Quote:
Originally Posted by volosong
Sorry, for once, I can't totally agree with you. If what you say is true, then why does my coupe handle so much better by installing Sportline bars (front and rear) in lieu of the stock bars?
However, you are partially correct. The 2.6 front bar is 25mm at its thickest while the 2.2 diesel's bar is 22mm. That is a 14% increase in the maximum thickness for the front bar. But, the plan doesn't stop there. While the 2.6 rear bar is only 14mm, (only a 1mm increase over the 2.2 diesel bar), the 2.3-16 rear bar is 16mm, for an increase of 23% in maximum thickness.
So, yes, the front bar will be thicker, but the rear bar will be a "lot" thicker, relatively. 14% thicker on the front, 23% on the rear. But, that is not all.
In addition, I'm chucking the OEM struts/shocks and installing Bilstein HD struts/shocks. The Bilstein Comfort are the equivalent of the OEM struts/shocks and the Bilstein Sport are akin to MB Sportline. I have Bilstein HD on my 300CE, and couldn't be happier.
And one more. Going are the original 14" wheels that are only 5" wide. The recommended tire for the 14x5 ET50 OEM tire is 175/70R14. It can be pushed one size to run 185/65R14. I picked up two 15x6 ET49 wheels today with a 201 part number that has a recommended tire size of 185/65R15, which can be pushed one size to 195/60R15 (as the two I picked up have). What this means is that instead of a 7" wide tire with 6" in contact with the ground, I can now have a 7.75" wide tire with 7.25" on the ground. That is an increase of 21% more rubber in contact with the asphalt.
So, while agree with you that only doing the front bar is dangerous, going with thicker bars front and rear in addition to wider tires and HD shocks result in a package that will handle a whole lot better than the stock setup. Before making my changes to the coupe, it tended to drift on the road. After the suspension upgrade, it tracks straight and true. I noticed that the diesel will tend to drift too. Not as much as the coupe used to, but more than the coupe does now. With the full package, it should have a positive, confident handling characteristic to it.
Besides...with only 72 horsepower, I'm not going to be blasting through any mountain roads anytime soon. I just want more positive handling. It worked on the coupe, I have no doubt that with all three, (thicker bars, heavy duty struts/shocks, wider wheels/tires), that the diesel sedan will see a likewise improvement.
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One paragraph at a time.
When you put sportline bars on BOTH ends of your car, you were stiffening the rear bar along with the front. Additionally, you are saying that your car "handles better." How are you determining that? I will remind you that handling improvement involves making the car go where you steer it, NOT decreasing body lean.
Now as for stiffness increases, let's go back to some seventh grade math. The stiffness of the bar is NOT determined by the diameter, rather the cross section. Using a simple calcluation of the area of a circle, the front bars in your examples have a 29% difference in stiffness, while the rear bar, again in your examples, have a 51% delta. SO, in the case of changing the sway bars you cited, you are almost doubling the added stiffness of the rear sway bar as compared to the added stiffness of the front sway bar. This means that this sway bar change is STIFFENING the rear bar significantly more than the front, thus taking out SOME of the understeer. THAT's why this combination is improving handling.
Your third paragraph is indicating even MORE reason why this combination is improving handling. The sway bars are only one part of the equation. Stiffening springs on the same end of the car has the same effect as stiffening sway bars. Most people who seek to change handling don't go so far as to change springs. It is quick and simple to change sway bars, so they stop there. Also changing sway bars will not effect ride except in very particular situations like going over a speed bump at an angle.
Your tire/wheel combination is indeed part of your package and is indeed part of the equation and I'm glad it all works for you.
All that said, the fact remains that, with no other changes involved, stiffening the rear sway bar takes out understeer while stiffening the front sway bar ADDS understeer. The context of my earlier post was aimed toward the OP. It sounded to me as if he was changing sway bars ONLY. He was not undertaking a total suspension makeover as you did. There's nothing wrong with stiffening the front sway bar as long as you are stiffening the rear bar considerably more and if springs are being changed, that is taken into account as well.
SO, in the case of improving the handling of a relatively stock, non performance car, via no changes other than sway bars, leave the front one thin and stiffen the daylights out of the rear one.