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Old 07-24-2013, 04:33 PM   #41
fred flintstone
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Originally Posted by ragtoplvr View Post
If you have less area below the piston, to do the same work, a higher pressure is needed. Higher pressures increase wear and need upgraded and more expensive materials. And the oil shears down quicker. Rebound damping is important.

So shaft diameter IS quite important and WAS chosen for many reasons. Or do not believe me and my years of hydraulic system design experience.

+1 There are a whole cascade of things that happen when you need to increase the shaft diameter. As I am sure you know. One of the simplest, for people who have not worked in this industry is the gas pressure. Larger shaft means larger shaft cross sectional area relative to (floating) piston area. This reduces amount of attainable peak damping force (PSI*diff area). Also INCREASES static gas offset force (PSI* shaft area). But then to get more peak damping force you have to increase internal gas pressure. That increases the static offset force as well as raises internal stresses on seals etc. etc.

It really is a very involved design trade off, and as someone else said you better have a good reason to want the larger diameter shaft as a primary concern and then be willing to accept the compromises. But the thing is it increases stresses on other parts while at the same time the extra loads you'd want it for in the first place also does that.

FYI I used to work for/with a guy who made custom automotive racing shocks, and rebuilt other high-end shocks (Penskes Ohlins etc.) for major pro teams. I learned a lot but certainly no expert. Enough to know how complicated this is and how much of a black art in many ways. Any reputable high end aftermarket shock manuf has put in many thousands of hours minimum in design trade offs and computer sim CAD time on exactly these issues.
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