I know positive caster is good. Is there too much? What happens at extreme amounts, and what is considered extreme?
In general, learn me caster.
I know positive caster is good. Is there too much? What happens at extreme amounts, and what is considered extreme?
In general, learn me caster.
Adding castor adds directly to weight of steering. I need to check my setup sheets but believe I managed to get 4degrees positive caster which really made a huge difference in the dynamic camber. I'm able to run less negative camber at -2.5degrees and still have the turn in response desired.
On non-power steering cars like my rabbit heavy caster makes it a real workout.
Caster also causes weight jacking, so lots of caster will un-weight the inside rear tire more in turns. Because of this, some cars will like more, some will like less.
I run somewhere around 8 degrees of caster on the Jeep. The weight jacking is noticeable, but compared to running less caster, the steering feels better, the Jeep turns better and it's got more front end grip (due to more dynamic camber gain as you turn).
Too much caster does cause a lack of front end grip in very slow, tight turns though as you'll end up gaining a lot of camber when you're near full lock (significantly more than you need).
Positive caster is also what makes the steering return to center. That's all I got.
Positive caster allows more road shock to be transmitted to the suspension and steering. It also increases the possibility of steering shimmy. That is why most cars/trucks with 6+ degrees of caster use a steering dampener. Last, but not least, it causes tire wear when turning (think Big Wheel/chopper m/cycle). Thus, the need for 4x4 trucks (6+ degrees) to rotate tires often.
Ok. So, extreme would be considered 6+ degrees.
We have power steering, so that shouldn't be too much of a concern.
I should have been more specific.
This is a double a arm suspension, very similar to a 66 mustang. Dedicated race car ( c prepared, challenge, and hopefully hillclimb) on slicks. V8 and rear wheel drive with leafs in the vack. I'm currently fibbing strut rods and lca mods, and trying to set it up for baseline settings in the middle of the adjustment rage for most tuning ability. Trying to determine the ends of the spectrum I'm designing get to.
66 Mustang needs more than caster. Watch the /engineering videos by fatman. They need a taller spindle to fix camber and bump steer issues.
Too much caster will cause too much camber gain in a turn.
For a race car I'd say you'd want 3~6deg of caster. If you can get a good camber curve through A-arm design, you can run less caster. To keep the steering light and minimize negative steering effects such as tramlining, you ideally want to stay on the low side of that range.
Another side-note, more caster also increases the car's tendency to "self-countersteer" and drift cars run a lot of caster for this reason - it's easy for the driver to dial in a ton of countersteer quickly just by tossing the wheel in the right direction, or even just by releasing the wheel.
GameboyRMH wrote: Another side-note, more caster also increases the car's tendency to "self-countersteer" and drift cars run a lot of caster for this reason - it's easy for the driver to dial in a ton of countersteer quickly just by tossing the wheel in the right direction, or even just by *releasing* the wheel.
This. Lots of caster makes for buckets of fun in the snow. You can throw it sideways and it takes just a little flick of the wheel to snap the tail back in line when you're ready. Makes it really easy to Tokyo Drift your entire commute in the snow 
Does wheelbase affect recommend caster? We're working with a 98 inch wheelbase.
Most BMW's come from the factory with over 8 degrees of caster and in the case of the E30 M3 bumped that up even higher.
Dusterbd13 wrote: Does wheelbase affect recommend caster? We're working with a 98 inch wheelbase.
Not really, the only relationship between the two is that any negative steering effects from large amounts of caster will be worse with a shorter wheelbase!
I always hears you can't have too much caster. On my 350Z it's got like 1.2 degrees of camber and 8.5 degrees of caster, neither of which is adjustable. The result is better than expected turn in for a camber limited setup but it crosses a threshold as you input more steering, suddenly it's nothing but understeer. I'd gladly trade 3 degrees of caster for 1 more degree of camber.
evildky wrote: I always hears you can't have too much caster. On my 350Z it's got like 1.2 degrees of camber and 8.5 degrees of caster, neither of which is adjustable. The result is better than expected turn in for a camber limited setup but it crosses a threshold as you input more steering, suddenly it's nothing but understeer. I'd gladly trade 3 degrees of caster for 1 more degree of camber.
With that tradeoff, I've found some cars like lots of caster in sweeping turns, etc. But it does hurt front end grip in tight stuff, so there's definitely a point of too much. Where that point is varies based on the chassis and how you're using it.
Needed caster also very much depends upon load - a mid-engine car will need more. Just throwing in another variable.
In reply to evildky:
Damn you! I was just about to use your car as an example of too much caster.
Dusterbd13 wrote: In general, learn me caster.
kb58 wrote: Needed caster also very much depends upon load - a mid-engine car will need more. Just throwing in another variable.
Are you sure that has to do with load? I think that's an attempt to keep the front wheels further from zero or negative effective caster under brake dive, which mid-engined cars typically have more of.
Oh another fun fact about caster: Some American land-yachts from the pre-PS era run zero or negative caster to make the steering lighter. Negative caster means the steering will be inherently unstable (like a modern car while reversing) 
Jumper K. Balls wrote: Most BMW's come from the factory with over 8 degrees of caster and in the case of the E30 M3 bumped that up even higher.
10 degrees here in my E30 with M3 style offset control arm bushings. Oh and that's with manual steering too...combine that with sweet V8 torques and she'll give you a workout on an autocross course.
ross2004 wrote:Jumper K. Balls wrote: Most BMW's come from the factory with over 8 degrees of caster and in the case of the E30 M3 bumped that up even higher.10 degrees here in my E30 with M3 style offset control arm bushings. Oh and that's with manual steering too...combine that with sweet V8 torques and she'll give you a workout on an autocross course.
Fun fact: For all you E46 non-M folks, you can substitute BMW OEM Z4M front control arm lollipops to get a high durometer, offset cast bushing with a nice increase in caster.
I didn't want to go to a pillowball style strut mount for my coilovers, so Ground Control has a really nice one. It has very little caster adjustment, ~1 degree. The Z4M bushings got me as much caster as I would have ever wanted for a dual-purpose car, and one less thing to knock out of alignment.
The way it worked out, I can adjust from zero to 20 degrees positive. Once it's on track, we can start testing.
You'll need to log in to post.
