Can we talk about caster?

learn me adjustment of caster for performance and optimized feedback. Thanks.

You want more.

You can never get enough.

More is moving the strut (on a MacStrut) back towards the windshield, right (tilting the spindle back)? And is this more negative or more positive caster?

And why is it good.... better turn in?

Note- too much caster, and your steering wheel won't return to center. It may not even move. Which means manually steering it 24/7. I slammed my ae86 once, while the gain was awesome, I wasn't able to do no handed drifting because the wheel wouldn't return to zero. I used to make money from my friends doing stunts like no handed drifting.

That would be caster that is 'too negative' or, since it's rarely less than 0, 'not positive enough'. Positive caster causes steering angle to lift one side of the car, so the steering will be trying to return to center even when the car isn't rolling (not that it will, but the forces are there).

So do we want NEGATIVE or POSITIVE?

Positive. Negative is very unstable, the steering will try to move off center. But it does seem that if you get too much positive, the wheel stops trying to return when you get near the lock stops. I've come across this on my Locost. I also ran it with negative caster at one point with some experimental upper arms, that was not a happy day.

Thanks to the amount of assist available with EPAS, the new Miata runs a LOT of caster.

Doesn't a lot of positive caster just make for anti-dive, especially under suspension compression?

A lot of positive castor can have an interesting effect on handling because you are changing the cross weight mid turn, and then again as you come out of the turn. Also, if you adjust from the bottom you are adjusting the wheel base as well which can affect Ackerman. But it sure helps turn in. Major castor equals major improvement. Then mid turn everything goes for a E36 M3.

Increasing positive castor magnifies your dynamic camber. In simple terms you get the same increase in turn in response that you would get from extreme negative camber while maintaining your contact patch. There is more too it as listed above but go get what you can. Other negative not discussed above is a significant increase in force on the steering wheel make it take more strength to turn at low speeds.

I can see how having too much positive caster could let you go 'over-center' with the weight jacking and then have gravity trying to feed in MORE steering, but i'm actually surprised that that much is possible without significant mods. The most positive caster i have ever (knowingly) run was less than 6 degrees. But in my head it also seems that tire width and wheel offset would play into at what point the steering forces would change direction, so if you ran stretched tires on low offset wheels it would actually happen sooner than wide tires on high (positive) offset wheels even with the same positive caster.

Caster also sets pull on a RWD vehicle. If you are driving on public roads, you always want a half degree more on the right side to compensate for road crown.

I did 9 degrees once. Most of the negatives discussed already became apparent. So building a custom set of upper control arms foe ridiculous amounts of positive caster is not a beneficial use of time. 5.5-6 seems to be the sweet spot to me.

Better feel, better turn in, better return.

In reply to WildScotsRacing:

Oh yes you can. If you get too much positive camber you will jack the front of the car up on the inside wheel and will fight the steering in every turn. This is one of those things where if 4 is good, 6 is better but 12... not so much. Like recreational Oxycontin.

We use to run 3+ and 3- on the dwarf to get it to pull it self in to the left corner. Caster effects weight jacking that is to say when you turn the centerline of the axle stub move up and down as it moves left to right.

I learned it as a very young lad messing around with aftermarket leaf spring shackles on an old CJ. I bent one of the stock shackles off-roading and decided to replace them with stronger (and longer) aftermarket ones. My first foray into suspension geometry did not go so well. The thing became miraculously easier to steer and was great when off-road. On road however, it was practically undrivable. It felt like it was always on ice. This all happened just prior to the Internet and it took me awhile to read up enough to figure it out. In simple terms, the more negative it is (think long front shackles on an archaic old relic or wagon with leaf springs) the easier it will be to steer but the less stabil it will be to drive. Think about what those long shackles are doing to the steering's axis of rotation. Go look at an old dragster which makes it really easy to visualize. The caster will be so positive (opposite of my old jeep) that you can see the weird angle that the tie rod operates at. And indeed when turned sharp this is why the wheels actually "flop over" a bit.

About caster, do fwd double wishbone cars not need as much as a mac strut car? I noticed most double wishbone civics and integras have around 1-3 degrees of caster.

Posts I've read online people have tried to add caster, but it wasn't necessarily faster and some saw impact the reliability of axles

I can't answer that. My experience is all rwd. But I can see the axle life shortened.

Huckleberry wrote: In reply to WildScotsRacing: Oh yes you can. If you get too much positive camber you will jack the front of the car up on the inside wheel and will fight the steering in every turn. This is one of those things where if 4 is good, 6 is better but 12... not so much. Like recreational Oxycontin.

All true. But, my point was it's hard to get too much when dealing with OEM suspension and steering mounting points. Especially with MacStrut cars.

NickD wrote: Caster also sets pull on a RWD vehicle. If you are driving on public roads, you always want a half degree more on the right side to compensate for road crown.

The first guy who did alignments for me used to think this. But it's wrong, unless you only ever drive in the right lane and on roads that are designed to drain to both sides and there are no grooves from trucks and there's no banking. In the variable real world, you want even caster on both sides so the car is consistent.

Javelin wrote: Doesn't a lot of positive caster just make for anti-dive, especially under suspension compression?

Nope, it doesn't affect anti-dive, it affects spring motion ratio (on a macstrut car, if you change it by moving the upper shock mount point). Anti-dive is all in the fore-aft lean of the suspension arms.

aw614 wrote: About caster, do fwd double wishbone cars not need as much as a mac strut car? I noticed most double wishbone civics and integras have around 1-3 degrees of caster. Posts I've read online people have tried to add caster, but it wasn't necessarily faster and some saw impact the reliability of axles

A good way to think about one aspect of caster is thinking of it as dynamic camber that is added with increased steering angle.

Then you have the weight-jacking/self-centering side of the equation that comes with it.

There is such a thing as too much camber. How much is that? Depends on the application. SLA (double wishbone) has better camber curves than Strut suspensions, so they may not need as much camber contribution from caster as a Strut car. If doing a clean sheet design you will want some caster contribution as the self centering effect is desirable.

How does it effect tramlining or does it at all?

For the RWD cars I've owned, it's usually been a "maximum OEM adjustment" for the caster. That's 6-6.5° for both the S2000 and E39 Touring, and both of them have fantastic steering feel and centering characteristics.