220mm eye to eye. Do i need a 215 or 230 shock?

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220mm eye to eye. Do i need a 215 or 230 shock?
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Posted: Jul 1, 2022 at 18:38 Quote
I measured my eye to eye length on my ancient demo and it is showing 220mm.

For a replacement shock I only see 215mm and 230mm being sold. Which one do I need?

I checked the measurment 3x but i measured it from the center of each bolt.

Posted: Jul 1, 2022 at 19:11 Quote
Not entirely sure, but it may be imperial and measured in inches.

Posted: Jul 2, 2022 at 0:32 Quote
Sounds like it wants an 8.75x2.75 inch shock, now aka 222x70 mm.

Posted: Jul 2, 2022 at 4:45 Quote
boozed wrote:
Sounds like it wants an 8.75x2.75 inch shock, now aka 222x70 mm.

Can one of the 215 or 230 metric shocks be used in its place?

Posted: Jul 2, 2022 at 23:07 Quote
Thepoor wrote:
boozed wrote:
Sounds like it wants an 8.75x2.75 inch shock, now aka 222x70 mm.

Can one of the 215 or 230 metric shocks be used in its place?

I think the general advice is not to.

However, this is an opportunity to explore the alternatives. I think the 215 you're referring to is actually a 216x63 mm (FKA 8.5x2.5 inch) because 215 mm doesn't appear to be a standard metric size. In both cases the difference in eye-to-eye length is significant and on a Demo (beginning leverage ratio of about 3 to 3.5 depending on year) the 216 would result in it sitting 20-25 mm into its travel at rest compared to the 222, while 230 would be the opposite - sitting 20-25 mm higher at rest. As a result, the 230 mm shock would also put the linkages outside their normal operating ranges, which is probably not a good idea and might not even work properly.

Both alternative shocks have shorter stroke than the 222x70 - 63 mm for the 216 and 65 mm max for the 230 - so I don't think you'd have to worry about anything colliding with the frame under compression. The 216x63 has the same compressed length as the 222x70, so under full compression the bike would be sitting at the same height - you've just lost 20-25 mm before the wheel even moves. A 230x65 (if it even works) would have the rear riding 20-25 mm higher AND end up with less overall travel (probably around 15 mm less), so it would also bottom-out quite a lot higher than it normally would.

While 216x63 might get you by I think it's worth looking for a 222x70 shock, anything else will be a compromise, or worse!

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