I admit that I have a weakness for expensive dampers. Not that I own expensive dampers -- but they just seem so cool. But I have no idea what advantages are offered by remote or external reservoir shocks? Better cooling? More damping because of fluid volume?
What say you?
Rob
One of the better primers out there http://farnorthracing.com/autocross_secrets6.html
aaaaaaaand now I know what I'm reading at work today.
Yeah I wouldn't go out of your way for a remote reservoir setup unless you're having problems with heat or travel - that is, basically only offroad applications.
Which car are you looking at them for?
I'd be looking at AST or Hanchey Vehicle Technology for my own track car. In fact, I purchased XIDAs for the Miata (essentially AST's with Emilio at 949Racing's own valving setup).
I considered the HVT's for the dual damping, but couldn't justify the price difference.
Thanks for posting that.
From my daze of motorcycle racing, remote reservoir shocks were/are very important. Since oil does not compress, that means a single tube shock can't be completely filled with oil because you have to allow for the volume of the shock shaft. This means an air bubble inside the shock which can compress as the shock rod displaces the oil. Even under pressure it's possible for the oil to foam at the oil/air interface and foam does not damp well.
The reservoir has either a moving piston or sometimes a bladder which separates the air from the oil and the 'gas' side is pressurized, removing the foaming problem. As the shock piston enters the body, the non compressible oil will either move the floating piston or compress the bladder. AS the shock shaft exits the shock body the compressed gas either moves the piston or expands the bladder, keeping the oil under pressure.
Shaft speed, shock travel and cycles per second are important considerations also, typically a long stroke shock operating with rapid cycling is more in need of a remote reservoir than a short stroke shock under rapid cycling, such as on a race car on smooth pavement. But there's another consideration: heat. From personal experience the remote reservoirs on my dirt bikes would get too hot to touch.
A short travel shock on a car on pavement can still generate a surprising amount of heat, it just takes longer than a long travel shock. In a short AX, this isn't generally a problem so remote reservoir shocks could be considered an extravagance but the same car in a 2 hour enduro might have a problem. In that case a remote reservoir with cooling fins can definitely help keep shock temps manageable.
One disadvantage to RR shocks is that the hose will create some hysteresis that an internal reservoir shock will not.
Also good shocks will have a piston that separates the oil and gas.
Edit: Another thing that's neat to look at is Base Valved shocks. Do some googling they're relatively new, but supposedly good stuff in the roundy round world.
Base valves are used in all twin tube dampers - not a new technology by any stretch of the imagination... though it's seeing some new(ish) application in monotubes. A remote reservoir is usually required on a monotube damper IF there isn't enough space to have the 'reservoir' in the damper. A remote reservoir damper (in and of itself) would not offer performance improvements compared to a monotube that has the 'reservoir' at the base of the damper. That said, the remote reservoir offers some packaging advantages, and compression damping adjustment more easily added to a rr shock. Twin tubes are something else entirely, and very rarely use remote reservoirs. At the end of the day - valving is way more important than what technology is used, but different technologies allow you to do different things with valving (force-displacement characteristics).
Nathan (ex-damper designer for military vehicles)
Thanks, all! Now I know.
In short, for demanding competition applications where you really need optimized damping, remotes are often called for. I wouldn't spend the money unless there's genuine need though.
Chris Billings runs Shock-Shop in Portland OR. He was a racer for many years, bought a shock dyno when he retired and it became a second career. Also, he's something like chief suspension judge for the formula SAE organization.
I worked with him over last winter to revalve my (very fancy, remote reservoir, paid for by the previous ownner's deep pockets) Penske shocks on my race car. He has a very methodical data and calculation driven system that involves measuring and weighing about everything on the car. Sprung/unsprung weight, motion ratios, spring/anti-roll bar/tire rates, etc etc etc. He crunches all the numbers and you receive your shocks in what is purportedly an ideal valving configuration and with that valving setup so the clickers are in sweet spot.
My dyno charts looked excellent, and with his valving/settings/suggested spring and bar rates the car was essentially flawless right off the trailer. I've evolved the setup a bit on the basis of tire temps/pressure/wear, but he nailed it.
His website has excellent real world information on shock selection. Dig into it, look around - there's a lot there.
tpwalsh wrote: One of the better primers out there http://farnorthracing.com/autocross_secrets6.html
That's fantastic. Thank you for posting that!
I will say that these came up recently at a NASA-MA race at VIR. The agreement amongst the AI Mustang drivers was that they weren't needed for races under 25 minutes, soon after which is when they are seeing temps raise too high. How that applied to other cars, well, that math is above what I will attempt while awaiting Steve Earl and the Dukes to take the stage.
S2000s come stock with a remote reservoir.
The main advantage of the remote reservoirs is more travel, since you don't need a separator piston and nitrogen chamber at the bottom (or top) of the shock body.
While you're at it, might as well read this page from Dennis Grant's site too: http://farnorthracing.com/autocross_secrets18.html
It might convince you that you don't need adjustable shocks. It sure did to me. Now I have a Bilstein valving kit and I'm buliding a shock dyno.
You'll need to log in to post.
