Beginners' Guide to Front-End Angles, Part 2

This article was first published in 2006.

Last week we defined all the different front end angles – camber, toe, castor, castor trail, steering axis inclination and Ackermann. This time we take a look at the relevance of all these angles to the road.

But first, a major qualification. It is almost impossible to get universal agreement amongst ‘experts’ with regard to front-end geometry. Not only do various people have a diversity of views but even the most widely agreed upon ideas change over time. Sometimes that’s because technology has changed (eg the advent of near universal power steering means that more castor is now accepted than when manual steering was widely used) but in other cases (eg toe-in, neutral toe or toe-out) the story varies even more.

For example, I once had a small turbo front-wheel drive road car that I occasionally ran at the track. I thought a change in wheel alignment angles could make a big difference so on the Friday I requested a ‘track’ alignment. But by Saturday morning I realised the car was almost undriveable – it darted all over the road whenever I accelerated hard. I’d made a commitment to be at the racetrack by 9am and at eight I was desperately searching for someone who could do a wheel alignment – anyone! I found a backyard garage that was happy to remove the toe-out that had been set. In this car, static toe-out probably combined with power toe-out to make the car twitchy in the extreme. But in other cars, just the same amount of toe-out would have given the quicker turn-in that this setting often results in...

Therefore, no-one can be absolutely certain of how well a wheel alignment will work until the set-up has been tried. Not only is there suspension bush movement that dynamically results in often quite different angles to the static angles set during a wheel alignment, but it’s the combination of the angles (not to mention how those angles work with tyres, damper rates, spring rates, steering ratio and the driver’s preferences!) which will dictate what is optimal.

That’s not meant to be a wimp-out (in fact it’s easy to be dogmatically authoritative: (“camber should be set to minus 2 degrees”), but a realistic appraisal of the situation.

Toe

As with all front-end angles, the first looks should be at the manufacturer’s recommended value and then at what the car is currently running. Broadly speaking, zero toe or toe-in is the norm. Toe-out reduces lateral stability and increases tyre wear on the outside shoulder. Toe-out will usually improve turn-in response (but may make it twitchy) while toe-in will dampen this change in yaw response. Toe is adjustable on all cars and so it costs little to change – you won’t need to shell out for a special suspension ‘kit’. For this reason alone, it’s worth experimenting with it.

Camber

Negative camber reduces longitudinal (accelerative and braking) grip and aggravates any existing tramlining. (Tramlining is where the wheels follow every longitudinal imperfection in the road). In addition, if a car isn't driven hard enough, tyres with plenty of negative camber will suffer dramatic wear on the inner tyre shoulders. However, negative camber is often used as a pre-emptive approach to improving handling. This is because as a car goes through a corner, its alignment angles change due to chassis and suspension component movement, and bush deflection. These changes see the outside wheel move away from its usual upright position towards positive camber. However, by dialing-in some negative camber when the car is stationary, the camber position of the outside (ie loaded) wheel under full cornering loads becomes closer to upright. This delivers the maximum available cornering grip.

Camber is generally not factory adjustable (or is adjustable by only a tiny amount) and so changing the camber can be quite expensive as – for example – upper or lower strut mounts or bolts may need to be changed.

Not often mentioned but an important point to know is that an increase in negative camber requires an increase in toe-in, and the combination of the two can change steering feel quite a lot. As with all front-end angles, being initially conservative is wise – start with the factory angles and change them only a little, even if you’ve added a suspension kit that gives you a lot of power over wheel alignment.

Castor

Positive castor increases the amount of negative camber that occurs during cornering, which means that the outside tyre ends up being closer to vertical than it otherwise would have been. This means better cornering grip. However, unlike simply dialing-in negative camber, positive castor brings no problems in relation to longitudinal grip, tramlining or tyre wear. The only ill-effect is slightly increased steering effort - and this shouldn't be a problem on cars with power steering.

Changing castor invariably requires modification to the suspension – for example, commonly the tension rod is swapped for an adjustable design that allows the wheel to be pulled further forward. Another approach is to use an eccentric or firmer bush.

Steering Axis Inclination

Steering Axis Inclination (or kingpin angle) is normally only able to be adjusted if you’re building a vehicle from scratch. Steering axis inclination should be maintained at an angle as close to vertical as possible but still resulting in a steering axis inclination that gives slightly positive or slightly negative scrub radius.

When building a vehicle, the important aspects to look at are the mounting positions of the upper and lower balljoints (or on a McPherson strut car, the lower balljoint and the upper strut mount) and the wheel offset. The combination of these factors will dictate steering axis inclination. For example, the lower balljoint will often need to be well within the dish of the wheel if the steering axis inclination isn’t to become too great and the wheels with available offsets are still able to be used.

Ackermann

Ackermann angles are only able to be adjusted if you’re either building a car from scratch or making major modifications to the steering. Ackermann is of most relevance for slow speed manoeuvres, where most references suggest steering as per traditional Ackermann angles is best. However, if you’re setting-up a high-speed car and want to look at the effects of Ackermann, http://www.smithees-racetech.com.au/ackerman.html will give you plenty to read.

Note that the actual wheel angles achieved in cornering are very hard to calculate from just simple drawings, as not only will bush deflection (etc) alter them, but in cars with steering boxes, as the steering tie rods move laterally, the inner ball-joints move through fore-aft arcs which affect the actual steering angles actually achieved.

Warning! Car manufacturers develop suspension systems through massive engineering development – from design to construction to durability testing. It’s fair to say that no aftermarket suspension manufacturer does even a fraction of the OEM testing before selling products (like suspension kits) that can radically alter suspension angles. Normally, a warning of this sort would then go on to expound on how manufacturers know best about handling for enthusiasts, and that you shouldn’t tinker with this stuff as the car might become an evil monster. Which, if you go overboard, is true enough. But this warning is not about that. Instead, we’re concerned that some aftermarket suspension components may simply not be sufficiently durable or well designed to be long-term safe. In one of the earliest AutoSpeed articles we covered the fitting of replacement aftermarket upper A arms on a Nissan Skyline GTR – see Camber Corrections. In that story we highlighted what we considered to be poor workmanship: a thread on a securing nut was burred; the plating was badly done (and one nut had been welded into place after the assembly had been plated!); washers were only mild steel and bowed as the adjusting bolts were done up; and the bolts were misaligned with their holes. In Suspension Intervention we told you how a Nissan Pulsar GTiR driver experienced massive toe changes after driving hard. The culprits? Front aftermarket camber bolts that were bending. More recently in Fitting Front Camber Adjusters I expressed concern about the undersizing of camber adjustment bolts incorporating eccentrics... ...and how aftermarket manufacturers who used a different design of camber adjustment that claimed not to be using undersize bolts were often in fact doing just that. (Note also the response from Whiteline Suspension’s Jim Gurief in a letter to AutoSpeed – Response.) In that story I fitted camber adjustment bolts to a front-wheel drive Toyota Prius – hardly a powerful car. To make absolutely sure the slotted washers (which were inserted into oversized holes drilled in the strut) could not move I had them tack-welded into place. The altered camber was then maintained by the tension of the bolts acting on lock washers. In retrospect, I should have been more critical of this design approach – if the bolts lost tension by stretching or the nuts came loose, the camber could radically change in an instant. Which is exactly what happened. One day, without warning, the camber changed so much (and therefore so did the toe) that the steering wheel needed to be turned 90 degrees to keep the car straight. As a result, one front tyre wore to the metal in just the 15 or so kilometres it took to nurse the car home. I had watched the camber adjustment bolts done up and they were certainly tightened sufficiently; it’s my gut feeling that they stretched. Either way, when I thought about the fact that just the friction of the serrated washers acting against the welded-on tabs stopped the camber changing, I wasn’t happy about the safety of the car. As it happens I had a second pair of factory front struts available and I installed these in place of the modified units. Yes, camber went back to being close to zero, but I fitted stickier tyres and the overall handling – if anything – actually improved. This is not to dissuade you from having aftermarket suspension components fitted. Aftermarket springs, for example, seem to be generally well made and seldom - if ever - fail in service. But I think it pays to be very careful when considering suspension kits that alter castor, camber or other major angles. After all, your life is dependent on the integrity of these components....