[choaderboy2]

New experiments in handling

My latest stuff is based on experiances gained working with Motorsports and Nismo suspension engineer, Jeff Lesher who is a hell of a guy.

He taught me about frequency matching of the front and rear suspensions, basicaly the rear suspension needs to have a higher natural frequency than the front so bobing and other chassis exciting, traction reducing effects of bumps and undulations can be reduced. You tune so they will cancel out in 1/2 cycle.

Basicaly in a close to 1:1 motion ratio suspension like ours, this means the rear spring rates must be higher than the fronts. I am starting to do this based on his equations, using roll bars to make up the gradient in roll stiffness that this causes.

The results I have experianced so far are pretty interesting, bobing can be greatly reduced without needing more damping and the tires are getting shocked less with less bobbing and less damping. It seems to work well.

Also a big trend in the motorsports world is to adjust dampers so when you intergrate piston velocity over time the curve has an equal distribution for attack and decay. Need LDPT's to do that which are expensive but I do have the dfata loggers now.

So lately my spring rate recomendations are way different from the status qou. I will have more experiance with this so and will be changing some of the good old standard rule of thumb spring rates soon.

The OEM's are catching on with this lately. Wonder why the Spec V, Maxima, Altima and some other makes of car have such a high rear wheel rate?

Mike

 

[choaderboy2]

I'm assuming this new revelation on suspension frequency and higher rear and softer front spring rates factors in the body natural flex and tolerance? Does bracing all the weak points help change the suspension frequency?

L

Its too hard to model with the math tools I have but its better than nothing.

 

[choaderboy2]

You can't articulate why the Koni is better then another damper or why another damper may be better then a Koni in such a simple fashion. People like to simplfy things and say "well it's double adjustable" or some other objective thing. In the end the damper that keeps the tires on the ground and most effectively maintains traction is the best damper for handling. The most common Koni's we use on our cars hit a perfect middle ground between performance and cost. Especially the Spec V and Maxima units. Problem with the Koni is they are not off the shelf easy to do. They require extra steps. This does not begin to adress the need for shortened units needed so badly on the fronts of a Sentra. But even this is a over simplification for a street car as many coilovers are actually to short and don't have enough shaft travel to work properly on a street car.

I my opinion what people feel in "Koni type damping" is actualy a linear curve and somewhat less than ideal for a performance application.

AGX's are more digressive which should work better for a street car, actualy any car but digressive curves often give a more jiggly ride at low speeds and are more suceptable to freeway hop sort of ride artifacts unless the knee point of the curve is very carefuly tuned to try to not do this while still maintaining body control.

Its sort of why a twin tube shock like a Koni or Tokiko can also give a better ride in the same areas as the higher gas reaction force acts like spring preload. The rate doesnt change, just the force needed to intialy move things.

For true high speed perfromance driving, both single tube high pressure and digressive curves tend to work better if they are tuned correctly due to better control of dynamic weight transfer and better frequency response of valving with more accurate damping.

The new Koni 8611's and I belive 8610's have a more digressive curve as well.

 

[choaderboy2]

All the curves I have ever seen from koni's are digressive. It's a matter of degree. Plus, one curve does not tell the tale. Would you rate your first Truechoice setup as better then the AGX's you had before? It was not as digressive but you said it was worlds better then the AGX's and it was the old 8611 style with too much compression dampening. What it boils down to is for nearlly the same amount of money as a set of AGX's you can get a shorter strut. Thats the biggest deal. AND (if you pick the right strut) for $135 a corner you can get a strut that will easily handle 450lb springs and is several inch's shorter then AGX's and has less compression dampending then your original 8611. You may say the AGX's have a better dyno curve. But on the road and the track you can't get a car to handle as well with AGX, not by a long shot. They are simply to long and don't have the ability of the Koni's for rebound control. Plus, AGX's seem to shock the tires too much on the street. B13's in particular like to get bouncy with them. Thats not good handling is it?

The dyno cuve I have for the AGX is more digressive than the one I have seen for the koni red for instance.

Of course the truechoice is better, it has well travel and enough damping for the spring rates. The AGX shock is better for near stock ride height. My Truechoice suspension does not have the STD 8611 compression damping, it has around 120 lbs compression damping on soft and about 200 lbs full stiff.

The AGX's I have seen that are boncy are because the car is too low/no travel, shock is blown because of running to low, etc. The AGX/Hyperco second gen does not seem bouncy to me.

I havent tried your Maxima combo. The shortened Sentra Koni red is underdamped.

 

[choaderboy2]

Back in the day, the B13 front was the only option commonly tired. Now we have Spec V and Maxima inserts. Even back then the standard SE-R fronts are ok up to the 325lb range. Thats the setup Matt (a very good instructor) is using on his SE-R on a roadcourse.
http://www.sr20forum.com/showthread.php?t=47637
But, knowing what I know now, I recommend the SpecV insert. The cost is less then $10 more.
BTW, the Maxima insert ($135 from tirerack) as tested by Koni has nearly the same starting rebound dampening as the 8611 but with out the overly stiff compression portion. It's my favorite setup for the front. The B14 Koni front has about 10% less starting dampening as the 8611 and makes a great rear unit for a B13 GC car. In the end my criteria for a shock are:

1 Shorter then stock
2 Adjustable
3 Easily Revalvable
4 Of a know high Quality
5 Adaptable to a variety of setups
6 Race Proven
7 Will survive a daily driver

Very few shocks make that list. VERY, VERY few.

And all this talk of Digressive dampening curves kinda makes me wonder about all the SE-R Cup cars running Koni's in the past. Take a look at the Advance Design setup.
http://honda-tech.com/zerothread/1104049
It's not even that digressive (I know it's tunable). Like I said in my post a little while back. There is a heck of a lot more in picking a damper then just looking at a dyno curve. I will take "1 inch plus shorter then stock Koni" over the AGX setup any day of the week on a lowered car. If I was to build up any B13/14/15 my first and only choice would be either a set of Spec V or Maxima/B14 setup depending on the springs I was using. I would recommend Progress stuff, but I'm still mad at progress for making my S13 swaybar wrong and not replacing it. I can't imagine buying a $1200 setup of coilovers and getting the same service I have recieved with my simple to make but poorly made swaybar. I will stick with recommending Koni's as they are proven to be a reliable long term performer with great customer service. Just to be clear, it's not "my Maxima" setup in the sense that you have to pay me to get it done. I have posted how to do all this stuff on your own. It's off the shelf simple

The AD chart supplied looks pretty digressive to me. Look how steep the curve is in the 1-2" veloctiy range. In fact it looks slightly more digressive than my front SE-R cup spec and definatly more than my rear spec curves.

But look at Koni reds.

Most modern shocks can be made more digressive, since blow off valves have been added to the circuits.

Results also vary on who is setting up the car to a great deal

Here is a pic of Tom Paules AD equppied car hitting the FIA curbs. Note its bouncing off the ground. The shocks are the old AD valving and Tom is really bad at shock setup. He is such a good driver that minor details like that don't bother him! Following him I could see his car hopping and bounding off of the curbs and bobbing in the rough coners. You can see how much the chassis is upset by the cars attitude and how its heeling over.

As a contrast, Annie Sams old style 8611's in the same turn with the same hit. Its planted. Look how flat the body is at close to max G. This car was the first I tried harmonics tuning on and is set up really well. A lot of attention was paid to the chassis set up on this car. Now its not as good because of changes to the front spring rates. This car works exceddingly well with "old" technology shocks.

Finaly my car with custom spec AD valving. I really clouted the curbs trying to shave every bit off of the track during a time attack. Look how the wheels are all on the ground and the chassis isnt even upset. This is an exccedingly hard hit as well, most other car are launched on two wheels when you do this sort of stuff. Look at the bodys attitude and how flat it is even though the car is at max G here. When my car hits curbs, its a gentile bloop and it goes on, its not a big bounce and slide. Sometimes I even hook my inside tires on the inside of the curbs to try and get more speed. Well set up dampers allow this with little drama.

So how a damper works isnt exatly related to brand. This is what Steve is alluding to. If you are good at tuning what you have, you can make things work.

 

[choaderboy2]

Great discussion guys.

Could one of you brainiacs please enlighten me (the forum) on the suspension differences between the three chassis?

I got the B13, McPhereson struts X 4, IRS, blah, blah, blah. I quoted someone.

The B14 has a rear beam instead of IRS with McPherson struts. The beam needs to be bent (already linked a couple of threads on that). The B14 has some issue with less travel (?) in the rear that is different than a B13. Maybe....I think.

And that is the sum total of my knowledge.

Can one of you guys not only explain the differences but what it means from an enthusiasts standpoint? A "Readers Digest" version of what your average forum head needs to know.

Gracias.

The B13/B14 front suspension is virturaly identical. The B14 rear suspension works but has some inherit flaws, mostly a super high roll center. B14's require beam bending and a lot of rear roll stiffness to work.

When sused out B14's handle pretty good.

 

[choaderboy2]

Unless you don't have enough shaft travel. Then it's kinda a lost cause. Hence my confusion of you recommending AGX's again all of a sudden.

I like them for near stock ride height. For sure not lowered.

 

[choaderboy2]

Is this something that can be applied to the street then? What sort of front to rear ratio for the spring rates do your calculations show we need? Has testing showed the calculations are pretty close to what actually works? Werent you working on a large rear sway bar awhile back? With the stiff springs in the rear I'd think you would be going with a larger sway bar in the front now. One last question, whats an LDPT? Some sort of data logging sensor?

It works for street cars, some Nismo suspesion packages like the Altima and Maxima are tuned like this as is the C6 vette.

You want the bob of the front and rear to cancel out within 1/2 cycle of your target speed. I use 70-80 mph or so for a race car. Street cars use 50-60 mph or so.

A LDPT is a linear varible resistor on a rod used to datalog suspension movement with a very high resolution. I have the data logger but the buggers are expensive. I have some string pots but they don't have the resolution to do what I want to do next, looking at the distribution of shock piston velocity over time.

 

[choaderboy2]

So whats with the big rear sway bar you had been developing? I would think you'd be going with a bigger front, not rear now.

How do I actually calculate this stuff? I started messing around with some equations but I'm not sure if what I've come up with means anything. I figured tune for 60 mph, which is 88 feet/sec. Wheel base is 95.7 inches, so at 60 mph the time difference between the front and rear hitting a bump is .090625 seconds. On a tech paper on optimumg, it said a typical ride frequency is 1.5 to 2.0 hertz on a race car. I used 1.5 hertz for the front, then used the mathematical description of a wave (Acos2pi ((x/lamdba)(t/T)) ) to calculate the time the wave takes to cross the x axis (1/2 cycle). From what I can tell it doesnt matter what you use for wavelength or amplitude (because x is going to be half of the wavelength so you always get .5 for x/wavelength). I came up with 1/3 of a second for t. 1/3 minus the .090625 I found earlier equals .2427 seconds. Thats the time you need the rear to cross the x axis, so multiply that by two gives you the period, and one over that is the frequency, which I get to be 2.06. So, with a 1.5 hertz front ride frequency I get a 2.06 rear. Am I even close to being right on any of this?

I don't want to sound like a dick but I get paid as a consultant to do this stuff and there are a few things that I want to keep to my self.

Since I am the only one in the aftermarket to do this sort of thing to my knowlege and I have gotten a few jobs with this in the motorsports world with very statisfied customers, I am keeping it as my secret for now.

 

[choaderboy2]

This is definitely the place for structural bracing, got a whole section on it. As you can tell, pretty much anything having to do with the suspension gets included.

Feel free to PM me or post again on exactly what you would like to see included. I am grateful to anyone that contributes "reasonable knowledge and practice" to this thread.

Since I have no knowledge and am oftentimes unreasonable, I sure can't contribute much myself.

Stiffness is very important in suspension tuning.

 

[choaderboy2]

IV. Bushings

(Applications: B13, B14, B15)



Very informative thread on rear suspension bind on the B13, which includes links to other threads on the same issue:
http://www.sr20forum.com/showthread.php?t=134794
I took Steve's sage advice and I did search around the Forum.



Another very good thread with Steve dropping knowledge on the issue of suspension bind:
http://www.sr20forum.com/showthread.php?t=168950

If you are not going to the track, perhaps you utilize the car as a daily driver and occasional autocross, this is something to carefully consider:

This stuff about suspension bind is baloney. Sure there is some bind but if you take the damper out and stroke the suspension though its range of normal motion by hand you can see that the bind is minimal, like it adds perhaps 5 lbs to the wheel rate, perhaps as much as 10 and there is no way you are going to feel that in a sedan!

What will happen is that the suspension will tend to move towards toe out under trail braking which exagerates trailing throttle oversteer. If you have dirven a car with stiff suspension, sticky tires and stock bushings you will know what I mean, its a vauge feeling.

If you drive a car with stock bushings and a full ES set there is a big difference.

Socres of guys who actualy race these cars or drive on the track with full ES sets are not wrong.

Your suspension is not going to lock up sending you into wild oversteer. In fact it will be the opposite as less delfection will lead into to more toe in under roll. In fact the latest thing I do on race B13's is to incline the strut rearwards to reduce this tendency.

 

[choaderboy2]

I understand your point and I sincerely appreciate you looking so closely at this thread. I want the information in this thread to be as accurate as possible and you happen to be one of my most quoted experts.



It appears that Steve, Slartitbartfast, and Johnand all state the the rear trailing arm is in fact a problem. It must be repeatedly lubricated or it will bind.

Do the guys on the racetracks frequently lube the bushing? Zirk fittings and grease?

Or do they install the ES bushings in the rear and just leave them alone, with no issues?

Do you think that ES bushings (including the trailing arm) are A-OK for a daily driver, and someone who is not going to take the time to lubricate the ES bushings?

I am not mechanically knowledgeable nor experienced enough to argue either way. I could not even tell you which suspension part is the trailing arm. Again, I just want accurate information for the masses.

I PM'd Steve requesting that he discuss this issue further with you.

Gracias!

PS. Remember the Oscar Meyer song - B-O-L-O....G-N-A.

Theorticaly what they are saying is sound and correct but practicaly its not that big of an issue. If I was designing a suspension from scratch its not how I would have done it but for most of us, we are stuck with what we got by the rules or by money one is willing to spend. Note that none of these guys actualy race or do much track driving, testing or development.

If somone thinks this is wrong, they can see what I am talking about by taking off the spring and cycling the suspension through the range of normal motion as constrained by the damper, then remove the damper and move the suspension through the same range, from normal ride height to close to bottomed out as defiend by touching the bumpstop. Sure you can feel some bind but its easily overcome by hand pressure. Note that there is also bind from the stock rubber as well. The bind does not become severe until the suspension is cycled past the point it can move as limited by the damper!

The small amount that this bind adds to the wheel rate is unfeelable in this sort of car. You can feel the difference in the toe change cause by compliance here.

Now certain car like Hondas have bushings in their rear trailing arm that cannot be replaced with urethane without bind issues but the amount of bind that we get our suspension is very small in relation to this.

As far as maintanance, I normaly wrap the bushings pivots with a couple of layers of teflon tape then apply silicon grease. This stays smooth, quiet and sticshion free for a very long time. In fact I havent ever had to service a bushing after this trick.

I got this idea from a fellow list member, what a great idea! I wish I had thought of it.

 

[choaderboy2]

I did the same thing. Thats how I came to the opinion. Maybe it's a east coast/west coast thing. In a place that gets rain regularly ES bushings suck. Especially if you can replace some of the worst offenders with spherical bearings and totally eliminate the binding and friction.

Try the teflon tape thing, it makes a big difference.

Like I said, there is bind but it turns a 600 in/lb spring to a 610 in/lb spring or so.

 

[choaderboy2]

My other issue with ES bushings is that they don't move smoothly. They tend to grab, let go, grab. Very inconsistent. I guess if they are smooth they should be ok. I have found that even on my simple Front LCA (on my 240 that I sold) I needed to not tq down the bolt very much to insure this did not happen. I had to locktite it in place otherwise it would back out. Too tight = bind, too loose = sloopy arm with toe change. Get it right and it was ok. I installed grease fittings so I can relube it easily.

Try the teflon tape trick.

 

[choaderboy2]

So Mike, are you suggesting replacing ALL rear bushings (both parallel arms AND the trailing arm front and rear bushings) is recommended?

I do and so does every racing B13 chassis car out their. Our cars still lack front grip even after that!

 

[choaderboy2]

I would give it another shot IF I had a car I was going to do this too. Since you say it works fine I will defer to that. I have no intention of ruining my perfectly good DD with ES bushings or other mods. Those with B13's should try it I guess. I would still recommend keeping an eye on the links to make sure they have not frozen up solid. My S13 took less then a year to do that (with out the tape trick). Race cars and seldom driven cars can get away with a lot more then a true DD in my experience.

Happy Tinkering.

There are literaly hundreds of cars here DD with the bushings. I guess with rain, salt and snow it might be different. My guess is the teflon tape will probably help alot here.

I used to regrease stuff after about a year of DD when it started to squeak. With the tape it never seems to get to that point.

 

[choaderboy2]

How do you wrap the trailing link to frame bushing with teflon? That is the worst offender in the rear. It has a 4 inch circle touching the frame that has lots of friction built into it?

I think the grease film stays ok in there. I think the bushings with less side contact like the LCA dry out faster. In fact those are the ones that develop squeaks in my experiance.

A cool thing to try would be to get the thin teflon sheets that McMaster-Carr sells and put them on the sides.

 

[choaderboy2]

McMaster or MSC-direct teflon sheets do work well..I have used some on my ES bushings. You can buy teflon sheeting in 100' continuous rolls & pass some sheets onto your kids..never again waste your money on Plumbers tape!! I also bought some solid teflon rod & drilled out a 3/8" hole through the center & used as them as the front sway bushings for awhile...NO binding!! Worked well...

I did just that on my Mustang a long time ago and tore the bar mounts right out of the chassis

 

[choaderboy2]

I think I finaly get the beam axle to really handle well

For not much money.

So I have been inadvertantly experimenting with a cheap way to get the B14 to handle correctly. I have been struggling with this ever since I started to race one of these things. I think I am finaly on to how to get one of these to turn right.

In my development of the B14 I have struggled to fix a couple of handing issues that were very stubbon. The first is a vauge rubbery feeling in the back with some unpredictableness in how the rear end responds. One, this feels bad, espicaly on high speed turns, two, it is unpredicable and not consistant when oversteer will finaly happen.

The second is a nearly relentless tendancy for grinding low speed understeer, unless tricky driving is done (like lots of trail and left foot braking). This is caused by the car falling over on its outside front wheel in hard turns which I think is a roll axis location issue. The falling over causes it to loose camber and contact patch and thus grip.

I have been working on different ways to fix this without hurting the B14's good points, which is really forgiving and self correcting recovery from real sideways. All of my fixes have been high dollar and custom parts, not what your average guy can come up with.

A lot of the problem is around the rear axle. This rear axle is really quirky but highly engineered so it is real hard to get a good understanding on how it works and how to fix it for high performance. I spent a good amount of time going backwards until I hit the nail close to the head.

First I bent the beam for zero toe. This is critcal as the B14 handles like utter dogsh*t unless you do this. It has 1/4" of toe-in stock and you just can't overcome that with suspension turning. 1/4" of toe make it push like a pig and suddenly let loose if you try the normal bar and spring thing to fix the push. YOU CANNOT MAKE A B14 handle without this. See Steve, he will fix you up unless you dick him around. DON'T DICK STEVE AROUND AND GET HIM MAD. For most of you he is your only option for beam bending. The other option is that you can ship your car and lots of money to me and I'll do it for you.

Next I installed hard urethane bushings in the trailling arms of the suspension. This made a pretty big difference as the soft rubber bits actualy damped out the effect of bar and spring rate change due to the 1/2" of gush they have. Now the car was more preditable in trail braking but still was nothing great. You get these bushings from Global Performance Products. The car was now sort of ok but no B13 and certainly no Honda. I raced the car like this for many years, it still won lots of races, sat on poles, did ok at time attacks and held a few lap records.

After building the Dog III, I had a spare B15 Spec-V Scott-Russel linkage lying around. Looking at the B14 linkage I noted big mushy busings and a pretty wimpy stamping holding it all together.

The Spec v part is way more substantial, has a forged aluminum link and smaller harder bushings. I had to drill out one of the steel sleeves to 12 mm or something to get it to fit on the B14 but it was mostly a bolt on.

Whoo wee I thought, this would fix the remaining vaugeness of the rear end. I was wrongo. The rear of the car felt much more planted and stable, really good in fact but the car pushed like a pig, like back to square one.

I did some thinking and figured out the the stock beam depended on the flex in the scot-russel link to give the back of the car toe steer to make it turnable. You see the Spec-V is an evolution of this car and it has only about 1/16"-1/8" of toe in the beam stock with less toe steer in the linkage

I then took a careful look at the motion ratio of the rear suspension and figured that it was greater than the B13 as the shocks are way inboard, forward and at an angle inward. Much stiffer springs were in order. I started to up the rear rate and found the car working better and better. With the Spec-V rear link, I ended up at 25% stiffer rear springs, for my race car this means 600 front and 800 rear. Hummm, the spec-v comes with stiffer rear than front springs stock....

I mean I am thinking of going even stiffer in the rear but your average guy might not find this much oversteer to his liking and the suspension harmonics numbers start going away. I am going to experiment with getting more front grip instead.

Now the car has been transformed, the understeer is gone unless your really hamfist it. With trail braking or lift throttle the car pivots around the nose, infact the rear tires wear faster than the front! At high speeds it four wheel drifts with the front leading slightly. The rolling over on the front feel is mostly gone and pictures of the car cornering show this as well.

The rear slides nice and is solid and predictable feeling. So this gets rid of all of the B14's weak points over the B13 and makes it feel almost like a Honda. The dog car feels almost as good as my buddys H4 DC2 Integra now.

The progress bars are full stiff in the rear and middle in the front. Future tweeks will be to revalve the shocks for more rear rebound and more lowspeed front rebound damping and it should be real good. Maybe a little more rear spring.

So what did I learn that you can copy?

Bend rear beam to zero toe
Urethane rear trailing arm bushings
Spec-V Scott-Russel linkage
25-30% more rear than front spring rate

Kick some ass.

 

[choaderboy2]

Very interesting. Would you suggest running B13 rear progress sway on full stiff as well? 300/250 rates.

Thanks.

Dudeman

Well you put your bar on full stiff and you tell me!