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Old 08-06-2013, 10:54 AM
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Tuning the Track Width with Wheel Spacers

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). Track width difference is 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.

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. There are exceptions to almost every rule ... this one too.

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. Not good. 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.

I prefer to use spacers on the rear end only, so as not to affect the scrub radius in the front.

For the Warrior Cars & Track Warrior Front Frame & Suspension Packages I designed 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. The 315 front tire set-up has a “standard track width” of 56”. We can adjust the front track width from 55-1/4” to 56-3/4" without spacers. The 335 front tire set-up has a “standard track width” of 57”. We can adjust the front track width from 56-1/4” to 57-3/4" without spacers.

The rear end in the Warrior cars, and almost all cars I build or design, I “start” with spacers that can be removed … and of course, spacers can be added. At a minimum, I like to build the rear end with 1/2" spacers on each side placing the rear tires at their widest point ... and allowing the track width to be narrowed by up to 1". This is an simple, easy, predictable tuning tool at the track to balance the front to rear handling. In our Track Warrior cars, we use 1" spacers on each side … for a 2” adjustable track width range in the rear.

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 the 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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Ron Sutton

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Last edited by Ron Sutton; 12-06-2014 at 07:42 PM.
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