[Ram]

Originally Posted by Boom Shiva

What about if you park your car with one side on a higher position than the other? Like sometimes when there's debris (e.g. all over bombay) and the left wheels are resting on the elevation and the right wheels are on the road? How badly does this affect your suspension etc?

My experience is that parking with one side of wheels higher than the other side, does not hurt the car, as long as you don't "bottom-out" and hit the rubber bump-stops. The "travel" in the suspension, is supposed to accomodate this,

When I spent three months in Warrington, Cheshire, UK, I saw car owners, maximizing the street available to other people, by parking their cars at night with two wheels on the raised pavement-- it was upto six inches taller than the street level. Also noticed this at Kings Cross, Woolloomooloo, Sydney Australia.

Automobile suspensions are designed to have a certain amount of “give” or suspension travel. When that travel has been completely used up at either extreme, the suspension is said to have “bottomed-out”.

Off-road 4x4s (particularly coil-sprung ones) have much more suspension travel, than cars. However even with the right kind of leaf spring, significant travel is possible.

The picture below illustrates a test performed on a military “Shaktiman” 3-ton truck manufactured at Vehicle Factory Jabalpur under license from MAN Commercial Vehicles AG, Munich-Allach, Germany.



This truck was shipped back to the principals: MAN Commercial Vehicles AG for testing. That's why it's wearing German license plates.

You can see the extremes of wheel travel, a well-designed suspension is capable of, even with leaf springs.

The 5-ton MAN 630 is de-rated to 3-tons and license-manufactured in India under the name “Shaktiman”. It is produced with a 110 bhp engine with both soft-top and steel cabin driver’s cabs. Available in both two-wheel drive and four-wheel drive versions, the basic version is a tarpaulin covered lorry with dualie rear axle.

[santosh.s]

Nice information, Ram. I used to wonder about the sound (resembling flowing liquid) produced when steering is in extreme left or right position and I push it further, got it clarified!


However, to me, your posts #5 and #10 seems to be contradicting. Swiveling caster example tends to imply negative caster as per your definition (pivot towards front and contact patch of the wheel towards rear). We know that this one straightens out on itself, but in post #5 you say -ve caster should wander

[Technocrat]

Great Explaination Ram. I was telling similar thing to people here ona thread about HPS & EPS but it wasnt this detailed & hence no one believed :(

[Ram]

Originally Posted by santosh.s

Nice information, Ram. I used to wonder about the sound (resembling flowing liquid) produced when steering is in extreme left or right position and I push it further, got it clarified!

Thanks for the compliment, santosh.s.

Originally Posted by santosh.s

However, to me, your posts #5 and #10 seem to be contradicting.
Swiveling caster example tends to imply negative caster as per your definition (pivot towards front and contact patch of the wheel towards rear).

We know that this one straightens out on itself, but in post #5 you say -ve caster should wander

I still maintain that negative caster will cause wander.

The swiveling caster example (shopping cart case) does not imply negative caster, even as per my definition (pivot towards front and contact patch of the wheel towards rear).



In a car, the pivot is not at 90 degrees to the road surface.
It is angled backward so that the top of the pivot leans toward the rear of the car. This causes the extension of the kingpin onto the road to lead the point of contact. (See diagram below)


In post#5, I said that, when observed from the side of the car,
if the top of the pivot leans toward the rear of the car, the caster is positive
and the steering will center after a turn.
The more positive the caster angle the heavier the steering will be.

On the other hand, if the top of the pivot leans toward the front of the car,
the caster is negative.
Steering will be light and the car will wander all over, after a turn.

In post #10, I said that steered wheels return to the straight ahead position only due to
the "caster" angle of the kingpin, leading the point of contact of the wheel on the road.

The "caster" angle of the kingpin, can only lead the point of contact by leaning backwards, so that the caster axis when extended, contacts the road at the blue spot, ahead of the red tire contact patch.

Have I been able to explain in a better way, now?

Warm regards
Ram

[jyobeb]

Well Ram, that was well written and explained. One doubt however. Leaving the wheels fully turned with the engine off, probably doesn't create any problems. How about when you start the car with the wheels fully turned? Won't the entire system be put through a lot of sudden high pressure. Yes, wheels are supposed to be turned away from the kerb to stop cars from running away on a slope but I'm sure that you're not required to turn it all the way! Just my two bits worth!

[vivekiny2k]

one doubt, I understand that in a rear wheel drive, the caster will try to realign the wheel straight. because the rear wheel keeps pushing the car in foward diection straight.


how does it work in front wheel drive? when the steered wheel itself is giving all the traction.

forgive me for seeking an answer to a question which probably takes hours of classes in mech/auto engg.

[santosh.s]

Ram, sorry I somehow missed your posting which had very detailed explanation... and ended up seeing it after two whole weeks! Got the point, the position of caster axis matters, rather than the top of pivot.

However, I tend to agree with Vivek. All this should hold good for rear wheel drive vehicles (always) or front wheel drive vehicles while braking only, when front wheels in a way are pulling the rest of the body backward. What about front wheel drive case (under which most of the cars tody fall) while accelerating? The straight position of wheels with +ve caster which is stable during braking will turn into unstable and vice versa... any comments?

[pgsagar]

My cousin own a CRDi Accent. His parking space is so tight that he leaves the car overnight with steering wheel truned to a side so that it is easy to back out in the morning in the same position. His mech says doing this in a hydraulic power steering car will wreck the P.S. system. Is it true? can any TeamBhpian shed some light on this.

[clevermax]

This cannot wreck the PS system. Your friend can try changing the orientation of the car on alternate days, if he is so concerned about leaving the steering to one extreme every night.

[Jaggu]

More than steering or suspension it might induce load on the tires, thats what i feel

[joecherian]

There is a similar thread which I had started some time back. Thought these two could be merged

http://www.team-bhp.com/forum/techni...-straight.html

[honda3938]

Originally Posted by pgsagar

My cousin own a CRDi Accent. His parking space is so tight that he leaves the car overnight with steering wheel truned to a side so that it is easy to back out in the morning in the same position. His mech says doing this in a hydraulic power steering car will wreck the P.S. system. Is it true? can any TeamBhpian shed some light on this.

yes leaving the wheels turned can stress the hydraulic power steering and suspension components also.

[gomzi]

Great informative posts Ram! Keeping the wheels turned or not while parking was a old forgotten question of mine also good info regarding the parking on uneven surfaces.

Yay! I learnt something new for today

[del.guy22]

just make sure that the wheels are straight, at times I have seen vehicles parked and the front wheel is out moe than the body. A fool may just bang it at night, since the lanes in India are really narrow.

[freewheelburnin]

Really interesting info!!!Never knew so much about the Castor.

Originally Posted by Ram

Hi Ramky:

Let me explain one of the three important angles in steering and suspension geometry of a car.

When you turn your steering wheel, your front wheels swivel on a pivot defined in the suspension system. The angle of this pivot is called Caster.

When observed from the side of the car,
if the top of the pivot leans toward the rear of the car, the caster is positive and the steering will center after a turn. The more positive the caster angle the heavier the steering will be.

On the other hand, if the top of the pivot leans toward the front of the car, the caster is negative. Steering will be light and the car will wander all over, after a turn.

If the caster on the left side is not equal to that on the right side, the car will continually pull to the side with the less positive caster.

So, in a moving car, after completing a turn, the front wheels return to the straight-ahead position, not due to imaginary tension springs in the steering system, but due to caster.

Rest assured, there is no harm leaving the wheels fully turned either to right or left.

In fact, the California Directorate of Motor Vehicles (DMV) handbook advises that…

QUOTE
When you park on a hill:

• On a sloping driveway, turn the wheels so the car will not roll into the street if the brakes fail.
• Headed downhill, turn your front wheels into the curb or toward the side of the road. Set the parking brake.
• Headed uphill, turn your front wheels away from the curb and let your vehicle roll back a few inches. The back of the front wheel should gently touch the curb. Set the parking brake.
• Headed either uphill or downhill and there is no curb, turn the wheels so the car will roll away from the center of the road if the brakes fail.

Always set your parking brake and leave the vehicle in gear or the "park" position.
UNQUOTE

I rest my case…
Ram