General how Swaybars and Diffs interact thread.

[NitroDann]

So I thought Id open this so we could continue to discuss why you would change swaybars and how to determine if what you have chosen isnt working well with the diff.

So ask away.

Dann

[Magpie]

My decision to not have a rear sway bar was based on reading Fatcat motorsports website as well as from some limited information on the web relating to sway bars and torsen diffs.

Sway bars do (among other things) keep the car 'flat' to keep a large contact patch with the road. A torsen diff whilst not acheiving a large contact patch (what sway bars do) transfers power through a mechanical biases to a wheel with the most torque. The limit of a torsen diff is that if a wheel comes off the ground then it can not work. So yes a sway bar and a torsen can live together and yes if you keep lifting a rear wheel off the ground then yes you will need a sway bar to keep it on the ground. However this maybe driver technique that needs to be changed to match the way the car is set up or the setup needs to be changed to match the driver.

My point is that you can not look at just one part in isolation. NitroDann makes some good points in knowing what you want as end result needs to be communicated but first you need to understand what you want! Do you want to drift, track, daily drive with the occasional spirited drive? What is your driving style are you fluid or do you jerk the car or are you learning, do you want to corner faster or is straight line speed your goal?

Something to think about to get the discussions going http://www.turnfast.com/tech_handling/handling_weightxfr :
The rate of weight transfer impacts the responsiveness of the car to driver inputs. The faster the weight transfer, the quicker the response. This allows the driver to have greater control of the car. However, a faster weight transfer requires greater skill of the driver. Smoothness and quicker reaction sensitivity to the tire traction are needed. It turns out that shocks have the largest impact on rate of weight transfer. The stiffer they are, the faster the tranfser.

The impact of weight transfer on suspension geometry has to do with maintaining as large and flat a tire contact patch as possible. When the body rolls, dives, or squats as a result of weight transfer, the geometric relationship of the suspension components to the body and the wheel changes the shape of the contact patch. For the unloaded tires, the patch size will be reduced. This effect must be minimized. Changes in shocks, springs, anti-roll bars, and wheel alignment are made to maximize the tire contact patches of all tires during the dynamic changes of weight transfer.

Maybe we could come up with a posting format like the for sale section to help get all the relevant info over?


Note: thanks for starting this thread NitroDann.

[hks_kansei]

Also to add to the conversation.

Is flat cornering really necessary? (let's assume a road car here)


I've always considered that the rigidity of the car should be matched to the level of grip it has.
ie: the stiffer the car is, via swaybars/springs/shocks/etc the more grip it needs (softer tyres or better tyres)


I'd be interested to see a comparison of a stock MX5, vs one with HD swaybars, vs stock with semi slicks
I wouldn't be surprised if the stock + sways is the slower of the 3.



My experience with rigid MX5s is that the grip level seems somewhat lower than the softer ones. (I'm guessing while it's cornering flat, the tyre still deflects, and also skips over small bumps rather than absorbing them)




(for reference my car has OEM swaybars, 25mm lowered progressive rate springs (about 30% stiffer than the factory, can't remember the exact rate), OEM shocks, a torsen T2, and 205/50/15 road tyres)

[NitroDann]

Im a little busy so a quick post.

Yes sway bars lower the effective travel of the inside suspension and in a situation where just one end of the car has a very stiff sway bar you can pull that tyre off the ground and this leaves your torsen useless.

Yes you need more grip if you want more stiffness. Adding stiffness alone makes the car handle worse as it cannot roll the suspension over, get the camber curves working and instead it just sits on the inside edge of the tyre.

Dann

[manga_blue]

Yes well, I admit I've got a shedful of springs and swaybars but only one torsen.

My general approach is to use FatCatMotorsports calculations to get as close to my target front roll couple using springs first and then fine tune with sway bars. Target FRC for me is around 53-55%, which gives me a moderate bias towards oversteer. This suits the main uses of the car: track and coastal roads. Because many of the roads are bumpy (as are some of the tracks these days) I have a preference for minimising sways because they limit the independence of the suspension, which limits grip in bumpy conditions. The bumps also lead me towards higher spring rates in order to get higher bounce frequencies to enable the wheels to move with the bumps faster.

At the moment I run 10/7 springs with stock NA8 sways. Prior to that it was 10/7 with no sways. On that no-sway setup I had great grip and control and really good drive out of the corners, meaning the torsen was working really well. The setup was absolutely brilliant for grip and ride on dirt too. The downside was that it was too unstable under heavy braking. Adding the stock sways stabilised braking at the cost of a mild loss of grip over bumps and ripple strips, but at least the torsen did not seem to be affected on the track.

I have played with all sorts of combos of stock, mid-range, heavy and no-sways. What's probably most relevant to the diff discussion is that a few years ago I played with Whiteline adjustable sways, with 5/4, 7/5 and 10/7 springs. These sways are reasonably heavy at 24mm/16mm (vs stock NA8 of 19/11).

There were good and bad points for these heavy sways as my daily driver. On smooth roads any of those combinations was brilliantly flat and the car was very controlled. On dirt and corrugated bitumen they were just diabolical, with the car very skittish. What happens with sways is that when one wheel is pushed up then the bar transfers that force across the axle and pushes the other wheel up. On heavy sways if you hit a bump with the right wheel then the left wheel loses grip. This impacts the sideways grip as well as drive grip. I don't think the torsen handled it at all well - I simply could not accelerate out of corners on our crap roads.

I had more serious problems with them on the track. Ripple strips threw the car off line easily. I also couldn't get drive out of certain corners, mostly where the front was fairly well loaded, for example the Fishhook and turn 10 at Wakie and MG at the Island - downhill corners with slightly challenging camber on apex or exits. I think the sways took so much load off the inside rear that the torsen gave up being a torsen and I was spinning the inside rear like a ute.

That's just my experience. What I do is probably not for everyone, it just suits my driving style. The quickest non-turbo/non-barge in the NSW club runs 14/10 springs and massive sways and doesn't seem to have grip problems, but then he's running a locker diff.