Adding track width. Effects? (2024)

I have been reading that by widening the track width,you effectively make it more difficult for that end of the car to lean on to the tires because it is now longer and flatter in that direction. And I have heard that if you do this you can use it to dial in or out understeer and oversteer. My real question comes in as this: how much of an affect does this have? And how much of it do you have to do in order to gain a noticeable effect?

The main reason I ask is that I am looking to space my rear tires out approximately a half of an inch, the fronts are fine. And for right now I am not running any sway bars front and back until I assessmore of what the car needs.

In reply to Trackmouse :

Increasing the track width does two bad things,makes the car wider so it has to travel further through the cones. A few inches of added travel may not seem like a big deal but considering how close some races are that may not be a handicap you want

Wider car pushes more air, that increases the drag.

Are you talking about stagger? Years ago, I tried “reverse stagger” (i.e., front track wider than rear track) on my E30 track car. It was recommended by my good buddy, who was a regional autocrosschamp.

My issue was the E30 had too much grip and not enough HP torotate under power. I don’t know if it was simply the widerfront track or maybe increased weight-jacking effect, but the net effect wasthe outside rear tire would load upmore dramatically. That let me control the rear end better under throttle without having to do so much trailbraking.

Old-school supercars like 512Testarossas and Diablosused regular stagger (rear width greater than front), presumably to have the opposite effect and stabilize the rear under power.

In reply to LanEvo : stagger is that he difference between the left and right tire diameter( usually measured by circumference ) not track width.

Normally a large difference aids turn in ( in one direction) increases over steer. ( circle track speak loose)

A small or no difference will add to the stability increases understeer ( circle track speak push)

rslifkin SuperDork
3/6/18 10:09 a.m.

JBasham HalfDork
3/6/18 11:28 a.m.

If I'm looking to adjust corner entry and corner exit balance, and class rules allow it, adjustable shocks are an easier and more effective route for me.

Also in the past I have tried to address understeer in cars that came from the factory with staggered wheels. I was told a square setup was the way to go. It didn't make much difference, but at least I could rotate the wheels around. Camber plates made a big difference, and brake/throttle approaches came in second. Ultimately, front engine cars like to understeer and there's only so much I can do about that.

Basic vehicle dynamics: the wider the track, the lower the amount of weight transfer. This means more grip. If you only widen at one end, then that end will gain traction and the other will not which changes the handling balance.

A good introduction to the theory

As always, there are edge cases with regards to range of motion limits and you will change your effective spring rate (aka wheel rate).

Driven5 SuperDork
3/6/18 12:48 p.m.

loosecannon said:

Adding track width softens the spring rate...

Keith Tanner said:

...and you will change your effective spring rate (aka wheel rate).

A common misconception. Inroll or one wheel bump for a live or beam axle, it will. On most typicalindependent suspensions, it will not.

Driven5 SuperDork
3/6/18 12:57 p.m.

Motion ratio is based on shock mount location relative tolower ball joint location, not tire contact patch.

A free body diagram will show that moving only the tire contact patch further outboard will not change the vertical component of the force being fed in at the lower ball joint. It will however create an additional moment about the lower ball joint that will be fed laterally into the control arms.

rslifkin SuperDork
3/6/18 12:58 p.m.

It’s SRA, not IRS. Thanksfor the input guys! I’m still debating on whether I’ll do it, and I think I’ll only do this once sways are on and I need to fine tune it. The tires are the same section width, but the 5x4.5 Bassett’s only come as 3.75 backspacing in a 7” wheel. The fronts are 15x7, but are four lug, so it has the 4” BS.

What irks me is that the rear wheels USED to stick out further than the fronts when I had the 14x8’s on the back. Itjust looks a little silly to have the back wheels more inboard than the front, especially since the front has such a nice poke! Aesthetics be damned though. Form follows function.

Driven5 said:

Motion ratio is based on shock mount location relative tolower ball joint location, not tire contact patch.

A free body diagram will show that moving only the tire contact patch further outboard will not change the vertical component of the force being fed in at the lower ball joint. It will however create an additional moment about the lower ball joint that will be fed laterally into the control arms.

I don't agree with this. Moving the contact patch further outboard changes the geometry, meaning less spring movement for a given amount of vertical wheel movement.

Driven5 SuperDork
3/6/18 1:24 p.m.

rslifkin said:

On a solid axle, adding spacers will not soften the suspension in roll, only in 1 wheel bump. Roll stiffness (as far as body lean angle for a given cornering load) is based on spring location relative to the body, not the wheels.

My mistake.

Keith Tanner said:

I don't agree with this. Moving the contact patch further outboard changes the geometry, meaning less spring movement for a given amount of vertical wheel movement.

Depending on how much camber gain your suspension has, maybe very slightly, as the wheel centerline has a non-zero amount more vertical movement than the lower balljoint. But we're talking something like a 0.00X of an inch (insignificant) difference at the center line of the wheelper 1 inch of bump at the lower balljoint, fora 0.5 inch offset increase froma 1 degree per 1 inch bumpcamber gain suspension. Then add inthe actual contact patch movement due to the effects from wheel width and tire deformation, and we're really getting farther in than can be readily determined manually.

Assume a 0 camber gain suspension (parallel equal length double wishbone) though, for the sake of simplicity, and there is absolutely no difference in balljoint movement vs contact patch movementregardless of wheel offset changes.

Driven5 said:

Assume a 0 camber gain suspension (parallel equal length double wishbone) though, for the sake of simplicity, and there is absolutely no difference in balljoint movement vs contact patch movementregardless of wheel offset changes.

That's the part I was having trouble with. I've got it sorted out now, thanks.

Driven5 SuperDork
3/6/18 3:50 p.m.

Trackmouse said:

Aesthetics be damned though. Form follows function.

Why not have both if you can? I'd argue that the performance effects will probably be a non-issueeither way. Realistically, playing wheel offset is about affecting where the wheel sits in the wheel well. Put the wheels where you want them, and get the handling you want by tuning the suspension withsprings, sways, and shocks.

Driven5 said:

Trackmouse said:

Aesthetics be damned though. Form follows function.

Why not have both if you can? I'd argue that the performance effects will probably be a non-issueeither way. Realistically, playing wheel offset is about affecting where the wheel sits in the wheel well. Put the wheels where you want them, and get the handling you want by tuning the suspension withsprings, sways, and shocks.

That’s truth! I’m supposing with a 1 inch spacer would look about right, considering I lost half of an inch going down to a 1 inch narrower wheel, and then lost a quarter of an inch with the backspacing. So one inchshould do it some justice and bring it flush again, just so I can have that JDM yo stance!