F1 weight distibution-where's it going?

[RWC]

I allways wondered why they started the current desperate trend of building light cars just so they can add mass to the front of the car.Yes it does help share the cornering loads evenly between front & back ,but wouldn't it be best to optimise everything at the back for the all important acceleration?Then it clicked(ok i'm slow)It's better to optimise breaking than acceleration!Because they can break at up to 3+(?)G's,while acceleration is rather tame at 1.5 G's.It all makes sense now!

[Luc]

The main reason for the lightweight cars is that they can put the ballast in the floor of the car. Like this they can lower the center of gravity radically. And another reason is they can distribute the weight underneath the car to compensate for lack of downforce at the front or rear end, depending on the wing and car status.

[RWC]

yep thanks,i did know about those things.I used to think they were the only reasons for moving the weight around.What i realized was because an F1 car can slow down much better than it can speed up(because the brakes are much stonger than the engine)-Then it would make sense to put more aerodynamic and mass loads towards the front of the car............(?)

[Luc]

The placing of ballast is a very complex item. It can also be used to increase or decrease over- or understeer.
There are so many variables in this matter that only the real specialist will be able to explain it all.

Problem is that those specialists are most of the times employed by a team and therefor hardly release a detail.

by the technical director is often the problem with details in F1.

[av8rirl]

Aside from adjusting weight bias front to rear, it is also possible to adjust adjust weight bias left to right (therefore moving CoG left to right too). The shifting of weight left and right can help a car to corner better therefore making more time in the corners.

The ability to move mass around the car is quite a big topic and ties in to different variables such as wing, downforce, understeer, oversteer, track and the last (and most unpredictible) variable being driver preference.

I think that to conclude that the weight is shifted forward to help braking is incorrect. You will certainly make more time from acceleration than braking. If you can accelerate more quickly you should always reach a higher top speed at the end of a straight (ie gaining some time). Whereas if you can brake harder you might gain a few 000's but you have to be mouch more precise with the braking than accelerating. You run the chance of missing the braking point, locking wheels, flatspotting tyres, missing the apex, late on the power, etc...

All in all, I think that it is much more likely that all teams would rather accelerate out of a corner earlier and quicker than be able to brake later. Slow in fast out...

Just my thoughts. If someone REALLY knows the answer please share the knowledge and contradict me (cause I too would love to know the real reason).

[enzo]

Actually, for optimal braking, you want the static weight load to be biased heavily towards the rear.

Tire grip does not increase linearly with increased download, so as weight transferes from under braking, you lose more braking potential from the rear tires than you gain at the front.

The same hold true for grip and weight transfer in cornering.

What the teams are actually trying to do is optimise accelleration off of the corners. With the rear tires being as small as they are, the desire is to get the front tires to do as much work as possible so that there is enough rear traction available to allow the driver to get on the throttle as early in the corner as possible.

[av8rirl]

Thanks for keeping this thread alive enzo. I thought it was doomed. Although you talk of F1 cars, this is true for all cars and is a point for me to bear in mind when I eventually start building that bloody Vee.

If you have more knowledge and ideas (which I'm sure you have in abundance), don't be afraid to let us know, so that we can learn and maybe return the favour one day.

[RWC]

Mmm,some interesting thoughts.i thought tyre grip DID increase linearly with increased download-well, within limits of course.I'd been led to believe that by someone who should (?) know.
Hey av8rirl,do you mean you're building a formula v?

[av8rirl]

RWC: Its the longest build in history. I've got certain objectives for the car (which are added to every few weeks). I've got the plans. I've got the plans rev.2, all the way to plans rev.8 I know what material I'll use, how the engine will be mounted, etc.... Don't know how quick it will be.

I can't weld.

So that Vee is the reason why my personal ten-tenths fav forum is the Techie forum.

[Adam43]

I thought tyre grip was proportional to the force downwards (the weight if we neglect aerodynamics) - F=m*friction coefficient. This then increased the force needed to be applied to exceed this grip. However the cornering force from Newton's second law was also proportional on mass (F=ma).

If you equate the frictional "grip" force to the acceleration due to cornering (i.e. being on the limit!) then the amount of acceleration (or cornering g) is just proportional to the friction coefficient of the tyres (the grip).

A similar argument applies to straight line acceleration.

The front and rear weight distribution is the thing that changes under straightline acceleration. Shifting to the front for braking, which can give the front more grip and causing the rear to break away.

This can be combated by changing the weight distribution (and also eased by changing the break balance). I vaguely remember some DTM system a few years back that actually had moving ballast.

Anyway, I think this tallies with most of above. I just thought I'd enter my musings on the subject.

[enzo]

No, grip does NOT increase linearly with increased download. The actual ratio depends greatly on the tires compound and it's inherant hysterisis. You are dealing with the strength of the bond of the sticky rubber, and with the tensile strength of the hot rubber, not just simple frictional coefficients.

It is for just that reason that designers go to such extreme lengths to lower the center of gravity, and to widen the track as much as the rules allow - less weight gets transfered, and the overall grip level is kept as high as possible.

It is also why you pay no apparant penalty for long wheelbase cars - the increased braking performance outweghs the increased polar moment of inertia. The longer WB also aids in pitch sensetivity on the aero front.

[Adam43]

Humour me for a second. If the grip of the tyre is dependent on the force acting downwards and it's frictional component.

Can not what you have said be described as a changing of the frictional coefficient. Is what you are saying that other effects such as the load on the tyre (effecting compression, temperature etc..) change the performance of the tyre.

Which leads to a situation where the frictional coefficient should be replaced by a function that is dependent on speed and load (for example).

Lowering the c.o.g. and widening the track surely would give the same advantages even if it was a linear relationship.

I agree with what you are saying, but am surprised that the situation is so non-linear as to be important. Are you saying that the grip is sublinear or superlinear to the downwards force? (in normal working conditions).

[enzo]

The relationship is sublinear, as you put it - ie - if 500 lbs normal force gave 1500 lbs of grip, doubling the normal force to 1000 lbs would not double the grip to 3000 lbs. It would be something less, say maybe 2400 lbs. Another increase of 500 lbs normal, for 1500 total, may then gain only a further 600 lbs of grip, etc. It will depend on the construction, the compound, the tire temp, the track surface, etc.
This is a well known phenomina about tires, and is mapped religiously by the tire companies (but try and get that info from them!).

If the relationship was perfectly linear, then there would be no need to get so fanatical about lowering the CG to keep weight transfer down.

[RWC]

I bet they religiously map the characteristics!
I've also heard of 'kinetic'friction from 500 gp bikes.These tyres were described as giving their best grip when they're sliding a little.I imagine drag car tyres are very much that way.Anybody know much about this?

[enzo]

That is actually the slip angle that they are talking about. To generate a cornering force, tires must generate a slip angle. The angle generated depends on the load and the construction of the tire, as well as the compound's characteristics.

The term "slip" is actually a misnomer - the tire is not actually 'slipping' - which people confuse with sliding - sideways. The carcass and the rubber is distorting under load such that each segment of the contact patch that is just coming into contact with the road is slightly offset sideways comparred to those segments already in contact.

Full race slicks such as those used b Indy cars may generate a slip angle of only 1-2 degrees, whereas a street tire may generate 15-20 degrees. I imagine that the bike tire is probably in the 5-8 range.

[RWC]

Ahh yes!i have had various dirt bikes on which i usually use MX tyres even on tarmac.Those things REALLY walk sideways when cornering.I Oz here we even have retreaded dirt tyres.I haven't tried the fronts but the rears have a few strange characteristics,one is that if you go into a corner on tarmac somewhere near the limit & cut the throttle the rear tyre will step WAY out.Weird!

[enzo]

Nothing wierd about that at all. Since the tire is alread doing all the work it can, shutting the throttle down just adds more work than it can handle (decelleration). Pretty standard reaction.