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Incidentally, I just gave a call out to California to chat with KW.
KW makes the coilovers that Gollum is wearing, reputedly based on their own KW V1 solution, but it's not that simple.
John, who was most helpful, explained that the from KW's perspective, the JCW Coils are "private label" products.
This means KW designs and blueprints the solution and delivers that to their OEM customer, who then has to manufacture the result. KW does NOT manufacture them.
That also means that KW cannot provide the progressive spring rate graph for the final product as offered by MINI. Quelle domage.
John sympathizes with our predicament, but could only offer the insight that the KW branded competition solution for the F56 Works car has a linear spring, with rates starting at 400 pounds.
Maybe Yegor will prevail, he's still chewing on it.
In my travels I have seen reference to front rates as low as 230 /b/in, and as high as 685 lb/in, mentioned by folks living on ugly B roads and other folks racing on smooth tracks.
In sum, what I would do is most likely exactly what you've decided - go with the 400s, and polish my driving technique.
Sorry, but someone put a grain of sand in my oyster....
No pearls, but only this.
The reasoning which underpins roll bar choices. A deep dive, but worth it. In my view it's the punchline of a rather serious course on chassis/suspension dynamics.
This is also why smooth is fast, and why all race drivers are load transfer managers.
Doubling the load on a tire does increase it's lateral grip, but NOT proportionally. There is a net loss, and it gets greater as the load limit for the tire is approached. The implications of this when considering the rate of load transfer on front and rear axles is my takeaway. The result is understeer, balance, or oversteer.
In the picture of your car, consider this. My left front (static - corner weight) has 885 pounds of load. It's supported by a Falken Azeni RT660 at 225/45-17 with a load limit of 1,477 pounds.
Now with 3 degrees of body roll, and equal pitch, I speculate as follows. We know that at LEAST 500 pounds of load has gone somewhere, because that is the static load on our cars for RR and LR and the RR is way up in the air! I'll be conservative and assume that two thirds of that load went to the left rear, and one third went too the front axle. That's because the wheelbase is about 100 inches and the track is about 70 inches, with the CG 61% forward.
So static was - LF 885 -RF 885 -LR 500 -RR 500 but we've shifted 500, allocating 333 to LR, and sending 166 to the front axle. So what about that front axle?
In the picture, I observe that the outer half of the RF tire is not in contact with the pavement, so I then assume (that's 2) that the load on that tire is sharply reduced. Assumption three is that is is halved from 885, so again we've shifted the weight to the only remaining corner - the left front.
So let's review the sums transferred at the front axle.
We've got 166 pounds transferred from out back, so we'll make assumption number four that two thirds descends on the left front.
So now how much is my Falken bearing?
885 static load
447.5 transfer from RF
110.5 referred from rear axle
1443 total - remember the limit is 1447!
So final is - LF 1443 -RF 503 -LR 833 -RR 0 at the moment the picture occurred (maybe).
The left front tire deforms and cannot compensate for this grand responsibility! Anyway, an amusing thought exercise.
Sorry, but someone put a grain of sand in my oyster....
No pearls, but only this.
The reasoning which underpins roll bar choices. A deep dive, but worth it. In my view it's the punchline of a rather serious course on chassis/suspension dynamics.
This is also why smooth is fast, and why all race drivers are load transfer managers.
Doubling the load on a tire does increase it's lateral grip, but NOT proportionally. There is a net loss, and it gets greater as the load limit for the tire is approached. The implications of this when considering the rate of load transfer on front and rear axles is my takeaway. The result is understeer, balance, or oversteer.
In the picture of your car, consider this. My left front (static - corner weight) has 885 pounds of load. It's supported by a Falken Azeni RT660 at 225/45-17 with a load limit of 1,477 pounds.
Now with 3 degrees of body roll, and equal pitch, I speculate as follows. We know that at LEAST 500 pounds of load has gone somewhere, because that is the static load on our cars for RR and LR and the RR is way up in the air! I'll be conservative and assume that two thirds of that load went to the left rear, and one third went too the front axle. That's because the wheelbase is about 100 inches and the track is about 70 inches, with the CG 61% forward.
So static was - LF 885 -RF 885 -LR 500 -RR 500 but we've shifted 500, allocating 333 to LR, and sending 166 to the front axle. So what about that front axle?
In the picture, I observe that the outer half of the RF tire is not in contact with the pavement, so I then assume (that's 2) that the load on that tire is sharply reduced. Assumption three is that is is halved from 895, so again we've shifted the weight to the only remaining corner - the left front.
So let's review the sums transferred at the front axle.
We've got 166 pounds transferred from out back, so we'll make assumption number four that two thirds descends on the left front.
So now how much is my Falken bearing?
885 static load
447.5 transfer from RF
110.5 referred from rear axle
1443 total - remember the limit is 1447!
So final is - LF 1443 -RF 503 -LR 833 -RR 0 at the moment the picture occurred (maybe).
The left front tire deforms and cannot compensate for this grand responsibility! Anyway, an amusing thought exercise.
Cheers,
Charlie
Must watch this video but 3.00 am in the uk and the wifes asleep…
so if thicker bars and stronger springs will always push-back against this transfer overload, it seems counterintuitive that this isn’t always the best solution for going quicker. Without any understanding of tyre dynamics I know letting out the air/pressure must reduce the ultimate rating / load
Yet it seems this is what we all do on a track day, when things get hot, must be a Venn diagram out there with tyre temperatures/ contact area / direction of travel meets another diagram about load transfer rates, as it stands the rubber must be the “final spring” that we all tune without thinking about it in these terms.
Must watch this video but 3.00 am in the uk and the wifes asleep…
so if thicker bars and stronger springs will always push-back against this transfer overload, it seems counterintuitive that this isn’t always the best solution for going quicker. Without any understanding of tyre dynamics I know letting out the air/pressure must reduce the ultimate rating / load
Yet it seems this is what we all do on a track day, when things get hot, must be a Venn diagram out there with tyre temperatures/ contact area / direction of travel meets another diagram about load transfer rates, as it stands the rubber must be the “final spring” that we all tune without thinking about it in these terms.
Not to give you a headache, this material might be relevant. If I've understood...
Good morning all,
I am very much enjoying this thread. Here is the quick update, I am in my office and wont be able to read/watch all the material that has been listed until this weekend. The 400 pound springs come today and I plan to install them this weekend. Hearing the challenge cars run nearly 700 pound springs I have a feeling I am going to become an expert at changing springs. More updates to come! I will read/watch everything posted in the thread.
Not sure but I believe I was coming in way too hot into a slalom section. In later runs I smoothed things out but not sure. I still have a lot of work to do as a driver.
With all that has been discussed here for “fixing” a car’s handling, which, I am sure is good, this:
I still have a lot of work to do as a driver
actually is the best fix.
Set your car up, then leave it while you work on driving skills. This is what I did for learning how to drive on the track. To actually learn how to drive, I had access to both in-car instructors and classroom instruction. Teaching yourself is really hard to do and can lead to bad habits. And changing the car while learning will interfere with knowing if your skills have improved.
If you have access to someone who is a good instructor, have that person ride with you. Then pick out one or 2 turns to work on. One import thing to learn is how to “read” a new course as the course will change with each event. Then learn the general techniques for driving through each turn type and learn how to modify each technique for each of the actual turns that are in the course. This is much like learning how to alpine ski. One has to first learn how to make a ski turn, then has to learn how to modify that technique in order to navigate each of the runs that one may be on.
I know this is boring for a tinkerer (I know as that is my hobby, tinkering), but, as the saying goes, It is better to drive a slow car fast than a fast car slow.
Hope it all goes well for you, and looking forward to updates.
Lots of different opinions.
times from last weekend
2017 Mini COOPER S white 37.606 36.799 37.387 36.978 36.445 36.938 36.209
the really fast car was running in the 33's (2019 Subaru WRX STI) I recognize 3 seconds is a lot but still I was quicker than many
Last edited by johnnys2quick; 05-24-2024 at 11:21 AM.
Curiosity killed the cat, but mebbe I've made progress. Thanks to Yegor at Mini of Peabody for tracking this document down. I owe him a big one.
Here's the detailed specification for the JCW Pro Coil front spring. I'm trying to understand why the Ohlins MU001S solution appears to be a bit soft at the limit.
Since this is a progressive spring, with three primary coils, each coil has a different diameter. The larger the diameter (assuming equal spacing) the SMALLER is the torsional twist required to compress the coil, therefore the softer the rate for that coil.
Top (120 mm diameter) --> 357 lb/in
Middle (150 mm diameter) --> 183 lb/in
Bottom (89.5 mm diameter) --> 861 /b/in
Note: the calculator takes the inner diameter of the coil, excluding the wire width of 12.75 mm. In each case I asserted four coils, fooling the calculator to think I've a linear spring with the given diameter and the same coil count.
So as load is added to this spring, the softest coil will compress at the rate of183 lb/in until that coil binds (contacts itself). The next coil will compress at the rate of 357 lb/in until it also binds. Finally, as the spring approaches full compression, the third coil resists with 861 lb/in.
Given that the spring starts with a static load of 885 pounds, the middle coil should be bound unless the front end is partially unweighted and goes into "droop". That means I'm normally dealing with a rising rate varying between 357 and 691 pounds per inch of compression.
Here's Gollum, right front, static.
If I've worked this out correctly, it explains a few things, and also conforms to the wide spectrum of rates offered in linear sprung coil-overs.
However, you are treating it as a variable rate spring and MINI clearly states that it is linear.
I think that the first coils, top and bottom, are not counted (being too stiff to interact) and when the car is on the ground, at its ride height, the spring will act as a linear spring. I would subtract the top and bottom coils and make the calculations based on the coils that remain.
Left side is out, I need to go on a supply run and get a 22 mm open end, of course the largest in my tool box is 21 and my pass thru sockets stop at 19mm
What is the max camber that the Vorshlag plates give you? It looks like they may have max’ed out based on the inboard retaining bolts, but the slot for the bearing could give you more. Could you move those two inboard bolts to the other side (outboard side) of the two bolts that they are next to?
Not sure running a touch more than neg 2 degrees but I will let you know. I planning to order a camber gauge. They have more camber to give. Been studying a lot of suspension theory and I believe being able to adjust caster could be useful in that caster allows camber to increase in a corner. The f56 in stock form doesn’t all caster adjustment, to my knowledge.
Not sure running a touch more than neg 2 degrees but I will let you know. I planning to order a camber gauge. They have more camber to give. Been studying a lot of suspension theory and I believe being able to adjust caster could be useful in that caster allows camber to increase in a corner. The f56 in stock form doesn’t all caster adjustment, to my knowledge.
No, no caster adjustment.
Increase in caster is very important in autocross where steering angles are much larger than that seen in road course racing. Actually, negative camber is proportionally lost as steering angle increases. Caster becomes camber as steering input increases, which offsets the camber loss. Historically, increasing caster has been ignored in the aftermarket performance world for these cars, likely because of the minimal value in road racing where steering angle changes tend to be small (my guess).
It will be interesting to hear about what you find out there for increasing caster in these cars.
FWIW - A long time ago Grassroots Motorsports studied the effect of increasing the camber in a MINI Cooper. I seem to remember that they ended the study at -3.5 deg (or so). they found that alittle above -3 deg there was an increase in lap times at the road course they were using. This was a result of the reduced contact patch which decreased the car’s braking ability. I would set -3 as the max, unless you find you are not using much in the way of brakes.
Just an FYI - This is a link to a discussion on Grass Roots Motorsports about measuring spring rates. In there people note that a bit of preload of spring is desireable before starting the measurement in order to eliminate the effect of the end coils.
However, you are treating it as a variable rate spring and MINI clearly states that it is linear.
I think that the first coils, top and bottom, are not counted (being too stiff to interact) and when the car is on the ground, at its ride height, the spring will act as a linear spring. I would subtract the top and bottom coils and make the calculations based on the coils that remain.
They do have the word "linear" in that spec sheet, as noted.
But the JCW Pro Coil front spriings seem to me to be unmistakably progressive. The sharp variation in coil diameter (not wire diameter) is the giveaway.
One side benefit of the progressives is that unlike linear springs they do offer roll resistance, as in roll the outer spring rate rises, and the inner spring rate falls. The primary disadvantage seems to be complexity in dynamic modeling.
From my research coil diameter variation is used less often than coil spacing variation - but BMW seems to prefer the former. The differences are discussed here: https://www.eng-tips.com/viewthread.cfm?qid=392256.
But this is just my side show, as our OP took the linear path with the Ohlins.
Just an FYI - This is a link to a discussion on Grass Roots Motorsports about measuring spring rates. In there people note that a bit of preload of spring is desireable before starting the measurement in order to eliminate the effect of the end coils.
Got a friend that is willing to lend a horizontal wood splitter?
If so add a pressure gauge and some means of holding the spring in place.
Got a friend that is willing to lend a horizontal wood splitter?
If so add a pressure gauge and some means of holding the spring in place.
What could go wrong? ;-) Ever been in a shop when a spring got loose? In this case we'd need the better part of a ton of load to fully compress these springs....
Off topic for you johnny2quick, so my apologies. Wrapping my head around your challenge has made me curious regarding our setup differences.
Here's my best guess to date regarding the deflection curve under load for the JCW Pro Coils. Note the soft coils bind as previously described, hence the limit value of 1.8" of compression on each working coil.
But this is just me fiddling while you do actual work and testing... ;-)
As I expected, the middle coil binds even with the car at rest, the static load is greater than the capacity of that coil. It appears to act as a keeper, stabilizing the strut during droop.
Note that with 2 degrees of body roll (and our 70" track) the outer spring will compress 1.22 inches beyond static ride height, and the inner spring will extend an equal amount. At that point the outer is on the BOTTOM rate, and the inner is on the TOP rate (top coil not bound). The difference is 502 pounds, which is the "hidden" anti-roll effect of progressive springs.
Too many guesses to be accurate, but I think I'm close and applying the correct principles.
05-23-2024, 02:38 PM
