G-Force question

[Ritz S14]

I guess this is somewhat of a newbie question...

How hard is it to reach 1 lateral G either by braking or acceleration? I ask this because I just bought a Pioneer Avic N1, which has a built in G force meter (goes up to 1.25lg) which measures acceleration, braking, angular velocity and a few other things.

So last night after tap. ex. my cousin showed me his new work place. Pretty empty area at 11pm.. So I thought to myself..why not try out this G-force meter. I didn't really care about acelleration Gs, cause the motor is bone stock, and it probably wouldn't impress me one bit. Since the brakes are upgraded on all four corners (4 piston calipers up front, and 2 in the rear) I wanted to see what I can hit. So yeah, the best I could do was about .65 until the front left wheel locked up (no abs). Every time I'd try it I'd get the same reaction from the car..front left keeps locking up. The streets are wet, and the front tires are pretty crappy on my stock wheels.

side note>>But for some reason when the wheel locked up it felt like the whole shock assembly flexed backwards.... like as if the top shock mounts were lose. As soon as my tires come in, I'm sure I can hit a higher #.

So anyways back to the point. How hard is it (or what's required) to hit one lateral G by either means braking or acceleration. And another newbie question.. what exactly determines G force (in laymens terms :doh5: ).

I've read about it.. but never quite understood it.

Car 95 240sx

[hybrid2nr]

Lock it up going sideways!

j/k

Wouldn't it be longitudal g force when braking or accelerating? I always thought lateral g meant sideways as in cornering, oh well.

Actually, .65 g wet braking isn't that terrible considering that was the dry cornering limit for many cars not too long ago.

The stickier a tire is, the higher g it's capable of in all directions assuming the setups are optimized. The only time this couldn't be true is in the case of wrinkle wall slicks. A car that corners at 1g could be capable of braking that hard as well. Of course, hamsters on crack are required to do that going forward.

[Ritz S14]

bah... it says "lg" on the meter.. So you're probably right seeing that you know more about it than I do. The .65 is on 25% front tires, and 99% rear tires.

[ShadyDave]

Yes, "lateral" gee forces are cornering forces.

As for braking and acceleration, it's quite easy to reach one negative gee under braking. One gee of positive acceleration is harder. A good launch on slicks will pull a gee.

A gee is nothing more than a measure of acceleration. You've used the acceleration due to gravity constant 9.807 meters per second squared in physics classes dozens of times, most likely. Hitting one gee while braking merely means that your acceleration is equal to -9.807 m/s^2 when you stomp on the brakes.

[Ritz S14]

So.. That means I would have to decelerate at 32ft/second? yes?

And by " it's quite easy to reach one negative gee under braking" did you mean any car can do this? Or with less money? or a simple brake upgrade?

[hybrid2nr]

32.2 ft/second/second.

32.2 ft/sec is rate of velocity or speed

32.2 ft/sec/sec is the rate of acceleration or deceleration in any direction

Lame cars usually brake better than anything else. They'd have to.

Old school musclecars could accelerate well if they could get bite.

Drum front brakes would fade quickly, there go your negative g's. Thank God for discs which originated from aircraft apps.

Skinny tires have long footprints too. That helped longitudal g's but not lateral g performance. Wide low profile tires improved all around g's. More important, it was now capable of vastly improved lateral g's IF the suspension allowed optimized tire contact patch area. Now the car rolls further due to better cornering grip, necessitating suspension redesign and improvements in order to maintain tire contact patch. Around 1969, GM switched a lot of cars from positive camber gain to negative camber gain front suspension geometry to improve tire contact patch under suspension compression during cornering. They did this by lowering the UCA inner pivot mounting point and modding the UCA to deal with the changed upper ball joint pivot range.

Race car suspension designs are really dictated by what tire is used more than anything else. Start with what the strengths and weaknesses of a given tire are and you literally design the whole car around it.

The .65 is on 25% front tires, and 99% rear tires.
Does the g-meter say that?

[Sniper]

i'm thinking he means percentage of life left...as he stated the fronts suck.

[hybrid2nr]

Ah, stupid me. Thanks.

[Ritz S14]

Haha yeah.. fronts are teh suck, but suitable for daily driving.

Thanks guys for somewhat clearing things up.

[PNG]

There's no such thing as "negative g's". Acceleration is always a positive force, no matter which direction its vector takes. And braking is acceleration, in the sense that it's a change in velocity. So there.

[ShadyDave]

Oh, come now...acceleration is always negative while we're dealing with negative masses! :tounge:

But yes, any modern car can easily pull a gee braking.

The power of your brakes really doesn't mean much...it's ultimately the coefficent of friction between the tyres and the road that defines the force you can develop. Brake system upgrades will only allow you to reach that defined maximum faster (hopefully, with more control and feedback).

[PNG]

"Young lady, in this house we OBEY the laws of thermodynamics!"

Of course, it's all pointless now that Ol' Dirty Bastard is dead.

[hybrid2nr]

Okaaay smarty pants, define time:-P

When a plane pulls up, it's called positive g. When it pulls (pushes? There's no such....nm) down, it's called negative g. And it's not even braking. Ha!

[ShadyDave]

The "positive" and "negative" merely applies to the direction vector of the acceleration with respect to whatever origin you define.

PNG is quite right in that it's completely incorrect to refer to acceleration as a negative. Yes, the direction vector may have a negative sign, but you can't call it a negative acceleration. Otherwise, we'd have all sorts of negative forces or masses in the world...and I'd have my perpetual motion machine.

Alas, I get lazy and refer to negative accelerations all the time. Call it wishful thinking. ;)

[hybrid2nr]

I already have a perpetual motion machine. I'm completely sure it'll work. (Now if I could only remove that itzy bitzy amount of friction!)

Intake really isn't "suck' then, is it?

[Ritz S14]

Okaaay smarty pants, define time:-P

When a plane pulls up, it's called positive g. When it pulls (pushes? There's no such....nm) down, it's called negative g. And it's not even braking. Ha!


You have it the other way around. There is no such thing as "pull".

You can push a door, but you don't pull a door. Even when you're pulling you're pushing.

[PNG]

Yay! Let's talk about how centrifugal force is an illusion! (it's actually a manifestation of inertia)

[PhrozenLikwid]

Actually, I was under the impression that Centrifugal was a "force" depending on your frame of reference.

Ironic enough, In my physics class we are covering the mechanical forces right now, and last week I watched my professor (a small, portly asian man in his 50's) lay the proverbial bitch slap to a loud-mouthed girl in class after she argued about centrifugal vs. centripetal forces)

BTW ShadyDave, I take from some of your posts that you are a college student. You obviously seem to know you physics, and I was curious about what you are majoring in. I myself am a sophomore CS/Business Admin at UK, which puts me right in the middle of all those nasty physics classes.

[Ike]

There's already a centrifugal force = reality or not discussion going on in the rwd vs. awd. vs. fwd thread :rofl:

[Ritz S14]

Well.. Tried it again. I may have hit one, but I somewhat doubt it. The meter has 0, 0.5, then 1.25. On dry tires and drive pavement.. I believe I hit 1.75 or 1.8 (until LF tire locked up).. not quite there yet, can't wait to throw some new tires on there.

[PNG]

Nope. No such thing as "centrifugal force." It's just inertia.

[Ritz S14]

I was talking to a friend of mine who's hardcore into auto-x. He said that it's pretty damn hard to achieve 1G from braking, since my car isn't properly setup.

[ShadyDave]

With bald, hard tyres, I'd have to agree.