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Practical Corner Weighting: Left Weight Percentage and Rear Weight Percentage

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Left Weight Percentage and Rear Weight Percentage


00:00 - The left weight percentage is something we've touched on in the last module and it's one of the first measurements you should be making when corner weighting your car.
00:07 Similarly when we've got the car on the scales, we'll also want to check the rear weight percentage.
00:13 Both of these measurements give you a first look at how well your car is balanced.
00:17 If we look at the left weight percentage first, your goal here is going to be 50%.
00:23 That means that the weight of the car is equally spread between the left hand and right hand sides of the car.
00:29 The reason you want this is again going back to our balance and predictability on track.
00:33 With a 50% split here, the car will transfer its weight uniformly through left and right hand corners which will make the car's handling more consistent and predictable.
00:45 What you need to understand here is that getting a perfect 50% balance is tricky to achieve, particularly with most road cars as the driver usually creates a pretty substantial weight offset when sitting in the driver's seat.
00:57 On the other hand, most single seat racecars will usually have a good left weight percentage because the driver and the engine are both located very centrally.
01:06 In a similar vain to the left weight percentage, rear weight is essentially the same thing, except this time we're looking at the total weight on the rear two wheels expressed as a percentage of the total car weight.
01:19 Rear weight percentage is less important in most cases than left weight but it is something that you should look at during the corner weighting process.
01:27 Rear weight percentage will show us how much weight of the car is across the front and rear axle lines and this can affect how the car accelerates and brakes but it will also have an affect on the car's ability to transfer weight and rotate into a corner.
01:43 How we calculate these percentages is pretty basic, let's start by looking at the left weight percentage.
01:50 You'll need to start by having the car on the scales and don't worry, we're going to cover this in detail in the next set of modules.
01:56 Once you know your corner weight measurements, you need to take the weight for the front left tyre and the weight for the left rear tyre.
02:03 You then just add these two measurements together.
02:06 Once you have this, you'll also need the total weight of the car and now we can divide the left weight total by the total weight of the car.
02:15 This will give us a figure which we can then multiply by 100 to express as a percentage.
02:20 Calculating rear weight percentage is done in exactly the same way except this time you need the total weight of the rear two tyres divided by the total weight of the car to give us a percentage.
02:32 In reality, most commercial corner weight scales will automatically calculate these percentages for you, so you don't need to break out the calculator.
02:40 Now that we've got our base weight percentages measured, we can look at how we can make adjustments in order to get these values closer to an ideal 50%.
02:49 With a production based racecar, it's going to be unlikely that you will reach a perfect 50% left weight split but that's not to say that we can't improve it.
02:58 The common misconception here is that you can adjust the left weight percentage by changing the ride height on the left hand side of the car only with the theory being that this will increase the weight evenly to one side of the car.
03:11 This is not the case, as we'll see shortly with a practical demonstration.
03:15 When you adjust your car's ride height you'll be changing the amount of downwards pressure applied by the tyre to the ground and this is great but you need to realise that when you adjust the weight in this way you're actually affecting both the rear weight percentages and the cross weight percentages simultaneously.
03:31 The only truely effective way of adjusting your left weight percentage is by moving weight or adding ballast to the car.
03:38 I know this goes against everything you're taught in motorsport because lighter equals faster, however in many motorsport championships they will require a minimum weight and if this applies and your car is underweight, then this is a great opportunity to move the weight to the best location possible.
03:55 In most cases the ideal place to add mass to the car is where the passenger seat would be.
04:00 This is because the driver is usually a large off centred weight that needs to be counter balanced.
04:05 So this is usually a good starting point.
04:08 If you're already at the weight limit or you don't plan on adding weight to your car then you can think about moving heavy items around the car to help adjust your weight percentages.
04:18 Items like the battery, the fuel cell, the dry sump tank, the fire extinguisher, cool suit box, just to name a few, all of these items can be moved to give you a better result.
04:28 We can even take it to extremes by moving things like your water bottle if you use one, your datalogging equipment and in some cases teams will even go to the trouble of rerouting all of their wiring in order to help out.
04:41 Having a good left weight percentage is important for circuit racing however this isn't entirely applicable for oval racing or speedway style events.
04:50 Usually in these cases, the cars will be set up so that the left hand side will be different to the right hand side on purpose because the car is only turning in one direction.
05:00 Therefore you're more likely to balance the car towards the inside two wheels in order to keep the car's weight over these wheels, which will help keep them in contact with the ground.
05:10 We should also note that your left weight percentage and rear weight percentages should be calculated before making any adjustments to your cross weights which we'll cover in the next module.
05:20 They also need to be measured with the tyre pressure set to the normal hot running pressure and the anti roll bars disconnected.