Light Tall Springs vs Short Heavy Springs

[gxl_d4d Advanced Member Find all posts View Profile Close gxl_d4d]

Hi,

I'm in the process of selecting parts for my next suspension replacement. What the the pro's and cons of light tall springs vs short heavy springs for the front?

Thanks,

[Whitey Shockie Maker of the Month Award Find all posts View Profile Close Whitey]

Hey,

I was also very interested in this, as I'm trying to help my mate fix his front end, which is sitting at 730mm and nose-diving. So I started a new thread to try and get my head around coil selection;

http://www.pradopoint.com/showthread...0-series-Prado

In the process of doing this, I've read many times that folks will use standard length springs, eg. 380-400mm for the front (depending on what lift they want), but will use stiffer spring rates to avoid nose diving etc. I plan on using 150 series springs in my mates 120, which are 725ib/in compared to 617ib/in for the 120. He has a soverign bar and dual batteries up front.

With regards to shorter stiffer springs, Lovells do these, and there is one user who has 345mm 1125ib/in springs, which gave him over 2" lift on the front.

However, the coil working height may be an issue here if you choose very short coils, take a look at the last plot in my thread.

Hope this helps you out a bit.

Best

Mark

[AJ120 Out of control poster! Find all posts View Profile Close AJ120]

I read something a while ago on an American forum that really made sense to me.

You don't want to use spring rate to give you lift and you don't want to use spring length to give you carrying capacity. You need to get the correct rate at the right length to suit your needs.

So I guess somewhere in the middle would be best.

As whitey will tell you, there is a lot to working out what suits you best.

Cheers Andrew

[Whitey Shockie Maker of the Month Award Find all posts View Profile Close Whitey]

Excellent advice Andrew.

To give you an idea of my mates situation, he doesn't want lift, and would prefer the car at factory height.

As such, I'll be looking at using 375mm springs, and maybe a slightly stiffer KTFR101 at 660lb/in, and hopefully it will settle back to under 1" of lift with the weight of the bar and batteries, and hopefully won't nose dive as much.

If it does continue to nose dive, or the lift is still too high after settling, I'll look at 370mm springs at 725lb/in.

As Andrew says, it will be very specific to your lift and carrying requirements, and may take a bit of experimenting before you are happy with it.

Best

Mark

[gxl_d4d Advanced Member Find all posts View Profile Close gxl_d4d]

Thanks.

I've got lovells at the moment, 360mm long/800lbs. I've been told by a few suspension places that using heavy springs on the front is what's caused my shocks to leak prematurely. I want to maintain the ride height I have now, 770mm front, 805mm rear but use a lighter spring. I was thinking kings or dobinsons. My front springs have not sagged in the 3 years they've been installed. The rear settled 15mm when installed but have not sagged since.

[Anth120playdo Banned Find all posts View Profile Close Anth120playdo]

Excellent advice Andrew.

To give you an idea of my mates situation, he doesn't want lift, and would prefer the car at factory height.

As such, I'll be looking at using 375mm springs, and maybe a slightly stiffer KTFR101 at 660lb/in, and hopefully it will settle back to under 1" of lift with the weight of the bar and batteries, and hopefully won't nose dive as much.

If it does continue to nose dive, or the lift is still too high after settling, I'll look at 370mm springs at 725lb/in.

As Andrew says, it will be very specific to your lift and carrying requirements, and may take a bit of experimenting before you are happy with it.

Best

Mark

Ktfr101 & Ktrr 102 will be nice.
It gives 20-30mm in a diesel, without much weight added.
You couldn't pick it as lifted.
It will drive much better than stock.

[Razorback81 Advanced Member Find all posts View Profile Close Razorback81]

i have a few pairs of springs
1 x KTFR-101 these are used (no idea for how long
1 x KTFS-101 X these are brand new

then i have a full set of bilstiens front struts with springs & rear shocks + springs
fronts have KTFR-101HD
rears are KTRR-102

the shocks & springs from the car have 65,000km on them

[Whitey Shockie Maker of the Month Award Find all posts View Profile Close Whitey]

Hey ####,

If you have various ride heights from different manufacturer/length/rate coils, I'd really appreciate it if you could post some numbers and coil codes on my "Vehicle lift as a function of coil free length" thread.

http://www.pradopoint.com/showthread...0-series-Prado

You'll see that the plot for the front is pretty good, with lots of data, but the rear is still a bit thin on the ground, so hopefully you might be able to add some new points?

Thanks mate!

Best

Mark

[Anth120playdo Banned Find all posts View Profile Close Anth120playdo]

I have some Dobinsons part numbers & free heights in my head, do you have those already?

I don't remember the load, I just know what they do, as in which one to use to get the lift my customers want.

On a 120:

The fronts i use all start with c59-

296 - 378mm
300 - 385mm
302 - 395mm petrol full accessories 40-50mm lift
314 - 405mm diesel full accessories 40-50mm lift.

Rears c59-

325 - 420mm light & comfy. A great coil, but if u have constant load or really load up when u go away u will go down a lot.
327 - 410mm or whatever length I order popular coil. Medium & still comfy, I use this 90% on prados. Retains pretty well.
329 - 410mm heavy, comfy if loaded a little.

On a 150:

Rears are the same, always used 327.

Fronts c59-350 with steel Bullbar.
352 with the lot. It's 5mm longer, 10mm at the wheels, can't even remember free height :-)

Use those on front of Heavy hiluxes too.

[Whitey Shockie Maker of the Month Award Find all posts View Profile Close Whitey]

Hey everyone,

After doing some suspension frequency calculations, I think putting stiffer springs in the Prado front end is a bad idea in terms of suspension frequency ratio between the front and rear.

For a factory vehicle with 605lb/in front and 205lb/in rear, I get 1.28Hz for the front, and 1.12Hz for the rear, which is a 14% difference going the wrong way.

When you have a lower frequency in the rear, the vehicle is subject to pitch, which I have experienced in my current setup with 617/212, giving 1.21z/1.07Hz.

This ratio gets even worse with a loaded vehicle, and you will get excessive pitch through shallow divots, 1m wide x 10cm deep.

The way to fix this is to use stiffer springs in the rear, and to get the front:rear suspension ratio to be less than 1.0.

Some users have reported using using Dobinsons with 285lb/in in the rear, and I know some have used up to 320lb/in with Kings. Using 617/285 gets the ratio to 0.98, and at this stiffness, the ride is reported to be still ok for around town driving, eg. C59-329.

However, if you load the rear of the vehicle with say 200kg of gear, you will end up back over 1.0 for the frequency ratio.

One way to combat this problem is to use a progressive spring in the rear, eg., the KTPR-102 is 190-320lb/in. However, it's still too soft at the start.

While researching this, I came across this problem that Toyota Fortuna drivers in South Africa had been experiencing with an unstable rear end. The solution was to use a progressive spring in the rear with close to a a 1:2 ratio spring rate range, 275-545lb/in. Keep in mind that the Fortuna is built on a Hilux chassis from the same factory in Thailand.

See this link for a discussion of this problem...

http://go-southernafrica.com/gear-an...n#.VEDCUWeSzme

Note that with this high 545lb/in at the stiffest part of the coil, the front:rear suspension frequency ratio for the Fortuna ends up around 0.7.

This has got me interested in a custom progressive coil for the rear of the Prado, say over 285-500lb/in, with say 3 stages, 393lb/in in the middle.

Not having seen or heard of this spring rate range on the back of the Prado, I'd be interested to hear what others think.

I don't see the need for a progressive coil on the front of the Prado with a constant load. I will be keeping my front coils linear at no more than 617lb/in, and I will use a tall spring to get the lift I'm after, and use up to a 6mm strut spacer later to combat any sag. Either that or just get new sag-free springs!

Best

Mark

[Guest Close Guest]

The frequencies calculated are so low, is it significant to real world driving. Once you add the shocks, it all dampens after 1 cycle or so.

[Whitey Shockie Maker of the Month Award Find all posts View Profile Close Whitey]

The front:rear suspension frequency ratio with real world driving will be strongly dependent on wheelbase and speed.

Hey amts,

My pitching motion driving for example through 1m wide 10cm shallow divots in swales between dunes was severe at 20-30km/h, so severe it required heavy braking. This was in a typical heavily loaded vehicle. In this case the rear frequency was significantly lower than the front.

...and if your shocks are crap and too soft like I find my 712/713's, then they have no chance of damping out heavy pitching.

So yes, it is significant to real world driving.

Best

Mark