Front Shock info wanted

[pillowmeto]

I am assembling a set of front shocks for my vee, but do not really know where to start as far as valving goes. Can anyone supply some typical shim stack/piston information or dyno graphs?

[brian]

Depends on the shock used. On the balck Penskes I run .004 on compression and .006 on rebound. You can send the cchocks to Bob at LRE and he can set them up for you.

[pillowmeto]

Brian,
Do you use a full shim stack on each side?

I have had some front Penskes on a dyno, however, I do not believe them to be a fair representation of what most drivers are using. Before I put the shocks on my car for a weekend, I want to be aware of what the standard is.

-Matt

[brian]

You must use at least 3 shims, each one a different diameter, then use the spacers to make up the difference. The key is to make sure all the shims are held firmly in place. Some guys use progressive shim packs on a standard piston, but that gets really complicated and should be done in conjunction with a dyno. The small black shocks only come with a std. piston.

Most vee front shocks are fairly soft on compression and slightly higher on rebound to control the roll. Many have bleed holes to reduce stiffness as well.

When you say your shocks are not representing common practice, what are you meaning?

[pillowmeto]

I mean that the individual who allowed me to dyno his shocks, while very fast, uses a set up different than most, if not all; their front shocks are certainly set up drastically different that most FVs.

My goal is to find my own setup, but would like to know more about what other people are using (but not necessarily their secrets) so I can make an informed decision as to where to start. Knowing something about what type of force to expect at different speeds would very helpful, or simply a graph.

-Matt

[hardingfv32-1]

Brian... Why would you say that soft compression and higher rebound to control roll? It would seem to me you would want both stiffer to control roll. In a turn, the outside shock is in compression and the inside shock is in rebound.

Brian

[brian]

Here we go again.... Good point Brian, but for my taste, stiff compression on the front shocks make the car less compliant. Prior to the front red Penske shocks, Joe Stimola ran the softer compression and drilled bleed holes to soften the front end then ran a higher shim package for rebound. In the later red shocks with rebound control, users crank up the rebound to control the push. It is my understanding the desired effect of increased rebound control is to reduce the shift to the outside tire, i.e. roll.

[hardingfv32-1]

Just trying to understand if there is a benefit to your approach. I view the issue as both sides of the car playing a part in controlling roll. The outside shock controls roll while in compression and inside shock controls it while in rebound. What you are saying is that one side does all the work. What would be the benefit of this approach?

Is this all about using a single adjustable shock, so you can only adjust rebound? If it was double adjustable then would the approach be different?

Brian

[smsazzy]

McCarthy sets his shocks like that because the tracks he races on are not billiard table smooth like the ones Brian Harding races on.....

[brian]

Brian is making a good point here and the use of the triple adjustable shocks address this issue. The low speed travel, or long travel, is controlled separately from high speed, which is the short rapid travel. With this separation, the shock can provide compliance via the high speed circuit and still control the longer movements of the suspension. More and more teams are using the low speed circuits to control roll and both the compression and rebound are being used. Not being able to spend a fortune on shocks, my approach is restricted to the rebound side. Our second race at the Seattle national was in the rain and having the softest car on the track definitely helped with the win. On previous cars where my setup was stiffer, I found that adjusting the car for changing conditions was a challenge.

[smsazzy]

Seattle = NOT Billiard table smooth.......

[Mystique Racing]

Ask and you shall receive. Here is the dyno sheet from a Penske 7600 that I just purchased. This represents the factory standard valving.

[ external image ]

[hardingfv32-1]

Chassis or roll control has nothing to do with the track being rough. ALL shocks have a chassis control operating range and compliance operating range. From the above graph, the first part of the graph to about a velocity of 3-5 in/sec is concerned with chassis control. Beyond that would be bump or compliance control.

The above graph is very soft in the compliance zone. The overall shape and proportion is very unremarkable for a racing shock. Nothing unique to FV. It could be used on almost any race car, except for the overall softness.

Brian, so you are using a single adjustable front shock, you can only adjust rebound?

May we assume that the best setup, springs and shocks, for wet conditions is not as fast as a dry setup on a DRY track? If that is true, is it wise to always have your car setup for rain?

Brian

[brian]

On the graph above, you'll see on the left side of the graph, in the range before 1" per second, the effect of the bleed adjusters. Once the shock is really moving, the adjusters have little effect. The shaft adjusters most of us use control the amount of bleed before the shims take effect.

I'm not sure I agree with the idea that chassis control stops at < 3-5 in/sec. but have no way of explaining it. Virtually all of the front shocks in vees are single adjusters on the rebound. Some folks have splurged and bought remote canister, double adjustables for the front but I don't have the budget to explore that option. My front shocks have no adjustability. You can make an effect on ride quality with pressure changes on the small shocks but it isn't a major difference. Since the small black Penskes have fallen out of favor vs the red shocks, I have been able to purchase a couple of sets and have them shimmed for different conditions.

I think it's safe to assume a wet set up is limited to the wet, but I have adjusted towards the rain set up as the track gets slick from oil or use. The track we race on Sunday is never the same as Sat. morning and when you consider the Runoffs goes for days and days, being able to adjust the car on the fly to chase the track is critical. The engineers can expand, but it deals with grip levels and weight transfer. I never change springs for wet conditions but that goes back to the soft vs hard thing.

[hardingfv32-1]

<3-5 in/sec is a industrial standard for low speed valving. The only way the chassis is going to roll faster than that is if you introduce a atypical force such as a curb.

How can you say you control roll with rebound? What is the outside shock contributing to roll control in a turn when it would be in a state of compression? No argument, just trying to understand your approach.

Brian

[brian]

If the inside tire does not want to drop down during roll, then the car will have to lift the tire off the ground. Hence the rebound slows the roll. Let's not confuse roll rate control with absolute roll control. A anti-sway, or roll bar works more to control the rate than does rebound but both only control the rate at which the car rolls. Many articles on this subject show pictures of cars lifting their inside wheels to indicate too much roll control. Droop stops or cables act as roll limiters and completely stop roll. I have never liked stops since I can feel the car hitting them under cornering. An agressvely driven vee with droop cables on the front end, will lift the inside tire. The way I look at it is if you have 4 wheels, why not use them?

Frankly, with the rebound approach the outside shock is irrelevant. You can make it more stiff and that will control roll, but the car will be stiffer all the time and compliance will be suffer.

Bottom line is we're all looking for ways to control push inherent in a zero roll car. The two major ways is to either control the roll or reduce grip in the rear. Frankly, reducing rear grip is like two wrongs making a right so I've looked to roll control as a long term solution. Over the years I've seen a lot of solutions to control roll. The brighter folks have played with rocker geometry. Some have anti sway bars on the rear. Some make cars stiff enough not to have any movement. For me, it's a matter of feel and how the car reacts. I've tried most of all of them and really haven't found the golden bullet. A combination of roll control, grip balance (front to rear) and driving style works best for me. I think learning how to drive around a push is worthwhile. Not only will you be faster but your appetite for tires will diminish.

[jpetillo]

Brian (Mac), I agree with most of what you discussed - well said. I'm not sure I agree with the following statement, though.

An anti-sway, or roll bar works more to control the rate than does rebound but both only control the rate at which the car rolls.

If the roll bar only affected the roll rate, then when the car finally settles into a corner it would end up in the same position independent of the rollbar size. The same as a shock acts. That's not the case, though, right? I think the rollbar acts like a spring. A stiffer one will roll less. John

[brian]

You're right John. At some point an anti-sway bar will stop roll but initially it changes the rate. If it's stiff enough there will be no roll at all.

[jpetillo]

Brian, agreed, but it changes the rate similar to how switching to a stiffer spring changes the rate. I guess I'm saying that it functions more like a spring than a shock in terms of how it affects rate. Either way, I see your point.

[pillowmeto]

Thank you everyone who gave me some information. I was able to put together what I believe is a good starting point. I will be trying them out at the track this weekend.