Anti-ackerman steering

[Billzilla]

Just give the car about 75% Ackerman, it will be as close to as good as it's going to ever get.

to drive around the block ,participate at Indy 500 or in a autcross? it can´t be the same for all?

Yeah all of them.
Can't see why you'd need to move to less than 75%, maybe up around the 80% to 85% mark if you feel like fiddling.

[marcush.]

so you say formula 1 with anti ackerman is complete bollocks and they do it because newey snapped it up somewhere but you could not measure the effect?

Tyre characteristics are not the same for each and every tyre and all of them are load sensitive.A tyre that does not like much slipangle when only lightly loaded will respond more to antiackerman than a tyre that is not very sensitive to changes in occuring vertical load changes.
Maybe there is not a full second to be found per lap but then in a field where a tenth may decide if you drop out in Q1 or fight for participation in Q3 you just have to turn every stone upside down to gain .

[Greg Locock]

I’m missing your point. It would seem that Ackerman would be required by steel wheels on a rubber surface (high friction) rather than gravel (low friction)

In general, proper Ackerman is a function of the center of turn which differs from that of steel wheels as a result of slip angle that, in turn, is determined by over/understeer as a result of a bunch of other factors including roll moment/stiffness,.

With low slip angle tires and a short wheelbase, 100% Ackerman is a pretty good default baseline, though still requiring dial in to complement/correct other handling inputs.

Dunno. You babble on quoting techie phrases and yet seem to be missing any understanding. I may be misrepresenting you, but that is my perception.

[olefud]

I’m missing your point. It would seem that Ackerman would be required by steel wheels on a rubber surface (high friction) rather than gravel (low friction)

In general, proper Ackerman is a function of the center of turn which differs from that of steel wheels as a result of slip angle that, in turn, is determined by over/understeer as a result of a bunch of other factors including roll moment/stiffness,.

With low slip angle tires and a short wheelbase, 100% Ackerman is a pretty good default baseline, though still requiring dial in to complement/correct other handling inputs.

Dunno. You babble on quoting techie phrases and yet seem to be missing any understanding. I may be misrepresenting you, but that is my perception.

As to the first point, if two connected wheel are trying to go in differing directions, gravel would allow accommodating slippage while a rubber surface would cause more binding and chatter.

The second point is merely stating that in theory Ackerman is a simple concept. However, in practice with changing cornering radii and over/understeer conditions it becomes rather complicated with changing conditions yielding changing theoretical solutions. I suppose describing the lack of a definite answer qualifies as lacking understanding.

[DaveW]

Dunno. You babble on quoting techie phrases and yet seem to be missing any understanding.

Greg, I value your knowledge & experience, and your contributions generally add much value to a discussion. The above comment is not one of those, I'm afraid.

Whilst I am being critical, where I come from a properly engineered bolted coupling is much to be preferred, whilst a welded alternative would generally be frowned upon. To be fair, production car engineering remains a mystery to me.

As an aside (kind of), I was once presented with a damper "durability" test spec that consisted of a large sinusoidal input of 1 Hz, added to a still large sinusoidal input of 10Hz. I protested that the spec. might be reasonable for a "boulevard cruiser" on cross plies & no damper fluid, but it was unrepresentative for a reasonably well damped car on high performance tyres. I was told that the spec. had been used for ever, & they werent about to change it... We had to water cool the dampers & then to pause periodically to stop the water boiling.

[olefud]

In general, proper Ackerman is a function of the center of turn which differs from that of steel wheels as a result of slip angle that, in turn, is determined by over/understeer as a result of a bunch of other factors including roll moment/stiffness,.

With low slip angle tires and a short wheelbase, 100% Ackerman is a pretty good default baseline, though still requiring dial in to complement/correct other handling inputs.

Dunno. You babble on quoting techie phrases and yet seem to be missing any understanding. I may be misrepresenting you, but that is my perception.

I’ve thought a bit more on this since it shouldn’t be a hot button issue. By 100% Ackerman I mean that a “steering arm” extended through the king pin axis and the tie rod axis will intersect the center of the rear axle. Intersection forward of the axle is pro-Ackerman and behind the axle is anti-Ackerman.

And “…as a result of a bunch of other factors…” was intended to convey that the analysis fades into the perspective. Put another way, the conditions determining proper Ackerman keep changing during cornering making a determination, as it were, indeterminate. I can see that trying to follow my comment with the expectation of a tidy answer could be irritating. It may be one of my idiosyncrasies that knowing the degree to which something can be known is often important to me. In any event, I didn’t intend to waste your time and try your patience.

[WallyCarrera]

Now we are entering the corner introducing steering angle to change direction :
The coernering will introduce a shift of carnerweights/loads towards the outside wheels increasing vertical load.The driver will adjust the steering wheel to maximise the available grip during his aim to make the corner ...Too much ..the car washes out (lack of grip) too little the car leaves the track as the radius is too big.But there is also the inside tyre ...not carrying half axle load anymore but say a quarter of the original load.tyres are load sensitive..so what happens to the optimum slip angle ..it changes.if it does not change I need the same slip angle inside outside ..so no ackerman at all. If the unloaded tyre wants more slip angle .then I need pro ackermann and more slip angle introduced.
But ..it could be that our tyre wants to see less slip angle and we are going towards anti ackerman .

Thanks for this great explanation and I appreciate that this is an older post. But, re the part where you state 'no ackerman at all' - should this not be 'standard ackerman'? I think I understand the need for pro-Ackerman or anti-Ackerman as vertical tyre loads increase/decrease. But in the theoretical situation where there was equal tyre load, wouldn't it just be 'Ackerman' with no need for variation? Or, have I misunderstood? This is very probable. haha. Cheers.

[Rustem 1988]

I think that for different values of the tire pressure sensitivity of the tire may be different.

[Rustem 1988]

Caster does not affect the turning angle of the wheels?

[godlameroso]

It can by introducing dynamic camber.

[gambler]

The amount of "drive" on the inside rear tire will affect the turn radius (more so with a spool), so mindboggling as it seems. It probably would make for a great test to run it on a skid pad with an adjustable spindle to evlauate tire wear vs speed. It would be interesting.