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After a 1 year hiatus from tracking the 8, I started missing it out there, and decided to return to this. Throughout that year, I tracked my very well-prepped Miata. One oddly cool day in July, I put its track shoes on and took the 8 out for a track day on our local 1.3 mile road course. I immediately realized a major problem with the setup of the car is its alignment. My Miata has 3.5* of negative camber in the front, and 3.0* in the rear. The most I have been able to get in the front of the 8 has been 2.3*. The rear has been set around 2.0* for the most part.
It was quickly evident to me, upon driving it with a fresh perspective, that I was rolling the tires front and rear, and the roll in the rear was contributing to the snap oversteer. The front floats on the roll, and the rear snaps around, once rolled. I paid special attention to bump travel and never experienced a hard hit on the bump stops. I was previously over-driving the car like some kind of rookie. A year's worth of no-frills Miata experience had me backing off as soon as I felt it.
So, I decided to throw more money at the problem and have a set of offset spindle bushings installed to push the lower ball joint out a few millimeters to increase available camber about 1.5*. See this page for more information on that.
My current alignment settings are:
Front
Camber: -3.5
Caster: Max
Toe: 0.0
Rear
Camber -3.0
Toe: 1/32
I have a 4 day track excursion coming up October 12 through 15 for BMW Club instructor training at Hallett, and their insane safety rules for convertibles mean my Miata cannot qualify. That means taking the 8 for a trial by fire. Stay tuned for the results.
I'll be taking a selection of rear sway bars, because I have a feeling the rear roll stiffness will be increasing from the 11mm pencil I have back there now.
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Last edited by Steve Dallas; 09-22-2017 at 09:15 PM.
Well I'll just spell it out for you. Not sure where you came up with the idea of using a front/rear spring rate ratio, but nobody familiar with kinematic suspension design does it that way. The correct method is to choose ride frequency rates, which in turn then determine the spring rate. They then choose swaybars to balance the weight transfer ratio.
Increasing front ride freq increases response and turn in, which you did, but since you incorrectly used a pseudo-science ratio factor rather than ride freq you mistakenly chose too low of a rear spring rate. As counter-intuitive as it will seem to you, the handling issue you're experienced is from having too low of a rear rate relative to the front rate. By greatly increasing the front ride freq and not the rear the rear can't keep up with the front now. So rather than the weight transfer when exiting turns planting the tires down on the pavement the rear springs are instead compressing too easily, which is further exacerbated by the much higher front rate jacking the chassis attitude up and back to the rear.
Right now I'd take a guess since I don't know all the input parameters for your current setup; mass corner weight, unsprung corner weight, etc., but I'm betting the rear ride freq is quite a bit less than the front ride freq. This is great for a couch on wheels ride while cruising down the interstate, but very negative for performance handling. I'd suggest that you go back to your spread sheet and see what rear rate will achieve at least a 1.0 rear Hz freq/front Hz freq ratio, but something closer to 1.1 (rear freq 10% greater than front freq) would be closer to ideal for a performance car though a bit rougher riding for street use. Then you need to evaluate what sway bar rate is needed to achieve the necessary weight transfer balance.
IMO you'll need a stiffer rear spring rate with a matching stiffer front bar rate to solve the problem.
^ Right Hz. I understand. I just didn't want to get into natural frequency directly, because it is a lot more complicated to discuss on a forum. Rather, I went off into spring ratio, because it is easy to demonstrate that FCM and Ohlins are at 2 different extremes, where stock and Bilstein sit right in the middle.
That was 2 yrs ago and for me only exemplifies how he's all over the board without a true plan or focus. That's not intended as a criticism. Rather, it's to only help him gain focus on not just doing this *****-nilly. You can't trust FatCat to give you the correct MR anymore than the true unsprung suspension mass. This is GIGO in it's truest form. Do it right or why bother ...
The rest of what you posted seems like solid advice and very interesting IMO, and I'm not taking issue with any of it. Just saying that one criticism doesn't seem to have been warranted. I don't see that any of his posts is really inconsistent with the understanding he demonstrated in 2015, so I think it's safe to say his original understanding is intact.
Because if you have any experience with it then you'd know that 1.4x - 1.6x front spring rate/rear spring rate, which is heavily promoted throughout this thread, doesn't correlate to the proper ride frequencies needed in most situations (called bounce freq ratio on the FATCAT spreadsheet). As an example, in the original STX thread a 400f/325r rate combo was proposed. If you simply do the spring factor thing that's 1.25x. Well I can assure you that it's a great combo, though a bit on the light side, having used it myself. On my car in STX the freq ratio was 1.05.
How about the OEM 190f/200r combo on an otherwise factory stock RX8? The spring factor is 0.9, but having raced on them for years in Stock class the balance is not really bad, just too soft overall. However on the spread sheet I use the ride freq ratio is 1.11. Even on my new stiff high freq setup the spring ratio is 1.15, but the freq ratio is 1.08. It heavily favors the rear, but I'll have a big rear spoiler that will make the car understeer badly without it.
Aero is a whole other deal because it adds force factors that aren't present in an otherwise static vehicle. However, for a track car without aero there may be lift rather than downforce which people often don't account for. The spring factor being used in this thread doesn't take into account the actual corner mass forces that the spring and shock are working with. Without that then you aren't doing suspension design correctly.
Also, my intent is not to criticize, but to point out an error and assist with an understanding to correct the situation, which in my experience shock and alignment settings will only mask rather than solve. Some of you guys are simply too trigger sensitive, but I intentionally put effort into these replies to neither chide nor make joking remarks to try avoiding that.
Again, I don't know the specifics of that particular RX8, but unless it lost a lot of rear weight then in my estimation a 9kg front spring needs at least a 7 kg rear spring though I'd probably choose 8kg or something between those two using a lbf/in spring.
Assumptions are as important as inputs into any equation, and some context appears to have been missed or lost here. The assumptions are incorrect.
I am not trying to build the ultimate track weapon. I know how to do that, and that is what my Miata is for. I am trying to do the nearly impossible, which is make a car that is pleasant to drive on the street perform at a high-ish level on the track. And, I have nearly succeeded. All that remains is to solve some bad behavior and move the definition of 10/10s out as far as possible.
Having established that, all there is to do is nibble around the edges of what I have to see what can still be accomplished.
Aside from the snap oversteer problem, I'm working on the last 5 or 10% of what I believe the car is capable of doing, without going to a true track setup. This car is already fast. It is already beats the Spec Miata records at MSR and Hallett, for example. I just think it could be fast-ER, and I wish it would stop coming around on me unexpectedly at odd times. Not cornering on the outside 25% of its tires should go a long way to correct that.
I think I might be adding roll stiffness to the rear in a few weeks, because I went to as little rear bar as I could, without omitting it entirely, as a bandaid to deal with the oversteer problem. Of course, that predictably introduced corner entry understeer. If the alignment helps as much as I think it might, I will be able to add rear bar to make the car more neutral overall.
Yes, the most recent change is "just an alignment," but as a sister kisser, I mean Autocrosser, you know how much adding >1* of negative camber front and rear can change the handling characteristics of a car.
What you did with the rear bar explains the situation correctly. It will balance the weight transfer to some degree, but not address the ride freq difference that is leading to the chassis being easily upset at the limit of adhesion.
Not trying to argue, but the opposite change on the front; dropping to 8 or 7 kg, with again a larger front bar to compensate will have a similar affect while making for a better ride. While -3.5 deg camber is not going to assist the best possible ride endeavor it will easily compensate for front rate drop.
Regardless, telling people to use a 1.4 - 1.6x front/rear spring rate ratio is not supported by the physics and engineering design calculations the rest of the world is using.
Here is where we stand after 4 grueling days at Hallett.
I took the 8 with the alignment settings posted above, its OE rear sway bar, and an old set of Maxxis RC-1s I keep trying to kill, but refuse to die.
It was... Very neutral. The certification training was put on my BMW CCA, so there were obviously a lot of well-tuned Bimmers there, and I had no trouble keeping up with my peers. I ran in the top 3rd and was easily fast enough to beat the minimum established time for consideration AND put up a personal best time in the 8 at that track, which is saying something, considering the tires I was running.
The car stepped out only twice on me, and the same thing happened to each of the coaches about twice each. But, each time it happened to someone, it was from underestimating the available torque under throttle and/or overestimating the grip in those lousy tires and/or a faulty input when the rear was light: driver error in every case. It was so good, it was easy to get over-confident. It was easy to save for every driver, and no one spun it. That is definite improvement. The car is back to being a joy to drive.
Comments from the coaches that drove the car were along the lines of, "This thing HANDLES!!!" and "I had no idea these cars could be so FAST!!!" and "This thing is a refined Lotus!!!" and "WOO HOO!!!" and "Wait. Your engine hasn't asploded yet?!?!" That about sums it up.
Unfortunately, the tires still WILL NOT DIE! I thought having 5 or 6 different people driving the car over 4 days would finally do them in, but no. I didn't even bother to rotate them. To make matters worse, tire wear is very even now, so premature death is off the table. I'm going to be stuck with the damn things for another year. [Sigh]
Obviously, the car is not as fast as it could be with this setup, but it is plenty fast for HPDE applications, and I no longer walk away from it shaking my head and cursing at the end of a track session, which is something I have not been able to say for a long time. The crazy stupid dumb grin is back. Well, OK, let's not get ahead of ourselves here. One recently repaved track is only one data point. I hate that I will have to gather comparison data at other tracks to be sure. Really hate that.
Anyway, 5 of us passed and are receiving the certification. Now, when I get killed by a student, it will be totally legit.
Last edited by Steve Dallas; 10-17-2017 at 06:07 PM.
At my last event with the miata I was talking with another driver on rc1s in an mr2 that was frustrated by their immortality as well. Not a bad trait, really.
They are quite a bit slower than NT01s--at least as I drive them. Sloooooooow...
I bought them for the 8, because of how fast I was going through softer tires with my old setup. The car was eating a set of R888s or RE71Rs in 6 track hours back then. I have had the RC1s since September of 2016, and they have at least 10 track days on them now, and they are maybe half gone.
This tire has some positives. The RC1 is a tire that rewards precise driving and punishes sloppiness. It will really show you what you need to work on. They also provide good feedback that starts as a "wool" that progresses to a chirp. They will squeal just before they break loose. You don't want to hear the squeal. Drive to the chirp, and you will be getting all the grip they have.
NAP hit on something. I have 2 trackable cars now, and that affects cashflow. I would rather have money available for tires for the Miata, since it is my primary track car, so I am not going to dump the RC1s early. They are good enough for what I am doing with the 8 at the moment, so I'll just drive them for what they are. They were perfect for the "endurance" training last weekend and soaked up anything any driver could throw at them and never gave up. They are also good for a quick skills check, because they let you know when you have picked up bad habits--especially when paired with the softer springs I run on the 8.
BUT, NAP, I did just throw away a set of the Miata's R888s that had heat cycled out with half their tread left, and it wasn't easy to do. It was pretty hard to convince myself not to take them to 1 more track day just to be sure.
Pros and cons like anything else, but when I was driving my 8 last weekend, I REALLY wanted the grip of better tires, because there were some cars I could have easily chased down, if I had enough grip in the corners to exit faster.
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Last edited by Steve Dallas; 10-24-2017 at 08:22 AM.
So I'm buying a 2nd RX8 as a street car project per my 4-port engine turbo concept thread in the S1 Major HP forum. Which I also picked new set of Ohlins for a good price and intend to change the springs to use the rates I recommended in here along with a stiffer adjustable front bar to balance it (speedway style bar makes this so easy), which in the street spring rate range is to have the rear rate with 75 lb/in of the front rate give or take 25 lb/in in either direction depending on which springs I use (US std vs metric).
I intend to also use the imported 5-spd RX8 transmission which eventually should have a Par-Engineering gearset installed for greatly improved reliability and proper turbo gear ratios.
There are a set of FatCat coilovers for sale in the forums now.
Going from R3 suspension to used Ohlins R&T, I am actually a little disappointed. Even after a professional cornerweighting and alignment, I don't notice any benefit of the Ohlins over the R3 suspension on the street. In fact, I feel like the car is a little less stable mid-corner, and under heavy braking there's some shimmy.
Maybe some track time will change my mind.
There are a set of FatCat coilovers for sale in the forums now.
Going from R3 suspension to used Ohlins R&T, I am actually a little disappointed. Even after a professional cornerweighting and alignment, I don't notice any benefit of the Ohlins over the R3 suspension on the street. In fact, I feel like the car is a little less stable mid-corner, and under heavy braking there's some shimmy.
Maybe some track time will change my mind.
Used as in how used? Suspension is a wear item, so if you've purchased a set of used suspension you really don't know what you're getting. They could be pristine with 5 miles on them, or pristine with 5 miles on them and hit a curb with a blown shock, to 75,000 miles and tired.
For track use you might want to go a bit higher in spring rate than the standard Ohlins springs... 8/5 is a bit low.
Ohlins are pretty sensitive to rebound settings. I use 9 front and 8 rear on the street. 12 to 14 square is a good starting place on the track. Adjust as needed, obviously.
I'm thinking about getting either the KW or Öhlins but can't decide. Öhlins states this: Height adjustable (approx. 15 mm lower than standard). Does that mean that you can only lower the car 15mm? And KW states: Lowering FA/RA: 20-50mm/15-45mm.
Now i have H&R 35mm lowering springs and would like the car to be around the same height after i install coilovers.
I'm thinking about getting either the KW or Öhlins but can't decide. Öhlins states this: Height adjustable (approx. 15 mm lower than standard). Does that mean that you can only lower the car 15mm? And KW states: Lowering FA/RA: 20-50mm/15-45mm.
Now i have H&R 35mm lowering springs and would like the car to be around the same height after i install coilovers.
Thanks
That’s just the standard lowering, the Öhlins are infinitely adjustable. We sell nothing but Öhlins at this point... we’ve tried everything else and honestly it’s not worth getting anything less. We even make screw in sphericals for the rear, lowering cups to give you even more options for modifying spring rates and lowering further if needed, and floating front top hats as well.
We’ve got *2* open box kits in stock currently that we brought as display units to SevenStock... haven’t had time to list them. They are brand new and unused - just out for display only - full new warranty with SakeBomb and Öhlins. If anyone is interested please email info@sakebombgarage.com and I’ll see what I can do price wise.
i'm really liking my off the shelf ohlins compared to fortune autos. a bit better damping over bumps and irregular pavement. could also be the softer springs helping. setup was killer at my first event of the season. handling was completely predictable and controllable.
09-22-2017, 09:08 PM
