Or it's just preloaded and requires an extra effort.
Or it's just preloaded and requires an extra effort.
most of you guys are still making this way too complicated. stop thinking of preload as a force, and start thinking of it as a length (as has already been suggested).
and yes, the preload device does come free during shock compression. the spring remains fixed against the perch, but the preload device is allowed to move freely on the inside of the shock, using a piston and bumpstop. under tension, the preload device will apply equal pressure to the shock housing and to the spring, but when the spring is compressed the tension is relieved and the piston is allowed to move away from the bumpstop, and the forces become zero at both ends of the preload device. after this point the spring handles all the forces being applied to the suspsension, but before it, the spring handles none.
and yes, the preload device does come free during shock compression. the spring remains fixed against the perch, but the preload device is allowed to move freely on the inside of the shock, using a piston and bumpstop. under tension, the preload device will apply equal pressure to the shock housing and to the spring, but when the spring is compressed the tension is relieved and the piston is allowed to move away from the bumpstop, and the forces become zero at both ends of the preload device. after this point the spring handles all the forces being applied to the suspsension, but before it, the spring handles none.
omfg!!!
i think most of you have the right idea, but are over thinking it.
preload is simply a way of giving the car more effective suspension travel.
thats it.
if you have a 6 inch long 100 lb/in spring, and a 500 lb weight, the spring can only compress one more inch.
now that isnt very useful if you need to absorb shocks is it?
(actually it is already binding if the spring is only 6 inches long, lets say it has 6 inches of effective travel)
what preload says is that if you have a 9 inch spring with a 100 lb/in rate, and a 500 lb weight, and you preload it 4 inches, it will only compress one inch when you add the 500 lb weight, that way you have 4 inches of travel left for absorbing shocks in the road.
yes folks its really that simple.
preload is useful if you are limited by your lower (front) arms on your suspension.
the longer your arms, the longer your suspension travel.
in my camaro, the stock front spring rate is 750 lb/in.
sounds incredibly high.
well it needs to be, with no preload, and only 3 inches of travel, gm had no choice.
a common mod is to install a preloadable suspension and use either the same or softer springs for a better ride.
the real world application of preload in race cars is getting the cross weights accurate and even.
since the driver only sits on one side of the car (except in single seaters) most race cars have adjustable preload (using a device called a weight jack)
this lets the team adjust the suspension so that each front wheel is holding the same ammount of weight. same for the back wheels.
i think most of you have the right idea, but are over thinking it.
preload is simply a way of giving the car more effective suspension travel.
thats it.
if you have a 6 inch long 100 lb/in spring, and a 500 lb weight, the spring can only compress one more inch.
now that isnt very useful if you need to absorb shocks is it?
(actually it is already binding if the spring is only 6 inches long, lets say it has 6 inches of effective travel)
what preload says is that if you have a 9 inch spring with a 100 lb/in rate, and a 500 lb weight, and you preload it 4 inches, it will only compress one inch when you add the 500 lb weight, that way you have 4 inches of travel left for absorbing shocks in the road.
yes folks its really that simple.
preload is useful if you are limited by your lower (front) arms on your suspension.
the longer your arms, the longer your suspension travel.
in my camaro, the stock front spring rate is 750 lb/in.
sounds incredibly high.
well it needs to be, with no preload, and only 3 inches of travel, gm had no choice.
a common mod is to install a preloadable suspension and use either the same or softer springs for a better ride.
the real world application of preload in race cars is getting the cross weights accurate and even.
since the driver only sits on one side of the car (except in single seaters) most race cars have adjustable preload (using a device called a weight jack)
this lets the team adjust the suspension so that each front wheel is holding the same ammount of weight. same for the back wheels.
oh, and tristan you are right.
if a 100lb/in spring is preloaded (compressed by the suspension) one inch, and an 80 lb weight is applied, then the spring does not compress at all.
in a preloaded car suspension, or bike for that matter, you always want to have enough weight to at least compress the suspension a little bit with the cars weight.
if you have a situation like the 80 lb weight described above, then the car has essentially no suspension for a while then all the sudden bam, it compresses, which makes for very unpredictable handling, and is not a good thing.
if a 100lb/in spring is preloaded (compressed by the suspension) one inch, and an 80 lb weight is applied, then the spring does not compress at all.
in a preloaded car suspension, or bike for that matter, you always want to have enough weight to at least compress the suspension a little bit with the cars weight.
if you have a situation like the 80 lb weight described above, then the car has essentially no suspension for a while then all the sudden bam, it compresses, which makes for very unpredictable handling, and is not a good thing.
Hell of a bump there guy. You seen how old the thread is? 
LOL, but an interesting thread all the same 
True. I've learnt a little more from it.
whether it was the right info from the right people for instance...O_O'meh, ive seen worse lol.
sorry bout that.
sorry bout that.
Sadly, that isn't it. Preload is used to tune the handling and control the aerodynamic platform as well.
It is unlikely that a race car will ever have such soft springs and such little travel unless the designer was a fool. With stiffer springs and bellcrank suspension it's more likely to be 600lb wheel rate and 300lb load with a bit of preload to stop excessive initial sag (possibly combined with a droop limiter).
Indeed.
Whilst the basic maths IS that simple, it's usage isn't.
Or if you run a droop limiter, or if you have any aerodynamic reliance on the car, or if you want the car to behave differently at the turn in point or over curbs.
If only it was quite that simple.
What is the wheel rate and the wheel frequency?
If only it were that simple.
No, you use the pushrods for that, and try to keep the preloads and spring lengths as similar as possible, otherwise the car will feel different on left and right hand bends. Only use the spring platforms if you don't have pushrods. And often as not you only ever adjust the REAR suspension, and leave the front symmetrical.
A weight jack is found pretty much only in american 'race cars'.
Again, most race cars do that on the spring platform collar or on the pushrods if it has them.
Yes, we solved that query years ago.
Not always. Depends on the car and the application.
Unless you design for it - like on all F3 cars since 1994 and most F1 cars since 1980. Why have the suspension compress when all it does it soften everything up and upset the aerodynamics? If the car isn't designed for it - say a Seven type car, then yes, it would only be a very talented driver that tried it and made it work.
But thanks for contributing. If I need something explaining a couple of years too late then I'll be sure to ask.
I know where you're coming from but two things spring to mind (not saying they are correct though).
First is motorcycle suspension where spring preload is used to allow for a heavier/lighter rider.
Ok, we're agreed (I think) that the preload's purpose it to affect the ride height. We're also agreed that there is an optimum ride height that gives the correct geometry for both the suspension and the overall CoG and steering angle etc. So then, what is the purpose of the preload for allowing for riders of different weights? IF it has no affect on how much force is required to get the ride height to the correct setting what is the purpose of it for a rider of a different weight?
eg.. rider A weighs 70kg and lets assume this means the seat height (for the sake of convenience) is 100cm, which just happens to be optimum on this particular motorcycle. Now we all agree that if a 100kg rider sits on this bike the ride height is going to be lower, lets say 90cm, and therefore incorrect. So what do we do? we add preload, so that when the 100kg rider sits on the bike the ride height is once again 100cm. The question is: How can two different weight riders, (and therefore applied forces), result in the same deflection of the suspension system if the preload is not increasing the amount of force required to deflect the system initially?? or does the increased preload merely increase the initial height of the seat sans rider?
Second thought is. Isn't preload an analogue of torque settings in a bolt? which (I believe) affect the amount of force required to be placed on the bolt before it starts to deform?
Like I said, just questions/ideas. Not saying they're correct as I have to admit I find it a little confusing.
I can't see how this pre-load that you're adjusting. It doesn't have the effect you are describing. The obtain less deflection with a given load, you have to make the spring stiffer.
If pre-load is set by distance, then a stiffer spring will automatically result in more pre-load (force), but that still wouldn't mean it was the pre-load itself you were adjusting.
You're probably right, I haven't really thought it through. I just know that preload is used on motorcycles to either
a) Get the suspension back to the correct ride height for a different weight rider.
or
b) Alter the ride height for the same rider.
I've never thought to measure if there is any actual change of seat height (sans rider) with any change of preload so it may well just be that the overall suspension deflection changes too with the different weight riders.
Even so, the analogy with the torque of a bolt still seems interesting unless I've totally misunderstood how that works also.
The post you quoted was an earlier one from before I realised that the preload is created by the spring platforms not allowing the spring to expand - i.e. the damper internal bumpstops are reacting the spring preload. My test of putting a load on a free spring wasn't fair, accurate or indeed true.
So, with that in mind, let's move on...
Indeed it is, because bikes are sensitive to rake angle (overall) and ride height, so preload is used to ensure that the bike is sitting at the correct attitude for a given rider, but still allowing some sag for droop travel, which again is important for handling (i.e. will greatly affect tankslappers for example).
Let us say that the bike in question works best with 1" of droop with the rider onboard, statically. If you put a light rider on there, they might not be heavy enough to deflect the suspension enough, so less preload is used to compensate. That means that the preload force is overcome more easily, and the spring starts to move (compress) earlier. Put a heavy rider on, and the same settings will mean the spring will compress the 1" plus whatever the weight difference between the two riders is, hence the bike will now be too low... So more preload is required to maintain optimum heights.
The limits to the amount of preload are that the spring must never, ever rattle free on full droop, and the spring must never ever be compressed more than 80% of it's travel even when at full bump (for fatigue reasons). Within those limits you can do what you like really.
If the dampers were free to expend with no limit (clearly not possible), then yes more preload would result in a greater unladen ride height. But the damper can't expend beyond it's limits. In this instance then the spring is just compressed a bit more at max extension - i.e. a greater preload force.
Indeed. When you torque a bolt you are trying to preload that bolt to a certain figure (usually about 85% of the yield strength). Torque measurements are inaccurate, because they require the bolting conditions to be exactly the same - no more and no less lubrication on the threads, so imperfections in the threads and so on. The better way is a torque angle - torque to a lower value then add x degrees of turn. The best way is to accurately measure the length of the bolt before and after fitting so you can get precisely the right preload (stress being proportional to strain) even though the head torque to do that might differ by a large margin on seemingly identical bolts.
Conrod bolts are more often installed by measuring the length, as are other critical bolts. But frequently you can't measure the installed length of a fastener (e.g. cylinder head bolts), so you have to rely on one of the other two techniques.
Changing the material or grade of the threaded fastener WILL adjust the preload/torque required, as will adding lubrication. ARP bolts, for example, are given torque values using their specific lubricant.
Hope that helps. I've spent quite a long time on preload, droop limiters and such like for my motor racing.
So, with that in mind, let's move on...
Indeed it is, because bikes are sensitive to rake angle (overall) and ride height, so preload is used to ensure that the bike is sitting at the correct attitude for a given rider, but still allowing some sag for droop travel, which again is important for handling (i.e. will greatly affect tankslappers for example).
Let us say that the bike in question works best with 1" of droop with the rider onboard, statically. If you put a light rider on there, they might not be heavy enough to deflect the suspension enough, so less preload is used to compensate. That means that the preload force is overcome more easily, and the spring starts to move (compress) earlier. Put a heavy rider on, and the same settings will mean the spring will compress the 1" plus whatever the weight difference between the two riders is, hence the bike will now be too low... So more preload is required to maintain optimum heights.
The limits to the amount of preload are that the spring must never, ever rattle free on full droop, and the spring must never ever be compressed more than 80% of it's travel even when at full bump (for fatigue reasons). Within those limits you can do what you like really.
If the dampers were free to expend with no limit (clearly not possible), then yes more preload would result in a greater unladen ride height. But the damper can't expend beyond it's limits. In this instance then the spring is just compressed a bit more at max extension - i.e. a greater preload force.
Indeed. When you torque a bolt you are trying to preload that bolt to a certain figure (usually about 85% of the yield strength). Torque measurements are inaccurate, because they require the bolting conditions to be exactly the same - no more and no less lubrication on the threads, so imperfections in the threads and so on. The better way is a torque angle - torque to a lower value then add x degrees of turn. The best way is to accurately measure the length of the bolt before and after fitting so you can get precisely the right preload (stress being proportional to strain) even though the head torque to do that might differ by a large margin on seemingly identical bolts.
Conrod bolts are more often installed by measuring the length, as are other critical bolts. But frequently you can't measure the installed length of a fastener (e.g. cylinder head bolts), so you have to rely on one of the other two techniques.
Changing the material or grade of the threaded fastener WILL adjust the preload/torque required, as will adding lubrication. ARP bolts, for example, are given torque values using their specific lubricant.
Hope that helps. I've spent quite a long time on preload, droop limiters and such like for my motor racing.
Maybe I can help. I hope your imagination can keep up with this imagery.
On suspension the spring length DOES NOT MATTER as the wheels are not bolted to it. They are bolted to the damper body (or spring carrier if separate springs and dampers). Therefore the damper length is what matters.
If you put a spring on the damper so that when the damper is fully extended the spring just touches the platforms then there is no preload at all. Any force applied by the suspension is absorbed by the spring and results in spring/damper compression. A 50kg load will result in half as much travel as a 100kg load, and the force is directly proportional to deflection. Let us say that the movements are 5mm and 10mm respectively.
Now screw the spring platforms on the damper by a couple of turns. This is difficult as you are having to compress the spring. The extended damper length is the same though, and the force on the spring is reacted by the damper internals. The spring is now preloaded, and this is usually quoted by distance because it is always the same even if you change the spring rate. However, the force can easily be calculated if you know the deflection (the preload distance) and the spring rate.
In this case let us say that the spring is deflected by 2mm, which results in 20kg of force acting between the spring and the damper's internal stops (you can work out the spring rate, but I'm not going to, and chances are the numbers won't be consistent anyway).
Now apply the 50kg load to the damper - the first 20kg of that load is 'used up' by overcoming the force in the damper, and therefore results in no movement. The remaining 30kg deflects the spring/damper (in this case by 3mm). The 100kg load will deflect the damper 8mm.
Imagine we want the same compression from the heavy load that we got from the ligher load (a bit like the bike riders problem). With no preload we know the light load deflected the bike/spring/damper 5mm. To get that deflection with the heavier rider/load without changing the spring rate then we need 5mm preload. If the lighter rider was to get back on now then there would be no deflection at all...
Does that make sense? You can control static ride height by increasing the preload, without changing the eventual wheel rate. Which means that a lighter rider and a heavier rider have the same wheel rates, the same static deflection and, potentially, the same handling!!!
Hope it helps.
Motorcycle Spring Rate and Preload (handy dandy graphs included)
tristan, do you have to be such a, well, jerk?
yes, if you have a single seat race car where you have a more complex suspension than lower a arms and struts, then you adjust the suspension differently.
i have an 'american' car (as you put it) so that is the method i am familiar with.
your average joe should not go around thinking that its ok to preload the suspension so that there is no spring deflection at normal loading.
this was something that "lowriders" used to do back before air springs were affordable. thats why they bounce all over the road.
(they would remove the shock, put a long bolt through the spring and torque a lawnmower blade or similar down so that it would compress the suspension.)
in F1 and that type of racing, the tires do a lot of absorbing shocks.
besides, there arent pot holes on your typical lemans track.
oh, and if i remember correctly, the motion ratio for my front suspension is around 1.4-1.6 i think
yes, if you have a single seat race car where you have a more complex suspension than lower a arms and struts, then you adjust the suspension differently.
i have an 'american' car (as you put it) so that is the method i am familiar with.
your average joe should not go around thinking that its ok to preload the suspension so that there is no spring deflection at normal loading.
this was something that "lowriders" used to do back before air springs were affordable. thats why they bounce all over the road.
(they would remove the shock, put a long bolt through the spring and torque a lawnmower blade or similar down so that it would compress the suspension.)
in F1 and that type of racing, the tires do a lot of absorbing shocks.
besides, there arent pot holes on your typical lemans track.
oh, and if i remember correctly, the motion ratio for my front suspension is around 1.4-1.6 i think
Whether you have double unparallel wishbones or a sliding pillar makes no difference to preload, what it does, how it does it, and why you may or may not want it.
The average Joe shouldn't change the springs, dampers or wheels on their car, but they do. If they want to play with preload or zero droop suspensions then they can. Sure, on a bumpy road using a car that is meant for commuting, shopping, fun they will quickly realise that it's a bad idea, but they can do it if they like.
You've never been to Lemans, have you?!
If I remember correctly, then the motion ratio for my front suspension in roll is 1.397 and in ride it is 0.884. At the rear it is 1.81 (roll) and 1.22 (ride). Who cares...
Be aware that this is a forum about racing, in a thread about racing. I don't care what you do on your Oldsmobile that uses Jurassic technology, as it's not nothing to do with this thread. The thread is about preloading springs on a single seater race car. Along the way we might divert onto motorbikes or road cars slightly, but I'm not going to play nicely if you think most of this thread has anything to do with road cars or what the average Joe does to them.
By all means try and enlighten me on the application of preload with regard racing, aerodynamics, damping, handling and lap time. But I'm not interested in being chastised by someone who thinks F1 still uses the tyres as the main springing medium.
The average Joe shouldn't change the springs, dampers or wheels on their car, but they do. If they want to play with preload or zero droop suspensions then they can. Sure, on a bumpy road using a car that is meant for commuting, shopping, fun they will quickly realise that it's a bad idea, but they can do it if they like.
You've never been to Lemans, have you?!
If I remember correctly, then the motion ratio for my front suspension in roll is 1.397 and in ride it is 0.884. At the rear it is 1.81 (roll) and 1.22 (ride). Who cares...
Be aware that this is a forum about racing, in a thread about racing. I don't care what you do on your Oldsmobile that uses Jurassic technology, as it's not nothing to do with this thread. The thread is about preloading springs on a single seater race car. Along the way we might divert onto motorbikes or road cars slightly, but I'm not going to play nicely if you think most of this thread has anything to do with road cars or what the average Joe does to them.
By all means try and enlighten me on the application of preload with regard racing, aerodynamics, damping, handling and lap time. But I'm not interested in being chastised by someone who thinks F1 still uses the tyres as the main springing medium.
its quite amazing how much brighter you appear now that kev isnt there to outshine your sense of humour anymore
So to a degree it would be useful to have preload settings in LFS, am I wrong?
Go on
Yes, that would be great. Not one single simulator has managed to grasp single seater suspension yet, with preload, pushrod lengths, droop limiters, monoshocks, triple/quadruple shocks etc. Netkar might claim to, but the setups in that are awful, so I think it's not done well.
What is there to say? When F1 generated huge downforce via ground effect (and I don't mean pseudo ground effect that the current diffusers are being described as, but the awesomely huge amounts of downforce from the 80s) they went to virtually solid suspension.
But watch a modern F1 car and whilst there is little perceptable roll movement on the front axle, there is a visible, albeit pretty tiny, amount of dive, and at the rear the wheels are all over the place in roll and squat/lift. That is not 'using the tyres as the only suspension' in my book.
the current ride height setting does exactly the same as it is
You know, I have often wondered why most single seaters use tyres with what would be considered very high aspect ratios on a road car based race series. Why is that?? I mean I know the tyres themselves are of a completely different construction and therefore play a completely different role in terms of the suspension performance etc. What I'm not clear on is what is the benefit of the set up compared to the larger wheels/low profile tyre approach used on tin tops? Is it purely down to unsprung weight or is there something else going on? Would love to know.
I think it's mostly to keep the brakes on formula cars at a sensible size. The current fashion for low profile tyres on the road is daft though, as there are no benefits to it other than, in some eyes, looks.
I think higher profile tyres are more forgiving in their break away characteristics, have a lower spring rate, wear more evenly, accept more camber with less overheating and such like, without actually reducing the ultimate 'grip'.
But I'm not really sure, so I can't give you a certain answer...
I think higher profile tyres are more forgiving in their break away characteristics, have a lower spring rate, wear more evenly, accept more camber with less overheating and such like, without actually reducing the ultimate 'grip'.
But I'm not really sure, so I can't give you a certain answer...
No, it doesn't. Preload maintains suspension range while shifting the force over travel curve, which can mean the car/bike sits higher with more preload with a given load. True ride height is adjusted via an offset while maintaining suspension range (along with almost everything else).
In LFS, "ride height" changes the suspension range and spring length while maintaining spring rate (i.e. longer but fewer coils per unit length), which also changes how high the car sits (ride height). It's a very odd way of doing it.
In a way, I suppose it's similar to preload in that your load capacity increases, but you don't lose anything on droop. This also means you have less control over the car's stance.
Forbin's right. LFS always seems to run with zero preload, so the slightest load will reduce ride height.
LFS also needs bump stops and packers (ideally bump stops with a quoted rate), because the moment the underside of the car hits the ground first.
I would rather this aspect of LFS is improved before Scawen ruins it by adding blingy graphical effects.
LFS also needs bump stops and packers (ideally bump stops with a quoted rate), because the moment the underside of the car hits the ground first.
I would rather this aspect of LFS is improved before Scawen ruins it by adding blingy graphical effects.
Spring preload
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