19 replies to this topic

[Dekraa]

How does packers work? Are they most efficient when they are compressed on the straights and at the same time doesnt run on bump stopppers during cornering?

[Dekraa]

Is this right?

If someone use relative soft springs, the suspension travel in the telemetry data will be higher than it would if he had fitted stiff springs. But if he fits packers, this suspension travel will get lowered, though at the end working as a stiff springs during cornering. Unless he would add so many packers that it eventually runs on bump stoppers and therefore running on extreme stiff springs (undriveable). So suspension travel is a messaurement by how soft or stiff springs someone is having?

But on a track like hungary, where I suppose soft springs would be ideal, the ride height would also end up quite high? Unless he add packers, to lower the suspension travel and thus can lower the ride height to gain undercar downforce. But if he add packers, doesnt he then negate the effects of the soft springs because the springs will act a bit stiffer because of the suspension travel has been lowered. Wouldnt that be a waste?

Why add packers at all? Because they will only make the suspension stiffer, why dont set up the springs as stiff from the beginning? Wouldnt that create the same result?

Im a bit confussed:)

[Antoine]

Pakers are just to adjust the gap before the the bumstop!
On very high aero downforce car you can play with pakers to avoid the car to touch at max speed!
so with pakers you can lower the ride height because the car don't touch in strait line! and the suspension stiffness still the same in corner!

So you keep the same spring but you put some pakers to avoid the car touch in strait with a low ride height!

[desmo]

Isn't this sort of thing- essentialy a very positionally tunable spring rate if I understand what you mean- usually done in F1 by adding/changing/subtracting stacked bellevilles/elastomers on the 3rd damper? That way they don't come into play on single wheel deflections like curb strikes.

[Greg Locock]

I think Dekra has slightly missed the point - adding packers (if I understand the term correctly) changes the ride height but not the spring rate. This means you get the grip advantages of the softer springs, but still maintain your stationary ride height at whatever level is deemed appropriate.

On prototype cars our take apart shocks have threaded spring seats so we can quickly adjust ride heights for each new set of springs.

[dc21]

All that follows is from the setup of an F3 car. How applicable it is to F1 I don't know.

Static Ride Height is adjusted using a threaded adjuster on the pushrod.

Preload is set using the threaded adjuster on the spring platform. This results in a small change in ride height.

Packers are used to limit the amount of travel in the suspension. They are harder than the bump stops. They are useful when the travel in the suspension during acceleration, braking and cornering is less than that caused by downforce. At no time do you want to be cornering whilst running on the bump stops.

Dave

[dc21]

Should probably add, the packers change the position of the bump rubber.

Dave

[desmo]

Could someone please direct me to a photo of either a bump rubber or a "packer" on a modern torsion bar sprung F1 car, the third spring/damper bits aforementioned aside?

[Greg Locock]

Ah, I missed some of the point as well. I can see there's an aerodynamic advantage in limiting pitch, do you use them as roll limiters? I think not.

[Antoine]

Right Desmo if you have a third damper, it's better to use the pakers and bumpstop on this 3rd damper.
In other case, you put the pakers on the damper but you musn't touch the bumstop during a corner! The two possibilities are touch the bumstop before the corner and stay like that during the corner (fast corner with a lot of aero downforce) or don't touch the bumstop during the corner!

When you touch the bumstop during a corner you stiff this wheel suspension and made U/S or O/S very quickly!

[Fat Boy]

Packers are the little plastic bits that are 'C' shaped, fit over the damper shaft, and space the bump rubber to come in at a certain amount of damper compression.

In situations where you can't run a 3rd spring (usually due to rules), I find they work great. I've been at circuits where they were worth over 5mm of ride height, which is a massive gain from such a simple piece of kit. They can be a bit edgy to set up. If you're playing with them, you better have some damper pots to keep tabs on what's going on.

As far as when you can run into them, down the straights is the obvious answer. On the front under braking is also common. If your bump rubber is too stiff, then you will get bouncing and skipping over bumps on the brakes. In general, though, it's no big deal. I often run in the bump rubbers on the loaded side of the car in high speed corners. The trick is that when the car gets to the corner is has to already be into the packers. You can't go 1/2 way. You want the car to be into them when you get to the corner and never come out. At some tracks you can use them to get a high spring rate for high speed stability while cornering, a soft spring rate for low speed cornering, and a lower ride height everywhere. Where they screw you up is mid-speed corners that would have them bouncing in and out of the bump rubber. That's when you're just forced to pull the packers out and raise the car. It sucks, but it's either that or stiffen the car as a whole. Finding out exactly how hard you can use the packers without upsetting the car is always a fun game.

Packers are particularly efficiently at street circuits where you have slow 90 degree corners and relatively long straights. These tracks are usually bumpy(i.e. soft springs and lots of motion) and you generally run a good chunk of downforce (large ride height change due to speed). Taking all of that into account means that a little time spent getting the packers right is well worth the effort.

I generally make mine out of Delrin rod and a whole mess of them cost maybe $25 out of pocket. The thinnest one I make is 1mm, but I choose the thicknesses so I can adjust them in 1/2 mm increments.

[Admiral Thrawn]

How would you stop an open-wheel car bottoming out while going through Eau Rouge at Spa-Francorchamps?

Because of the nature of the turn, and the way the track drops downwards on entry, and then steeply upwards, the suspension gets very compressed and the car bottoms out. As there isn't an elevation change like this anywhere else on the circuit, how can you set up the car to take into account this corner without compromising the rest of the lap? Is the only way to prevent the bottom scraping by using packers?

Thanks in advance,

James.

[F3000]

Admiral,

A Spa set up is always a compromise between Eau Rouge and the rest of the lap, especially when setting the car up for the race with full tanks (lap 1, cold tyres, heavy car...) A small packer gap does help, in conjunction with stiffer-than-usual springs. At least the downforce levels are a bit lower than at an average circuit.

[McGuire]

Snapped these Lolas at the champ car open test at Sebring this week:

[desmo]

Look at the difference between the third dampers fited to those two cars. OK, can the elastomers on the third shocks' shafts be called packers? And look how faired in the inside of the back wheel is in the top picture. The various suspension pieces look chunky and rugged compared to F1 bits.

[McGuire]

Originally posted by desmo
Look at the difference between the third dampers fited to those two cars. OK, can the elastomers on the third shocks' shafts be called packers? And look how faired in the inside of the back wheel is in the top picture. The various suspension pieces look chunky and rugged compared to F1 bits.

Well, they call 'em packers so I suppose they must be.

Note the first photo shows that in the third shock location there is in fact no shock...just a shaft with a shuttle, a spacer and a stop. This car happens to be from the Dale Coyne stable, so its setup is quite probably based on the shrewd calculation that two dampers are cheaper than three.

The second photo shows a damper in the third location but no coil spring. At the test this week I saw cars equipped with or without. These cars can also run a similar setup at the front...some teams opted for it at Sebring while others ran a two-spring deal up there. Guess I could have taken more photos hmmm.

Quite so, the hardware here is considerably clunkier than recent F1 practice. These cars are heavier than in F1 (1550 lbs) and are also designed to handle oval track cornering loads and wall impacts. Also, this chassis (Lola BK-01) was designed in 2000 -- the specs were frozen by the series in 2001 with composite components, flexures, etc. prohibited.

While Lola continues to manufacture and support this car it only sells two to four complete chassis per year, so many of the cars pounding around out here are now going on five and six years old. Consequently these cars hold very few secrets technically speaking (though some probably have some interesting tales to tell eh). Just about all possible development has been wrung from this combination...one of the approaches this year is weight reduction & relocation.

[Fat Boy]

Originally posted by desmo
Look at the difference between the third dampers fited to those two cars. OK, can the elastomers on the third shocks' shafts be called packers? And look how faired in the inside of the back wheel is in the top picture. The various suspension pieces look chunky and rugged compared to F1 bits.

The first picture has bump rubbers on the shocks and no packers. On the third spring there are a couple packers and a couple bump rubbers. The packers are white, the bump rubbers are a maroon/brown. On the second picture, the bump rubbers are green and the packers are white. The green bump rubbers in the second picture are very stiff chunks of rubber that you cannot touch during cornering. They are only good as ride height control. The bump rubbers in the first picture are Ohlins standard issue that you can touch during cornering. The car that McG said is a Coyne car is running older Ohlins TT44 Mk I dampers and the second car (not sure whose, but obviously better funded) is running the new Ohlins TTX damper.

Hope that gets everyone on the same page as far as terminology.

[Antoine]

You can use the pakers to set up the pitch angle and ride height in straight and fast corner.
Yeah the green bumstop seems to be very stiff!

[McGuire]

Originally posted by Fat Boy
The car that McG said is a Coyne car is running older Ohlins TT44 Mk I dampers and the second car (not sure whose, but obviously better funded) is running the new Ohlins TTX damper.

The second car is one of Walker's "new" Lolas, which came from Rahal I believe.

Originally posted by Fat Boy
Hope that gets everyone on the same page as far as terminology.

Works for me.

[desmo]

Originally posted by Fat Boy




Hope that gets everyone on the same page as far as terminology.

Excellent clarification, thanks