Penske Front Shocks

[Chris Elwell]

What is the difference between the red front shocks and the black ones?


Chris

[problemchild]

The black ones have a smaller bore, are out of production, use tough to find replacement parts, are lighter, are not externally adjustable, have smaller frontal area .... and probably work better.

[Chris Elwell]

What's the model number for the red ones? And what's externally adjustable on them?

[sracing]

On the base red units, nothing is externally adjustable on them. However you can add the external canistor giving you some control. On the base units, either can be valved to dyno exactly the same. (On either you can also vary the nitrogen pressures which can increase your effective spring rate.) The red are larger (aero) and slightly heavier. The only real advantage is the red are prettier.

[Bruce]

This from Penske
The 7500 Series is our most popular short track shock option, featuring an aluminum body and nitrogen separator piston for increased performance. This damper is offered in a coilover or non-coilover style in all body lengths and is available as sealed, non-adjustable unit or with a single shaft adjuster. Single shaft adjuster options include rebound, compression, or open bleed bypass. A selection of fixed bleed jets are available for the non-adjustable version. The 7500 series is offered with either a 5/8" or 3/4" diameter shaft depending on the application. For increased accessibility, a remote cockpit adjuster is available as an additional option.

[Tiago Santos]

Most reds that I have seen as FV fronts are the ones with the shaft rebound adjuster.. But maybe it's just a localized North West thing

[Mark Filip]

On the base red units, nothing is externally adjustable on them. However you can add the external canistor giving you some control. On the base units, either can be valved to dyno exactly the same. (On either you can also vary the nitrogen pressures which can increase your effective spring rate.) The red are larger (aero) and slightly heavier. The only real advantage is the red are prettier.

Jim I'm pretty sure the amount of Nitrogen put into the shocks has no affect on compression or rebound it only stop the fluid from foaming, low pressure will foam and hign could also foam. But I'm no shock expert it was something I have read about these shocks.


Mark

[sracing]

Jim I'm pretty sure the amount of Nitrogen put into the shocks has no affect on compression or rebound it only stop the fluid from foaming, low pressure will foam and hign could also foam. But I'm no shock expert it was something I have read about these shocks.

Correct. It will have little to no effect on damping. As I said however, it will effect the effective spring rate.

[Mark Filip]

Correct. It will have little to no effect on damping. As I said however, it will effect the effective spring rate.

I understand Jim, the problem is most people think these shocks are like "air shocks on a chevy" and the more you pump in the stiffer it will be and the amount of change is very minimal as I understand it. Or am I wrong? again I'm no shock expert just woundering

Mark

[sracing]

Yes. That is not the purpose of the Nitrogen. But, people often use it in a range of 50 to 150 psi to effectively stiffen the front spring a bit.

[budawe]

yes, the basic purpose for nitrogen is to prevent foaming and cavitation which reduces the efficency of the shims and valving. Additionally, while not always agreed upon, gas pressure will effect the spring rates, on vee fronts, it can effect grip. I adjust front pressure quite often to change compliance. On a black shocks you can go down to about 50psi before effecting the shock but it does quiet down the front end on a bumpy track. An advantage of pressure changes is that it can be done quite quickly like when it rains just before you go out.

The significant negative associated with the black fronts is that alternative pistons are not made for them. Progressive and digressive pistons are used to change the linear behavior of standard pistons. There are folks that can create progressive and digressive shim packs but they tend to be slightly less effective than the alternative pistons. But, let's be honest, all this stuff is to the right of the decimal and very minimal in the grand scheme of things.

[grapefarmeral]

I once saw Jim Kearney finish a close second at Nelson Ledges with one front damper just dangling in the wind....makes you wonder about the effectiveness of talent over technology..

[Tiago Santos]

Ah yes, but was he running wheel covers?!

[romoman]

Pressures in the reservoir do affect the spring rate. It's not linear and changes with shock displacement. It's caused by the shaft taking up space that oil previously occupied and forcing the seperator piston to compress the gas charge more. Most shock guys will tell you to run the minimum pressure to keep the valving pistons from cavitating to keep stiction down.