Suspension Geometry

Trying to explain suspension geometry is not an easy thing. I will try to give you an overall picture of what 'geometry' is and does - and give you some general hints on what changes affect the handling of your car. (Change your car, practice, change your car, practice, change your car, practice..... ) You sometimes just have to make a change to the car and try it - and do your best to pick out the difference. Suspension geometry refers to a lot of things. Basically, it is the various angles and mounting points of wheels, axles, suspension arms and uprights. Shock absorber mounting positions can also be considered to be suspension geometry. Words MOST commonly heard when talking about suspension geometry are camber, caster, ride height and toe-in. If you don't understand what's meant by these terms - look them up on Google or a dictionary there fairly simple to understand.

Camber

Camber is probably the easiest component of suspension geometry to adjust - if your car is fitted with turnbuckles or some kind of threaded rod for an upper suspension link. Here are some general rules of thumb.

Front Camber

On the front of your car or truck - adding negative camber will, in general, slightly increase steering up to a certain point - and then decrease it after that. That point is around 3-4 degrees. I would suggest that you start with about 2 degrees of negative camber (whatever the car) and NEVER adjust it more than 1 degree either way. Running more negative camber will simply take away too much steering and add unpredictability to your car's handling, while running positive camber of any kind is generally not a great idea. Positive camber can induce unstable handling - and a particular loss of traction for the outside tire in any corner (and the outside tire is the one that does about 80% of the work).

Rear Camber

On the rear things get a little more complicated. We need to consider both driving traction and cornering traction. Driving traction is what gets us going in a straight line - the more you have, the faster you can accelerate. Cornering traction is what helps the car to track around corners - without the back of the car spinning out. In general, the most driving traction comes with the tires at 0 degrees camber - neither positive or negative. This is because the tire is flat to the track with the most possible amount of rubber touching for more grip.

Unfortunately, cornering traction can be enhanced by adding a little negative camber - just like the front of the car. Interestingly enough, most cars will run fairly consistently with around 2 degrees of negative camber on the rear. Again - as per the front, I would suggest that you adjust this by only 1 degree either way. Again, NEVER run positive camber – it will lead to unpredictable driving traction - and probably a lot of spinouts in corners.


Camber Link Mounting Positions

Many modern R/C racecars have some options for mounting the camber links in different positions. Manufacturers spend a lot of time testing the cars and the kit settings will be the most consistent for the vast majority of racing conditions. There are no valid generalizations that I can give you to help decide when and how to change the mounting location of your camber links. Suffice to say, that I believe firmly that you should trust the manufacturers judgment in this matter. If you feel the need to try some other options - then try the holes immediately adjacent to the standard position. Really, it is a case of trial and error.


Caster and Anti-Squat

Caster and Anti-Squat are basically the same thing - except that caster refers to the angle of the suspension 'upright' (and is generally used in reference to front suspension) while anti-squat refers to the angle from horizontal of the whole suspension arm mounting pin (and is generally used in reference to rear suspension). Let's take a look.

Caster adjustment on the front of most buggies is by using different front uprights. In most cases, 2wd cars run between 20 and 30 degrees of caster, while 4wd cars run a bit less - typically 10 to 15 degrees. This is another instance where your manufacturer has done a lot of work to find the best answer - in general you should trust them. However, there are some generalizations that can be made. Adding caster (leaning the uprights further back) will generally give less initial turn-in, but more on-power steering and better straight line stability, while decreasing caster will generally add some turn-in, but at the expense of on-power steering and straight line stability.

The other possibility is that your car may be fitted with a 'variable caster' or 'active caster' setup. This means that as the suspension compresses, or extends, the caster automatically changes. While common in on-road cars, variable (or 'active') caster is less common on the dirt.

Anti-squat adjustments are available on the rear of most modern buggies and trucks. Anti-squat is typically adjusted by either replacing the rear suspension arm mounts, or placing washers or wedges under one end or the other of the mount before tightening the mounting screws. This results in a change in the angling the suspension arm - lifting the front edge of the arm higher than the rear edge. Anti-squat does exactly what you might guess by its name - it prevents the rear end of the car from squatting under power as the car accelerates and weight transfers rearwards. Anti-squat does also have some other effects (as with any adjustment – there is always a trade off). Let's take a look at the effect of altering anti-squat on both acceleration and cornering.

Adding Anti-Squat
If you add anti-squat, your car will (in general) get more 'driving traction' and hence accelerate faster. When you come out of corners, you will be able to use more throttle and your car will be more stable. But (and it's a BIG but), when you back off to turn into a corner, your car will have less rear grip. This might result in your car spinning out when you back off the throttle. Adding anti-squat also affects the way your car drives through bumps on the track. If the track is bumpy right where you want to accelerate, anti-squat is not a good thing - it will make the rear of your car very 'bouncy'. On the other hand, if the rough stuff is in a place where you are cruising on constant throttle, or even decelerating, then anti-squat will actually help your car to 'cruise' through the bumps more smoothly.

Decreasing Anti-Squat
When you decrease anti-squat you lose rear 'driving' traction. Your car will be a little more prone to power slides and fishtails. However, you will have more traction on a trailing throttle - resulting in your car being more stable into corners. It will also accelerate better through bumpy parts of the track.


Toe

The adjustment of toe is one of the most useful fine-tuning aids in making your car handle just how you like it. On the front of your car, lengthening or shortening the steering rods adjusts toe; while on the rear it is usually adjusted by changing the suspension arm mounts, or using different hub carriers or suspension uprights.

Essentially, toe adjustment works like this: Adding toe-in (front of wheels point inward) adds straight-line stability, while adding toe-out (front of wheels point outward) tends to make the car wander a little. Like all suspension geometry adjustments - this is only true up to a certain point - beyond which the results are generally unpredictable. Let's look at that in a little more detail.

Front adjustment
Changing toe on the front wheels is probably the best way to get that last little fine tuning adjustment right. Adding a little toe-in will reduce turn in slightly, and produce a car that tracks well in a straight line. On the other hand, reducing toe-in, or adding a little (very little) toe-out can provide a slight increase in steering. As with all suspension adjustments - go a little at a time. Front toe adjustment should never exceed 3 degrees negative, or 1-degree positive.

Rear adjustment
Due to the nature of rear toe-in (adjusted by replacing suspension mounts or hub carriers/uprights), adjustment of rear toe-in is quite uncommon. Just as with the front adjustment, more toe-in will add traction and stability, while less will promote sliding and instability. Rear toe-in should probably never exceed 4 degrees negative or be less than 2 degrees negative. Most modern cars are supplied at 3 degrees negative and will never need to be changed.

The other interesting part of rear toe adjustment is that some cars use different suspension arm mounts to achieve the adjustment, while others use different suspension uprights to make the change. The first case (suspension arm mounts) is called 'inboard toe-in' because adjustment is made at the inboard end of the suspension arm and affects the whole arm. Altering the upright is called 'outboard toe-in' because (you guessed it) it's making an adjustment at the outboard end of the arm. Inboard toe-in can produce slightly different handling characteristics to outboard toe-in in rough track conditions.


Ride Height

Ride height describes the distance between the track surface and the underside of your car's chassis. Sounds simple. The simple truth is, ride height adjustment can sometimes be easy to get wrong - and can have a devastating effect on your car. Fortunately, there are some relatively simple rules that you can follow to help make sure you get the ride height correct - most of the time.

First, let's accept this basic fact: Ride height is controlled by the amount of pre-load applied to your springs through the use of spring spacers, or the movement of an adjustable spring collar. Adding spring spacers does not stiffen the spring - it just lifts the car higher off the ground. You can also adjust ride height by using travel limiters inside the shock absorber or by selecting different shock mounting positions on some cars. Basically though - spring pre-load is it.

Simple Rule 1
Always run the car with the chassis level. That is - the ride height at the front must equal the ride height at the rear. While there may be some very odd circumstances where you'll want to run the front higher than the rear (or some even more odd circumstances where you'll want to run the front lower than the rear), it is true for most conditions that the car will be most consistent if the front and rear ride heights are equal.

Simple Rule 2
The rougher the track, the higher the ride height must be. As the race day progresses, if the track starts to break up - one very simple method of adjusting your car to cope with the changing conditions is to slightly (and I emphasize the word slightly) raise ride height. Make adjustments on the spring collars of about 2 mm per time.

Simple Rule 3
The higher the traction, the lower the ride height. If traction is very high (wet track, or good grippy clay, or 'blue groove' conditions) your car will handle best (and resist traction rolling) with a lower ride height. If the track is very grippy, and very rough - then you've got a typical suspension tuning situation - you need to compromise.

Simple Rule 4
Remember that changing tires can drastically change ride height. Always be aware that when you change your tires - you might have to re-adjust your ride height.


Anti-Roll Bars

Anti-roll bars (or 'sway bars' as they are sometimes known) do one thing. Prevent, or inhibit a cars natural tendency to have chassis 'roll' or 'lean' towards the outside of a turn. A lot of the car weight wants to keep going straight ahead - thus throwing more weight onto the right side (or outside) suspension and cause the whole car to 'lean' over.

The anti-roll bar prevents this lean by transferring some of the 'leaning force' across to the other side of the car. Anti-roll bars (as the name suggests) help your car to sit 'flatter' through corners. Anti-roll bars are most useful in high grip, smooth track conditions - and probably in high-speed corners too.

In lower grip, or rougher conditions, anti-roll bars can take away grip from the end of the car you use them on, or simply prevent the suspension from working as freely as it possibly can.

Variables with anti-roll bars include the thickness of the bar, the location of the anti-roll bar mount on the suspension arm, and the location of the mounting joint on the anti-roll bar. Basically it's like this - to 'stiffen' the bar (or increase it's effectiveness) use a thicker anti-roll bar, mount the anti-roll bar further out on the suspension arms, or mount the connecting joint further 'up' the bar (closer to the bend). To 'soften' the anti-roll bar - do the opposite: use a thinner bar, mount closer to the center of the car, or further out along the bar itself.

Note that for testing purposes, if you've got an anti-roll bar fitted to your car and you want to disconnect it, you can simply disconnect one end of the bar. That will remove the 'anti-roll' effect and leave you free to try without it. In racing situations, it's always safer to completely remove the anti-roll bar from the car if you don't want to use it.

On a 4wd it is a very good idea to have an anti-roll bar available for the rear of your car. In my experience, 4wd cars use an anti-roll bar at least 50% of the time. 4wd electric cars are different from 2wd in that the saddle pack battery setup means that more weight is distributed further out along the chassis - thus increasing chassis roll.

On a 2wd you are not going to use an anti-roll bar anywhere near as often. You should be able to race very happily without any form of anti-roll bar on your 2wd (although having said that - a soft anti-roll bar is a very good tuning tool to have - particularly on fast, smooth, high grip tracks.

I have personally never seen an anti-roll bar used on a Truck. Not sure why - perhaps trucks tend to sit flatter due to different shock mounting positions. If you're a truck racer there's certainly no need to rush out a pick up an anti-roll bar.

Other ways to get anti-roll: you can also get some kind of anti-roll effect from using different shock mount positions. This topic is covered in Section (5). Remember though, if you change the shock mount positions to get better anti-roll effect - you'll probably upset some other part of the suspension setup.


Suspension Drop

Suspension drop is adjusted by the use of shock travel limiters inside the shock, or by mounting the shocks in different positions on the tower or arm. Simply put, more drop is useful on a rough track, or sometimes in case of a slippery surface. More drop can also help your car to land better after big jumps. Less drop results in sharper handling and is best used on a smooth, high-speed track. Less drop will help your car to change direction more quickly.

Why is active caster not more common with off-road cars. I just got back into racing, and I am not impressed by the newer cars that are out. I have been out for about 7 years, and cars really has not drastically changed. Performance wise, they are more stable, have a lil bit more steering, but nothing that has given me the WOW factor.

Even to this day my Double X with Schumachers Active Caster sysem will out steer a B4 or XXX. I am trying to modify my B4 so I can run a active caster system in the front.

So why even after all these years companies do not try running the same concept Schumacher has done with their old 2wd cars.

It seems like all these manufacturers are taking ideas from each other. Look at Associated when Losi came out wit the Double X. Associated basically copied the concept that Losi came up with. Why does neither of these manuf. try Schumachers idea and improve on it. Why would they not want awesome steering. Match that awesome steering with the stability of the newer cars and you will have one fast 2wd buggy.