2003 Kia Sorento - What Rear Coil Springs?

[zakmuh]

Hi,

I've got a Sorento which came with a lot stiffer rear coil springs. It's got a tow bar so I believe the previous owner changed it. The ride at the back is so hammering and uncomfortable. It's got normal shocks (not SLS) which are not faulty, and now I need to source the correct coils to replace to do a DIY job.

How do I go about finding out the right one (any specs for it)?

Thanks in advance

[GreenV8S]

In theory you can estimate the stiffness by measuring the dimensions of the coils, but in practice it's so sensitive to tiny variations in coil thickness that you can't rely on measuring that accurately enough with a typical corroded/painted spring. You can get a rough idea, though.

If you take the spring off the vehicle, it is possible to measure the stiffness by loading it and measuring the deflection. Unless you have specialist equipment you will be limited to getting somebody to sit on it and measure the (small) deflection. This can give you a reasonably accurate figure.

If the spring is still on the vehicle you can add a known weight to the vehicle and measure the deflection. You will need to take careful measurements of the suspension geometry to calculate the overall effective leverage between the body and the damper and can calculate the effective spring stiffness from that. This will involve a lot of work.

Before you get too far into that I suggest you might want to measure the actual vertical stiffness of the rear suspension, since that is what you are feeling in terms of ride comfort. Again, this is just a matter of adding a known weight roughly inline with the axle and seeing how much the height changes. Best to roll the vehicle a few feet to take out bump scrub effects and bounce it a bit to take out stiction in the bushes, but it doesn't need anything fancy.

If you find you need to take a few guesses at this, mass produced springs are relatively cheap.

You might want to consider who'll fit them. The tools needed are not expensive but loading and unloading a spring can be extremely dangerous without the right procedures. If you have them fitted professionally, the cost of labour is likely to be much more than the parts.

[zakmuh]

Thanks V8S,

I have replaced coils before on shogun, so I've got this compression tools and jacks. I'll try one and see if I could do it before doing both.

Would this information be helpful? My measurement is 710mm : http://www.pedders.co.uk/kia-sorento-20022007mid-r...

Edited by zakmuh on Thursday 11th May 13:07

[stevieturbo]

zakmuh said:

Hi,

I've got a Sorento which came with a lot stiffer rear coil springs. It's got a tow bar so I believe the previous owner changed it. The ride at the back is so hammering and uncomfortable. It's got normal shocks (not SLS) which are not faulty, and now I need to source the correct coils to replace to do a DIY job.

How do I go about finding out the right one (any specs for it)?

Thanks in advance

Go to Kia dealer, ask them to get you springs for your vehicle. Fit them.

Job done.

[zakmuh]

It's bit more complicated that just walking into the dealer I guess. They say it came with SLS shocks but mine has normal ones. So if self-levelling shocks contribute anything to spring stiffness, then I need to get the right spec one to avoid too much/less bouncing or any hammering effect at the back.

Cheers

[zakmuh]

I just spoke to Kia and they gave me this part number for saying its for non SLS system coil 551013E120. They couldn't very if its standard or heavy duty coils.

I read on caravan forums that for towing, heavy duty ones are recommended. I think I should go for a pair of standard ones from Eurocarparts....

[Mignon]

You're making a hell of a meal of all this and not paying too much attention to good advice you've already been given. The first thing to do is see what the approximate body movement is for a given load to get an estimate of the current spring stiffness. In fact the spring stiffness itself is not that relevant as it might operate almost directly on the wheel like a McPherson strut or it might be inboard on a wishbone and move much less than the wheel which means it needs to be proportionately stiffer to allow for the suspension leverage ratio.

What is relevant is what we call the "wheel rate" stiffness which is the extra load in lbs directly over a wheel to achieve a 1 inch deflection of the body in relation to the wheel at that corner. The wheel rate as a function of the unsprung vehicle weight on that wheel can then be used to calculate the suspension oscillation frequency and for either ride comfort or sports handling the suspension frequencies for road cars fall into fairly narrow well defined bands. For shopping car comfort about 80 cycles per minute, for taut sportier handling with less body roll about 100 cpm and anything over 125 cpm is getting pretty stiff and uncomfortable on normal roads.

For a vehicle of this weight (circa 4,000 to 5,000 lbs unladen/laden), what appears to be about 58/42 % front/rear weight distribution from some googling then the wheel rates at the back end which would correspond to each of those categories are approx 150 lb/in shopping car, 200-250 lb/in sporty and anything over 350 lb/in would be getting pretty stiff.

Those are the rates at each corner so for the whole back end then double them so for a soft ride we would expect about 300 lbs extra load for each inch of total body deflection, 400-500 lbs for something a bit more sporty and 700 lbs plus is heading for uncomfortable.

This is easy to measure as you've already been told. Set up a ruler vertically against each rear wheel arch, (measure both sides and average the two readings), get a few adult friends or a lot of bags of sand, some bathroom scales and plot the deflection against load with the weight right at the back end so it doesn't affect the front of the car any more than can be managed. If two average adults compress the whole back end by about an inch then there's nothing wrong with the springs you already have. Ideally you want about 600 lbs load to really see what's happening so 4 adults ought to move the rear end of the car body about 2 inches for shopping car ride quality.

If the back end is moving much less than the amounts I've suggested for a shopping car ride then either the springs are very stiff or there's something seized in the suspension. If the body movement looks reasonable but the ride is still very poor then it would point to dampers not doing doing their job. Simples!

Edited by Mignon on Thursday 11th May 20:39

[zakmuh]

Mignon, thanks for your detailed instruction. I'll get these measurements and deflections marked and take it from there. Thanks to all

Cheers

[zakmuh]

Hi,

I've managed to measure the deflection against weight (kg). I couldn't find few people or any other weights. So I got one guy in the boot -63kg. Pics below shows the weights with and without 63kg..

Spring dimensions (without taking it out) : outer diameter 120mm, outer length 200mm, wire thickness 15mm

|https://thumbsnap.com/yDkc1XKR[/url]

1st- rear o/s




2nd- rear o/s



3rd- rear n/s



4th- rear n/s

[url]


From what I've observed, o/s only deflects 5mm (i think the stopper is touching the bottom), n/s deflects 10mm and a 10mm gap is there for the stopper.

Whats your take on these coils please?

Cheers

[Mignon]

Using the ribs on the tyre sidewall as a guide I only see 3mm deflection on one side and 7mm on the other. Averaging those to 5mm for 63 kg would indicate about 700 lbs per inch which is what I said would be very stiff for a road car. 63 kg is too little to get much of an indication though as I have already told you. Do you not have a few fat mates you can call on? Or get some sacks, fill them with soil and load the car up with a few hundred kg. It ain't rocket surgery to scratch up a bit of load weight from somewhere surely?

However the spring only appears to have 3 working coils which is highly unusual, twice that number is more normal, and the rubber bump stops appear to be stopping the suspension working properly anyway. The suspension should be at the bottom of its travel before the bump stops ever come into play. Unladen I would expect 2 to 3 inches clear space below each bump stop. Maybe more.

I suggest you compare the ride height, springs and bump stops against another identical model year vehicle because something looks very wrong there.

Looking at pics online in Google of other 2003 Sorentos the gap between tyre and wheelarch on yours seems to be about 2 inches or more smaller than normal so I think someone has lowered this car and used up all the suspension travel thus preventing it working properly. It may be they just cut some coils off the stock springs and it's possible the front end has been butchered as well.

[GreenV8S]

zakmuh said:

i think the stopper is touching the bottom

Hard to see from this angle but it does look as if the bump stops are very close to touching. You should have a good couple of inches of wheel travel before the bump stop touches. Didn't you mention on another thread that a dealer had checked this car over for you? I'm puzzled how they could miss that. It shouldn't normally touch the bump stops - if it's hitting them routinely, the ride will be terrible.

[karona]

Stock 2003 Sorento, never been modded, and there's room to get my fingers between the bump stops and the bump plate.

[zakmuh]

Thanks your reply and pics guys. I honestly couldn't gather any more people or weight. Its such a lovely sunny day and no one seemed to be around for help!

Yeah, from what you all are saying, the car should be raised more. I guess the coils are worn to its max? I'm gonna check the new spring length with my one tomorrow


[url]


|https://thumbsnap.com/ll7gf0DW[/url]

[zakmuh]

SOLVED



Hi Guys,


I've managed to sort out the hammering suspension issue. See pics below.


Checking the recommended aftermarket coils from www.7zap.com (OEM part number and diagram website for Kia), I ordered Kilen coil springs KIL54930 (for non SLS suspension), £40 each including VAT and now the car runs well smoothly!

I took both wheels off, undid both shocks and this dropped the axle down significantly. Then using a timber plank I pushed the axle further (50mm) and pull the coil out. Same way the new ones went in - it was just an easy job. It took less than 1 hour to take both the old ones out and put the new one on my driveway.

I hugely appreciate all your help and advice on going about solving this suspension problem I had.

However, it also has raised the rear side of the car giving a 130mm clearance on n/s and a reduced 120mm o/s between the wheel arch and top of the 265.70R16 tyre. I suspect this would be stabiliser link issue?



New ones....











Cheers

Edited by zakmuh on Wednesday 17th May 13:42

[GreenV8S]

zakmuh said:

I suspect this would be stabiliser link issue?

More likely a combination of stiction in the suspension, and the ground not being perfectly flat.

[zakmuh]

I tried it on flat driveway as well and its the same. I'll try on a couple of more place for assurance

[Mignon]

Well, ok, kudos to you for getting it sorted after testing our patience but congrats for a successful outcome. I can honestly say I've not seen OE coil springs distorted as much as yours seem to be but if new ones have fixed the problem then good on you. In future, one thread, not multiple threads and people in here will always try to help.