Rear/Front track width

[RacingManiac]

pretty sure he means the opposite...wider track at one end usually means more grip at that end....

[DaveW]

Tom - reasonably so. Increasing the front bar or increasing the front track should cause the front axle to carry more of the cornering roll moment and the rear axle to carry less. Either change should, I think, move lateral balance towards understeer.

[nas]

I am sure he doesn't... He would've meant the opposite if the chassis had a joint between the axles allowing them to roll independently, but as the chassis is relatively rigid (relative to the suspension that is), the wider track will take more of the lateral load transfer as the overall vehicle roll will cause greater relative displacement of the wheels belonging to that axle.

[Jersey Tom]

You may want to check Milliken on that.

[nas]

This is exactly where I am coming from - it was their book that put me right - check the load transfer formulas for the complete (2-axle) vehicle, play with the track widths and see the results.

[DaveW]

Apologies, I didn't intend to be controversial. I wonder if we are talking at cross purposes. A wider track should improve cornering ability in general (all else being equal), and increasing the front track only may well increase max lateral acceleration overall. But I think lateral balance will also change as I suggested.

[RacingManiac]

I think its an interesting discussion, for me anyhow. I am trying to see how the grip increases with the wider track at one axle. Since I do think it is true that the roll resistance increases as the track increase, which should correspond to increased lateral load transfer.

[DaveW]

RM - If your last post was to me, then I would reply that max lateral acceleration is normally proportional to average_track/c.g_height (amongst other things). Increase the track at either axle (as the only change) and the average_track will increase, so it is reasonable to expect max lateral to increase.

However, expect a driver to complain if an increase in performance is accompanied by a lateral balance shift (assuming he wasn't complaining in the first place) - and he would be right, because performance should be improved further by the additional changes I suggested.

[nas]

Not a problem DaveW, in fact apologies if I was sounding controversial and my second post was directed more towards Jersey Tom's reference to the Milliken's book

[Belatti]

The easiest way to see this is using equations.



Increasing track width does not increase grip or lateral force, but decreases lateral weight transference.

Decreasing lateral weight transference:



you improve lateral force coefficient (see the 900lb curve peak is higher than the 1800lb one). That means that the outer wheel will loose some grip but the inner one will gain more than what the outer losses and thus overall (inner+outer) grip increases.

This is why you will always prefer max track width permited by the rules and do not use it to tune the vehicle (as Jersey Tom pointed out) UNLESS (sory for shouting) your car lacks suspension (kart case) or your stock car lacks aerodynamic treatment so that wheels disturbs airflow and in very fast circuits aero turns more important that lateral weight transference and Im sure there are other cases.



Early 90s TC: note how the wheels where compared to the front



2009 TC: wider and modeled front with lateral protections to increase safety in case of lateral impacts

EDIT: OOT for sure our aero mates will explain us all about that steped rear spoiler we can see in the green Ford in thisthread .

[Jersey Tom]

I did misspeak earlier. If you keep your wheel rate the same and change track width purely by wheel spacer or what have you, increase in front track width bumps the TLLTD forward.

Initially I'd just seen the 1/t term out front but that doesn't dominate the split.

With the rough numbers I used, even adding a half inch of spacing on the front track only gives 0.1% bump in TLLTD(front), but it's there. In any event given how big of a track change you'd need on a standard size chassis.. I'd change spring, bar, tire pressure, and diff first... and I've never seen track width as a tuning tool on a full size car given how many other options there are.

[PlatinumZealot]

If i remember correctly; the Ferrari F-50 has a wider front track.

[DaveW]

Thank you JT. I appreciate your last post & agree completely that springs, dampers, bars, diff, & sometimes tyre pressures and ballast are the primary mechanical tuning tools - but, with respect, that wasn't the question.

The point of my original post was to try to suggest (clumsily, as it turned out) that lap time is often not linearly related to set-up changes. Thus changes that appear to have a negligible effect on a flat track can, in reality, have a large effect on lap time especially when they relax other constraints.

Improving the ability to kerb would be an example, because slow corners often precede long straights. In that case a small improvement in exit speed will have integrated to a large time delta by the time the brakes are next used (without an unaided driver being aware of the fact).

[Belatti]

The point of my original post was to try to suggest (clumsily, as it turned out) that lap time is often not linearly related to set-up changes.

Of course not, but that is almost everything we-who-do-not-drive can do. I say almost because you can always have data acquisition or use your simple eyes and ears to feedback the driver, but thats that.

You can even improve the setup for one driver and have a worse laptime if another driver cant adapt (the M. Schumacher case is the example number 1). Or you can improve the setup and have a worse laptime searching for endurance, such is the case at Le Mans.

Ultimately, what you have to balance is not a setup, its a compromise

[alelanza]

That means that the outer wheel will loose some grip but the inner one will gain more than what the outer losses

You sure about that one? I think the smaller weight transfer accounts for a smaller loss of total grip, but grip does not increase linearly with weight, as your graph proves. Otherwise a heavier car would have the same braking distance as a lighter one under the same conditions no?