Thread: Koni purists...

Don't sweat it.
The 8240 series is merely a twin tube 82 series with 80psi nitrogen in the outer tube instead of air at atmospheric pressure. It helps prevent cavitation. It'll have little to no consequence on ride quality, and the 8240 series can be run sans nitrogen anyway, but why would you want to ?
The actual lifting force/nose pressure at 80 psi is 24.5 lb, so in theory it will take an extra 24.5lb to get the shock moving, which can be countered in the bump valving and in practice I doubt you will feel.

FWIW, OME Nitrochargers are pressurised at around 80psi, and 80psi is the recommended minimum in the LTR's.

Dan,

I fitted 4 Koni heavy track low pressure gas to the rear of a 110, and the ride was still excellent. This vehicle was used fully loaded on horrific roads and the owner reported zero fade and excellent control, even pounded on a 40 degree day for hours.

I drove it after the fit up on bitumen and it felt fine, not really stiff atall, just heaps of control and I found myself looking for big dips and bumps in the road to feel the rebound control, which was fantastic. had the landing characteristics of a group A rally car. Well nearly.

I'd agree with Rick and go the gas ones.

JC

Well, I've a pair of the 8240series sitting in my office and will fit them tonight.
FWIW I know exactly what gas charging is designed to do, I just don't like it's side effects. Generally this technique is used on inferior monotube designs to overcome the lack of oil capacity inherent in the design. Most Koni aficionados including me consider this to be a gimmick which is unnecessary if the component is designed correctly in the first place. Big-bore Konis did not need this and so offered superior damping control and many years of service (an average cheap shock can be killed in a matter of hours if punished), while still delivering limosine quality ride comfort.

BTW local ARB agent quoted me $425EACH for LTRs, I laughed then sighed.

Thanks to Brad (Sith) who PM'd me a lead on a set in WA, but when I rang today he had sold out

Five vehicles on my Madigan Line trip in two months time have just fitted Koni 8240's. Three Defenders and two Disco II's. Also, at least one other Defender is also running Koni's - not sure what type though as he has had them on for a few years already.

The Madigan Line between camps 6 and 14 is described as 'the spinifex moguls' and it has been reported that average speed is about six (6) km/h

We'll be doing a 'Product Test' report for our club magazine when trip is over - should be a good test and make interesting reading.

Originally Posted by oldzook

<snip>
Generally this technique is used on inferior monotube designs to overcome the lack of oil capacity inherent in the design. Most Koni aficionados including me consider this to be a gimmick which is unnecessary if the component is designed correctly in the first place.
<snip>

whoa there nelly, inferior design and lack of oil in a mono tube ?
methinks not.
Gimmick ? I really don't think you understand how each damper design works.

FWIW, most of the 'harshness' that most complain about in a lot of Billies is due to copious amounts of low speed bump valving which the engineers there feel is necessary to counter the high unsprung weight and body roll of a solid axle 4WD. There are certain design features of a Bilstein that I don't really like, but being gas charged isn't one of them, well, at least not in principle. I think some of the 'harshness' that is blamed on the gas pressure is actually friction in the damper. Some of it is from the larger diameter piston, and in Billies in particular, shaft flex from side loads.
I can get someway towards the same characteristic with a twin tube Koni if I put enough pre-load on the foot valve stack. It's just a difference in philosophy to damping and a (generally) greater piston area in a mono-tube enabling greater damping forces to be generated at smaller shaft displacements, more than an inherent gas design characteristic.

Contrary to popular opinion, gas pressure has absolutely no effect on the damping. It merely contributes to the 'nose pressure' or force needed to be overcome to get the piston/shaft moving. This 'pressure' is a function of the shaft area multiplied by the gas pressure. In race cars with nil drooped and pre-loaded suspension this becomes a consideration and is a true 'nose force' that has to be overcome before the suspension begins to move, yet in our situation with unconstrained suspension it can be shown that this nose force or pre-load created by the gas pressure is cancelled out by the increase in static ride height. It actually becomes a lifting force, raising the vehicle and cancelling out the pre-load aspect. In either situation it contributes nothing to the spring rate.


Out of interest, Koni's top of the range road race damper, the 2812 series are mono-tubes and most all serious off road race dampers, from Bilstein to Ohlins, King to Reiger, Fox to Drummond are all mono-tubes. Even the new generation of twin tube road race dampers from Ohlins and Sachs still utilise a floating dividing piston and gas chamber.

Bottom line is that there are certain design elements in both damper designs that are good, one isn't totally superior to the other in all situations. Some designers have combined what they think are the best ideas from both styles into the one damper, JRZ from Holland being one, which uses a mono-tube damper with remote reservoir. Rebound damping is a shim stack on the piston and both bump damping circuits are shim stacks in the can to mimic the foot valve in a Koni twin tube. Donerre from France went the other way by using a coil spring energised rebound valve, although I believe he uses a Ricor rebound valve these days. (The same basic arrangement that Edelbrock from the US licensed and market for road registered cars and off roaders. The RICOR valve gives a compliant valving at low shaft speeds, and uses an inertia weight to stiffen the valving at higher shaft speeds )

Jeez I just love being wrong... It's a little hard to tune into the back end as I still have the OME nitrochargers up front distracting me ($$) but so far these 8240s seem just as good as the original, I'm very very happy with them. Certainly a lot better ride than Billies or of course OME nitrochargers.

Rick you sound as though you have a lot of experience with dampers, and I am not setting out to be argumentative with this response
"Gimmick & inferior" was probably a little bit harsh (boom-boom), guess I'm just a Koni snob LOL.
FWIW I have never had an old straight oil fade on me nor have I seen one fail on several friends cars, seen plenty other brands lose the plot though.

Rick, so what are the advantages of a monotube over a twin tube? Or in what way is a twin tube inferior? Is it possibly a build cost factor or size restrictions? Is it just simply as you say a different philosophy?
In a racing environment it would be fair to say comfort is not on the agenda, in a street car used on rough terrain (the average 4WD) it is highly desirable.
And I am not being contrite when I say I really don't understand this;

Originally Posted by rick130

this nose force or pre-load created by the gas pressure is cancelled out by the increase in static ride height. It actually becomes a lifting force, raising the vehicle and cancelling out the pre-load aspect. In either situation it contributes nothing to the spring rate.

If it is a lifting force raising the vehicle then it is acting as a spring is it not? The likes of Monroe from my memory take pride in the fact their shocks help alleviate the problem of sagged springs. To me that's just not how you make pudding. The spring does it's job and then the damper does it's separate job.
I would actually be interested in a safe way to bleed off the charge in the OME nitrochargers I have to see what effect it has on the initial bump feel, this would demonstrate what effect the gas has. Anyway, in general I find them to be complete rubbish - over damped on compression and under damped on rebound.

Oh and did I say I am happy with the 8240s?