Anti roll bar info required

[Steve I]

Hi all I'm still trying to sort the handling of the three wheeler, I see in previous posts that the standard anti roll bar is 12mm and the "Poor road" and "special" suspensions had 16mm anti-roll bar can anyone please confirm this as Betty seems to llready have a 16mm bar.
When the car is at rest the bar links are set at an angle sloping out from the top. can anyone tell me if this Is normal? Or should they be vertical?
here's hoping someone can help. steve i

 

[Steve I]

insppiration

Having followed a Lorry today I saw that it had two anti-roll bars mounted one on top of the other, they were just clamped together. Anyone tried this on a R4? I'm tempted to have a go mounting a standard bar under the one thats on the car any suggestions on whether it would work?

 

[malcolm]

It's an accepted technique to clamp anti-roll bars together. They do that all the time in car development. Clamps can probably be found in shops that cater for race/rally types. You need 2 clamps each side.

I thought the standard bar at the front was 10mm and the rough road one 12mm. That'll explain why the bits I bought for my rough road spec don't fit!

 

[Steve I]

HI Malcolm. I found the info on roll bar thickens in a post about stiffer ant roll bar and Angle had posted the 12mm and 16mm sizes. I can make the clamps myself. you say they need 2 each side, would that be one on the straight section and one near the end?

 

[angel]

Maybe 10 and 12mm are pre-69 sizes. Post -69 are definitely 12mm and 16mm, and there is also a mystery 18mm that I found on a customer's car, and it is not from a R5, for sure.

The outer anti-roll bar mountings should look exactly as you described Steve, and check also that the angle is roughly equal on each side.
It would be interesting to hear what the result was with twin anti-roll bars, even though the chassis is not an R4.

 

[Steve I]

I suppose I’ll have to put out a request in for a 10mm bar and try it . Any one have a spare anti roll bar, to aid the experiment?

 

[Andrew C]

Keeping it simple

I'm not sure 'keeping it simple' is the right heading for this reply, because if we were interested in that, why would we mess about with old Renaults, let alone convert them into 3 wheeled specials?

However, before going down the path of doubling up on the anti roll bar, what does anyone think of reducing the mounting compliance by incorporating some polybushes?

I think the inner mounts would probably be catered for by a pair of these

http://www.superflex.co.uk/datasheets/Universal_ARB_mounts.pdf

so fairly easy to try that first, although replacing the outer FARB rubber would take a bit more thought.

I've just fitted some AVO's to the front of my car after seeing Steve's post about what a difference it made, and I might try polybushes next if I still have a lingering roll stiffness issue myself (although there are 16 'clicks' of adjustment to play with first, which at the current mileage addition rate for the 'Rundown Races Special' will probably take until well after Xmas to fully assess)

One final point that I'll post on here in case anyone else is mad enough to build an R4 based trike and has similar issues. I phoned Keith Hamer, the 'K' of DRK the other day, and he was good enough to spend some time discussing the straightline stability issues Steve has mentioned and I've experienced. He basically said that the suspension was fitted in standard form (R4 or R6), with no modifications, and tracking was set to 'toe out' as per specs. Some kitcar reviews of the DRK do mention a front suspension mod to improve stability, but Keith said this never actually happened, and stability was never a problem. I have tried going to 'toe in' tracking recently and that does seem to have reduced the tendency to wander slightly further

The DRK page on Keiths very interesting website is

http://www.scholar-racing96.com/drk.htm

I have tried contacting the DRK owners club for info on any mods any owners might have carried out, but so far no reply

best regards,

Andrew

 

[Andrew C]

Anti roll bar maths

Using the photo of an R4 underside on page 233 of the Haynes manual to take some approximate dimensions, I've done some rough maths on anti roll bar rates using this equation

K (lbs/in) = ( 500000 ( D^4) ) / (((0.4244 j ^2) x L) + (0.2264 A^3))

The source was Automotive Math Handbook by Forbes Aird, American as you can probably tell from the title/authors name, so everything is in inches. The 500000 must be some kind of stiffness value for a general roll bar steel.

For the R4 GTL front dimensions, you can simplify the equation to

K (lbs/in) = 1205 x D^4 (D being the dia. of the bar)

This gives 10mm bar = 30lb/in, 12mm bar = 60lb/in, 16mm bar = 190lb/in (I only had to round a lb or so, which was suprising)

The mystery 18mm bar mentioned by Angel will be 300lb/in

I think stiffnesses will be additive, so a 12mm bar plus a 10mm bar will be 90lbs/in

I did some similar sums on the torsion bars (16.5mm dia.) when I was designing the special, and got an approximate spring rate of 40lbs/in, so its not suprising an R4 feels so soft. However, I believe Colin Chapman said the secret of good handling and road holding was soft springs / firm damping, so the AVO's probably are a good idea.

I'm not sure any of the above helps the discussion, but I have the kind of mind that likes putting numbers to things

 

[Steve I]

I agree Andrew keep it simple. Ive already fitted new poly mountings, it all makes it better but it's still not quite right. fitting the 15" spoked wheels has improved the situation as well. I have a gordini wheel for the rear that may also improve the situation but I have to rebuild the rear body to get that in.
The trouble with the calculations it's all thrown out with the car only having three points of contact with the road the rear being a pivot point. The lack of the one rear wheel and shock doesn't have that as a stabilizer. Having acquired a build sheet from a DRK it does say highlighted you need a anti roll bar from a TS which is thicker, 20mm I think I may have found a 18mm one so I'll try that and as they say watch this space.
Is there a way of calculating what the bar should be? I had to weigh the three corners to get the right spring rate for the rear. would this help? I'm gratefully for any help especially with calculations. I get to three and seem to stop

 

[wheeltapper]

DRK 3 wheeler

Hi all I'm still trying to sort the handling of the three wheeler, I see in previous posts that the standard anti roll bar is 12mm and the "Poor road" and "special" suspensions had 16mm anti-roll bar can anyone please confirm this as Betty seems to llready have a 16mm bar.
When the car is at rest the bar links are set at an angle sloping out from the top. can anyone tell me if this Is normal? Or should they be vertical?
here's hoping someone can help. steve i

Steve,
Have only just dropped into this website and hope you havent given up on sorting the DRK. I have owned one since 1995 and you are probably my nearest neighbour with one ! The 16mm anti roll bar (from the van I understand) should have improved matters but also I found the camber and toe in set up was critical. Also be sure that the correct ride height of the chassis via the adjustment of the anti roll bars is correct. I am on the outskirts of Northampton just off junction 15 of the M1 and if you want help I am willing so that you can really enjoy the normally good handling of the DRK.

Paul

 

[petec]

In the early 90's my mate and I built ourselves three wheelers from scratch which were based on Mk1 R5's. Mine was based on a Gordini - eventually put a Gordini Turbo in - so had a thicker anti roll bar but my mate's used a standard R5 anti roll bar. Mine was very controlled but my mate's rolled quite a lot more. We fitted a second standard anti roll bar to his, not by clamping it to the original but by adding some extra brackets to the front of the lower wishbone and adding the second bar ahead of the front wheels, so it had one in front and one behind the wheels (hope that makes sense - pre digital camera so no pics handy - I could get some if it was useful). Anyway, that tamed it pretty well. We both found that the steering rack position was fairly critical to avoid bump steer and also that a narrower rear tyre was better than a wider one - I tried wider low profile (175 or 185 if I remember) but found it followed the worn parts of roads and joints in surfaces much more than a standard 145 did. Once sorted, both cars were very stable and left most things for dead out of roundabouts (with the Turbo in, mine left most things for dead in a straight line as well). Mine is hiding in a corner of my garage waiting for me to rebuild the engine and sort out years of neglect, my mate's is doing the same in a corner of his garden. One day I may get time again...