On midengined cars and driving

[Terminus]

Originally Posted by KLM

On two different days in two different corners of the same track I experienced enough oversteer to warrant (what I thought) a sizable correction.
...
What surprised me was during the movements from left to right, while getting progressively smaller angles, there was very little if any "on center" feel. It felt like trying to balance on a knife egde; even the smallest movement had the rear step out. In both situations, the result was a spin.

Hmmm... not having spun (yet, knock on wood) what I can say is that on the track I found all my corrections were slight, and that controlling the rear through turns was (intentionally) a balancing act between slight oversteer/neutral handling using mostly just slight throttle position changes.

[KLM]

Originally Posted by Terminus

Hmmm... not having spun (yet, knock on wood) what I can say is that on the track I found all my corrections were slight, and that controlling the rear through turns was (intentionally) a balancing act between slight oversteer/neutral handling using mostly just slight throttle position changes.

No argument there Term. My issue and interest was not in the initial breakaway, it was the second and third "pendulum swings" that I was seeking clarification and resolution.

[fpitas]

Originally Posted by KLM

Just read through the whole thread (again) and would like some input my experience.

During my last two track days I have encountered multiple forms of over and understeer which were readily explainable. What has been more difficult to understand and rectify is best described previously by the "pendulum effect" of the Elise in this thread.

On two different days in two different corners of the same track I experienced enough oversteer to warrant (what I thought) a sizable correction. In other situations I have learned a quick, but early correction settled the car. Those saves/catches were generally in slower, tighter turns. In the faster turns, my correction was too large and too late or so it would seem. The response to my attempt to save was tail out in the opposite direction (and another); a car version of a motorcycle tankslapper. What surprised me was during the movements from left to right, while getting progressively smaller angles, there was very little if any "on center" feel. It felt like trying to balance on a knife egde; even the smallest movement had the rear step out. In both situations, the result was a spin. If/When this occurs again, any suggestions? It is clear my gas, brake and steering inputs were incorrect. Should it be "two feet in" if I do not straighten it out after the first correction? That seems like the easy way out and I would like to learn through this experience. Thanks guys.

PS - shims are still in - this is a base car with RAC wheels - contributing factors?
PSS - age of tires were not the determining factor (first event was on new A048 - slide started with lift throttle oversteer / second event six months later on worn A048s exiting uphill, off camber - right rear spinning hard - the fun began when it caught).

My take on this phenomenon, FWIW, is that it is a mid-engined car, and will always be a bit tricky because of the rearward weight distribution, but the stability can be improved significantly by using relatively more front spring rate vs. rear spring rate and adding a (light) rear sway bar to eliminate the resulting understeer. I plan on trying this with my Elise, although I am having a little difficulty figuring out an easy place to locate a rear bar that won't need a bunch of bends.

[Vantage]

KLM, BTW, what tire sizes are you running on those RACs?

[KLM]

Originally Posted by Vantage

KLM, BTW, what tire sizes are you running on those RACs?

OEM Sport Pack sizes F 195/50/16 R 225/45/17 - nothing fancy

[ct20b drifter]

The normal driver reaction is to panic. And panic is not good. If you abruptly lift on the throttle, jerk the steering wheel, or worse, slam on your brakes (which most people do).... you cause some things to happen. You transfer weight to the front of the car so now the front increases it's grip, but the rear loses grip. And the rear wants to lead. The rear end will start a very bad oversteer where the car starts to spin. Even if you can catch it, often the correction will induce a huge spin in the opposite direction.

took me nearly a year to be able to catch it on the snap back. scary stuff even in a big parking lot! one thing i never did was panic and that saved my mr2 sooooo many times

[KLM]

Originally Posted by ct20b drifter

took me nearly a year to be able to catch it on the snap back. scary stuff even in a big parking lot! one thing i never did was panic and that saved my mr2 sooooo many times

I have been assuming my (over)corrections were too much. Just trying to see if others have had the same experience and what they did and/or if my setup encouraged this behavior.

Either way, it will not keep me from the track. It the best classroom there is.

[LarryB]

I'll admit haven't pushed the Elise all that hard. Did one throttle off oversteer, touch of opposite "lock" and back on throttle and it was like nothing happen. Was use to pushing the MR2 Turbo hard the '91-92 (had a '91), the rear would toe out under load, unload them and they would toe back in that plus the nature of a mid-engine car, would take 3-4 tail wags to settle in. So was surprised by how easy the Elise was to catch.

KLM- I'd guess since this is happening on the higher speed stuff for you, it's more a matter throwing the back end out with a lot more momentum, which makes it harder to catch... a good sign to take entry a hair slower.

[mrluky]

As of the last few months, I've been ever increasingly enamored with breaking rear traction in the Exige. Ive been experimenting with different inputs, and taking mental notes of events that, in practice, are way different than I what expected, in theory.

All of the following situations are on clean, wet roads, with wear bar rears, NA Exige. no LSD. TC off(and performed on a closed course). unless otherwise noted.

This is what I call a controlled slide, in that what happens, in practice, is what I expected to happen, in theory:
Approaching a turn, in gear, turn in, and apply throttle. The rear breaks loose. Counter steer. Spinning rears. Minuscule amount of lift(<1mm. Adding throttle, or maintaining throttle, I found, just spin the tires), and immediate(the lift and reapply is one motion of up-down asap) reapply of throttle brings everything back in order quickly.
I found that sometimes during mid slide, lifting(TINY amount of lift. 1mm max) stopped the increase of slide angle(spinning rears), and reapplication of throttle straightened it out smoothly. It depends on the amount of throttle used during initial breaking of traction. The lift helps tires grab. Now I'm not sure, since I didn't try, but I think if I didn't lift in the instances where I did, I would have spun right around.

Besides slight throttle input variations(noted in parenthesis above), this is a constant, controlled, repeatable event. This is what I usually try, and successfully, attempt.

Unexpected events:

1. Mid turn, rear breaks loose, total lift. Counter steer. Throttle. Car straightens out. No additional slide angle.
2.As noted in the "controlled" paragraph, following proper theory(apply more throttle) didn't work in some instances.

Before, I always thought that in a slide, one must not lift. But after these events, I can only come to a conclusion that a throttle induced slide requires different actions compared to a throttle-lift included slides. And lifting once over steer has occured doesn't

Anyway, I think that covers it.

Thoughts? Additions?

Disclaimer: Anything you do in your car is not my problem.

[JonOrangeElise]

Originally Posted by mrluky

As of the last few months, I've been ever increasingly enamored with breaking rear traction in the Exige. Ive been experimenting with different inputs, and taking mental notes of events that, in practice, are way different than I what expected, in theory.

All of the following situations are on clean, wet roads, with wear bar rears, NA Exige. no LSD. TC off(and performed on a closed course). unless otherwise noted.

This is what I call a controlled slide, in that what happens, in practice, is what I expected to happen, in theory:
Approaching a turn, in gear, turn in, and apply throttle. The rear breaks loose. Counter steer. Spinning rears. Minuscule amount of lift(<1mm. Adding throttle, or maintaining throttle, I found, just spin the tires), and immediate(the lift and reapply is one motion of up-down asap) reapply of throttle brings everything back in order quickly.
I found that sometimes during mid slide, lifting(TINY amount of lift. 1mm max) stopped the increase of slide angle(spinning rears), and reapplication of throttle straightened it out smoothly. It depends on the amount of throttle used during initial breaking of traction. The lift helps tires grab. Now I'm not sure, since I didn't try, but I think if I didn't lift in the instances where I did, I would have spun right around.

Besides slight throttle input variations(noted in parenthesis above), this is a constant, controlled, repeatable event. This is what I usually try, and successfully, attempt.

Unexpected events:

1. Mid turn, rear breaks loose, total lift. Counter steer. Throttle. Car straightens out. No additional slide angle.
2.As noted in the "controlled" paragraph, following proper theory(apply more throttle) didn't work in some instances.

Before, I always thought that in a slide, one must not lift. But after these events, I can only come to a conclusion that a throttle induced slide requires different actions compared to a throttle-lift included slides. And lifting once over steer has occured doesn't

Anyway, I think that covers it.

Thoughts? Additions?

Disclaimer: Anything you do in your car is not my problem.

Thoughts/Additions: One would have to be an idiot to try car control exercises anywhere but on a skidpad, autocross, or (maybe, possibly) a track. Were you really doing this on a public road? You have to be kidding us, right? You have always seemed like such a wise, level-headed dude.

[mrluky]

Didn't you read that it was all performed on a closed course?

[JonOrangeElise]

Originally Posted by mrluky

Didn't you read that it was all performed on a closed course?

Ah, I see now... What I read was "clean, wet roads"... and I don't equate "road" with "track" (which explains why the magazine is called Road AND Track). And because autocross is never held on a road, to me it sounded like you were driving on public roads.

Regardless, even if you were on a road that was somehow closed off to the public, it's still a road. And most of the roads I've driven are many times more unkind to spinning cars than race tracks. (you can hit trees, rocks, walls, etc in what we call "accident tangents.")

[LarryB]

At a track day late last year- throttle lift oversteer saved my bacon (T3 Sears Point). Drove in the rain/ wet course in the morning for the first time. Was feeling out of sync on a dry course in the afternoon. Had a instructor jump in. He quickly pin pointed that there were a few turns, I was doing a early apex and pinching off the exit. So I come up to this turn (uphill approach, downhill exit). I pull a early apex, however this time I have the speed and throttle for a late apex. I'm coming up to the edge of the track and that outside wall is looking damn close. If I did a full fledge lift and tried to hit the brakes, I'd spin and be carried into the wall. If I let it go off, with the wet grass I may not avoid kissing the wall. I did a quick lift. By doing so I gave up traction on the rear tires, with that extra weight on them it allow the rear to swing around- getting me to turn in. Back on throttle and on my merry way.

So I'd agree knowing how to use throttle lift can be a good tool to have. But you better be pretty darn aware of how the car reacts to it. Higher speed turns your on a very tight rope. In my case it was more of a mid-speed. Have been driving mid-engines for a few year and already done a few lifts on the Elise and found it pretty benign. It was more of a reflex action.

[Shorty111R]

Originally Posted by MattG

Good writeup. The part about panicing in a corner is one that really needs to be emphasized.

+1

Not that I think this point needs any more emphasizing to the guys on here, but I learned this lesson the hard way.

I knew had learned from reading and general common sense that one should NEVER break in a fast turn.

I knew I wasn't supposed to brake in that 65 mph turn, but I panicked, and I did.

End result was that I ended up with a body restyling free of charge, courtesy of Mother Nature and physics. It gave my car that neat "guard rail" enhanced look. Classic.

It was actually an easy lesson to learn, but just would've preferred to learn it a different way.


Oh well, at least I got it out of my system before I got my Elise!



Good write-up, thanks!

[Beanie]

We (MR2 guys on another forum) were just talking about the physics of midengined cars and someone posted a link to this excellent topic, which I remember reading before. I just thought it could use a BUMP for all the Lotus owners who may not have seen it.

[Nachtmensch]

Originally Posted by Beanie

We (MR2 guys on another forum) were just talking about the physics of midengined cars and someone posted a link to this excellent topic, which I remember reading before. I just thought it could use a BUMP for all the Lotus owners who may not have seen it.

t'was I who linked it.