When working with wheel rates and spring rates, what is the variable "wheel travel"? Is it the entire range of motion of the wheel (from full droop to fully compressed) or is it any distance defined by you?
eg. The wheel can move an absolute distance of 10", so I plug 10" into my formula
OR
I raise the wheel up 1", and so I plug 1" into my formula
for wheel travel.
It looks to make a huge difference in the final rates, so I'm guessing its kind of important

 

The more I think about it, the more it makes sense that "total wheel travel" is the total amount of travel you allow the wheel to have in any situation, whether it is during cornering or road imperfections.
Looks like a softer spring rate allows more wheel travel (duh), which provides an easier ride (double duh...), and vice versa (omgimmagenius).
Did I miss anything?

 

one point you should remember,
is that the ammount the shock moves is different than the ammount the wheel moves.

i believe the shock actually moves 25% less than the wheel does..

 

Right the motion ratio was an easy calculation to make, but determining an effective spring rate is where it gets tricky for me, without knowing what exactly the "total wheel travel" variable is.

 

The effective spring rate is what ever your actual spring rate is, times the motion ratio...

500 (lb/in) x .7 (motion ratio) = effective spring rate (lb/in)

 

My ultimate goal is determining the appropriate spring rate for a given application, though. So I need to factor in wheel travel, along with spring angle and sprung cornerweight. The last two I can find easily enough, its wheel travel that is messing me up.
edit: So in a way I am working backwards from where most people begin, as they are less concerned with finding the spring rate as they are in finding out how much of the spring rate is acting on the wheel.

 

I would think wheel travel should be measured from your wheels location at static ride height, to it's location at full compression. The amount of droop is incosequential...

If that's the case, then you could just triagulate your suspension location (in relation to the chassis) at the center of your hub with your car on the ground. Then remove your wheel/spring/bumpstop and measure from that triangulated point, all the way up to full compression.

Sounds resonable...

 

Thats the assumption I'm working off of at the moment, and the results are definitely reasonable.
Although I have been measuring with the car jacked up, wheel off, so there was a bit of suspension droop. Even the slightest change in total wheel travel makes a HUGE difference in the overall spring rate you come out with, so I'll have to take static ride height into consideration. Thanks for the heads up

 

With the whole car on jackstands, put a jack under one of the LCA's. Lift that LCA until the chassis just barely comes off the nearest jackstand. Now take your static ride height measurement (should be VERY accurate like that). Then do the same without the spring/bumpstop installed. Now jack up the LCA again until the shock completely bottoms out and barely lifts the chassis off the jackstand again. Take your second measurement...

Oh yeah, and check some suspennsion websites to make sure this is how your wheel travel is supposed to be calculated (eibach has good info)...

 

Excellent, I'll give that a go this afternoon. Thanks again

 

No problem. Make sure to update this thread. Your project sounds pretty interesting...

 

Interesting note: the angle of the spring plays a very small part in the ultimate desired spring rate. So although an angle correction factor is necessary, its not as crucial as I first expected it to be, so it doesn't explain my 10kF/8kR-springs-work-on-a-WRX-and-Civics-too problem.
Doesn't bode well for me, as it looks like my first batch of WRX coilovers are going back to the factory for revalves and rebuilds. But we'll see what the numbers say I suppose.

 

I didn't realize you designed coilovers...

 

I dabble
I've been into cars for maybe 6-7 years now, but only recently did I become involved in the suspension side of things. Coincidentally, a few months back, my father and I were introduced to a few guys in Taiwan who run a factory that is capable of producing some very high quality coilovers. They needed a market, and to be honest, my dad and I wanted to get into a fairly lucrative market. So here we are presented with a once-in-a-lifetime opportunity to actually give back to the motorsport world we love so much, its all very exciting!
As you can see there's a bit of confusion as to what goes exactly in Taiwan regarding the production of coilovers, and its such a convoluted situation that I don't understand it myself. All I know is that we have a chance to produce a coilover of a craftsmanship and performance that has yet to come out of Taiwan, and thats what we are aiming to do. Its taking quite a bit of time, but we all suspected as much getting into it. The U.S. market is a demanding one, and we don't want to let anyone down.

 

Aside from any wheel rate calculations the biggest factor in choosing a spring rate would be what the car is going to be used for. Street, Autocross, Track, Drag, will all have different ideal rates not to mention driver preference.

Personally I think Ground Control has the right idea of letting the customer pick their own spring rates or have a suggestion if the customer is clueless.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">Aside from any wheel rate calculations the biggest factor in choosing a spring rate would be what the car is going to be used for. Street, Autocross, Track, Drag, will all have different ideal rates not to mention driver preference.</TD></TR></TABLE>
Definitely, these things will be taken into consideration, but I want to know where to start from initially.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">Personally I think Ground Control has the right idea of letting the customer pick their own spring rates or have a suggestion if the customer is clueless.</TD></TR></TABLE>
Ground Control is fortunate enough to be able to provide precise spring rates. At this point, I am only able to source certain spring rates due to the way they are produced. In a previous thread I had said that each reel of wire could only produce one spring rate, and I was corrected, and I was indeed wrong. I spoke to the guy who produces our coils again, and while we *could* produce a range of spring rates from one reel, they cannot do that for us for whatever reason. So for now, we will stick with the rates we have, and hopefully the numbers I get support the use of what I have available (4.5k, 6k, 8k, 10k, 12k, 14k, 18k) for most applications.

 

you don't need to know the total wheel travel to determine spring rates. The motion ratio is actually an equation relating wheel travel to shock travel (often approximated to a constant). Spring rate = Wheel rate*MR^2 , where MR is motion ratio of shock to wheel.

The spring rate will be dependent upon corner weight, but you will need to choose spring rates to acheive the ride height, ride frequency, motion control (yaw, pitch, roll) as well as what kind of roll stiffness distribution you need. There's a lot more than that, too.

 

It looks like I would need total wheel travel to calculate wheel rate, which is the necessary to calculate spring rate. So total wheel travel is indirectly related to spring rate, no?
This is the equation that I'm using for Wheel Rate:
Wheel Rate = Sprung Weight / (.4)(Total Wheel Travel)
In which case, it looks like wheel travel is taken into consideration but in a roundabout way.
And from there I would calculate motion ratio and finally spring rate. I haven't even begun to think about things like ride frequency and that sort of thing.

 

The motion ratio is dependent only on the geometry of the suspension. An easy to find it is to take off the spring put the wheel in full droop...that's your zero position. Move the wheel in bump 0.5", and measure the shock compression. Then move the wheel another 0.5" and get plot an equation between shock travel and wheel travel. You don't need to know the total wheel travel, since you aren't changing the mounting positions off your damper and your "total wheel travel" is going to be determined by when your shock bottoms and tops out (unless you have an UCA hitting your fender).

Your wheel rate is determined from your spring rate...it doesn't really make much sense to do it the other way around.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">Your wheel rate is determined from your spring rate...it doesn't really make much sense to do it the other way around.</TD></TR></TABLE>
The reason I do it the other way around is to determine what the correct spring rate *should* be, given the other factors. My end goal isn't to determine wheel rate, but spring rate. So I am asking,
"Given this wheel rate, what spring rate should I be using?"
instead of asking,
"I have this spring here, with this spring rate. I wonder how much of the spring rate is effective at the wheel?"

 

How are you going to find a wheel rate without knowing a spring rate?

So you basically have a required wheel rate, and you are trying to find the spring rate to match. So your new problem is finding the optimal wheel rate.

 

Sort of. Because I wasn't too sure what total wheel travel was. What 94eg says makes sense, so I will be going by those numbers. I've done some more thinking about it, and I will also try and vary total wheel travel and see what sort of numbers I come out with.
It looks like total wheel travel can be varied, and which would result in different spring rates, following the principle that shorter total wheel travel would require a higher spring rate, and conversely a longer total wheel travel would require lower spring rates (assuming physical suspension geometry remains unchanged).
In the formula
Wheel Rate = Sprung Weight / (.4)(Total Wheel Travel)
I can vary total wheel travel, which would yield different wheel rates. Small changes in total wheel travel have significant changes in the final spring rate, so it plays a major role in these calculations. By using the method that you and 94eg described to find total wheel travel (get static ride height, then remove springs and compress the lca with a jack until the wheel hits the fender), I can vary the total wheel travel.
If, by using stock static ride height, I get X total wheel travel, I can say "That is too much wheel travel, I want to limit it to X-2"." The final spring range changes dramatically, which IMO is to reflect the decreased amount of total wheel travel allowed. In other words, you are limiting body roll, the compression of the suspension over bumps, increasing suspension frequency (harsher ride, no?) and other things associated with wheel travel. In doing this, I don't change the way that motion ratio is calculated at all.
This is where I might be stretching it, but I'd like to see what you guys think: How can I vary total wheel travel, if its defined by static ride height, and the physical suspension geometry (where the wheel will hit the fender)? I think that the stiffer springs add a "limit" to total wheel travel, on top of the physical limits of the suspension geometry. So its possbily that the spring rate is stiff enough that in no situation would the wheel ever make physical contact with the the fender, but instead body movement would be controlled to the point where the spring is the actual limit, not allowing the wheel to move any further.

Of course, in a real world situation, there will be times when so much force is applied that it overcomes the spring rate, and if the static ride height is too low, then the wheel will bottom out. Go back to this equation:
Wheel Rate = Sprung Weight / (.4)(Total Wheel Travel)
in which case total wheel travel has been increased, but only because more force than normal has been applied to the suspension (sprung weight), while wheel rate has remained the same.
In any case, what I'm trying to say is that wheel travel can be limited by spring rate,
and because what you want to do with stiffer springs is control body motion,
and total wheel travel is directly related to body motion,
you can find the proper spring rate needed to achieve the desired total wheel travel in the above formula by simply entering in your desired wheel travel.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Noob4life &raquo;</TD></TR><TR><TD CLASS="quote">So its possbily that the spring rate is stiff enough that in no situation would the wheel ever make physical contact with the the fender, but instead body movement would be controlled to the point where the spring is the actual limit, not allowing the wheel to move any further.
[</TD></TR></TABLE>

The hardest part is going ot be guessing the traction limits of your customers vehicles. While most street cars cannot pull 1g, slicks on racecars are capable of significantly more (requiring higher spring rates). I think these formulas would work a little better if you were designing a suspension for one particular car, but everybodies civics are setup differently (even stock ones).

 

Ah tires. I haven't factored in tires.
It will definitely be tough to find the "holy grail" of spring rates for each application, but it would be nice to find out at least how to approach it. On the production side of things, its not our concern to find the perfect spring rate for each application, because it be nearly impossible, or at least not financially feasible (at this time). What we'd like to do is determine what is good, and be able to justify why we offer what we offer with some empirical evidence.

 

I can appreciate that...