Does rear upright need a caster angle and a kingpin?

[firasf1dream]

Hello Gentlemen,
not sure if this is the right category to ask my question, I am designing a rear upright for a F1 rc car, so my question is does the rear upright need a caster angle and a kingpin axis ?
I am trying to think about it this way, a rear wheel is not steering while on track so the self centering effect is not actually needed but when I rethink again I would say it needs a bit of self centering to keep the wheel straight after giving it a negative toe in static position. Is my logic right ? Does F1 cars in reality have a caster and a kingpin ?

Thank you in advance

[Greg Locock]

Those numbers are reported, and widely ignored. I have never seen a problem introduced by them, in practice. usually your rear suspension geometry has bigger fish to fry.

[Tim.Wright]

There's no kinematic reason to have "caster and kingpin" on a non-steered rear axle.

I'd even say that if the axle isn't steered then there is no caster or kingpin angle on the rear axle.

[firasf1dream]

There's no kinematic reason to have "caster and kingpin" on a non-steered rear axle.

I'd even say that if the axle isn't steered then there is no caster or kingpin angle on the rear axle.

ok thank you for the reply

[JordanMugen]

There's no kinematic reason to have "caster and kingpin" on a non-steered rear axle.

I'd even say that if the axle isn't steered then there is no caster or kingpin angle on the rear axle.

How about the toe changes under compression or extension?

Or how about beam axles with active rear steering like on the Renault Megane 2016-present (below)? How are caster and kingpin defined on a beam axle, noting that many older compact cars had beam axles on the front (sorry I don't know anything about suspension )?

I guess the Megane has two additional rear balljoints on each side for the normally "fixed" rear knuckles to pivot around? While the more traditional Peugeot 306 type passive rear steering would involve the entire beam rotating about it's two mounting bushes...?

[Tim.Wright]

How about the toe changes under compression or extension?

That got nothing to do with the steering axis.

Or how about beam axles with active rear steering like on the Renault Megane 2016-present (below)?

This is a not a "non-steered" axle then. There must be joints on the wheel carrier/upright that define a steering axis.

[Greg Locock]

To be honest I'm not really sure how one would define KPI and castor angle, scrub radius and mech trail, in the absence of the ability to steer the wheel directly. I suspect they are reverse engineered from the compliances, in other words they are talking about elastic centres, which while they certainly do matter, are better considered in their own right rather than confusing them with kinematics. You could look at the response of the wheel angles etc to MZ, that defines a fake steering axis.

For example, scrub radius is somewhat analogous to toe under traction, or toe in braking. But if that is what you are interested in, measure that, don't call it some kinematic name.

[firasf1dream]

I am actually doing it on a RC F1 car not a road car, looking at PaulsF1 work I took into consideration his chosen numbers after doing some search and I decided to adopt 5 degrees for kingping axis and 2 degrees for camber but no castor

[godlameroso]

Hello Gentlemen,
not sure if this is the right category to ask my question, I am designing a rear upright for a F1 rc car, so my question is does the rear upright need a caster angle and a kingpin axis ?
I am trying to think about it this way, a rear wheel is not steering while on track so the self centering effect is not actually needed but when I rethink again I would say it needs a bit of self centering to keep the wheel straight after giving it a negative toe in static position. Is my logic right ? Does F1 cars in reality have a caster and a kingpin ?

Thank you in advance

Caster isn't something critical on the rear end of any wheeled vehicle except for fork lifts that have the steering linkage in the rear. The closest thing I can think of is KPI and that's pretty much determined by where you stick your track rod.

[firasf1dream]

Hello Gentlemen,
not sure if this is the right category to ask my question, I am designing a rear upright for a F1 rc car, so my question is does the rear upright need a caster angle and a kingpin axis ?
I am trying to think about it this way, a rear wheel is not steering while on track so the self centering effect is not actually needed but when I rethink again I would say it needs a bit of self centering to keep the wheel straight after giving it a negative toe in static position. Is my logic right ? Does F1 cars in reality have a caster and a kingpin ?

Thank you in advance

Caster isn't something critical on the rear end of any wheeled vehicle except for fork lifts that have the steering linkage in the rear. The closest thing I can think of is KPI and that's pretty much determined by where you stick your track rod.

Thank you for your reply and what about a 2 degrees camber is that a must ? I mean the camber is it a must at the rear ?

[godlameroso]

2 degrees is fine even for most road cars.

[firasf1dream]

2 degrees is fine even for most road cars.

ok thank you

[Mchamilton]

Hello Gentlemen,
not sure if this is the right category to ask my question, I am designing a rear upright for a F1 rc car, so my question is does the rear upright need a caster angle and a kingpin axis ?
I am trying to think about it this way, a rear wheel is not steering while on track so the self centering effect is not actually needed but when I rethink again I would say it needs a bit of self centering to keep the wheel straight after giving it a negative toe in static position. Is my logic right ? Does F1 cars in reality have a caster and a kingpin ?

Thank you in advance

Caster isn't something critical on the rear end of any wheeled vehicle except for fork lifts that have the steering linkage in the rear. The closest thing I can think of is KPI and that's pretty much determined by where you stick your track rod.

How is kpi determined by where you put your track rod?

[godlameroso]

Hello Gentlemen,
not sure if this is the right category to ask my question, I am designing a rear upright for a F1 rc car, so my question is does the rear upright need a caster angle and a kingpin axis ?
I am trying to think about it this way, a rear wheel is not steering while on track so the self centering effect is not actually needed but when I rethink again I would say it needs a bit of self centering to keep the wheel straight after giving it a negative toe in static position. Is my logic right ? Does F1 cars in reality have a caster and a kingpin ?

Thank you in advance

Caster isn't something critical on the rear end of any wheeled vehicle except for fork lifts that have the steering linkage in the rear. The closest thing I can think of is KPI and that's pretty much determined by where you stick your track rod.

How is kpi determined by where you put your track rod?

Because the track rod determines the toe gain/loss while the suspension articulates. The track rod does what the steering rack does without the steering part. If you attach the track rod further or closer to the upright relative to the upper arm you change KPI.

[Tim.Wright]

KPI is the front view steering axis inclination angle. It has nothing to do with the track-rod/toe-link/steering-arm what ever you want to call it.

Bumpsteer is affected by all the links. Not just the toe-link.