actuated, hydraulic system Lotus tried counts I suppose but classic antidive is all about side view instant center.

[chrismorse]

I'm not sure what you are after, antidive reduces front suspension movement, but the weight transfe ris still there.
Is it an issue of maintaining ground clearance under hard decel and not grinding off some of the chasis/body???
The more anti dive you use, the harsher the ride and you might even encounter suspension binding, which wouldn't help cornering on uneven surfaces, the ride rate would shoot up and the car really wouldn't like it, for sure, lap times would suffer.

If you start building in a lot of anti-dive, you might want to check the bump steer curves, front and rear, to make sure that both ends of the car are going to be happy, in turns, over bumps.

no easy answers,
chris

[winders]

Originally Posted by chrismorse

The more anti dive you use, the harsher the ride and you might even encounter suspension binding, which wouldn't help cornering on uneven surfaces, the ride rate would shoot up and the car really wouldn't like it, for sure, lap times would suffer.

Since anti-dive combats dive not using the suspension, how could it contribute to "suspension binding"?

Binding occurs when the limits of bump are reached whether through coil bind or running out of suspension travel.

Scott

[island911]

We do see them on cars ..newer Porsches (see PASM)... I suspect that MBz also.. it's a pseudo-active suspension system.

Anyway, the issue is, if ya jab the brakes on an old 911 (lets say a deer jumps in front of you while clipping down a country road) the front end is initially so light that the initial grab just isn't there. ...not until the suspension is loaded up (braking weight transfer) do the tires have maximum load. --Anti dive (or call it damper lock-down) make this all happen much faster .. ...happy happy joy joy . . bambi lives another day . . . or the cop didn't notice a quick nose pitch

[island911]

Originally Posted by winders

...

Why? Because they made braking worse because ant-dive transferred the load faster which could cause the brakes to lock faster and the tire to lose grip sooner. .....

Scott

please explain "ant-dive transferred the load faster which could cause the brakes to lock faster "

How does increasing the force of the tire on the pavement (grip) cause the brakes to lock faster?

[Flieger]

I think what he is getting at is that you can get wheel hop on the front but instead of due to spinning rear wheels it is due to the antidive and causes brake lockup in a stick-slip manner. Chatter, if you will.

[winders]

Originally Posted by island911

please explain "ant-dive transferred the load faster which could cause the brakes to lock faster "

How does increasing the force of the tire on the pavement (grip) cause the brakes to lock faster?

Roll your eyes at something you clearly don't know much about.

Anti-dive, any way you get it, causes the load to be transferred faster to the front contact patches. The total load transferred is going to be pretty much the same, but how fast it gets transferred is the difference. Transfer the load too fast, and the tires get overwhelmed and slide too much. Anti-dive can be good but too much is bad.

Anti-dive, like a jacking force, is transmitted through the front suspension linkage to the contact patch.

Do you understand that?

Scott

[LJ851]

For starters, motorcycles and cars are completely different in this respect, on a bike you want the front to dive to decrease the steering head angle and allow steering with intense front end loads. On an analog car this is not really a have your cake and eat it too situation. You can have smooth, plush ride and brake dive or a firm, sporty ride and less brake dive with side effects from both setups.There is no free lunch without very fancy electronic control.

[island911]

Thanks for the effort, Flieger, But winder is just tap-dancing and trying to drive this subject off topic. --it's all he ever does,

[island911]

LJ, I'm expecting a "fancy electronic control" solution. ...although MEMS are rather common place these days. .. I'm surprised that there isn't a phone app for this yet.

[LJ851]

Originally Posted by island911

I'm surprised that there isn't a phone app for this yet.

You are looking in the right direction, i'm guessing a retrofit solution is what you will end up wanting/finding. There are cubic dollars at stake at the moment....

[winders]

Originally Posted by island911

Thanks for the effort, Flieger, But winder is just tap-dancing and trying to drive this subject off topic. --it's all he ever does,

You are the one that made a bogus statement on how anti-dive improves braking on bikes.

You are the one that said having the load transfer faster was better for braking on cars.

I didn't bring any of that stuff up. I don't tap dance either. That is what you are doing here. You are trying to take the focus off your incorrect assumptions and somehow blame me for taking this thread off topic.

As I said earlier, if you want to control dive on your torsion bar 911, I would do it with stiffer torsion bars, different valving on the shocks, or a combination of the two.

Scott

[island911]

Ah winders, my shadow troll... dumber than a box of rocks, chiming in again to tell the board that increased down-force makes a tire have less traction. --cute. better inform those guys at F1 that they are inducing extra drag for that aero down-force ... down-force which clearly only makes "the tires get overwhelmed and slide too much.".

[winders]

Originally Posted by island911

Ah winders, my shadow troll... dumber than a box of rocks, chiming in again to tell the board that increased down-force makes a tire have less traction. --cute. better inform those guys at F1 that they are inducing extra drag for that aero down-force ... down-force which clearly only makes "the tires get overwhelmed and slide too much.".

Wow! It's ironic that you write that I am "dumber than a box of rocks".

It's clear you don't understand the difference between the vertical load provided by aerodynamic devices and the vertical load transferred when cornering or braking.

First, it is important to note that the grip provided by a tire is not a constant. The vertical load you put on a tire, the more grip it generates. But, increasing the vertical load on a tire 100% does not increase the grip 100%. The grip increases at a rate slower than the vertical load.

When a vertical load is transferred to a tire during cornering or braking, it is accompanied by a longitudinal or lateral load as well. The vertical load does not increase at a rate high enough to increase the grip enough to match the longitudinal or lateral load. In other words, the grip of the more loaded tire is reduced, not increased.

Aerodynamic devices do not introduce any longitudinal or lateral loads with the vertical load. So, grip is increased.

Scott

[Flieger]

Too much antidive?

[Canada Kev]

Ya gotta know his butt got kinda warm from sliding like that...