shock question

[powerslide]

i read and hear people talk about low speed/high speed on shocks. We started rebuilding shocks and got a shock dyno a couple years back. Havent gotten much out of the box from what manu suggest for shim stacks. Bumps are high speed and roll is low speed stuff i understand that. But what speed is the LR running when its dropping off the bars? Shock and spring behind. Trying to figure out on which part of the graph we can work on to get some more compression to help with dropping off the bars. Maybe that penske guy who was hanging around earlier in the season could enlighten me.

[MasterSbilt_Racer]

i read and hear people talk about low speed/high speed on shocks. We started rebuilding shocks and got a shock dyno a couple years back. Havent gotten much out of the box from what manu suggest for shim stacks. Bumps are high speed and roll is low speed stuff i understand that. But what speed is the LR running when its dropping off the bars? Shock and spring behind. Trying to figure out on which part of the graph we can work on to get some more compression to help with dropping off the bars. Maybe that penske guy who was hanging around earlier in the season could enlighten me.

The instant that the chassis starts to drop, the speed is zero.

[hucktyson]

Data acquisition with linear potentiometers at each corner are the only way to really answer that question.

[powerslide]

The instant that the chassis starts to drop, the speed is zero.

zero? Not even 1inch?

[MasterSbilt_Racer]

zero? Not even 1inch?

You start at zero, then accelerate from there. The easiest way to get shock shaft velocity would be with data acq. as Huck said.

The easiest way to keep the speed down is to damp more at the slow speeds. What happens at 1"/sec will effect the max speed achieved. And the more damping you add at slow speeds, the looser your corner entry will get.

[PenskeShocks]

Good question, and the only way to really tell is with data. It makes life so much easier. With data we have seen on these cars, at most your probably seeing around 1-3" per second. it will depend on the roughness of the track, but your rebound velocity will alway be less then your compression. Bleed, piston dish, is what really affects your low speed damping and is really critical when it comes to grip, and platform control.

[powerslide]

So it looks like everyone here is saying without data acq its impossible to tell. But that it makes most sense to concentrate on the low speed because it will effect the high speed as well. It sounds like a digressive would be better than a linear on this corner? I am strictly looking at the dropping off the bars. I'm sure banking and speed has an effect on that as well. The track i noticed it dropping hard at is a high banked 3/8.

What is the ID on the penske pistons? We have bilsteins and they offer an 8mm to 12mm adapter. Wasnt sure which brand that would adapt to. I have heard of people putting ohlins pistons in bilsteins.

[zeroracing]

You can put the Ohlins piston in the bilstein shocks, I do not think the outside diameter of the Penske shocks is the same. That said, Penske I think offers a one on one class on rebuilding shocks, proper methods so if you bought Penske shocks you could get actual training. It was on their old website, I have not been on their website lately. Also you can find a ton of old nascar Penske pistons on eBay, I have NO CLUE if any of them would work for dirt cars but they is a large selection available.

[Brian Gray]

We are very successful at changing the low speed numbers while keeping your high speed numbers . now keep in mind that there is a transition speed though a shaft speed or so but it is possible to pinpoint the rates at various speeds and even inside various marks in the travel range. Not all shock builders believe or agree with this.

[Ltemodel]

To tell you the truth, I believe much of shock valving on the LR is driver dependent. Many of the guys I do shocks for like a lot of low speed (90-100 lbs at 1") then a low slope to about (200 - 225 at 6").
They don't like holding the car up with side bite and usually roll back on the gas slowly.
Like it was mentioned above this will make the car a little looser on the way in, but it ca usually be compensated for in other areas.
The low speed in this example may be way too much for guys who like to run their cars a little more sideways and can hold their cars up with side bite. Personally, I believe this is naturally a little better, but too many guys can't hold their cars up with their driving.
I just crutch the shock and work with other parts of the car to compensate.
I don't know if there is a perfect rule of thumb to go buy. Just keep experimenting, watching how each driver drives, and compare it to what they say about the car.

Good Luck,
Kevin

[powerslide]

I agree trail braking has alot to do with keeping it on the bars. Felt like at this track I was concentrating so hard on keeping it on the bars it was distracting. I'm sure it's something that comes with laps until then I think we will work on those low speed numbers.

[powerslide]

So we have been working on shocks and discussing rod pressure and how drivers sometimes complain about losing feel when changing to a monotube shock. Do you feel like it is the rod pressure that causes this or is it the difference in how the graph is shaped between the mono tube and twin tube?

[Ltemodel]

There are really too many factors which contribute to the feel of the shock on the car, it is impossible to pin point exactly what is effecting feel. A good mono tube shock needs to be pressure balanced to make it respond to the best of its capacity. Excessive gas pressure definitely has it's disadvantages; bad response and excessive seal drag to name a few. I don't think this is as big of a problem as it was years ago with the first generation of mono tube shocks.
The mono tube shocks nowadays, I feel, are far better than what is offered for twin tube.
The thing I geek out on now is position sensitive valving. I think the first company to market a position sensitive shock which is tunable will kill it. We are currently crutching shocks to get body attitude what we want. And, I believe we are probably leaving a little traction on the table.

Thanks,
Kevin

[PenskeShocks]

Kevin is right. There are so many factors that come into what a driver is feeling in his shocks. Rod force is only one thing, and its not always bad. Sometimes that rod force can be good depending how quickly and hard you want to work your tire. Position sensitive damping is coming a long way. it is being done in higher forms of racing like F1 and other Road Race series. Off road has been doing it for years. What we are all after is a shock that will keep the attitude of the car at its optimum, but also act like a shock and dampen out some bumps, get the best mechanical and aero grip.

[Matt49]

So Penske, do you see an application for some form of FRIC in dirt late model racing. One that would help keep the car angled (as opposed to flat like in F1) to improve aero grip?
If you don't answer, we're all going to assume that this is what you have under Bloomer's car :-)
Just kidding...but seriously, I'm interested in your opinion on FRIC in dirt racing.