Geoff Dixon Posted January 20, 2002 Share Posted January 20, 2002 Have just checked the setting for the Radius Arms on my K series De Dion. It is fixed in the higher of the 2 positions - the "comfort" setting. How much different does it make to the handling by repositioning the arms in the lower setting and is it just a case of undoing the fixing bolts, moving the arm down and replacing the bolts in the lower setting. Link to comment Share on other sites More sharing options...
Pete Posted January 20, 2002 Share Posted January 20, 2002 Hi Geoff As far as I know the difference in handling is not much. The destructions in the build manual assume that you bolt the front end of the radius arm to the body first. Tighten the bolt to 35 lbft with the radius arm parallel to the ground in order to pre-load the bush. The bolt at the rear end should only be torqued up when the weight of the car is taken on the de-dion tube. regards pete Link to comment Share on other sites More sharing options...
millsn Posted January 20, 2002 Share Posted January 20, 2002 I found the differnece in handling little. What did improve was the ride! I moved from the top position to the lower one. The top one is suposed to be the comfort position but it semes to me that the geometry is poorer in this position i.e. you get rear steer in the top position. I still run the lower as (I think) do most. Nigel Mills - 2.0 Zetec carbs Link to comment Share on other sites More sharing options...
Geoff Dixon Posted January 20, 2002 Author Share Posted January 20, 2002 Nigel, to alter the settings is it just a case of undoing the bolt, lowering the arm and installing the bolt in the new hole or is it more complex ie does unfastening the front end of the radius arm cause the de dion tube to drop or something. Link to comment Share on other sites More sharing options...
Alex Wong1697456877 Posted January 20, 2002 Share Posted January 20, 2002 Jack the car up by the A frame mounting on the tube. Ideally, support the car using 2 axle stands on the tube. Remove rear wheels. Remove the anti roll bar link if you have one (theres a metal spring clip which can be removed and the link just pulls out) Loosen but don't remove the bolt holding the arm to the tube Move the front of the arm down to the lower position - you may need to tap the rust out of the lower position threads Tighten everything up again (not sure about the torque settings off hand) and re-attach the ARB link. Repeat for the other side As the car is supported by the tube, it is effectively as if it was on the ground so it can be tightened with the wheels off. Alex Edited by - Alex Wong on 20 Jan 2002 21:58:10 Link to comment Share on other sites More sharing options...
Geoff Dixon Posted January 20, 2002 Author Share Posted January 20, 2002 Thanks Alex, job for tomorrow night. Link to comment Share on other sites More sharing options...
STEVE GILBERT Posted January 21, 2002 Share Posted January 21, 2002 Not quite thas simple on my Dec95 car. The lower mounting is not tapped for the bolt, rather it is of a larger I.D and requires a bolt to be passed right through into the cockpit. My internal Lamipanels were not drilled to let the bolt pass and had to have circular holes cut. My panels were released anyway due to re spray and the hole really needs to be as big as the washer you must place between chassis and bolt. It is not good practice to sandwich soft ali in this application. If the wings are on and you have no hole in the lamipannels expect a fiddle even locating the hole because of the restricted access in the wheelarch. With big holes cut you need an 80mm long bolt,i think, must be in 12.9 and new locknuts. My local fastner shop could only supply this spec in socket head which was fine. I also had the seats out of the car and the wings off. All.Knowing1@talk21.com Link to comment Share on other sites More sharing options...
Alex Wong1697456877 Posted January 21, 2002 Share Posted January 21, 2002 Good point. My 97 chassis has the threads brazed into the chassis tubes and they're therefore captive which makes it much easier. Link to comment Share on other sites More sharing options...
Ted_7 Posted January 22, 2002 Share Posted January 22, 2002 The Belgian dealer GPS told me that leaving the radius arm at the higher point was dangerous because it's more exposed to torsions, so it may brake up easily. Is that correct or just a legend ? Se7enly, Ted_7 Link to comment Share on other sites More sharing options...
EFA Posted January 22, 2002 Share Posted January 22, 2002 The lower position reduces the roll induced oversteer to a point somewhere between that of the upper position and the elimination the watts link provides. As the usefullness of the watts link is questionable, through its reduction of oversteer it increases understeer, I would say the lower psoition is the best option. The only way in which it effects comfort in the upper position is that it means you are more likey to crash into things forwards rather than backwards - more crumple zone.....! Fat Arn The NOW PROVEN R500 Eaterid=red> See the Lotus Seven Club 4 Counties Area Website hereid=green> Link to comment Share on other sites More sharing options...
John.JBT Posted February 4, 2002 Share Posted February 4, 2002 My cousin has just purchased and begun to build a Caterham car and last Saturday I helped him install the differential and then the offside rear rear suspension. It has the lower type anti roll bar (not the super type whose mountings bolt to the inertia reel seat belt bolts), and a Watts linkage locating the De Dion tube. We are keen to understand the design aims of the suspension configuration. Below are our thoughts. We would be grateful if anyone could explain how the various effects combine and what is the resulting suspension behaviour? Our thoughts:- 1. Anti roll bars - easy to understand - a wheel rising over a bump or on cornering transmits some lift to the other wheel, helping to limit the distance the body moves upwards. 2. Watts linkage. If both links were to be of equal length, then presumably the bell crank arms would be equal in length ie. the pivot fixing to the De Dion bracket would be central on the bell crank. The rear links are shorter so the lower bell crank length has to be longer. 3. How do they work? Assume that both links are horizontal and therefore parallel to the road and the chassis. As the wheels raise or lower about this horizontal line, the bell crank will rotate and maintain the De Dion beam in a vertical path perpendicular to the chassis, thus maintaining a constant track length (distance from the front wheels). Is this the design objective? 4. If however the fixed ends of one or both links are raised or lowered, the effect of vertical movement will be to move the bell crank pivot and hence the De Dion tube forwards or backwards. For example, consider raising the front link fixing from the horizontal. As the wheel lifts, the top of the bell crank will move proportionately more rearwards instead of forwards and the axle will move rearwards. Is this correct? This would be a castor effect, a touch of rear wheel steering on cornering. Is this what is intended? 5. We presume the triangular brace to the bottom centre of the De Dion tube is to prevent tube rotation on braking. It will be in tension on forward braking. If however, point 4. is all correct, moving the end of the De Dion tube forwards or rearwards will create a rotational effect on the De Dion tube, which since it is constrained at the centre point by the triangular brace, will move the other wheel in the opposite direction. There are several effects going on together. What is the final result? 6. We realise that by bolting the diff. to the chassis, the problem of rotational effects of acceleration and breaking transmitted to the suspension in a normal back axle tube are eliminated. So the only rotational effects which have to be counteracted are braking torques. Finally, do Caterham issue a design note on aspects of their design such as the suspension? Link to comment Share on other sites More sharing options...
Chelspeed Posted February 4, 2002 Share Posted February 4, 2002 1 Sort of, good enough way of thinking about it. 2 Spot on. 3 Again sort of. Instead of thinking of the vertical movement maintaining the front to rear track constant, think of the car in roll. As the car rolls you want both sides of the rear axle, de dion tube, to stay perpendicular to the chassis in other words no rear steer. So in an ideal world both sides of the de dion tube would move vertically only. The watts linkage gets much closer to this than the alternative, the radius arm, which describes an arc. 4 I can see what you're getting at but I think you're on the wrong track, the concern is movement of the rear axle relative to the chassis. Relative to the chassis the chassis end of the arms can't move so not a worry. As above the whole point of the watts linkage is to minimise rear wheel steer. 5 The triangular bit on the de dion tube locates the axle end of the A frame. The A frame serves two jobs, one it locates the bottom of the de dion tube in the fore and aft plane, two it stops the de dion tube moving sideways relative to the chassis. For job one look at it from side on, the watts linkage stops the top of the de dion moving anywhere but up and down, the a frame stops the bottom moving anywhere but up and down (well actually in an arc...). For job two look at the chassis from above, the de dion tube can't go sideways because the two sides of the A frame are on the diagonal. Classic bit of the Chapman, one lump of steel does the job of both the bottom radius arms and the panhard rod. You're right the complete set of watts links and a frame stops the de dion tube rotating under both acceleration and braking forces. 6 I think you're wrong here. It's the wheels that transmit braking and acceleration to the road, they will also provide an equal and opposite force to their mountings, thats the ear attached to the de dion. So the watts and a frame must transmit these forces into the chassis. I hope this helps but it may of course all be bollocks but it doesn't matter as someone far more erudite will be along shortly to put me right - Peter? And no unfortunately Caterham don't provide any technical info, this list does that job for them. Good luck with the build and with understanding why things are done the way they are. Link to comment Share on other sites More sharing options...
Peter Carmichael Posted February 5, 2002 Share Posted February 5, 2002 1a. In a bump it will *bump* the other side too, making the ride worse. 1b. In roll, it resists the roll angle, not the upwards movement. Does what it says on the tin. 2,3 & 4. All correct. A bit of roll rear steer is required and the Watt's linkage means the amount you get is more or less independent of rear loading. Radius arm equipped Sevens understeer more when you add a passenger. Do not think of vertical as being the desired path. 5.Chelspeed has got point 5 correct. The connection from the chassis to the de Dion tube is a three point mounting. There are never any residual twisting forces loaded into the de Dion tube apart from those from twisting up the bushes (unlike the Sylva Striker/Fisher Fury rear axle arrangement). Think of the axle movement in three modes: a. Both sides up/down (acceleration/braking) b. Each side opposite (roll in cornering) c. One side moves only (bump) c. is a combination of a. and b. so if you can visualise those you can work out c. The other purely engineering way to think about it is to look at the degrees of freedom of the axle. An unconstrained object can move in three dimensions (x(fore/aft) y(side to side) and z (up down)) and can rotate around three axes (X, Y and Z). It has three degrees of freedom. Let's concentrate on the centre of the triangle of the de Dion tube and start by attaching the A-frame. It can now only travel in a vertical arc and has more or less no fore/aft movement and no left/right movement. We have eliminated the x and y degrees of freedom and leave z free, which is required for brakign and acceleration. If we then attach one of the radius arms/Watts linkages, the axle can now no longer rotate about the Y axis, flopping forward, without twisting sideways. When we attach the other radius arm it can no longer rotate about the Z axis, steering arbitrarily. The axle remains able to move up and down (z) and rotate in roll (X), just as we need. This approach demonstrates that there is no redundancy in the linkages and therefore no residual force in the de Dion tube. [i have taken a bit of licence because most of the constraints are arcs and the axes that are constrained are not quite orthogonal, but the overall effect comes to much the same]. 6. Entirely correct. Ignore Chelspeed. Engine braking would have been a very minor force, but accleration is significant. A live axle is not an ideal solution for more powerful Sevens, but its light weight is of obvious benefit to a low powered Seven like the Fireblade. Bolting the diff to the chassis means that the centre tunnel has to react the torque from the propshaft and in the de Dion chassis this tunnel is beefed up for this reason. Link to comment Share on other sites More sharing options...
Chelspeed Posted February 5, 2002 Share Posted February 5, 2002 See I knew I was talking bollocks. I can see the point now re acceleration, it's the diff providing turning motion on the wheels not the ear so the diff reacts against the chassis. Likewise with engine braking. But normal braking does go through the ear and de dion tube? It must do because the calipers grip the rotating discs and they pass the forces into the ear. As you can go 100-0mph in half the time it takes to go 0-100mph it would seem that the braking forces are much higher than the acceleration forces so are more critical. Link to comment Share on other sites More sharing options...
John.JBT Posted February 7, 2002 Share Posted February 7, 2002 To Chelspeed and Peter Carmichael, Thank you for responding to our questions with very helpful answers. We have a much better basic understanding now. If you know of a good book on the subject, not too heavy but which compares suspension designs, relative merits and effects on performance, I'll mention it to Father Christmas when he asks me for ideas. John.JBT Link to comment Share on other sites More sharing options...
Ted_7 Posted February 11, 2002 Share Posted February 11, 2002 Funny, I just asked something about that radius arm, and what happened on Saturday ? I was driving on the freeway to Waterloo at 150/160 kph, suddenly I hear a "clac" on the rear and at the very same moment I lose control of the car which is turning on the left with no reason, I hit the side protection of the road for 50 at least meters and hopefully, I can force the car not to make a 360°. So 300 meters later I stop the car on the emergency lane ! The bolt from the right radius arm just... disappeared ! The right wheel was turning to the left, didn't know what to do at that moment ! Hopefully another Belgian sevener came to the place, we've jacked the car and just put back a new bolt on the radius arm. The car is still running, the only "damage" is a scratch on the wheel, and the fear of my life ! Se7enly, Ted_7 Link to comment Share on other sites More sharing options...
elie boone Posted February 11, 2002 Share Posted February 11, 2002 And again some work for me. cool.gif oops 8.20 must start to work on your car TED_7 Link to comment Share on other sites More sharing options...
Alex Wong1697456877 Posted February 11, 2002 Share Posted February 11, 2002 Did the bolt fall out or shear off? Link to comment Share on other sites More sharing options...
garyedwardc Posted February 11, 2002 Share Posted February 11, 2002 I must admit your comment in favour of the "threaded bush in the chassis" fitting had me raising my eyebrows Alex. I've never been able to be confident that the bolts are not working loose and presumably neither were Caterham as they've reverted to the old "bolt through from the inside with a nylocked nut" idea. Me, I've gone for belt and braces with a longer higher tensile bolt through from the outside and a locking nut on the inside making sure it can't come out Link to comment Share on other sites More sharing options...
Alex Wong1697456877 Posted February 12, 2002 Share Posted February 12, 2002 Not in favour of it, just stating what my chassis has. Link to comment Share on other sites More sharing options...
Ted_7 Posted February 12, 2002 Share Posted February 12, 2002 Elie said : And again some work for me. oops 8.20 must start to work on your car TED_7 Let me introduce you to the guy who forgot to tighten the radius arm bolt the last time I came to check up my car wink.gif Say Elie, what do u think about garyedwardc comment ? "I've gone for belt and braces with a longer higher tensile bolt through from the outside and a locking nut on the inside making sure it can't come out" Se7enly, Ted_7 Link to comment Share on other sites More sharing options...
elie boone Posted February 12, 2002 Share Posted February 12, 2002 Ted_7 your car has nearly all the nuts welded to the chassis, the only advantage is that it looks neat. The downside is that every time you undo a bolt there is wear on the nuts, how little it may be. With a nut and bolt arangement you just put new bolts in everytime you thake them off. Did someone forgot to tighten your nuts, well i am only human you know. I will take a look at them tomorrow evening. Link to comment Share on other sites More sharing options...
elie boone Posted February 12, 2002 Share Posted February 12, 2002 Today is "Foot loose and fancy free " cool.gif cool.gif cool.gif cool.gif Link to comment Share on other sites More sharing options...
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