GoLowDrew

I noticed late model FWD cars seem to have a wider front track than the rear.

Sort of a tear drop shape.

Maybe I didn't really notice in the past. Either case, why is that? What does a wider front track do for handling?

Or is that an aerodynamic issue? (The tear drop shape that force the rear track to be more narrow.)



Example Mazda6. Hard to tell from the pic, but the front is wider than the rear.

kristo

Interesting Q.

But maybe you should post this in 'Track/Road Racing'.

meb58

All other things eqaul, a wider front track allows the front tires to perform more work and since that's where 60% -62% of the mass is it is certainly beneficial. A wider front track will also introduce a little more understeer and reduce turn-in speed a hair.

I altered track width over front and rear axles quite a bit with track cars. Although the changes provide some real world results, they have to be considered along with all of the other track type modifications.

Wider is almost always better...but at some point it can hurt transient repsonse - like in a slalom. But I think that realm is fairly far off of the normal driver's radar.

for what its worth, the Mini's front track is slightly more narrow than the back and this helps the car turn-in very quickly, in addition to its ultr-fast steering gear...too fast actually.

Track width changes affect roll rate and therefore spring, shock and swaybar rates. If you were to tune a car and you had all three of these at your disposal you would begin in that order; track width, spring rate, damping needs and swaybar rate/wheel rate.

GoLowDrew

^^ good info.

1. Does it also mean a narrower rear track (or wider front track) would mean the rear more likely to fishtail?

2. How about straight line stability?

3. Wheel spacer is the we would do to increase track, right?

I know there are other factors as you explained, but for the NewB 101.... Educate me.

meb58

Sorry, forgot about this one...

1. No...the car will understeer more and you will notice this more during initial turn-in

2. toe is a much bigger influenc, especially rear toe

3. you can use spacers or change whell offset - watch back space and use longer bolts

Increasing track width - front for example - decreases roll moment - the car will lean less but because roll resistance has been increased over that axle RELATIVE to the rear axle we get more understeer. The reverse is true.

If you have 1,000 lb/in springs in the back and 300 lb/in springs in the front you won't necessarily notice more understeer, you will notice less oversteer. I wrote this statment because everything you change affects everything you change.

If you take your stock car from the factory and add 5mm spacers that car will undertseer more but have more front end grip...because the front end cannot lean as much - less weight transfer - and the tires perform more work.

Stinkycheezmonky

meb, would you mind posting credentials/experience? Some of what you're saying directly contrasts what other experienced engineers have said here.

Edit: And what I've found with my own experience on track.

Wai

wut??

Egezzy

iTrader: (2)

-ummm what?

-less weight transfer doesnt always equal faster car.

string

What is the difference between "more understeer" and "less oversteer"?

Contradiction. More front-end work yet more understeer?

Egezzy

iTrader: (2)

well the equation would be speed x radius of turn / velocity (steering wheel angle - slip angle) + (psi1 + psi2 + psi3 + psi4) / 4 x (front track / rear track) = WHHAAAAT! lol.

Stinkycheezmonky

Just so everyone knows, meb hasn't signed on since that last post. We'll see how it goes from there

meb58

Okay, I know this is a little hard this is to grasp because it does sound contradictory.

I can keep explaining it in this way; roll resistance over the front axle increaes understeer, no matter where the roll resistance is coming from. However, in the case of making the track wider, less weight is transfered over the front axle and the front tires can perform more work. The same is true for the rear - except we get oversteer.

Or, and this is really the best way to feel the difference. Install 5mm or 15mm spacers on the front axle and take the car to an autoX course or a track and give it a run.


Egezzy, I don't think I wrote that less weight transfer means a quicker car, only that tires can perform more work. There are so many other factors at work here, as you know.

String, you have to look at your question relative to the example I chose. 1,000lb springs in the rear and 300lb springs up front might yield a car that oversteers with in a blink. So, if you increase front track by say 5mm, oversteer isn't going away, it is being tamed a bit, make sense?

Credentials...I'm a Landscape Architect, I have two children, son is 18, daughter is 22, I have been happily married to a gorgeous woman for 25 years, I've been playing with cars and working with suspension engineers for about 30 years, I held a USFC Cat 3 bicycle racing license up until 5 years ago...I've gone off track a few times and have found that wisdom is nothing more than success made from making lots of mistakes...I've made my share and will continue to do so. i love Italian wine and have a small collection and I love to eat!

Shall I gather a very scientific, rather, mathmatical answer?

del sol noob

i like your credentials

Egezzy

iTrader: (2)

i think thats all that needs to be said.




hahaha. outstanding.

meb58

I'm sure that our suspension dialogue, if paired with great food and wine, would prove out some rather interesting philosophies.

But on a different note, because I haven't had my head in this stuff for nearly a decade, I will get a very specific formula for what i have been trying to describe. I mean only to help...in the beginning I struggled and most folks suggested i leave my cars alone. Since that advice went in one ear and out the other my only option was to learn as much as I could...and I haven't learned enough.

Egezzy

iTrader: (2)

yep. never can learn enough.

meb58

...thought of something here...I hope we're not comparing the roll resistance qualities of a wider track with a larger front swaybar? I agree that too much front roll resistance will eventually lift the inside front wheel off the ground...acceptable in a powerful rearwheel drive car.

Happy Easter..if you celebrate...or Buona Pasqua

Egezzy

iTrader: (2)

i dont think they/i were. thicker bar is obviously going to "have more resistance to roll" than a thinner bar. whether or not that is a good thing comes down to the eye of the beholder.

slammed_93_hatch

I went around with this guy before... (https://honda-tech.com/forums/suspension-brakes-54/wheel-spacers-2735362/)

and here is what it boils down to.

He assumes that you have optimal grip up front already. So yes going wider would make the car push (as would going narrower).

IMO it's kind of foolish to think you are starting with optimal grip up front...

beanbag

yes, because I'm not sure I believe this part:

As far as I know, calling something understeer or oversteer has to do with total available grip front vs rear. and total available grip has to do with (among other things) how evenly weight is distributed between the inner and outer tires. So as you said, increasing track tends to even out the weight distribution between the front tires due to lateral forces, but at the same time the front of the car wants to lean by less, which means that (relatively) the rear wants to lean by more and applies a twisting force to the front that tries to lift the inner front, thus increasing the disparity of weight distribution, thus cancelling out some of the benefits. I'm not sure which effect is greater. It probably has something to do with roll centers and roll stiffness and etc.

I think most people's experience is that increasing front track decreases understeer, even if the front roll resistance increases.

edit: just read the link by s93h.

meb: I still don't agree with this statement:
"roll resistance over the front axle increases understeer, no matter where the roll resistance is coming from"

I would modify it to say that increasing the roll resistance in the front CAN create some understeer tendancies due to interactions with the rear roll stiffness BUT it can be more than cancelled out by the increases to the front grip. And you don't get to say something results in oversteer or understeer until you are done tallying up all the changes. For example:

If you get a bigger front bar, the front roll stiffness increases AND there is otherwise no improvement to front grip distribution if you consider the front half alone, so result is understeer.

If you increase front track, the front roll stiffness increases, so via interaction with the rear of the car, that has SOME understeering tendancies, BUT it also evens out the weight distribution between the front tires, which has a BIGGER oversteer tendency, so overall it increases oversteer.

Etc etc.

Egezzy

iTrader: (2)

meb. i had to stop reading after the second quote. my head hurts..slammed said wider track equal more mechanical grip. then you say wider track means understeer through more grip though mechanical "leverage" but in the next quote you say well if the track is increased then so is grip.

i also think that under/oversteer are two abused terms. "if i put on one of dem dur 32mm asr barz my car will have mad tyte ov3rsteeR!"..i seem to like the term rotation better.

beanbag

Since meb has not come back yet to clarify his points, I will say that I think these three things are true:
1) If you increase front roll stiffness ONLY (without changing anything else), then it will increase understeer
2) However, adding wheel spacers does more than just increase roll resistance only, IT ALSO increase track.
3) The added benefits of extra track cancel out the effects of increased roll resistance, leading in most cases to more oversteer.

essex

This is interesting for me. I love how everyone is questioning this guy. When beanbag opened a koni everyone freaked out and told him he was crazy. "Just send it to koni"
they screamed. Beanbag said spacers have little to no effect on spring rate in our cars and no one questioned him even though all of these years we have been told otherwise.What are beanbags credentials? Could he be a spy from Bilstein here to infiltrate a koni biased board? Who exactly is RR98ITR? Who exactly is descartesfool? Who are these people?

Seeing How meb has explained his experience I would love to here about the experience of the others because I follow everyone's posts as they are very interesting.

Stinkycheezmonky

beanbag has been questioned in the past. So has Scott (RR98). I don't know that Claude (descartes) has ever come under scrutiny.

unusual71

this was hands down the most paranoid post i've seen in the suspension forum lol
Love the discussion though its giving me ideas for future mods, i think people need to keep in mind that under different conditions different things are going to happen. its never as simple as a change in this results in a different that, what if the car is going uphill, downhill, into a corner, out of a corner, part throttle, part braking etc etc.