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MotaLeira Coilover Springs What rating?
nitram38 - 6/4/10 at 08:14 AM

Right I'm going to change my air suspension to coilovers with hydraulic rams. My reason is that the car needs to be more predictable than a variable spring rate that I have now. That also coupled with the ability to dial in shock rates too.

Anyhow, I need to calculate what spring rate I need to start off with.
I have a corner weight guage to check each wheel, but the complications are the pushrod angles and the cam ratio's for the inboard shocks.
I need a formula to work out a starting point, because I'll probably end up changing them a few times, but I don't want to be a long way off to start with.
The car weighs 480kg so with two people I guess about 680kg.
So if anyone can give me a simple starting point to work out my springs, I'd be grateful

nitram38 - 6/4/10 at 09:33 AM

To be honest I haven't measured them yet but I know they are un-equal cams. Shocks will be normal way up but more horizontal.

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Frosty - 6/4/10 at 10:11 AM

You need the SPRUNG weight of the corner, and also the suspension leverage. It's a geometrical nightmare to work out on paper when dealing with inboard suspension, so my advice to you would be to work out the motion ratio by doing the following:

1) Decide on a base ride height.

2) Jack the car up, remove the damper, and then jack a wheel up so that it sits at base ride height in relation to the chassis (perhaps mark the pushrod and the body when car is on the ground, and when they line up in the air, you know you are at target ride height).

3) Put a ruler next to the wheel, and a dial gauge on the end of the bell-crank where the damper bolt connects..

4) Jack the wheel up by exactly 10mm, and see what 10mm equates to on the dial gauge (be as accurate as you can).

From this you will know what a 10mm movement at the wheel equates to at the damper, and from here you can calculate the suspension leverage ratio.

(Be warned that this ratio is not constant throughout the suspension compression, but ignore that for now).

Now you can work out a suitable spring to use. The calculations for spring rates in Allan Staniforth's Competition Car Suspension is extremely helpful. You need the corner weight, and the suspension leverage which you will now have.

You will be able to get very close to an ideal spring based on the above.

nitram38 - 6/4/10 at 11:36 AM

Right some measurements!

Front suspension no driver passenger. Corner weight gauge is 220 lbs

Rear Suspension
Corner weight gauge 300 lbs

Ratios:

Front: Rod movement 10mm Shock moves 7mm

Rear: Rod movement 10mm Shock moves 5mm

Weights are about right 480Kg is roughly 1060 lbs

need to add 200kg taking weight to 1500 lbs total

On an approx 60/40 split

Front should be 600 lb (300 lb per side)
Rear should be 900 lb (450 lb per side)

Now the ratios need to be taken into account

Am I right in thinking the rear ratio is
450 X 0.5 = 225 Lb

Front is 300 X 0.7= 210 lb?

Should I add some lbs to allow for errors?

Front would have to be minimum of 225 lb but go for 250 lb rears?

[Edited on 6/4/2010 by nitram38]

Bluemoon - 6/4/10 at 12:12 PM

quote:
Originally posted by nitram38
Right some measurements!

Front suspension no driver passenger. Corner weight gauge is 220 lbs

Rear Suspension
Corner weight gauge 300 lbs

Ratios:

Front: Rod movement 10mm Shock moves 7mm

Rear: Rod movement 10mm Shock moves 5mm

Weights are about right 480Kg is roughly 1060 lbs

need to add 200kg taking weight to 1500 lbs total

On an approx 60/40 split

Front should be 600 lb (300 lb per side)
Rear should be 900 lb (450 lb per side)

Now the ratios need to be taken into account

Am I right in thinking the rear ratio is
450 X 0.5 = 225 Lb

Front is 300 X 0.7= 210 lb?

Should I add some lbs to allow for errors?

Front would have to be minimum of 225 lb but go for 250 lb rears?

[Edited on 6/4/2010 by nitram38]


I think you should have:

450/0.5
450/0.7

.. As the springs need to be a higher rate as you have less movement than at the wheels...

Not an expert! Please check!!!

Dan

nitram38 - 6/4/10 at 12:24 PM

Originally when I had a 1:1 ratio on my rear springs, the air shocks could not lift the car. I changed it to a 2:1 ratio in favor of the air shocks and now it works. Therefore the shocks require less effort to lift the car not more.
I am assuming the same for the springs.
Less lbs on the spring side.

hughpinder - 6/4/10 at 12:42 PM

I think that, taking the rear suspension, you need 450lbs 'pressure' from lever arm. If 10 mm of movement at the wheel = 5mm at the spring then you have a lever with a 2:1 mechanical advantage - e.g the spring 'sees' 900lbs. If you want a spring to support this with 1 inch compression you need a 900lb/inch spring. If you only want to compress the spring 3/4 of an inch the spring rate will be 1200lb/inch, etc.
Then you work out the 'wheel rate' for a 900lb spring and find out that you're going to loose your teeth pretty quick!

IRRC, Wheel rate = (((motion ratio)^2)*spring rate)*sin(spring inclination))
=0.25*900*1 (assume spring at 90 deg to lever) = 225

Also IRRC Staniforth says F1 cars have a wheel rate 400+, soft road cars 60-70, sports cars up to 120, So it sounds like that would be pretty hard suspension!

There was something about front wheel rate should be higher than rear as well, or maybe the other way round - I can't remember - must do some homework tonight.

I hope that I remembered all that right!
Regards
Hugh

Frosty - 6/4/10 at 12:48 PM

That was quick

I assume with a corner weight gauge you are measuring just the total corner weight and not just the sprung weight. You need just the sprung weight.

Let's assume for a moment that 220lbs is the spring weight (excludes wheel and tyre etc).

First we'll work out the suspension leverage based on your measurements.

If the front rod moves 10mm and gives 7mm at the damper, 10 / 7 = 1.43, so your front dampers have a leverage ratio of 1.43 (so force on the damper is 1.43 times greater than it is on the wheel).

Allan Staniforth recommends that a track based car should start at 130CPM and you might adjust a little from there.

The calculation to work out suspension CPM is 187.8 x sqrt( (spring rate / suspension leverage squared) / corner weight)

So your calculation based on a 200lb spring will be 187.8 x sqrt( (200 / 2.05) / 100 )

This gives a frequency of 125CPM, so looking at a 225lb spring, that will give 133CPM so I'd go with this on the front.

You need to work out how how much weight the car will be carrying when it needs to be at its best and factor this into the total weight of the car, then to the calculations again. Best to use corner weight scales with driver (or driver and passenger) to get the total weights at each corner.

a 225lb spring will not give 133CPM when carrying two 100kg passengers you see - it will be less.

As for the rear, because of the massive leverage (2:1 ratio), you would need a 600lb spring to give you 133CPM. Again, this is with no weight in the car, so doing these calculations again with driver and passenger would show the need for even heavier springs.

Frosty - 6/4/10 at 12:51 PM

Well done Hugh that's the right way to think about it. It took me a while to type out my post but basically the same conclusion.

Run a super-strong rear spring, or alter the leverage.

I think it's far better to change the leverage since the bell crank mounts will be under some serious strain with that ratio and a high spring rate.

daviep - 6/4/10 at 01:36 PM

quote:
Originally posted by hughpinder
I think that, taking the rear suspension, you need 450lbs 'pressure' from lever arm. If 10 mm of movement at the wheel = 5mm at the spring then you have a lever with a 2:1 mechanical advantage - e.g the spring 'sees' 900lbs. If you want a spring to support this with 1 inch compression you need a 900lb/inch spring. If you only want to compress the spring 3/4 of an inch the spring rate will be 1200lb/inch, etc.


Regards
Hugh


Nah that's definately backwards, I can say this without any calculation at all, look at the pictures, the shock is on the long arm of the pivot.

Davie

nitram38 - 6/4/10 at 01:36 PM

quote:
Originally posted by nitram38
Originally when I had a 1:1 ratio on my rear springs, the air shocks could not lift the car. I changed it to a 2:1 ratio in favor of the air shocks and now it works. Therefore the shocks require less effort to lift the car not more.
I am assuming the same for the springs.
Less lbs on the spring side.


I'm a bit confused, so why did this work?
The air spring was the same before and after the cam change, except it worked under the 2:1 ratio.
Surely the load on the air spring was reduced not increased, therefore required less effort from the air spring?

daviep - 6/4/10 at 01:40 PM

quote:
Originally posted by nitram38
quote:
Originally posted by nitram38
Originally when I had a 1:1 ratio on my rear springs, the air shocks could not lift the car. I changed it to a 2:1 ratio in favor of the air shocks and now it works. Therefore the shocks require less effort to lift the car not more.
I am assuming the same for the springs.
Less lbs on the spring side.


I'm a bit confused, so why did this work?
The air spring was the same before and after the cam change, except it worked under the 2:1 ratio.
Surely the load on the air spring was reduced not increased, therefore required less effort from the air spring?


I agree.

nitram38 - 6/4/10 at 01:43 PM

Cheers, I didn't think I was going mad!

matt_gsxr - 6/4/10 at 01:50 PM

Isn't it the wheel movement that is important, not the rod movement.


The ratio of wheel motion to spring compression is the important thing. Then you need to remember to square this before determining the spring as described above.


Regarding the Staniforth recommendations, i.e. ~100cycle per minute, most people run stiffer than this. It isn't clear why Staniforth is too soft (his numbers are based on successful hillclimb cars), but it might be that we have higher unsprung mass, which is another nasty free variable.


Matt

Frosty - 6/4/10 at 02:06 PM

quote:
Originally posted by matt_gsxr
Isn't it the wheel movement that is important, not the rod movement.


The ratio of wheel motion to spring compression is the important thing. Then you need to remember to square this before determining the spring as described above.


Regarding the Staniforth recommendations, i.e. ~100cycle per minute, most people run stiffer than this. It isn't clear why Staniforth is too soft (his numbers are based on successful hillclimb cars), but it might be that we have higher unsprung mass, which is another nasty free variable.


Matt

Yes.

When I suggested that the motion ratio was measured, it should be measured by moving the wheel 10mm upwards and seeing what comes out at the other end so to speak.

Looking at the bell cranks, it doesn't look like a 2:1 ratio to me, even with the push-rod angle being what it is.

nitram38 - 6/4/10 at 02:17 PM

Springs on my car will hardly move a great deal because the car is so low. My whole reason I'm changing from the airspring to spring is to give me a constant spring rate, irrespective of my ride height and to give me an adjustable damper because I get a very slight oscellation on motorways without a passenger.
Im going to fit hydraulic cylinder rams under the spring to raise the car over obstacles. The spring rate will stay the same as it is only the shock getting extended and they will only be used at low speed over speed humps etc.
Surely my air springs are working at the correct rate to lift the car off the deck and drive perfectly well without ripping my mounts off therefore the replacement steel spring must be the same rate as my airspring to lift the car so should not pose any more of problem?

[Edited on 6/4/2010 by nitram38]

nitram38 - 6/4/10 at 02:22 PM

quote:
Originally posted by Frosty
quote:
Originally posted by matt_gsxr
Isn't it the wheel movement that is important, not the rod movement.


The ratio of wheel motion to spring compression is the important thing. Then you need to remember to square this before determining the spring as described above.


Regarding the Staniforth recommendations, i.e. ~100cycle per minute, most people run stiffer than this. It isn't clear why Staniforth is too soft (his numbers are based on successful hillclimb cars), but it might be that we have higher unsprung mass, which is another nasty free variable.


Matt

Yes.

When I suggested that the motion ratio was measured, it should be measured by moving the wheel 10mm upwards and seeing what comes out at the other end so to speak.

Looking at the bell cranks, it doesn't look like a 2:1 ratio to me, even with the push-rod angle being what it is.


I can only go by what my measurement told me.
I measured both points of the cam arm, lowered my car so that the pushrod moved 10mm and then measured the shock mount and that moved 5mm.
That is 2:1?

hughpinder - 6/4/10 at 02:28 PM

Don't forget that what was asked was the movement at the spring end for 10mm movement of the wheel - the mount for the rod that pushes the bell crank will be part way down the arm and may account for some of the overall ratio seen. The bell crank itself may have a 1:1, but if the push rod is half way down the suspension arm.....

Regards
Hugh

hughpinder - 6/4/10 at 02:31 PM

Sorry, I misread that,

I see you measured 10mm of rod movement - so probably 15+mm of wheel movement, is that right?

Hugh

nitram38 - 6/4/10 at 02:35 PM

My pushrod fixes just behind the bottom wheel hub and within the wheel it'self.
I cant see the ratio being greatly altered.

Frosty - 6/4/10 at 02:44 PM

quote:
Originally posted by nitram38
My pushrod fixes just behind the bottom wheel hub and within the wheel it'self.
I cant see the ratio being greatly altered.

Yes but the pushrod is not vertical, so the angle of it reduces movement.

Pushrods are usually about 45 degrees on a car, but just to make the point, imagine if it were at 90 degrees (horizontal). The wheels moves, but you would have zero movement on the bell-crank.

nitram38 - 6/4/10 at 02:44 PM

As for spring rates and talk of osscillation etc, I need a spring that supports the car plus passengers, not too soft that the car hits the deck or rolls excessively, not to hard that there is no give.
Surely my choice of spring is limited by whats available and the closest best guess?
I bet after all the calcs I end up changing them again!

Why hasn't some bright spark come up with a pressure type gauge that you fit in place of the coilover that tells you the actual weight required?
That would erase all this need for calcs!!

[Edited on 6/4/2010 by nitram38]

hughpinder - 6/4/10 at 03:00 PM

'Why hasn't some bright spark come up with a pressure type gauge that you fit in place of the coilover that tells you the actual weight required?
That would erase all this need for calcs!! '

I like that idea - its just that calculations are free and can be done before you build the car, wheras measuring needs the car to already exist, (and you'd probably want to set all 4 wheels at once). This wold give you the actual force needed to support the car. You would still need to decide how much compression of the spring is going to be used to hold the weight of the car, and also decide what wheel rate you want to use.

Regarding an earlier comment on Staniforths wheel rates being on the low side - could this be because he suggests using an ARB which allows the use of softer springs?
Hugh

MikeRJ - 6/4/10 at 04:11 PM

quote:
Originally posted by nitram38
Surely my choice of spring is limited by whats available


If you are using standard size coil overs with 1.9" or 2.25" springs then your choice is absolutely massive, both in spring rate and free length.

People have mentioned the frequency of the suspension simply because it's a very simple way of working out what spring rate is suitable for the weight of your car and a given application (road, track etc.).

As for the ratio between wheel and spring, why not measure it empirically, i.e. jack the car up and raise and lower the wheel whilst measuring damper movement. Presumably you have designed the system to give a rising rate anyway, and combined with your variable height control this is going to make your calculations somewhat more complex.

nitram38 - 6/4/10 at 04:28 PM

The new set up will be at a fixed height with the ability to raise the car without compressing the spring. So I need a spring calculated for the intial fixed height. When the car is raised it will not matter as it will be used for low speed obstacles. The car will be set up on this intial low height.
My springs are going to be limited to, the weight required to be carried, the length of spring by the length of my shock and hydraulic ram (meaning shorter springs) and the shock diameter.
The shock diameter is fixed, the length I need is fixed, only the rate I need to work out.
Maybe there is a massive range of springs, but there will only be one set at the given diameter and length I need available.
So therefore only one spring will do.
Allowing for set poundages available, I'm limited to the poundages available

[Edited on 6/4/2010 by nitram38]

MikeRJ - 6/4/10 at 05:06 PM

quote:
Originally posted by nitram38

Maybe there is a massive range of springs, but there will only be one set at the given diameter and length I need available.
So therefore only one spring will do.


Absolutely, my point was that you are most unlikely to be limited by "what's available". Once you have worked out what you require, the chances are very good that it will be easily available.

nitram38 - 6/4/10 at 05:10 PM

Right for 10mm of wheel travel off the ground I get the shock retracting

Front 5mm
Rear 7mm

Front before calc 300 lb fully laden
Rear before calc 450 lb fully laden

So anyone, whats your guesses?

[Edited on 6/4/2010 by nitram38]

Ivan - 6/4/10 at 05:50 PM

Don't forget that the rear springs should have a slightly higher CPM (normally 5% to 10% more) than the front that is calculated using the wheelbase and design speed to stop the very osselations you are talking about - again Stanniforth is your friend for the maths.

nitram38 - 6/4/10 at 08:23 PM

quote:
Originally posted by Ivan
Don't forget that the rear springs should have a slightly higher CPM (normally 5% to 10% more) than the front that is calculated using the wheelbase and design speed to stop the very osselations you are talking about - again Stanniforth is your friend for the maths.


What are the maths?
That was my original question!

andylancaster3000 - 6/4/10 at 09:45 PM

Have only read through the thread quickly so apologies for any repetition. I would strongly advise getting hold of a copy of this book:



The late Staniforth gives a very easy to read and follow answer to this very problem. All the maths you need is in there.

Unfortunately there there is no one simple formula that will give you the answer. As has been mentioned the first step is determine your desired wheel frequency, from this you can calculate your required wheel rate (this is a function of the unsprung and sprung mass at the corner). Once you have got this you will be able to determine the spring rate by finding the motion ratio between wheel and damper through doing a bit of geometry/trig calcs (or empirically as has also been suggested to get a rough idea).

This should give you a ball park figure of where to start.

nitram38 - 6/4/10 at 10:07 PM

Guy's I'm sure Allan's book is fantastic, but I came to this forum to find help in calculating my spring rate.
I don't want to buy the book for this.
All I asked was for some help.
Instead I feel like I've just been beaten over the head with the book.
You may love this book and good on you, but if all you can suggest is buy the book, why are you on this forum?
Sorry if I've affended anyone, but I've spent hundreds of posts trying to explain in laymans terms my knowledge.
All I'm asking for is some in return.

nitram38 - 6/4/10 at 10:12 PM

quote:
Originally posted by Frosty
That was quick

I assume with a corner weight gauge you are measuring just the total corner weight and not just the sprung weight. You need just the sprung weight.

Let's assume for a moment that 220lbs is the spring weight (excludes wheel and tyre etc).

First we'll work out the suspension leverage based on your measurements.

If the front rod moves 10mm and gives 7mm at the damper, 10 / 7 = 1.43, so your front dampers have a leverage ratio of 1.43 (so force on the damper is 1.43 times greater than it is on the wheel).

Allan Staniforth recommends that a track based car should start at 130CPM and you might adjust a little from there.

The calculation to work out suspension CPM is 187.8 x sqrt( (spring rate / suspension leverage squared) / corner weight)

So your calculation based on a 200lb spring will be 187.8 x sqrt( (200 / 2.05) / 100 )

This gives a frequency of 125CPM, so looking at a 225lb spring, that will give 133CPM so I'd go with this on the front.

You need to work out how how much weight the car will be carrying when it needs to be at its best and factor this into the total weight of the car, then to the calculations again. Best to use corner weight scales with driver (or driver and passenger) to get the total weights at each corner.

a 225lb spring will not give 133CPM when carrying two 100kg passengers you see - it will be less.

As for the rear, because of the massive leverage (2:1 ratio), you would need a 600lb spring to give you 133CPM. Again, this is with no weight in the car, so doing these calculations again with driver and passenger would show the need for even heavier springs.


Frosty, in your calcs, where did your corner weight of 100 come from?
My front corner weights were 300 lb.
If I can understand this part of your calcs I can figure the rest thanks

Frosty - 6/4/10 at 11:48 PM

quote:
Originally posted by nitram38
quote:
Originally posted by Frosty
That was quick

I assume with a corner weight gauge you are measuring just the total corner weight and not just the sprung weight. You need just the sprung weight.

Let's assume for a moment that 220lbs is the spring weight (excludes wheel and tyre etc).

First we'll work out the suspension leverage based on your measurements.

If the front rod moves 10mm and gives 7mm at the damper, 10 / 7 = 1.43, so your front dampers have a leverage ratio of 1.43 (so force on the damper is 1.43 times greater than it is on the wheel).

Allan Staniforth recommends that a track based car should start at 130CPM and you might adjust a little from there.

The calculation to work out suspension CPM is 187.8 x sqrt( (spring rate / suspension leverage squared) / corner weight)

So your calculation based on a 200lb spring will be 187.8 x sqrt( (200 / 2.05) / 100 )

This gives a frequency of 125CPM, so looking at a 225lb spring, that will give 133CPM so I'd go with this on the front.

You need to work out how how much weight the car will be carrying when it needs to be at its best and factor this into the total weight of the car, then to the calculations again. Best to use corner weight scales with driver (or driver and passenger) to get the total weights at each corner.

a 225lb spring will not give 133CPM when carrying two 100kg passengers you see - it will be less.

As for the rear, because of the massive leverage (2:1 ratio), you would need a 600lb spring to give you 133CPM. Again, this is with no weight in the car, so doing these calculations again with driver and passenger would show the need for even heavier springs.


Frosty, in your calcs, where did your corner weight of 100 come from?
My front corner weights were 300 lb.
If I can understand this part of your calcs I can figure the rest thanks

Sorry that 100 should be 220.

I wrote it in kg and not lbs, but obviously is has to be relative to the spring, so 100 should be 220, which is the corner weight you mentioned back on page 1. This is where I got the corner weight from.

If all you want is just to know a good starting point for the springs, you can work it out from the above.

nitram38 - 7/4/10 at 06:10 AM

Thank you, it was the only part of the formula that confused me!
I now understand how it works and the results might suprise everyone!
I'll redo my sums later and post them.

nitram38 - 7/4/10 at 08:18 AM

Front ratio is 10/5 = 2
Rear ratio is 10/7= 1.43

Front 187.7 x sqrt (575/4/300) = 129.93

Rear 187.7 x sqrt (450/2.05/450) = 131.2

This figures do make sense considering the rear cams give the spring more leverage (spring on longer side of cam) and the fronts give the wheel more leverage (spring on shorter side of cam).

Wierd as it seems the results are

575 lbs front 450 lbs rear

hughpinder - 7/4/10 at 10:54 AM

Your calcs look correct to me.
I might say go for slightly higher rear cpm to get to the reccommended 5 to 10% higher rate at the rear, as commented earlier

Regards
Hugh

nitram38 - 7/4/10 at 04:52 PM

so 475 or 500?

MikeRJ - 7/4/10 at 08:54 PM

quote:
Originally posted by nitram38
Front ratio is 10/5 = 2
Rear ratio is 10/7= 1.43

Front 187.7 x sqrt (575/4/300) = 129.93

Rear 187.7 x sqrt (450/2.05/450) = 131.2


The motion ratio is the ratio of spring movement to wheel movement, in your case:

Front: 5/10=0.5
Rear: 7/10=0.7


The full formula is:

SF = 187.8 * SQRT( ( MR^2 * SR ) / SW )

If you want to find spring rate for a given sprung weight and frequency then re-arrange:

SR = ( SW * (SF/187.8)^2 ) / MR^2

Where
SF = Suspension frequency in cycles per minute (cpm)
MR = Motion ratio (spring motion/wheel motion)
^2 = Squared
SQRT() = Square Root
SR = Spring rate
SW = Sprung Weight i.e corner weight minus the unsprung weight.

The sprung weight part is important; for lightweight cars where the sprung weight is often a significant fraction of the corner weight ignoring this will lead to a softer than intended spring rate.


Or you can use this online suspension rate calculator, but be aware that "Suspension leverage" is expressed the other way, i.e. 0.5 for the above formula would be 2:1 for the web page above.

nitram38 - 7/4/10 at 09:06 PM

I totally give up!
You are saying to calculate the ratio one way and Frosty another.
I don't know who the hell to believe!

prawnabie - 7/4/10 at 09:08 PM

Perhaps a conversation with procomp might yield some more information?

prawnabie - 7/4/10 at 09:08 PM

Perhaps a conversation with procomp might yield some more information?

radom - 7/4/10 at 09:45 PM

quote:
Originally posted by nitram38
I totally give up!
You are saying to calculate the ratio one way and Frosty another.
I don't know who the hell to believe!


imho these formulas will give the same result,
the only difference is that Mike is multiplying spring-to-wheel ratio instead of division by wheel-to-spring ratio

MikeRJ - 7/4/10 at 10:07 PM

quote:
Originally posted by nitram38
I totally give up!
You are saying to calculate the ratio one way and Frosty another.
I don't know who the hell to believe!


Well, the notes I have agree with both the online calculator I gave you the link to and Eibachs suspension worksheet. Your choice.

Taking unsprung weight into account is important though.

[Edited on 7/4/10 by MikeRJ]

Frosty - 7/4/10 at 10:58 PM

quote:
Originally posted by radom
quote:
Originally posted by nitram38
I totally give up!
You are saying to calculate the ratio one way and Frosty another.
I don't know who the hell to believe!


imho these formulas will give the same result,
the only difference is that Mike is multiplying spring-to-wheel ratio instead of division by wheel-to-spring ratio

That's correct. As you say, Mike suggests you multiply when using motion ratio, and have have suggested you divide using suspension leverage ratio. It will give you the same answer though.

10 * 0.5 is the same as 10 / 2.

With your 10mm travel = 5mm at the damper, Mike says you should multiply by 0.5 squared, whereas I have given a formula where you divide by 2 squared - they give exactly the same answer.

If you want me to explain why this calculation comes back the same then I will, but I fear you just want a quick answer and that is that, in which case you should go with the springs you decided on back in page for which look right based on what you are telling us.

Just ensure that the weight you are calculating with is only sprung weight. As has already been said, unsprung weight will distort your calculations quite a bit on a light car.

nitram38 - 8/4/10 at 05:08 AM

Well my airshock spring rating tops out at 735lb and are rated from 135lb.
I run the air at around 80 psi. Max is around 100 psi. This generally gives me the impression that my spring rates will be close enough, but I reckon I'll end up changing them!

nitram38 - 19/5/10 at 10:23 AM

I've fitted the front shocks so far and after a road test seem spot on!


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