Suspension Ideas and Questions

[mep]

Little off topic, but is Forza Motorsprt 3 a good way to learn about how to tune a car?

I don't know but F1 Challenge or R-factor are good to play around with setups and telemetry. Just sad that they are really old now. Something new would be great. F1 2010 is crap.

[rjs]

It's a book.

[C09]

Okay... now to find a copy...

Jeez, how few people play FM3? It seems I'm the only one in the world, almost.
I thought it'd be more popular, seeing how awesome the graphics are. In photo mode, you can see just how much detail went into the game. The valve stems look real. The brake rotors have crap graphics, though. Kinda odd. But the cars are gorgeous, even on a 17" screen with a crap@$$ contrast ratio. (Like, 1:300) I wonder if the cars in FM3 had their suspension geometry measured to improve the accuracy of the game.

[Jersey Tom]

Little off topic, but is Forza Motorsprt 3 a good way to learn about how to tune a car? About how accurate are the tuning options in game compared to real life?Thanx.

Eh, yes and no. Is it a vehicle "sim"? Yeah, more or less. Are some things going to be accurate? Sure. Some won't be. Some might only be accurate within the limit of whatever car and tire set you're playing with. Basic stuff like moving roll stiffness to the front or rear is probably represented accurately.

Ultimately, trial and error isn't a great way to learn vehicle dynamics and tuning. You're getting a lot of "what" through observations and not much "why." The latter is very important, IMO.

[forty-two]

By the way, welcome to the Forum C09.

Glad to see you're asking interesting questions so soon after joining. I lurked around for some time before plucking up the courage to start asking questions!

On topic, could it be that the MP4-25 (and 24 to an extent) was suffering precisely from the inner wheel camber issue raised above, leading to both LH and JB locking up the inside wheel so frequently, or do you guys think it's as simple as McLaren running super stiff?

[Jersey Tom]

Not that simple. There are relatively straight forward ways to mitigate inside front lockup under the brakes, but it's always at the expense of something else.

I'm sure the McLaren race engineers felt it was the lesser of a variety of evils and would ultimately give the best lap time.

[forty-two]

Not that simple. There are relatively straight forward ways to mitigate inside front lockup under the brakes, but it's always at the expense of something else.

I'm sure the McLaren race engineers felt it was the lesser of a variety of evils and would ultimately give the best lap time.

I'm sure you're right, but I wondered if this might have been a contributory factor. I was always surprised to see JB locking the fronts last season. Totally out of character for him, but he didn't seem to mind!

[Ciro Pabón]

Okay... now to find a copy...

You can do it at Amazon, there are no alternatives that I had found.

At Google Books you can find Engineering to Win (well, at least the bits they publish). Here is the link that will take you to the references to Tune to Win that you can find in that book:

http://books.google.com/books?vid=ISBN0 ... zTSQtWzsPs

This could be enlightening (I'm transcribing here, so don't nag me, emphasis is mine):

The preponderance of vertical load on the outside tire ensures that, as soon as lateral load transfer begins, all the toe out will be on the inside front tire. What static front toe out does, then, is to increase the steer angle (and therefore the slip angle) of the inside front tire. It is easy enough to visualize how this will encourage the car to turn in. If our original theory regarding Ackerman geometry and the racing car were correct, once the car has turned in and taken in set, front toe out should be detrimental to the generation of front adhesion. BUT such is not the case: Front toe out helps in all of the phases of cornering, not just in the initial point department. So, we just may have been missing something here.

None of us LIKE to use static front toe out because we are afraid that it will make the car unstable under the brakes (Ciro's note: Oh, yeah! It will... and I have the scars to prove it) and we are afraid that it will increase the rolling resistance of the front tires to the point that it might slow down the car down in a straight line. Some of us have been using toe out in bump at the front to achieve pretty much the same effect. I have never been able to substitute toe out in bump for static toe out, but I have been able to reduce the amount of static toe out required. When we arrive at the street courses, we use both.

If I am not mistaken, Ayrton Senna has a similar comment on his immortal Ayrton Senna's Principles of Race Car Driving. So, there you go. What you want is not geometric perfection nor strict Euclidean analysis but to go, hopefully, faster. So, listen to Jersey Tom. We all do...

[Caito]

You're saying you want static toe out at the front to increase the slip angle of the unloaded wheel, hence improving total grip.

We're assuming that the driver wheel keep loaded wheel at peak angle, so we try to maximize the lateral force generated by the unloaded tire. If in an f1, we would have to reduce toe out(peak slip angle increases with load)

We could achieve a similar effect with ackerman, I think. You increase the ackerman and get higher slip angle on the inner wheel.


When you say toe out in bump. Do you mean in droop? The unladen wheel is in droop when cornering, if you want to increase its slip angle, you have to toe out in droop, and toe in in bump. Am I right? Or maybe I'm missing a piece. That way you'd have "roll steer" in the font. If not (just guessing) you'd get steering opposing the turn. You turn your wheel, the car rolls, as the car rolls you lose steering, so you have to steer more. IDK if this is good. Else you'd have you steer, the car starts to roll, car turns in more, you have to remove steering.

EDIT:
If you use toe in in bump you could get stability while braking(the car dives) but still have your static toe out

[Jersey Tom]

There is so so so much more to this in terms of steering response and stability...

[747heavy]

None of us LIKE to use static front toe out because we are afraid that it will make the car unstable under the brakes (Ciro's note: Oh, yeah! It will... and I have the scars to prove it) and we are afraid that it will increase the rolling resistance of the front tires to the point that it might slow down the car down

I agree with what JT says in this context, that it is difficult (wrong/missleading) to look/think about tire geometry in isolation and in static/purely geometric terms.
Sometimes (more often then not I hope) you do things for a reason, even if what you do at times in isolations seems wrong/detrimal, it can make a lot of sense when seen in context with other factors.

one factor which comes to mind is suspension stiffness.
Very few people actually know (IMHO) what is "true" position/angle of the tire to the ground (camber & toe) during cornering.

It´s easy to overlook things like rim deflection, wheelbearing deflection and/or buckling of toe links etc. under load.
And please don´t tell me, that it´s "bad design" when thing likes this happen, you try to built a race car not a tank.
And these things will happen on race and championship winning cars. The trick is, to be aware of it and to deal with it, so that it does not has a detrimal effect on performance.

Just one thought to keep in mind, in regards to the statement made in the quote.
In which direction would a tire with negative camber roll, when not constrained?
Which forces would this generate?
Could toe-out be benefical to counter this forces?
Could it be benefical to reduce tire "drag" in a combined condition?

It´s probably more relevant to cars (like Touring/GT cars) which use large(r) amounts of negative camber and (relative) narrow tires.

[marcush.]

+1 jumbo.
at the end of the day you look at what reduces your lap time.if a differnt ackermann percentage will net a better dynamic toe ..you will do what is needed to change it and you will in your mind kill the bloody bastard who designed your
front suspension not allowing for adjustable ackerman.... maybe commiting suicide was the correct reaction as you designed the thing by yourself

[Ciro Pabón]

Well, it's not that complicated either. I agree with Marcus. As Robert Mitchum, the famous actor once said: "You show on time, say your lines and get to the marks and that's it".

Racing is simple, like all good things in life (love, kids, learning, honor, death).

I have to disagree on one point: you can watch the camber alright. You can watch all the angles you want in an open wheeler, like a Kart.

For example, camber is nothing compared to tyre tuck. I mean, the patch moves under the rim, doesn't it? By this, I mean that the tyre is stretched sideways. In a Leopard class kart the tuck (or whatever is the word) is so high that the rim sometimes touches the ground, specially in the rain when you deflate the tyres.

So, I don't know how important is tuck compared with other things, but in my experience (35 years and counting), a bit of camber in droop or in bump is nothing compared with wall rigidity and static camber... and that's just one example.

It's much more important tyre pressure and how you treat the temperature that anything else. Specially in open wheelers, where the suspension doesn't work a bit... you run on the tyres, not on the suspension, let's be frank (or else!).

I've run rookie karts with 8 mm positive camber per side with good results and a "grippie exit" and I've seen people running Leopards with 5 mm negative. I concede we're concentrating here in rear lift, but... And if someone can explain this difference in terms other than wall rigidity and lateral inertia, be my guest. Yeah, yeah, I know: I drive an old Beemer these days and the Z-link rear suspension is a pleasure to my ears and to my "racing butt", but, hey, it's not a racing car, at least not a purebreed, ain't it?

I can tell you something else: in the end, after some years, you know how to put the wheels on the ground and that's all there is about racing. You can see how the colour of the tyres change with a minute, delicate flick of a wrist and you feel the tyre temperature rising, don't you? Then, you just look ahead, you feel the breeze on your cheeks and you know that the world is allll right and the zen invades you. That's how to race: forget idealized suspensions, forget winning. After all, ALL racing works because of four patches the size of your hands, even at 350 kph and it's the feeling of the driver what moves those little patches (and a very good engine!) more than anything else. Any other approach and you kill the joy... and it's about joy.

I swear I haven't drink to write the previous paragraph, btw. Sorry for the (lame attempt at) poetry...

Please, make a queue to nag me... order is everything in a forum!

[marcush.]

++++1 ciro!

you are riding the 4 contact patches.Funny that some of the F1 drivers seem to know nothing about all that or they make a mickey of us stating silly things ..or they don´t know howe to explain themselves..(poor track engineers having to work with such a bastard..)natably Sutil was on the record admitting to not realising that he had two differnt compounds on the car after his pitstop.. .It´s beyond me when a driver is unable to distinguish the two tyres he has used the whole weekend on this track how he could report back anything useful in the briefings...but maybe he was trying to make a joke.

on the other hand some tyres do not really react to tyre pressures ..you will feel a degree of mushyness but then its already on the verge of a catastrophic failure.I have seen that with Dunlops a few years ago .funny that a lot of Dunlop teams seemed to suffer from punctures as well ..leaded me to the suspecicion that teams tended to run them underinflated ?

[C09]

Nice one Ciro. I think most motorists and mechnics and teams Kinda get lost in the haze of winning. F1 is all about the art of making raw materials into something great, not just about winning. It's about hammering steel and forging aluminum and baking carbon fiber and smashing every obstacle. It's about the terrible risk of death if something goes wrong, the challenge of limited resources and strict regulations, the spirit of competing with other gearheads just like yourself, the path to the top, that's what it's all about. F1 is all about the journey, not where you end up, but how and why.

Did I just write that? I sound like a poet.

This got off topic pretty quick, but good spirit is always a good thing, no?