Adjustable Front ARB - Is it Worth It?

[JP]

As part of my rebuild, I'm now thinking about possible changes to make when I reassemble.  I currently have a supersport set up with adjustable rear ARB (the one that sits above the diff) and a green bush front ARB.  The car is a road car that will do track days.  I have no intention of racing this car.

I'm, wondering whether to go for an adjustable, but I've been reading old posts on BlatChat which seem to suggest that the front adjustable is heavier than a standard ARB and at its softest setting is still stiffer than the orange bar.

So, if I already have an adjustable rear ARB should that, mated with an appropriate front ARB, be enough to find whatever balance I want for my intended purposes or is there a significant benefit to having an adjustable front ARB as well?

[Roger Ford]

Kind of depends how much of a 'fiddler' you are and whether you think every ounce counts. If you stick a red bar on the front it should be fine for most situations, but you might find a fractional advantage on track if you move to orange or adjust your adjustable ARB to suit. I like the adjustable one just because it's a lot less faff to alter. Since we have minimum race weights a few extra ounces doesn't bother me, that's just a tiny bit less lead to add.

[Drumster]

I have one of Freestyle's original adjustable ARBs (it replaced a green one in Feb '10) and I used to play around with it quite a bit in the first couple of years. I think it's been on the softest setting for at least 7/8 years! I tend to adjust the dampers instead.

I also changed my rear over the diff ARB to an under the diff ARB as with wide rear wheels it caused a few issues. If you go this route Arch will drill the lower chassis and weld in bosses for you. I used the same ARB mounts and found a cheap 2nd hand ARB. Personally I found this arrangement makes adjustment easier. Photos here 

 

[JP]

#2 - Thanks Roger - I think I saw yours when I came to collect some ally cleaner earlier this year.  Nice set up.

#3 - if one moves the rear ARB to a lower mounting position, can you re-use the old ARB or does the lower mounted ARB have different dimensions from the top mounted one?

[Drumster]

JP the lower ARB is a different length, shorter from memory. I think I paid £20 form a race team

[Nigel B]

Interesting post!

I wish I’d found the Blatchat posts that suggested the adjustable front arb’s softest setting is stiffer than the Caterham orange bar as, after much experimentation this year, I reached the same conclusion independently.

I fitted an adjustable front ARB from Meteor Motorsport last year & I’ve since replaced it with a Caterham ‘orange’ bar, which is definitely softer than the adjustable bar on it’s softest setting.

I think the Meteor Motorsport adjustable bar is a good product & it’s beautifully made & finished, it just wasn’t quite right for my needs. 

I’ve been using my car on the road for the past couple of years, but I may do a track day or two next year, in which case I’ll probably refit the Meteor bar. I think having the ability to fine tune both ends of the car is useful, but for me it’s a little too stiff for road use.

How did you find the handling of your car with the ‘green’ front bar fitted? That sounds very stiff to me for road use, but if a stiffer front bar works for you, then you’d probably find the Meteor adjustable bar ideal.

 

[Simon.Rogers]

FYi

The adjustable ARB produces the following figures.

45.2lb force in full soft

70.55lb at full hard

The Red Caterham ARB is 66.1lb

I have 2 kits left on the shelf and am not sure we will produce any more going forward.

[Nigel Blandin]

I have a Meteor bar and tend to run it in full soft which works spot on for me, I have tried it all the way through the range and settled there, especially on track in the dry. 

Out of interest Simon, do you have the comparative figures for the other colour Caterham bars?

[Simon.Rogers]

I don't sorry.

I was told originally it went from softer than softest Caterham to harder than the hardest.

I run my special double bladed bar at full soft.

[Shortshift]

I've always been intrigued by the stiffness and sizing of the CC rollbars and their relationship to Simon's adjustable blade version (which I have had fitted since 2015).  Based on the snippets of information above and looking at the data on the CC online parts store, I have invested 30 minutes of my life trying to make sense of things as follows:

CC bar for Series 3 (listed in ascending size/stiffness order):

• Orange   1/2" (12.5mm)
• Blue        9/16" (14.3mm)
• Red         5/8" (15.9mm)
• Green     18mm

CC bar for CSR:

• Orange   1/2" (12.5mm)
• Option    9/16" (14.3mm)

Now, based (a) on the data point provided by Simon that the CC red bar is 66.1lb force (not sure what that is, actually, or how it is measured, but it matters not for comparison purposes) and (b) that, with all other parameters unchanged, the stiffness of a circular-section solid bar increases as the fourth power of an increase in its diameter, then using the S3 red bar as a datum we end up with:

• Orange  37% of datum, or 24.5lb
• Blue       65% of datum, or 43.0lb
• Red       100% of datum, quoted as 66.1lb
• Green    163% of datum, or 107.6lb

Then finally, using Simon's quoted figures for the adjustable blade we find that:

• When fully soft (42.5lb) the blade bar is a very close approximation to the CC Blue bar
• When fully hard (70.5lb) the blade bar is only a squidge stiffer than the CC Red bar (and is nowhere close to the stiffness of the CC Green bar).

This indicates that the original claim of the blade bar offering adjustability ranging from 'softer than CC's thinnest bar' through to 'stiffer than CC's thickest bar' looks to be somewhat questionable, which is kinda borne out by the number of people who buy the adjustable bar and end up fixing it in its softest setting.  We now know that is pretty much inline with the Blue bar stiffness; oh for some adjustability below this point!

I know that Simon has said he has no plans to restock the adjustable blade bars once the existing units have sold but I wonder whether a tweaked version, running from say 35lb to 66lb (so a slightly softer range than at present) might have broader appeal?  I say that given the number of people who buy the bar and end up with it 'fixed' in its current softest setting (me included), and who would probably like to have the ability to make it softer than at present particularly in wet conditions, etc. 

James

PS:  no responsibility accepted for the mathematics deployed here.  Firstly, it's still early in the day for accuracy and, secondly, my methodology involves a number of broad-brush assumptions, with no attempt having been made (for instance) to reflect the actual geometry of the CC bars in the stiffness calculations.

 

[SLR No.77]

So having a blade at both ends would enable softer settings ...

[Shortshift]

Indeed so.

But without another data point, it's not possible to estimate the comparable stiffness value of the double-ended bar as, in this configuration there are three elements making up the total stiffness - the rotational blade at each end, and the torsion bar/tube running transversely across the car. 

We know the stiffness comparable (say, 66.1 lb) for the 'standard' torsion tube plus one blade but we don't know how much each of the blade and the tube contributes to the total, meaning we can't calculate the value for the double-bladed version.

James

[7 wonders of the world]

Which is what Simon says he has, again on the softest setting, which supports James maths, which to my mind are correct.

There is of course another option - take it off !

[Nigel Blandin]

That's interesting thanks. I hadn't considered the twin blade going softer yet- makes sense though. 
why would anyone go towards the hard end though? The car would push like hell and you'd have to loosen up the back then...It would be all over the place( unless you ran it rock hard?)

All the factory set Sevens I have driven understeer too much for me, then snap at the back when you try to provoke it not to, although they do steer nicely. Just my impressions.

[ECR]

Took the front anti roll bar off my 2.0VX years ago....,

[Shortshift]

"Took the front anti roll bar off my 2.0VX years ago..."

Whatever the performance characteristics, the adjustable bars do look really cool though...  You can judge how superficial I am!

James

[Shortshift]

"Why would anyone go towards the hard end though? The car would push like hell..."

And even more so in the wet!

Hence my suggestion that a tweaked spec adjustable bar would suit more people, more of the time.  With the mid-point of adjustability placed somewhere closer to, or around, the CC Blue bar stiffness value rather than where it is at present, positioned close to the significantly stiffer CC Red bar.

James

[7 wonders of the world]

James,

if you want a front end that not only works, but looks absolutely superb to go Freestyle.... 

 

[Shortshift]

You know, I'm not so sure when it comes to Freestyle.  Brilliant concept but the detailed execution is (was), perhaps, a bit lacking?

Way off topic now, and probably heresy as well!

James

[Simon.Rogers]

I don't think there would be any customers for the adjustable ARB.

Given the current production costs I would expect to have to retail the kit for closet to if not in excess of £300.00 excl vat

A double blade would add at least £150.00

myself I would use either of the 2 softest Caterham bars.

I have always said this to customers.

if we were to make the overall tube thinner or smaller diameter we would have issues attaching the blade to it.

 

[Shortshift]

"If we were to make the overall tube thinner or smaller diameter we would have issues attaching the blade to it"

Would it not be a case of making the blade thinner (in either depth, or width, or possibly both) rather than playing around with the transverse tube?

James

[7 wonders of the world]

Off with his head.... 

Gary was certainly constrained by the chassis design and the ability to make the 'kit' available as an add on that didn't require the chassis to be reworked, hence the dampers being sited in the tower etc where as the CSR was a clean sheet at both ends

[Shortshift]

As we're now talking Freestyle...  I think a lot of the conceptual work is brilliant, including (if I remember correctly) the incorporation of rising-rate on the front suspension, whereas the CSR has a falling-rate front set up.  It's just the execution into hardware that has always left me wanting more whenever I take a close look at a Freestyle car; the ultra-low fabrication and build volumes are clear to see.

Probably best to draw a line at this point and allow the discussion to revert to topic!

James