£20 DIY Corner Weight Measurement

[Roy Kemp]

Just managed a couple of hours in the workshop. Been meaning to get the corner weights measured for a while, so have had a bit of time to thing about how to do it without handing over the car to a competition prep company or shelling out a fortune for proper corner weight scales. So... The Kemp Method. You will need:

8 pieces of 30mm thick decking board, cut to 320mm long. 4 need bevelled edges.

1 Salter Max Bathroom scale, rated to 250kg, or equivalent.

Arrange as shown, the bevels used for getting the car on and off the wooden step more easily, so are placed at the rear.

Then, one corner at a time, replace the front wooden step with the scales and roll the car forward.

I took three measurements on each corner, and worked out an average:

NSF = 184.0 / 184.0 / 183.5 = 183.83kg

OSF = 167.1 / 167.1 / 167.6 = 167.43kg

NSR = 167.0 / 166.3 / 166.3 = 166.53kg

OSR = 167.4 / 166.6 / 166.2 = 166.73kg

So, this gives a total weight of 684.53kg, and a front/rear split of 351.27/333.27kg, which works out at 51.3% front to 48.7% at the rear.

Buggered if I can figure out why the left front is so heavy. Could be an un-even ness in the garage floor, or maybe the right front spring is stuffed? But, either way, I'd have expected to see the difference reflected in the diagonally opposite corner.

Anyway, that's how to get your corner weights (and puzzle yourself with the results) for twenty quid.

[James Doulton]

I did a similar thing but with 4 sets of 'real' scales from Tescos at £4.50 each. They were only rated to 130Kg, so I used 2 under each wheel with a plank to spread the load as I did one axle at a time.

My Melos weighed 620Kg with a Pinto engine and an Escort gearbox. My NSF was also heaviest which I put down to the engine being offset from the centre of the car by about 1".

[Dave Adams]

floor has to be mirror flat to get accurate measurement...

springs......i made my own spring rate measuring machine it is a frame work over a platform on which i place a bottle jack on top of a set of bath room scales.... i compress the springs either 1/2 inch or a full inch....and take a reading i have two bathroom scales and they read very similar. i also do three reading and average the scores....my 150 lb/in springs came out at 148 lb by using this method....  

i have weighed two of my phaetons the pinto engined one was 440 kg front axle and 330 kg rear.....heavy.

i went to my local VOSA HGV axle weigh bridge.... they are free to use. and are VERY accurate.

my last phaeton was a 1.8 zetec and it was 320 front and 310 rear...... from experience i would recommend springs about 180 lb/in front and about 130 lb/in rears i have seen cars with 250 lb/in springs up front and 200 lb/in at the rear (driven them as well.....) they were all awful on the road sliding all over the place and harsh to drive the softer springs improve the ride and keep the car glued to the road.

[James Doulton]

@Roy you can calculate the spring rate if you measure the wire thickness, the spring diameter and the number of turns. There are online calculators, like here.

[James Doulton]

@BV so yours was heavy on the same corner as Roy's - interesting. Just a fluke?

[Roy Kemp]

Oh, and just in case anyone else has the same crappy bike shocks as me, they're 11 & 3/8" between the centres of the eyelets in the fully open position, and 8 & 1/2" in the closed. And there's no poundage info stamped into the springs anywhere, so don't waste your time looking!

[Big Vern]

@SteveK now why didn't I think of that LOL

[Roy Kemp]

Funny you say that Vern, I know my top wishbone bushes are a bit iffy - the rubbers appear decent but the bolts are seized in the tubes...

[Steve Kerswell]

This is what you need Big V, works a treat for me

[Roy Kemp]

To be honest, I'm not looking to set corner weights right now, it was just to gather some data so I can order a decent set of front coilovers. The numbers I've come up with will mean the springs and dampers will be a decent "baseline" spec for the car weight as opposed to complete guesswork.

[Big Vern]

The main problem with cheap scales is they are very inaccurate at the high weight ranges. I step on mine every morning and they keep saying 16stone which can't possibly be right :o

What is more important is the distribution of the weight. Roy's odd NSF corner weight could be a measurement error nut it could easily be real with more preload, a sticky damper or bush.

For info these are our results:

q562fdd corner weights
Maximum Speed 110 mph on A45 (bottle out)

Measured Corner Weights                           Axle weights      Total Weight      Avg Corner Weights

                                                                                       
Kerb Front  181.Kg   167.Kg   51.86%              348.Kg              671.Kg                174.Kg
         Rear  162.Kg    161.Kg  48.14%              323.Kg                                          161.5Kg