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Author Topic: Steering geometry  (Read 120 times)

StefanN

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Steering geometry
« on: 09 July 2019, 10:14:09 pm »
I found it very stable in a straight line, but as Rhys said, this means it takes a lot of effort to turn it in.
Out of interest what diameter is your steering wheel and how long is your Pitman arm?

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RhysN

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Re: Steering geometry
« Reply #1 on: 10 July 2019, 01:41:41 am »
If you have a look at Grahams MG you will see a large steering wheel, iMHO hard work.

StefanN

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Re: Steering geometry
« Reply #2 on: 10 July 2019, 05:08:15 am »
If you have a look at Grahams MG you will see a large steering wheel, iMHO hard work.
Not sure what you mean?  Please could you explain.

RhysN

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Re: Steering geometry
« Reply #3 on: 10 July 2019, 07:03:12 am »
His car has a steering wheel which is more scale than most, and still heavy steering. I suggested to him he experiment with less castor to see what happens. It's hard work in his car even at low speed.
I think relative length of the steering arms compared to what you have called pitman arm, while affecting the weight of the steering to some extent, are more an effect felt by how much you turn the wheel to achieve steering angles at the wheels.
« Last Edit: 10 July 2019, 07:05:31 am by RhysN »

ChrisS

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Re: Steering geometry
« Reply #4 on: 10 July 2019, 08:46:37 am »
I found it very stable in a straight line, but as Rhys said, this means it takes a lot of effort to turn it in.
Out of interest what diameter is your steering wheel and how long is your Pitman arm?


My steering wheel is 13 inch and my pitman arm is 62mm between centres, my Gemini steering arms are 100mm between centres.
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StefanN

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Re: Steering geometry - dimensions
« Reply #5 on: 10 July 2019, 12:51:58 pm »
Thought I'd tabulate the info from anyone who shares it.  Steering leverage factor is a term I just made up which comprises Pitman arm between centres/(steering wheel radius x steering arm between centres) - a lower factor should mean lighter steering all else being equal...I think!
WhoSteering wheel radiusPitman arm between centresSteering armsteering leverage factor
Chris S ERA165621003.75
Stefan N Bugatti172501052.77
Chris B Morgan150751503.33
Bill A Maserati150651103.94

all in millimeters
« Last Edit: 10 July 2019, 09:07:38 pm by StefanN »
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Chris Brown

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Re: Steering geometry
« Reply #6 on: 10 July 2019, 04:25:43 pm »
My figures are: Steering wheel radius 150mm; Pitman 75mm; steering arm 150mm.

I've got 3 possible positions on the steering arm and 2 on the pitman, so these measurements may change.

Can't comment on how good the steering geometry works, as the column bearings were binding at Stretton in May, so the steering was VERY heavy.

Castor is difficult to determine, as part of it is due to the stub axle being behind the slider.


Will start on the various bits of re-working shortly, then I'll be able to give it another test run, and report back.

TheGiantTribble

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Re: Steering geometry
« Reply #7 on: 10 July 2019, 04:44:27 pm »
My steering wheel radius is 150mm
Pitman 65mm
Steering arm 110mm

I will mention tyre pressures, low pressure on the front increases steering weight from light (with current pressures) to Oh wow, heave!
Pressures are front 20 psi, and rears 28 psi.

Steve Cole

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Re: Steering geometry
« Reply #8 on: 11 July 2019, 10:42:01 pm »
Sorry folks, since Sunday I just haven’t had chance to measure up, I’ll try to do it at the weekend
Steve

StefanN

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Re: Steering geometry
« Reply #9 on: 18 July 2019, 06:51:16 pm »
So other factors that affect steering feel:

Castor and KPI - leading to jacking,
Tyres/tyre pressure
« Last Edit: 20 July 2019, 10:50:34 pm by StefanN »

RhysN

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Re: Steering geometry
« Reply #10 on: 20 July 2019, 07:47:29 pm »
As well as whatever bearing/friction system is in the steering column, stub axles...

RhysN

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Re: Steering geometry
« Reply #11 on: 29 July 2019, 03:24:28 pm »
Just because they were at hand, I measured a set of stubs and the pitman arm from a kart (compatible pair). Pitman is 50 mm centre to centre, steering arms 100 mm. In the past I have generally been close to equal. I'm confused now!