Hi Guys,
just thought I'd post the spreadsheet I used to try to estimate the height of my centre of gravity.
I still think the only way to measure it is to balance the car on its left wheels & measure the angle - maybe check on right too - any brave souls
tried it?
Anybody reckon their Cof G is only a foot up? any evidence???
cheers
Bob
I calculated mine with a spreadsheet too, measuring x and y coordinates of every component. In my mid-engine Mini it ended up 16" above ground.
The engine and driver were the main reasons it's so high.
quote:
Originally posted by Bob C
Hi Guys,
just thought I'd post the spreadsheet I used to try to estimate the height of my centre of gravity.
I still think the only way to measure it is to balance the car on its left wheels & measure the angle - maybe check on right too - any brave souls tried it?
Anybody reckon their Cof G is only a foot up? any evidence???
cheers
Bob
There is another way to calculate the height of C of G.
Weigh the corners of the car with the car level.
Then jack-up the front of the car to a height equal to 25% of the wheel base and re-weigh the four corners.
The weight distribution will have changed and this plus some maths will give the height of the C of G above the tyre contact patch.
I happen to know that most fwd saloon cars have thier C of G in the 450-600mm range. I estimated my car at 320mm and used that in my brake balance
calculations.
looking at your spreadsheet, I think you have put some things a bit high. The wheels and suspension are likely to have a CofG around 250mm unless you have huge wheels. the engine will be a bit lower as will the bonnet and rear body work. Most of the book chassis is 13" high and has 4-5" of ground clearance so the CofG will be more like 300mm. Your centre of gravity will be lower than the 400mm of your estimate.
I can't think of a single reason why I would want to know the height of the centre of gravity of my car, sorry and all that.
peteff - are you not the teensiest bit curious.....
simple answer is that SVA need it for their brake bias calculationss - better answer is that YOU need it for your brake bias calculations!!
The 30mm CoG for the wheels was based on an inflated wheel being 2ft diameter - I think that's one of my better estimates.....
Engine - god knows where the CoG of that is - 1/2 way up?
chassis - most of it is13" high but the biggest tube is the rollover bar & that's well over a meter high!
Yeah - JAGs method would work - I might try it one day to see how good it feels from a "build-up of inaccuracies" viewpoint (mind you
I'd be using bathroom scales.....). See if it agrees with the "tip it on its side" method!
cheers
Bob
Have you taken into account the internals of the engine.
Crankshaft represents a large amount of an alloy engine.
Oil may be 5kgs, but then depending if the engine is running will depend on the position of the oil.
Do centrilfugal forces effect Cof G on moving parts, wheels, cams,gearbox
Oh my, Oh my,so complicated and so pointless.
Sorry just having a laugh.
I put my battery in the engine bay to reduce the CofG so I can't say too much.
About 375 mm
The SVA man told me they use the centre of the crank when I took mine. Their computer takes care of the calculations and mine passed so I'll leave it to them.
No no no
The engine will be running, right, so you really need to come up with a model to predict the oil distribution in the engine during those circumstances
or how can you possibly calculate the COG?!
Also, consider that as you brake your car will dive on the suspension, so you have a dynamic COG. You really need, therefore, to express the COG as a
function of braking force if you're going to come up with useful results.
Liam
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[Edited on 5/4/06 by Liam]
The 30mm CoG for the wheels was based on an inflated wheel being 2ft diameter - I think that's one of my better estimates.....
Time for an edit I think
Sorry........couldn't resist it
Mick
That has been said, but I'm not one to take umbrage. If the engine's not running, why the f**k do I need the brakes.
[Edited on 5/4/06 by Peteff]
quote:
Originally posted by Peteff
The SVA man told me they use the centre of the crank .
Petraff drive up a hill in th ePeak District and switch of the engine and depress the clutch then you will know why you need brakes with the engine
not running!!!!
Caber
Cabrer - But most Locosts don't have servos, so if you turn the engine off and apply the brake pedal, you will err......stop!
SVA bloke DOES use centre of crank for calculations, regardless. The computer takes care of the rest.
Me, I just slapped a master cylinder on and drove the thing - no calculations - passed SVA no problems.
Marcus