Swaybars on the modern race car

Most of us have heard about sway bars, and can recognize them when we see them. But what do they do? Quite simply they control the transfer of weight from one side of the car to the other. When does this happen? Why when the car goes around a turn. When the car leans over, from the force of inertia, the stiffness of the bar, which is the only component connecting both corners of the car, resists this action. That is why they are commonly called roll bars.

When you look at the tube frame GT1/Trans-Am cars you immediately notice that the sway bars are different from your street car, or a stock car. Not only do they look different but they are in a different location. That is partly by necessity, partly from design even thought they serve the same function. We will look at each of the two separately. For the purpose of this discussion we will only be talking about the front bar.

On the stock car the bar is typically mounted as low as possible, in front of the wheels. Earlier designs were mounted in two blocks on the bottom of the frame rails, like your street car. Newer designs place it inside a tube which connects the frame rails. This allows the car to be run at a slightly lower ride height. The arms are removable and slip onto splined ends on the sway bar itself. These arms connect the bar to the lower control arm. This design, while not adjustable, is simple and effective.  Its placement is made possible by the “kickup” on the front subframe.

The first thing you notice about the swaybar on a tube frame GT car is its placement. Unlike the stock car, it is mounted high, above the upper frame rail, and generally in front of the wheels. (see the picture above) The reason for this location is that these cars use a flat frame rail. Thus there is no room under the car to mount the bar. The bars are generally mounted in one of two ways. The traditional way is for it to be sandwiched in a pair of split blocks bolted to the upper frame rails. Some newer designs have a heim joint threaded through the bar itself, this is simply attached to a bracket on the upper frame rail with a bolt. Regardless, it like the stock car design is connected to the lower control arm. In this case be tubular bars with heim joints in either end for adjustability of length.

The ends on these  bars are a mixture of fixed and rotating ends. (see the picture for an example of a fixed arm) The fixed arm, while it has different mounting locations  for the links, is not adjustable once attached. The rotating end is unique in that it is driver adjustable while the vehicle is in motion. It consists of a flat bar which is bolted to the sway bar. Mounted inside a bearing on the sway bar, it is free to turn.  The other end of course is, like the non adjustable end, attached to the control arm via means of a link. Driver adjustablity is by means of a cable run back to a quadrant mounted inside the cockpit. By moving the lever the cable causes the blade to be rotated from the vertical. This reduces its ability to resist the vertical forces on it, thus reducing the resistance to roll. While this provides the driver with an ability to reduce handling  problems during the race it is not perfect. The change is not linear. There is no constant amount of change per movement of the bar.

This of course is just a simplistic explanation of sway bars, and I welcome your comments.

Example of sway bar mounting on 2011 Trans-Am car.

The almost Xmas blahs.

Chevy Beretta Trans-Am type car

While running around getting ready for Christmas I thought I would throw this picture up.This is a car that was built to be a spare car for the team. Never finished, it was recently sold to someone who hopefully will complete and put it on the track. Very nice piece though.

We haven’t forgotten the post on sway bars, but it may have to wait until after Christmas.

Merry Christmas to all, be safe and spend as much time as you can with family and friends.

To centerlok or not centerlok, that is the question, – Part Deux

Left front of Trans-Am Car 2010

To centerlok, or not to centerlok, that is the question

For years now one of the trademarks of a first class SCCA Trans-Am, or IMSA GTO car was the centerlok wheels. Just by a glance at the wheels you could tell who was a serious contender, or a pretender. Generally those wheels were made by BBS, although Jongbloed and a couple of others were occasionally seen.

What was the reason that the centerlok, more properly center knockoffs, rather than the almost universal 5 x 5 pattern wheels were used? Basically there were three reasons.
1. Unsprung weight. The suspension components and hubs were lighter than on an equivalent 5 x 5 assembly.

2. Suspension geometry. Most designers are proponents of the “zero scrub” design. This requires getting the wheel mounting flange as far outboard as possible. In other words a typical three piece centerlok front wheel will have a 1″ or 1.5″ outer rim half. Because of its spindle design a 5 x 5″ wheel has to use a wider outer rim half, perhaps 3.5″ or 4″.
3. Pit stops. With the single nut, the time to change tires was less. Admittedly this was the least important of the three factors.

But nothing is without drawbacks, and this is no exception. The price of a centerlok suspension assembly is far more than that of a 5 x 5. How much, did you say? Well it varies but it is hundreds of dollars per corner. Wheels for the 5 x 5 are far more readily available and at a fraction of the cost. And lastly since most races no longer require pit stops the speed of tire changing is pretty much irrelevant.

I should note that there is a hybrid design, used back in the 90’s by Peerless and a few others that adapted a 5 x 5 hub to use centerlok wheels. This was neither fish nor fowl, didn’t solve the geometry issue, and added about one pound of weight per corner.

So which is the right way to go? Depends on your wallet I guess. If money is the most important thing than by all means go with the 5 x 5. But if performance, and looking the part, are critical than the centerlok is still the way to go.

Do you measure up?

The GT1 Mustang of Tim Lyons, crew chief Darryl Hunter

 

Get your mind out of the gutter, I’m talking horsepower here.

Whats the first thing people talk about when discussing racecars? How much power the thing has of course. And few things are more misrepresented. Regardless of what it is everybody feels compelled to believe they have the most powerful engine out there. (unless you get beat when the engine was down on power, of course).

But what numbers are we really talking about? There was a time not too long ago, when a really strong 310 CID engine would put out around 700 HP. Some of course did a fair bit more. But these were limited to one or maybe two teams. And while they would sell those engines, they didn’t seem to do as well with the new owners. Some say the heads were changed before the motors were delivered, but I digress.

Then with the introduction of the e Nascar 358 engines, horsepower went up to around 800 +/-. And a whole new world appeared. Transmissionssuddenly became a problem, as did tire management.

A couple of years ago, when the new generation of engines arrived in Nascar the old SB2.2’s, and Ford’s w’Yates heads became obsolete. The teams needed a market so some of them found their way to the road aracing scene. And for prices that were too cheap to pass up. And now the power level was up to 835 approximately.

Last year things progressed even further. People found that even with that power they couldn’t keep up at the power tracks. Why, you ask? Well it seems that there was a generation of cylinder heads produced, by both Ford and GM, that was not approved by Nascar. These heads, or at least some of them have found their way onto the track. And by the way they are completely legal. But one builder told me they were worth 25 horsepower on his engine. His driver said that he can finally run with the top cars after the upgrade. Power? 850 +.

So whats next in the quest for “more power!”

Corvette

Recently we have put a few photos of Gt cars racing in South America. Just goes to show that we dont have the market cornered on this type of racing. One big difference is that down there they use a lot of 18″ tires and of course wheels.
Some would say that would not be a bad thing here.

Looking good at 3Rivers

John Baucom's Mustang at 3Rivers. Note the "Roadraceparts" decal on the door

After the TransAm race at VIR yesterday I thought it would be appropriate to talk about how the cars have evolved over the years.
Of course in the beginning, the mid 60’s, we had the basic unibody cars. These were by the rules almost what we would call improved touring cars. They were so close to stock that with the Mustangs, they had trouble keeping the front ends in line. The reason? The stock tierod ends would stretch and flex. And these revelations caused the racers to push for changes. Like most other forms of motorsports, these were made in the name of “safety”. Of course with that came more creativity and expense. So much so that they slowly morphed into the fire breathing monsters/beauties that we love today.