irish44j

iTrader: (38)

true that....

200k...

do you realize that at current gas prices, that is over $25,000 in super unleaded

irish44j

iTrader: (38)

one last question for you:


"what am I doing sitting on my couch at midnight on a Saturday night....?"






































oh, that's right...I'm married

in any case, time to get some shuteye. nice discussing with you.....bring some of these thoughts into the autocross and suspension forums so that some of the org's other non-5th-gen experts can chime in (BEJAY, Matt, etc...)

Mike T

Your reading too much into my statements. When I say it doesn't do a whole lot, I mean in the way of measurable torsional resistance of the chassis, which I of course can only guess at, I am not a chassis engineer, I only play one on Maxima.org. I would be the last to deny that emproving the feel of the chassis will allow a driver to extract more from the car, thats why I said it would be a "worthwhile mod."

I simply used the fox chassis as a counter to the Maxima for arguments sake.

So much for not having anything more to say...

Mike T

Same here, married with child, and a 29 year old full time student, I am quite confused! Its been fun...

DrKlop

iTrader: (3)

So you are saying that you would prefer not to bottom out once in a while on the city streets, even if it means that you will not be able use the shocks that work best with your springs during hard cornering??

I, personally, would rather have the car tuned for a better handling over the normal roads...

BTW, Eibach+ Illuminas all around should solve both of these problems.

That's probably correct, but what's wrong with having softer springs in the front? As long as the car does not go into excessive oversteer it should not be a problem... It's even better if you keep stock f/r spring rate proportion, because the brake bias was set for the OEM springs and it can not be altered towards the rear. Am I missing anything?

DrKlop

iTrader: (3)

BTW, regarding the motor mounts... I don't think they position the engine lower in the engine bay, if you are talking about the inserts. I would assume that in order for them to lower the engine position, the size of the mounts has to be smaller than OEM. However, since smaller mounts will simply fall out of the brackets, ES mounts must be of the OEM size. Besides, ES mounts replace only two out of the four OEM mounts, so they can't change anything.

If anything they should raise it even higher, because ES mounts are stiffer than OEM, so they do not compress as much under the weight of the engine.

It's an interesting idea though... If only someone could fabricate the brackets in such a way that the engine would be positioned lower in the engine bay. Lowering center of graving without increasing the roll center would be very beneficially for us.

Mike T

It is something I heard stated by one person who installed the ES bushings in their Maxima, so it is not confirmed. But, from what they stated, the stock motor mount bushing has its mount hole slightly off-center (slightly raised), while the ES bushing has the hole in the dead center, that is where the drop comes from, again, its just a rumor at this point, the motor mounts on the sides are too soft to win a battle against the poly bushings, so the engine would likely drop some, if this is all true. As my LTB is already extremely close to the stock exhaust, lowering the engine would be a problem for me. Also, one thing to keep in mind, is that lowering the engine also lowers the transaxle. If your car is already lowered, it puts the CV joints at an even higher angle, something to keep in mind.

Mike T

Reread what I said more closely... Damper function can be plotted on a graph with velocity on one axis, and resistance on the other axis. If you plot the points, you will rarely see a linear relationship in the function, especially with cheap OE dampers. Also, the graph will not continue on into infinite values, at some point you will see a significant drop in the dampers ability to resist very high velocity movement, it is THAT point which I am talking about, not the "meat of the curve." Performance shocks, atleast good ones, can retain effective dampening ability at the higher velocity end of the graph, much better than OE shocks can.

Mike T

It is at least unorthodox, and probably less than ideal from a strict performance perspective. As far as brake balance, well, we messed that up by bolting 6th gen brakes on the front of our cars. But, higher rate front springs help the suspension handle the vastly increased braking forces. I know my car would be standing on its nose if it still had the stock front spring rates.

Mike T

I am of course not arguing that the Maxima has a spectacular chassis, I simply believe that comments like "noodle chassis" and "horribly weak frame" are unfair representations as well. I think it is important to think about modern unibody chassis's has the complex, often esoteric, systems that they are. A unibody chassis cannot be thought of as just a single component, it is much more complex than that. It is possible, as I think might be the case for the Maxima, that the overall structure is reasonable stout. That would be reflected in the chassis's resistance to torqing and bending. However, sub assemblies, like the floor or firewall, for example only, while providing strong tensile and compression strength, which is important for the overall strength of the chassis, are not as resistant to movement on other planes, that starts getting into harmonics. I think that is where problems may lie in the A33 chassis. But, it's all conjecture until one of us strips an A33 chassis bare, and starts measuring resonances and angular deflection under torsional loads, and I'm busy next week, sorry .

I am not trying to discount the value of chassis strengthening, I am well aware of the value of a rock solid chassis for a road going vehicle, I just want to help focus the conversation, as I think talking about the "chassis's stiffness" is a little too unspecific.

Maybe this conversation should be moved to http://eng-tips.com/ this conversation itself may start to become too esoteric.

irish44j

iTrader: (38)

unibody sucks....body-on-frame, FTW!

DrKlop

iTrader: (3)

Right, but isn't it better to have the meat of the curve matched with the spring rates, than have the whole curve higher on the graph than it needs to be?

I agree, for optimal braking performance the front springs have to be stiffer (because it decreases nose dive, resulting in less weight transfer to the front wheels) but you also have to shift the brake bias more towards the back in order for you to take advantage of this setup. Otherwise your front brakes will start locking up before the rear ones. Installing 6th gen front brakes in this case will make the situation even worse. However, if you install an aftermarket spring kit with the front/rear rate ratio even lower than stock, your rear brakes will start locking up earlier... but this time 6th gen front brakes will actually fix the problem.

Mike T

This conversation is getting unnecissairily theoretical. Back to my original point: from running stock shocks on the rear, and HP blues on the rear, the HP blues seem to do a better job overall at properly dampening the stock rear springs under a wider range of conditions, without overdampening, far from it.

Mike T

Its not that simple. Actually, you are starting to hit on more complex issues in suspension systems, that would probably be better discussed over E-mail (MikeThomasNC@hotmail.com). I can try to explain what I can, and/or direct you to proper publications, which discuss this more clearly that I likely could. But the distilled form: dont confuse the effect that the relationship in compliance between the front and rear suspensions has on the distribution of vehicle mass and resulting tire loads and slip angles during lateral acceleration (i.e. understeer/oversteer), with suspension behavior and tire friction levels during longitudinal acceleration (deceleration). They are in many ways very different animals, e-mail me if you want to talk further about this.

DrKlop

iTrader: (3)

I think you are making it more complicated than it really is... Other factors do make an affect on the load transfer between the front and rear tires patches, but for the most part, I think it's all about how much weight you allow to shift when you compress the suspension. I actually noticed the affect I have described in my previous post in the real life. Back when my suspension was stock, both front and rear tires would start locking up at approximately same time. After I installed coilovers with 8kg/cm front and 6kg/cm rear springs I feel that the front tires reach their braking limit before the rear tires.

Anyways, I'll probably hit you up via email when I will be up to upgrading my brakes. Although I, personally, would rather discuss it here as other people can benefit from the conversation as well.

DrKlop

iTrader: (3)

Hey irish, check the thread about the HPs affecting the tire wear. I posted a question to you in that thread.

Mike T

No, I'm not making it more complicated than it is, it's more complicated than you think. The primary reason you are experiencing more rear wheel traction during braking is more due to the lower CG. Remember, suspension-compression is a "side effect" of weight transfer. Whether you have super soft springs, or weld the suspension in place, weight transfer is still going on. It is a function of the acceleration, the tire's contact patches, CG, and the angles of the force vectors between those points (the simplified description). The conversation can keep going around and around like this. If you really want to learn more about suspension systems, pick up some suspension engineering publications, like "Tires, Suspension and Handling" by John C Dixon (he uses english). There are also great SAE publications on various suspension topics, and a good book my "Millican??" I can't quite remember his name. You can find most of them on Amazon.

Trurida18

iTrader: (4)

so the 05 calipers DO bolt on directly to the 2k1 maxima

DrKlop

iTrader: (3)

My bad, I overlooked this, but that's still only a part of the reason.

Once suspension compresses you have even more weight on the front wheels.
CG and the angles of the force vectors change while suspension compresses. Thus, considering that suspension compresses more with the softer springs, the load on the tires also changes more with the softer springs.

Thanks, but I think I read enough on this topic to have a good understanding of what we are discussing. If you are interested I can recommend you a few books as well.

Mike T

Unless you are driving an ice cream truck with a piano on the roof, the positional shift of CG in relation to the tire contact patches is negligible, especially during braking and acceleration, because the distances involved are greater, accounting for maybe 1 percent of absolute tire loads.

Skylowmax

Interesting...nice write-Up!!!

DrKlop

iTrader: (3)

Well, when you are slowing down the range of motion suspension is going through is pretty much equivalent (if not greater) to the drop most people have, (I lowered mine by 1.8") add to this the change in direction of the forces (in relation to the body) and this should make quite a difference, possibly even more significant then the change in the CG.

sciff5

iTrader: (1)

I am happy with my mods thus far, the front just feels too loose, and I still feel like I'm getting a lot of under steer. To get the most from the car I really feel like I need to transfer a lot of weight to the front to get around corners without understeering.. I am hoping the poly suspension bushings will help this but I think the problem lays in the bushings where the front subframe attaches to the chassis.

Mike T

A LTB, if you dont have one, and the ES bushings, primarily the trailing arm bushings, should remove the "looseness". The rear bushings will definately remove almost all signs of understeer, when combined with your other mods, possibly pushing you into the oversteer side of the spectrum. I didn't think that there are bushings between the front subframe assembly and the chassis mounting points, AFAIK it's directly bolted . BTW, the ES bushings, while improving handling, will definately remove the last bit of "luxury" in your Infiniti's ride

Mike T

To clarify, are you saying that if two identical cars are braking at identical rates, and the only difference between them is the spring rates in the suspension, and positional shift of CG is removed from the scenario, that the vehicle with the softer front springs is transferring more weight to the front wheels on account of it's increased suspension compression and body dive? (Man that was a run on sentence!!!)

DrKlop

iTrader: (3)

yap. In other words, body motion allows the center of mass move closer to where it is needed the least. (in our case it's the front tires)

sciff5

iTrader: (1)

I would think that the springs would take a lot more away from the ride than replacing the bushings. Although poly bushings are more stiff than the rubber ones they're replacing, its not a radical difference, at least nothing like the derlin (hard plastic stuff) and solid bushings I'm using on my track car.

The feeling I get in the front of the car is that the front end initially feels distant from the rest of the car, so initial turn in is weak and doesnt tell the driver much of whats going on up front, then once your into the corner a little bit the car holds on really nice. I believe the issue is where the front subframe connects to the chassis which is via a set of bushings, thats one of the mods in development for the maxima, a set of solid bushings to tie the front subframe into the chassis and vritually eliminate the bushings.

I think this problem is compounded by the fact that my car is mysteriously missing a couple metal braces that other peoples car have from the factory. These braces seem to bolt into the chassis and limit motion of the front subframe in relation to the chassis.

I have some rust to deal with in my project car so I figure I am going to be buying a mig welder in the near future, chances are once I get more comfortable with it I will prob fabricate a brace thats similar to the one that came from the factory and have it bolt into my subframe connectors.

Mike T

Bushings and Springs affect the ride differently. While springs absorb larger bumps in the road, the bushings absorb much smaller road irregularities and vibrations. On my car, the change was noticeable, but I have mostly gotten used to it, so that I don't really notice it anymore. Probably the biggest change you will notice is increased vibration through the seats, and increased road noise. It's not really that bad, but my initial reaction was that it is a little "out of character" for an Infiniti, but, does that really matter? We'll, as long as you don't plan on selling the car anytime soon.

Mike T

That is sort of like how my car was before the ES trailing arm bushings, weak initial turn-in with "initial understeer", but then the car would quickly settle into a good balance. The "play" in the rear bushings was the cause of that. The stock bushings had to be compressed a fair amount before the torsion beam and RSB could do their job. With the ES bushings, there effectively is no more slop, and the roll resistance of the rear torsion beam and RSB is engaged immediately.

Mike T

Please be more specific, because we already established in my "theoretical example" that the center of gravity (center of mass), was positionally constant in relation to the tire's contact patches, which goes back to my "piano and ice cream truck" post (very strange sentence!).

DrKlop

iTrader: (3)

Well in my opinion it's not constant...

It moves to which ever side (left, right, front, back) the car leans to.


Edit: and that's the point I've been trying to make

pedxing

Really good write-up. I tried to approach suspension mods with the same sort of science. My install order went like this:

1. Rear anti-sway bar -- made a noticable difference in body roll and reduced torque steer. I use a Stillen knock-off that is all metal...no rubber brushings like Progress.

2. Front strut brace -- nothing noticible. Might help a bit during hard corners.

3. Illuminas and H&R Sports (installed at the same time). HUGE effect. This virtually elimitated toque steer. Ride now maybe 15% stiffer than stock. Interestingly, the ride feels very much like my stock 01 Corvette (ride, not cornering!). With the proper tire inflation, the car handles very neutrally with slight oversteer at the limits. Drop ended up being about 1 inch all around.

4. 20 mm H&R wheel spacers. After the springs I defintely noticed the inset look on the back wheels. After some research on the org I went with 20 mm. Looks great but now I get some rubbing. Not bottoming out exactly, but it appears to hit the bracket that attaches the bumper to the quarter panel. This occurs on high speed (80 mph) dips or large speed humps.

5. 17x7 Centerline RPM Forged rims. Went with the stock size to reduce weight and so I could keep my existing tires which were pretty new (Toyo Proxes). This reduced the frequency of bottoming out. These rims are nearly 10 lbs lighter EACH than stock 2002 GLE rims. (About 15 lbs each). I also noticed a bump in throttle response. Based on my calculations of differences in rotating mass, these rims result in a 5-6 hp gain over stock. 40 lbs of unsprung mass eliminated will be noticed.

6. Dumped the spare tire, jack, etc. This came to about 50 lbs. Replaced with a 2 lb air compressor, tire patch kit, and cell phone. Effect? I don't know, it makes me feel good.

7. Hawk HPS brake pads are next (haven't gotten around to it because my stock pads are still ok.) That was a good tip about the 05 rotors and calipers...I need to look into that.

Mike T

Polyurethane bushings...

Sounds like a nice set up, the full set of H&R springs looks better on Maximas with autos, IMO the manual trans Maximas just sit too high in front in relation to the rear, because of the lighter transmission.

Mike T

As I said, even though it does shift, the amount is negligible. But we don't need to rely on opinions, we can create a model, and apply some basic trigonometry. Here are the specs for the "test subject." This is approximately like the Maxima, but is not a DIRECT representation.
Wheelbase: 110"
Weight Distribution: 67% Front / 33% Rear placing the center of mass 36.3" behind the front axle centerline, and we will assume a CG height of 18" from ground level (kinda high, but it will do for this test).
Vehicle Weight: 3400lbs (2278lbs on front axle, 1122lbs on rear axle)

I don't guarantee that there isn't an error somewhere in my calculations, it happens. And I am not taking suspension geometry into the equations, because it will make things messy, and isn't important for this little "experiment."

1st test, soft springs (x and y) spring rates:
Ok, now lets assume that during hard braking, the front end will drop 1.5 inches at the front wheels, and the rear will raise by 1.0" at the rear wheels, giving us a total shift of 2.5 inches. 2.5" across the 110" WB give us 1.30 degrees. So the body is "diving" 1.3 degrees. Judging by the difference between the height changes in the front and rear suspension, the rotional axis of the body occures arround 66" behind the front axle, meaning it is behind the CG by 29.7". When the body has shifted 1.3 degrees, the CG has moved forward .41 inches, and has dropped by .68 inches. The CG is now 35.89" behind the front axle. With the body in this instantaneous position, the static weight distribution is 67.37% / 32.63%, I am not yet taking inertial effect into the equation. This only represents the shift in mass related to the positional shift of CG.

Now, in this attitude of the body, the front axle now carries 2290.6lbs in the front, and 1109.4lbs in the rear, a change of 12.6lbs, or 0.37% of body mass.

2nd Test, with same static ride height, but spring rates 2x as high on the front and rear, 2x and 2y:
The attitude of the body during hard braking shifts by .65 degrees. CG shifts forward .21", and downward .34". The new CG position is 36.1" behind the front axle. The front end now carries 2284.1lbs. A difference of 6.1 lbs from the original, and 6.5lbs less than the soft spring test. I still see that as "marginal."

However, here is the catch (and remember, for this test, static ride height is constant). While the longitudinal position of the center of mass shifts forward 0.18% more with the soft springs, the center of mass DROPS 1.90% more than the firm springs. So when inertia is factored into the equation, LESS weight will be transferred forward with the softer spring rate. This is because since the CG is so far forward, with this being a FWD car, the CG is pretty far ahead of the roational axis of the body, so when the body dives, the CG drops accordingly. Now typically, stiffer springs are also going to give a lower ride height, and thus a lower overall CG, but we were discussing the effects of spring rates only.

DrKlop

iTrader: (3)

Could you explain how you got these numbers using results from the previous calculations?

Mike T

As I don't want to have to recreate all the calculations in a clearly discernible form on this thread, please ask for a specific aspect of the equations. Or you could attempt them on your own. Everything you need, I provided in the model's specs. From there it's just high school trig.

DrKlop

iTrader: (3)

That's a specific question... We have 1.3 degrees angle between the chassis and x-axis, and 29.7" between the rotational axis and the CG. So the question I have is how exactly did you use this data to determine that CG has moved forward .41 inches, and has dropped by .68 inches?

Mike T

Those are the specifics I needed. I needed to know where in the equations I could begin, if there were any "given" values. In my original equation, in all honesty, I used a simple method to calculate longitudinal CG shift that would provide your side of the argument with a more favorable result. I wasn't trying to "fix" the results in my favor; instead I was trying to give you the benefit of the doubt. My original method was to rotate the CG 1.3 deg. about the point it vertically intersects with the ground, which would maximize CG shift, thus .41". Calculating the shift in CG about the rotational axis of the body, as you mentioned, was how I calculated CG drop. And that method is a more accurate indicator of positional shift of CG. Using that method, if the distance between the vertical position of CG on the X-axis, and the rotational axis on the X-axis, is 29.7", and the rotational axis is assumed to be on the plane between the centerlines of the front and rear wheels (for simplicity's sake), which is lets say 12" above ground level, that means that the CG lies 6" above the plane. That sets up our triangle (90deg opposite 30.3", 11.4deg opposite 6", 78.6deg opposite 29.7"), shift that triangle 1.3 degrees, and leave the hypotenuse constant (you end up with a height of 5.31" and a length of 29.83". So, CG has dropped 0.69" and has moved forward only 0.13"). Unless you see something wrong with my methodology, the numbers don't lie. You can even drastically change given values, but the resulting shift in CG will remain minimal.

DrKlop

iTrader: (3)

Ok, I think I have to agree with you. There are a few things in your calculations that I don't understand 100% but for the most part they seem to make sense.

It was a nice discussion though!

Maxim(a)SerjVQ

it's funny. I used to race go-karts and my dad, being the mechanical engineer he was, used all sorts of mehtodology to balance weight transfer to the various corners of the kart under racing conditions. the result was sometimes to the chagrin of people with 15 years more experience, and there was no suspension to speak of. I do like the point made that tells of the weight transfer taking place regardless of suspension.