Making the 2 Handle Power

[maxuz]

We started into a conversation on what you can do to the suspension / brakes to make a 2 safe with about 60 more HP over in an off-topic thread (http://www.mazdas247.com/forum/showthread.php?123804907-Judging-interest-turbo-kit/page3), so I'm starting this thread over here to continue the discussion without threadjacking the turbo interest.

Quotes from that thread of note:

When I put it on my wifes car, I selected a target of 5 PSI and the GT-15 was too small.
The GT-20 does not need an FMIC so if the kit is being built... that is a way to make a "Entry" Kit and a "Pro" Kit.

Offer the FMIC as an option. Either way, at only 5 PSI you need to run 91 or better, which means that the IAT can be higher without much risk of detonationEven curently at 5PSI the car is too fast for it's brakes. The car is Entry Level, nothing on it is designed to support 150 HP...

Anything more than 5PSI and people are going to start killing themselves.

we have springs and rims on the Turbo 2 and it's still a handfull. Not as comfortable as driving the P5... That car, I literally can throw into a corner at pretty much any speed and my heart doesn't go over 80...

Parked iin the driveway and I am scared that the 2 Will Kill Me.

Ebach Springs which lower the car 2".. Yokohama Parads Spec2 Rubber.. No Roll Bar. The car is Dangerous... It isn't like a Mazda 3 or stable like a Protege... It is like driving something that would rather be upside down... and is actively trying to get that way.

it's 1" narrower, 3" shorter (less long, not less tall), and 9" taller than an 06 MX5, which is working with slightly more HP than the proposed turbo. Wheelbase is 91.7" for the Miata, 98.1" for the 2. FWD vs RWD wouldn't be a factor in roll here, but suspension set-up obviously would be. someone with more math-fu than me is welcome to physics that to some theoretical % more likelihood to roll, but it doesn't sound insurmountable to me. I would think a solid set of roll bars (hopefully like what racing beat is currently rocking) would do a good deal to address the roll issue, but i'm no expert. Thoughts?

well, I see the thread got jacked a bit, but let me weigh in on the handling of the two;

First thing the 2 needs is shocks and springs. We currently are running BC 2ways all around on the NA test car. BC is not as well known as say Moton, or Penske, but they are reasonably priced, and very adjustable. These are set up with rubber top mounts for street work.

We are running 6K front springs( about 350 lbs/in), and 8K rear( about 550lbs/in), which is a stiff, but very streetable set up. 4K front 6k rear would be about right for a full time street car, and still be fun to toss around.

Bars are 20mm front and a 32mm solid read beam bar( which btw works perfectly well on a beam axle car, look back at the old rabbits)

Wheels are 17X7 Kossei with 205 50 17 Hankooks( we tear up tires around here, so that will change quick)

Camber is set to 2.1deg neg front, 1deg neg rear, zero toe( I don't suggest this for a street car) and as much caster as we could get and even.

Brakes on this car are 6 piston mono block fronts with 328mmX 32MM floating rotors( something we are thinking about marketing here in the states), and rears are stock right now on this car but we do have a 260mmX28mm 4 piston set up on the turbo car.

With this set up, and our CBE and tuning, the car is about dead even on a short track with a spec miata for times. However segment times show the 2 is far quicker in the braking/corner entry area(remember those massive fronts!), and much quicker thru the apex and corner out. The Miata has the advantage from corner out to the next corner, but that is what we would expect because of the hp/weight ratio.

The point of this post is to show you what the 2 can do. It is a very neutral handling car set up this way, and can be tossed at will. Having raced the Protege MP3, I will tell you that this is very close to the same feel, well with lots less tq! The car is simply a riot to drive, the turbo car is a riot squared!

How are you getting camber in the rear? Camber plates or something? I didn't see any adjustment back there.

 

[Richard_rsp]

Thanks for the new post, maxuz! I was hesitant to talk about much suspension related in the other post.

With power, I def think the Mazda2 needs brakes. It actually was one of my biggest concerns when I first got this car - braking times seem pretty long for such a lightweight car. Braking from 60mph is a little scary now, I can only imagine braking from 100mph!!! (boom06) I hope to find an inexpensive brake upgrade path...

As far as suspension: I currently have racing beat springs and sway bars installed. I can tell that there is a need for better-than-stock valved shocks.... I can only imagine that this would be exacerbated by adding power. We NEED adjustable shocks!

 

[JamesCH]

I don't own a MZ2, but I do know quite a bit about vehicle dynamics.

-Dropping the ride height without VERY careful consideration can (and frequently does) reduce roll stiffness. Eibach springs have been known to do this. The problem is that the roll center moves away from the center of gravity, increasing the axle's roll couple more than the spring rate is increased. Anti roll bars (ARBs) do help with this, but will reduce the ultimate grip of that axle because of the increased weight transfer they cause. See diagram below for the geometry I am referring to.

-The car's 60-0 braking distance is still nominally the same because the turbo system won't add a large amount of weight. It's true that the car will reach 60mph faster, but it's ability to stop from 60 is largely unaffected. If the brakes were anemic to begin with, I would look at more aggressive pads to start with, and then better tires. Bigger wheels will NEGATIVELY impact braking ability because of their added rotational inertia.

The setup jmac36 sounds (and clearly is) good. I would be surprised if brakes that big were actually required, I think a more aggressive brake pad would work just fine. A proportioning valve might help a lot of the OE brakes aren't well-balanced.

 

[maxuz]

I'm betting better tires and a more aggressive pad compound would go a long way to fix the brake problems, too. I know in the Spec-B race writeups that were floating around when the fit and the 2 did their initial race said that they never had any fade issues on the 2, and i believe they were running stock pads, so it's just a matter of getting something with a little more bite.

I've been looking at the RB springs specifically because they do drop it so little, but increase spring rate. and i'm definitely looking forward to shocks being out there.

Richard, you say we definitely need shocks, but if you had it to do again, would you still get the RB suspension, or would you go a different route? does it get you some of the way to where you wanted to be, and the shocks would get you the rest of the way, or are the shocks working against those suspension changes at this point?

 

[zps2004]

As far as brakes are concerned the brakes on the 2 are really good. Tires are the main limiting factor. Put some good tires on there like when I had my RE-11's and it stopped really quickly. As said above, the only things effecting braking performance is weight, tire grip, and heat resistance, cooling, and speed.

Having more power allows you to go faster, but at the same speeds it doesn’t make any difference in braking. If you like doing 120 on the street though that is up to you, but not recommended or necessary.

My main test for brakes is going on one of my long mountain runs downhill. You are going from 30-60mph downhill. It puts a huge amount of heat into the brakes and there isn't much flow or time for them to cool off. I have yet to have a problem with the brakes on the 2. I don't even think with the RE-11's I would have a problem. Other than that getting good fluid, and good pads will go a long way. If you are still overheating the brakes, then you will need, cooling ducts, or larger brakes for more cooling area, and the ability to absorb more heat.

As far as everything else, I really don't like lowering springs partially for the reason that James brought up. Even more so, they aren’t stiff enough to make up for the lack of stroke in the stock suspension. As I posted in one of my threads if you lower the stock suspension 1” you only have 0.5” of stroke left in the front of the car, not good. Cutting the bump stops will do wonders and there is a lot that can be cut on the 2.

As far as the stability of the car I think it handles amazingly well from stock for the power it has, but it really needs better shocks. Shocks are the biggest factor for stability. Unfortunately there are no good low cost shocks besides koni yellows IMO. I am really looking forward to these for the 2. They will make a huge difference in the stability of the car. The stock shocks are really soft and it doesn’t take much to push the car hard enough to overcome the ability of the shocks.
For sway bars, the comments above are not 100% true. If you add a stiffer sway bar it doesn’t make that end of the car have less grip. Grip comes from weight. The weight on the front or rear end doesn’t get affected by the sway bar. Only the distribution of the grip from side to side on that axle gets effected. So if you know that on a turn the outside tire is sliding before the inside a stiffer front will help increase the load on that tire giving it more grip. This gets slightly more complicates when you add drive forces from the engine on that given axle.

Either way the 2 is a very capable chassis. With some good shocks, and springs, and tires it will be easily capable of handling a lot of power.


Sorry for the book.

 

[XCLR8TN]

As far as the brakes, I swapped my stock pads out with 2,000 miles on the car. The only thing I could find was Porterfield R4S, and they were a noticeable improvement (after one good stop/a little heat they really work well). HOWEVER, under hard braking the rears definitely are not doing enough of the work. I'd like to see a better compound shoe (I think Carbotech will make them), a disc swap kit, or a proportioning valve stuck in the system to offset this. I've done 3 track days with just front pads and I know I could be doing better... but I've gotten used to how hard I can hit the brakes w/o the rear end wanting to pass me lol.

I'm not sure where the R4S ranks in terms of comparing to Hawk pads but they don't feel near as grippy as an HP+ pad. Maybe *slightly* below a Hawk HPS. I haven't had any fade yet. Hawk did come out with a HPS and HP+ recently that I plan to try next year.

Agreed on shocks. Need better ones if you want to really handle (I have H&R springs on stock shocks).

I want more info on the BCs jmac is running!! Are they off the shelf for another car and fit or...? I'd make the switch in an instant with info on where to buy them.

 

[JamesCH]

For sway bars, the comments above are not 100% true. If you add a stiffer sway bar it doesnt make that end of the car have less grip. Grip comes from weight. The weight on the front or rear end doesnt get affected by the sway bar. Only the distribution of the grip from side to side on that axle gets effected. So if you know that on a turn the outside tire is sliding before the inside a stiffer front will help increase the load on that tire giving it more grip. This gets slightly more complicates when you add drive forces from the engine on that given axle.

[emphasis mine]

If you add a stiffer sway bar to an axle, it reduces the overall grip of that axle because it increases weight transfer. Yes the outside wheel has more grip than it once did, but the inside wheel loses more grip than the outside wheel gains, thus the axle as a whole (both inside and outside tires) loses grip. It is important to keep in mind that a tire's coefficient of friction decreases with normal load (the weight on it) making it less efficient at generating grip as more load is applied.

A stiffer rear sway bar induces oversteer by reducing the grip of the rear axle. This is the same way a stiffer front bar induces understeer.

 

[XCLR8TN]

On that note^^ I added the Corksport rear torsion bar and love it. Far less understeering tendencies and (with my sticky tires) the rear end won't kick out unless you simply push it too far too quickly.

 

[zps2004]

So after looking it up some it makes sense for the tire itself, but what is the gain for having the sway bar then? I mean fastest cars out there still have them, talking F1 and LMP, not street cars. Maybe to help keep heat in the tires? Cold tires suck.

Also I still think that my thinking still has some effect. Mainly when looking at the front of the car in a turn where you have two different slip angles on each tire, one will loose grip before the other. Once it starts to slide the other will have to make up for the additional cornering load, or that entire end of the car will start to slide. Correctly matched sway bars can get both tires to hit their peak for the loading at the same time. Again this is with just cornering forces, when you add drive forces things change for each different car.

This thread has been getting pretty good.

[emphasis mine]

If you add a stiffer sway bar to an axle, it reduces the overall grip of that axle because it increases weight transfer. Yes the outside wheel has more grip than it once did, but the inside wheel loses more grip than the outside wheel gains, thus the axle as a whole (both inside and outside tires) loses grip. It is important to keep in mind that a tire's coefficient of friction decreases with normal load (the weight on it) making it less efficient at generating grip as more load is applied.

A stiffer rear sway bar induces oversteer by reducing the grip of the rear axle. This is the same way a stiffer front bar induces understeer.

 

[Richard_rsp]

I'm betting better tires and a more aggressive pad compound would go a long way to fix the brake problems, too.

Agreed.

Richard, you say we definitely need shocks, but if you had it to do again, would you still get the RB suspension, or would you go a different route? does it get you some of the way to where you wanted to be, and the shocks would get you the rest of the way, or are the shocks working against those suspension changes at this point?

I absolutely would go the same route! these springs are perfect for a daily driven, occasional autoxed, 2. The shocks are just needed because the stock shocks seem underdampened, ie. they dont seem to "settle down" after going over a bump. (a little bit of "boat motion" after speedbumps, etc.) at least more than I would like.

The ONLY thing that I have questioned since purchasing was the RB rear sway bar. Im not a huge fan of the way it attaches to the beam... i have had to retighten it twice. While its not a big deal, it is still maintenance. Also, while it does an awesome job of preventing cornering flex, that also means it severely limits the wheel travel. This means that I am "three-wheelin" when turning into some driveways... Not always the best for a daily driver. But it is absolutely awesome for autox. The rear can step out on a sweeping curve on command and it really allows for throttle steering throughout the corner. Very balanced feeling.

Overall, I am very happy! I plan on getting shocks as soon as they are available (and I can afford them). Well, and some tires too!

 

[JamesCH]

Larger wheels will only effect braking distances negatively IF they are heavier than stock.And the effect is not quite as noticable as you would think.

Not necessarily. A lighter wheel can have a larger rotational inertia than a heavier wheel if its mass is located further away from its center of rotation. Part of my job as a mechanical engineer is designing prototype automotive wheels. I realize that the wheel might not be a huge effect, but I would opt for a different wheel before upgrading brakes. That would be my personal design decision though, I'm not criticizing yours.

Also, you might want to take a look at most of the modern touring car type FWD suspension set ups, as most now are running the roll center undergound. For example our mazdaspeed 3 runs the front and rear as far as 2 " underground. This allows us to use lots softer springs and still have great tire temps

How do you deal with the increased roll couple and soft springs? Does putting the roll couple under ground help? Or is it something that must be overcome?

So after looking it up some it makes sense for the tire itself, but what is the gain for having the sway bar then? I mean fastest cars out there still have them, talking F1 and LMP, not street cars. Maybe to help keep heat in the tires? Cold tires suck.

Also I still think that my thinking still has some effect. Mainly when looking at the front of the car in a turn where you have two different slip angles on each tire, one will loose grip before the other. Once it starts to slide the other will have to make up for the additional cornering load, or that entire end of the car will start to slide. Correctly matched sway bars can get both tires to hit their peak for the loading at the same time. Again this is with just cornering forces, when you add drive forces things change for each different car.

This thread has been getting pretty good.

Roll bars are good because the prevent roll... tada! A tire's lateral grip is heavily influenced by camber, and camber changes with roll (typically in a bad way).

Edit: Thus, by limiting roll, the sway bars can improve grip, but this improvement may or may not be offset by traction losses from increased weight transfer. I think that more often than not the losses from weight transfer are greater than the gains from better camber. Bump-steer effects may also be reduced by sway bars.

One could make the suspension springs stiff enough to not need a roll bar, but the car would be much more sensitive to road imperfections and would have a very harsh ride. This would also degrade the tire's performance. The stiffer springs would also make the shocks work a lot harder, i.e. wear them out prematurely and/or overheat them. Sway bars also allow for very quick adjustments of the car's balance without replacing suspension springs.

You are correct in saying that matched sway bars bring both axles to their peak grip at the same time, thus making the car neutral.

Every single choice is a compromise. For example: you could put on lighter wheels to reduce unpsprung and rotating weight and improve turn in and to fit on bigger brakes. But the bigger brakes add upsprung and rotating weight, the bigger wheel may have more rotating inertia, and the bigger brake disc certain does... so which one is better? I don't know.

 

[JamesCH]

Care to share anything specific instead of being vague and cryptic? FTR: I never mentioned anything about FWD-specific suspension.

Most of my suspension experience (perhaps limited) has been with real-world double a-arm suspensions (FSAE cars and Miatas) but I don't deal with it on a professional level anymore so if I'm missing something important feel free to point it out, I'm always happy to learn (spin)

Edit: I do, in fact, race on a fairly regular basis, so I am very much aware that theory and the real world don't always get along. They do agree fairly regularly though. I am relating knowledge that I've experienced first-hand on cars that I've driven.

 

[zps2004]

We got all kinds of ME's in here. I am one as well.

Anyway I thought about it more. If you have a certain amount of roll, then take the sway bar off, and stiffen the springs to make up for the roll resistance, you still will have the same amount of weight transfer overall. So overall the bar will be good since it keeps the springs lighter keeping the car overall better over bumps and road imperfections. Again there is a limit to this. The swaybar can then be used to keep the camber in check.

To me the lower roll center isn't preferred if you can help it. I am usually more concerned with the lack of suspension travel form lowering than the roll center. If you have good shocks then you can control the stiffer springs well. I have learned that the hard way. I went from K-sports to koni yellows on my old civic, and the ride comfort and performance got better with much stiffer springs on the koni's. On the Miata, I have Ohlins DFV's and even on rough autocross courses with the rates I am running, it just doesn't care about any bumps. Overall the dampers are the key to me.

In the end don't forget what our friend Colin Chaplin who said, any suspension no matter how bad of a design can be made to work well when it is made to not move. Well it was something like that. Also just because it works, or works well, doesn't mean it can't be improved.

 

[PGTBrow]

F= MA
Thats about all I got...

 

[Sarein]

Great read, I am so happy there are people getting in-depth with the m2. I will be following this thread ( and the turbo one) very closely (2thumbs)

 

[JamesCH]

Very cool GRM article on suspension changes: http://grassrootsmotorsports.com/articles/g-whiz/

When adding a rear sway bar, performance improved (I assume because the car became more balanced) but when a front bar was added performance dropped (I assume because the car became less balanced). The article also briefly mentions correcting roll centers after the (macphearson strut suspension) car is dropped and how it made a noticeable difference.

I really like GRM's scientific and quantifiable approach.

 

[zps2004]

I have been referencing a number of books on chassis setup, and the all do say how keeping the weight transfer to a minimum yields the maximum overall grip, but in a lot of scenarios, this would cause the handling balance to be really messed up so overall it would be slower.

Also when it comes to cornering, for a particular car you need a certain amount of weight transfer to achieve the maximum cornering for the tires. Doesn't matter where that weight transfer comes from sway bars or springs.

It is unfortunate that for more cornering force you need more weight transfer, which causes the tires to be less efficient. You'll still be faster though.

 

[JamesCH]

Is the weight transfer beneficial because it changes the suspension's geometry in a favorable way? i.e. weight transfer loads the outside suspension, which causes a camber loss (more negative camber) which improves the tire's lateral grip?

 

[zps2004]

The weight transfer is basically necessary for cornering. The more cornering force, the more weight transfer there is going to be. Basically the weight transfer from one side to the other counter acts the roll created. There are things which you can do to lower the amount of weight transfer for a given cornering force, but springs and sway bars make no difference.

To pit it simply, if you picture a car just sitting there not moving. Now imagine the ground pushing from left to right on the bottom of the tires. This will cause the car to roll around the CG. That force is applied at the ground and the CG is above the ground. This will give an overall torque to the chassis. As everyone knows every force has an equal and opposite force. Well the opposite force to the car rolling is the weight transfer on the tires. The left tires will have more load than the right. This difference in the load causes the equal and opposite torque on the chassis through the CG.

The higher the side load (cornering) on the tires the more weight transfer is required to oppose it. Also from this the springs and sway bars have nothing to do with the weight transfer of the car. They will effect how much roll the car will see, but now the loading.

So it isn't really a matter of the weight transfer being beneficial, it is just necessary. Not sure if that answers your question.

 

[Joker2]

I like to think of this in two different ways:
1. Do not shock the tires. Meaning, allowing the roll rate to match the tire grip loading rate. A lower grip tire needs more roll to load the tire, etc.
2. Keep the car as flat as you can as long as you have the tire grip to match. High grip tires will load up a stiff suspension very quickly.

In the rain, most racers soften up the ARBs or disconnect them in order to allow the car to roll more to gently load the tires (see the connection between 1 and 2?) and often drive off the dry line to get more grip from the concrete or asphalt that is not polished but granular. Tires generate grip by interlocking their molecules with the surface in addition to sliding across them.

YMMV