Chassis development

From TechWiki
Jump to: navigation, search

Chassis development…or why is everybody telling me to get my car ‘Geo’d’?

So you bought yourself a nice, shiny Elise or Exige, and have driven the first couple of thousand miles? That’s the point where lots of owners are hit by the ‘go faster blues’ and either start investing in go faster parts, or walk away not knowing where to start.

In this article, I’d like to give some insights to the updates you can do to get more fun out of your car without the need to install a 200+bhp engine for starters.

One of the regular remarks on the forum is ‘get yourself upgraded’. Of course, driving and racing courses will make you go faster! Everyone who’s even a little active within the Seloc community knows the name Andrew Walsh (aka Walshy). He can sure help you to understand your car and make you go faster. Besides - it’s great fun to do!

Time to go for the first engine mod? Run out of possibilities to go any faster? Not quite! There are more possibilities to make you go faster without the need to improve the power output of your car’s engine. The trickery which makes this possible is Geometry. I can hear people say ‘Lotus is the best chassis developer in the world, so why would I fiddle around with their settings?’ The answer is as easy as it is logical - Lotus has created a car which needs to be everyone’s friend. It needs to be entertaining for the beginner but at the same time Lotus wouldn’t want to make its handling tricky. If you’re a bit further down the line, have built up track experience and have some training courses under your belt, you might opt for a bit more entertainment, so you could start playing with the geometry of your car. Before doing that, I’d advise you to buy your first upgrade: a stiffer and adjustable front anti-roll bar. This simple and relatively cheap upgrade will enable you to play around with the balance between under- and over-steer. (understeer, in which the car starts sliding over its front wheels while entering a corner; over-steer, in which the rear of the car attempts to overtake the front, ultimately resulting in a spin).

Mind you, the balancing act of the anti roll bar (ARB) will not improve grip. A lot of people hate under-steer and prefer over-steer as long as it’s controllable. Control is exactly what you can get by setting up the ARB. Another effect of this device is the reduction of body roll - that does improve grip! How does grip work? When you think of the four patches of rubber which are the contact of the car with the road surface, you can appreciate the basic grip of the tyre. The more sticky the tyre, the more grip you will have. Well not exactly - another thing you wouldn’t want is to lose the weight on one of these patches. If you do, that specific tyre will not be able to provide you with the grip you’re used to. Getting back to the ARB, body roll actually is moving the weight on to the tyres. If you steer into a corner, the mass of your car will want to move on in a straight line. This will cause the body to roll over the car’s roll centre. The less the body is able to roll, the more weight you will keep in the same place, so there you go - it will produce more grip in a corner and will help you to go faster! The next step to improve your feeling with the car could be to start fiddling with the Geometry of the car. To do so, you’ll have to understand the basics of Geometry. If you really want to understand what you’re doing and even want to do it yourself, I would strongly suggest you pick up the parts manual first and buy yourself a pile of shims. You will need them!

First, the basics. There are a couple of things you’ll need to understand first - All settings are measured per axle!

Toe-in / Toe-out

Chassis development toe.png

Looking on the axle from above, if the fronts of the wheels are closer to each other then the rears, this is called Toe-in. If the opposite is true, e.g. the rear side of the wheels are closer to each other then the fronts, this is called Toe-out.

Toe-in will produce high-speed straight line stability but will make the car a slow turner. You have to work harder to get into corners.

Toe-out will not help you for straight line stability. The car will be pretty nervous, but it will want to attack each and every corner. There is no such thing as the perfect setting for Toe-in / Toe-out. The ideal setting for a (semi)-professional race car driver might be horrible for you. Keep in mind, the more toe you set, the harder your tyres will wear!

Camber

Chassis development camber.png

You will now have to look at the wheel from the front or the rear. The camber can be called negative if the top of the wheels are closer to each other than the bottom.

Positive camber is the setting where the bottom of the wheels are closer to each other than the top.

Where camber is concerned nearly every possible setting, the camber will be negative. The only question is.. how far should you go? The effect of negative camber might be loss of straight-line grip. As you’re setting the surface of the tyre in an angle to the surface of the road, you are losing grip. But as soon as you enter a corner (which is the place where you lose most speed when track- driving), the surface of the tyre will deform and, when your setup would be 0 Camber, you’ll lose grip. Having the car set with negative camber, the road surface contact will actually increase in the corner, thus improving grip. Exactly what you want!

Castor

Chassis development castor.png

This one is a little more difficult to explain.. You will have to look at the wheel from the side. The hub is behind the wheel and if you look at it, you will see that there's an angle between the top and bottom connection of the wishbones. This angle is called Castor. Castor is controlled by shims at the connection points of the upper front wishbone.

If the castor angle is too small, the car will feel very unstable at high speeds and will react very nervously on any steering action. If the castor angle is too big, the tyres will wear very quickly and you will lose grip in corners. The reason for this is that castor (on the front wheels) will produce camber as soon as you turn the wheels. Finding the right balance is key again.

I can hear you thinking now: ‘The workshop I’m visiting has a very expensive test setup to do these alignments. How could I possibly do that on my garage floor?’ The good news is - you can! The bad news is… it’ll take you some time to get there. If you are serious about this, you could bring your car to this workshop to try a new setting you’ve figured out, but in the end, it would cost quite some money. An optimal setup for a nice, warm, dry track is different to that for the cold, wet roads at home, so you might end up queuing at the workshop every week.

So it’s time to make a decision here. Are you going to try a handful of general setups during a season? You might opt for the workshop. If you would like to end up making your own setup per different track or according to weather, you could start investing in your own equipment. You could look at companies like www.longacreracing.com who are selling quite interesting low-budget solutions for Geometry modifications. If you search on the Internet, you will also find other companies, and also descriptions of doing a setup yourself using small ropes.

There’s one thing which is important to understand before you start. The floor you are doing the setup on needs to be level and you must put some weight in the driver’s seat (preferably something that matches your own).

One more thing: say you’ve added a shim in the front suspension. You’ve lifted the car, removed the wheel, done the shimming and built it all together again. After doing that you should check what you’ve done, but you shouldn’t just measure again after lowering the car! Roll it forward and roll it back again! The suspension needs to settle, and you do that while rolling the car back and forth.

Your car came out of the factory with what you’d call a general setup. Depending on what you want to achieve, there are a couple of different setups that you can use as a starting point to find your own. Lotus has released quite a few setups for the Elise, Exige and 340R. You can choose one of these as a starting point and start modifying from there. If you’re doing your own Geo for the first time, I’d advise you to take it step by step: e.g. first do the Toe-in / Toe-out until you’re satisfied with the behaviour. Next step could be the camber, etc.

It’s winter - a good time to start understanding all of this and preparing yourself for a new season. Once you’re able to do your own Geo, I’ll start nagging you about bump steer settings and springs and dampers.

This artice, written by Yvo Tuk, is taken from issue 2 of the Lotus Enthusiast, the magazine for SELOC Members.