LocostUSA.com

Thanks for the pictures and explanation, Seven13bt. This seems like a pretty standard approach then.

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
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The lower A-frame on Lotus 7s worked well, but also destroyed many axles due applying suspension forces to the center of the axle casing. Most if not all 7's that are raced have a strengthened axle case. If the axle case isn't reinforced the mating flange tended to warp allowing the gear oil to drain itself. I can also state that the lower bracket on the axle case needs to be reinforced unless the metalastic bushing is swapped for a spherical bearing. The bracket broke on dear old dads Caterham, luckily at low speed.

Chunky employed a slightly different axle mounting on the Series 1 7's (and Elevens), the cars had 4 trailing links, but the offside lower link (RH lower) was triangulated, the outer mounts pick up just like a trailing arm (axle and chassis ends), but the triangulated bit picks up at the base of the driveshaft tunnel hoop.

Hey, don't look at me! I read it on the internet so it's gotta be true, right? But I believe the original (which got named the Series 1 after the fact) was a four link with panhard, and that's my story and I'm sticking to it. Until I discover it's not true, at which point I will edit this post so nobody will ever know I was ever wrong about anything.

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Locost builder and adventurer, and founder (but no longer owner) of Kinetic Vehicles

Jack,
Here are a few pics of the axle location on the Series 1 Seven and Eleven. I wouldn't quite call it a panhard, but it does somewhat locate the axle in the same fashion.





The thin rod at the rear of the axle is the hand brake actuating rod.

From the shop manuals for Series 2, 3 and 4:
The Series 2 diff was from Standard Triumph while the Series 3 diff was from Ford Escort and the lower A-bars were not interchangeable.

Hi Jack, oops didn't mean to pick on you I just grabbed a sentence to use to ask the question.

So I like both these solutions compared to a Panhard bar because they very simply and obviously connect to the frame to places that are strong and should also be well triangulated by at least the floor if nothing else. The low as possible roll center is also a big advantage.

I was wondering what the roll center of the later version with the triangulated lower link would be. On the three link version it is like a Watt's linkage and the roll center would be at the diff pivot. I was unsure at first on the four link version, but I think it amounts to the same thing. The triangulated link provides the only transverse location of the axle and would also be the roll center, I think anyways...

An interesting point here is that previously we have had long discussions on wether the transverse or side to side location of the roll center amounts to anything. Here I think we see that it does not matter. The height of this roll center is the same ( about ) in the series 2 and 3 designs, but the roll center would move all the way to the outside where the pivot is in the 4 link version. I imagine the handling of these cars was not in fact radically different - so it is the height of the roll center that is important to us, not the transverse location.

When we are designing our front suspensions the fact the roll center is moving across the car or perhaps falls outside the wheelbase of the car on the inside or outside in a turn matters not. It is the height of the roll center that affects the distribution of weight transfer.

There would be some secondary effect in the case of these rear suspension because as the car corners the axle would develop a bit of a tilt due to the tires deforming. The triangulated 4 link would be more susceptible to this.

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.

So Rod, the Westfield 11 guys didn't use the triangulated lower link. Any idea why?

Yes, the weakness of the 3-link is the ability of the diff housing to transmit the torque from the upper link to the lower link, as shown in the drawing. Solutions are to beef-up the housing, use a beefier housing, or use a 4-link. The Westfield approach was the 4-link.

I think the drawing above is misleading.. In the 4 link the torque is resisted by the distance between the upper and lower links. The torque though is still coming from the diff, the pinion gear is trying to climb up the ring gear in either case, that is where the torque comes from.

Perhaps it's more difficult to make a nice attachment point on the diff, but the diff puts the torque into the axle tubes in either case. That's my first thought anyway....

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.

The Locost 4 link evenly constrains the axle so it sees mostly torsion. The Lotus 3-link creates a weird bending and torsion across the entire axle body.

I haven't been around a lot of British rear axles but the ones I have seen do not appear to be very thick around the differential. Obviously its strong enough to handle whatever torque goes through it but I still think you can get into situations where braking and hard driving create even higher loading. Early on I was cautioned not to jack the Sprite by the differential - apparently you can introduce positive camber by doing so.

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-Andrew
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Thus the Satchell Link configuration was born.

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-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

To be honest, I have no idea why Chris Smith designed the Westie with a panhard rod. I would assume it was easier to build as all the trailing arms & panhard rod are straight.

I think a Panhard rod would be a lot easier to build than modifying the differential case. You could build a nice plate that fit under the diff cover but that would cost a lot more money than just working out a Panhard rod.

I did simplify a bit above. The torque from the brakes does go thru the axle housing. So the choices that don't have a link on the diff put less load on the diff during braking.

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.

Poking around looking for three-link discussion I've just read this entire thread.
I'm planning to use an unmodified Alfa 105 rear live axle.
The triangle is at the top and apparently that may not be ideal but I'm trying to minimize custom mods of donor parts.
At half the original vehicle weight and only 2" suspension droop, 3" compression, and basically stock engine I doubt there are any real torque/strength issues.
I do need to calculate the upper and lower arm lengths to prevent excess diff rotation.

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If I must be a one-man PC free zone, so be it!

If it's relevant the Suzuki Sidekick also uses a 3link. (someone mentioned Jeep Liberty and at least the Sidekick is going to have narrower, lighter weight parts).

I tried to find pics. If you look closely, they attached the 3rd link to the diff casting which then is bolted and seal the the axle. Bizarre - and yet I have no leakage on mine, or other I have seen.

First one shows all components in a lifted ride height

Second one lean your head 40 deg to the left (and the lower links don't show, even to me who knows where they should be), but shows everything at normal right height