Hi!
Maybe someone has calculated how high is front RC for locost "book" suspension?
And how high (low) is resonable (optimal)?
And also - just stupid crazy idea - what happens if I construct suspension with RC higher than CM? Would car lean towards inside of curve?
I did, for a car with a ride height of 6", book chassis and wishbones, and Cortina uprights, and came up with about 3.5" for a RC height.
Answers may vary 
, but I think it's in the ball park. Seems pretty reasonable, as it would be about 1/3 of the rear RC height using 13"
wheels and a Panhard rod.
Somewhere I read that a RC above the Cg would cause the car to lean in, but if this were a great idea it would be standard practice, I suppose. High
RCs cause lateral thrust and wheel jacking. Don't ask me explain this last point; I understood it at one time, but the knowledge has fallen out
of my ear.
Pete
Thanks a lot for your answer!
Only problem is that my rear RC is quite low (102mm, when ride height is 140 mm). And I don't know shoul I try to lower it or no. Also there is
no much room for that. Maybe I just leave it and put rear anti rollbar...
Recently found usefull advice - You should design your suspension BEFORE you design a chasis.
Wish I knew it couple months earlier. 
I've got an analysis of the book chassis on my site at http://www.7builder.com/SuspensionGeometry/ based on some measurements of the book
uprights I got off the web.
Close to Pete's, the RC I get is 3.3" on the front. From what I've read, you want the front RC lower than the rear. I've no
practical experience to validate that.
Suspension program is my own (so ymmv), the measurements that I used are from the drawing that's available there too.
HTH!
It's not too late to check your design and to make sure that your front and rear camber curves and RC movements are in control and compatible
with each other. You may have done this already, but if you haven't, I mentioned some good free tools on this thread:
http://www.locostbuilders.co.uk/viewthread.php?tid=11057&page=2
You must have your suspension geometry worked out at this stage of your build, but springing and anti-roll bars can wait until the car is otherwise
finished, and you can weigh the corners and determine Cg location. At that point, you can determine if the springing needed to control roll is too
stiff for comfort, in which case you will need ARBs. It would probably be good to assume that you are going to use them.
A great example of an analysis that would do the job is Smithees Weight Transfer
Worksheet. Notice how they are able to predict the roll angle of the chassis at 1G lateral force, and relative roll stiffness given by the
front and rear suspensions (which affects oversteer/understeer).
I also suggest that you contact Tudor Miron, who has at times generously offered to use his suspension design software to help other builders.
BTW, I really like your Russian drill! Got a hammer and sickle to go with that?
Pete
Thanxs!
It seems that there is lot of research to do ...
Ok, gettin' back to CADs
As stated in Autocar story about an experimental independent rear suspension 7.
Original Deon chassis
rear RC 120mm
front RC 60mm
New Indy design
rear RC 65mm
front RC 30mm
And for interest this is the original Elise
rear RC 75mm
front RC 30mm
My own analysis suggests that low is good down to about 1 to 1.5 inches. The new Caterham and the Elise front RC values fall right in the middle of
this range. Below this RC height road bumps can cause some strange effects on suspension geometry. F1 cars go down to about 3/4 inch at the front but
these have near zero suspension movement and run on near perfectly flat race tracks.
quote:
Original Deon chassis
rear RC 120mm
Were there any other clues in the article about camber change, etc? quote:
I wonder, how do they get it so low?
). A WOBlink or Mumford link would be the best way to get a low RC on a solid axle, particularly the Mumford as the
RC point is virtual rather than a physical point on the linkage, helping greatly with ground clearance issues. 
) Can't imagine Caterham using a WOBlink or a Mumford link, hence my confusion.
Pete
scuse my ignorance, but what the hell is roll centre
I still cant work out what the engine types all mean. DOHC SOHC WTF etc. Ok not the last one!
I also cant work out how any of this matters. You dont like it, then you goto the scrappy and change it!
Dominic,
You need to read Alan Staniforth's book 'The Race and Rally Car Source Book' which details the string computer. This unbelievably
simple tool allows an almost infinite number of suspension measurements to be visualised and measured in less time than you would believe possible.
quote:
Originally posted by Kitlooney1000
scuse my ignorance, but what the hell is roll centre
If you built by the book, you're in good shape. 
Pete,
I'm in agreement with all of that except for
quote:I would qualify the word "lower" there to be "further away from the centre of gravity". The distance between the CG and RC is called the roll couple. The roll couple is the lever arm that cornering forces acts on to roll the chassis around the roll centre. You already know that of course, this re-iteration is just for kitlooney's benefit.
The lower the RC, the more the car will roll.
I have some schematics and descriptive text if anyone is interested. Dominic,
I forgot you have struts! So I just did a Google and found a schematic showing how an RC is determined with struts; here's a link for those who
are interested:
http://www.miracerros.com/mustang/t_roll_center.htm
I've been staring at this thing for the past 20 minutes.
I think a 3-position analysis (similar to what's on my website) would work, solving for the bottom chassis pivot point.
Considering given data:
1. The outboard control arm position and strut angle are as per the donor uprights.
2. I'm wondering, is there such a thing as an optimal height for a strut, or do you just make them as long as possible, for the least change in
IC length with chassis movements? There's got to be some reason they make them so long! Or maybe you've got a particular strut you are
using, in which case the upper strut mounting position is now a known factor.
So, armed with these three points and a preliminary assumption for RC height, you could plot your chassis in three positions, with the wheel at the
desired camber, and see if there is an inboard control arm pivot that will satisfy the conditions.
Maybe you'll remember some time ago that you and I were discussing 4-bar linkages (on Locost Theory, I think) and how to solve them. After that,
I read an engineering mechanics book and learned about 3-position analysis for solving linkages, on which my drawing exercise is based. As I recall,
the technique works on sliding joints (such as a strut, before the innuendo starts) as well.
The way this went for me with the wishbones was that I didn't quite get the camber I wanted. However, my expectations were unrealistic, as I
later learned, and what I had was about as good as could be expected. RC control was perfect.
Hope this helps, really!!
Pete
I did calculations of my front and rear suspension, and got results:
Front
Rc height 3.2 inches
At 2degree right roll, left wheel camber -1.33, right 1.27, rc lateral movement -0.013 inches
At 1 inch bump wheel camber 0.48 degrees, at 1 inch drop -0.67.
Rear
RC height 6.59, static camber 0.3 degrees
At 2degree right roll, left wheel camber -1.09, right 0.4, rc lateral movement -0.26 inches
At 1 inch bump wheel camber 1.15 degrees, at 1 inch drop -1.85
May be you can share your numbers just to compare or give some judgement how bad is it?
Struts are made long because the braking torque is trying to put a bend in them. This makes them stick under braking - so your going into a corner
with the brakes on & the suspension stops moving - not good! Of course if you have inboard brakes it's OK.........
The longer the strut the less the brake induced stiction.
Bob C
quote:
Originally posted by Tigers
I did calculations of my front and rear suspension, and got results:
Front
Rc height 3.2 inches
At 2degree right roll, left wheel camber -1.33, right 1.27, rc lateral movement -0.013 inches
At 1 inch bump wheel camber 0.48 degrees, at 1 inch drop -0.67.
Rear
RC height 6.59, static camber 0.3 degrees
At 2degree right roll, left wheel camber -1.09, right 0.4, rc lateral movement -0.26 inches
At 1 inch bump wheel camber 1.15 degrees, at 1 inch drop -1.85
May be you can share your numbers just to compare or give some judgement how bad is it?
I plugged in 0
static camber for comparability. Syd,
Won't disagree that there aren't a few ways to skin this cat I thought that perhaps we had an issue as far as whether the cat required
skinning at all 
Mr. Bura to you (apparently)
quote:
Originally posted by Syd Bridge
What's all this talk about cats, and removing the coverings thereof??(Pussy fetish/obsession??)
I enjoy slightly fractured metaphors, btw, and use them frequently. I wonder how Tigers did his? thanks for the explanation, i now have a head ache so i think i will stick to the books design for now.
If read quite a bit about this stuff myself out of interest - but no good real world experience. I *think* Pete's in the same boat - sorry if
I've assumed too much Pete. How about you Syd? I'd love to hear some war stories like: "We were having a real problem with the car,
till we realized the roll center was too high/low (or moving too much, or whatever). We fixed it by ... and it handled great after that".
I might have stories of my own like this once I get my own car on the road - but I hope not .
Good call, Mike, indeed I am a tyro
I think most people will agree, though, that you can learn a lot by watching, listening, and reading. It gives you a bit of a head start on the
doing. This MO has worked for me for car repairs, messing with computers, gardening, carpentry, and many other tasks, so why not car-building?
Again, studying is a head start, not expert knowledge. To a certain extent, this is physics, so I feel OK about commenting in a limited way. You
won't catch me saying boo-wah about welding, though
Agreed that it would be great to hear some war stories
Pete
[Edited on 11/3/04 by pbura]
What me? I skinn no cats. Me love cats )))))
As for me, then in my desing there are lot of constraints - things I can't change. And I build as I can. But also I would like to know how to
change things I can change to make it handle normal. And the way people (who understand something) don't laugh when I show them my car.
Ps. Excuse my french ))
Caterham used an "A" link for the lower location with the apex of the A below the axle banjo on the solid axle, the de Dion tube had a extension bracket going downward so the A frame could locate in a similar position
quote:
Originally posted by pburaOriginal Deon chassis rear RC 120mm
I wonder, how do they get it so low?
). I suspect that the Caterham, like a lot of the early
Lotii, is using an A-frame to locate the rear end. In that case the rear roll centre is the point where the A-frame links to the bottom of the diff
housing (or de Dion tube). In that case 120mm is almost mandatory. Ah, I had puzzled at Britishtrident's post, having forgotten my question because this thread has taken some twists and turns.
Cheers to both for the explanation, and to Dominic for the wine tour
Pete
It's funny, I hadn't even seen Britishtrident's post when I wrote my reply. Great minds, across the globe, converging simultaneously
on an answer
As for the wine tour.... if you're able to get your hands on some McLaren Vale reds over there I really do reccomend them very highly. Wirra
Wirra "Church Block" may be the best medium priced red wine in Australia! A spectacular wine for the money - as little as AUD$16 a bottle
in case lots which is the only way to buy it. One bottle will definitely not be enough
Anyone who want a guided tour of my wine cellar need only come and visit
Best regards,
Dominic
The Caterham locates its rear axle by a large A frame link with the point of the A under the axle centre and the base pivoting on the chassis tube
equivalent to tube B1 in the lowcost book.
The five link arrangement is totally unnecessary. A three link with lower A arm locating the axle centre and two upper inks above the axle and
parallel to the chassis sides is all you need. A four link or Satchell link is also very simple and can handle a lot of power. Five links are for
people who like making extra parts or own shares in bush making companies.
The elise swing axle lengths are about 170 inches at the front and 120 at the back. These values are very close to the suggestion made by Mike Costin
(as in COSworth) in the chassis book by Costin and Phipps. The Mazda Miata/MX5 has the swing axle lengths shorter at the front than at the back. This
might be a better choice for the lowcost.
I wouldn't advise going any lower than 1.5 inches on a home built car. Very low roll centres do some strange things when wheels move during roll
and bump. the higher the roll centre the more stable the geometric situation but at the cost of feel. A look through the data available shows that
many designs end up with roll centres between 1.5 and 3.5 inches at the front with the rear roll centres being between 2.5 to 6.5 inches.