Damper rate

[stephenh]

I am mystified. If the rear right corner is 148mm above datum level, and rear left is 161mm above datum level, then how can the front be level in relation to datum, unless the chassis is twisted? Otherwise, the front left would have to be higher than the front right! Maybe the chassis is being twisted by the differental forces being exerted on it by the springs, but it sounds like quite a lot of twist to have permanently in the chassis.

If I jack up one corner of my car,lets say for this purpose the right rear, then the chassis rotates around an axis running between the left rear and the right front. As a result, the left front corner drops. Conversely, if by lowering the spring seat on the right rear corner of my car I lower the right rear then the chassis will again pivot around an axis running between the left rear and the right front, and the left front corner will rise.

So how come in the case of Adam's car the right rear is much lower than the left rear, and yet the front ride heights are identical, and he tells us he has a level floor from which he is measuring?

[nikpro]

So how come in the case of Adam's car the right rear is much lower than the left rear, and yet the front ride heights are identical, and he tells us he has a level floor from which he is measuring?

Because each spring platform is independently adjustable so each wheel supports a different proportion of the weight of the car - the front ride heights can be the same but the spring platforms on each front shock will be in a different location.

For corner weighting imagine the car is a table with 4 legs. If you put a weight in the centre of the table the weight is evenly distributed down the legs to the floor.

To reduce the weight on one of the legs you would shorten it, therefore the other three legs would carry the weight and the shorter leg would carry none.

With a vehicle; to reduce the weight carried by a wheel you lower the ride height/take out pre-load (unwind the spring collar) of that wheel - hence the offside rear in a corner weighted seven will be lower ride height wise.

HTH

[stephenh]

To reduce the weight on one of the legs you would shorten it, therefore the other three legs would carry the weight and the shorter leg would carry none.

Nikpro, I'm agreeing with everything you've said in your last post, but to take it a stage further, if by adding weight to the corner with the short leg (to simulate the effect of a driver getting into the car) that corner drops, and what happens to the opposite corner? In my experience, it rises. If it didn't, then the tabletop is flexing.

So how come that isn't happening with Adam's car? In Adam's case, assuming his measurements are accurate, his chassis is horizontal latterally at the front, but not at the back. How? Is that normal?

[John Loudon - Sponsorship Liaison]

I can see what Stephen is referring to. The figures for Adams ride heights have the 2 fronts equal but one of the rears higher than the other which under normal circumastances would make the opposite front lower than the other front. I guess it depends on where the CoG is located front to rear and whether there was some very slight inaccurracy in the measurement of the RH's. I doubt very much that the chassis is twisted

[Frosty]

To reduce the weight on one of the legs you would shorten it, therefore the other three legs would carry the weight and the shorter leg would carry none.

Nikpro, I'm agreeing with everything you've said in your last post, but to take it a stage further, if by adding weight to the corner with the short leg (to simulate the effect of a driver getting into the car) that corner drops, and what happens to the opposite corner? In my experience, it rises. If it didn't, then the tabletop is flexing.

So how come that isn't happening with Adam's car? In Adam's case, assuming his measurements are accurate, his chassis is horizontal latterally at the front, but not at the back. How? Is that normal?

You must take nikpro's example as an example, but don't try and compare the physics of a table to the physics of a car directly. A table is rigid, but a car is sprung, and the springs don't alow the same rocking effect that the table will give with a short leg.

If you put more weight over a shortened leg then the table will tip or rock, but this will not happen in a car since the springs dilute this effect.

In corner weight terms, what you do to one corner, you do to the diagonally opposite corner too. So if you lower your left rear, is will become lighter, and so will the right front.

This you can think of in table terms too. If you shorten a leg, the table rocks back on forward on this leg, and the one diagonally opposite.

So by lowering the table on one corner, that one and the corner diagonally opposite are both lightened as a result, because the other two legs take more of the weight.

[stephenh]

Frosty and Nikpro, you're missing the point, although John now sees it. How can the front corners be at the same height, but the back corners aren't? It is nothing to do with springs, my point would be equally valid if you took the springs off altogether and sat the chassis on a couple of tressles.

It isn't possible unless the loadings are such that the chassis is permanently twisted. Is that what corner weighting does?          

[nikpro]

I can see what Stephen is referring to. The figures for Adams ride heights have the 2 fronts equal but one of the rears higher than the other which under normal circumastances would make the opposite front lower than the other front. I guess it depends on where the CoG is located front to rear and whether there was some very slight inaccurracy in the measurement of the RH's. I doubt very much that the chassis is twisted

Thanks to frosty for explaining things better than me!

John,

I suspect there is also slight inaccuracies in the measurements but also remeber that the front of the Westfield Chassis is much narrower than the rear and behaves more like a 'triangle' than a 'rectangle'.

(God I'm s**t at explaining things in words!!)

[stephenh]

Thank you!

Although I doubt it really helps the O/P. I guess that we really all think that if Adam's knowledge of suspension is limited, then he probably ought to get the car looked at professionally, because at the moment, it ain't right.

I seem to remember seeing Adam's car lurching (that is the only word I can think of to describe what was happening) through the Molehill when I was marshalling on the WSCC trackday, and thinking the suspension needed sorting.

[Frosty]

Frosty and Nikpro, you're missing the point, although John now sees it. How can the front corners be at the same height, but the back corners aren't? It is nothing to do with springs, my point would be equally valid if you took the springs off altogether and sat the chassis on a couple of tressles.

It isn't possible unless the loadings are such that the chassis is permanently twisted. Is that what corner weighting does?          

I think I might be missing the point. If you put the car on a perfectly flat floor, and stood the car on axle stands - assuming the chassis is straight, the ride height would be the same at all 4 measurement points with the driver on board.

This is because you are bypassing the springs. The axle stands would all have a different weight on top of them though. If you had a scale pad between the chassis and each axle stand, you would not see an identical weight on each scale - you would see differences on each scale pad, but the ride height would obviously be the same since the axle stands are not compressible.

So to make things simple, say the car has 200lb springs both front and rear. Also let's assume that the leverages and effective rates are identical front and rear too. We'll also say we set the springs to have the same amount of preload front and rear. We'll also assume that the damper mounting brackets are positioned so ride height is the same front and rear for a given fitted spring length. Basically an identical front and rear end.

So now when we drop the car to the floor, will we have even ride heights all round with the driver sat in?

Probably not is the answer, because the weight differences which were acting on the axle stands are now acting on the springs, so the less even the weight distribution is, the greater the difference in ride height.

So you might be left with 130mm FR and 125mm FL, so then to even up the ride height you would just add 5mm to one or take 5mm off the other, then you have even front ride height. It does not mean the chassis is bent. It just means you have adjusted your spring platforms differently from 1 side to the other.

Sorry if I'm being thick, but I can't see where I'm going wrong.

[adamnreeves]

Didn't imagine this thread would get so long ;-) I am glad I've been too busy at work with comments like twisted chassis being made! I would say there's more than slight inaccuracies in my measurements. I did measure three times and it agreed three times but I do not have a laser levelled floor and using a set square, etc, etc. I only really put my measurements up as an indication of how much lower the rear right was when I thought like many others that the weight with the heavier weight should be higher but as Fraser has said actually its the reverse. Which I am happy to be confirmed. Tonight I pushed the car a few feet back in my garage and re-measured the front, it measures 143 left and 137 right. I have checked my floor with a spirit level in many places and the bubble is in the middle but a spirit level floor is not going to produce millimeter accurate measurements, its all just a guide. Yes the front is much narrower than the rear, so the datum points at the front being a much smaller distance apart means a greater angle is achieved than the rear for the same difference in heights. This was apparent back when I set my initial ride height.

[John Loudon - Sponsorship Liaison]

Frosty - Adams ride heights are:-

Front Left 141mm

Front Right 141mm

Rear Left 161mm

Rear Right 148mm

The fronts are equal so if this was resting on a flat floor, one of the rears would be higher than the other rear by 13mm

Do you see Stephens point now?

Nikpro has now seen it I think and summarises that the front of the chassis is narrower than the rear and the fact that some measuring inaccuracies of the ride heights may account for the difference which I tend to agree with

[adamnreeves]

Firstly, my post was not intended as a wise crack, merely an observation.

Anyway, at that point had you lifted/braked? As you say it's difficult from a still photo to make meaningful suggestions as we can't tell what inputs you were making prior to  and during the corner. Did you have chance to get a more experienced driver to sit in the passenger seat and give you feed back?

As Fraser as said, maybe your driving as well as the suspension needs modifying. I found the course that I mentioned in my previous post very helpful.

John

John,

This track day was organised relatively quickly and being busy at work I haven't really had time to think about tuition. I didn't take anyone round the track in my car.

My cliche at the moment is "My ability is far below that of the car, I don't give it justice". I've a lot to learn. I was okay on the rest of the track and some of the people I was talking to were saying the car looks well planted. I know I slid on four occasions on this bend and wondering if this was one such time because my position on the track is all wrong. I know my fundamental error on the first corner on the molehill was going in too fast. All part of the learning process. Thanks

[Frosty]

Frosty - Adams ride heights are:-

Front Left 141mm

Front Right 141mm

Rear Left 161mm

Rear Right 148mm

The fronts are equal so if this was resting on a flat floor, one of the rears would be higher than the other rear by 13mm

Do you see Stephens point now?

Nikpro has now seen it I think and summarises that the front of the chassis is narrower than the rear and the fact that some measuring inaccuracies of the ride heights may account for the difference which I tend to agree with

No sorry I still don't see the point. What is wrong with this?

Most of the weight of the driver goes to the back of the car, so I would expect at least a 10mm difference in ride height from left to right to compensate.

Please help me understand what is being said, because it doesn't make sense to me.

[John Loudon - Sponsorship Liaison]

Frosty - we are talking ride heights here and nothing to do with weights. The front end of the chassis is the same dimension from the ground on both sides so the rear should also be the same height from the ground on both sides but its not

[adamnreeves]

I'd just like to add the extra weight on the right hand rear side is not just me, my battery is installed in the boot box on the right hand-side. Before you say why didn't I install on the left, because I knew less back then than I know now and the construction manual said to. It also just so happens that the extra weight that could not be dialled out is very close to double the weight of the battery so moving to the left would achieve perfect balance. However, I'm in no rush to do this.