Design weights
Discussion
This has probably been discussed before but here goes,
just filling VOSA form in to apply for SVA, the only question bugging me is this, according to build manual it's approx 680kg total gross but how do i work out axle weight design for front and rear ?
If i took car to pulic weighbridge and got computer readout would that be enough to satisfy 'official documentation' as the build manual is not much more than photocopied handwriting !
just filling VOSA form in to apply for SVA, the only question bugging me is this, according to build manual it's approx 680kg total gross but how do i work out axle weight design for front and rear ?
If i took car to pulic weighbridge and got computer readout would that be enough to satisfy 'official documentation' as the build manual is not much more than photocopied handwriting !
If you doubt the manufacturer's information and / or they won't split it into front and rear axle weights for you, that's the only way you'll do it. I've taken cars (on a trailer of course!) to my local scrap metal merchant before now and asked to use the weighbridge. The car needs to be as finished as possible with all the stuff you'd normally carry (jack, spare wheel, screenwash, full tank of fuel, CD changer etc). In addition, you'll need a weight of 68kg in each seat and 7kg for each occupant in the boot. If you can't find people who weigh this much, make up the difference with bags of sand or similar. Roll the car so that the front axle ONLY is on the weighbridge. It doesn't matter where - just as long as the rear wheels are still on the ground off the weighbridge. Ask for a ticket (usually only a couple of quid). REMEMBER not to stand on the weighbridge while the weight is being taken! Then roll the whole car on and do the same. Finally, roll it so that just the rear axle is on and get a third ticket. You don't have to do all three (just front and rear axle) but I like to get the total to check that the front and rear axle weights add up to the same as the total (given that these weighbridges usually weigh 10 ton trucks so they might well be 10-20kg out at small loads)!
The weights that you get SHOULD be your "design weights" for front axle, rear axle and total respectively. YOU CAN DECLARE MORES THAN THIS, but not less! In fact, I think it's always a good idea to add another 50kg to each axle to allow for any extras that you might add in future as well as discrepancies between the weighbridge there and at VOSA.
The weights you declare are used in the brake test. The lower the weight, the easier it will be for the car to pass on overall braking efficiency, but the more chance you have of failing because you've under-declared the car's design weights. As most kits use brakes off something MUCH heavier, I tend to err on the heavy side. If you go too far, the wheels might lock up in the rollers before they reach the required braking efficiency because there isn't enough weight on them during the test.
The weights that you get SHOULD be your "design weights" for front axle, rear axle and total respectively. YOU CAN DECLARE MORES THAN THIS, but not less! In fact, I think it's always a good idea to add another 50kg to each axle to allow for any extras that you might add in future as well as discrepancies between the weighbridge there and at VOSA.
The weights you declare are used in the brake test. The lower the weight, the easier it will be for the car to pass on overall braking efficiency, but the more chance you have of failing because you've under-declared the car's design weights. As most kits use brakes off something MUCH heavier, I tend to err on the heavy side. If you go too far, the wheels might lock up in the rollers before they reach the required braking efficiency because there isn't enough weight on them during the test.
Only guessing - don't take it as gospel.
Get the weight of the car with fluids. Add to that 2 X 80Kg for occupants, plus say 50Kg for luggage. Distribute the exra weight across the front/rear axles, and you shouldn't be far off.
Having said that; here are the SVA figures from my GTM Libra which is a mid engined car, note how the design weights are rather high!
Actual weights: axle 1 360, axle 2 474
(Note - somehow my Libra is 834Kgs - the heaviest I know!)
Weight with driver: axle 1 404, axle 2 510
(Note - I don't know if at SVA they weigh the car and driver, then take off his declared weight, or weigh it empty and add his weight on)
Design weights: axle 1 595, axle 2 795
(This has produced a design gross weight of 1200 That's a LOT!)
Anyway - hope it helps.
Get the weight of the car with fluids. Add to that 2 X 80Kg for occupants, plus say 50Kg for luggage. Distribute the exra weight across the front/rear axles, and you shouldn't be far off.
Having said that; here are the SVA figures from my GTM Libra which is a mid engined car, note how the design weights are rather high!
Actual weights: axle 1 360, axle 2 474
(Note - somehow my Libra is 834Kgs - the heaviest I know!)
Weight with driver: axle 1 404, axle 2 510
(Note - I don't know if at SVA they weigh the car and driver, then take off his declared weight, or weigh it empty and add his weight on)
Design weights: axle 1 595, axle 2 795
(This has produced a design gross weight of 1200 That's a LOT!)
Anyway - hope it helps.
I would suggest hiring or borrowing a proper set of corner weight scales. Most race workshops should have them, if you know someone there they would probably let you borrow them. If not I'm sure it wouldn't cost much to hire them. Accurate weights for all corners, cross weights, F/R & L/R splits.
When my car was SVA'ed, I used figures for a similar car (same make & model). Come test day, the guy weighed it but said I didn't have enough allowance for driver, passenger and luggage. Bascially, my car was relatively heavy for type (being full of crap like A/C etc) so being the helpful and practical guy he was, the tester just suggested some more realistic figures. The importance of getting them close-ish to something sensible is that the tester uses them for the brake efficiency test and also when assessing the chassis and suspension. Basically, if you say the design weight is 4 tons, he will expect lorry-like suspension & chassis and it's unlikely the brake figures would pass.
HTH
HTH
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