Un sprung weight. Landrover 90.

[Paul Woodward]

Today I finally got around to weighing my 90 in order to sort out some better springs.

I've got 1112kg on the front axle and 943kg on the rear.

To work out the rates required I need some idea what the front and rear unsprung weights would be.

Anyone got any ideas or suggestions?

Thanks.

[landroversforever]

There is a thread on here somewhere with some component weights... might be worth a look in there? I think it was in the build section.

[Bowie69]

There is a component weight thread, but nothing on Rover axles, but IIRc they have been listed as about 120Kg for front, 100Kg for rear.

Then... you need to add for the front:

Track rod (5Kg stock, 10Kg HD)

Half the drag link (5Kg stock, 10Kg HD, so 2.5 or 5Kg)

Ball joints (0.2Kg each, so 0.6Kg)

Some of the steering damper, if fitted to the drag link (4Kg, so maybe 1Kg)

2/3 of each radius arm (as most of the weight is axle end, 20Kg, so 15Kg each)

Rims and tyres (10 Kg for RRC alloys, no idea on others, tyres vary so massively depending on size and construction, I wouldn't like to guess, but say in this application, 15Kg)

Half the springs (4Kg, so 2Kg each)

Half the dampers (4Kg, so 2Kg each)

Total: 120+5+0.6+1+30+50+4+4 ~ 214.6Kg, assuming HD track rod and drag link.

And the rear:

Half the trailing arms (10Kg, so 5Kg each)

Half the a-frame (20Kg, so 10Kg)

Half the springs (4Kg, so 2Kg each)

Half the dampers (4Kg, so 2Kg each)

Rims and tyres (10 Kg for RRC alloys, no idea on others, tyres vary so massively depending on size and construction, I wouldn't like to guess, but say in this application, 15Kg)

Total: 100+10+10+4+4+50 ~ 178Kg

Without know the specs of your truck, it's hard to say what the component weights are, but complete guesses are in brackets afterwards.

Any arithmetic issues are down to being a bit tired atm

*edit* If you use Trev's spring calculator, you need to convert it to pounds first

http://www.lr90.com/calculator.html

[Anderzander]

If you wouldn't mind posting up the calculations as you work through it it would make a very useful thread for others to follow ..

[Paul Woodward]

Thanks that's great. I found the thread about component weights and yes it mentions 100 & 120kg for the axles. According to BFG the tyres weigh 55lbs.

I know what is fitted at present so I'll calculate backwards from the fitted length to see what that works out at.

[Dave W]

I don't have the figures to hand but I went through a similar process last year and ended up working out the sprung weight from the springs that were fitted and their compressed and free lengths.

This method worked out pretty accurately and the replacement springs put the vehicle within a couple of mm of the calculated height.

I have a feeling that the unsprung weigHt worked out to be a lot more than I'd anticipated. I'll see if I can find the spreadsheet I put together.

[Paul Woodward]

Ok then, this is what's on there at the moment;

Front.

Britpart DA4202 (I know, I know!!) 390mm/15.35" free length. 230 lb/in.

Fitted length 11.46" averaged between both sides.

Therefore 3.89" @ 230 lb/in = 894.7 lb each side so 1789.4 lb for both. That's 813.4 kg.

The measured load is 1112 kg. 1112 - 813.4 = 298.6 kg unsprung.

Rear.

Bearmach BA2102. 445mm/17.5" free length. 295 lb/in.

Fitted length 14.5" averaged between both sides.

Therefore 3" @ 295 lb/in = 885 lb each side so 1770 lb for both. That's 804.5 kg.

The measured load is 943 kg. 943 - 804.5 = 138.5 kg unsprung.

That's not too far away from the figures approximated by Bowie69 above. I'll try the figures in the spring calculator and see what it comes up with.

It'll be interesting to compare your calculations Dave.

[Bowie69]

Well, I call that a fair way out actually, my figures I mean, not yours!

You are possibly missing one thing, possible tolerance in spring poundage, especially the Britpart!

[elbekko]

Should be fairly easy to calculate by amount of coils and coil thickness, no?

[Bowie69]

And the variance in quality of the steel...

[Dave W]

Found the figures for mine

My calculated unladen front spring weight was 363kg and unladen rear sprung weight was 394kg (each side)

Weighbridge had the front axle at 1060kg and 1000Kg rear (TD5 auto 90 hard top with full roll cage).

So, front axle unsprung weight each side would be 1060/2 - 363 = 167kg per side or 334kg complete.

Rear axle unsprung weight would be 1000/2 - 394 = 106kg per side or 212kg complete.

On mine I was looking for a specific height front and rear when the 90 is in expedition trim all loaded up but that didn't need a ladder to get in when it was unladen. For that reason the spreadsheet was used to bracket the heights (laden/unladen) for all the springs I could find data on. I'm pretty confident in the calculation because for both laden and unladen weights the spring height at each corner is within a few mm of the calculated height.

I think the front axle complete with CV etc... weighs significantly more than the rear axle. I can lift a rear axle case on my own but can't get close to lifting a front axle case with it's swivel housing etc... 20kg difference doesn't sound right to me. I don't think the calculated front axle weight includes the full swivel/cv housing. I can tell you a complete swivel housing without the hub weighs a damn site more than 10kg !

There might also be an effect of the bushes and gas shock absorbers as they can resist movement and supplement the springs respectively. The Koni shockers on mine, for example take nearly my full upper body weight to compress... assuming unsprung weight = total weight - sprung weight may not be reliable unless you replace all the suspension bushes with rose joints and remove the shock absorbers.

The important thing is that the sprung weights are in the right ball park given the shock absorbers you are using and the bushes you are using.