Kurvhgr you're a friggin GENIUS!!! (sorry I just had to scream that one out...). I decided, what the hey, and order me a set for the front and back 375lb spring, and I thought I had it good with the 8kg that MR supplied!!?? No Way!! This set up far exceeds the ride/handling over the 8kg and it tightens the back end nicely.

The ride/handling feels a lot more balanced over the other set ups I've had with the MRs. I still haven't taken it on a long trip, just around town. The usual bad freeways we have around here and side roads and so far no bumpstopping. I will agree completely with your assesment on your original post here.

Now, because of the heavier car of mine (cabrio), I decided to go with the 7"=177.8mm up front instead of the 150mm original. I simply adjusted the pre-load nut 15mm downward (from my settings with the 8kg) to compensate for the additional length of the spring. I tried to maintain as much damper travel as possible via this change. I don't have much more room to lower the front of the car but maybe 1/4", but I really like where it sits right now and don't want to go any lower. Let me just say that I would not recommend
this on non-cabrio Minis 'cause you'll loose a considerable amount of ride heigth adjustability via the pre-load nut.

Overall, it really does provide a smooth ride over the bumpies, nice tight handling, and a very balanced and controlled feel when pushing the car.

What gets me is that it seems that we, the consumer, have been the ones that have continued to look for better solutions to the original problem.

Thanks again, Kurvhugr, for sticking with this one...

 

Nice to read kurvhugr!

You've gone a similar route; I'm simply changing out the front springs for eibach 375# springs and leaving the rears. I'm installing 15mm spacers and this reduces wheel rate by about 10%. some my final wheel rates will be fairly equal and a little lighter than yours - should feel like 340# springs all around...or a hair higher up front.

The 469# spring offered as a fix from Megan does work, but as was pointed by kurvhugr, balance suffers as do kidneys - you got it right Doc! I also think those springs are too long. A shorter spring will allow the spring to tensioned just enough at the very top of the threads, retaining as much travel as possible.

I did not know Megan's offered new bump stops ???

 

hey guys. Would this 375-400 lbs/in spring rate be recommended for any coilover system, or just megans? I'm not sure what rate to specify when buying coilovers.

 

Great to hear! Was your pre-load similar to Kurvhugr's?

Interesting on the Megan site, the C/O's come 6K/6K.

 

I don't have mine yet, but the preload on the 469# springs from Megan was too much...and the coils do make a lot of noise. 8" springs should be fine. The 8" spring's travel at 2.5" is 4.88". The 2.25 in dia springs' travel is 4.36". As kurvhugr pointed out, these are slightly barreled to allow for more travel...and perhaps less noise.

Mine came from Truechoice. I won't install these until spring - no punn! There are other subtle changes come as well.

 

Megan quoted me that anything over 150mm in the front is unnecessary due to piston travel limitations. What length did you order? Thanks for the help.

 

More similar than you know! I happen to have 5mm spacers up front, plus the 7.5" wheels w/ +42mm offset.

I matched the original spring lengths.

Here's a pic I took of the bumpstops - it's a lousy pic, but good enough for the purpose - original on the left and retrofit on the right.

 

Okay, my bumpstops look almost the same...mine were cut by hand

Also, something else to learn and look at here; Block length and block rate define two other spring characterisitics. Block length is the total compressed length of a spring. Block rate is the spring's rate that nano second before it is fully compressed. Here's a comparison between two 375# springs 8" long, one spring is 2.25" dia and the other is 2.5"dia - inside dia.

2.25" Block length 3.64" Block rate 1,636#

2.5" Block length 3.12" Block rate 1,829#

So here we have a have two springs with seemingly identical characterisitics, if you look at rate only. But the 2.5" dia spring has more travel and more rate as it reach block height. This may or may not be a concern for some applications while important for others.

My 15mm spacers will be used with 38mm offset wheels up front and the 5mm spacers with the same offset in the rear.

 

I'm afraid it doesn't carry over that easily. It depends on the characteristics of the coilover dampers, spring lengths, etc. It's one thing to get lucky (like I did) in making an adjustment after you already have experience with a set of coilovers. Specifying a custom rate without an experiential starting point is a real cr*p shoot. However, anyone selling coilovers with custom spring options will have (hopefully) experienced and tested them, and should be able to advise you well. I would just call them, ask them to try describe the character of the standard setup ride, etc, and then describe what you're hoping to end up with.

 

Michael, you've mentioned 8" springs twice now.....where are you stuffing those? For the benefit of anyone else following along, the original Megan springs are 150mm front (~5.9") and 180mm rear (~7.1").

 

Here's a big generalization and it does not inlcude damper characterisitics. Linear rates only and for car weighing in at around 2,500 - 2,600 lbs.

180-250 street to sporting street driving

250 - 350 lbs sporting street to occasional track driving

350 - 450 and above, occasional track driving to track only

These rates are determined by vibrations per second or minute...in other words, the car body sans (I think?) unsprung mass is stimulated in some way so that as it moves up and down its natural virbrational frequencies can be counted. The final number is given in mega hertz and a then a baseline spring rate used selcted based upon intended use, and expeirennce. The someone hopefully drives the hell out of the car to make the rates work as intended...read, R&D

 

Thanks - just passing along something that worked for me.

I'm surprised you used a longer spring in the front. I remember discussing longer springs in your other Megans thread but I think I dropped that idea when I read about increased ride height with the 8kg springs. I suppose I also wanted to end up with something that didn't require spring preload. Anyway, I would probably have just upped the rate to maybe 400 lb/in and stuck with 6" length, but it sounds like your choice is working out great for you.

I know a lot of people look at the Megans as pure cr*p now, but I think they wrote them off too early. Yes, they should have come from the manufacturer without the travel problem, but they're not so happy about how this worked out either. However, once you pair the dampers up with the "right" springs, they're a very nice piece of kit.

 

I ordered my springs from memory...I hope 8" is correct. I'll confirm this weekend. I remember the megan 469# springs as 10" springs...whatever they are, they're about an inch or two too long.

375# x7" spring have a block rate about 200# less than the 8" spring...one reason the 7"ers as they compress.

 

The natural frequency (what your refering to) is SQRT(k/m). There may be a 2 pi in there as well... But this gets modified by two things...
1) Weight bias. For cars like ours, the front springs (using this method) should be 50% stiffer than the rear, as the car has a 60/40 weight distribution.
2) Geometry considerations. The spring in the front compresses less than the one in the rear for the same wheel hieght change, so the front should be stiffer still!

But this is the physics take on matching the ressonant frequencies, then you'd dampen each appropriately.

Also, in thinking about this, why did the soft front ever take as a philosophy? Seems to me the increased travel for a given bump will make the car more prone to bottoming, and also slow weight transitions and the car taking a set. To figt this, you have to increase dampening, then the front end is all out of sorts, with dampening that is wayyyy to hight for the spring rate. Seems to me the fronts should be stiffer (a lot) than the rears, and the rear should get an even bigger rear bar to work the wieght transfer. Seems like soft front spring and stiff rears are attacking weight transfer in excatly the wrong way.....

 

You might want to reconsider that order until you get a chance to check what you already have.

I still have the original 5kg fronts and, since I didn't use them, the 8kg replacements Megan sent - they're all 150mm (~5.9").

That doesn't tell you much about the 8kg springs they sent you though since you got yours well ahead of the rest of us, to test, and they may have been other than 150mm. Steve (from Megan) told me the 8kg springs he used on his MINI were 160mm (~6.3") because that's what he had available when he needed to test that rate, so who knows what he sent you?

 

By the way, if anyone's interested I have one set of springs I didn't use (still new in the box). They are 150mm length and 2.5" ID to match the original Megan fronts, but they're the slightly barrel shaped (and red) GC-spec Eibachs. Their rate is marked at 77N/mm.....check my math if you're interested but I think that translates to 440 lb/in, vice the 469 lb/in solution from Megan.

 

Understood, the weight bias of any car as well as other things that affect springs rates such as control arm length all must be factored into a spring selection.

I'm not an engineer Doc So I cannot answer the last question with an engineering response. I can tell this type of spring rate bias works. I can also suggest that one must begin with an appropriate rate up front since that is where most of the mass is with regard to a mini...the very reason I do not like H-Sport springs is due to the very light rate up front. I wouldn't argue necessarily with the balance as an example, just the rates. I can write from experience, that wheel base will affect how effective spring bias is - I know this a no brainer. My 99 Si has a longer wheel base than my mini and might benefit from a bigger front to rear weight bias. But I think the defining rate is as you suggest, should be determined by where the bulk of the mass is. To that end, then a swaybar is used to fine tune, as I've always suggested.

And yes, a damper that is set to high for a given rate will cause sluggish reactions since the spring is over-controlled. On the flip side, a weak damper will cause very nervous conditions because the spring is not controlled properly.

Again, I'm not an engineer, but I believe springs and swaybars act in different ways.

 

Lots of information here guys! Keep it comming, I'm trying to absorb all these, and make sense of it...

Kurvhugr, where do you have your dampers set at? I'm still trying to figure out the best setting for the front...

 

Believe it or not, I'm at 16 clicks from full hard - dead smack in the middle.

Of course that's probably not much help to you given the differences in our setups. Me: Hardtop MC, 6" springs, 3-4mm preload. You: Cabrio MCS, 7" springs, 15mm preload.

 

Thank, I'll try that and see how it performs given that spring rate are the same.

 

I'm at 12 clicks from full hard...never been at 16...I'll give it a try.

I'm going to inlcude a little spring selection guide here and it focuses on travel as it relates to spring rate and spring length.

Lets isolate one front corner. My Mini was corner weighted at basically 850lbs per front corner, so I'll use this as our example.

From 850lbs, subtract unpsrung weight; wheel/tire/brake, control arm etc. I figure about 80lbs. This leaves 770lbs for sprung mass. Now take the spring rate you desire - I'll use 375# for this example - and divide this into 770lbs. This yields 2.05. 2.05 is the number of inches the spring will compress when the full static weight of the car is on the spring. Next, you need to find the spring travel for for a 375# spring at the length you have selected. Lets use two examples here, a 6"x375 and a 7"x375. The 6" semi barrel shaped spring kurvhugr is using have a spring travel of 3.96" and the 7" 375# springs have a spring travel of 4.79". Subtract the 2.05" from either one of these and you get the amount of spring travel left. 6"x375 leaves 1.91" of spring travel and 7"x375 leaves 2.74" of spring travel. Is one better than the other? If the damper's stroke length is 1.5" for example, the 6" spring works here because it has enough travel, it is smaller and therefore weighs less, is less apt to bind and less apt ot bend over itself which really long springs can and will do.

The semi barrel shaped springs are not on Eibachs spread sheets. But basically, these posses nearly an inch more travel than their corresponding non-barrel shped springs. In other words, a 7" semi barrel has a spring travel length of 4.79" while the standard 7" spring is about 4" even. I never knew these were available, a great find kurvhugr!!!

 

Meb, what's the formula you're using to calculate travel?

 

k is the spring constant, x is the displacement. Travel of a spring is based on it's design, and isn't calculated. The max compression is when the coils start to bind.

Matt

 

If you are purchasing from Eibach, they have a chart with all the info you need on line. The springs Kurvhugr wrote about are not on the chart, this info came directly from Ground control...and were developed specifically for the Mini and new GTI - or previous GTI to mate with a set of shortened and specially valved Koni yellows. I didn't ask how much the kits cost, but I would guess around $2,000.

I'm going try the exact spring Kurvhugr suggests. I did order a 7" springs, but I don't think there is 2" of travel in this setup. I thought I might play tonight, but it's now snowing and raining a freezing raining:impatient

Max compression as Doc wrote is called block height, as I wrote above, and block rate is the spring rate that nano second before block height...something you'd better hope you never achieve while driving, especially on a track. Longer springs will have a higher block rate becasue there is more spring to compress and it takes more force to compress a longer spring completely. However, at one inch compression for example, a 6"x375# spring has the same rate as a 10"x375# spring, got it? Same at two inches and at threes inches and so on.

 

Doc,

Are you sure that maybe you don't have it backwards, as I was speaking to the US distributer for Leda today and he told me to put 325's in the front and 250's in the rear?