Bob C
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| posted on 10/2/06 at 12:03 AM |
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wheel weighting
I was down at aldi today - bought 2 sets of bathroom scales at £3.99 each.
That's me sorted when I want to set my spring perches!
They go up to 130kg, though you'd probably get 10 or 20kg more on by winding it back from zero. Plenty for a 500kg car.
cheers
Bob
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Kissy
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| posted on 10/2/06 at 06:55 AM |
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Borrow some calibrated/known weights just to know what you actually have as opposed to what is reading on the scales.
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smart51
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| posted on 10/2/06 at 08:10 AM |
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for corner weighting, your scales don't need to be calibrated. So long as all readings are the same, then you're OK.
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Bob C
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| posted on 10/2/06 at 09:04 AM |
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me - I've got a calibrated lardy body ideal for the purpose....
bob
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MikeRJ
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| posted on 10/2/06 at 11:12 AM |
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quote:
Originally posted by Bob C
I was down at aldi today - bought 2 sets of bathroom scales at £3.99 each.
That's me sorted when I want to set my spring perches!
They go up to 130kg, though you'd probably get 10 or 20kg more on by winding it back from zero. Plenty for a 500kg car.
cheers
Bob
500/4 = 125kg, and I doubt the front rear split of a locost is 50/50, so you may find scales not useable directly at one end of the car.
Would be quite simple to make a lever system to reduce the weight seen by the scales though.
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Hellfire
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| posted on 10/2/06 at 01:05 PM |
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Don't forget also, that when corner weighting, you need to take into account the weight of the driver, so don't forget to add this to your
vehicle weight 
Phil
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kb58
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| posted on 10/2/06 at 03:08 PM |
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... and while you're sitting in the car you won't be able to read the scales... so a helper's needed.
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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C10CoryM
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| posted on 11/2/06 at 03:29 AM |
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If the weight is too high for the single scale put two under each wheel with a 2x6 across them. You will have to weigh front/back seperately but oh
well.
Also if you manage to make it work one under each wheel be carefull lowering onto the scales. You will need 2 jacks otherwise the weight will be too
high on one end while jacking the other.
Cheers.
"Our watchword evermore shall be: The Maple Leaf Forever!"
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JB
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| posted on 11/2/06 at 07:56 AM |
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Corner Weight Advice
The easy way to see if scales are the smae is to stand on them!
When setting corner weights accuracy is normally harder to achive than you think.
1) The scales need to be level. How you level them is the difficult part. I used an 1800mm Stabila level which was accurate (I think to 0.5mm
in1,000mm) This is as accurate as Lazer levels and cost under £40.
Level is important for the following reason. If you have springs that are for example 500lb / inch, and you have a 12.5mm (1/2" level
inaccuary you will then have a 250lb inaccuracy in your corner weights! I know this is an extreme as the springs are likely to be softer and hopefully
the level better, but it does show how critical level of the scales is.
One problem with the bathroom scales is they normally move down when weight is applied, effecting the level!
2) Suspension and tyre stiction. You need your suspension as free and easy as possible, so it sits in its as running position. When you jack up an
independant suspension there is camber change which effects ride hieght if the suspension is not settled.
So remove or slacken off the dampers and roll the car backwards and forwards whilst bouncing the suspension. I know this is difficult when you have to
get the car onto scales.
You can get trick and build some plywood or aluminium setup wheels with sideways sliding bearings on the bottom.
Or even simplier 2 pieces of steel with oil between them under each wheel.
3)Driver weight. You must ballast the car with weight to represent the driver. I used bags of sand on the seat and the floor to represent my legs.
4) How to set up the wheel weights.
There are different ways to do this. The common way is to try to get the balance the same each side, which is quite simple on a single seater. On an
offset vehicle the way is to get the front wheels the same and live with any descrepincy on the rear.
However there is another way that accepts you will have different wieght each side in an offset vehicle, so you get the front rear proportion the same
on each side.
5) Repeatability. To check how accurate you are, take the car for a drive and then recheck your corner wieghts and see if they are still the same.
Often getting good repeatability to within even 100lbs is difficult.
6) DIY balance beam.
I made a balance beam. Make a strong level beam with a pivot in the middle and sit the front wheels on it. The rear wheels are on level pads. Then put
a spirit level on the beam and adjust the corner weights until the beam sits level.
I used this method and then checked it with real digital scales and it was surprisingly accurate. The best bit is that is cost nothing to make as I
was using up steel from my chassis build.
John
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Peteff
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| posted on 11/2/06 at 10:00 AM |
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I was down at aldi today - bought 2 sets of bathroom scales at £3.99 each.
An added benefit of this is if you stand with one foot on each you only weigh half as much  , instant weight loss. What happens then when you have a
passenger or luggage or the tank is low? Is it a bit extreme for road use, I just fiddle about with the springs till it feels drivable and
doesn't throw itself at the scenery, am I missing the point?
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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JB
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| posted on 11/2/06 at 10:17 AM |
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quote:
Originally posted by Peteff
What happens then when you have a passenger or luggage or the tank is low? Is it a bit extreme for road use, I just fiddle about with the springs
till it feels drivable and doesn't throw itself at the scenery, am I missing the point?
You are correct that if you add a passenger then the corner weights will then go out. You have to decide on what you think will be your normal
driving.
A bit extreme for road use? It all depends on how you view the effort required toget the corner weights close. For me it is part of the set up. You go
to lots of effort to build a car so why not get the most out of what you have built. You would not run an engine without getting it tuned correctly or
not set your tracking or balance the wheels or set the camber and caster etc.
Effectivly it is free handling.
However I am unsure just how much difference to the feel and ultimate grip there is to having accurate corner weights and having wiildy different
ones.
Think of a table with 2 opposite legs longer than the others.
John
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C10CoryM
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| posted on 11/2/06 at 02:59 PM |
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If you are running swaybars with adjustable end links you can also set them up. Swaybars should be diconnected for weighing but when thats done
reconnect and adjust swaybar endlinks until the load is the same on both sides.
"Our watchword evermore shall be: The Maple Leaf Forever!"
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Bob C
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| posted on 11/2/06 at 05:25 PM |
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JB - balance bar - love it! (though actually it would cost me more than 2 sets of scales....)
The thing I'm anxious to avoid (re corner weighting) is the situation where all the weight is on front right and back left. This would look
straight and level & slide all over the place!
I take the points about doing it on a level surface plus the effects of stiction in the suspension - my solution was going to be to physically lift
the front (say) of the car up with a jack; slot the scales in place then put the car down on them. After JB's post though I think a better plan
is to use a spirit level and jack to determine the balance point front and rear (find the position between left and right where car doesn't
pitch sideways when the jack starts to lift it)
I'll still use the scales to cross check and measure weights for SVA!
BTW JB - been a fan of your work for some time...
Cheers
Bob
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