Custom Anti Roll Bar- Cheap opportunity!

I'm tempted to give it a try because I'm running standard tyres and that's going to be a limit. I really want it more level in regular driving conditions, not handle like a modern car.

Typically the difference between a base model and "GTI" is 100% or so. The trouble is we're starting from by modern standards such a low base its difficult to judge.
 
As you saw Peter, Colin's anecdotal evidence from a couple of his customers with them fitted is "it makes the car handle like an Audi A3"
It's quite confusing frankly. Perhaps there is a sweet spot where it gets a lot better suddenly, but then plateaus the stiffer it gets? Hence everyone's good reviews with any larger size bar?
Jim
 
would be really interesting to know what size the rover test mules had... i'm pretty sure it's been mentioned before that it got pared back by the bean counters....
 
I've no idea. I'd be extremely surprised if a 50 year old RWD car handled anything like a modern Audi regardless of what you did to it.
 
corazon said:
As you saw Peter, Colin's anecdotal evidence from a couple of his customers with them fitted is "it makes the car handle like an Audi A3"
It's quite confusing frankly. Perhaps there is a sweet spot where it gets a lot better suddenly, but then plateaus the stiffer it gets? Hence everyone's good reviews with any larger size bar?
Jim
Click to expand...
diminishing returns i guess... and obviously you (well i :) ) dont want to lose the rover's supple ride in the process....
 
I think that you are comparing bars just from their thickness, pressuming that they are all made from the same meterial.
Frankly, i cannot see why the original Rover anti-roll bar, the Peugeot 306 rear torsion bar, a bar from someone else in UK, NZ or whatever else should be made from a material with the same specification.
 
Dimitris you have a very valid point.
Colin has yet to mention the material but when I originally enquired about getting bars made myself the general options were chrome vanadium and silicon chrome alloys. One company specified 735A51 Chrome vanadium
One thing I often think of when machining an existing donor bar is strength. Aren't the spring steels used heat treated after forming?
I wonder what the original rover bar is actually made from?
Jim
 
Demetris, the properties of anything referred to as "spring steel" seems not to vary so much in torsion from what I've read barely a few percent in fact. How this feeds back in the calculations, I don't know.

Most modern vehicles have hollow bars with walls in varying thickness to engineer the desired properties rather than radical changes in diameter which of course makes sense when it comes to engineering mounting points and clearances etc. I'm guessing economics limits the material choices, although Audi do use a aluminium/carbon composite. Bear in mind there seems to be no road-going difference from a manufacturer between a standard and "sports" model that is anything like the 400% people have done here. That looks like the realm of the track boys to me. However of course its all relevant to where we start, which is without exception a whole lot stiffer than a P6.

I'm guessing on standard tyres and without any other changes Colin's 19mm bar works noticeably well in a safe way and gives a fair bang-per-buck result. The difference between acceptable roll and alarming barge-like handling might be subtle given all the complexities of the oddball suspension and any extra control will push the handing envelope in that direction. I'm wondering without other changes and better tyres that the results might not be so happy going stiffer. One of the interesting things for me is how safe the P6 is. In fact it doesn't always feel so much like a RWD car at all in some ways with its understeery feel. I've never unstuck the rear of it except deliberately in a wet car park and I would not like to throw the balance of this too far the other way.

I don't plan on much more than this bar, HD rear springs and gas dampers. If I did I would buy a 10 year old BMW with a big 6 cylinder engine for a couple of £1000 and have all the engineering done properly :)
 
Sounds to me like there needs to be some form of back to back scientific style testing done to compare the various thicknesses that everyone wants? What's desirable for one individual is almost certainly not going to be desirable to another!
 
True.... the other issue is nearly everyone has done this in combination with other changes. The combinations of which can radically change the effect.
 
PeterZRH said:
True.... the other issue is nearly everyone has done this in combination with other changes. The combinations of which can radically change the effect.
Click to expand...

Very true, for suspension upgrades usually you'd expect there to be previous experience over the years which has culminated in a relatively agreeable stage 1, 2, 3 etc. On the P6 with it's odd suspension layout that seems to not be the case until more recently where the interest in upgrading has started to grow.

In my experience with stiffer springs, adjustable dampers, and lowered ride height bodyroll is vastly reduced with the standard ARB still in place, and the ride still being comparable to a modern car, although not exactly 'plush'. The additional second ARB I've fitted has almost completely eliminated the feel of bodyroll, though more extensive testing/driving is planned later in the year....
 
Hi,


I started to write a reply but then I had a quick look further back in the thread, I wrote this after testing the proposed 25.4mm (1”) bar, I think it's still valid:


Hi,

Firstly an apology for the length of time it’s taken to get to the point of reviewing this ABR, you make plans and then life gets in the way, anyway it’s on the car and I’ve driven it!!! :shock:

The bar is very well made, radius’s are as large as are practical (good for fatigue resistance) and the fit is excellent. Please note the area of the inner wings of our car have already been opened up slightly to provide clearance around our previous ABR, it appears some cars need this and some don’t, each car is different, in fact each side of each car is different. Bare this in mind if you order one, any extra clearance needed will be small and easily achieve with a little gentle tin bashing/jacking.

On the road the transformation is remarkable; please understand that our car is quite modified now so it is difficult (impossible) to assess this modification in isolation but even compared to our previous 24mm bar this 25.4mm the feel is different, even less roll in the corners. Considering “normal” driving, the bar modernises the feel of the car, you’ll have to decide yourself if that’s a good thing or not? Gone is the rolling nature of the drive, replaced by a much flatter attitude, as I say much more like a modern car would be.

OK so with all of the above said should we all rush out now and order one? Unfortunately a question that sounds as simple as this is surprisingly hard to actually answer. To make an attempt to answer it we need to go through a few things regarding P6 handling and more specifically what the front end is doing. Gavin is way more up on all this stuff than me but this is the just of things, he may come along and elaborate or correct me :oops:

Lack of front camber recovery in roll is a big issue with the front suspension geometry, ie when the car rolls the geometry of the front suspension fails to correct for this and the front wheel tucks in under the car and it understeers. This can be seen in the picture below (24mm bar fitted), this eats tires as well as losing loads of time, and it also feels very disconcerting as the bloody thing just won’t turn!!! Increasing the roll stiffness at the front has an obvious effect on this, more stiffness = less roll = less wheel tucking in = better turning = improved times, which is all good :LOL: but unfortunately the front suspension is not working in isolation. A much stiffer front end, and this 25.4mm bar increases it by some 220% over standard, will increase weight transfer at the front which in turn reduces grip and will result in increased understeer. So we have two opposing effects contributing to our original goal of improved handling :evil: With our car we have increase rear spring rates so we have stiffened the rear as well so this lessens the weight transfer effect so we can take full benefit of the improved camber control without so much of the negative issues.

It is extremely hard to know how an otherwise standard car would handle with just this ABR fitted, my gut feel is that it may well be too stiff and all though the car would indeed roll less in the corners overall front end grip might actually be worse.

To most on here all of this is of little consequence as we are talking at the limit handling here, if you fit this bar and drive the car well within its limit all you will notice is the much reduced body roll, which will make it feel more modern. If you want to get the best out of it then fit in along with stronger rear springs, for an otherwise standard car it might be worth considering a mid-stiffness bar. A 22mm bar has been talked about, this might be more appropriate for an otherwise standard car, for reference torsional stiffness percentages over “standard” are listed below (Gav. feel free to check my math :?: ):
22mm bar 145%
24mm bar 188%
25.4mm bar 223%
If you go with stronger rear springs then obviously you can move towards the stiffer bars.

Please understand this is not an exhaustive scientific test, just the best we can do with short run time and limited resources, it would be nice to do back to back trials with various diameter options. The event on the 11th was in fact cancelled due to lack of entries so we are still seeking a full anger event to run on. The above is a review of our observations so far.

On a side note our car went through the MOT this morning without issue, MOT’s here are all state run, no garages, there is no “advisory” process it’s either right and passes or it fails. As most will know our car is no oil painting but it’s right in all the right places :wink: it’s nice to see that the look didn't prejudice the test

All for now, Tim
 

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Hi,

As Whiteline states the table only works for bars of the same shape, material etc.... standard bar is an 11/16" Hex (17.4mm across flats and 19.5mm across points) as such it behaves like an ~18.2mm round section bar. If you use 18.2mm in Whitelines table, you’ll need to interpolate the numbers as they don’t list fractional bar diameters, you should get numbers close to what I have.

I think my maths is right but I'm sat at work away from my original cals.

Tim
 
Thanks for that Tim, that's a key element we were neglecting.
So if we treat the standard bar as a round 18.2mm, the 19mm bar if round also is even less of an increase.
Something only in the region of 20%, I think that's correct?
Jim
 
Hi Jim,

I believe that's correct, you would be hard pushed to notice an increase to 19mm round section.

Tim
 
PeterZRH said:
So the best solution would actually be a round bar with hex ends so it could be thinner.
Click to expand...

Hi,

Yes all the uprated bars I've seen are like that, round bar with a section of hex at both ends, this makes the torsion calcs a bit more complicated so the numbers quoted I have are a bit of a of a fudge as they ignore this unevenness in cross section. Don't panic too much about this as the round section is still much longer than the hex'ed so the assumption isn't a wild one. Just think of the numbers as a guide, I'd say you'd hardly feel a 19mm bar as a change, 21/22mm would be the start of a meaningful effect, by 24mm and above you really need to be matching the back end or things are going to potentially get interesting.

Tim
 
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For that reason it makes sense to me to slightly overestimate the diameter you want, going on percentage increase.
The worst that could happen up to 25mm is you'd need to uprate your rear springs/dampers.
Personally I'm doing that with my project anyway so this has just cemented my want for at least a 24mm bar.
It's either that or I'm following Simon and the NZ race car's lead with a lower front mounted donor bar..
Jim
 
Hi
I thought i would add my experience on uprated roll bars.
I purchased 3 uprated ones from Alan at class parts about 3 years ago,fitted one to my dads 3500 and one to my friends 3500s .
Both cars were in standard spec and once fitted noticed a big improvement when driving on roundabouts. Will prob work better with wider wheels or other suspension mods.
Been in garage tonight and measured my spare bar.its 25 mm.
Not sure if he is still selling them.
cheers clive.
 
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