When to renew dampers?

[Tim Falce]

I am having a bit of trouble with the setup on my car and seem to be going back-wards in the road holding department, I was at Donington yesterday and I was slower than 3 years ago, even allowing for a lack of talent I normally improve on previous lap times, not drop 2 seconds.
I am thinking of altering the spring rates to make the car softer and someone suggested I change my dampers after I said they are 10 years old.
To me they seem OK, they go in and out, don't leak and have resistance so I had never thought or worried about them. They have probably done about 4k miles on the road and 6 years of racing, probably over 50 races.
So how long would you expect dampers to last under racing conditions and should I change them?

[Al Weyman]

I would have thought they work or they don't. I mean if they are adjustable maybe it is worth just tweeking them a bit, Konis have a lifetime warranty don't they?. There could have been a host of factors especially at Donnington which can be very slippy especially if some environmentally freindly 747 has just dumped its excess fuel over the track:-(.

It was very greasy at Thruxton yesterday as well, maybe something in the air:-).

Several people have advised me to stay clear of gas filled ones what are yours?

[Notso Swift]

Unless they are cheap, and what is these days, don't replace them before you get them dyno'ed. Any reputable expert will have a shock dyno so you can see exactly what they are doing.

Just like an engine, the Oil does go away, and sometimes all you need to do is replace it, along with the various seals, most good brands can be rebuilt, although some willl charge more than new ones (!) at least yo uhave a verified starting point with a dyno sheet, so next time you have a question you can dyno and compare.

No reason to keep away from Gas units, yes the gas can leak out, but they are more heat stable than hydraulic units, so the oil shoudl get an easier time of things, making them less prone to damage (the heat can melt the seals) and fade, swings and round abouts really.

[Al Weyman]

The reasons I was given for staying away from gas shockers was:

(a) They cannot be rebuilt.

(b) the gas excerts an upward pressure on the shock acting as a small spring and this makes it more difficult to set up and confuses the issue.

(c) I was told you cannot have a two way adjusting gas shocker and some very experienced people have told me that a double adjusting (separate adjustment for rebound) is essential if you want to get the most out of the car especially at circuits like Mallory Park.

As I understood from this gas filled single adjustment shockers are more for road use than for race cars where a roadcar will do many thousands of miles. I hasten to add I am quoting someone else here and have no experience of these double adjusters (yet) but have some on order from the US so I will report back as Tim (Falcemob) knows the shocker issue I currently have (Gas filled Bilstiens on the rear) after trailing me at Brands. Isn't this why the real expensive race shockers have a separate oil reservoir so with that set up I cannot imagine they would be gas pressurised but I may be wrong.

PS Hey thats a cheap setup advertised at the bottom of the page, shame its for a toy car! Sorry for double post maybe admin can delete the first one for me!

[greenamex2]

Originally Posted by Al Weyman

The reasons I was given for staying away from gas shockers was:

(a) They cannot be rebuilt.

(b) the gas excerts an upward pressure on the shock acting as a small spring and this makes it more difficult to set up and confuses the issue.

(c) I was told you cannot have a two way adjusting gas shocker and some very experienced people have told me that a double adjusting (separate adjustment for rebound) is essential if you want to get the most out of the car especially at circuits like Mallory Park.

As I understood from this gas filled single adjustment shockers are more for road use than for race cars where a roadcar will do many thousands of miles. I hasten to add I am quoting someone else here and have no experience of these double adjusters (yet) but have some on order from the US so I will report back as Tim (Falcemob) knows the shocker issue I currently have (Gas filled Bilstiens on the rear) after trailing me at Brands. Isn't this why the real expensive race shockers have a separate oil reservoir so with that set up I cannot imagine they would be gas pressurised but I may be wrong.

PS Hey thats a cheap setup advertised at the bottom of the page, shame its for a toy car! Sorry for double post maybe admin can delete the first one for me!

I use Koni double adjustable gas dampers and I think you've been misinformed.

a) They can be rebuilt, just not by yourself. Rebuilds are pretty cheap.

b) Do you really think a spring with a 40lb constant force is going to make much difference?

c) I have them.

I have single adjustable gas on the front of the kit car (Nitron) and they are lovely.

Al, contact me if you want to dicuss further.

[Al Weyman]

The guy from Koni UK told me some of that maybe I misheard him! We were in fact talking about custome built units and when I asked if they were gas he said you don't want them and no we can't do a custom gas. Surely 40lbs upward force especially on a light car like yours or Tim's would make a difference.

[greenamex2]

Originally Posted by Al Weyman

The guy from Koni UK told me some of that maybe I misheard him! We were in fact talking about custome built units and when I asked if they were gas he said you don't want them and no we can't do a custom gas. Surely 40lbs upward force especially on a light car like yours or Tim's would make a difference.

Depends which bit of Koni you talk to, I think the road based and pure competition based bits are seperate 'business units'!

I get mine done by what used to be 'Koni technical', now part of Sportsline Suspension (01280-702 633, Paul Drake).

We spent a lot of time blaiming the extra load on how handling problems. Paul dropped the pressure a lot and we still had the problems. Eventually the actual cause was found elsewhere (OK, several elsewheres).

Yes the 40lb INITIAL force does mean on an otherwise optimal setup you would have to reduce spring rates a tad. However that is on a car with about a third of the rear weight being unsprung (and hence not working on the damper) and only about 2.5 inches of bump travel. On your bigger beasties I doubt if you would be that badly off.

They also do oil double adjustable dampers but these aren't as 'sensitive' to small movements, and when you only have a couple of inches bump travel MOST movement is small!!!

[Tim Falce]

Mine are AVO oil filled with a single adjuster knob. I am not too sure about the double adjustable shocks purely on the grounds of it is yet another setting to throw into the equation and I know nothing about them.
I was under the impression that the dampers with a separate oil chamber were for saving unsprung weight.

[TEAM78]

get them tested, its the only way to get the guess work out of this, its only £25 when I had two done at LEDA. so it aint expensive and losing 2 seconds is serious really as thats huge...
let us know what it is when you find out what the problem is

cheers

[greenamex2]

Originally Posted by falcemob

I was under the impression that the dampers with a separate oil chamber were for saving unsprung weight.

I'm pretty sure it is more to do with maximum stroke for a given damper size. My monotube gas dampers DON'T have a remote cylinder and have a fairly poor damper size/stroke ratio compared to the AVO's I used to use on my kit car. However they are cheaper as a result!

Double adjustment can be simpler in many respects once you get used to the idea and if 'your driver' can work out what your car is doing wrong at each end. We rarely touch the bump and just concentrate on rebound which most single adjustables don't allow you to do.

[Tim Falce]

Originally Posted by TEAM78

get them tested, its the only way to get the guess work out of this, its only £25 when I had two done at LEDA. so it aint expensive and losing 2 seconds is serious really as thats huge...
let us know what it is when you find out what the problem is

cheers

I think the main problem is that the car is running too stiff, I have put wider wheels on and I think it may have stiffened the sidewalls of the tyres up. I run very stiff springs 850/900 F/R and it was just too lively at 980KG.
The changing the dampers bit came about in a conversation about my setup and the guy was surprised I still had the original dampers fitted.

[Al Weyman]

Is that the actual wheel rate or the spring rate Tim as it sounds very high especially at the back. The new springs I have ordered from the States are 350 front and 200 rear (actual wheel rate) but my car must weigh a hell of a lot more than yours and these rates have been advised to me by people who hopefully know a lot more about racing my model car than I do! Hey dont you have 4 springs on the back as well!

[Tim Falce]

Al, that's spring rate, how do you work out wheel rate?

[Al Weyman]

Well I will give you an example. On a car with coil over suspension say in a McPherson strut set up the spring rate is the same as the coil rate as it is more or less 1:1. On a car with a double wishbone suspension as in my Yellow Camaro with the spring seat generally half way along the length of the lower wishbone there is then a leverage action on the spring so the actual rate is a lot less than the spring rate. On my car it is midway along the wishbone and actually you sqaure the spring rate in this set up (see Fred Phuhns Book How to Make Your Car Handle for the formula) so in actual fact the spring rate is divided by 4! I run a 1000lb spring in the front of that car which I had to have specially made because of the rules I was racing too and it cost me an arm and a leg but the wheel rate is only 250lbs. That is why I am keen to get this coil over conversion for the black car as it uses a more direct Mcpherson strut arrangement and means the actual wheel rate will actually be 350lbs the same as the spring rate. Also it uses the standard competition springs that are cheaply available.

On the yellow car (completely different suspension arrangements on the two cars) I am stuck with what I have although a chat to a competitor at Thruxton told me that in fact a Camaro had been converted to front coil over legally with in their rules so maybe I will look at that again as 250lbs wheel rate is IMHO still a bit light for that car.

[Notso Swift]

Originally Posted by Denis Bassom

I use Koni double adjustable gas dampers and I think you've been misinformed.

a) They can be rebuilt, just not by yourself. Rebuilds are pretty cheap.

b) Do you really think a spring with a 40lb constant force is going to make much difference?

c) I have them.

I have single adjustable gas on the front of the kit car (Nitron) and they are lovely.

Al, contact me if you want to dicuss further.

Mine aren't Koni, they are DMS, but again you can get race quality double adjustable gas shocks URL="http://www.dmshocks.com/default.asp"]http://www.dmshocks.com/default.asp[/URL]

With the remote reservoir type, I am lead to believe, (by Koni in Aus) that one of the reasons this is done is because they are actually easier to make, and a little more hardy. (because the delicate stuff is suspended). They use a needle valve, but the draw back it is not as accurate, even if there are 20 positions the steps they are not linier.
The way Koni (and my DMS) do it is the valve consists of shim packs, which is more progressive
May be crap, but a $1500 (600GBP) each for mine I am not going to back to back to find out!

[Al Weyman]

I have some QA1 all alloy double adjustable rose jointed coil overs on order, dunno what they are like but the yanks seem to rate them!