Suspension Setup Theory: Conflicts and Confusions….Help!
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Coming with a good amount of experience with suspension setup in the motorcycling world and trying to apply that to setting up my Elise has my head spinning!
From what I've been reading the collar that puts more or less pressure on the spring (called Pre-Load in the motorcycling world) is used to set up both ride height and corner weight balance. I.e. by adding more or less pressure on the spring you alter the height, thus the weight balance of the vehicle.
Now, I do think I understand why the corners need to be balanced, but using spring preload seems wrong.
In motorcycles, spring preload is set so that there is a certain amount of sag of the vehicle as it sits statically. The purpose of this is to allow for a certain amount of the suspension travel to "drop" into a hole or depression and also to allow a certain part of the suspension to handle "bumps." Also that usually sets the suspension to operate in it's intended sweet spot.
In motorcycles the ride height is then set by extending or shortening the actual component independent of the spring preload.
If I had my way, I'd rather set up my Elise like that. Can anyone help shed some light on this for me? :sad:
From what I've been reading the collar that puts more or less pressure on the spring (called Pre-Load in the motorcycling world) is used to set up both ride height and corner weight balance. I.e. by adding more or less pressure on the spring you alter the height, thus the weight balance of the vehicle.
Now, I do think I understand why the corners need to be balanced, but using spring preload seems wrong.
In motorcycles, spring preload is set so that there is a certain amount of sag of the vehicle as it sits statically. The purpose of this is to allow for a certain amount of the suspension travel to "drop" into a hole or depression and also to allow a certain part of the suspension to handle "bumps." Also that usually sets the suspension to operate in it's intended sweet spot.
In motorcycles the ride height is then set by extending or shortening the actual component independent of the spring preload.
If I had my way, I'd rather set up my Elise like that. Can anyone help shed some light on this for me? :sad:
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Semantics to some extent, but for me preload is when the suspension spring still is compressed some amount at full rebound travel. As you go stiffer on spring rate on standard shock travel you end up at less or even no preload on the Elige depending on ride height you choose. Roughly, you are at zero preload at 500+ lb/in front spring and 600+ lb/in rear and slightly lower than stock ride height. Above those spring rates and at lower ride heights, preload is gone, you are losing bump travel, and helper/tender springs enter the setup equation. Of course, you also can choose to decrease suspension travel in total and change the ratio of bump to rebound travel (you call it "sweet spot").
If you want to run equal preload side to side and corner balance (set ride height) then you need an adjustable end on the shocks (option on some race shocks). And, if you want to run preload at higher spring rates you must give up some rebound travel -- probably not a good idea for street driven cars.
Net is that what you describe for motorcycles can be done on our cars. Preload is another suspension tuning variable, but it has some effects on a car that are not there (I think) on a motorcycle.
Bob L
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The simple answer is that most Lotus shocks simply lack a ride height adjustment, so people compensate by playing with preload. The bad part is that in order to lower the car, you have to reduce the preload, which is really the opposite of what you want if you're limiting available suspension compression. To compensate, you need to play with spring rates. Overall, it makes suspension tuning substantially more difficult. Some of the higher end setups have proper adjustments at the shock mounts.
Motorcycles are far easier to check for proper spring rates because, as you know, you simply sit on the bike and measure. On the other hand, the driver weight isn't really relevant in a Lotus, so a 150 lb driver will probably have the same ideal spring rate as a 175 lb driver. Obviously not the case on a motorcycle.
FYI, some motorcycle shocks have position controlled valving. I have no idea how it works though.
Motorcycles are far easier to check for proper spring rates because, as you know, you simply sit on the bike and measure. On the other hand, the driver weight isn't really relevant in a Lotus, so a 150 lb driver will probably have the same ideal spring rate as a 175 lb driver. Obviously not the case on a motorcycle.
FYI, some motorcycle shocks have position controlled valving. I have no idea how it works though.
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Quite possibly so, however if the car is set up so that it sags too much, as in the case of wanting to lower the car with preload, then the car is sitting far into it's available travel, possibly leaving less of it's available travel for bumps.
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That is one of the dangers of lowering any car too much. Luckily for our cars, you can install aftermarket uprights that will lower the car without taking away any travel of the suspension.
It's just a pricey proposition that only track focused cars take advantage.
It's just a pricey proposition that only track focused cars take advantage.
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Is sag (the measurement of how far down the shocks are compressed or sitting with just the weight of the car + drive) ever measured when setting up car suspension? Too much sag and you sacrifice bump travel. Too little sag and you sacrifice rebound travel.
I'm thinking, set the sag, then change ride height and corner balancing with changing the shock length. Since I have the Nitron 3 ways with separate preload and separate shock length adjustment, maybe that will work?
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Thanks, this is all beginning to make more sense to me. :coolnana:
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Not really for cars. For bikes of course it's important because a) the rider's weight is a significant fraction of the total weight, b) the range of suspension movement is relatively large, c) the sag affects the rake.
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True, but it depends. For a pavement road race car, I can't think of an instance where one would want to run out of bump travel in a corner. For starters, your suspension spring suddenly is out of the equation and the tire becomes the primary suspension spring, etc., etc.
On a high downforce race car, particularly with a lot of sensitivity to ride height, suspension travel will be small and the bump/rebound ratio very important. Of course this doesn't describe the Elige and our ride height doesn't have dramatic effects on total downforce. Most of us probably can feel the effects of ride height changes on out cars as the result of weight transfer changes when cornering, however.
For our Eliges that do double duty as street and track bars, just simplify by going with 117/122 mm ride height F/R good Penske, Nitron, or Ohlins shocks with spring rates around 500/700 lb/ in F/R and enjoy it for a while before digging seriously into suspension optimization. In other words spend more time on tuning the driver.
Happy holidays!
Bob L
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Definitely! So let's see, I wonder if I can set the sag for 1/3 of the suspension travel, effectively using 2/3s of the travel for bump, then 1/3 for rebound. Then play with ride height and weight balance. Crap, way more complicated than tuning a motorcycle!
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Doc
What are you really trying to accomplish? Do you want to set the corner weights?
Toss out your 2-wheel thinking and think 4 wheels. Think in terms of a 4-leg table. If 2 legs on the same side are longer then they will carry more of the table's weight. If 2 diagonal legs are longer then they carry more weight. Thus if say the RR corner of your car is heavier than the LR corner go to the LF corner and lower the spring perch. Just like you'd do if you had a table that rocked.
Cheers,
Kiyoshi
What are you really trying to accomplish? Do you want to set the corner weights?
Toss out your 2-wheel thinking and think 4 wheels. Think in terms of a 4-leg table. If 2 legs on the same side are longer then they will carry more of the table's weight. If 2 diagonal legs are longer then they carry more weight. Thus if say the RR corner of your car is heavier than the LR corner go to the LF corner and lower the spring perch. Just like you'd do if you had a table that rocked.
Cheers,
Kiyoshi
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