Front torsion bars

[KiwiBirkin]

I have noticed on a lot of Sevens that they dont have a front torsion bar setup it seems very common on the Caterhams not too have this yet all the Birkins seem to have one, what reason would Caterham not have a torsion bar as I thought they helped out making the car stiffer, any reason not too have one.

[scannon]

Kiwi,

 

By torsion bar, do you mean an anti-sway bar that connects left and right suspensions to prevent leaning in a corner? If so, the Lotus 7 and early Caterhams had the bar as part of the upper suspension. It replaced the front part of the upper A arm. Later Caterhams have separate sway bars. I don't recall seeing any that didn't have them on the front. My Caterham has a rear one as well.

 

On this side of the pond, a torsion bar in an automobile usually means a replacement for a coil or leaf spring, it is a bar that is twisted to provide springing for the suspension. Not too many cars use them these days, it was common on Chrysler products in the 60s and 70s. Early VW Beetles and Porsche 911s had them too.

 

Skip

[KiwiBirkin]

Yes its the anti sway bar

[West7se]

Although I have one, i think the main reason for most NOT having them is due to the cars very low centre of gravity, which in turn creates less roll generally. Also most of our cars do have fairly stiff springing which counteracts any roll. They are mostly only used on circuit based cars where the use of slick or sticky tyres would create more grip and cause body roll, and prevent the camber change associated with roll, also they are used for fine tuning the geo setup. Thats how I see it anyway.

[lowflyer]

The Stalker is made without a "sway bar", but I decided to make my own.

 

It was quite simple. I used a 5/8" piece of solid round stock, mostly because the adjustable end links that I found were 5/8". They came from a Formula Mazda race car.

 

The bar is mounted in 5/8" Heim joints. The joints are mounted in small sections of steel tubing welded to the frame of the car. At the ends I used the lower mounting bolt for the shock absorber.

 

The amount of added spring stiffness computes to between 280 and 360 lbs, depending on the placement of the adjustable end link.

 

The overall net effect is substantial, taking most of the body roll out of the car without adding to the ride stiffness.

 

http://www471.pair.com/stalkerv/gallery2/main.php?g2_itemId=3798&g2_page=2

http://www471.pair.com/stalkerv/gallery2/main.php?g2_itemId=3798&g2_page=3

 

Photos available at the link shown above.

[KiwiBirkin]

Nice car Lowflyer and thanks for the info.

[Kitcat]

LowFlyer:

 

Didn't the front bar add "push" (understeer)? If so, how did you restore the car's handling neutrality? Typically a rear bar would be added but I don't see that you did that.

 

Mike

[lowflyer]

The Stalker has never been a real "pusher", as far as understeer is concerned. Plus, it can always be overcome with the throttle.

 

What I was seeing in photos that were taken of the car at local autocross events was body roll so bad that the inside wheels (both front and rear) were becoming so "light" that overall handling was effected. The outside tires were doing so much of the work that the car simply wasn't operating at maximum efficiency. The outside front tire, especially is being overworked, which certainly can cause understeer.

 

Check out these two photos. The first was taken before the sway bar was put on. As a matter of fact, it was the main reason I felt that the car needed one.

 

The second photo is taken with the bar. Both photos are taken with the car in the middle of a 35-40 mph corner, both with the same tires.

 

If you notice, in the first photo the car is rolled over so much that the inside tires are doing very little. Check the distance between the top of the rear tire and the bottom of the fender. The inside rear tire is so "light" that it's easy to spin.

 

In the second photo the roll is under control, to the point that inside rear tire spin is pretty much not an issue. BTW, I'm running a Torsen LSD, so the car will continue forward with the inside tire spinning.

 

Since I'm using the 15" tire/wheel combo, the ride height is greater than the Stalkers that use the 13" race tire set up, which increases the roll center. Some of the owners running the car recognized the problem and came up with shims to stiffen the front springs, which increases roll resistance. My solution does the same thing, except that it doesn't increase static spring stiffness, so I can leave the springs alone for street driving and still have the benefit.

 

I thought about putting a rear bar on, as well, but haven't seen the need for it.

 

As an aside, one of my friends has a Stalker which runs the 13" race tires. He had a strange wear pattern on the inside of the rear tires, which he couldn't understand. After looking at some photos of his car (no sway bar), I suggested it was caused by the car "rolling over" far enough that the outside of the rear tire (the tire inside the turn) was lifting off the road, and spinning. The race tires have a very stiff carcass/side wall, which in my opinion, caused the tire wear.

 

Either way, I like the bar for both street and the occasional autocross. BTW, the original Lotus 7 used a front bar, but not a rear one.

Edited June 11, 2009 by lowflyer