## Steering Forces

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Hello, i wonder if you can help.

Thinking about starting a project but i have a few questions first and as i am new to this i thought this would be the best place to get expert advice.

I am thinking about the forces (N) that act on a vehicles steering rack during cornering. How do these forces get translated into the steering column? ie, Do the forces get 'scaled' down / reduced through the rack and pinion?

I am sure this is a sill question, sorry.

Best regards
G_N
Ginja_Ninja
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Joined: 30 May 2010

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..

I would say look at a karts steering system for simplicity
Last edited by N12ck on Sat Jun 30, 2012 5:37 pm, edited 2 times in total.
Budding F1 Engineer
N12ck
11

Joined: 19 Dec 2010

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Here's how the forces get from the contact patch to the steering wheel rim. The lateral force at the contact patch FY acts a certain distance behind the kingpin axis, T , generating a moment MKP=T*FY. This is reacted by a force FTR in the tie rod, where FTR=MKP*steering lever arm, which is roughly the distance of the OTR to the wheel centre in side view.

In a rack and pinion we usually characterise the gear ratio as the C factor, mm of rack travel for one turn of the pinion.

rack force is the sum of the two tie rod forces.

Rack force*C/1000=2*pi*steering column torque.

steering column torque=steering wheel torque

SWT=force from one hand at rim*dia of steering wheel, if you are using both hands.
Greg Locock
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Joined: 29 Jun 2012

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Hi Greg, joined the darkside now??

N12ck wrote:
I don't know of how many steering systems use Rack and pinion anymore, look at a karts steering system for simplicity

Every proper race car and pretty much every road car use rack and pinion. The go kart system doesn't have enough reduction for cars which weigh more than a couple hundred kilos

Tim
Tim.Wright
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Joined: 13 Feb 2009

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Sorry misread the sentence when I posted,
Budding F1 Engineer
N12ck
11

Joined: 19 Dec 2010

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Greg Locock wrote:Here's how the forces get from the contact patch to the steering wheel rim. The lateral force at the contact patch FY acts a certain distance behind the kingpin axis, T , generating a moment MKP=T*FY. This is reacted by a force FTR in the tie rod, where FTR=MKP*steering lever arm, which is roughly the distance of the OTR to the wheel centre in side view.

In a rack and pinion we usually characterise the gear ratio as the C factor, mm of rack travel for one turn of the pinion.

rack force is the sum of the two tie rod forces.

Rack force*C/1000=2*pi*steering column torque.

steering column torque=steering wheel torque

SWT=force from one hand at rim*dia of steering wheel, if you are using both hands.

Fantastic ! Thank you so much, i will be needing my trusty calc i think
Ginja_Ninja
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Joined: 30 May 2010