macfly
November 2nd 2003, 04:30
Dinan has developed a set of caster plates which fit the Z8 and are supposed to improve the car's handling. Dinan fits them on full S2 modified Z8s which means they are used in conjunction with Dinan's slightly lower/stiffer spring package. They also offer them as a separate item.
Most people are familiar with the concept of increasing the negative camber (as opposed to caster) settings on a performance car to improve its cornering ability. Doing so tilts the top of the tire towards the middle of the car which is supposed to counteract the tire's tendency to lean out during cornering, thereby keeping more of the tire's contact patch in touch with the pavement during cornering. This is a static change which means the negative camber setting is a constant factor and as a result, there are some trade-offs. Under straight ahead driving, inside tire wear will be accelerated due to the extra pressure applied to the insides of the tires and the tire will have less grip due to the uneven pressure across the tire's contact patch.
An alternative approach to counteracting the tire's tendency to lean out during cornering is to change the caster setting more towards positive. This may or may not result in a small static negative camber increase (depends on the plates used) but more importantly, it also results in a more pronounced negative camber setting during cornering, which is just where we want it to come in. The beauty of this approach is that you don't have to pay the penalty for increased static negative camber settings yet you get increased negative camber during cornering. One big benefit of this approach is that your front tires have more even pressure across their contact patch in straight running and this means they will react more quickly to steering input. Excessive static negative camber up front means less steering response. Another effect of increasing positive caster is that the steering becomes more stable, especially at high speeds. Someone running a very tight autocross might want to go the other direction with caster changes to make the car more maneuverable, but I doubt that is what most Z8 owners want to do with their cars. Increased positive caster also makes it harder to turn the steering wheel so there is a limit to what is beneficial, although today's power steering makes this mostly an academic point for street applications. Finally, increased positive caster gives the car better on center steering feel, sort of like the difference between an overly power assisted steering system which tends to be vague and the ones BMW usually builds into their cars which provide much better feel for what the car is doing.
Dinan's caster plates mount on top of the spring/struts and add app. 1/2 degree of positive caster to a stock Z8 and closer to 1 degree of positive caster to an ACS lowered Z8. Because they are mounted on top of the existing strut parts, they do raise the front of the car app. 1/4".
It has already begun snowing where I live, so my driving experience with the caster plates installed has been somewhat limited. It should be mentioned that my Z8 has the ACS suspension kit, Dinan adjustable anti-roll bars and I am running SO-3s in stock sizes on stock wheels. The changes to the car's handling are positive, though I don't believe I have their full measure yet. Steering accuracy and stability at high speeds (straight line and cornering) is noticeably better, especially when the road surface is uneven (less hunting). Steering response is an interesting mix: the steering feels a tiny bit slower during small inputs (this is to be expected) but much better during quick transitions since the increased negative camber begins to come into play. Overall, understeer has been reduced slightly and cornering ability has improved. The other thing you'll notice is the steering wheel wants to return to center more than before (this is also to be expected with positive caster changes). Overall, I like the changes and plan to put many more miles on the set-up before I give my final recommendation.
An interesting part of this process was the changes made to the car's overall alignment settings. Up front, I ended up with 7.5 degrees of positive caster, 1.0 degree of static negative camber and I set toe-in to essentially zero. Toe would normally be set "in" a bit to keep the car from wandering on uneven surfaces but the increased caster allowed me to go straight ahead which improves the tire's response to steering input (autocrossers often run toe out for this very reason). In the rear, I ended up running a small amount of toe-in (never use toe out in the rear) and 1.7 degrees of static negative camber. The combination works extremely well. While researching this set-up, I discovered that the E46 M3 uses virtually the same alignment settings right from the factory. Maybe we're on to something here!
For those of you who are not familiar with the term caster, let me go into a little more detail. Caster is defined as the angle between a line drawn vertically through a wheel's centerline and the axis around which the wheel is steered. It is also sometime's referred to as the kingpin angle. An easier way to visualize this is to picture one of those motorcycle's with its front wheel waaaaay out front, aka a chopper. This front suspension set-up has a ton of positive caster. These bikes are very stable in a straight line (they make great cruisers) but are very reluctant to go around sharp corners. You may also have noticed that when their front wheel is turned, it tends to lay over on its side quite a bit. That is the increased negative camber during cornering I referred to.
In any case, I will report back if and when I get some more miles on the set-up.
Originally posted by 'Grease Monkey' on Roadfly
Most people are familiar with the concept of increasing the negative camber (as opposed to caster) settings on a performance car to improve its cornering ability. Doing so tilts the top of the tire towards the middle of the car which is supposed to counteract the tire's tendency to lean out during cornering, thereby keeping more of the tire's contact patch in touch with the pavement during cornering. This is a static change which means the negative camber setting is a constant factor and as a result, there are some trade-offs. Under straight ahead driving, inside tire wear will be accelerated due to the extra pressure applied to the insides of the tires and the tire will have less grip due to the uneven pressure across the tire's contact patch.
An alternative approach to counteracting the tire's tendency to lean out during cornering is to change the caster setting more towards positive. This may or may not result in a small static negative camber increase (depends on the plates used) but more importantly, it also results in a more pronounced negative camber setting during cornering, which is just where we want it to come in. The beauty of this approach is that you don't have to pay the penalty for increased static negative camber settings yet you get increased negative camber during cornering. One big benefit of this approach is that your front tires have more even pressure across their contact patch in straight running and this means they will react more quickly to steering input. Excessive static negative camber up front means less steering response. Another effect of increasing positive caster is that the steering becomes more stable, especially at high speeds. Someone running a very tight autocross might want to go the other direction with caster changes to make the car more maneuverable, but I doubt that is what most Z8 owners want to do with their cars. Increased positive caster also makes it harder to turn the steering wheel so there is a limit to what is beneficial, although today's power steering makes this mostly an academic point for street applications. Finally, increased positive caster gives the car better on center steering feel, sort of like the difference between an overly power assisted steering system which tends to be vague and the ones BMW usually builds into their cars which provide much better feel for what the car is doing.
Dinan's caster plates mount on top of the spring/struts and add app. 1/2 degree of positive caster to a stock Z8 and closer to 1 degree of positive caster to an ACS lowered Z8. Because they are mounted on top of the existing strut parts, they do raise the front of the car app. 1/4".
It has already begun snowing where I live, so my driving experience with the caster plates installed has been somewhat limited. It should be mentioned that my Z8 has the ACS suspension kit, Dinan adjustable anti-roll bars and I am running SO-3s in stock sizes on stock wheels. The changes to the car's handling are positive, though I don't believe I have their full measure yet. Steering accuracy and stability at high speeds (straight line and cornering) is noticeably better, especially when the road surface is uneven (less hunting). Steering response is an interesting mix: the steering feels a tiny bit slower during small inputs (this is to be expected) but much better during quick transitions since the increased negative camber begins to come into play. Overall, understeer has been reduced slightly and cornering ability has improved. The other thing you'll notice is the steering wheel wants to return to center more than before (this is also to be expected with positive caster changes). Overall, I like the changes and plan to put many more miles on the set-up before I give my final recommendation.
An interesting part of this process was the changes made to the car's overall alignment settings. Up front, I ended up with 7.5 degrees of positive caster, 1.0 degree of static negative camber and I set toe-in to essentially zero. Toe would normally be set "in" a bit to keep the car from wandering on uneven surfaces but the increased caster allowed me to go straight ahead which improves the tire's response to steering input (autocrossers often run toe out for this very reason). In the rear, I ended up running a small amount of toe-in (never use toe out in the rear) and 1.7 degrees of static negative camber. The combination works extremely well. While researching this set-up, I discovered that the E46 M3 uses virtually the same alignment settings right from the factory. Maybe we're on to something here!
For those of you who are not familiar with the term caster, let me go into a little more detail. Caster is defined as the angle between a line drawn vertically through a wheel's centerline and the axis around which the wheel is steered. It is also sometime's referred to as the kingpin angle. An easier way to visualize this is to picture one of those motorcycle's with its front wheel waaaaay out front, aka a chopper. This front suspension set-up has a ton of positive caster. These bikes are very stable in a straight line (they make great cruisers) but are very reluctant to go around sharp corners. You may also have noticed that when their front wheel is turned, it tends to lay over on its side quite a bit. That is the increased negative camber during cornering I referred to.
In any case, I will report back if and when I get some more miles on the set-up.
Originally posted by 'Grease Monkey' on Roadfly