Budget Big Brakes.

[jamal]

Alright, well, lets go with that example of 50lb being transferred due to CG change because of soft suspension. Now lets say you have a soft suspension that doesn't compress as much, and the transfer due to CG movement is only 30lb.

That gives us a pretty small difference in weight transfer between a stiffly sprung car and a softer one, doesn't it?

The total amount of weight transfer when braking at high g is going probably be somewhere around 500-700lb. So, the difference between the soft car and the hard car is going to be something like 3% of the total weight transfer on a 3000lb car. I don't really consider that to be significant at all, especially not in regard to stopping distances.

The point I'm trying to get to is that the g force is responsible for the weight transfer, not the suspension movement. Your post seems to imply that they are the same and that more suspension motion transfers more weight. While technically it does, it is almost not a factor. A softer car should stop in pretty much the same distance as a stiff one, if not shorter on a rougher surface. This assumes we're not riding on the bumpstops or blown struts.

[93forestpearl]

You can't just say that g forces are solely responsible for weight transfer. The center of gravity height has just as much if not more to with it. Think about t. The higher the weight is in the car the more of a lever arm it has to act upon.

I'll agree in certain situations, a soft car will brake better than a stiff car, and that obviously has to do with keeping contact with the surface. A rally car is prime example.

Generally, stiffer cars are lower, which changes everything.

What I've been trying to get at is that you cannot pin one performance criterion (such as braking) to one particular attribute of the car, wether it be tires, camber, pad material, rotor size, etc. There are many many many things that play into how a car brakes, handles, accelerates, etc. Saying purely tires are responsible for stopping distances is shortsighted. Yes, they give you largest improvement in braking that you'll see, and the rest of the possible modifications end up being smaller and smaller gains. Just like suspension. Tires first, then everything else is a proportionally smaller and smaller gain.


Cars are extremely dynamic and intertwined things that one affects another, which affects another, and so on. It was ever more apparent when I was designing the suspension for the FSAE. You wanted one thing, but it changed ten others, but another constraint might not even let you get what you want in the end. Everything is a compromise.

[jamal]

You can't just say that g forces are solely responsible for weight transfer. The center of gravity height has just as much if not more to with it. Think about t. The higher the weight is in the car the more of a lever arm it has to act upon.

I don't recall ever saying that g force was the sole thing responsible for weight transfer. I just didn't mention the wheelbase and cg height because for these purposes we're looking at the same car with different spring rates and brake biases so the wb and cgt stay constant.

This is turning into one of those silly internet arguments where everyone is arguing a different point while sort of ignoring what the other person is actually saying. All I did was point out that stiffer suspension does not really create less weight transfer because there is less dive (except for that very small amount), and that brake bias will also not really effect the amount of dive. Phil post seemed to imply that they were all sort of the same thing.

[BAC5.2]

You can see real-world stopping distance differences between soft and stiff cars with the same brakes. It boils down to an awful lot of things. Geometry change through wheel travel, extension out back loses camber and significant compression up front similarly loses camber at the end of the strut travel.

I did snowball it all into one thing, again for simplicity sake. Apparently, I made an incorrect generalization and assumed that people would understand the concept behind stopping distances and how they relate to suspension changes.

Brake bias, weight transfer, geometry change, and suspension motion all have some impact on stopping distances. The goal of my post was not at all to discuss all things concerning stopping distances. Rather, my intention was to discuss bias. Greater rear bias keeps the car more flat during braking, limiting weight transfer and geometry change allowing for more consistent braking with shorter stopping distances. I've actually spoken to Stoptech engineers about this very thing.

[ciper]

A quick way to demonstrate how a soft/hard car behaves differently during braking or high speed maneuvers is like so -
Once with 40 PSI tire pressure
Once with 26 PSI tire pressure

[jamal]

A quick way to demonstrate how a soft/hard car behaves differently during braking or high speed maneuvers is like so -
Once with 40 PSI tire pressure
Once with 26 PSI tire pressure

except the tire pressure has a huge effect on ultimate grip.

[93forestpearl]

I've actually spoken to Stoptech engineers about this very thing.

I wish I was kind of a big deal, and people knew me, and had many leather-bound books, and my place smelled of rich mohaugany.




Cool. Now that we're all on the same page, lol.

[skid542]

I've kept out of this discussion but have been intently watching it.

I do want to add this thought though.

When I first upgraded my brakes on my 93' L, I upgraded the rears first to the turbo setup. This increased the piston size and moved the bias rearward to the point that the rears would lock first. This decreased my nose dive, it also drastically changed how the car handled when braking into a corner. When I upgraded the fronts to a larger rotor, my nose dive increased again. My braking distance was reduced with each upgrade. My suspension and tires remained constant.

Just wanted to provide a 'physical real-world' example of how brake bias changed weight transfer and nose dive.

It all still defaults to the fact that braking is a very dynamic system and I'm not wanting to add/argue any of the points that have been brought up so far, just wanted to provide an observation.

BTW, I've loved the discussion in this thread.

[BAC5.2]

I've actually spoken to Stoptech engineers about this very thing.

I wish I was kind of a big deal, and people knew me, and had many leather-bound books, and my place smelled of rich mohaugany.

Lol, Matt at Stoptech is really helpful and our place smells less of mohaugany and more of gear oil and header-wrap.

Minor internet celebrity status only gets you so far.