Corner weighing

[Graeme Smith]

I've just noticed the rear end of my live-axle Seven looks very lop-sided. The drivers side is perhaps an inch or more higher than the passenger side (driver-out but still higher with driver in). I had new springs and dampers put on during the winter, and the car flat-floored. (The car was set up over-height to allow the springs, etc to settle. without ending up under minimum height - its a Graduate race car).

 

When I first drove it on the track after I hated the set-up, so I've raised the rear, lowered the front and increased the ARB diameter. Maybe during this I've turned an adjuster the wrong way and screwed up the balance... Certainly the passenger-side platform is very near the bottom of its adjustment, whilst the drivers-side one is higher up the thread.

 

I could do with sorting this out ASAP as I'm racing at Pembrey next weekend. I was thinking about using some bathroom scales to see if the rear corner weights were badly out, but reading some of the past threads is not as simple as it sounds...? But might it help me figure out if thecar if badly un-balnced? (I was going to buy a pair of 150kg scales. Just weighing the rear would tip the car forward making the rear end light enough to weigh on 150kg scales. I'm not too bothered about ultimate corner weighting here; just seeing if there's a major problem. Am I barking up the wrong tree?).

 

Or does anyone know a garage with corner-weight scales near Macclesfield (Cheshire)?

 

Sightly off-subject, but why do corner weight scale cost so much. Four sets of bathroom scale = £80. Cheapest set of corner weight scales = £1000. Okay they will be more durable, but you'd think a company could do a set for occassional amateur use...

[NickD]

A simple & cheap setup is to buy 8 sets of ordinary (19stone) bathroom scales (£3.99 each from Homebase). Cut 4 planks of wood and use 2 scales/1 plank on each corner. I've weighed several cars and then checked their weights on the Oulton Park weighbridge and they match to the nearest kg. You have to do some sums but I've produced an Excel sheet to give the weights and % splits which I could email to you if required.

[stevefoster]

I DIY this too.

Having a flatfloor is key to success.

Phil and I put down a screed and then levelling compound to

get this.

[Allan Haighton]

I'd echo Nick and Steve on this. A pair of 150kg scales doesn't work too well and is very fiddly to work with. However, 8 of Argos's cheapest and 4 short planks is easy peasy in comparison - but you do need a flattish garage floor.

 

There's a set of a simple equations for working out what the corner weights should be - just use a calculator. E-mail me if you need them.

 

With a car set up to allow for the driver's weight, I'd expect the drivers side spring collars to be a bit higher up the sleeve than the passenger's side.

[Allan Haighton]

Should have put this in the last post - some sample data might help.

 

Car: live axle x-flow with too many non-essential parts on it.

Corner weights measured using 8 bathroom scales this weekend:

 

1 With 80kg of of bricks in the passenger seat, a full tank of fuel, no spare wheel.

Front nearside 155kg

Front offside 161kg

Rear nearside 165kg

Rear offside 175kg

Ride height: 75mm under sump,

130mm at rear of front wishbone,

146mm at front of rear wheelarch

I calculate these weigths are correct to about 1 kg (lucky or what)

 

2 Same car, with the bricks removed

Front nearside 156kg

Front offside 138kg

Rear nearside 138kg

Rear offside 143kg

 

Hope this helps.

 

 

 

 

 

[stevefoster]

Forgot to say, I am lucky enough to have borrowed

4 roller plate that allow the front suspension droop and sag

to be taken up. The scales won't like a sideays force as the

front of the car is lowered. you really only need 1 roller plate

and 3 planks of the same height to keep things level.

[garyedwardc]

Shouldn't the weight on each diagonal be equal?

[Graeme Smith]

Thanks for all the replies. I've found a local garage with some corner weight scales and I'm going there tomorrow night. I spoke to the mechanic and he was on about disconnecting the ARB for the weighing - any comments on this?

[Dave Wilson]

You must disconnect both anti roll bars when setting up corner weights. If you are setting up for competition use, it's worth spending loads of time on corner weights and ride heights, it will pat dividends

[Graeme Smith]

Do you need to disconnect the ARB just for weighing? Its only got a front ARB. If I do make any adjustments, its just going to be to the rear (it was flat floored properly, but the rear's where I think I screwed it up) - would having the front connected mess up any rear adjustments.

 

Tonight is only 15 minutes on the scales to see if I've got problems and make rough adjustments before the weekend's race. I'll get it done properly when I've more time.

[ECR]

Yes you should disconnect anti roll bars. This is because they may well be exerting a preload (due to twist in manufacture for example). However you should also remove any twist when re fitting (not always possible I appreciate.)

[Barry H]

ARB disconnection is an interesting point. Philosophically I have difficulty understanding the need to disconnect for the following reason:-

 

If the car is set up, as say Allan's is (bricks et al) with the ARB disconnected, as soon as Allan (or bricks) get into the car with the ARB reconnected the corner weighting will be different from the set up with the ARB disconnected. This must be the case because the front ARB is resisting the twisting caused by Allan's weight by weighting up the front wheels differently.

 

Therefore to my mind it would seem logical to set up the car with ARB connected as that is how it will run, pre-load and all.

 

I am sure I must be wrong so can someone please explain.

 

Barry

 

 

[Paul Ranson]

Ideally you set the car up on the scales without the arbs, then you refit the arbs and the weights don't change. This is obviously unlikely with a Caterham front bar.

 

Paul

[Allan Haighton]

A bit late, I know, but my impression was that removing the arb is necessary if a 'PACE' type corner weight guage is used, rather than weigh scales.

 

With a 'Pace' type gauge, one wheel at a time is lifted clear of the floor. With the arb in place, this will produce an incorrect reading.

 

With a complete set of scales, all four wheels stay in their normal position (ie on the ground) during measurement. So I leave the arb in place.

 

[stevefoster]

I set mine up with the ARB on.

It was handling/gripping/braking very nicely at Lydden. There are some trail braking corners, some drifts, some heavy braking zones, and an understeery/oversteery hairpin.

I will not change the set up.

to me you want it set up as it will run on the road i.e. ARB on

or it might be different when it's connected.

I was using the 8 B&Q scales method