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Lowering (images)

5K views 25 replies 8 participants last post by  johnlear 
#1 · (Edited)
Just in case anyone is really interested, here's a couple of images showing Eibach Pro Kit springs on 2 cars. This is what -30mm (compared to Veloce springs) look like. I posted comments ages ago about Koni Str.t dampers seemingly adding about 10mm on the front ride height. Anyway, judge for yourselves. I couldn't make up my mind for ages and measured many times.
Blue car is a JTS with Koni Str.t dampers.
Red car is an early TS with factory dampers.

Both cars were photographed after the springs had been installed for 9 months or so. I have been careful to ensure the wishbone to horseshoe bracket was tightened with weight on the wheels so as not to stress the bush.
I measured ride height recently but the blue car is 10mm higher. From memory, it has a wheel centre to wheelarch gap of around F:350mm, R:355mm.
Finally, purely for accuracy, both cars have Pirelli Cinturato tyres except the blue JTS which has worn Bridgestone T001 Evos on the front.
I did my best to position both cars in similar positions on a concrete surface and try to keep similar perspective.
 

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#2 ·
Great reference pictures. We keep this thread open for people to post various suspension setups. Red does indeed seem lower on the front end!
I will try and do a similar picture of my blue RST on sport pack springs (and another one, when I get around to upgrading my suspension).
 
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#4 · (Edited)
Images of springs

First pic shows sagging TS Sportpack front spring compared to Eibach Pro Kit spring. This spring is originally 10 coils or 9.8 to be precise. The sagging original spring provided 345mm of ride height which was almost identical to the new Eibach. The slight difference in free length suggests the Eibach spring rating is not much higher.

Second pic shows JTS Veloce spring next to Eibach. Note this has only 9 coils, or 8.8 to be precise.
Third spring shows JTS Veloce rear spring next to Eibach.

Just so everyone knows, I think the 9 coil JTS spring is actually both more reliable and more pliant which is shouldn't be as the shorter spring wire should make a stiffer spring. Perhaps this was something to do with the 147 comfort pack of softer front springs but tauter dampers filtering through to the 156.
 

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#5 ·
Just so everyone knows, I think the 9 coil JTS spring is actually both more reliable and more pliant which is shouldn't be as the shorter spring wire should make a stiffer spring.
Comparitive wire diameters? The shorter the wire the stiffer the spring, and the thinner the wire the softer the spring (of course). A small increase in wire diameter may 'overwhelm' a longer wire, resulting in a stiffer spring with a longer wire compared to a spring with a shorter but slightly thinner wire???

Regards,
John.
 
#6 ·
You definitely must be right about the increase of height with Str.T dampers. I much prefer the stance of the red 156 up front, a shame the rear doesn't go as low as the front. As a result, the blue 156 seems more level and is more visually appealing, but I'm a sucker for the "as low as possible" look. A Sportline spring in the rear of the red 156 will match the rear and make it look super mean, probably a bit uncomfortable though.
 
#7 ·
The Pro Kit and Sportline spring rates are the same (same diameter of spring wire) so ride will be unchanged. For a road car though, going that low just means more negative camber so the inside edges of the tyres will tend to wear more. Personally, I think the blue car should be 10mm higher for what I consider to be the best compromise.
 
#9 ·
I always thought Sportlines were harsher as well, besides their extra lowering. Good to know they're the same rate. I tested a 147 with Sportlines and Koni dampers and the rear especially was extremely stiff -by sitting in the rear, less than a finger arch gap was lost. Does that sound about right on the Pro Kit as well? I'm 70 kilos.
 
#10 ·
Yes, there is not much suspension sag with load at all now.
I checked the Eibach technical page and the spring wire diameter and number of coils are the same for Pro Kit and Sportline.
I don't find the ride is harsh but taut. It depends on which struts are used. The Koni Str.T orange dampers are fixed rate but the yellow Sport dampers are adjustable and can be set from pliant to solid.
 
#11 ·
I have been thinking - maybe Eibachs do lose their strength after a while - I'm saying that because a friend of mine has had a Pro Kit on his car since almost new and he complains of rear wheel rub over speed bumps and pothole with 4 people in the car - not even 5 and no luggage too! On the other hand, the Sportline equipped car didn't have the problem. What about you, Fruity? The age of your springs will be a good addition too.
 
#12 ·
If the ride height hasn't dropped, it will be softening of the dampers or perhaps simply a larger girth due to being a bit older.?
John Lear has made detailed posts of the effects of what happens when springs get older (weaker) which is why I posted the picture of the original TS front springs which have a 30mm reduced free length which was exactly the same as the reduction in ride height.

I think we can all be a bit better informed.
Thanks @johnlear
 
#14 ·
If the ride height hasn't dropped, it will be softening of the dampers or perhaps simply a larger girth due to being a bit older.��
Worn dampers wouldn't help. Worn damper = less resistance to bump motion, so bottoming out is much more likely.

John Lear has made detailed posts of the effects of what happens when springs get older (weaker) which is why I posted the picture of the original TS front springs which have a 30mm reduced free length which was exactly the same as the reduction in ride height.
@johnlear
Sagged springs don't become "weaker", which I think you realise. But, IMO using such words to describe the real changes that do occur with a sagged spring adds to the confusion.

A sagged spring can give the impression that it has weakened because it may allow the suspension to contact the bump stops much more easily, but simply because the bump travel has been diminished by the shorter free length of the spring and the resulting lowering of ride height.

I don't know this because I am particularly clever. Like many others, I used to think that sagged springs were weakened springs (i.e. suffered a loss of original spring rate), and that different spring steels (with different heat treatments etc) had a material affect on the stiffness of the spring. This just seemed 'common sense', and was apparently 'common knowledge' which I had come across many times. But it was just an uneducated assumption. I was set straight by a proffessional suspension engineer (who worked for TVR), and further research confirmed that he was correct...

Regards,
John.
 
#13 · (Edited)
As John himself touched on this topic in my thread, ride height is dictated by the springs for the most part.

You can compress the rod on a new strut just by pushing it by hand - I don't think there could possibly be a strut firm enough to support the weight of passengers, especially factory dampers, thus making the springs the only weight supporting item in the suspension. But that's just me thinking out loud.

My friend had filled the car with 4 middle sized males - about 75-80 kilos each. Perhaps the suspension is sagging as per normal with Eibach springs, but on speed humps and potholes, his possibly worn dampers can't absorb the energy thus causing rubbing.

But let's say you do the "bounce test" - is the amount of travel the car squats while pushed down and how hard it is to push it dictated by shockers or springs?
 
#15 ·
As John himself touched on this topic in my thread, ride height is dictated by the springs for the most part.

You can compress the rod on a new strut just by pushing it by hand - I don't think there could possibly be a strut firm enough to support the weight of passengers, especially factory dampers, thus making the springs the only weight supporting item in the suspension. But that's just me thinking out loud.

My friend had filled the car with 4 middle sized males - about 75-80 kilos each. Perhaps the suspension is sagging as per normal with Eibach springs, but on speed humps and potholes, his possibly worn dampers can't absorb the energy thus causing rubbing.
That is a lot of added mass.

How much load the damper can hold up on its' own is due to the gas pressure in the damper (how heavily you have to lean on the damper to hold the rod at a compressed or partially compressed length when manually compressing it). How fast you can compress it is due to the bump valving in the damper. The pressure is very little relative to the weight of the car, so it has very little affect on load carrying capacity. The valving is way more important to control momentary increases in load (i.e. to prevent bottoming out and / or excessive transitory bump motion).

Note that if you have rubbing issues before the suspension bottoms out, then you need to look at your clearances.

But let's say you do the "bounce test" - is the amount of travel the car squats while pushed down and how hard it is to push it dictated by shockers or springs?
Both. But the dampers are very important for passing the 'bounce test'.

But it isn't a very valid test. I've had dampers that passed the 'bounce test' with flying colours, but were hopeless on the road. I've had dampers that didn't do all that well on the bounce test, yet on the road were at least acceptable. The bounce test can pick up dampers that are absolutely shagged, and might show up dampers that are weak, but the real test is how well do the dampers work on the road.

Note that a damper with worn bump valving may still pass the 'bounce test' because the rebound valving is OK and still strong enough to prevent the damper from extending too quickly, so the chassis won't too rapidly 'bounce' back upward when you stop pushing down (so you won't get uncontrolled spring oscillation where the chassis continues 'bouncing' after having pushed down on it). If the bump valving is OK but the rebound valving is worn, then a similar thing will occur, the damper adds restance to bump loading (and it will be relatively hard to rapidly push the chassis downward) but not to rebound (the damper may pass the bounce test but not work well on the road).

Regards,
John.
 
#17 ·
As a short note to add to John's comments, I think a Bilstein B6 will have reduced bump travel in many situations over the Koni Str.T. Koni dampers are low pressure twin tube dampers. Bilstein (sport) dampers are high pressure monotube units with especially large pistons which displace more fluid than twin tubes. That is quite a sweeping statement as high and low speed (of piston rod) settings make a difference and they work on slightly different principles. Nonetheless I suspect Bilstein will have greater compressive resistance on account of being a monotube and also by having a slightly more immediate damping effect for the same reason.
 
#18 · (Edited)
Fruity, my (probably flawed) understanding:

Resistance to bump motion is mostly a function of the bump valving, i.e. how restrictive the valve is. All else being equal, a twin tube damper with 'stiffer' bump valving will tend to have less bump motion than a mono tube with softer bump valving, and vice versa. So, I doubt that any difference in bump motion between the B6 and the Koni dampers will be due to one being mono tube and the other being twin tube (or in the difference in gas pressure, though this won't have zero effect), but directly due to any 'stiffness' difference in the bump valving.

However, mono tube dampers do generally have larger diameter pistons than twin tube dampers. Larger pistons means larger piston seals with a greater contact area with the damper tube wall. Greater seal / tube contact area creates greater friction and 'stiction' than with smaller diameter seals with less contact area. 'Stiction' means a resistance to initial movement, i.e. the stationary seals 'stick' to the tube wall which requires a certain amount of force to 'break them free' and get them moving. So, mono tube dampers tend to require a bit more force to start the piston moving, but once the piston is moving the 'stiction' disappears. I suspect that this may be where the idea of mono tube dampers having a 'more immediate' damping effect may come from, i.e. the greater 'stiction' effect gives the impression of 'more immediate'. And, somewhat harsher, which is arguably true.

There is still friction created by the piston seals, and larger seals mean (all else being equal) more internal friction as the piston is moving. Once the piston is moving this friction has some degree of damping effect, added to the hydraulic damping effect. The hydraulic damping effect is far greater than the damping effect caused by the seal friction, but can be significantly more when the seals are new (i.e. before 'bedding in'). This is why dampers can feel a bit stiffer when brand new and often seem to soften just a bit after some use.

Due to greater 'stiction', mono tube dampers can tend to feel a bit harsher than twin tube dampers on smaller bumps and rough surfaces (not so much more substantial bumps as 'lumpy' surfaces, with numerous smaller 'bumps'). With a bit less seal 'stiction' twin tube dampers tend to be a bit smoother riding on roughish surfaces and smaller bumps, but this doesn't necessarily mean less damping effect on larger bumps and undulations. The larger piston in a mono tube could be seen as disadvantageous due to the tendency to greater 'stiction', but mono tube dampers have other advantages, especially for a damper in extremis (i.e. being worked hard).

Larger pistons will mean more fluid moves through the valves as the suspension moves. So a larger diameter mono tube damper piston implies that for X damping effect a mono tube damper will have freer flowing valves than a twin tube damper with a smaller diameter piston (through which less fluid passes). This may be one of the advantages of a mono tube damper, i.e. for X damping effect more fluid moves through less restrictive valves, which I suspect might reduce fluid cavitation (lessening fluid aeration), maybe...

And, a mono tube damper has the 'working' fluid in direct contact with the outer wall of the damper, as opposed to a twin tube having the 'working' fluid in contact only with the internal tube, and so with an insulating layer of 'non working' fluid between the 'working' fluid and the outer wall. This means that a mono tube damper can get rid of heat more effectively than a twin tube damper (the 'working' damper wall being in direct contact with the surrounding air, as opposed to a twin tube where the 'working' wall is buried well inside the damper). This allows the mono tube damper to work 'harder' than a twin tube, with less heat build up and so a reduced tendency to cavitate the fluid.

Regards,
John
 
#19 · (Edited)
Koni front dampers raise ride height 7-8mm

I just fitted Koni Str.T dampers to the front of the red 156 also. This time I decided to measure the dampers. See for yourselves but the ride height has increased by 5-10mm. The final photo is meant to show a slightly shortened damper rod which is why they are suitable for lowering springs.

Anyway, I have driven the red 156 since fitting the Koni fronts. However, there is still more pitching than the blue 156 so clearly the rear dampers are a bit soft.

Text Tape measure Ruler Font Soil


Material property Pipe Tool Tool accessory Cylinder


Tool Hammer drill
 
#20 ·
I just fitted Koni Str.T dampers to the front of the red 156 also. This time I decided to measure the dampers. See for yourselves but the ride height has increased by 5-10mm.
From the photos; the Konis are about 8 to 9mm longer (than the standard dampers) between the spring seat and the 'eye' through which the pinch bolt passes. This would account for a higher ride height with the Konis (as I expect you realise).

I think your photos demonstrate that not all interchangable dampers are the same length (in the section of the damper where it affects ride height), and that differences in ride height are much more likely to be due to this than any other difference between any two make / model of damper.

Regards,
John.
 
#22 · (Edited)
I believe the difference you noticed between std damper and Koni Str doesn't just stop between only those two. As most people would say, dampers throughout the 147/156/GT range are interchangeable, but after changing my tired rear shocks to new shocks albeit 156SW ones, I noticed a firmer ride and a very slight increase in ride height, about 0.6cm. Not sure if it was the worn dampers before, but as springs are mainly responsible for ride height, I believe the shocks do differ a tiny bit. They're quite firm too, they feel almost like uprated sport dampers. I like it like that as I can carry 5 in the car without a problem now, but buyers be aware. Before(Left) and After(Right) pictures uploaded.
 

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#23 ·
Why on earth would Koni make an aftermarket shock with increased ride height? Makes absolutely no sense to me!

I suppose you could machine the thread so it goes down the tube further?
 
#26 ·
Why on earth would Koni make an aftermarket shock with increased ride height? Makes absolutely no sense to me!
Nor me. Yet we have Fruitys' photographic evidence that the Koni Str dampers are indeed not the same length (as the OE dampers) between the lower spring seat and the 'hook' eye. This is the dimension that determines ride height, all else being equal (i.e. springs).

Is Koni the only manufacurer of non OE dampers to do this? Is it intentional, or just carelessness?

I suppose you could machine the thread so it goes down the tube further?
?

Regards,
John.
 
#24 ·
No idea. Your idea of machining the threads would only increase the spring preload at full extension and have no effect on ride height.

I've been playing around with things to see whilst trying to fabricate platforms for the rear springs to raise them (for those who don't want to go as low as lowering springs and for those with SW) but I can't really see a cheap way this could be cheaply produced in production batches.

One of the ideas I have is using the JTD/V6 springs in a TS/JTS to provide 15mm of lowering from Sportpack/Veloce springs if using the mentioned rear spacers.

As already mentioned, it would allow SW owners correct height lowering. It may also be useful for 147TS owners as 156/GT rear springs wouldn't quite raise the rear as much (up to 10mm) as JTD/V6 front springs do (15mm).

Eibach (and probably every other brand) spring rates are all the same irrespective of model, engine or type (Pro Kit or Sportline). The are simply coiled to different lengths from the same spring wire.
 
#25 ·
The trouble with all this (overthinking) is making me think that the 7.8 coil GTA front springs would make more sense if a coil was cut off and then used in a TS/JTS and simply having rear springs made with 0.5mm greater wire diameter and coiled to 25mm less free length than factory dimension would have been the way to go but that would have no TUV (ABE) certification.
 
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