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I've been evaluating rear sway bars: there is a big gap between a 19mm bar and a 22mm bar. 19mm bars are not stiff enough, and 22mm bars are too stiff, IMHO.
Seems to me that the first setting of a 19mm bar is so little change vs. OEM "S"as to be useless. It takes a 30-50% change in sway bar stiffness on the MINI to make a difference that's worth changing.
On the other hand, the hardest setting with a 22mm bar, I can tell you from experience, is for track use, and the two lower ones are still quite a bit if you have other mods that decrease understeer.
These numbers are calculated, but this is a case where the physics are pretty simple and the calculations are straightforward. These ratios will apply when the effective "arm" length of the bars compared is the same, and this should be true of any steel bar with three positions - the middle hole should be at the stock length in order to keep the connecting link at nearly the same angle.
So to recap, here are the relevant ratios for solid swaybars, in the range that applies to MINIs. 9.9x would mean 9.9 times stiffer than a 17mm "S" bar:
Cooper 16mm .79x
S 17mm 1.0
19mm 1.56x
20mm 1.92x
22mm 2.80x
The placement of the holes also affects the stiffness. Given that the center hole of a 3-holer has to be in the original position, and that all the mfrs. of three-holers drill the three holes equally spaced, you can figure that the harder position creates about 1.4x times the center position, and the softer hole will be about .75 of the middle hole, i.e. you will get a choice of ratios, again, related to the stock S 17mm bar:
These ratios all work out to within a few % of the figures specified by the manufacturers, which is close enough for decision-making. Here's my observations:
- Softest position on a 19mm bar would be useful on a Cooper, but not a useful change on an S.
- The softest position on a 22mm bar is more than 2x stiffer than stock, and that is quite a bit for many street-only cars and drivers.
- 19 mm bar doesn't go firm enough for track, and a 22mm bar doesn't adjust soft enough for street.
- It would be useful to have an only-a-little-more-stiff position available, for use in winter, for example. Somewhere around 1.3-1.5x would be nice.
For myself, before recently adding IE Fixed camber plates, I was happy with a 22mm bar set at Medium. After the camber plates, and with other mods that decrease understeer, I tried the 22mm bar on soft. That was still a bit tail-heavy for me, so I've installed this 20mm bar, which gives me a very slightly softer Middle setting for normal spirited use, while still offering a useful range of adjustment both harder and softer.
The 20mm bar is seldom seen here in the US, but this one is available from JSCspeed or MiniMania (wildly over-priced from MM, IMHO). The bar is the same, from Whiteline in Australia.
The Whiteline bar is a quality piece, with forged bar-ends, not welded, and three holes for adjustment. (Welded bar-ends, like the Alta, are more prone to fail under stress.) The same bar fits either 1st or 2nd-gen cars.
The urethane bushings supplied use the stock u-brackets, so they are a snug fit on the 20mm bar - this removes some of the "wind-up" feeling of many bars that use thicker bushings. The bushings have a pebble surface on the inside, which should help retain grease (supplied) and thus reduce squeaking.
The settings on the Whiteline are just right, IMHO - a softer setting if camber plates are used, middle for stiffer but still road-able, and firmest for the track. The 20mm bar seems to me to be the "sweet-spot" size for any S that's not a track-monster.
P.S. - After installing IE fixed camber plates several months later, I am now using the softest setting on the 20mm bar, and it's Perfect for fast twisty roads.
