FSAEracer03

Correct me if I'm mistaken, but body roll effectively "absorbs" the part of the weight transfer. Body roll uses some of the sideward corning force and translates it to a jacking force... right?

Sorry about the weight transfer comment.. rereading it, I see that what was in my head, and what I typed were not quite lined up, lol Let me see if I can't restate what I meant to say. Body roll changes the contact patch of the tires (not weight transfer)... and with proper static camber settings this can improve traction and corner exit speed while mainting some predictability.

Songzzz

Learn to brake with your left foot.

However engine-braking can sometimes be vital on the freeway, especially when you are going 150mph and a F*&#ing truck cuts into your lane abruptly.

Edited.

FSAEracer03

explain what you're saying Andrew

iloveporsches

He's saying learn left-foot breaking, but engine breaking is neccesary when someone cuts you off on the highway and you need to stop FAST.

FSAEracer03

Well I got cut off at over 115 on a downhill bridge... I actually liked my threshold braking, personally, lol... I managed to match speeds with the guy about 10-15ft from his bumper (long story!). Why would you bother left footing it, however... or are we getting into left foot braking and clutchless downshifting now?? ... I think I might need a goodnight's sleep to dive into that one (uh oh), lol.

gnight guys,
Kevin

gnosis

Kevin,

I agree that body roll has annoying effects for contact patch, and thus it should be eliminated. It also has a destabilising effect on the driver because humans can handle lateral accelerations much better than rolling accelerations. This is why people get more car sick in cars with soft suspensions, the same as they lose their lunches on boats due to the rolling motions of the waves. Note that nobody loses their lunch in elevators because they don't roll. Agressive negative camber can compensate for body roll, but it affects accelerating and especially braking efficiency by reducing the contact patch when you're not rolling (and you're not rolling when you do most of your braking and a good deal of your accelerating). So you're better off having less body roll and requiring less negative camber.

But weight transfer remains the same no matter what you do with body roll. You can't "absorb" weight. It has to be distributed between the four wheels (or three if your setup can't keep all the wheels on the ground - a no-no in itself).

Regarding Andrew's comment about left foot braking, I fully endorse it. I find it to be a fantastic technique. I use it all the time on the road and track, and with the Super Tourer it was easy because you didn't have to use the clutch. You could drive the whole race like a kart if you liked.

However I don't understand Andrew's comment about engine braking to avoid accidents. Stopping quickly is definitely the job of the middle pedal.

Clayton

iloveporsches

Not sure of the benefits of left-foot breaking, but there are some I guess. It is how you drive an FSAE car though

Rich Sandor

I'm not planning on putting 1000lbs springs on my 951 - but you must admit that the stock 180# or 190# springs are NOT cutting it. Especially when I get some slicks on there. I was thinking more like 400# all around. Perhaps ditching the rear torsion bar. or keeping it and matching the rear springs accordingly..


Either way you look at it, body rolls sucks.

iloveporsches

Body roll changes camber, making the car's handling less predictable, and since the camber is changing so much and leaving it's optimum range, the available traction from the tires suffers even more.

Songzzz

Clayton.. My 86' does not come with ABS

gnosis

And ABS stops with a few thousand horsepower of retarding force. Engine braking is almost as useless as coasting. I can't see how relying on engine braking can slow anyone down fast enough to avoid an accident. If I relied on engine braking to slow my car down from 100km/h, I'd still be rolling along at idle 20 minutes later.

Sorry, but I just don't understand why people won't use the brakes. That's what they're for.

Clayton

Rich Sandor

I have to agree with the engine braking being useless. My dad used to do it in my car and I told him a valve and bearing job is more expensive than brake pads. USE THE BRAKES.



He doesn't drive my car much anymore..

iloveporsches

But do full brakes (not locked) + engine braking = quicker stopping time?

Personally I don't engine brake. If I accidently do I get pissed that I didn't shift smoothly.

gnosis

Rich, I agree that around 200lbs isn't enough for a high performance road tyre on a relatively smooth surface like a race track. My guess is around 400 - 500lbs for front engines Porsches, but I haven't tried anything above the standard 160lb springs in my car. I will get around to it when I rebuild my suspension. But I also have the issue of whether I want a track car that I use on the road, or a road car that I use on the track. Unfortunately, these setups are different. And it's not just down to springs at each wheel. The anti-sway bars are effectively springs too.

But I agree totally with your comment about body roll being bad. I hear that absolutely none isn't a good idea because humans detect movement and respond better when there is some roll, but I'm talking tiny amounts.

The trick is to reduce body roll without increasing your spring rates so you don't cause traction to suffer. Tricky, and to date there haven't been any good solutions to this problem.

Clayton

gnosis

full brakes (not locked) + engine braking = locked rears and a spin. Don't do it. Your brakes have ample capacity to lock your wheels. Your engine isn't needed to help out with that.

I should point out that this is hardly an issue since the engine braking adds so little to the braking force. Even without rev matching, you'll spin the engine up much easier than you'll lock a wheel. But if you're rev matching properly with good heel-toe technique, you can slip the gear in without unsettling the car even the slightest, and this allows you to brake right on your limit and be confidently ready in the gear you need for corner exit.

Clayton.