[hiren.mistry]

Geez all this stuff about technicalities is boggling my illiterate mind.

As mentioned up-thread I had this rather simple piece installed on my Civic yesterday. It was fairly straight forward. Have it installed on all four corners and the first impressions are positive. The ride is slightly on the firmer side but not disconcerting at all infact it can hardly be felt, and the car seems to have gained around 3/4th of an inch in ride height all around. Installed the runner at the bottom up front and in the center at the rear.

Also got the alignment done post the install. Will keep this thread updated as and when I notice something.

But its very, very early to say anything as I've barely done 50 KMS post fitting it. Have taken a few pics will upload them shortly.

[Sutripta]

Hi,
@Vina
Great post. Whether you model it as original spring + helper in parallel, or as original spring cut + remaining original spring 'stiffened' and placed in series, on crunching the numbers, the results should be the same.

In real world usage, problems crop up in calculating 'effective turns'. eg. there are different correction factors for open ends, closed ends, closed and ground ends etc.

For driving and handling, may I suggest getting your hands dirty, and checking out messrs Millikan and Gillespie in your college library! I think you'll do it justice.

Originally Posted by dot

@Sutripta, I have access to a UTM with a 50kN load cell, will this do?

Should do, esp if readout is electronic. Is it a four post design? Is the extention/ compression reading accurate. (In my experience, certifying agencies just bring a proof ring. They don't even look at the extention!)

Actually, if I were to do it for myself, there are numerous ways in which I could obtain the readings. Simply. However, if you have to sign off on a piece of paper, or authoritively state figures to someone, then your options are greatly reduced. That is when the UTM comes in.

Even more important is interpreting what those numbers mean in terms of ride and handling. I prefer to think of it as black magic.

Originally Posted by dhanushs

The Rubber reduces the suspension travel, and hence increases the GC on load, and hence there is no bottoming out, or scraping the belly.

Depends on suspension travel in the modified system. And system geometry.

Regards
Sutripta

[dot]

Originally Posted by Sutripta

Should do, esp if readout is electronic. Is it a four post design? Is the extention/ compression reading accurate. (In my experience, certifying agencies just bring a proof ring. They don't even look at the extention!)

Actually, if I were to do it for myself, there are numerous ways in which I could obtain the readings. Simply. However, if you have to sign off on a piece of paper, or authoritively state figures to someone, then your options are greatly reduced. That is when the UTM comes in.

It is a regular Zwick UTM. The data is interpreted by software. Not sure of the model number. It belongs to our company where I work in R&D. We can take the stress strain reading of the coil first and then with the rubber insert in elongation mode and compression mode. I wonder if the regular dog-bone grips can hold a spring. Maybe the ends of the coil needs to be modified.

[Sutripta]

^^^
Hi,
For accuracy, you'll have to mimic the original seating pads.

Safety first. You have to ensure the spring doesn't fly out causing mayhem.

If I were you, given the fact that you have access to such a machine, I would measure the spring and elastomer separately, and then together. And see whether our theoretical assumptions are met.

If it could be measured, it would be interesting to find out the life of the elastomer in terms of number of cycles. Remember the polyurethane 'spring' of a jogging shoe has a (very limited) life.

Regards
Sutripta

[dot]

Originally Posted by Sutripta

Hi,
For accuracy, you'll have to mimic the original seating pads.

Safety first. You have to ensure the spring doesn't fly out causing mayhem.

If I were you, given the fact that you have access to such a machine, I would measure the spring and elastomer separately, and then together. And see whether our theoretical assumptions are met.

Good idea, but how to get a coil and the rubber part?

Originally Posted by Sutripta

If it could be measured, it would be interesting to find out the life of the elastomer in terms of number of cycles. Remember the polyurethane 'spring' of a jogging shoe has a (very limited) life.

To conduct such a test, one needs a fatigue testing machine. Such an instrument can monitor performance over cycles. Unfortunately we don't have fatigue testing capability.

[ananthkamath]

I was wrong about the number of active coils taken out - it is indeed 1 turn less and not 2 as I stated previously. So the effective initial stiffness change in the spring is closer to 25%, not 66%.

That being said, calculating the effective spring stiffness is only the first step of many in trying to objectively predict the effects on real world handling (forget predicting ride). You can read Milliken all you want, but most of the data required to do this with any useful accuracy is unavailable to most people outside the core vehicle dynamics guys at the OEM.

So for simplicity's sake, lets just say, again for emphasis, that predicting the impact on handling is best done by driving CAUTIOUSLY at first and then slowly building up to your normal driving style.

[sgiitk]

I do not think why we need to get involved in the technicalities. Let me try and simplify the matter. You have five gaps. have some spring rate. Now you block out one of them. So you are left with four. Spring constant is the change in length per unit deformation. So the rate becomes 5/4x of what it was previously, since now you will need more load to get the same deformation. So it is stiffer.

But - for small movements like road irregularities the rubber will allow near normal deformation. So the spring constant does not change much from stock, and you have normal behaviour on small movements.

Effectively, you have a variable rate spring which gets stiffened as the deformation becomes larger.

[hiren.mistry]

Originally Posted by sgiitk

I do not think why we need to get involved in the technicalities. Let me try and simplify the matter. You have five gaps. have some spring rate. Now you block out one of them. So you are left with four. Spring constant is the change in length per unit deformation. So the rate becomes 5/4x of what it was previously, since now you will need more load to get the same deformation. So it is stiffer.

But - for small movements like road irregularities the rubber will allow near normal deformation. So the spring constant does not much change from stock, and you have normal behaviour on small movements.

Effectively, you have a variable rate spring which gets stiffened as the deformation becomes larger.

Thanks for this prof, very plausible and I can attest to this. With only me in the car, I can hardly feel the stiffness caused by the runner.

I still have to drive it with a full load. But even if this solution provides a 50% relief from the bottoming issue on full load, I will be a very happy person.

[GTO]

Update after a 180 kms drive with ONLY driver + 2 passengers:

- Plan for performance suspension back on . This Mod does absolutely nothing to the dynamics or grip levels. Car behaved just as it does on a ghat section that I'm very familiar with. Understeer on the limit included.

- Big area of improvement : No mid-corner bottoming out (severe problem with stock Civics). Because of this improvement alone, I'm sticking with Auto Runner (until I get her a set of Koni FSDs).

- Scraping problem over speed-breakers nearly eliminated, and I'm talking with 5 passengers + fully loaded trunk. The only one breaker where I really hit the bottom is at the end of the trip, where I was distracted & didn't slow down for an XL size bump.

Originally Posted by GTO

Report after 180 kms on the highway with 5 onboard + a trunk full of luggage

- With full occupancy onboard (5 + fully loaded trunk), the Civic did not scrape over speed breakers; this was a revelation. Even the poorly designed toll naka speed-breakers were dismissed off without complaint.

- The car is bottoming out a LOT less. Before, the suspension used to easily bottom out on road dips & ups at any speed over 50 kph. I would say the bottoming out is 60 - 70% less than before. Even the rear end bounciness is far better controlled.

- Unfortunately, it's NOT improved the full-load handling at all. Feels about the same (no advantage), and there is no perceptible difference in grip, nor any perceptible decrease in body roll (still rolls the same as it did before with 5 onboard).

I'll know if it handles better with a lesser load only on Sunday, when I'm driving the 180 kms back with 2 passengers (instead of 4).

[sgiitk]

@GTO; Your experience attests to what I have said above. I do not expect any improvement except a reduction in the tendency to bottom out.

[dinu2506]

Originally Posted by sgiitk

@GTO; Your experience attests to what I have said above. I do not expect any improvement except a reduction in the tendency to bottom out.

Zero improvement or deterioration in dynamics with a reduction in tendency to bottom out is in itself a reason to go ahead with this cost effective mod. In my 5 years experience with Civic, bottoming out and scraping the belly were couple of the very few negatives in an otherwise wonderful car.

[vina]

Originally Posted by sgiitk

I do not think why we need to get involved in the technicalities. Let me try and simplify the matter. You have five gaps. have some spring rate. Now you block out one of them. So you are left with four. Spring constant is the change in length per unit deformation. So the rate becomes 5/4x of what it was previously, since now you will need more load to get the same deformation. So it is stiffer.

But - for small movements like road irregularities the rubber will allow near normal deformation. So the spring constant does not change much from stock, and you have normal behaviour on small movements.

Effectively, you have a variable rate spring which gets stiffened as the deformation becomes larger.

well Sir, that's what I wrote in the first part of the post - though I would humbly add that the rubber is probably pre-stressed and so even for small road irregularities some effect should be discernible.


Anyway, I had earlier asked about Amazon.com: AIR LIFT 60769 1000 Series Rear Air Spring Kit: Automotive whether this would help. This is a cylindrical air balloon to be fixed inside the coil spring of a suspension (provided the damper is some place else), completely reversible and tunable in your home garage (by changing the pressure according to the load). So for most of the daily driving you can keep low pressure and for the weekend trips with family add pressure and get back the dynamics.

Can you comment on this - this is a guaranteed progressive rate spring (I have seen a PDF with all the calculations, as well done some myself)?

The cost is only Rs5000 so I'm really considering this. I had seen some comments 4 months ago from people who had used it before. I might be traveling to US soon and might pick a set up from there if these are good, however I'm worried how long these can last.

[vina]

http://www.team-bhp.com/forum/modifi...ded-sedan.html

This is what I have been referring to. From the website of the manufacturer it seems this work for all sorts of loading conditions and they seem to provide lifetime warranty too !

[ananthkamath]

The airlift thing is what I would install if I were in this situation. We've used similar products for vehicles where the GVW-to-curb weight ratio is high and it works very well because

1) it is tuneable (the rate curve is mildly progressive at all inflation pressures, with linearity improving at higher inflation pressures)

2) it can be completely "switched off" when not desired.

3) it does not affect spring durability due to water entrapment between the donut and spring, or even in the unlikely case of exceeding the fatigue strength of the coil spring. (BTW I don't think you can exceed the yield strength of the coil spring just by installing the donut, if anything it may fatigue, but it wont fail instantly - guaranteed).

[sgiitk]

@vina; Please read my post again. But - for small movements like road irregularities the rubber will allow near normal deformation. The rubber pre-stressing is included in this. This is why I said near normal and not normal. The rubber will be at least 10x more compliant that the spring, so the contribution to the hardness will be negligible.