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Front suspension.......

 
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Paul Gething
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Joined: 10 Feb 2006
Posts: 91
Location: Redditch Worcs UK

PostPosted: Thu Oct 30, 2008 9:39 pm    Post subject: Front suspension....... Reply with quote

Dave-M

I made quite a few adjustments to the front suspension...............that is after I had finished the rear suspension as in the other thread.

I took out the Riley torsion bars and replaced them with Morris Minor, which are thicker and therefore stiffer. I then carefully measured the suspension dimensions and had written a computer program which would show me the roll centre movement (the point about which the body rotates), together with the change in camber as the car rolls.

By this time I had already decided on the design and parameters of the rear suspension and as it is connected to the front suspension by that big bracket we call the monocoque, I wanted to make sure that the two would work well together.

Firstly the the original set up of the front suspension had a long swing axle length, which meant that in bump and droop the wheel would stay close to its original static camber angle. Nice, but the downside is that in roll it would generate huge amounts of positive camber and reduce the grip of the front outside wheel in a corner, reducing cornering speeds at the front.....Now if I change the swing axle length to a very short measurement, it may well be better in a corner, keeping the desirable negative camber....but when I hit the brakes in a straight line, the camber change, in bump, would wind on a huge amount of negative camber and I would be trying to brake on the inside section of the front tyres and, no doubt be locking up the front wheels and reducing front brake efficiency.

So............I worked out that by moving the damper mounting/suspension pick up point, the lever arm damper also acts as the top wishbone, I could get close to the geometry I needed......I then plotted where the rack should be mounted to ensure that there was no bump steer.

The geometry at the front gave a very similar leverage through the roll centre as that at the rear..hence why the car looks balanced in the photo.

I then got rid of the original front roll bar and replaced it with Morris minor track control arms, you can see in the picture. This was because I did not like having a fixed anti roll bar and because I wanted to dial in some anti dive, as mentioned in the previous thread.........sticky tyres, high speed, good brakes, I did not want the nose diving too much and upsetting the carefully thought out geometry.

I then fabricated a new front anti roll bar and mountings starting with 0.5" 16swg tube and adjustable top links.....which in fact was slightly stiffer than the original bar...........as I increased the rear spring stiffness I eventually ended up with the 1" 8swg bar in the photo.....substantially stiffer than the original.



This huge increase in roll stiffness meant that the Rochdale was very good in corners and with adjustable rear dampers (Caterham 7), in both bump/rebound and ride height....and an adjustable front roll bar it was very tunable and adaptable to any course or weather conditions. To help it into corners I took apart the lever arm dampers and wound the valve springs up tight and replaced the 'gnats p!ss' damper oil with engine oil. The seals held and the thing turned into a corner like an F1 car......Oh yes, I also set up the front suspension with about 1.5 degree's of negative camber by shimming out the lower suspension arm.

All of the above meant that the 185/60x13 tyres kept as much of their tread on the road at all times and gave me maximum grip. Being able to tune the handling with all of the adjustables meant that it handled superbly and was more than a match for any road going Lotus...........For 2 years running I finished second at the Lotus Drivers Club sprint at Wellesbourne, when most of the opposition were roadgoing Elans, Sevens and Europa's...........only an old F3 Lotus single seater was quicker.

It was always driven to a meeting, never trailered.........and is a great 'Early Sunday Morning' car.

In terms of power I only ever put it on a rolling road once, it produced 109bhp at the rear wheels at 5500rpm......but the problem with the light weight and the soft Yokohama's, it was trying to fly off the rollers, meant it probably not representative......couldn't go higher on the revs otherwise it might leap off and take the building with it.

In terms of performance it did a 38 secs up Shelsley Walsh, a 55 up Prescott, a 37 at Curborough and ran the ss 1/4 mile at Long Marston Drag strip in 13 secs and 104mph.

Harewood.........sorry Dave....I only ever did Harewood in this.....54secs Embarassed
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Dave-M
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Joined: 20 Jan 2006
Posts: 377
Location: Yorkshire, England

PostPosted: Fri Oct 31, 2008 9:39 pm    Post subject: Reply with quote

Paul, Thanks for the very comprehensive reply, much of the information can be applied to our Phase 2' s even though our suspension is quite different.
What did surprise me was the strength of your front anti-roll bar, it's the equivalent of an 11/16" solid bar, massive!!
Don't suppose you know the equivalent spring rate (lb/in) of the torsion bar?
Also how much anti dive did you build in?
Regarding your single seater (Anson ? ) at Harewood, you better watch out as you are only 15 seconds quicker than my 1293 mini.
Needless to say, you have got me fired up to put my Rochdale on the Hills
Regards
Dave
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zefarelly
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Joined: 26 Nov 2007
Posts: 91

PostPosted: Sat Nov 01, 2008 7:32 am    Post subject: Reply with quote

funny you mention ARB's, I ran a 1" solid one on the COrtina for a few years, back to 7/8" now

the std one looks pathetic, and the Turner I've had in had what I think was a GT6 ARB with adjustable ends, I'm on the look out for one of those.
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Paul Gething
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Joined: 10 Feb 2006
Posts: 91
Location: Redditch Worcs UK

PostPosted: Sat Nov 01, 2008 1:33 pm    Post subject: Reply with quote

Yes Dave it is an Anson SA4 tub...They were designed by Gary Anderson, who did the early Jordan F1 cars, including the gorgeous first one.


He did his apprenticeship at Brabham under Gordan Murray. When he designed the Anson he virtually copied the front suspension and tub loadings from the Brabham BT49....which Nelson Piquet won the World Championship.

In the back of it is a 450bhp Rover V8 driving through a Hewland FG400 gearbox.

Anyway back to the Rochdales................

The existing anti roll bar is 3 times stiffer than the original 5/8ths one......although you can see in the photo that I have it set with the lever arm shorter than the original. In practice it is giving approx four times the roll resistance of the standard fitment. The equivilent, using the same length lever arm, is approx 0.8" solid bar.....don't forget that on a solid bar the metal as it gets closer to the centre is doing very little in torsional resistance.

I needed to run the car stiffer in roll and I could not run stiffer springs on the front, unless I built in additional coil springs and that goes against the spirit of what I was trying to do......So I ran the stiffest springs possible on the rear, bearing in mind ride quality, and then kept increasing the size of the roll bar until I could balance out the front to rear roll stiffness. The much stiffer dampers helped the instaneous transitional loads that in reality I would have prefered to have been controlled by the springs.....but hey ....life is a compromise isn't it?

I did fit a rear anti roll bar for a short time...until it broke Embarassed It worked well but when I fitted a limited slip diff there was no real need to run one, so it never went back on.
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TonyS
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Joined: 17 Jan 2006
Posts: 230
Location: Worcestershire

PostPosted: Sun Nov 02, 2008 10:45 am    Post subject: Reply with quote





Front Suspension "DUFFY"


Last edited by TonyS on Thu Jan 01, 2009 9:41 am; edited 1 time in total
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zefarelly
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Joined: 26 Nov 2007
Posts: 91

PostPosted: Wed Nov 05, 2008 1:28 pm    Post subject: Reply with quote

slightly modified then!

theres enough space up front there to store a few cases of wine on the return from LeMans next summer!
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calex_fr
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Joined: 18 Jul 2008
Posts: 408
Location: Champagne (France)

PostPosted: Tue Sep 22, 2009 3:22 pm    Post subject: Reply with quote

Do you know what are this shocks :


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Alexandre Contat

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Dave-M
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Joined: 20 Jan 2006
Posts: 377
Location: Yorkshire, England

PostPosted: Tue Sep 22, 2009 10:22 pm    Post subject: front susp Reply with quote

lotus elan? spax?
Dave
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GT with Rochdale Chassis
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calex_fr
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Location: Champagne (France)

PostPosted: Wed Sep 23, 2009 7:49 am    Post subject: Reply with quote

Yes Elan, Spax I don't know.
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Alexandre Contat

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