IRS for S3

[Shortshift]

Some of us recently hijacked a 'Marketplace' thread and ended up talking about the possibility of fitting independent rear suspension to a S3 chassis. 

I have just come across

which is rather interesting!

James

[gileshudson]

James,
Owain Davies from Caterham Cars built one too and it was apparently featured in the October 2008 issue of LowFlying.
Some pics below and more details on it in a PDF on the link below.
Giles

https://www.dropbox.com/s/wvbt0z7shjo1gyn/IRS%20R500%20details.pdf

 



IRS R500 details.pdf
 

[7 wonders of the world]

  

 

[Shortshift]

Thanks Giles - good find from the Lowflying archives.  That's the car (I think) that is now owned by Chris (R300Chris) and has been discussed - at some length - in the MarketPlace thread I mentioned, which is here if anyone is interested (read towards the end).

James

[Shortshift]

I think that sourcing the hub carriers (which seems to involve either:- bespoke fabrication; or bespoke CNC machining from a solid billet; or using the CSR part) is perhaps the biggest practical obstacle.  Would be nice to think of this as a commercially viable update on a S3 platform.

I wonder what the reaction was at CC to Owain Davies' efforts?  I can't believe they wouldn't have been aware and assessed it.

James

[7 wonders of the world]

Probably the same reaction as Gary's inboard front suspension for the S3 recieved -  'we don't want to cannibalise sales of the CSR' 

There's a slight irony in this now that the CSR was sadly dropped from mainstream sales.....

 

[Shortshift]

That could well have been a valid commercial justification at the time, but with CSR effectively no longer available in the UK, an IRS S3 derivative might open up a significant new stream of opportunity.  I can imagine demand from existing owners for whom such an obvious, attractive and substantial technical improvement would be a solid justification for upgrading to a new car, as well as appealing as a premium option to buyers who would be purchasing for the first time.

Probably best not to try to do David Ridley's job for him! 

James

[DJ.]

There are plenty of Seven designs with IRS out there. I think designing the set up to suit some existing hub carriers from Westfield for example would speed up development.

Having previously built and owned an independent Westfield SeiW, I have to say, I much prefer the way my DeDion Caterham S3 drives. There are theoretical advantages to IRS, but I would prefer a well developed live axle or DeDion chassis to a poorly designed IRS every time.

Duncan

[7 wonders of the world]

DJ,

I had the same thought regarding the rear hubs as a friend has a Westie

Problem I found with my Westie and my firiend also agrees, is that form the factory they are very over sprung, dropping the spring rates all round made a huge difference.

https://parts.westfield-sportscars.co.uk/suspension-braking/rear-suspension?product_id=146

 

[7 wonders of the world]

I would lke a nice light Dedion tube for mine though, like the Ti version that was made, or maybe a redesign using thinwall Reynolds tubes or similar.... with provion for a spherical centre mount for the A frame too.....

[DJ.]

A much lighter DeDion with better location would be more than halfway to IRS with a lot less bother. I fitted a powerflex bush to my DeDion and it reduced the rear wheel steer quite a lot.

[7 wonders of the world]

My A frame I Powerflexed too, I'd just like some more angular rotation in the A frame to Dedion tube mount as the current set up puts torsional stress thro the A frame as the Dedion rotates during single wheel impact or cornering load.

Also made the control arms adjustable, with double rose joints so you can adjust the Dedion to be perpendicular to the centre line.

[DJ.]

That sounds an interesting modification

[bluenose]

I spoke to someone at Caterham at the Autosport show shortly after Owain built his IRS R500 and he said that it was a good experiment but was assessed as providing little benefit over the dedion set up and I think he said it was heavier?  

Regarding dedion tubes, my original one circa year 2000 was a great lighter than my replacement.  When I spoke to Bruce at Arch Motors he said the gauge of tube had been increased from 12 to 10 which I assume was due to failures? A titanium one would be nice.

 

 

[7 wonders of the world]

I think with careful redesign and choice of material, suitable supports etc you could save a good few kilos of unsprung mass.

The change in gauge was belt and braces, the failures were on the lower mount - very well documented on here, but the addition of buttresses in this area dealt with it,

you could even look at hydrorming the main tube into more benefical profiles allied with butting too......

[DJ.]

The early Lotus De Dion tubes were curved and included the wheel bearing mounts without using  ears. I believe they also used inboard rear brakes which would reduce unsprung mass considerably. They also had a larger diameter, but I presume a thinner gauge steel.

I found a photo of an Eleven, but I've seen similar fitted to a Seven chassis.

http://www.britishracecar.com/GlennStephens-Lotus-Eleven/GlennStephens-Lotus-Eleven-DE.jpg

[ECR]

At the time, the received  wisdom was that a dedion arrangement provided less opportunities for owners to badly adjust their suspension and thus create a reputation for poorly handling Caterhams

[elie boone]

I think that if you convert the current DD set up to the same as a 5 link Live axle set up it would improve on all dynamic's, for sure it would offer more squat and be a lot lighter and most important there is no chassis modification needed.

[Golf Juliet Tango]

At the time, the received  wisdom was that a de Dion arrangement provided less opportunities for owners to badly adjust their suspension and thus create a reputation for poorly handling Caterhams

That is a very respectable position for Caterham Cars.

And this is what was written on the subject for us after the de Dion was introduced: https://www.lotus7.club/guides/technical-information/de-dion-or-irs

[Shortshift]

Perhaps 'convenient' rather than 'respectable'?

I'm not aware of the CSR suffering from any such poor reputation, despite the freedom for owners to freely adjust till the cows come home...

But thanks for pointing to the old (1998 +/-) Lowflying article.  It makes interesting reading but the bottom line is that time (and capability) moves on.  Nothing new under the sun!

James
 

[Doctor]

the only drawback of CSR IRS arrangement is the lack of rear anti roll bar. Irrelevant on the road, excessive lean on the track.