[ananthkamath]

Originally Posted by vina

In that case, the wheel-rate is roughly equal to (spring rate)/cos2(theta) where theta=angle the spring makes from the vertical, and cos2 means "cos squared" I we consider symmetric loads.

This would be true if the spring were installed directly on the centerline of the tire, which is almost never the case. In the case of the Honda the spring is mounted vertically, but roughly 2/3rds of the way inboard from the wheel centerline. From data that I have with similar architecture vehicles, I'd say the installation ratio is roughly 1.5:1 to 1.6:1.

Originally Posted by vina

Since the angle will change as the spring gets compressed, the wheel rate can increase faster than spring rate (e.g. if initially the spring was vertical, but eventually ends up at 45deg from vertical, the wheel rate would become double of spring rate - don't know whether that much deflection is possible or even likely though).

This is almost never the case either....the wheel rate is almost always roughly constant or slightly falling.

Originally Posted by vina

I must be missing something here because you said effective change in wheel rate is 32% and not 20% (or 25%, depending on whether you take initial value or final value as the base) - this is a pretty big difference and calls for a big chnage in theta above (25deg if the spring was vertical to begin with).

I did not consider the wheel rate progression for this at all. That was a simple calculation based on only 3 things:

1) Wheel Rate before installation of donut (assumed to be 18 N/mm using data I have for similar vehicles)

2) Corner weight increase at one rear wheel due to 3 passengers of 76 kg each (assumed to be 80% of 3*76/2 = 91.2 kg or roughly 900 N )

From (1) and (2) you can calculate the wheel center deflection at 900/18 = 50 mm.

3) GTO said the rear deflects 12-15 mm less. The best case would be 12 mm, so that gives you a new wheel rate of 900/(50-12) = 23.7 N/mm

which is an increase of roughly 32%.

The only fudge factor here is the 80% number which is my assumption on the weight distribution of the 3 rear passengers. If you assume 100% of their weight is on the rear wheels, then the stiffness increase is something like 25%. Realistically, the rear passengers on a normal sedan result in a 80-90% rear load increase, so I think my 32% number is fairly close to reality PROVIDED the 12 mm number by GTO is in the ballpark.

Accuracy can be improved if we know the actual wheel center deflection before and after the donut the installed, at the same load obviously, but no one in this thread has done this so far.

[vina]

Originally Posted by ananthkamath

This would be true if the spring were installed directly on the centerline of the tire, which is almost never the case. In the case of the Honda the spring is mounted vertically, but roughly 2/3rds of the way inboard from the wheel centerline. From data that I have with similar architecture vehicles, I'd say the installation ratio is roughly 1.5:1 to 1.6:1.

You are right - I missed it in my simple model. However this is like the multiplier you'll expect coming from the action of lever and this will just change the formula I had written with a constant factor.

My reasoning that percentage change in spring rate should be same as percentage change in wheel rate will still be valid.

Originally Posted by ananthkamath

This is almost never the case either....the wheel rate is almost always roughly constant or slightly falling.

I guessed it'll remain roughly constant (or falling - if by that you mean spring gets stiffer - otherwise this is not a progressively stiffer rate and I don't see why anybody would want to have an effective springy system that becomes less stiff under higher load. Progressive rate springs actually try to do opposite of that)

As I wrote theta will probably not change much in any well designed suspension - that means wheel rate to spring rate conversion should not change. Also if the initial angle was almost vertical then slight changes will have almost no effect anyway because cos(theta) will still be zero.

Originally Posted by ananthkamath

I did not consider the wheel rate progression for this at all. That was a simple calculation based on only 3 things:

1) Wheel Rate before installation of donut (assumed to be 18 N/mm using data I have for similar vehicles)

2) Corner weight increase at one rear wheel due to 3 passengers of 76 kg each (assumed to be 80% of 3*76/2 = 91.2 kg or roughly 900 N )

From (1) and (2) you can calculate the wheel center deflection at 900/18 = 50 mm.

3) GTO said the rear deflects 12-15 mm less. The best case would be 12 mm, so that gives you a new wheel rate of 900/(50-12) = 23.7 N/mm

which is an increase of roughly 32%.

The only fudge factor here is the 80% number which is my assumption on the weight distribution of the 3 rear passengers. If you assume 100% of their weight is on the rear wheels, then the stiffness increase is something like 25%. Realistically, the rear passengers on a normal sedan result in a 80-90% rear load increase, so I think my 32% number is fairly close to reality PROVIDED the 12 mm number by GTO is in the ballpark.

See, my question is that while wheel rate (as defined by you) may be different from the spring rate by a constant factor (depending on lever-arm formed by wishbones, angle of installation ...), that will still not explain why the percentage change in the two should be different. For example if X is two times Y always then if X changes 10% so does Y.

In fact any well designed suspension would have them almost linearly related, and for the 50mm you have calculated compared to the max range for which suspension is designed, the non-linearity will be pretty small (unless it is intended to be present - which your comment on wheel rate being constant tells me is not so)

Also If you just manipulate your estimate slightly (say instead of 18N/mm use 16N/mm - GTO's springs are old and he mentions they have noticeably lost stiffness over the years) you'll get 56mm as the initial deflection and [(56/(56-12) -1)*100] = 27% - practically same as the 25% number that comes from assuming 4 turns instead of 5 (that'll be (5/4 -1)*100 - your calculation insists on taking the smaller number on the numerator this is consistent with that)


Also if in GTO's car the rear passenger's CG is almost completely above the rear wheels, then 100% of their weight will have to be supported by the rear wheels (otherwise in the Force diagram the torques will not balance at equilibrium). For it to be 80% veon rear (and 20% on front) wheels, assuming a roughly 2.5m wheelbase the passengers has to be sitting anout 0.5m ahead of the wheel (CG wise) - I somehow don't believe that is the case. I would actually go with the 90% number (passengers still sit about 1 feet ahead of the rear wheels) - that change in fudge factor alone will make you 32% figure go to 28% - much closer to the original 25% from calculation (and for this you don't have to modify the 18N/mm rate you assumed). In fact if the passengers were standing inside the boot slightly behind the wheels, this will be even worse - that weight supported by rear wheels will be more than 100% (that is to say some of the load will shift from the front wheels to the rear)



Needless to say that relying on 12mm number from GTO and 18N/mm from some similar system you know of is not a very good idea unless you have a theoretical basis of why the wheel rate should change by a different percentage than the spring rate does.

Originally Posted by ananthkamath

Accuracy can be improved if we know the actual wheel center deflection before and after the donut the installed, at the same load obviously, but no one in this thread has done this so far.

I'll do that in a few weeks once my Figo is delivered and I get a chance to install the donuts.

[ananthkamath]

Originally Posted by vina

My reasoning that percentage change in spring rate should be same as percentage change in wheel rate will still be valid.

I am not disagreeing anywhere. I just dont see how it is relevant?

Originally Posted by vina

I guessed it'll remain roughly constant (or falling - if by that you mean spring gets stiffer - otherwise this is not a progressively stiffer rate and I don't see why anybody would want to have an effective springy system that becomes less stiff under higher load. Progressive rate springs actually try to do opposite of that)

You're right about progression. I meant to say that installation ratio either remains constant or falls slightly (spring moves less and less as the wheel travels further up), not wheel rate. Sorry for the confusion.

Originally Posted by vina

Also If you just manipulate your estimate slightly (say instead of 18N/mm use 16N/mm - GTO's springs are old and he mentions they have noticeably lost stiffness over the years) you'll get 56mm as the initial deflection and [(56/(56-12) -1)*100] = 27% - practically same as the 25% number that comes from assuming 4 turns instead of 5 (that'll be (5/4 -1)*100 - your calculation insists on taking the smaller number on the numerator this is consistent with that)

Yup I agreed before that it could be as low as 25%, so what are we saying different here?

Originally Posted by vina

For it to be 80% veon rear (and 20% on front) wheels, assuming a roughly 2.5m wheelbase the passengers has to be sitting anout 0.5m ahead of the wheel (CG wise) - I somehow don't believe that is the case. I would actually go with the 90% number (passengers still sit about 1 feet ahead of the rear wheels)

Pull up a line drawing for a 2006 Honda Civic sedan (2700 mm wheelbase) off of google and then see where it comes out to be. FYI the CG of the passenger is about 4" ahead of the seat surface in side view. I have full confidence in the 80% number. Maybe +/- 3%.

Originally Posted by vina

Needless to say that relying on 12mm number from GTO and 18N/mm from some similar system you know of is not a very good idea

It's not as bad of an idea as you think. I used data I had access to in order to come up with a better estimate than just using the number of active coils on the spring.

The unreliability comes from that 12-15 mm measurement (it results in a stiffness increase between 32 and 43% - yup, not very accurate) because I think it was just eyeballed, not actually measured. If you can accurately measure that number, then you can calculate what the stiffness change is pretty conveniently without the use of any assumptions.

[vina]

Originally Posted by ananthkamath

I am not disagreeing anywhere. I just dont see how it is relevant?



You're right about progression. I meant to say that installation ratio either remains constant or falls slightly (spring moves less and less as the wheel travels further up), not wheel rate. Sorry for the confusion.




Yup I agreed before that it could be as low as 25%, so what are we saying different here?



Pull up a line drawing for a 2006 Honda Civic sedan (2700 mm wheelbase) off of google and then see where it comes out to be. FYI the CG of the passenger is about 4" ahead of the seat surface in side view. I have full confidence in the 80% number. Maybe +/- 3%.



It's not as bad of an idea as you think. I used data I had access to in order to come up with a better estimate than just using the number of active coils on the spring.

The unreliability comes from that 12-15 mm measurement (it results in a stiffness increase between 32 and 43% - yup, not very accurate) because I think it was just eyeballed, not actually measured. If you can accurately measure that number, then you can calculate what the stiffness change is pretty conveniently without the use of any assumptions.

We mostly agree, I just thought, looking at your original post, that there is some maths I haven't followed. Was trying to figure it out that's all.

I looked at City after writing the earlier post, I agree fully with you, the figure will be close to 80%. The torso upward will be about 80%-85% and the legs (significant weight in the body thanks to the large bones) will be 70%-80%, overall may be actually less than 80% (for example if the guys lean forward, or just because of the posture taken), on top of the +/-3% margin of error.

On the 12-15mm I'm skeptical myself. For all I know the numbers may be less - For example without donut you calculates total deflection to be 50mm. This means 10mm per turn of the spring (with 5 turns, this is rough because the top turn will probably have less than this). Now the donut will eliminate at most one turn worth of deflection not more. Even with 10% here and there on spring rate/wheel rate data this can go max 11mm. And rubber is not incompressible - it'll compress too, so the actual should be slightly less.

The first post I sent I asked someone to do the simple measurements. I guess I'll do them myself sometime next month once my car is here.

[raghu.t.k]

I am looking at getting one for the astar. After changing to a 185/60/R14, it does scrape if occupied by 4-5 persons. It also scrapes when it hits a pothole or a depression.

Regards
Raghu

[sanagg1]

Any more update by actual users ?

Bhpian's who have used for a longer duration, say upward of 2000 Kms.

Would some one oblige with a review ?

Cheers

[deepakchiniwal]

I got them installed on a the DZire Diesel. She is 1.5 yrs old now.

Initial Impressions: Wow a low cost solution and such a wonderful product.

Why Did I get it installed: While the vehicle was fully loaded (read 3 Adults @ back and full luggage) the vehicle used to lower a lot @ the back. Resulting in scrapping humps. Plus used to feel a lot of drag and not so comfortable drive, there used to be body roll while you take corners etc.

Which one did I install: Loadrunner B2 at the back (1")

First 100 Kms: Could not make out much difference, since it was more of bumper to bumper driving in Bangalore traffic.

101 - 1500 kms after installation: The lowering of the vehicle has reduced and the scrapping of humps is gone. The body roll still exists but has reduced by about 50%. The Drive all of a sudden has sought of found some life and is lot more fun now. Small humps are just gobbled up without much of reluctance.

What I Fear: I feel sometimes that the rubber might come out and the vehicle will become unstable. This is one of the fear I have within me, like I have one more feeling since I started driving, on a junction someone would come and bang right in between the vehicle. But still those are just my fears and wont happen .

Would I want to continue using it?: Yes, why not? Need to test them a little more before I can decide on getting rid of them.

Satisfaction level: 50%, reduced by 25% since I want to test them for few more days/drives.

[dinu2506]

Originally Posted by sanagg1

Any more update by actual users ?

Bhpian's who have used for a longer duration, say upward of 2000 Kms.

Would some one oblige with a review ?

Cheers

Been around 3 weeks since I installed. With light load, not much change, car feels the same though I'm able to go over speedbreakers without any worry like earlier. Last week, I took a full load (read 5 big adults), and drove over a speedbreaker that I could earlier never escape without a good scrape even with stop and go. I managed to clear it with only a faint skim over the surface without even stopping.
So, yes, it surely meets my requirements. Bangalore speedbreakers, here I come.

Spirited driving, never tried, maybe never will since its not my style, so cannit comment on the handling at the limits.

[sushrutha]

Got my Civic fitted with the Assisters(Darryl calls them assisters instead of adjusters) last weekend.
I got them fitted for the rear coil springs at the centre portion.
As of now, I'm not finding any difference in driving or Handling when driving alone.
I haven't taken my car for a spin with people at the rear seat. Will be going for 1K kms road trip this weekend , then only I can comment on these assisters.
I have attached the document containing the Instruction to fit the assisters, which is sent by Darryl.
Application instruction for email.docx

I haven't cut the rubber as how GTO has got it done. Installed them stock.
This gives a slight increase in the height of the car. Based on the handling + scraping of the humps , I'll take a decision as to cut the rubber by 1.5" or not.

Please Note: For ppl in BLR, Darryl refers A1 auto care to get these assisters fitted.
I had been to A1 auto care, but the guy there asks for a cool 1K rs to get these fitted.
That's insane labour price ,That's way too much for a 10min job.
I went to a local garage to get this fitted, hardly a 10min job paid him 100rs(he told me give me whatever(Change) you want). He as fitted them at the centre of the coil springs, I showed him the pics as how to and where to fit them.
Anybody can get this work done as a DIY. It's very easy too, slight concern is when one has to fit at the rear right coil spring, it's not as easy the left one, remember silencer comes here.

Thanks Patron, Hiren & Dinu for the pointers.

[sushrutha]

Back from a 1000Kms drive in Civic.
Yes the coil spring assisters have done their job. Not much of scraping the underbelly now as much as it used to scrape previously. But still sometimes, if not careful, one may scrape when you have passengers at the rear.
Had kept the rear tyre pressure to 32Psi, found the rear to be tossing(jumping sideways) in rough road a lil bit after this assisters installation, when driving alone. With the same tryre pressure & driving alone tossing of the rear was quite less previously.
With spirited driving(taking corners at 100kmph), i could experience slight increase in understeering.(Not marginally high, but very minimal, but can be noticed easily when driving alone without any passengers. With passengers at the rear understeering is unnoticeable)
So A marginal decrease in the handling I can say.
EOD, i would still be using these assisters, coz can't see the car royally scraping the speedbreakers of Bangalore & unscientific road humps on highways.
Rest, will be slightly careful when taking the corners at highspeed when driving alone.
Goodthing is removal and refitting would hardly take 15mins in total.

[vina]

I'm planning to put these on my Figo - two questions:

(1) Are they effective? (I'll put them anyway, but if another Figo owner has used them - your views will be very helpful)
(2) What about my warranty? Will it be void just because I use these mods?

[dhanushs]

Originally Posted by vina

(1) Are they effective? (I'll put them anyway, but if another Figo owner has used them - your views will be very helpful)

What you should expect is - prevent excessive suspension travel under full load, and hence prevent scraping on load.

Originally Posted by vina

(2) What about my warranty? Will it be void just because I use these mods?

Installing and removing is just a 15mins job. You can take it off while on A.S.S trips.

[vina]

Originally Posted by dhanushs

Installing and removing is just a 15mins job. You can take it off while on A.S.S trips.

Thanks Dhanush, but from the descriptions before it didn't seem to be a DIY job, most people have got some professional garage to put it in. So 15min may not be it.

also what happens in case of an accident? I don't think anybody would be removing it post accident, and I'm afraid both the manufacturer and the insurance company can void their promises.

[dhanushs]

Originally Posted by vina

Thanks Dhanush, but from the descriptions before it didn't seem to be a DIY job, most people have got some professional garage to put it in. So 15min may not be it.

Yes, a workshop is required only for jacking up the car. Installation requires no expertise. Before going to the A.S.S, you can jack up your car for 50bucks at the near by service station.

Originally Posted by vina

also what happens in case of an accident? I don't think anybody would be removing it post accident, and I'm afraid both the manufacturer and the insurance company can void their promises.

Well, theoretically, even wider tyres, alloys, performance suspension, FFE, CAI et al do not qualify for warranty. However, as for insurance, I guess you should not have a problem. AFAIK, cars with the above mentioned mods have got insurance.

[vina]

Originally Posted by dhanushs

Yes, a workshop is required only for jacking up the car. Installation requires no expertise. Before going to the A.S.S, you can jack up your car for 50bucks at the near by service station.

a thought: can one jack the car up using the usual tyre-changing stuff and install this one? I guess suspension spring will be fully extended in this case to