How Important Is Power Steering For The Drivers?

[Jersey Tom]

You can make a modern open wheel car without power steering - see IndyCar. It does require a lot of effort.

If a current F1 car had its power steering fail mid-lap would it be impossible to drive? Probably, I'd think so.

Would taking power steering away from F1 make the racing any better? No, I can't imagine it would.

[BanMeToo]

I'm still curious about GP2. What is so different on the suspension there vs F1?

[Tommy Cookers]

the F1 car must behave more like a rally car than does an Indy car (or a GP2 car ??)
presumably F1 steering needs to rather isolate the wheel holder from his 'curb-smashing' to help him do it

anyway both suspension and steering geometry are in some ways sacrificed to give a layout advantageous to aero and structure

[bill shoe]

Power steering gives the team & driver another item to get better or worse than the competition. Kimi spent lots of time at Lotus/Renault tweaking the feel of their power-steering, and Renault is probably still benefiting from that work today. Every tunable feature raises the importance of a good test/development driver.

In case you hadn't noticed, this is why Ferrari keeps re-upping Kimi year after year despite mediocre results at the races. He brings a development focus and ability that the Alonso/Vettel superstars can't match even though they have better outright pace.

[garyjpaterson]

If we turn back the clock 60 years to when road cars, by and large, did not have PAS, you need

-large scrub radius (say +100 mm) - this allows the wheel to roll when you are parking on a flat surface (ie no brakes) = only important at very low speeds

-small castor and in particular kpi - try and reduce jacking

-bignum steering ratios

-big steering wheels.

-big biceps

Once you have PAS you can get rid of those limitations and start to concentrate more on what the driver would /like/ as opposed to /need/.

Might be a bit OT, but always wondered about this;

In old cars, particularly pre-war, you often see positive camber at the front. I always assumed with was to minimise the scrub radius, so the contact patch basically rotates around the intersection of the KPI axis. And I thought this was to reduce steering effort and kickback.

I guess I'm completely wrong given what you say about having a large scrub radius, allowing the wheel to roll.
Any ideas why this was then?

[Tommy Cookers]

what you describe was the ideal of 'centre-point' steering geometry
the ideal was ever harder to reach as tyres became less narrow

so the scrub radius was made deliberately large
because PAS's prime benefit is to incompetent (as today's) drivers who expect to steer while stationary
so the hundred million manual steering versions of these cars suffered from the large scrub radius

large scrub radius drove the use of 'kingpin' inclination/'castor' combinations giving a lot of 'jacking'
(there was the school of negative scrub radius)

people might look at the Citroen DS and SM steering geometries

btw
bicycle and motorcycle steering geometry has generally not departed from 'zero jacking' - discovered c. 130 years ago
(a bicycle fitted with a replacement fork having less offset/'rake'/(curvature) than original is unstable and crashes if ridden 'no hands')

[Tim.Wright]

If we turn back the clock 60 years to when road cars, by and large, did not have PAS, you need

-large scrub radius (say +100 mm) - this allows the wheel to roll when you are parking on a flat surface (ie no brakes) = only important at very low speeds

I've though this one though on another occasion and to me a large scrub radius, while introducing a rolling movement, doesn't remove the scrubbing component at the contact patch. The 'turnslip', as Pacejka defines it, remains the same between a low and high scrub condition. With high scrub, you are effectively dragging the wheel through the same angle range but over a larger arc and at a higher velocity as a a wheel with a low scrub radius. What do you think?

[Greg Locock]

This all raises more historic questions than answers

Did the 2CV have centrepoint steering?

Was the VW Golf the first car with negative scrub radius as a deliberate choice?

Tim - i agree about the scrubbing thing, unfortunately it is a rather expensive test to figure out what the truth is. I suppose one argument in favor of small scrub radii is that it is feasible to turn the wheels even with the brakes on.

[zac510]

Unless it was quietly outlawed as some kind of cost-cutting measure in the last couple of years, the F1 cars mostly have variable ratio rack and pinion too (depending upon driver preference). The front wheels will turn more as the steering wheel is turned further.

[Jolle]

Unless it was quietly outlawed as some kind of cost-cutting measure in the last couple of years, the F1 cars mostly have variable ratio rack and pinion too (depending upon driver preference). The front wheels will turn more as the steering wheel is turned further.

There is no rule against a progressive steering input, but nothing beats a linear rack.

BMW has an option for a active rack, but it doesn't work on track because you never know exactly how much the wheel are going to turn so, compared to a linear rack, you miss the apexes just ever so slightly.

[zac510]

It's not an active rack. it's not electronically controlled. It just has a non-linear gear ratio curve.

[Tim.Wright]

The BMW system is active but it's at the column level not the rack.

There is an epicycloidal gearbox + motor in series in the steering column which can add or subtract to the angle input from the driver.

I can imagine it being annoying for track use.

[roon]

If we turn back the clock 60 years to when road cars, by and large, did not have PAS, you need

-large scrub radius (say +100 mm) - this allows the wheel to roll when you are parking on a flat surface (ie no brakes) = only important at very low speeds

-small castor and in particular kpi - try and reduce jacking

-bignum steering ratios

-big steering wheels.

-big biceps

Once you have PAS you can get rid of those limitations and start to concentrate more on what the driver would /like/ as opposed to /need/.

Do you think the '17 W08 & STR12 have, or would benefit from, negative scrub radius? Their upper pivots on the wheel uprights are far inboard of the lower pivots. Hard to tell exactly where the lower pivots are i.e. if they would provide such geometry.

Might be a bit OT, but always wondered about this; In old cars, particularly pre-war, you often see positive camber at the front. I always assumed with was to minimise the scrub radius, so the contact patch basically rotates around the intersection of the KPI axis. And I thought this was to reduce steering effort and kickback.

what you describe was the ideal of 'centre-point' steering geometry
the ideal was ever harder to reach as tyres became less narrow

Thanks as always, Tommy.