julians Posted January 30, 2001 Share Posted January 30, 2001 I noticed last time I was at a track day that I was getting quite a lot of body roll towards the rear of the car, so the other day I decided to stiffen up the rear ARB. Firstly I assume I'm right in saying that the hole towards the back of the car is the least stiff and the one at the front the most stiff. I also noticed that it is possible to change the length of the link between the ARB and the hub/whatever it is. Why is this, what effect does changing this have. Is there a recommended setting, I have just moved it to the stiffest position, went for a quick spin, not noticed a great deal of difference, I guess I will on the track. Julian Link to comment Share on other sites More sharing options...
EFA Posted January 30, 2001 Share Posted January 30, 2001 The more you stiffen the ARB (moving the links towards the front of the car) the more oversteery the car will become to the point that it is very very snappy. The extent to which you will notice this is dependent on at least 2 things: Thickness of the ARB - they come in 5/8, 7/16 and 1/2 inch. The half inch will make the car very snappy on any setting, they also had a tendency to snap as they made the rear end so rigid. Best option is the 5/8 on the 3rd from front setting, but I do have 210lbs springs on race dampers at the rear. Any significant roll you then get is down to incorrect springing or damping. The std blue springs (bilsteins) are 170lbs. If you have the sily 2 spring progressive set up, ditch it for a single spring solution - it'll sacrifice the ride quality slightly, but improve the handling immensely. Arnie Webb Organiser- L7C Le Mans Trip To book for this years Le Mans Trip see The Le Mans Trip Website It really is very very very very full now!!! Link to comment Share on other sites More sharing options...
julians Posted January 30, 2001 Author Share Posted January 30, 2001 what about the variable length link thingy, what does that do? Link to comment Share on other sites More sharing options...
EFA Posted January 30, 2001 Share Posted January 30, 2001 Julian The VLT (Variable Length Thingy) is just to remove any pre-load from the bar whne the car is on the ground. Arnie Webb Organiser- L7C Le Mans Trip To book for this years Le Mans Trip see The Le Mans Trip Website It really is very very very very full now!!! Link to comment Share on other sites More sharing options...
StewartG Posted January 30, 2001 Share Posted January 30, 2001 I don't agree with Arnie I think the progressive rate springs are best. I've tried stiffer rear springs and all they do is compromise the ride and the traction. I also think you can't talk about the rear ARB in isolation, how it matches the front ARB is important for overall balance and the rear ride height is just as important if not more so when tweaking over/understeer. Unless I've misread him (sorry) I think Arnie's ARB thickness analysis is incorrect. I think the three sizes are 1/2,9/16 and 5/8. It's not the 1/2 that will make for snappy oversteer that's the softest one which will give least oversteer everything else being equal. Edited by - stewartg on 30 Jan 2001 20:50:37 Link to comment Share on other sites More sharing options...
EFA Posted January 30, 2001 Share Posted January 30, 2001 Stewart, I just measured mine. Its 7/16ths. Yes the front end setup does have bearing on the effect of changes to the rear, but the front end is normally sorted with soem decent springs. If the front's too soft you get deflection of the steering when driving fast on bumpy roads - its easy to determine. Front anti roll is also easy to determine - too little the car pitches in corners, to much and the car understeers badly. Juno's adjustable bar is excellent for getting the perfect front anti roll rates. Traction again will be a problem if you are sprung too hard and the surface is uneven, but 200 - 230 lbs on the rear is not excessive. Traction problems are also very much related to the lock up rate in an LSD as the RRT ramp mods for the Sierra diff have shown. Believe me the thicker the rear ARB, and the firmer the setting the more difficult to correct the oversteer becomes. I have tried all three ARB's available for the didion over the years and the thinnest is best. This incidently is what the Vauxhall racers (and probably the SLR's also used) Arnie Webb Organiser- L7C Le Mans Trip To book for this years Le Mans Trip see The Le Mans Trip Website It really is very very very very full now!!! Link to comment Share on other sites More sharing options...
StewartG Posted January 31, 2001 Share Posted January 31, 2001 I think the ARB works in conjunction with the springs. I suspect that your thin ARB together with stiff springs feels very similar to my thick ARB and soft dual rate springs. The choice may well be down to track or road but I can't quite get my head around the science of this. Maybe PC will wade in with a logical arguement I know he prefers progressive springs too. As I said before the ride height and the ARB both contribute to under/oversteer I suppose I may be cancelling out the stiff ARB's oversteer with a low ride height. This gets a bit puzzleing! Where do you start? Ride height as per the book maybe? How do you tweak the drop links to get rid of pre-load on the ARB? I suppose disconnect them with the car on the ground and reconnect so they don't twist the ARB. Sounds extremely tedious with repeated wheel removals. I suppose that's why Caterham went for the underslung ARB. Edited by - stewartg on 31 Jan 2001 08:01:39 Link to comment Share on other sites More sharing options...
EFA Posted January 31, 2001 Share Posted January 31, 2001 Stewart, Remove the wheels, put the rear of the car on axle stands under the didion tube, adjust the linkages. refit the wheels. Simple! Arnie Webb Organiser- L7C Le Mans Trip To book for this years Le Mans Trip see The Le Mans Trip Website It really is very very very very full now!!! Link to comment Share on other sites More sharing options...
StewartG Posted February 1, 2001 Share Posted February 1, 2001 Thanks Arnie it's simple when you know how, why didn't I think of that, couldn't see the wood for the trees. Link to comment Share on other sites More sharing options...
StewartG Posted February 1, 2001 Share Posted February 1, 2001 Just set out to adjust the drop links as per Arnie's instructions and found the 9/16 ARB which I fitted new a few months ago was snapped. The flat end with the holes in had snapped clean off at the weld to the rod. It was dangling from the drop link and could have fouled the wheel or even flailed about and severed the petrol pipe. Judging by the rusted ends it probably happened a while ago. I'll be giving Caterham some stick in the morning. The funny thing is that the car has been handling really well lately with oversteer all but banished and the amount of grip has been amazing considering the greasy roads and cold tyres. I can only conclude that a minimun of ARB is what's needed exactly as per AW's recommendation. I've refitted the old 1/2 inch ARB on setting 3 from the pivot. What a pig of a job it is to wriggle it in, at least I managed it without taking a shock off this time! Edited by - stewartg on 1 Feb 2001 22:41:54 Link to comment Share on other sites More sharing options...
paul jacobs Posted February 2, 2001 Share Posted February 2, 2001 I think that Caterham will be well aware of this failing with the a/r bar, it also happened to one of our local club members on his Vx HPC a couple of years ago. It may only happen on older cars, but if not, then CC need their arses kicked [again?] Link to comment Share on other sites More sharing options...
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