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Motorsport Wheel Alignment: Suspension Bushes

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Suspension Bushes

05.17

00:00 - Suspension bushes are another one of those components that we often don't give too much thought to.
00:05 That is at least until your bushes are worn to the point where we have no option but to take notice and replace them.
00:11 Suspension bushes are located at each of the points where the movable suspension components connect to the chassis and they're there for two main reasons.
00:20 Firstly they provide a positive location for the suspension components, along with a pivot point to allow the suspension to actually do its job and move.
00:29 Secondly they isolate the chassis from noise, vibration and harshness generated as the car drives down the road.
00:36 This might seem pretty trivial but car manufacturers go to a lot of trouble to ensure the car is smooth and comfortable from the driver's seat and the suspension bushes play a major part in this.
00:46 While a factory rubber bush does an adequate job of locating the suspension, by their very nature these bushes are relatively soft which is essential for isolating noise and vibration from the chassis.
00:57 This means though that the suspension bushes can also be deformed relatively easily under the forces involved with accelerating, braking and cornering.
01:06 What this means is that our carefully adjusted alignment settings may all go out the window as soon as any force is applied to the suspension components.
01:14 To highlight just what this could look like, let's revisit the bushes in the rear trailing arms of multi-link suspension system which we already discussed in the toe module.
01:24 You'll recall that if we had set up our rear toe to provide zero toe while stationary, we may find that when the trailing arm bush is deformed under heavy braking, this can let the rear wheels move into toe out which can lead to some unpredictable handling.
01:41 Of course this situation only gets worse when the suspension bushes have aged and worn significantly and this will allow even more movement.
01:48 The problem with suspension bushes is that they wear slowly and you tend to not notice a sudden degradation in them unless they fail altogether.
01:57 What I mean here is that if you're dealing with a car that's got more than about 100,000 kilometres on it, chances are that the stock bushes are well past their use by date already.
02:07 Even forgetting for a moment about the potential for our alignment to move around, a stock suspension bush tends to dull down the feel that the driver has for what the car's doing.
02:17 This also makes the car less responsive to steering input since when the driver turns the wheel, the bushes will deform before any movement actually makes it to the wheels.
02:27 This all leads to a car that feels unresponsive and doughy to drive at input.
02:31 It also makes it difficult to be precise with positioning the car on the racetrack.
02:36 There are a couple of options available to us though that will rectify this situation.
02:41 The first and probably the most common is to fit an aftermarket suspension bush made of a harder material than stock.
02:48 These are available from a range of manufacturers such as Whiteline, Nolathane and SuperPro, just to name a few.
02:55 While each manufacturer has their own proprietary material specification, the idea is that these harder bushes offer less distortion under heavy load than a stock rubber bush.
03:06 Of course there's no free lunch though and the downside is that these harder bushes will also transmit more noise and vibration into the chassis.
03:13 This might not sound like a big deal but you may be quite surprised how obvious and pronounced that extra noise is.
03:20 While that's not a huge consideration for a dedicated competition car, if it's your daily driver that you only occasionally intend to take to the track, it could be a more serious consideration.
03:31 Even an aftermarket suspension bush will still allow some level of compliance under heavy load so if you want to take things a step further, a rod end or rose joint, or heim joint as they're also known, is the ultimate choice.
03:44 These include a spherical bearing through which a bolt can pass which is then pressed into a steel housing.
03:51 This allows the spherical bearing to swivel freely within the housing and provides for high levels of angular misalignment with virtually zero compliance.
04:00 We'll often find these rod ends used where the suspension arms attach to the chassis pickup points allowing smooth movement of the suspension arm with no chance of compliance affecting the alignment settings.
04:12 Understandably though, the rod end provides absolutely no isolation of the suspension components and as such all of the noise, vibration and harshness is transferred directly into the chassis.
04:23 These rod ends also don't last forever and depending on the conditions they're subjected to, they may require replacement once a year.
04:31 This may actually be much more frequent for applications such as offroad racing where it's easy for sand and dirt to act as an abrasive on the rod end's spherical bearing.
04:42 If you're considering your options for suspension bushes then you need to carefully consider the type of racing you're doing, alongside your budget.
04:48 While the rod end is unquestionably the best option purely from a performance perspective, they're expensive and require more maintenance than a conventional bush.
04:58 They also may not be road legal, depending on your local laws, so this needs to be considered too.