Towards a more accessable Technical Forum...

[Sparky]

I have received an email from a Ten-Tenths member, asking me if we could include some topics that might explain some of the more basic and fundamental technical queries that forum readers might have.

It seems that the less technically minded members might be put off from posting any comments or questions they may have for fear of ridicule.

(By the way, if this describes you, and you refrain from posting THAT question to save embarrassment, please feel free to email me your question, and I will post it here myself to guarantee your anonymity.)

There are quite a number of points that they have asked me to clarify, so I thought that I could post them here individually, to perhaps encourage discussion on the topic.

Please feel free to offer explanations or information, but try not to tease or belittle.
Members are trying to understand and enjoy racing from a different perspective.

So, the first topic is:

“When they say the car is "loose" or has "push", what does that actually mean?”

Thankyou.

[enzo]

OK. I'll bite on this one.

"Push" and "Understeer" are one and the same - a tendancy for the car to want to not turn , to go straight. Basically, there is not enough traction at the front compared to what is available at the rear.

"Looseness" and "Oversteer" are again one and the same - this time the car will turn in, but the rear wants to continue moveing sideways, ending up with either a "tail out" attitude, or ending up with a spin. Basically, there is not enough traction available at thr rear tires compared to the front.

[Sharky]

You can change the behaviour of the car with the suspension and wing settings to increase or decrease the grip on the front or the rear. You can see how the wing thing works in CART where they usually make a lot of adjustments to the wing during the pit stops.

So if you happen to listen to the radio you can hear the driver complaining about the car oversteering or understeering too much and then as he comes into the pits he would ask his crew to put or take X "turns" of front wing (it's called a turn because they turn a little lever at the nose of the car that cases the wing to change it's angle). So if the car understeers the driver will ask his crew to put some turns of front wing or take some turns of rear wing from the car therefore increasing the aerodynamic pressure in the front and therefore the grip of the front tyres....taking off wing from the rear will cause the exact opposite for the rear wheels.

And if the car oversteers then you do the opposite.

[marcus]

ok sharky..i understand all of that..but i race Karts so what would i do to stop push or understeer without the aid of wings??

so far Ive either had understeer or oversteer without a happy medium but i adjust my driving style and it seems to work OK but getting the kart sorted would help my chances further.

[marcus]

and I have another question on this matter.

you see it all the time in indy racing but how come we very rarely see wing changes during an F1 race ????

[KC]

On racing vehicles without the benefit of aero aids to help tuning it becomes more a matter of weight transfer. By narrowing or widening the track width of the kart, different weight transfer rates can be achieved. I am not sure what to tell you exactly, maybe some of the kart racers here can help out.

I too have seen the same thing concerning wing adjustments. I have a feeling that F1 teams have done so much testing and setup work during the build up to the GP that they have it pretty much sorted out ahead of time. I also think that CART chassis go through a much larger range of changes during a race. Possibly they are much more sensitive to weight changes as the fuel is used up or it is due to differences in tire wear.

[Sharky]

Mhhh....I don't know how that would work on a Kart as it doesn't have any wings or suspension.....If I was to take a guess then I would say that the only thing you could do is play a bit with the tyre pressure but I'm not so sure about that one.

As for F1 cars not making those changes....I think that KC is right....:Champ cars might be a lot more sensitive to weight changes....as well as changes in the track like the ammount of rubber layed down and such. I also think that it could be that chap cars are only fine tuned at the race as they get very little testing and time to set up the car (there will be absolutely no testing starting next year).

[Warwick]

On a kart you can change it by altering your track widths,widening the rear will tend to make it oversteer, narrowing it will make it understeer,front track width will also affect how it turns in,and all this can change with tyre pressures,relocating the seat can also help,move it forward for more weight on the front,or if you are underweight for your class,expiriment with putting the weight in different places and checking the effect it has.

[Liz]

CART pilots and Jacques Villeneuve sometimes complain that their cars rear ends "suddenly broke loose" - especially Gil used to complain of this in the old Walker car, and it always made him drop to about 12th and stay there, so presumably it can't really be corrected if it is a massive change. Jacques has complained frequently this year about the Zipmobile suffering attacks of massive looseness. What would make it happen suddenly and be uncorrectable?

[enzo]

A real good question, Liz, and one that can drive the engineers nuts trying to find the source of the problem. Where to start ?

If the car I'm working on suddenly goes loose like this, I'll first have to determine under just what conditions it has the problem. If it is all the time ( everywhere on the track, irregardless of accelleration, decelleration, corner entry, middle, or exit), then I'll look for a mechanical failure - something that is causing the rear suspension to bind up (usually the binding is it's worse in compression, not droop). With the delicacy of modern shocks (trying to fit a lot of adjuster parts into small packages), we'll quite often find that something in the shocks broke.

Other causes can be overheating of the rear shocks, bellcrank pivot bearing failure ( very rare!), rear anti-roll bar problems (again rare), or tire problems. It's rare to get a bad tire, but like anything man-made, it can be f*cked up on occasion!

If the sudden looseness is only in the middle of a particular corner (and usually a high load corner, or one with a sudden change in elevation like a bump), I'll look for an aero problem first. Quite often, especially with flat bottomed ground effects cars such as F1, Indy Lites, F3, F3000, etc, you can get bit by running the car too low. What will happen is that, under a higher than normal load situation, the leading edge of the undertray can touch the ground and momentarily shut off the airflow to the diffusor, causing a massive loss of downforce. You'll see this happen on occasion in the Indy Lites races at Homestead and Milwaukee.

For diffusor car with the exhaust dumping into the diffusor, it can be as simple as the driver selecting a too-tall gear! With the engine at lower revs, not enough exhaust is going to the tunnels, and downforce is lost.
For Indy cars on ovals, quite often it is a problem with the rear ride height going up, or a change in cross weight. Ride height will naturally increase with diminishing fuel load, and if the starting setup wasn't exactly perfect, combined with other things that effect ride height and can change during the race, the rear can rise too much and again cause an aero imbalance. When I say "too much", I'm talking on the order of .050 inches or so ! Normal ride height adjustments for fine-tuning balance are in the .010 range.

Corner weight jackers (little hydraulic pistons fitted between the spring and its seat on the shock, adjustable from the cockpit, and usually used on ovals only) can spring leaks, causing the rear corner weights to go way off. BIG problems for the driver if this happens, 'cause there is no way to adequately compensate with other adjustments.

Bad rear shocks can also be a culprit. They can be over-heated or break, as mentioned before, or they can spring a leak, which if bad enough, will eventually cause the shock to go dead, ie - no damping at all.

There are a thousand other scenarios for problems that can cause looseness like this, but these are the most common problems.

Hope it helped.

[Liz]

Wow! It's a miracle those cars work at all, with all those things that could and do go wrong.

Thanks, I will copy that into my Gizmo file and next year I will be able to hazard a guess as to which thing it was that might have gone West.

[Sharky]

That's a great explanation enzo. I think I'll save a copy on that explanation on my HD as well.