Wheelbase -vs-Tread(Track) Width

A lot has been written about proper WHEELBASE for a gravel rally car, but I don't recall much discussion of TREAD WIDTH. ( Not tire width. Wheel tread width.)( JVL says the word should be "Track", bah!)

For many years, it was commonly understood that handling could be improved (or made worse) simply by changing Tread Width. All you had to do was change the backspacing on your wheels, or swap out a rear end, or get some wheel spacers, etc., etc. It was a pretty cheap and easy way to help sort things out.

Making your Tread Width narrower or wider by even an inch or less, one way or the other, was thought to make a significant difference. From whatever beginning point you had, the conventional wisdom went something like this:

1. FRONT TREAD WIDER THAN REAR = Promotes Oversteer to aid turn-in & counteract Understeer.

2. REAR TREAD WIDER THAN FRONT = Promotes Understeer & improves straight line stablity.

3. NARROWING Wheel Tread (uniformly) = Improves straight line stability.

4. WIDENING Wheel Tread (uniformly) = Improves resistance to lateral rollover.

( Note that 1 & 2 above are at odds with each other. Likewise 3 & 4.)

These adjustments were consider normal in getting a car to handle better or suit road conditions (twisties -vs- straights), or your driving style. You just had to define your objective and apply the proper solution.

Should any of these principles be applied to sorting out your gravel car? Do you think they're BS or do you still use them?

Rich Smith





Edited 2 time(s). Last edit at 04/26/2007 09:01AM by Rich Smith.

Rich Smith Wrote:

Rich, I stink ze word you should be using is "Track" width.
the distance between centers of the front or back wheels viewed from the front.
I check my sooooper accurate memory, and can't recall hearing "tread " used as anything other than the tires footprint or tires pattern.

Maybe it's some Hungarian dialect descended from Mongolian, eh?
-------------------------------------------------------
> A lot has been written about proper WHEELBASE for
> a gravel rally car, but I don't recall much
> discussion of TREAD WIDTH. ( Not tire width. Wheel
> tread width.)
>
> For many years, it was commonly understood that
> handling could be improved (or made worse) simply
> by changing Tread Width. All you had to do was
> change the backspacing on your wheels, or swap out
> a rear end, or get some wheel spacers, etc., etc.
> It was a pretty cheap and easy way to help sort
> things out.
>
> Making your Tread Width narrower or wider by even
> an inch or less, one way or the other, was thought
> to make a significant difference. From whatever
> beginning point you had, the conventional wisdom
> went something like this:
>
> 1. FRONT TREAD WIDER THAN REAR = Promotes
> Oversteer to aid turn-in & counteract
> Understeer.
>
> 2. REAR TREAD WIDER THAN FRONT = Promotes
> Understeer & improves straight line stablity.
>
> 3. NARROWING Wheel Tread (uniformly) = Improves
> straight line stability.
>
> 4. WIDENING Wheel Tread (uniformly) = Improves
> resistance to lateral rollover.
>
> ( Note that 1 & 2 above are at odds with
> each other. Likewise 3 & 4.)
>
> These adjustments were consider normal in getting
> a car to handle better or suit road conditions
> (twisties -vs- straights), or your driving style.
> You just had to define your objective and apply
> the proper solution.
>
> Should any of these principles be applied to
> sorting out your gravel car? Do you think they're
> BS or do you still use them?
>
> Rich Smith
>
>

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

john vanlandingham Wrote:
-------------------------------------------------------
> Rich, I stink ze word you should be using is "Track" width. the distance between centers of the front or back wheels viewed from the front. I check my sooooper accurate memory, and can't recall hearing "tread " used as anything other than the tires footprint or tires pattern.
>
> Maybe it's some Hungarian dialect descended from
> Mongolian, eh?
> --------------------------------------------------

Comrade Twice-Pappa!

Ha! You have survived the rigors of the birthing room and returned to the Asylum once again?! Como esta su esposa y la bambina nueva? Muy bien?

But quit making fun of my hungaro-mongolian accent. I deedn't hinvent the term "tread" as applied in this post. Heevan my hold factory service manuals use that venerable and ancient term. I don't recall anyone using the term "track" until the capitalist dogs at Pontiac started their Wide-Track advertising campain in the 1960's. And so it goes.................

Rich Smith


"He's right.... and he's right! Tisk-tisk. They both can't be right!
(Reb Tevia, the milkman of Anatevka)




Edited 1 time(s). Last edit at 04/26/2007 12:28AM by Rich Smith.

I'd want to put some serious thought into what's happening at the pointy end of the car.

Mucking about with backspacing on the steering wheels can change bumpsteer characteristics and, ideally, you want the line passing through your balljoints to intersect the centerpoint of your tire's tread to minimize the "rip-the-wheel-outta-yer-hand" torque that's generated when the tire strikes an obstacle. Also reduces the load on your wheel bearings.

Cheers, Ted

---

Pure mathematics is the enemy of every truly creative man -- Sir Alec

Ted,

I agree that tread(track) adjustments are better done at the rear to maintain original steering design radius.

But as a practical matter for race/rally purposes, I'm not sure making a "modest" frontal width adjustment brings anything more noticeable than the result you are trying to achieve.

( A lot of guys even do it by accident when changing to a wheel with different backspacing without realizing the effect or consequence.)

Rich Smith

Ted Andkilde Wrote:
-------------------------------------------------------
> I'd want to put some serious thought into what's
> happening at the pointy end of the car.
>
> Mucking about with backspacing on the steering
> wheels can change bumpsteer characteristics and,
> ideally, you want the line passing through your
> balljoints to intersect the centerpoint of your
> tire's tread to minimize the
> "rip-the-wheel-outta-yer-hand" torque that's
> generated when the tire strikes an obstacle. Also
> reduces the load on your wheel bearings.
>
> Cheers, Ted
>
> Pure mathematics is the enemy of every truly
> creative man -- Sir Alec

I believe you are referring to scrub radius here. Bump steer is caused by the geometry of the steering arms and tie rods as the suspension cycles. I totally agree that slapping in some wheel spacers can really wreck the handling. Not only does it increase the leverage on your suspension from obstacles but also from acceleration and braking forces.

Tim

Tim Taylor Wrote:
-------------------------------------------------------
> T
> I believe you are referring to scrub radius here.
> Bump steer is caused by the geometry of the
> steering arms and tie rods as the suspension
> cycles. I totally agree that slapping in some
> wheel spacers can really wreck the handling. Not
> only does it increase the leverage on your
> suspension from obstacles but also from
> acceleration and braking forces.
>
> Tim
>

Yo' dawg scrub radius is it man, and it was the clever boys at Citroen and Saab that first (within 3 months of each other) came out with cars with zero scrub radius steering being talked of here.

But in a way, the spacers aren't always the horriblest thing, as Rich wisely said, may time guys slap on wheels with different offset ---and MFG supply wheels themselves with offsets differing by 8-10mm with no ill or even noticable effect..


Indeed what Ted mentioned, bump or I feel way worse the dreaded "droop steer" is a far more nasty feeling phenomenon.
All I can say there is to again quote the President of Mars: ACK!
>
>
>

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.