greg_in_london
07-27-2008, 02:25 PM
I've been expermenting periodically with suspension settings for the past few years, especially since the air assistance began to leak.
Initially I added a 1cm spacer which helped a little, but was not enough without the air pressure. Then I went to a 650lb spring, before deciding to upgrade. before the new spring arrived I fitted the spacer to the 650lb spring, but the thicker spring became coil bound on bumps in Irish roads and broke the spring seat. I fitted the upgraded shock after we'd limped home.
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[Problem with pasting table, please see attached excel worksheet]
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In case it's not clear, the columns are: spring rate, the free length of the spring, the fitted length, the amount of precompression (assuming no sag) and then the force on the suspension.
When I had the new suspension made I asked for it to be a 1/2" longer, so the next column gives the load after that 1/2" of travel - at would be fully extended on the standard shock.
I made a few assumptions (like about seven square inches internal area) to guess the force generated by the air pressure which I estimated as 500lb or 225kg, so the next column gives the combined spring and air pressure at rest (assuming no sag).
The last four columns are the equivalent figures at fully compressed, which is important as you need to be sure that springs not only don't become coil bound, but have some movement left so they do not weaken through over-compression.
To work out the air assisted max compression load I have used the same pressure figure. This could be grossly wrong, however, as the pressure may triple on full compression. I don't know for sure, though.
At present I have an 850lb/in spring fitted and it sits way too low - with little ground clearance and not much suspension travel left. I'm not sure how much preload I wound on on the coilover Gaz shocks, but it's not enough. I'm guessing that I preloaded it 1/2" and then it compressed another 1 1/2", leaving 15mm, just over 1/2" of movement
(equating to nearly 2" movement at the back wheel) - meaning that static, without a rider, by bike needs about 700kg force, 15-1700lb just to support its own weight. Without a sidecar, or with a lighter one you'd need less, with a trailer you'd need more.
In the next couple of days a 1000lb/in spring will arrive and I'll preload it at least 1/2" and prefereably closer to 1".
If you're thinking about upgrading your suspension, maybe the above will help - some car suspension manufacturers will find it hard to believe that spring weights as high as this are needed. Coilover springs are much safer to fit than the standard type of shock.
WARNING :backinmyday:
If you fit a heavier spring to your standard shock, DON'T RELY ON SPRING COMPRESSORS (you won't compress them enough anyway) - make up a jig, preferably with 12 or 14mm studs (4 off) to wind down the spring. If the spring were to break free when fully compressed and if you were too close it could kill you. :Bunny2::240:That's because you have to compress the spring enough to fit the circlip into the groove and with the 650lb spring that's practically a tonne of force on the spring.
Initially I added a 1cm spacer which helped a little, but was not enough without the air pressure. Then I went to a 650lb spring, before deciding to upgrade. before the new spring arrived I fitted the spacer to the 650lb spring, but the thicker spring became coil bound on bumps in Irish roads and broke the spring seat. I fitted the upgraded shock after we'd limped home.
**************************************************
[Problem with pasting table, please see attached excel worksheet]
**************************************************
In case it's not clear, the columns are: spring rate, the free length of the spring, the fitted length, the amount of precompression (assuming no sag) and then the force on the suspension.
When I had the new suspension made I asked for it to be a 1/2" longer, so the next column gives the load after that 1/2" of travel - at would be fully extended on the standard shock.
I made a few assumptions (like about seven square inches internal area) to guess the force generated by the air pressure which I estimated as 500lb or 225kg, so the next column gives the combined spring and air pressure at rest (assuming no sag).
The last four columns are the equivalent figures at fully compressed, which is important as you need to be sure that springs not only don't become coil bound, but have some movement left so they do not weaken through over-compression.
To work out the air assisted max compression load I have used the same pressure figure. This could be grossly wrong, however, as the pressure may triple on full compression. I don't know for sure, though.
At present I have an 850lb/in spring fitted and it sits way too low - with little ground clearance and not much suspension travel left. I'm not sure how much preload I wound on on the coilover Gaz shocks, but it's not enough. I'm guessing that I preloaded it 1/2" and then it compressed another 1 1/2", leaving 15mm, just over 1/2" of movement
(equating to nearly 2" movement at the back wheel) - meaning that static, without a rider, by bike needs about 700kg force, 15-1700lb just to support its own weight. Without a sidecar, or with a lighter one you'd need less, with a trailer you'd need more.
In the next couple of days a 1000lb/in spring will arrive and I'll preload it at least 1/2" and prefereably closer to 1".
If you're thinking about upgrading your suspension, maybe the above will help - some car suspension manufacturers will find it hard to believe that spring weights as high as this are needed. Coilover springs are much safer to fit than the standard type of shock.
WARNING :backinmyday:
If you fit a heavier spring to your standard shock, DON'T RELY ON SPRING COMPRESSORS (you won't compress them enough anyway) - make up a jig, preferably with 12 or 14mm studs (4 off) to wind down the spring. If the spring were to break free when fully compressed and if you were too close it could kill you. :Bunny2::240:That's because you have to compress the spring enough to fit the circlip into the groove and with the 650lb spring that's practically a tonne of force on the spring.