polly bushes anyone ??
- Thread starter plowy
- Start date
I use them a lot in off road Jeeps, mainly to combat the effects of the combination of oil, grease, mud and water wrecking standard rubber. On road cars they will make the suspension that much tighter and better suited to lock in decent settings if you want to go that route. They will take out a lot of the compliance that rubber gives you (read that as harsh ride)
I'd not do it on a road going car where comfort is a consideration, but then again it's all about what you want to achieve.
Hopefully Curtis will drop by and give his more track focussed opinion
I'd not do it on a road going car where comfort is a consideration, but then again it's all about what you want to achieve.
Hopefully Curtis will drop by and give his more track focussed opinion
I have been having lengthy discussions on the suspension issue with Curtis and this is the next area on my car to get some attention, i already have Eibach pro-kit springs but will be getting polly bushes and a rear limiter kit for the trailing arm bushings, also i have already adjusted the front camber on Curtis's advice and what a difference that has made in itself but the other bits will all complement, one done i shall be have a proper 4 wheel geo set up done to set it up proper, i have setting recommendations from curtis to follow with this.. 
As for where to source the bushes here is where i'm off.. :wink:
http://cgi.ebay.co.uk/POWERFLEX-SUSPENSION-BUSHES-KIT-BMW-Z4-E85-BUSH-M-COUPE_W0QQitemZ310046387503QQcmdZViewItem?hash=item310046387503&_trkparms=72%3A985%7C39%3A1%7C66%3A4%7C65%3A12%7C240%3A1318&_trksid=p3286.c0.m14
As for where to source the bushes here is where i'm off.. :wink:
http://cgi.ebay.co.uk/POWERFLEX-SUSPENSION-BUSHES-KIT-BMW-Z4-E85-BUSH-M-COUPE_W0QQitemZ310046387503QQcmdZViewItem?hash=item310046387503&_trkparms=72%3A985%7C39%3A1%7C66%3A4%7C65%3A12%7C240%3A1318&_trksid=p3286.c0.m14
Thanks for the offer plowy but I think I'll try to get every aspect covered in one post so I don 't have to go through anything else.
Starting with the absolute basics for people who don't know what all the fuss is about here we go!
Every aspect of a cars handling is completely dependent on the tyres and how they transfer grip to the ground during a variety of conditions such as acceleration, deceleration and cornering various speeds and angles. In a perfect world the tyre should remain flat to the ground ie have the greatest possible contact patch with the ground during every conceivable scenario. With the wheels/tyres mounted in a perfectly upright position perpendicular to the ground you will guarantee the maximum contact patch when your accelerating or braking or simply driving in a straight line. Unfortunately as you begin to turn the car into a corner the lateral load on the tyre as well as changes in the suspension/steering geometry will start to cause the loaded tyre ( this is the tyre running on the outside of a corner, the unloaded tyre is the one on the inside which you will often see lifting off the ground on race cars during cornering ) will deform and you will start to run on the outer edge of the tyre. This dramatically reduces the tyres contact patch on the ground. The smaller the contact patch the lower the available grip therefore you will find that although you have tremendous traction during acceleration and braking you have very little grip through the corners.
The alternative is to tilt the wheels/tyres inward at the top. This is called negative camber. ( there are many other crucial adjustments but I'll just concentrate on camber for now ) With the tyres tilted inwards you will find that you have a poor contact patch while travelling in a straight line because you will be running on the inner edge of the tyre. This means you will be more likely to break traction during acceleration and you are more likely to lock up during heavy braking. The upside of course is that as you turn into a corner the loaded tyre will start to flatten itself against the ground as the lateral forces start acting on it. The advantage is that you have maximum traction during cornering and therefore vastly improved cornering speed.
As I said earlier, in a perfect world you will have maximum tyre contact during every driving condition but without self adjusting suspension which can react to changing circumstances this is never going to be possible. The solution is to come up with the best possible compromise in steering/suspension geometry so that you can find a suitable balance of straight line and cornering traction. This isn't the place to discuss the merits or pitfalls of various setups so lets just leave it that finding the perfect geometry setup is absolutely crucial to maximising the handling characteristics of the car. All the fancy bolt on coilover kits and sway bars etc will have very limited benefits unless you take your time to adjust all the angles and settings to make them work to the best of their ability.
In an earlier thread I described this problem like this . . . . . It's like buying the best scope money can buy for your hunting rifle but not bothering to zero it. The next time you go out hunting you can't hit a buffalo at ten paces and you wonder why you bothered wasting all that money on a crappy scope thats made things worse than when you were using open sights.
It's not the scopes fault, it's because you didn't bother to set it up properly.
OK so now we've established that setup and geometry is one of the most important things you can do to improve the handling characteristics of a car. Assuming that you have gone out and found the perfect setup for your car you wouldn't want anything to compromise all that good work and that's where the problem of standard bushes comes into play.
If you consider that most geometry settings are adjusted to the mm or fraction of a degree it wouldn't take much to upset these vital figures. If all the suspension, steering and drivetrain components in the car were attached to the chassis using solid mounting points there wouldn't be any possibility of the geometry settings moving from their desired position. The problem is that ride comfort would be terrible because all the vibrations and impacts from the road would be transferred into the cabin space because there is nothing in place between the wheel and the chassis to absorb these vibrations.
Because of this problem car manufacturers mount all the suspension, steering and drivetrain components to the car using soft rubber bushes. This results in a beautifully smooth and quiet ride which is perfectly suitable for 99% of driving situations. If however you decide to drive the car vigorously there is an enormous price to pay for those soft bushes.
Earlier I mentioned that geometry setting are adjusted to the mm or fraction of a degree. Can you imagine what a disasterous effect there would be on the cars handling if you suddenly changed all your settings by 10mm or more? It would be extremely dramatic to say the least.
The rubber suspension bush that mounts the rear of the front wishbone to the chassis is a 66mm block of soft rubber. If you lever against this rubber mount with a screwdriver you can easily move the mounting by over 10mm without applying excessive pressure. Under driving conditions the pressures and loads applied to these bushes is vastly greater than a bit of leverage from a screwdriver and the problem becomes compounded because these wishbone bushes are only one example of many similar bushes fitted to the car.
So here's the problem so far. Geometry settings are critical and handling upgrades need to be setup to the mm but every time you drive the car these setting shift around massively under cornering, braking or acceleration because the soft rubber mountings for these components are free to bend and flex under load.
In racing, the solution is simply to completely illiminate all the flexible mountings and replace them with solid mountings and spherical joints. Problem solved!
On road cars we are again faced with the problem that we need to find a compromise. If everything was solid you would loose your hearing and your fillings and probably end up paralysed if you drove more than the usual commute to work unless you drove on perfectly smooth roads.
The solution is to fit uprated or stiffer bushes and mountings or in the case of the limiter kit you restrict the movement of the bushes beyond a certain point.
I have tried and tested various parts and even replaced some of the more obscure items such as the rear differential carrier mounting rubbers. The transformation is amazing but because my car is not a daily driver and I track it a lot I have erred more towards a race setup than road.
If you want to make a vast improvement on your Z without compromising ride quality there are two main items to concentrate on. The 66mm rubber mountings at the rear of the front wishbones and the rear trailing arm bushes which are a similar size. These bushes are so large and soft that they probably contribute by themselves to over 50% of the overall problem. I have replaced the front bushes with nylon and the rear trailing arm bushes with spherical joints. This is as close to full race as you can get but it's a bit too much for a road car. If you want the improvements without the negatives then the best solution is to fit Polyurethane bushes. They are much stiffer than the conventional rubber mounts but still absorb vibration and shock in a very similar manner to the originals.
I tried replacement Polybushes from Powerflex before moving to more extreme measures and I can highly recommend them. If I remember correctly a set of 4 bushes cost me about £100 and I fitted them myself in about 90 minutes. As an extra precaution I also fitted a rear limiter kit from Turner Motorsport in conjunction with the rear bushes. Combining those bushes with a proper geometry setup completely transformed the handling of the car.
These minor changes have probably contributed more to the cars handling ability's than the small fortune I spent on Intrax coilovers but with proper cornerweighting. Coilovers are probably the second most worthwhile additions I've made IMO. I should probably add that replacing the bushes does more than simply keep your geometry in check. The car will feel more responsive and generally "tighter" ie it won't have such sloppy handling any more. You may think your Z handles well already but trust me, there's a lot of room for improvement. I found that most people think that Z's handle well simply because their previous cars handled even worse. Just because your Z handles better than another type of car doesn't automatically mean it handles well!
That's about it for now, if you want me to go further and tell you the next steps I will but right now I'm knackered and a nice single malt whiskey is calling me! Hope this was useful.
Starting with the absolute basics for people who don't know what all the fuss is about here we go!
Every aspect of a cars handling is completely dependent on the tyres and how they transfer grip to the ground during a variety of conditions such as acceleration, deceleration and cornering various speeds and angles. In a perfect world the tyre should remain flat to the ground ie have the greatest possible contact patch with the ground during every conceivable scenario. With the wheels/tyres mounted in a perfectly upright position perpendicular to the ground you will guarantee the maximum contact patch when your accelerating or braking or simply driving in a straight line. Unfortunately as you begin to turn the car into a corner the lateral load on the tyre as well as changes in the suspension/steering geometry will start to cause the loaded tyre ( this is the tyre running on the outside of a corner, the unloaded tyre is the one on the inside which you will often see lifting off the ground on race cars during cornering ) will deform and you will start to run on the outer edge of the tyre. This dramatically reduces the tyres contact patch on the ground. The smaller the contact patch the lower the available grip therefore you will find that although you have tremendous traction during acceleration and braking you have very little grip through the corners.
The alternative is to tilt the wheels/tyres inward at the top. This is called negative camber. ( there are many other crucial adjustments but I'll just concentrate on camber for now ) With the tyres tilted inwards you will find that you have a poor contact patch while travelling in a straight line because you will be running on the inner edge of the tyre. This means you will be more likely to break traction during acceleration and you are more likely to lock up during heavy braking. The upside of course is that as you turn into a corner the loaded tyre will start to flatten itself against the ground as the lateral forces start acting on it. The advantage is that you have maximum traction during cornering and therefore vastly improved cornering speed.
As I said earlier, in a perfect world you will have maximum tyre contact during every driving condition but without self adjusting suspension which can react to changing circumstances this is never going to be possible. The solution is to come up with the best possible compromise in steering/suspension geometry so that you can find a suitable balance of straight line and cornering traction. This isn't the place to discuss the merits or pitfalls of various setups so lets just leave it that finding the perfect geometry setup is absolutely crucial to maximising the handling characteristics of the car. All the fancy bolt on coilover kits and sway bars etc will have very limited benefits unless you take your time to adjust all the angles and settings to make them work to the best of their ability.
In an earlier thread I described this problem like this . . . . . It's like buying the best scope money can buy for your hunting rifle but not bothering to zero it. The next time you go out hunting you can't hit a buffalo at ten paces and you wonder why you bothered wasting all that money on a crappy scope thats made things worse than when you were using open sights.
It's not the scopes fault, it's because you didn't bother to set it up properly.
OK so now we've established that setup and geometry is one of the most important things you can do to improve the handling characteristics of a car. Assuming that you have gone out and found the perfect setup for your car you wouldn't want anything to compromise all that good work and that's where the problem of standard bushes comes into play.
If you consider that most geometry settings are adjusted to the mm or fraction of a degree it wouldn't take much to upset these vital figures. If all the suspension, steering and drivetrain components in the car were attached to the chassis using solid mounting points there wouldn't be any possibility of the geometry settings moving from their desired position. The problem is that ride comfort would be terrible because all the vibrations and impacts from the road would be transferred into the cabin space because there is nothing in place between the wheel and the chassis to absorb these vibrations.
Because of this problem car manufacturers mount all the suspension, steering and drivetrain components to the car using soft rubber bushes. This results in a beautifully smooth and quiet ride which is perfectly suitable for 99% of driving situations. If however you decide to drive the car vigorously there is an enormous price to pay for those soft bushes.
Earlier I mentioned that geometry setting are adjusted to the mm or fraction of a degree. Can you imagine what a disasterous effect there would be on the cars handling if you suddenly changed all your settings by 10mm or more? It would be extremely dramatic to say the least.
The rubber suspension bush that mounts the rear of the front wishbone to the chassis is a 66mm block of soft rubber. If you lever against this rubber mount with a screwdriver you can easily move the mounting by over 10mm without applying excessive pressure. Under driving conditions the pressures and loads applied to these bushes is vastly greater than a bit of leverage from a screwdriver and the problem becomes compounded because these wishbone bushes are only one example of many similar bushes fitted to the car.
So here's the problem so far. Geometry settings are critical and handling upgrades need to be setup to the mm but every time you drive the car these setting shift around massively under cornering, braking or acceleration because the soft rubber mountings for these components are free to bend and flex under load.
In racing, the solution is simply to completely illiminate all the flexible mountings and replace them with solid mountings and spherical joints. Problem solved!
On road cars we are again faced with the problem that we need to find a compromise. If everything was solid you would loose your hearing and your fillings and probably end up paralysed if you drove more than the usual commute to work unless you drove on perfectly smooth roads.
The solution is to fit uprated or stiffer bushes and mountings or in the case of the limiter kit you restrict the movement of the bushes beyond a certain point.
I have tried and tested various parts and even replaced some of the more obscure items such as the rear differential carrier mounting rubbers. The transformation is amazing but because my car is not a daily driver and I track it a lot I have erred more towards a race setup than road.
If you want to make a vast improvement on your Z without compromising ride quality there are two main items to concentrate on. The 66mm rubber mountings at the rear of the front wishbones and the rear trailing arm bushes which are a similar size. These bushes are so large and soft that they probably contribute by themselves to over 50% of the overall problem. I have replaced the front bushes with nylon and the rear trailing arm bushes with spherical joints. This is as close to full race as you can get but it's a bit too much for a road car. If you want the improvements without the negatives then the best solution is to fit Polyurethane bushes. They are much stiffer than the conventional rubber mounts but still absorb vibration and shock in a very similar manner to the originals.
I tried replacement Polybushes from Powerflex before moving to more extreme measures and I can highly recommend them. If I remember correctly a set of 4 bushes cost me about £100 and I fitted them myself in about 90 minutes. As an extra precaution I also fitted a rear limiter kit from Turner Motorsport in conjunction with the rear bushes. Combining those bushes with a proper geometry setup completely transformed the handling of the car.
These minor changes have probably contributed more to the cars handling ability's than the small fortune I spent on Intrax coilovers but with proper cornerweighting. Coilovers are probably the second most worthwhile additions I've made IMO. I should probably add that replacing the bushes does more than simply keep your geometry in check. The car will feel more responsive and generally "tighter" ie it won't have such sloppy handling any more. You may think your Z handles well already but trust me, there's a lot of room for improvement. I found that most people think that Z's handle well simply because their previous cars handled even worse. Just because your Z handles better than another type of car doesn't automatically mean it handles well!
That's about it for now, if you want me to go further and tell you the next steps I will but right now I'm knackered and a nice single malt whiskey is calling me! Hope this was useful.