If you've got a rolling chassis, you could weigh it for yourself. I'm waiting until the car's built up to do that for springs.
Pete B.
Hi guys,
trying to do some calcs for brake compensator valve & to estimate weight transfer under barking I need to know the hieght of the centre of
gravity. Now I know that a lot of you have built 3D solid models of the vehicle (without driver...) and have attempted nifty suspension calculations
so I'm hoping the information is "out there". I'm looking at a bike engined car with sierra based IRS.
For those who will (undoubtedly) say get a bias bar arrangement instead - that's fair enough but you have to tweak it for the road conditions - a
well sussed compensator setup does it automatically for you!
Or better still - only use it when it's dry & sunny!
Cheers
Bob C
Just the other day I read about a guy who had his measured at 9.75" as part of his SVA exam, but blast if I can find it today so you could
compare cars.
If you've got a rolling chassis, you could weigh it for yourself. I'm waiting until the car's built up to do that for springs.
Pete B.
Bob, have you got a couple of bathroom scales, tape measure and a jack? You can measure your CoG, rather than relying on someone else's, possibly different/unreliable data.
Hmm - fraid measuring/weighing won't be an option for a year or more....... 10 inches sounds lower than I'd expect - I have a plan now
though - one or two guys have logged the weight of all therir bits - if I perm that against expected installation height I should get a result - job
for lunchtime....
Cheers
PS original post, meant braking! barking does apply to us all though dunnit....
For SVA purposes I'm sure they take the crankshaft level as the C of G in a car engined locost, but I don't think that would work in a bike
engined format as they are usually mounted higher in a cradle.
yours, Pete.
quote:
10 inches sounds lower than I'd expect
Well I whacked heights and weights of the biggest lumps into excel & got the answer 41cm. Course the biggest lump of all was me at 105kg..
Yeah rear proportioning valve thing - you can get adjustable ones off the main brake vendors - I'm still looking at lightweight willwood 2pot
calipers all round with a handbrake on the transmission (doubling as big cog for electric reverse and speedo sender) so I'll have to do some sums
to get my brakes right! Means brakes are same front and back - convenient.
Bob C
Just for a laugh:
[Edited on 13/8/03 by pbura]
nice pic - made me think about anti- dive suspension (OK so the pic is illustrating cornering behaviour) Has anyone bothered with anti squat &
anti dive suspension? (front inner wishbone pivots pointing up a bit at the back)(back opposite).
Just wondered what it was like (I reckon the 'dive' is part of the feedback & actually quite handy...)
cheers
Bob C
i designed one for F27 when i was at uni, a prototype was built but i don't know how it behaved . To achieve 100% anti squat and dive requires
the pivot points of the wisbones to point at the C of G, these angles really make the suspension design very complicated
I was wondering just yesterday how anti squat and dive would work, seems obvious now! that would feel odd wouldn't it though, the nose not dropping under braking? Makes for consistent steering i guess...
lots of talk about it here
clicky click click
The reason I put the pic up was because the CoG appears so incredibly low at maybe 13" for that big V8 sled, and here's poor Bob with a
16" CoG in a Locost! 
I don't think the picture's very lifelike with regard to the CoG or the 50/50 apparent weight distribution. However, it came from a very
interesting site with much good info about vehicle suspension and dynamics, even though geared to Trans Am-type cars:
http://members.aol.com/sccacuda/cars/1SmthTa.html
In either anti-dive or anti-squat, you're forcing the wheels into the droop position to cancel the downward motion. There's a couple of
methods, and you can have less than 100% "anti". It's best to read as much as you can for the pros and cons.
In Tune to Win (and I'm paraphrasing here), Carroll Smith doesn't like anti-dive in light cars because it causes the front suspension
to bind, but he thinks some anti-squat is OK in a high power-to-weight situation, but no more than 20% in most cases.
Superperformance says they use both, so it's worth thinking about. The front wishbones on the Superperformance are angled very slightly for just
a partial amount of anti-dive (10% is my guess). It's hard to tell what's going on at the rear.
Pete B.
As you brake, the weight feels like it falls onto the front wheels, but it really turns around the CoG. By aiming the wishbone pivots at the CoG the
braking force cant press down on them, so there is less or no dive. Usual WB pivots aim below the CoG so the weight is above their plane and can press
down.
Obviously you cant point the WB pivots to far otherwise their primary function would be compromised.
I think it is only suitable to cars with a low CoG, like F1 cars, which need to avoid pitch change cos they run very low.
and if you imagine a car with huge wheels, with the entire car suspended below the wishbones, its nose would rise under braking.
quote:
and if you imagine a car with huge wheels, with the entire car suspended below the wishbones, its nose would rise under braking.
I deleted most of my last post because it was way, way off the mark!
We had a massive power outage last night, so I spent a portion of my slack time staring at anti-dive diagrams until I finally got the point.
With full anti-dive, with the wishbones converging on the CoG, the shifting weight from the CoG pushes against the suspension but cannot get on top of
it, to compress the springs.
This is very similar to the situation of having the roll center at the same height as the CoG. The weight transfer stays lateral to the springs, and
is expressed as a thrust, binding the suspension.
Ta dah!
Pete B.
P.S. Geez, Joel, isn't this what you said?? Please excuse, I'm doing this as relief from a crushing work deadline that's driving me
nuts!
[Edited on 15/8/03 by pbura]