Reduced caster effect?

[GTP]

My mind got to wondering (wandering?) the other day about reducing my caster by the 0.7-degrees provided by my J&M camber plates.

Would this increase steering "feel" and decrease understeer?
Or is it too small to notice for a 3900# car on track?

Seems simple and easy enough to experiment with at the track.

Sponsored

 

[Ewheels]

More caster will give you an increased self-centering effect (steering feels "heavier") and camber gain in the corners.
Generally*, more caster = more corning grip.

 

[Roadsign]

It's always a compromise, More caster also means more weight jacking but with macpherson strut suspension you also get more camber gain. For the Mustang the camber gain outweighs the weight jacking imo

 

[TeeLew]

It's always a compromise, More caster also means more weight jacking but with macpherson strut suspension you also get more camber gain. For the Mustang the camber gain outweighs the weight jacking imo

It kind of depends on what camber you're running statically, but the added camber due to caster generally adds a bit of front grip. The cross-weighting that you get from caster is a very real thing and it jacks weight in the direction that would tend to make the car turn more. It has a greater effect in slow corners when you're using a lot of lock, but it's always in play.

Because of the weight-jacking, as you increase caster, you can get to the point where the weight-jacking makes the car too sensitive to steering angle. We're talking about some pretty small caster changes here, so I doubt we'd ever see this.

A 0.7* caster change is pretty small either way. You might feel a little less weight in the steering, but you could feel that by changing the steering assist. It's going to be tough to feel much of a handling change, because the dynamic camber and cross weight differences we're talking about here are small.

I think the 0.7* adjustment is just a way to make sure they're the same. I would imagine Ford's tolerances are close to 0.5*. If you drive your car on the street, it's usually worthwhile to run the FL caster lower than the FR by about 0.1-0.3*. This helps the car track straight because that's enough to counter the effect of the crown of the road.

 

[GTP]

Thanks for the input everyone. As a reminder my post #1 is asking about reducing caster, IOW moving the strut top as far forward in the hole as possible.

I don't understand weight jacking. I'm just looking for less slow speed understeer, which as we all know is near impossible to alleviate.

 

[TeeLew]

Don't over-charge the corner. It's a better fix than anything else you could ever do.

 

[GTP]

Good advice again @TeeLew.
It's a bad habit I'm trying to correct.

 

[Dana Pants]

Thanks for the input everyone. As a reminder my post #1 is asking about reducing caster, IOW moving the strut top as far forward in the hole as possible.

I don't understand weight jacking. I'm just looking for less slow speed understeer, which as we all know is near impossible to alleviate.

More camber and more caster = more front grip. Like -4 front camber and all the caster.

The “correct” way to deal with this is more throttle. My car is an absolute pig without the skinny pedal. It even self-corrects in the snow if I lift.

 

[TeeLew]

The “correct” way to deal with this is more throttle. My car is an absolute pig without the skinny pedal. It even self-corrects in the snow if I lift.

If you're trying to fix your understeer with the throttle, you've already fucked the corner.

 

[GTP]

It kind of depends on what camber you're running statically, but the added camber due to caster generally adds a bit of front grip. The cross-weighting that you get from caster is a very real thing and it jacks weight in the direction that would tend to make the car turn more. It has a greater effect in slow corners when you're using a lot of lock, but it's always in play.

Because of the weight-jacking, as you increase caster, you can get to the point where the weight-jacking makes the car too sensitive to steering angle. We're talking about some pretty small caster changes here, so I doubt we'd ever see this.

A 0.7* caster change is pretty small either way. You might feel a little less weight in the steering, but you could feel that by changing the steering assist. It's going to be tough to feel much of a handling change, because the dynamic camber and cross weight differences we're talking about here are small.

I think the 0.7* adjustment is just a way to make sure they're the same. I would imagine Ford's tolerances are close to 0.5*. If you drive your car on the street, it's usually worthwhile to run the FL caster lower than the FR by about 0.1-0.3*. This helps the car track straight because that's enough to counter the effect of the crown of the road.

That's been my suspicion, too, i.e. that the small caster adjustment is to even out left/right. As well as the non-equal angle from the factory is to help with the road crown.

What I fail to understand (because it is counterintuitive to me) is how increased caster increases front grip. If higher caster increases the self-centering effect, then why is that not also the same as more understeer? If that is due to associated camber increase or weight jacking, then okay. Even so, this assumes that more camber is helpful, i.e. it was not already at optimal camber.

After a careful string alignment my car drives so damn straight. So I think I will just adjust the caster to be as forward as possible but also equal left/right. I'm not expecting to notice much if any difference on track with a heavy car.

 

[DaveR.PP2]

I think what's been said here is all pretty much understandable and accurate for the most part. Ford factory caster wasn't just contrived by guesswork. Of course the car was built for myriad types of buyers.

Probably best not to over think making material caster changes until all your other suspension stuff is figured out. There are too many variables to contend with and for me caster is the absolute last variable to consider vs. factory setting because it already accomplishes a significant percentage of accomplishing virtually all driving applications the car was built to do.

Personally I get a kick from responses about how the car understeer oversteers and so on under high speed track conditions. This has much more to do with driver input and driver interpretation as to what they think is going on..... and that's highly subjective......... Yes, events and responses happen at speed but a lot of times negative outcomes surface as the result of driver input... I mean these S550's don't drive themselves.

Personally, I defer from making caster changes in what I do. These are essentially really great street cars with wide range of track application out of the box and I'll just leave it at that.

Sponsored