Practical Corner Weighting: Engine Position and Driven Wheels
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Engine Position and Driven Wheels
04.30
| 00:00 | - Where your engine is positioned in your car will play a big role in how your car handles and how the weight will be distributed across the vehicle. |
| 00:09 | Understandably, engines are one of the heaviest components of the car so their location plays a key role in the balance of any vehicle. |
| 00:17 | We may be dealing with a car that is front engined, mid engined or rear engined but the heavier axle, whether that's the front or the back is usually going to be the one that's closest to the engine. |
| 00:28 | Normally manufacturers will place the engine fairly central in the car from left to right to help improve its side to side weight distribution but it's difficult or impossible to locate the engine centrally between the front and rear axle lines. |
| 00:44 | Although there isn't much you can do about the position of your engine, it's important that you do understand the effect that this will have on your vehicle's handling. |
| 00:52 | Front engined cars are easily the most common we'll come across in terms of production road cars. |
| 00:59 | This design places more weight on the front axle line which in theory should make the car prone to oversteer however often the suspension geometry will be purposefully designed to generate understeer since it's considered safer for most drivers to deal with. |
| 01:14 | Understeer is also more pronounced with front engined front wheel drive chassis. |
| 01:19 | Mid engined cars are usually considered to be the best in terms of engine location and balance as the weight in theory should now be more equally spread between the front and rear axles and therefore the handling should be much more neutral, favouring neither understeer or oversteer. |
| 01:36 | Then we have rear engined cars and these will generally have a tendency to understeer but they'll also offer increased rear end grip and will have much better traction during acceleration if they're rear wheel drive. |
| 01:49 | The downside of a rear engined car is that if the rear of the car does start to slide, then there's a lot of momentum to continue that slide and it can be difficult for the driver to catch. |
| 02:00 | Porsche has been working on this for decades yet recently we've even seen them move to a mid mount location in their latest generation GT3 racecar. |
| 02:11 | It's worth mentioning that while the weight balance plays an important part on the handling characteristics of the car, the suspension design and geometry is also a major factor too. |
| 02:21 | You might be wondering at this stage why front engined rear wheel drive cars are so common for performance cars? The key consideration for the manufacturer is usually packaging and an inline engine and gearbox is easy to fit into the chassis. |
| 02:37 | The other benefit of this arrangement is that as the car accelerates, the weight is transferred backwards over the rear wheels and this will therefore give us better traction when accelerating when compared to a front wheel drive car. |
| 02:49 | As the engine is such a large mass, its location in the chassis will have a large effect on the height of the centre of gravity. |
| 02:57 | For this reason it's desirable to mount the engine as low as possible. |
| 03:01 | For manufacturers this is a compromise because they also need to protect the sump which is the lowest part of the engine from damage. |
| 03:08 | This is why it's common in purpose built race engines to use a dry sump lubrication system where the sump is much shorter than a normal factory sump, allowing the engine to be located much lower in the chassis with safety. |
| 03:21 | A four wheel drive car ideally would benefit from a more even weight split between the front and rear axles however it's also important to understand that the amount of torque being supplied to the front and rear axles isn't always a perfect 50/50 split and this affects the handling balance too. |
| 03:39 | While a road going car might have a torque split of 50/50 through to perhaps a 60/40 rear bias, a purpose build four wheel drive racecar is more likely to bias more torque to the rear wheels for use on a sealed surface. |
| 03:52 | This is because as the car accelerates, the car will transfer weight onto the rear wheels, meaning less traction is available at the front axle line. |
| 04:01 | Therefore we'd want the majority of the torque to go to the rear wheels to match the torque to the available grip. |
| 04:08 | When corner weighting our car we therefore need to consider which wheels are going to be doing the driving and account for this when moving weight around the car. |
| 04:16 | This is more important when you're designing and building a car from scratch since you've got a lot of flexibility here with component location, that is a lot more limited once the car is completed. |
