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Going Faster - A Driver's Perspective

Date:
September 2003

Article by:
RichardH


Introduction

Since having a bit of a spending freeze on FTO modifications (due to the arrival of a far more expensive little girl), there has not been a great deal to document in the 'FTO Workshop' department.

To be perfectly honest, though, that's not entirely true. Over the last year or so, I've spent at least half a day each month belting around a motorkhana training course, with an instructor in the passenger seat telling me what I'm doing right (ie. accidentally) and what I'm doing wrong (lots!).

Funnily enough, this has influenced every aspect of my driving, both on course and on public roads. It has also been a trial by fire of every handling modification made to the FTO over the last three years.

It seems like a suitable time, therefore, to jot down a number of observations made as a result of a bit of real-world performance driver training. Some of this will no doubt fall into the 'pretentious rubbish' category, but I guess that won't be the first time I've committed such a crime!


And why is this in the 'Workshop' section, I hear you ask? Well, we seem to spend a fortune trying to make our cars go faster and/or handle better. So why not invest similar amounts of time and money working on the driver? Just think of it as a performance upgrade for the ol' grey matter...!

Cornering On Public Roads (or anywhere, really)

A few weeks ago, I booked my FTO in for a wheel alignment. When it came time for the manager of the shop to take it for a test drive, I asked if I could hop in the passenger seat and tag along. The next five minutes were an eye-opening experience (to say the least), as he proceeded to tear around the streets in an uncannily familiar way. This was me, 18 months ago... exactly how I used to drive. As my white knuckles gripped the passenger door ever tighter, it brought home to me just how much my approach to driving had changed as a result of some amateur motorkhana experience.

So what was my driving like 18 months ago? Essentially, I thought I was trying to be a 'fast' driver. The average corner was taken as follows...

  • Approach the corner as fast as possible.
  • Brake as little as possible.
  • Finish braking, turn in.
  • Attempt to hold the car 'at the limit' all the way around the corner, wheels as close to the inside kerb as possible.
  • Once faced with a straight bit of road, floor the throttle.
  • Congratulate myself on being such a hero!

I thought I was getting the most out of the car by getting the tyres at the limit of traction from the start of the corner to the end.

So what was wrong with this approach? Well...

1. Although the mid-corner speed may have been fast, I wasn't able to get on the throttle until I was completely out the other side. The best I could hope for would be to come out of the corner at the same speed I entered it.

2. Seeing as I had arrived at corner entry so fast, I had no margin for error. What if I'd needed to brake because of a pothole or a dog? Forget it!

The alternative, as repeated again and again by the driver training instructors, goes as something like this:

  • Approach the corner.
  • Brake as late and hard as conditions allow. But really get the car slowed up in a straight line.
  • Turn in with an entry speed that is slower than the 'fastest possible' speed you could take that corner at.
  • Rotate the car quickly and smoothly, and get it pointed as 'straight' out of the corner as possible.
  • Unwind the steering, feeding on the throttle as you do so.
  • Pass the corner exit, already straightened, using as much throttle as appropriate.

This works on the track, on the road, anywhere. And the advantages?

1. Compared to the 'high speed cornering' approach, you can be way further down the road if you wash off some speed, turn in late and then get on the gas early. Essentially, you're creating a straight where there was previously just a corner... and straights mean acceleration!

2. By braking in a straight line to get that speed washed off, you have complete flexibility to make corrections, change direction and generally stay safe.

3. You choose the exit speed with your throttle instead of your entry speed.


Best of all, it makes for a more involving drive! It feels great getting the setup just right, so as to be on the throttle early and confidently. Then there are the added on-road bonuses, like seeing that annoying tailgater become a receding spec in the rear vision mirror!


Trail Braking

It has become evident after much fooling around on the motorkhana courses that the best way to get my FTO around corners is with a judicious amount of trail braking... a term that simply describes the combining of some brake application as you turn in.

If you read the purist performance driving books, most will recommend 'getting all of your braking out of the way before turning in'. The theory is that a motor vehicle can only do one thing well at a time, ie. brake, corner or accelerate. Asking a car to do two things at once, according to much of the material out there, is simply asking for trouble.

That's all well and good, but in the real world (in my car at least), there is most definitely a benefit in overlapping the final stages of pre-corner braking and initial turn-in. When you think about it, this all comes down to weight transfer.

When braking at the limit in a straight line, the weight of the vehicle transfers forward, loading up the front tyres.

When purely cornering at the limit (ie. no brake or throttle), the outside tyres are loaded up... especially the outside front!

The trick to smooth, fast driving is in the transitions. It makes no sense to back off on the brake pedal completely before starting to turn in. The vehicle is just going to go from a situation where the front tyres are fully loaded, through a neutral 'in-between' state as you back off the pedal, before being asked to load up the outside tyres as you apply steering lock. If you look at it from the point of view of the outside front wheel, it gets a heap of weight on it while the driver brakes, then unloads for a moment, then gets loaded up once again for the actual cornering. This on-again, off-again driver input is simply going to upset the balance of the vehicle.

Instead, why not attempt a smooth transition that keeps that outside front tyre loaded up consistently? As you begin to apply steering lock, start reducing the pressure on the brake pedal. Not all at once, but smoothly and in direct proportion to the amount of steering being applied. Simply trade braking for cornering in a progressive and consistent manner.

In theory, the ideal situation is to only have an instant when the vehicle is 'coasting' mid-corner... at the point where maximum steering lock is reached. Before then, some braking was still occurring. After that point, the driver will be unwinding the steering and rolling on the throttle. Again, the aim of the exercise when accelerating out of a corner should be a smooth transition from having the outside tyres loaded up to having the rear tyres being on the receiving end of the weight transfer when on the throttle.

The FTO responds very well to trail braking, and rotates beautifully when there's some extra weight transferred frontwards whilst turning in.

Note that asking the front tyres to do more than they are able will see the car just plough on ahead in an orgy of understeer. Not good. The other extreme is to transfer so much weight off the rear tyres that the back end attempts to overtake the front! Which is usually spectacular, if nothing else!

Weight Transfer, Body Roll and other Stories

Let's take a breather from all this pedal pushing action. It's time to explode a few myths and misconceptions! Have you ever read or overheard comments such as:

1. "Fitting rock-hard suspension to stop body roll eliminates weight transfer, resulting in better tyre grip all round."

2. "Having an after-market anti-lift kit fitted to a FWD car stops weight transfer to the back under acceleration, so the front drive wheels can better put power down."

Both these statements are downright inaccurate!

If the first statement were true, it would involve a complete rewrite of the laws of physics. Unless the car in question was completely flat like a sheet of paper, any action at ground level (ie. tyres) to change the velocity or direction of the vehicle will result in a 'roll' or 'pitch' twisting force on that vehicle. This is quite simply because the mass of the car is located up above ground level, but all the action is happening in those four small patches where the rubber meets the road.

Weight transfer exists whether the car body moves around like a boat, or whether it is carried on springs so solid that your fillings are shaken out of your teeth.

Body roll is a SYMPTOM of weight transfer, not the CAUSE of weight transfer!

Say we built a stupidly tall, thin car. And say the test driver found that each and every time they applied the brakes, the car simply fell over. Well, the guilty automotive engineers could not simply fix the problem by installing a set of super-firm Tein coilovers! It doesn't matter what the suspension does... weight transfer is weight transfer. It happens.


Have a look at the shape of the front right tyre in the above photograph. This vehicle is making a hard left turn at around 70km/h. That distortion is indicative of the weight transfer occurring, and is quite marked - especially considering that tyre was inflated to 41psi cold! Those round black things really work hard, don't they?

So why do people often recommend lowering the ride height and stiffening the suspension? Well, in regard to lowering a vehicle, there is something at work here that can affect 'weight transfer'... A lower ride height means a lower centre of gravity. Consequently, the twisting force (all else being equal) can be expected to reduce somewhat. If we extrapolate far enough, we get down to a hypothetical sheet-of-paper flat car! No weight transfer, but very little room for a subwoofer in the boot...

In case you STILL haven't died of boredom...

For a really in-depth look at this sort of stuff, check out getfaster.com - From the main page, select Tech Tips, then select Physics of Racing Series. As far as I can see, this same material has been made available from several other places on the web.


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