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Dave-M · Posted: Thu Oct 16, 2008 4:44 pm Post subject:

Joe if you look at the "AVO shockers"post at the beginning you will see the rear end travel based on the damper travel available with the "club" AVO's.
This might be revised a little when I finish the more accurate drawings.
Regards
Dave
_________________
Ph.2 Ford 1500 GT
GT with Rochdale Chassis

Dave-M · Posted: Thu Oct 16, 2008 5:58 pm Post subject:

Joe, I have done all the measurements and am on with the drawings now
(for the rear end).
What do you and others think about the following:-
One drawing showing bump, droop and static ride heights
Three drawings one for each of the above. They are drawn on tracing paper and can be laid on top of one another to show the three positions.
Also, to let me run these new dimensions through my spreadsheet to calculate a good starting point for the springs, have you got the following:-
The weight of a complete Ford back axle
The weight of a L.C. wheel and tyre.
It will save me loads of messing about if you have.
Regards
Dave

Rodsmith · Posted: Thu Oct 16, 2008 8:21 pm Post subject:

Keep at it Dave and Joe, I for one really appreciate the work you are both putting in to it.

Rod
_________________
" Stay lucky "

calex_fr · Posted: Thu Oct 16, 2008 8:25 pm Post subject:

yes fantastic !
_________________
Alexandre Contat

from France

zefarelly · Registered User Joined: 26 Nov 2007 Posts: 91

just nicked the bathroom scales . . .back in 20

right . . .PH2 unsprung rear end weight

Cortina axle casing with Rochdale ironwork attached 11kg
open planet wheel diff in iron nose 15.4kg
(ally nose is approx 5kg less )
GT halfshafts with studs and bearings 4.8kg each
GT backplates, drums and brake bits/shoes 7.5kg each side
rims (Dunlop D1 or steel 5 1/2J) 6kg
175/70 tyre is about 5-6kg from memory

so unsprung rear end weight is 'kin heavy

or 75kg with a few links, cables, pipes and mud attached

trailing arms are 3kg each

for reference, the COrtina race car runs 140lb leaves on the back, 550lb fronts and has approx 60/40 distribution so std Rochdale rear end rates I'm guessing wouldn't be far off for the rear, but the front would want to be a bit stiffer.

Dave-M · Posted: Fri Oct 17, 2008 2:51 pm Post subject:

Thanks Joe, that's just what I needed to know
I have done the drawings and will post them here a bit later on, I am just nipping out to collect my headlining stuff.
Regards
Dave
_________________
Ph.2 Ford 1500 GT
GT with Rochdale Chassis

Dave-M · Posted: Fri Oct 17, 2008 5:41 pm Post subject:

Dave-M · Posted: Sat Oct 18, 2008 8:56 am Post subject:

Here are the drawings I have done for the rear supension.
A little info first. I have drawn them full size to minimise any errors, the dimensions are as accurate as I could get.
They are based on 5" ground clearance under the flat floor pan and an 11" rolling radius 13 x 165 tyre.
I have thickened the lines on the drawings so I can get better photographs to post up.
The angles on the drawings are from the vertical and show the damper angle change. The last drawing shows the damper angles looking from the front to rear on the drivers side of the car.
What do you think to the geometry?
Regards
Dave

continued...

Dave-M · Posted: Sat Oct 18, 2008 8:58 am Post subject:

Regards
Dave

Rodsmith · Posted: Sat Oct 18, 2008 10:46 am Post subject:

Wow Dave, a lot of time and effort has gone into those drawings and calculations- I am still getting my head round them! You asked for thoughts, so here are my initial ones.

I am now thinking aloud--

1. I suppose ,for these calculations for a damper/spring unit, we can disregard the small upper torque reaction arm as the rotated angle of the axle is irrelevant, or am I missing something?

2. There will always be a difference in the damper angle, viewed from the side, from full bump to full droop, as the trailing arm moves in an arc. Here we have a difference of three degrees, is that excessive for a stem mounting on the damper, or not? The only way this measurement can be reduced is by moving the bottom damper mounting nearer to the body pivot , but that would bring a lot of load/strength issues etc with it. This could be solved with a loop mounting top and bottom of the damper. However...

3. Because the dampers, viewed from the front of the car towards the rear, are inclined towards the top, their angle will also change as the axle moves up and down. Therefore the loop mounting mentioned in thought 2 would not work. In theory this can be remedied by mounting the dampers upright, viewed front to back. In practice, the damper tops are as close to the outside of the bodyshell as they can be,( my shell has cracked there already), and would need moving an inch or two. If the bottom mount is moved inwards, apart from hitting the exhaust- a minor point, the loads would be on the side of the arm, again unacceptable unless new arms are made that attach nearer to the centreline of the car.

4. A rose joint, top and bottom, would, probably cope with all of these angle changes. They seem unduly "harsh" to me transmitting all the shocks into the car- okay for race but not for road. An earlier question I asked was how long do they last in the road environment?

5. A possible solution, using rose joints, if they have a useful life, is to mount the rose joint to the body with a large compliant rubber/poly washer as already fitted. I haven't thought out that part, but a rose joint may screw straight on to the top stem of the damper, and using a top hat arrangement mounted via a rubber, as you proposed for the front, is an idea?

Just my tuppence worth, I am sure we will all keep thinking!

Rod.

Dave-M · Posted: Wed Oct 22, 2008 12:03 pm Post subject:

Dave-M · Posted: Thu Oct 23, 2008 4:42 pm Post subject:

While I am at it I will tell you what I thought about my Olympic :- CRAP!!
Very harshly sprung, tremendous bump steer, serious roll oversteer and different handling in left and right turns when pressing on. Familiar?

After doing the drawings and thinking about it I think I may have the answer to the last two points in the above. Have a look at this:-

The load from bump or hard cornering is fed vertically up into the c/l of the axle, and because the pick up point of the trailing arm is behind the c/l of the axle, any load will try to rotate the axle about the trailing arm pivot point as shown above.
This rotation is stopped by the top arm.
Because the top arm is not on the c/l but 1/3 of the way along the axle the axle will twist different amounts to the same load, depending on the flex in the rubber bushes at the axle.
This will explain the different handling (left and right) as the rear axle will steer twice as much one way as it will the other.
Make sense?
It appears OK to me
What do you think?
Regards
Dave

Rodsmith · Posted: Thu Oct 23, 2008 7:49 pm Post subject:

I mentioned in another thread that the Turner has one torque arm, but uprated to two for the sports model. I can not see how one arm can work, and keep the axle lined up, unless it is on top of the diff housing running down the centre line of the car. Even when cornering the axle must move, end for end, and steer the back of the car, unless it is all mounted on metal bearings and not on deformable rubber/poly

Paul Gething's idea, albeit for a phase 1, seems a good system on the face of it?

Rod
_________________
" Stay lucky "

Paul Gething · Posted: Thu Oct 23, 2008 8:30 pm Post subject:

Dave,

On your drawings you show a short upper radius arm. Is that what it is?

Is there one on either side of the axle, so that you have a 4 link suspension and a panhard rod?

Sorry for the questions but I have a Ph1 and am unsure of the differences.

I junked my old Ph1 radius arms and panhard rod and redesigned the locations.

Firstly, I made all of the radius rods the same length and ensured that the location points at the axle end were equidistant from the centreline of the axle, when viewed from the side. This then equalizes the torque reaction forces you speak of.

Then, in terms of geometry, I ensured that the lower arm was parallel to the ground at normal laden ride height. The reason being is that the arms move in an arc around the axle end, describing a curve at the chassis end. As the car rolls in a left hand corner, if the arms are parallel to the ground then as the nearside front pick up goes up at the chassis end it is pulling that side of the axle forward....on the drivers side it is going down in roll and because it is also moving from parallel it is also pulling that side of the axle forward. Therefore it does not affect your handling..........

Now, let's say your chassis pick up points are above the axle pick up points, in other words the lower arm points up.

In the same left hand corner, the n/s arm front pick up is going up at an ever increasing rate and hence pulling your n/s rear wheel in....but on the drivers side as the pick up goes down towards parallel it is moving the drivers side wheel back as it effectively becomes longer. Hence you have rear end over steer......................

The reverse happens if the arms are pointing down.....rear end understeer and the car will be a bugger to turn into a corner......and of course, the more you steer in, the more the roll, the more the rear end tries to drive you straight on.

On mine I actually set it up with the lower arm pointing very slightly up as I wanted the car to be 'pointy' and be able to have good turn in to a corner......but not so much as to turn it into a drift car.

The location of the upper front pick up was determined by how much anti squat I wanted.........With soft wide tyres and a limited slip diff I would need to give the springs and dampers a little help with the grip I had. I didn't want the tail burying itself of the startline. Like all things too much is bad, better is a little moderation.....so I did some investigation and decided on 15% anti squat...............

I got out the corner weight gauge and weighed the front and rear and found out where centre of gravity lay between the front and rear wheels and marked it on my bit of paper. I had already plotted the line of the lower arm and marked the position of the upper rear pick up. I then had an educated guess at the height of the centre of gravity and then marked on my bit of paper 15% of the difference between the c of g height and the road........and then joined all of the dots as per the diagram below and that gave me the final pick up point.........Phew.

If you are still with me congratulations.......I think I need a lie down.

With the panhard rod I ran it across the full width of the axle at its centreline and parallel to the ground.

All of the above proved to be light years away from the original set up which was awful.....there was no rear end steer and it put down the power beautifully.......in fact it would cover the first 64 feet at a sprint in 2.3seconds.......that is getting on for 1.15g, which is good for a live axled car on road tyres.......it would also run 13 second standing 1/4 mile and ended up holding a number of sprint class records when up against Locaterfields (Lotus, Caterham, Westfields!!!)

Anyway Dave, to sort this

Dave-M · Posted: Thu Oct 23, 2008 10:33 pm Post subject:

Paul this is the conclusion I had come to:-