Turns out that he had just upgraded from a basic and inexpensive TA03F car to a highly adjustable and significantly more complex TRF kit.  He was used to fixed length upper links and suspension so basic that you can only assemble it correctly.  Not only did he not know how to set up the suspension on his new car, he wasn’t even aware that such a process existed.  When I picked up his TRF to check it out, it was immediately obvious that something was very, very wrong.  He’d complained that the car was a total handful all over the track: it wouldn’t go straight in the straight parts no matter how much he adjusted his radio, and in the turns it would turn too much to the left, and not enough to the right. A fellow driver had been able to confirm that his radio wasn’t the culprit, but was embroiled in his own issues and had been unable to diagnose the actual problem.  So what did we do to the car, and why was the change in performance so dramatic?

I had noticed that the front wheels were pointed in the same direction: one was toed in, the other toed out.  And I also saw that each of the four wheels had a significantly different camber setting.  Finally, by examining the rear tires, I knew that he had assembled the kit incorrectly.  Let’s examine some basic suspension settings and see what we can learn from my erstwhile pit buddy’s mistakes.

Toe

Starting at the front end, one of the most critical tuning adjustments you can make is to the toe settings of the front wheels.  Toe-in refers to a setting where the front edges of the tires are closer together than the rear edges.  When viewed from above, the tires describe a ‘V’ shape, with the V pointed toward the front of the car.  Front toe-in produces subtly different handling changes from car to car, but typically a little toe-in will add directional stability, which is most noticeable as the car travels in a straight line.  Is your car twitchy and unpredictable on the fast front straight?  The first thing I’d check is the toe-in.  Toe-in also takes away a little steering response, which is a good thing if your car tends to snap around and spin out very rapidly at the entrance to a sharp turn.  Because front toe-in decreases the turning arc of the inside wheel and increases the turning arc of the outside wheel (check it and see!), you may actually experience increased turn-in if your car’s shock springs and shock fluid are particularly soft.  That’s because soft suspension lets the chassis roll from side to side, and lots of chassis roll transfers weight to the outside wheel.  If it’s turned in more than usual, well, the car’s gonna turn more quickly.  However, since most folks in this part of the country run their shocks pretty stiff, that shouldn’t be an issue for most of us.

Here’s a clear example of front wheel toe-in.

Toe-out is, as you probably guessed, the exact opposite of toe-in.  The front edges of the wheels are a little farther apart than the rear edges of the wheels, so the V described by the front wheels is pointing toward the rear of the car.  A little bit of toe-out will add steering response to most sedans, and can make a mushy, sluggish car really come alive.  Interestingly enough, on some cars the same amount of toe-out can actually add directional stability, so it pays to do a little experimenting and find out how your particular chassis reacts.  Because toe-out increases the inside wheel’s turning radius for the same amount of steering input, you’ll notice more steering response if you use heavy sway bars.  Sway bars keep the car flat while cornering, so more weight remains on the inside wheel.  Since the turning radius of the outside wheel is decreased in a turn for the same amount of steering input, folks who have a soft suspension setup may actually experience a reduction in steering response when using toe-out.  Weird, but it shows that everything is relevant and nothing is the same in all situations.

Camber

Camber is a term that refers to the amount that the tire ‘leans in’ toward the centerline of the car’s chassis.  This is easily viewed if you place the chassis on a table and look at it straight on.  See how the wheels tilt?  On sedans with fixed upper links, the manufacturer has incorporated a camber setting that it feels will represent the best compromise for the greatest number of drivers.  Which is great, until you figure out that lowering ride height is one of the best ways to get your car to go faster around a turn.  Lowered ride height emphasizes the camber gain (that is, the tendency for the tire to lean in more when the suspension is compressed) inherent in most suspension designs.  Leaving you with a nicely lowered car with wheels that don’t look quite right.  And they’re not, because nobody needs extreme camber settings on asphalt.  So the first purchase you should make when lowering your car is a set of adjustable upper links.

See how the front wheel tilts toward the center of the car?  That’s camber!

The only reason we need to be concerned with camber settings is because our cars lean to the outside in turns, but we want our tires to be as perpendicular to the racing surface as possible at all times.  If we could make our cars run perfectly flat in the turns, kind of like pan cars do on carpet, we wouldn’t need to worry about camber at all.  That’s why high performance sedan cars that run on carpet have almost no camber at all.  On asphalt, we’ll put up with a little bit of initial camber, even though it reduces the contact patch presented to the ground and cuts down on rear traction when traveling in a straight line.  Why?  Because more of the tire will be exposed to the surface when we’re hammering through a tight turn and trying to out-accelerate that pesky guy who’s determined to pass us.  Neat!

Other conditions also determine optimum camber settings.  For example, you’ll need less initial camber as suspension and roll rate become softer.  In other words, if your car leans a whole bunch in the turns because you’re still using the oil and springs that came with your kit (shame!), you’ll need to compensate for that with less camber.  The same is true for chassis designs that have a fairly high roll rate. You can spot these by looking at the attachment points for the upper links- especially in the rear- when the car is sitting on your bench fully loaded.  If the outer attachment point at the hub carrier is significantly higher than the inner one on the shock tower, you’ve probably got a lot of roll rate and mechanical traction (in other words, your car doesn’t react to tire changes very much).  With a design like that, you’ll not only need a tad less initial camber, but the camber gain (that’s how much the camber increases as a function of suspension geometry as the suspension is compressed) will be very high. Finally, more camber change occurs with high chassis clearance and longer suspension movement, especially with less expensive models.  

Thoroughly confused?  Well, so was our pit buddy (remember him?).  Check the wear patterns on your tires, especially the rears.  If the inside of the tires exhibit more wear than the outside, you’ve got too much camber.  See a pattern of groovy or excessive wear on the outside edges?  Not enough camber.  That’s why the top drivers check their tires as soon as the car comes off of the track, and they never ever clean ‘em off or put traction compound on them until they’ve had a chance to examine the wear patterns. What they’re looking for is a nice, even wear pattern all across the tire.  Of course, if the track has too much traction and you’d like the back end to rotate a little faster, adding camber to reduce the tire patch is one way to get there.  Want another tip? Buy turnbuckles instead of using threaded rod for upper links.  If you don’t have to pull the ball links off to adjust the length of the link, your ball ends will stay tight.  Plus, sometimes you want to make an adjustment that’s less than a full half turn, the minimum you can make with a threaded rod.

Caster

Caster refers to the amount that the front kingpin (or an imaginary line drawn through the upper and lower front hub carrier screws) leans backward from vertical.  We won’t even discuss positive caster, because nobody uses it on radio control cars.  Although different cars react to caster changes in different ways, more caster typically results in slower on-power steering response and more off-power steering.  Here’s a good example: oval racers, who are on the power pretty much all of the time, use extreme caster angles to cut down steering response as they enter and exit high speed left handers.  And drag racers, who don’t want their cars to turn much at all, use very high caster enagles to ensure that the car will want to go straight as much as possible.

See how the front kingpins tilt backwards?  This is an excellent example of front caster.

On full suspension sedans, more caster can make your car much more efficient, especially on high speed corners.  That’s because less steering response allows you to set up the rear end much harder, so it will slide a little bit as it goes around the corner.  A good example of this would be the older Tamiya TA03F models that came out in the mid-Nineties.  Because of their front end motors and weight distribution, we had a hard time figuring out how to make them steer.  By installing front hub carriers from the previous series of TA02 cars, we wound up with greater steering response.  Associated offers multiple caster options for their World-caliber TC3 sedan to accommodate different track surfaces and driving styles.  Moving from carpet to asphalt or vice-versa?  I sugest you buy several different optional caster hubs for the front of your sedan and learn how your particular car reacts to these changes.

Rear Toe

OK, now we’re getting to some things that even experienced racers may not pay much attention to.  Rear toe-in is a critical but frequently ignored setting for sedan guys, but it’s very familiar to the dirt oval and off road crowd.  Zero toe-in at the rear, with both rear wheels parallel to each other, results in maximum drivetrain efficiency.  That’s fine for super high-bite surfaces like carpet, but bad when your baseline setup is off or the surface is slick or dusty.  Increasing rear toe from zero to up to 3 degrees will definitely increase rear traction and give you more dig out of slow turns.  You’ll know you’ve got too much rear toe when the car becomes pushy and sluggish.  Some cars like Kyosho’s TF series offer multiple rear toe adjustments without changing any parts.  Others like Associated’s TC3 use different rear arm mounts that have toe amounts molded in.  I’ve even seen cars that offer infinitely adjustable rear toe like Schumacher’s last several designs, or Robinson Racing’s older aftermarket kits for RC-10’s.  

With a little rear toe-in, you’ll have a lot more traction.  That lets you yank the throttle when exiting a tight turn.

Rear toe-in on front drive cars can also be critical.  An excellent example is Tamiya’s updated M03 front drive Mini Cooper.  On our East Coast asphalt, the optional 3 degree rear toe hub carriers make it possible to set up the front end for very aggressive steering without worrying about the car spinning out at the end of the straightaway.  Check out the picture of the M03 I used to qualify fourth at this year’s TCS Nationals: rear toe-in and aggressive front toe-out.  As bizarre as it looks- and believe me, I got  few comments - that combo brought me to within a few hundredths of TQ time.  Can’t find those optional rear hubs but know somebody who races an older TA02 series sedan?  The hub heights are the same, so with a little judicious grinding, you can make them fit your Mini in a pinch.  Guess what?  They’ve got the same 3 degrees of toe-in as the more expensive optional hubs shared with the TL01!

See how the rear wheels have toe-in, but the fronts use toe-out?  This setup really worked on the slippery Nats track.

While we’re slicing up rear TA02 hubs, think about removing the center portion of the rear upper hub carrier.  By doing so, the upper link fits between the ears that remain and offers a straight shot to the chassis attachment points.  Now, your upper links won’t bind and stick.  Cool and OK for Hobby Works racing, but not really TCS legal.  Of course, these cars are so rare in top-level TCS competition these days that the tech boys may not even know what they’re looking at!

One thing you never, ever want to do is wind up with rear wheels that toe out.  That’s what happened to our friend at the beginning of the article.  He swapped the left and right hub carriers by mistake, and those poor rear tires (with 3 degrees of rear toe-out) were fighting each other all the way around the track.

So, as you can see, all of your wheels need to be pointing more or less in the proper direction- left and right, back and forth, up and down.  Do a little experimenting with these suspension settings, make only one adjustment at a time, take notes on how the car reacts, and you’ll be way ahead of your competition come race day!

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