spring preload ?
Discussion
does increased spring preload increase percieved stiffness ?
I gather that the text books say no but imagine if the springs are progressive. If there is a lot of preload then the first bit of spring travel will be in a later phase and therefore a different rate than the first phase of spring compression. So surely that end of the car will have different suspension characteristics, i.e. will feel and behave stiffer. Also the force now required to first compress the spring will be greater ?
I'm not sure if it would make much difference if you are cornering hard and beyond a certain compression point but surely for everyday driving over bumps and ride quality etc.. there will be quite a difference subjectively ?
I gather that the text books say no but imagine if the springs are progressive. If there is a lot of preload then the first bit of spring travel will be in a later phase and therefore a different rate than the first phase of spring compression. So surely that end of the car will have different suspension characteristics, i.e. will feel and behave stiffer. Also the force now required to first compress the spring will be greater ?
I'm not sure if it would make much difference if you are cornering hard and beyond a certain compression point but surely for everyday driving over bumps and ride quality etc.. there will be quite a difference subjectively ?
Edited by jackal on Monday 24th August 14:30
jackal said:
does increased spring preload increase percieved stiffness ?
I gather that the text books say no but imagine if the springs are progressive. If there is a lot of preload then the first bit of spring travel will be in a later phase and therefore a different rate than the first phase of spring compression. So surely that end of the car will have different suspension characteristics, i.e. will feel and behave stiffer. Also the force now required to first compress the spring will be greater ?
The preload only tells you what the spring deflection is when the car is on its droop stops. When the car is resting on its suspension the spring deflection is determined purely from the weight of the car (and whatever leverage the suspension provides) and the spring stiffness. So, given that the weight is constant and assuming you aren't changing the ride height enough for the suspension leverage to change significantly, when you move the spring seats up and down you aren't changing the spring deflection or stiffness, you're just changing where abouts within the damper / suspension stroke the car sits at rest.I gather that the text books say no but imagine if the springs are progressive. If there is a lot of preload then the first bit of spring travel will be in a later phase and therefore a different rate than the first phase of spring compression. So surely that end of the car will have different suspension characteristics, i.e. will feel and behave stiffer. Also the force now required to first compress the spring will be greater ?
If you make the vehicle so low that the car comes close to the bump stops in normal use, you're likely to get some very uncomfortable characteristics as the suspension stiffens up suddenly when it hits the bump stops. Similarly (but to a lesser extent) if it's so close to the droop stops that it hits the droop stops in normal use, you'll feel it suddenly stiffen up and get notchy. If this only happens in extreme cases, inside wheels when unweighted underbraking and acceleration etc, then the weight on the wheel will already be so low that any notchiness is irrelevent. But if the loaded wheels are nudging the droop stops while you're swooping through bends and so on it might be more of a problem.
So, even if you have rising rate springs you won't change the effective spring rate at rest - all you're doing is changing how far the suspension can travel in bump and droop, before it hits the stops.
ok thanks
I dropped my ride height and took off the preload and the car drives much better
the nose feels a lot less 'uptight' and less perturbed by bumpy roads
the steering is also nicer with less of a stickyness to it
a lower ride height would not produce those results (you'd think the opposite in fact).. so there must be something else at work here
I dropped my ride height and took off the preload and the car drives much better
the nose feels a lot less 'uptight' and less perturbed by bumpy roads
the steering is also nicer with less of a stickyness to it
a lower ride height would not produce those results (you'd think the opposite in fact).. so there must be something else at work here
GreenV8S's explanation is a little over-simplified; there are several 'ifs' and 'buts' if you want to get in to the real technicalities, but the most important factor is simply that the energy stored by preloading the spring means that it will be trying to force the damper back to extension rather more sharply on the rebound.
GreenV8S said:
jackal said:
does increased spring preload increase percieved stiffness ?
I gather that the text books say no but imagine if the springs are progressive. If there is a lot of preload then the first bit of spring travel will be in a later phase and therefore a different rate than the first phase of spring compression. So surely that end of the car will have different suspension characteristics, i.e. will feel and behave stiffer. Also the force now required to first compress the spring will be greater ?
The preload only tells you what the spring deflection is when the car is on its droop stops. When the car is resting on its suspension the spring deflection is determined purely from the weight of the car (and whatever leverage the suspension provides) and the spring stiffness. So, given that the weight is constant and assuming you aren't changing the ride height enough for the suspension leverage to change significantly, when you move the spring seats up and down you aren't changing the spring deflection or stiffness, you're just changing where abouts within the damper / suspension stroke the car sits at rest.I gather that the text books say no but imagine if the springs are progressive. If there is a lot of preload then the first bit of spring travel will be in a later phase and therefore a different rate than the first phase of spring compression. So surely that end of the car will have different suspension characteristics, i.e. will feel and behave stiffer. Also the force now required to first compress the spring will be greater ?
If you make the vehicle so low that the car comes close to the bump stops in normal use, you're likely to get some very uncomfortable characteristics as the suspension stiffens up suddenly when it hits the bump stops. Similarly (but to a lesser extent) if it's so close to the droop stops that it hits the droop stops in normal use, you'll feel it suddenly stiffen up and get notchy. If this only happens in extreme cases, inside wheels when unweighted underbraking and acceleration etc, then the weight on the wheel will already be so low that any notchiness is irrelevent. But if the loaded wheels are nudging the droop stops while you're swooping through bends and so on it might be more of a problem.
So, even if you have rising rate springs you won't change the effective spring rate at rest - all you're doing is changing how far the suspension can travel in bump and droop, before it hits the stops.
ISTR motocross rising rate linkages that rise exponentially ensuring they can never be bottomed out.
Possibly.
Lots of bikes have rising rate springs and, obviously, preloading a rising rate spring takes out the 'soft' part of the spring's travel. Rising rate linkages can similarly mess things up.
But (and I realise it's a pretty big 'but', because few linkages give genuinely linear rate), if you have linear rate springs and linkages, the rate of the the springs themselves remain constant (over normal working range - until they become coil-bound or hit the bump stops), so once you've applied enough weight to overcome the preload, they will offer the same amount of linear resistance as they would have if there were no preload.
Another fairly big 'but' for you, though... if you have, say, 500lb of preload on a spring, that spring does not start to compress until you have applied more than 500lb of load to it (though thereafter it will compress at whatever the linear rate of the spring is) BUT... the spring may not compress over the first 500lb of load, but the tyres sure as hell do, and tyres themselves act as rising-rate springs in series with the road springs.
Like I said, GreenV8s was applying a very simplistic model of things. It's quite an accurate model if you have perfectly linear rate linkages, dampers that automatically compensate for rebound rates and solid steel tyres. After that, it gets a bit more complicated.
But (and I realise it's a pretty big 'but', because few linkages give genuinely linear rate), if you have linear rate springs and linkages, the rate of the the springs themselves remain constant (over normal working range - until they become coil-bound or hit the bump stops), so once you've applied enough weight to overcome the preload, they will offer the same amount of linear resistance as they would have if there were no preload.
Another fairly big 'but' for you, though... if you have, say, 500lb of preload on a spring, that spring does not start to compress until you have applied more than 500lb of load to it (though thereafter it will compress at whatever the linear rate of the spring is) BUT... the spring may not compress over the first 500lb of load, but the tyres sure as hell do, and tyres themselves act as rising-rate springs in series with the road springs.
Like I said, GreenV8s was applying a very simplistic model of things. It's quite an accurate model if you have perfectly linear rate linkages, dampers that automatically compensate for rebound rates and solid steel tyres. After that, it gets a bit more complicated.
Sam_68 said:
Lots of bikes have rising rate springs and, obviously, preloading a rising rate spring takes out the 'soft' part of the spring's travel.
so seemingly in line with what I have discovered ? i.e. small bumps won't move the spring anymore because they don't give enough force therefore you get a less compliant and harsher ride.. jackal said:
Sam_68 said:
Lots of bikes have rising rate springs and, obviously, preloading a rising rate spring takes out the 'soft' part of the spring's travel.
so seemingly in line with what I have discovered ? I'm guessing - because you've told us nothing about the vehicle in question - but I'd suggest that the biggest influence of winding off the preload on ride/handling will be due to reduced spring rebound.
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