I see.
I mention load transfer because of this:
Holden Monaro test, after using stiffer front spring rate:
load-transfer-handling: increased understeer
no-load-transfer-handling: not increased understeer
How exactly are you measuring understeer here and how are you ensuring that the conditions are exactly repeated for each run through?
Is the tyre grip being exceeded every single time and by how much, sorry to sound a bit negative but its a bit hard to form any definite opinion from just the above.
To help a Trico Pro understand why stiffening front spring rate add understeer, I give some more example since it seems grayout's guide mention acceleration only.
I will use Colcob's LFS GT suspension analyserV2-2.xls. Let's believe what Colcob said about Scawen (LFS main programmer) help him correct this excel file physics. For this experiment I change the car weight distribution to 50:50.
Code:
At no lateral and no longitudinal force, standing still, spring rate at 21.2/21.2 (F/R) the spring loads is:
left right
front 2882.6 2882.6
rear 2882.6 2882.6
[b]cruising[/b]
At -0.75g lateral and no longitudinal force, left turn cruising, spring rate still at 21.2/21.2 the spring loads is:
left right
front 1230.0 4535.3
rear 1230.0 4535.3
At -0.75g lateral and no longitudinal force, left turn cruising, spring rate change to 28.8/21.2 the spring loads is:
left right
front 916.5 4848.8
rear 1435.6 4329.7
[b]braking[/b]
At -0.75g lateral and -0.75 longitudinal force, left turn braking, spring rate still at 21.2/21.2 the spring loads is:
left right
front 2247.3 5552.6
rear 212.6 3517.9
At -0.75g lateral and -0.75 longitudinal force, left turn braking, spring rate change to 28.8/21.2 the spring loads is:
left right
front 1967.0 5899.3
rear 385.0 3279.2
[b]acceleration[/b]
At -0.75g lateral and 0.25 longitudinal force, left turn acceleration, spring rate still at 21.2/21.2 the spring loads is:
left right
front 890.9 4196.2
rear 1569.1 4874.4
At -0.75g lateral and 0.25 longitudinal force, left turn acceleration, spring rate change to 28.8/21.2 the spring loads is:
left right
front 566.3 4498.6
rear 1785.7 4679.9
Good interesting stuff
In all experiment, increasing front spring rate increase front outside suspension load. Don't know if this load exceed tire optimum traction or not. Exceeding = more understeer.
Yes if a single front tyre tyre is exceeding grip then we can say the car will have an understeer balance, however that is a very simplistic look at what is happening. True car balance comes not just by looking at which end looses grip first, but from looking at the actual Slip Angles (and if required the slip pecentages as well) for each tyre and then seeing how they compare to each other. I cover this in my first guide...
...so in a situation when grip has not been exceeded on a single (or more) tyre, then we need to look at a bit more info. Dynamic balance once grip has been exceeded is easy to judge, under the limit its far harder to predict.
If we assume that tire optimum traction is at 5000, then:
- at cruising stiffer front = more oversteer.
- at braking stiffer front = more understeer.
- at acceleration, stiffer front = more oversteer.
As I pointed out above its unfortunately not quite that simple in all cases, you see in all the cases you claim oversteer, if you actually look at the difference between the grip on each corner the front always has the biggest difference, so the front tyres are the ones with the poorer spread of grip and the ones most likely to be closer to the slip limits. Sorry but these all indicate understeer.
cruising
At -0.75g lateral and no longitudinal force, left turn cruising, spring rate change to 28.8/21.2 the spring loads is:
left right
front 916.5 4848.8 = 3932.3 difference
rear 1435.6 4329.7 = 2894.1 difference
The load is less evenly spread between the front tyres and the result will be understeer
braking
At -0.75g lateral and -0.75 longitudinal force, left turn braking, spring rate change to 28.8/21.2 the spring loads is:
left right
front 1967.0 5899.3 = 3932.3 difference
rear 385.0 3279.2 = 2894.2 difference
The load is less evenly spread between the front tyres and the result will be understeer, however as the front right has exceeded it limit we would be looking at quite extreme understeer.
acceleration
At -0.75g lateral and 0.25 longitudinal force, left turn acceleration, spring rate change to 28.8/21.2 the spring loads is:
left right
front 566.3 4498.6 = 3932.3 difference
rear 1785.7 4679.9 = 2894.2 difference
The load is less evenly spread between the front tyres and the result will be understeer, keep in mind that the front inside tyre (left) has almost no load on it at all, the resulting CF value would be extremely low and little grip would be being generated, a situation as bad as overloading a tyre.
Now if we take this last one a bit further and use the following graph (from a previous post of mine) as an example of CF generated by load...
..now I am going to divide your load value all by 10 to get some reading we can plot on the graph, and what we get (approx) is
Front
Left - 56.6 = CF 0.1
Right - 449.8 = CF 1.1
Rear
Left - 178.5 = CF 0.6
Right - 467.9 = CF 1.2
Now as all the tyres are below the limit we can clearly see the front left is the weak point here and no matter how much grip the front right is generating, as the left it not helping out its the front end of the car with the biggest problem. Looking at it very simply the front has a combined CF of 1.2 and the rear 1.8, clearly the front has less grip than the rear (despite the fact that neither end has actually lost grip).
we can even take this one step further and look at effective traction at each corner, think back to basic physics that frictional force = CF x vertical load we can calculate the following.
Front
Left - CF 0.1 * 56.6 = 5.66
Right - CF 1.1 * 449.8 = 494.78
Rear
Left - CF 0.6 * 178.5 = 107.1
Right - CF 1.2 * 467.9 = 561.48
Here we can see that front left tyre is the critical point, offering little in the way of real grip. Combine this with the previous factors and it doesn't look good at the front end.
You see what is critical is the manner in which the load is spread and how that will relate to slip angles, the more one tyre is asked to do at the expense of another (or the biggest difference in how load is shared at a given end) determines the balance, particularly if one or more tyre has not yet reached its limit.
Keep in mind that
both tyres at a given end need to be doing as equal a share of the work as possible to provide a good level of grip, and in this case the stiffened front is not allowing that.
The one exception that could develop from this would be the acceleration one, if you were able to apply sufficient power to a rear tyre(s) to get it/them to exceed the grip limit through acceleration alone (assuming rear wheel drive) then the result would be oversteer (of the power variety). This is one of the ways in which you can get a situation of understeer developing to oversteer as you power out of a corner.
BTW - the fact that the same differences can be seen in all cases would indicate that this is a fairly basic formula in application here, with very few 'realistic' variables in place.
Remember that this experiment assume that the lateral and longitudinal force are static, while in reality it can be dynamic too. Things can be different when weight shifting happen.
I don't disagree with that, but you have confused exactly how the spread of load at a given end works.
Consider a front heavy FR car. What I think happen when this car equipped with stiffer spring rate:
case 1: heavy braking. More understeer. Even if the shifted weight reduced and the front tire still at it's optimum traction according to weight distribution calculation, the tire will still be overload because during load transfer front tire will receive faster weight shifting. And faster weight shifting means more force at the same time will be feed to the front tire.
case 2: mild acceleration. More understeer. Even if the tire still bellow it optimum traction, it can be more understeer as there are still more sudden weight shifting at front, trying to lift the front tire, reducing more of it's traction.
For the reasons I outlined above this is still simply about how the load is spread not because of the speed of transfer. You are mixing up how the spring rates effect balance with how dampers effect balance.
Scaff, I assume spring rate has role in load transfer base from literature
University of Texas, Physics review & bond graphs: Mechanical Translational
Resistance not only come from damper but also from spring. Maybe you mean to say that spring range is too limited in GT4 compare to it's damper. But I think it's the other way around, I think damper range is too limited in a way that we can only notice significant difference on car behaviour when changing spring, not so noticable when changing damper.
That link does not constitute literature, rather a series of formula, however I have not at any point denied that spring can have a dampening effect....
Scaff
Unless you are looking at massively stiff spring rates (and I'm talking about far stiffer than GT4 will allow you to set) then spring rate has little effect on the speed of the load transfer. I always recommend keeping the following in mind "Springs determine how much the car will move, dampers will determine how quickly it does it", yes some interplay between these two does occur, but the fundamental statement is correct.
...however the damping effect from a coil spring is minor in comparison to that of the damper, one of the principal roles of a damper is to put resistance into the system. It would not be effective at this if the spring had a major role to play here. In fact if that was true then why would we need dampers at all (you are arguing here that spring rate changes have a effect on load transfer speeds to overide that of the dampers).
I also totally disagree that changes to damper rates has an insignificant role in speed of load transfer, the tests I carried out on this very subject with the Caterham clearly show that damper rates in GT4 have a significant effect on the speed of load transfer, illustrated by the visible difference in suspension system reaction and the totally different feel.
https://www.gtplanet.net/forum/showpost.php?p=2515759&postcount=272
BTW, Scaff, do I see correctly that your car in this picture is turning left?
The car is facing the 'wrong' way for the turn, I forgot to flip the image for the manual and have not found the time to correct it.
Regards
Scaff