Imperial vs. Metric rear anti roll bar for an S3.

[RedbeardRacing]

As my 2003 birkin didn't come with a rear anti roll bar, and Tom at birkin USA let me know their kits on have one for an IRS version. I have been researching caterham anti roll bars. Now supposedly the Birkin and caterham S3 are dimensionally similar, or so I have been told. I hope the aero screen I'm about to buy fits. But, my question is, is the Birkin similar to th imperial or metric caterham S3. As those are my two options for sway bars from kit car direct. I have contacted them, and they are unsure of the difference. 

 

You guys have came through clutch for me before. 

 

Thanks. 

[MV8]

https://www.pistonheads.com/gassing/topic.asp?t=1073731

 

Does this help? I don't know. One may be 1/2 inch where the other is only 13mm!?!

 

Sounds like either is workable but not a direct swap without some work. You could resell the one that will be more difficult to install.

[RedbeardRacing]

I have read that post, it helps identify caterhams, but not birkins. I was kinda upset that kit car direct didn't know the difference. I found contact info for Chris at Redline and will see if he knows next week when gets back in. I'm just curious more than anything at this point. I'm sure I could make either bar work. Crazy that no one sells parts for these in the US other than Tom. And those are Birkin only. 

[IamScotticus]

Are you a live axle?

[RedbeardRacing]

I am. 

[MV8]

You could make the bar from rod stock, fab the arms around two inch long dom tube reamed to a press fit over the bar, then braze the ends or pin. I don't know how well 4140 from mcmaster will work without additional heat treat, but I've been told 1020 is often used by oems (not heat treatable-low carbon common steel). There are also torsion bar kits with splined ends and different lengths available but the spline fit must be tight as the load reverses on an anti-roll bar.

 

 

[RedbeardRacing]

Kind of surprised that no one has an answer to this topic about the difference between the two...

[BirkinBernie]

I have the factory rear bar installed on my Birkin.  If you haven't seen one, I can post a couple pics.  Of course installing it moved the handling to oversteer - a bit too much oversteer actually.  I added a 5mm wheel spacer on each side to widen the track and that balanced the car back to neutral, at least at street speeds.  Of course how it affects your car depends on what springs you are using among other things.  I find that the car feels more stable and controlled, but I can't really quantify that - I just like it better with the bar.

 

I haven't tried autocross or a track day since I installed it.  Damn, that's been a long time.  I need to fix that.....

 

Happy Motoring!

[RedbeardRacing]

Thank you sir! I would love to see some pics. The car's primary use for me is autox and turn in is definitely not where I want it to be yet. I have a set of quantum one.zeros being built for the car right now. And will be running a soft spring in the rear so an anti roll bar is going to be a must. I see you are in Texas, north of Dallas looks like. I am sure the Lonestar Region SCCA would have you! Autox is a lot of fun. 

[BirkinBernie]

Hi Redbeard!  Actually, we are in Texas Region here, not Lonestar.  I ran my first autocross in Florida in 1972.  I quit around 1999 having been here in Texas for almost 10 years.  I was Texas Region Solo co-chair for a year, and did about every other job from Timing and Scoring chief to Safety Steward.  The last class I ran was F-Prepared in a RX-7, and with 4 or 5 guys within tenths (and frequently less) in the class it was great fun.  But I finally got burned out on it and called it quits.  I've run a couple autocrosses in the Birkin over the years, but never got serious about it. 

 

Anyway, here are a couple pics.  If you look behind the seats, you will likely find the mounting points for the bar welded to the frame, but covered from the rear compartment by the aluminum skin.  You can see that I added a spacer to move the bar a bit farther away from the body to clear the hand brake mechanism.  They drilled and tapped holes in the head of the lower coilover mounting bolt for the connecting rod to the axle.  HTH!

 

 

[RedbeardRacing]

Sounds like you have done it all already! I just started autoxing in May of 2020. I am a drag racing convert. I love it, the people, the competition, it's great fun. I went from a cam-t foxbody mustang to the Birkin and it's a whole new world, as they say. 

Thank you much for the pictures, I am curious to see if I have the same mounting points. And that's a neat trick with the bolt head, I'm sure some head scratching went into that!