Right, So I'm going down the sierra based De Dion route. My original plan was to fit this within the existing Five point link for the live axle. However some people have said that this is not neccessary and I should use a Satchell link in this situation.

So some questions:

Am I right in saying that a satchell link is where the top two links are the same as a five point link but the bottom two links go inwards towards the transmission tunnel doing away with the need for a Panhard rod?

Can any one tell me if, and why, one is any better than the other? (Obviously the Satchell has fewer joints and slightly less steel.)

If the Satchell is better, or as good, why is it not gennerally used with the live axle rather than a five point?

In a Satchell link are the pivots of the lower links paralell to those of the top links or perpendicular to the bottom links?

I have seen photos of some of the Caterham bits and they seem to use a pair of lower 'A' frames rather than single links on the bottom - Is there any advantage to this?

I await the reply of the wise ones

Cheers

Phil

While I'm at it:

Do the top links (or all links on a five point) need to be paralell to the chassis (or perpendicular to the axle)? or can they be angled out so that if I've got a wider axle I can place the pick ups nearer the end of the axle? (or is it not even worth thinking about?).

Phil

The Satchel link is as you describe it.

Two upper links parallel to the car centre line as viewed from above (they may be angled as viewed from the side to get anti squat/dive) and two lower links angled inwards at about 45 degrees to the car centre line as viewed from above (again they may be angled as viewed from the side to get anti squat/dive) from the axle ends to chassis pickups near the rear of the transmission tunnel.

The lower links define the height of the roll centre so for a low roll centre and a bit of anti dive you could try axle mounts at about four to five inches above ground level and chassis mounts at about five to six inches above ground level. The obvious place to fix the chassis mounts is on the rear faces of tube B1 or tubes e and f. If you use e and f then they should be one inch square, not 3/4 inch, as they will need the extra strength.

The advantages of the Satchel link are that it is simpler than any other beam axle linkage. All other linkages require either A frame fabrication or additional tubes and bushings as in a five link. It can take big power and can be made to handle well.

Satchel link was used on the original rover V8 saloons with a deon axle and is also found on the Reynard racing designed Strathcarron sportscar. The Caterham two link and A frame arrangement is geometrically similar to a Satchel link but puts a lot more stress on the deon tube as cornering loads are fed through the tube to the central A frame connection.

I think the real reason that five link is so popular is that most people copy what already exists and what already exists is mainly five link.

The only area I can think of where a five link may be better is in comfort. Theoretically a five link with the panard rod rose jointed and the trailing links rubber bushed will give more comfort than a Satchel link with rose jointed lower links and rubber bushed upper links.

I hope that helps.

Just found a fly in my metaphorical ointment.

The chassis mounting point for the trailing arms is somewhat far forward of the rear of the tunnel. This means that it would be very dificult to get the longitudinal length of the lower arms on the satchel link anywhere near that of the trailing arms.

I could put them up the tunnel but the dif would be in the way and if I mounted them on the outside of the tunnel it would very severely restrict the already limited seat space. Mounting them further back on the axle is an option but would still not make up the diference.

So:

Is it a problem if the lower links aree shorter ?(I presume that it would just rotate the axle as it moved).

Is it a problem that the angle of the lower links would be relatively shallow.

Is it probably the case that every one uses a five point link not a satchel as a satchel does not fit in on this chassis?

I eagerly await your wise words.

Cheers

Phil.

Hi Phil,

Suggest you check out this :- www.rpmnet.com/techart/4link.shtml

Some interesting advice here.

Dick

[Edited on 12/12/02 by Dick Axtell]

Interesting, and some help.

However I am still concerned at the sidways loading on the lower satchel links with the shallow angle that would result from the much shorter lower links.

Phil

Phil,

Is there a piccie of a satchel link installation anywhere? Or perhaps a drawing (dwg or dxf format)? It would be very interesting to see this set-up in more detail.

TIA
Dick

Err No! is the simple answer. I'll do a couple of sketches if I get chance later today and post them.

Cheers

Phil

I ran across your web site by accident but I see there are many questions about the satchell link rear suspension. Since I have many years designing and developing both race cars and passenger cars I could provide more insight into the subject matter. Feel free to email me and ask questions. ts200@aol.com

Well Terry, I'll say Hi and welcome to the forum if no-one else will

I'm sure your level of expertise will be most welcome.

I think they all must be in shock at you posting.

Cheers,

Alan B

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Well Terry, I'll say Hi and welcome to the forum if no-one else will

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Originally posted by Alan B
I think they all must be in shock at you posting.
Alan B

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"I already know of at least two F1 designers who visit the forum to pinch our ideas"

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Thank you all for the welcoming comments. I would like to address the comments of Mr Syd Bridge. Besides my production car experience I am a road racer first and a roundy round racer second. I can state that the ovals are a tremendous challenge as they are very much "concentrated cornering". You are right about having links that are as long as practical to control a rear axle. But there is a lot more to it than that. There are basically five factors that have a major impact on how the car performs, they are roll center height, roll steer, side view swing arm length, anti-lift and anti-squat. How all of these factors are simultaneously controlled is the issue of how the links are arranged. I can give you a four link geometry that will be horrible or one that you will love. Yes the springs and bars and shocks are also important, but all of this works together and having a good geometry means less compromise with the springs and bars.

Does anyone have any feel for the maximum angle between the car centre line and the lower links? This is of interest to us as the short distance from the seat back to the axle forces a high angle unless one of the following applies-
1) a deon axle is used with the lower arms mounted on the tube running behind the diff (i.e. about 4 to 6 inches further back than a live axle)
2) a live axle is used but the lower link mounts are swept back from the axle to give a better angle.
Any thoughts guys?

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Does anyone have any feel for the maximum angle between the car centre line and the lower links? This is of interest to us as the short distance from the seat back to the axle forces a high angle

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Cymtricks - you have hit the nail on the head old chap. This is exactly the point I have been getting at (but out more succinctly).

Just to add to that however - if (as I assume) the bushes on the ends of the lower link run perpendicular to the centre line of the car as they get shorter the sideways load on the bushes will become higher (I think) on bushes (if, like me you are using metalastic or polyuerathane) that are not designed to be loaded in that direction. - Discuss.

Cheers,

phil.

pics please

The questions about the angle of the lower arms in the plan view, the answer is they should be as close to 45 degrees as possible. This gives the stiffest lateral restraint. The Satchell link is just a special arrange of a four link. I had built some race cars with around 650 HP with a Cortina style lower A-arm and two upper arms. After racing the car a while we came to realize that the roll center was too low ( at the vertex of the lower A-arm). The Satchell link was created to give all the same characteristics but with a higher roll center. It works fine. It has been built into many cars since that time with no negatives.

The question of a 5-link vs a Satchell link is an interesting one. A 5-link actually has a redundant link. A live axle has two degrees of freedom of motion relative to the sprung mass- heave and roll. To kinematically control two degrees of freedom it takes only 4-links. What people have done is put 4 relatively parallel links in the fore-aft direction and then added a lateral restraint link. It can be a panhard bar or a watts-link. In actuality a 3-link with a panhard or watts works quite well. If any one has a particular design issue or difficult package problem, I would be willing to help work it out with you.