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Rear Leaf Spring Elimination Kit


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did someone try this wishbone software? http://www.locostusa....php?f=5&t=1438

 

unfortunately, it will not run on vista/w7, but there is a workaround at pg 8 of this thread.

 

hth,

 

harry

 

edit: http://www.racingasp...ions.com/?p=286

http://www.susprog.com/index.htm

http://locost7.info/mirror/suspension.php

Edited by oviwan
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Chris - those are very nice looking pieces. Too bad Triumph didn't go with something like that (with a double inboard pick up) - they look robust enough to stop any toe change or any castor change due to the spring twisting.... but "I'm no engineer" !

We are currently loading all suspension data (front and rear) into a computer suspension analyzing program - like Mitchell, and hope to be able to figure out what to do based on those results.

The image i posted is a photoshop retouch of an image or Chuck Pelly's GT6 in Kas Kastner's latest book, with made up suspension links...

 

 

Re: GT's comment about club racing tires vs. "spec race tires from the "pros" - in the US, club racers use Goodyear and Hoosier slicks that provide typically far better grip than any series spec tire - as shown by lap times run on the same track with both tires, on the same car. These two companies have been in competition for decades to make the stickiest (on most durable) racing slicks for us "club racers". A set for the GT6 or Spitfire cost about $850 US, and the softer compounds will last a couple of race weekends, the harder will last three or more. Of course the more heat cycles, the grip will diminish. They both also make TREMENDOUS rain tires with unbelievable grip - but don't run them when the track dries out!

 

Cheers, Clark

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Controlling the top of the upright has got to be better with this type of attachment than with the spring waggling around from the diff, and the outer end sitting in soft bushings.

 

That spring eye bush is not soft at all. It's rock solid and metal sleeved.

As for the spring waggling around.The fore/aft rigidity of a transverse leaf spring of this size is just HUGE.

You don't stand an earthly chance of it twisting or bending in that plane.

That's why they used it on Escorts and Cortinas. (and it's dirt cheap).

 

If you check however, the SINGLE biggest problem are the rear diff bushes and the front bulkhead/chassis flex.

 

In the rear suspension in view of the positioning of that bush each mm of movement down there gets multiplied 10 fold at the other ends, like a gigantic lever.

 

The whole thing is rocking and jumping from that point upwards under high loads.

 

The front chassis flex is SO BAD on the original car, that once you fit some strongish springs, you'll easily get 1-2cm movement between the bulkhead and the engine without the suspension even moving.

 

Add up to the 2 ends and it's the margin between holding the car sideways on the limit, and it just suddenly snapping around and letting go completely. (hence the fantastic extra effect by using prog springs).

 

Put some solid bushes in the diff, and bolt the engine direct into the chassis (no rubber), and it's a different car.

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That spring eye bush is not soft at all. It's rock solid and metal sleeved.

As for the spring waggling around.The fore/aft rigidity of a transverse leaf spring of this size is just HUGE.

You don't stand an earthly chance of it twisting or bending in that plane.

That's why they used it on Escorts and Cortinas. (and it's dirt cheap).

 

If you check however, the SINGLE biggest problem are the rear diff bushes and the front bulkhead/chassis flex.

 

In the rear suspension in view of the positioning of that bush each mm of movement down there gets multiplied 10 fold at the other ends, like a gigantic lever.

 

The whole thing is rocking and jumping from that point upwards under high loads.

 

The front chassis flex is SO BAD on the original car, that once you fit some strongish springs, you'll easily get 1-2cm movement between the bulkhead and the engine without the suspension even moving.

 

Add up to the 2 ends and it's the margin between holding the car sideways on the limit, and it just suddenly snapping around and letting go completely. (hence the fantastic extra effect by using prog springs).

 

Put some solid bushes in the diff, and bolt the engine direct into the chassis (no rubber), and it's a different car.

 

I guess I mis interpreted your earlier comments about the leaf spring, and I am having trouble visualizing some of your other comments. BUT, since you seem to have considerable experience in racing GT6's (with IRS, I hope) maybe you could answer some questions so I can better understand.

 

Leaf spring: - what size/rate and what "arch" or offset on top of the diff?

-what specific bush at the out board attachment?

 

Coil overs: - using for adjustability of ride hight and corner weights - how do you do this without them?

- I am currently using the bottom leaf of a "new" stock MKIII GT6 spring with 400lb springs on the Spax coil overs (this is very common

on SCCA Spit racers (Spits run lighter spring rates)

 

Lower wishbone: - mine is the stock casting with rod end fitted to the inboard side for camber adj. I plan to replace it with a tubular part with rod end at all three attachments.

 

Trailing arms (radius arms): - mine are stock. Plan is to fab up new ones with rod ends and either attach to the frame or reinforced body floor points. Is the height of the attachment point on the upright optimum for a lowered race car? Did you ever fit an upper trailing arm to stabilize the top of the upright?

 

Diff: Mine will be solid mounted - it now sits on half thickness stock bushes. How about the rear long transverse bolt ?

 

Engine: solid mounting the engine - did this cause any wear damage (cracking/breaks) to the engine/exhaust or other parts? BTW, my rollcage is pretty extensive and starts at the front suspension towers. Torque testing has revealed little if any twisting...

 

Thanks, Clark

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Clark , if you are going to fabricate new wishbones , please explain why you would not change to double chassis mounting points , pref' still wider than mine , as this in it self must have a dramatic effect on stabilising the VL/hub and means you should no longer need the radius arm which is surly one of the causes of VL twist ?

 

GT , you do not seem too concerned about the wishbone/spring differences in length or do I misread you ? I should of thought an upper arm design along the lines Clark has shown , if linked into the chassis for extra rigidity ( as I fully appreciate your comments about the diff movement being exagerated by length ) has to give a significant advantage , no ?

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Clark , if you are going to fabricate new wishbones , please explain why you would not change to double chassis mounting points , pref' still wider than mine , as this in it self must have a dramatic effect on stabilising the VL/hub and means you should no longer need the radius arm which is surly one of the causes of VL twist ?

 

GT , you do not seem too concerned about the wishbone/spring differences in length or do I misread you ? I should of thought an upper arm design along the lines Clark has shown , if linked into the chassis for extra rigidity ( as I fully appreciate your comments about the diff movement being exagerated by length ) has to give a significant advantage , no ?

 

Actually what I am showing is a wide based lower wishbone w/double pick up on chassis. The extra "joint" on the outboard end of the forward arm I added in to deal with any potential stressing at that point. It may not be necessary - once the geometry is laid out and checked.

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Impressed by the pic but I was thinking along the lines of Chris' Pantera pic . That VL is going nowhere it should n't and receives no twisting from a radius arm . Why use a radius arm unless you are going to use a pair , upper and lower when they then compliment each other .

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my favorite car of all time DE TOMASO PANTERA (group 4 spec).

 

I no doubt won't exactly excite you to say, the De Tomaso Pantera is the perfect example of the WORST handling car ever invented.

 

They are absolutely disastrous, look exotic, sound really LOUD, on a track day, we ended up lapping the darn things, because they were totally pathetic in the bends.

 

Like many exotica, especially Ferrari, look carlos fandango, sound like a bunga-bunga party, but in reality are utterly useless on a fast A road, or in the wet.

The fact is, Ferrari make suspension for obese yanks to show off, but any Lotus (even a modern one) will leave it for dead on a REAL road or track, especially a wet one.

 

Even my favourite (V12 Lambo) get ultimately undriveable in driving rain, unless the suspension has been completely redone.

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TBH, if you want to get rid of the spring as the top supension arm then all you have to do is SHACKLE it.

(but it would need a ball joint or rose joint in the shackle link)

 

I was going to do this, as it eliminates the need to put a plate under the spring on top of the diff.

All you would then need to do is pick up the radius arm point a lot higher up, and a single arm inboard from the vertical link.

 

The leaf spring is not at all bad, it provides a nice soft spring rate at full droop and a very stiff one at full travel.

The problem really occurs as it has that sharp change of length from semi elliptic to flat.

This is the notorious "weirdo" you get and it was worsened on the Vitesse with lever arms

(remember that? It got really dodgy with levers at certain points of travel on the original cars, esp in fast mid corner bumps!)

 

What it needs for damping is soft rebound settings and more stiff bump setting, with dual adjustable rate on "fast" or "slow".

 

You will struggle with a coil spring in the space to get the progressive characteristic of a leaf spring...even Mk2 Jags had them, and they work.

(although life is a lot simpler with a live axle and LSD isn't it?)

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  • 1 month later...

I'm enjoying this thread.

 

I took ideas from the GRM car when I designed a set up for a mates V8 spit. I'm no suspension engineer and a bit of string calculator work and guessing on top of what seemed common sense was the route i took.

 

Removed spring and trailing arm.

Lower wishbone with twin mounting points on the chassis - as far apart as possible to cope with twisting action.

Coil over shock mounted on reinforced extended chassis mount.

 

Where i ran out of talent was with the top wishbone. As seen in the pics earlier in the thread some people fix long ones back into the top if the diff (Which if i read it correctly GT says eliminates squat) some use short.

 

If the upper wishbone is longer than the lower it must go into positive camber as the wheel goes into bump. Surely this is not desirable?

 

I designed a the upper wishbone fractionally shorter than the lower one to introduce a little negative camber in bump.

 

Unfortunately the guy building it had enthusiam but very little idea about engineering and the result wasn't as detailed as I'd designed and he just put it on the road and drove it without any fine tuning so I've no idea how good it could have been, but on the couple of occasions I drove it the concept seem perfectly comfortable firing through north devon country roads at a ton plus.

 

I wanted to look at roll bars too but he wasn't interested so it didn't have one.

 

So questions are:

 

Roll bar - requirement and best execution?

Top wishbone - comparative length?

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