[Ron Sutton]

Originally Posted by carbuff

In a similar vein to the TW / WB ratio question, at what point would having a wider front TW compared to the rear TW start to decrease handling performance? Or stated a different way, is there such thing as too much front TW compared to the rear?

In case new people drop in on our conversation, track width is center of tread to center of tread. Tread width is outside tread to outside tread (not the sidewall).

I don’t think of track width difference as decreasing handling performance. I think of it as a tuning tool … if the track width is adjustable … or a tuning challenge if it is too far biased on one end and NOT adjustable.

While there are exceptions to almost every rule, I typically don’t want to see the track width difference more than 1” on either end. Even that can be a challenge if it the difference is the wrong direction.

Within reasonable differences making the front track width wider than the rear … or the rear wider than the front can be a practical tuning tool. Making the front track width wider than the rear = tightens the car … too much makes it push. Wider rear track width than front track width = frees the car … too much makes it loose.

Put even more simply, regardless of what is going on at the other end …
a. Moving the front tires out tightens the car.*
b. Moving the front tires in frees the car.*
c. Moving the rear tires in tightens the car.
d. Moving the rear tires out frees the car.

*Note: Adding spacers to the front hubs, increases the scrub radius. So when I can use … either adjustable LCA’s … or simply replace the LCA’s for the track width I want … that is how I prefer to do it, versus adding wheel spacers to the front. I have used wheel spacers in the front many, many times. It’s just not my preferred method. Sometimes class rules dictate the decision.

A LOT of racers use small (1/8” to 1”) wheel spacers to tune … and in fact, many design & build their rear end & front hub combination with spacers as a part of it, so they can be removed to go “in” if needed … and of course, go “out” with more spacer as needed.

For the car I designed for myself with an AutoX priority, the lower control arms use adjustable threaded ends to allow up to 3/4” width change per side … 1.5” total track width adjustment, without affecting the scrub radius. With 335 tires on all 4 corners, my “standard track width” is 55” front & 54.5” rear. I can adjust the front from 54” to 55.5” without spacers.

The rear end in my car will “start” with spacers that can be removed & of course, spacers can be added, for a 2” adjustable track width range in the rear from 53.5” to 55.5” As far as spacers go, I prefer to use them on the rear end only, so as not to affect the scrub radius.

Additional tips: For cars with “high travel/low roll” suspension strategies, the front to rear “track width split” favoring the front works best. For cars with “low travel/high roll” suspension strategies, the front to rear track width split favoring the rear works best.

If your car is already “designed & built” … and the track width is a wider in the front, that will “contribute” to the car being tight/pushy a degree. If the track width is a narrower in the front, that will “contribute” to the car being free/loose to a degree. I use the word contribute, because there are a lot of other suspension & geometry factors affecting the grip at each end of the car. If the track width is not adjustable at either end, you will need to tune with roll center, springs & sway bars to balance the car.

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