Metric v Imperial

[Neil220]

Is there a known definitive list of the differences between the two?

I guess the threads in the bosses of the chassis changed and therefore corresponding bolts?

Is this when the chassis changed from brazed at Arch to welded elsewhere?

Are the overall dimensions different?

Someone advertised wanting a boot cover for a metric car and I asked what the difference was between a metric and imperial boot cover?

He didn't know,  nor know if there was a difference 

[paul richards]

Roll bar on metric car is a different style than imperial therefore boot cover likely to be different. Don't expect all bolts on a metric chassis to be metric. For example bushes on suspension are imperial therefore bolts are imperial. Seat belt mounts are universally 7/16 unf. 

[Jonathan Kay]

Information on fasteners and fastener packs.

And I have a large collection of Assembly Guides for different years and models. Free to Members: please send me a Private Message with your email address.

Jonathan

[Neil220]

Thanks both for your replies.

Does anyone know if the actual dimensions/structure of the chassis is different apart from threads?

[simon_h]

There are detail differences in the tubes used in various places. It's one of those things where everything looks the same but it's mostly slightly different 

[Rich Goddard]

Specific to the cockpit, when I was recently replacing my S3 car (imperial) with an S3 (metric) I had cause to ask Arch about the differences.  This was specific to pedal positions and cockpit length only.  Where my imperial had 3 pedal options/positions, in the metric I was looking there were only 2.  At 6' 3" tall I knew I just fitted my legs in an imperial S3 (with Tillett right back, and pedals in forward of the 3 positions), but I wasn't sure about the metric.

This is their reply:
"The front [brake and clutch pedal] bush appears to be 5/8" further back in the Metric chassis than the forward-most position of the 3 in the imperial. (approx 16mm).
The cockpit length (base of chassis) is exactly the same even though the Metric heel-tube is 3/4" and the Imperial 1/2".  Just measured both chassis at 43 3/4" (1111mm)"

[paul richards]

Overall dimensions of imperial and metric chassis are pretty similar but differences exist in type of tubes used and different designs of pedal box and various internal tubes/braces. 

[Neil220]

#5 #6 #7

Interesting. 

Thanks