Erik95LS

not quite lifting. http://youtu.be/ggOEoyA5k8g

MBellRacing

Gotta post a couple pictures that SHG_Mike posted in the Conti thread...

This is Turner Motorsport's lead GS car. It has been setup by some big time engineers that have worked for teams like PTG (former factory BMW ALMS team). The driver is Bill Auberlen who is regarded as one of the best car setup drivers in the world... not 100% off the ground, but you can't tell me that the front inside tire is doing ANYTHING grip wise.



The next team is one that is rumored to pay photographers not to post pictures of them lifting wheels because there is such a controversy-- but the fact that they worry about pictures means it obviously happens. Same corner, same issue:

RR98ITR

Matt, Matt, Matt...

The game is over, the jig is up, the cat is out of the bag, the horse has left the barn, the train has left the station, the carriage has turned into a pumpkin, the milk has spilt, the water has done gone under the bridge, the Rubicon has been crossed, the crank has fallen out the block, Elvis has left the building...

Think...THINK MAN...how much faster poor ol' Billy Auberlin would be going if he was getting some work out of that inside front tire there! I mean "HOLY HEIGHTENED CG BATMAN!"

Burn this into your memory banks people: it's not merely gentlemanly to keep all four in contact wtih the tarmac, it's a clear sign of enlightenment. And it is surely a sign of the dismal times we live in that those who should know better can't be troubled to behave!

Scott, who thinks maybe Lotus could pick up five or six seconds that they're just throwing away with these kind of shenanigans...that said, I could see a rational for keeping the inside rear on an fwd on the ground as follows: fiddle brakes, a solenoid switch activated across the rear axle proportioning valve to get some oversteering moment out of the inside rear...but I don't want to be That busy when I drive...

Kozy.

What's with the pictures of cars with wheels barely off the ground?

To me, there is clearly a difference between this amount of lift:



...and something like this...

MBellRacing

You know what's funny, Scott? When I was working at a Mitsubishi racing company we were discussing installing something like a lateral prop valve on both front and rear brake systems to allow the inside tires to rotate more or less than the outside depending on steering angle. Didn't happen since the program was dropped, would have been interesting to see how it worked!

Komodo, I'm basically saying that a tire that is grazing the ground has very little traction and isn't worth worrying about. That Mk2 you show is suffering from no front sway bar and too soft front spring, causing the front to dive too far, lifting the rear tire. Same rule applies, the BMW's above are making only a fraction more traction on their inside front as that GTI is making on its rear.

VTECIntegra9

Quickly back to the K&C Testing:

Here's the rig we (my team of 4, and about 2.5months to do it) made for my senior project a little over a year ago.... I dont get to show it off to anyone who may give a hoot very often so you guys get to enjoy for 20seconds (more if u check my youtube vids)

Braking:
http://www.youtube.com/watch?v=TumCf...er_profilepage

Body Roll:
http://www.youtube.com/watch?v=Q3hhB...er_profilepage

Back on topic-..-

Now, Matt. I 100% agree with your thought - if the tire is just kissing the tarmac or if it's 6" off the ground... it doesnt matter at that point because the normal force on that tire is 0N... but that K&C data from Morse is very interesting... Look again at how the body roll vs. lateral acceleration are related at that point..

That can surely have an impact on how your car is going to react when your roll rate increases and roll displacement (°) increases.

But then again - if the car handles great.. so be it! Weight distribution, anti-squat and anti-dive geometry play a part in this... but with a production car you're right - it will happen because there are so many compromises for ride comfort, pitch centers, etc that we can't have em all. I'm just glad Honda did a pretty damn good job with the DC2 and I'm happy to have one to work on and have a blast with.

Gustav129

I was told this was going to be impossible in the Stock Saab 9-3 Turbo FWD I was autocrossing. Once the owner saw this pic, he didn't let me race his car again.

RR98ITR

Let's think about this image. After noting that the degrees per g increases after inside rear liftoff, what's the next thing you notice - or the thing you had to implicitly notice to have noticed what you just noticed? That the g's "increase"? So if we assume that the outside front tire is in a happy place at the top of that trace, then what exactly is the problem? Right, hoisting the cg upward. What happens when most cars roll? The outside compresses and the inside unloads? Which direction does that resultant take the cg? Depends right? So maybe we can accept that we'd like a low low low b-low ground KRC/FBMC/whatever on the front of our fwd kaa so there's no positive jacking on the outside front, even allowing for how little displacement you'd get from just a little bit of it. How much displacement of the cg do you get from your combination of caster, kpi, and scrub radius? I don't know either. But of course it doesn't matter if the rear end is behaving like you wish it would and the wheel is straight anyway. But either of these, presumably less than if the car were lifting that inside rear super high anyway. So what kind of kaa lifts that much? One that's running soft and high usually. Like they weren't all that concerned about the height of the cg in the first place.

Oh, right, we were going to think about that image. As a problem. What if we didn't lift the inside rear quite off the ground, and there was no inflection point in the roll stiffness, AND the trace didn't peak quite so far to the right - is that better? Which end of the car do you think is responsible for where that curve peaks on the g axis? Everybody always seems to think that the rear keeps doing it's job as the front pair continue to transfer load till equilibrium is reached and or passed between the fronts increasing lateral load and it's diminishing potential of available grip. But if the g's are increasing, albeit modestly per the trace, so is what's being asked of the rear. So if the rear was hitting the limit, by all means you would try to get some more work out of the pair, kill the lift, leave a little load on them. And if it was the front, and everything was giving it's best, then you'd have to try wider or stickier front tires, skinnier or slipperier rears, or more front splitter, or less rear wing, or something. If the car represented in that trace is Not Oversteering at the limit, then reducing lift to zero must necessarily limit the trace to lesser g's after all corrections/resetting of camber etc, since it will necessarily be spending more time with more load transferred between the front pair reducing their grip.

It so often comes down to this: the inside rear is lifting or at least puffing under trailing brake, and the car is still pushy, and the front tires are as happy camber and temperature wise as they can be - What do you do? Besides travel back in time and instead buy a more proper race kaa?

Scott, who sometimes feels like Captain Kirk sittin in the neural neutralizer on the Tantalus penal colony and you guys are turnin the **** to 11...but it's cool cause I'm rockin out...

577HondaPrelude

Rune no 1 for FWD race cars: do EVERYTHING you can to max the grip of the front tires! Even if it makes the rear of the car have less grip. Getting max load transfer from the inside rear to the outside rear means the inside rear has no load on it. This means the load transfer from inside front tire to outside front tire has been reduced Vs having some load still on the inside rear tire. Minimizing the load transfer at the front during a max G-force turn will allways make a front heavy production based FWD car corrner better.

If you have done everything to max the grip at the front end and you still have a pushy car, then start taking grip away from the rear. Use smaller tires in the back, over inflate the rear tires, go with toe out in the rear, ect... Yup, thats right, some times you have to take grip away from one end of the car to make it faster. If you can't throttle steer the race car then you need to fix something on the setup.

Lo-Buck EF

this goes right along with my 'quest for slow corner grip'

Gustav129

Hey, Thanks for the great info about setups so far!

Kozy.

Disagreed. I'm sure Rule 2 of racing any-wheel-drive is 'Don't to throw away grip at one end to compensate for the other'. Certainly doesn't seem to work for me when I used R comps up front and road tyres on the rear, while corner exit is improved, the car just becomes to unstable on the brakes on corner entry. Given a FWD's tendancy to reward a fast in, slow out approach over the traditional slow in fast out, reducing rear grip seems a bit counter intuitive to me. I mean, how far do you go? You could put the rear wheels on baking trays, that would mean LOADS of grip at the front wouldn't it? I'm pretty damn certain that would be a slow assed car though. Pretty likely to crash too from the videos I've seen on youtube...

Surely a better plan would be to increase total roll stiffness in order to keep the outside front tyre at a better angle to the road? If your 40% TLLTD setup is still pushing with 2° roll on the limit, I can't see how chucking grip away at the back is going to make it faster. For one, you're not actually improving front grip. Reducing front load transfer increases front grip. Increasing front tyre size increases grip. Increasing front -ive camber increases grip. I can't see how reducing rear grip by running sub-optimal camber or tyres increases front grip though, other than in proportion to rear grip, with the total overall grip being lower.

I can see how keeping that 40% TLLTD but reduced to 1° roll would be faster however. Load transfer remains the same, that inside rear is probably still off the ground, albeit only slightly, but most importantly that outside front is kept at a better camber angle to the road. You can then run less static -ive camber which will also help in straighline longitudinal accelerations.

Sure, you'll be running the kind of frequencies normally reserved for downforce cars, but I figured those frequency bands were more like guidelines than actual rules...

On reflection though, we are probably talking about vastly different speeds and corner radii...

914Racer

One thing we have left out of this conversation is the limited slip differential. In our FWD cars it contributes more to the picture than in other arrangements. According to some of the reading I have been doing about the BTCC Supertouring cars, the diff made big gains in drivability in the slower corners.

Another thing that we don't cover much because many of you are using stock suspension is the antis, anti-squat, anti-dive, etc. They tend to help out in many cases for us as well. But there may not be much you can do with what you have.

We really need a different front upright in order to lower the chassis further down and correct the suspension geometry. This could help in several cases. It would correct the roll center locations, it would all the CG to get even lower, could built a race car specific geometry to help handling in a race situation.

But many race classes don't allow these changes.

descartesfool

Once you lose the roll stiffness from one axle after one wheel lifts, total roll stiffness drops down to the other axle's roll stiffness, which might be around half of what the total was, so car begins to roll significantly around the outside rear tire for a FWD car. What happens is that you get to the extremes of the camber curves on the front suspension, which is not going to help grip. What also happens is that you lower the front axle's grip as you un-equalize the front tire's loads more and more. Inside rear goes to very high camber as the car lifts and rolls more, which also reduces its grip. So car's lateral acceleration quickly hits the g limit as car rolls more and more around the outside rear, as shown on the chart. So nothing really good happens at lift off, but nothing really bad either, as grip barely increases to speak of, but it doesn't drop off, and this is what one feels when driving a 3-legged dog. This is of course for pure cornering with no acceleration or braking.

If the inside rear fender is lifting more than the outside front is dropping, then cg height is increasing, since the car is rotating about the outside rear. If cg is going up, no good will come of it.

Perhaps it's better because you can continue to tune the suspension in the four paws on the ground condition. How do you tune the suspension for the lift condition? Tuning ability stops once a wheel lifts. Rear axle tuning becomes irrelevant, except for alignment, but since rear axle stops moving, all there is to tune is the camber and toe at the moment of lift off, after that it is the tire's response characteristics as it rolls more and more with constant load.

Move weight toward the rear? Lower the CG? Change the toe? Change the diff? Bring slip angle into the discussion?

I'm still hoping for some alien technology to make my FWD car into a proper track kaa..All grippy and no pushy.

solo-x

Wait, are we talking about grip here, or are we talking about balance? In my book, the two are not mutually inclusive. If the front is doing all it can (grip) and it still pushes (balance) than I conclude that the rear is generating more grip than the fronts and reduce the rear grip to achieve the balance I desire. It's really not as terrible as many would make you think.

RR98ITR

What alot of people don't realize is that this is "the whole problem" with driving cars around corners at high speeds. When I think of all the potential grip being wasted when I turn the wheel I just about want to start crying.

More seriously, a benefit of a tall upright is that the camber curve isn't that fast at the extreme of travel / UCA angle.

And even more seriously, low cg - yes please.

And as serious as I can be: I got no problem with keeping all four down...unless it means throwing away time. The car will tell you everything. How to set it up. How to drive it. You can argue with the car, but it has the last word.

Scott, who wonders if that thingy in the ceiling will give me a tan too...

exgr

i think i needed a lot more droop? 1 wheel on the ground is the fast way here.



May 19, 2012 Marc Gene sets a new unofficial record at Laguna Seca with 1'05.786 in a Ferrari F2003-GA during the 2012 Ferrari Racing Days. I took this one...