Indispension units (upside down)
madteg - 5/9/14 at 08:21 PM
Just thinking about building a towing dolly using suspension units upside down to get car lower. Will it work.
Sam_68 - 5/9/14 at 08:37 PM
quote:
Originally posted by madteg
Will it work.
No.
owelly - 5/9/14 at 08:44 PM
I ran a pair on my boat trailer upside down to make it lower and it was fine. The suspension doesn't know which way round they are....
Sam_68 - 5/9/14 at 08:55 PM
quote:
Originally posted by owelly
The suspension doesn't know which way round they are....
Actually, the suspension geometry does.
The Indespension unit trailing arms are designed to droop 45 degrees when unladen, but to flatten out to about 13 degrees under normal static load,
which means they give a geometrically rising rate (to add to the rubber's natural rising rate characteristics) within their normal working
range.
If you simply invert them, they start out angled upwards at 45 degrees, and get steeper when laden, which means they will end up very
steeply angled upwards under load, giving a geometrically falling rate, and end up almost vertical under any serious bump load.
Really not a good idea, honestly!
owelly - 5/9/14 at 09:07 PM
I stand corrected. But I won't be dashing out to change my boat trailer as it's doing sterling service for the past 15 years....
Sam_68 - 5/9/14 at 09:17 PM
quote:
Originally posted by owelly
I stand corrected. But I won't be dashing out to change my boat trailer as it's doing sterling service for the past 15 years....
I suspect that if it's working fine, you must have a much higher load-rated Indespension unit than the weight of the boat you're carrying,
hence keeping the deflections within a tolerable range... or you've rotated the trailing arm within the suspension rubbers to correct the
trailing arm angle?
You can (or at least could - I don't know if the latest units still allow it) invert the mounting bracket so that it fits to the top of the
chassis rail instead of underneath it (ie. underslung chassis) by rotating the box section of the trailing arm within the square section void in the
rubber, so that you reduce the ground clearance whilst retaining the correct working angle for the trailing arm. This is the correct way of doing t,
but it's certainly not the same as simply inverting the unit without changing the trailing arm alignment.
britishtrident - 7/9/14 at 07:38 AM
quote:
Originally posted by Sam_68
quote:
Originally posted by owelly
The suspension doesn't know which way round they are....
Actually, the suspension geometry does.
The Indespension unit trailing arms are designed to droop 45 degrees when unladen, but to flatten out to about 13 degrees under normal static load,
which means they give a geometrically rising rate (to add to the rubber's natural rising rate characteristics) within their normal working
range.
If you simply invert them, they start out angled upwards at 45 degrees, and get steeper when laden, which means they will end up very
steeply angled upwards under load, giving a geometrically falling rate, and end up almost vertical under any serious bump load.
Really not a good idea, honestly!
Actually the geometry of mounting upside down has exactly the opposite effect a a very steeply rising rate .
Sam_68 - 7/9/14 at 08:27 AM
quote:
Originally posted by britishtrident
Actually the geometry of mounting upside down has exactly the opposite effect a a very steeply rising rate .
Yes, you're right, it does.
My apologies - not concentrating!
... so less bad than a steeply falling rate, to be fair (albeit it risks higher instantaneous loads than the components were designed for), but
it's still putting the working range of the unit somewhere it shouldn't be, compared to its rated load.