Strange handling

[Trond]

Lately my car's rear end has been acting a little "nervous" when driving both on dry and wet roads. Feels like the car is doing some steering of its own on my rear wheels.

On some wet parts of the road today, when it seemed one of my rear tires had less friction than the other, my cars rear end would start moving (no acceleration/no turn), noticeably from side to side. When friction was equal, the movement stopped. The tarmac was pretty new, and the difference in friction was only caused by a THIN layer of water .

I had to stop my car, and check that no parts in my rear suspension were loose because I've never felt anything like that in any car I've driven...

Also when driving on dry tarmac, it sometimes feels like my rear is "searching" a little to one of the sides.

Changes made lately are:
Comptech sway bars - set to middle hole position both front and rear.

SoS/AP Racing front and rear brake kit.

I have 10x19'' in the rear with Yokohama AVS 275/30-19'', Bilstein/Comptech suspension.

Anyone ever experienced something similar or have any ideas ??

Could it be the stiffer rear sway bar causing the problem ?

Feels like I've got more oversteer than before as well.

Trond.

[This message has been edited by Trond (edited 07 September 2002).]

 

[len3.8]

Originally posted by Trond:
Lately my car's rear end has been acting a little "nervous" when driving both on dry and wet roads. Feels like the car is doing some steering of its own on my rear wheels.

On some wet parts of the road today, when it seemed one of my rear tires had less friction than the other, my cars rear end would start moving (no acceleration/no turn), noticeably from side to side. When friction was equal, the movement stopped. The tarmac was pretty new, and the difference in friction was only caused by a THIN layer of water .

I had to stop my car, and check that no parts in my rear suspension were loose because I've never felt anything like that in any car I've driven...

Also when driving on dry tarmac, it sometimes feels like my rear is "searching" a little to one of the sides.

Changes made lately are:
Comptech sway bars - set to middle hole position both front and rear.

SoS/AP Racing front and rear brake kit.

I have 10x19'' in the rear with Yokohama AVS 275/30-19'', Bilstein/Comptech suspension.

Anyone ever experienced something similar or have any ideas ??

Could it be the stiffer rear sway bar causing the problem ?

Feels like I've got more oversteer than before as well.

Trond.

[This message has been edited by Trond (edited 07 September 2002).]

Hello Trond.
I have Similar setup on my car and have noticed similar handling situations.
Went over the suspension points as you to make sure everything back there was tight.
Talked to a friend that sets up cars, he thinks it's tire related the fact that we are
running 19's with relatively short sidewalls,
and the fact that my tires are starting to wear, is having a not-yet adverse effect on my handling. Also in my case with the camber adjusted away from factory engineered specs.
So I too am looking for a definate.
What he says makes sense. I just don't know if that's the cause.
Len
n9s5x-t

 

[Trond]

Hi, len3.8 !

What are your sway bar settings ?

Tire brand ?

My rears have only 3mm left I guess.

Before installing the sway bars I went from 35psi to 40psi in both my front and rear tires. Feeling that helped my cars left-right movement tendency on worn tarmac (spike tires are allowed in winter here in Norway - you can imagine the grooves in the tarmac on some roads...)

Today I tried with 32 psi in my rear tires and 34 in my front ones, and this seemed to help a little. With 40 psi in them going to the tracks, the problem seemed worse than before installing the sway bars.

I will also adjust my rear sway bar to the soft position on Tuesday, to see how that affect things.
Shouldn't I get more understeer that way ?

Thanks

Trond.

[This message has been edited by Trond (edited 08 September 2002).]

 

[nsxtasy]

If you still have your original wheels and tires, I suggest you switch back to them to see if the problem goes away. If so, it's the size wheels/tires (or something else associated with the wheels/tires) and not the suspension, alignment, etc.

 

[len3.8]

Originally posted by Trond:
Hi, len3.8 !

What are your sway bar settings ?

Set at middle setting. I have never moved them even at the track.

Tire brand ?
Pirelli

My rears have only 3mm left I guess.
May have something to do with it.
Tread getting a little low.
Mine are less than 60% tread left.

I am guessing tires and the 19 inch wheels
that we are running.
JAO
Len
n9s5x-t

 

[Trond]

Yes, I still have my old ones, BUT I was driving 2-3 months with the 18/19'' set-up prior to the sway bar installation, and never detected any rear end movement. The front tires always were a little nervous on worn tarmac with grooves. But never the rear.

The only thing I can see have changed is sway bars and the rears getting down to 3mm instead of maybe 6mm last time I drove it. (Lent the car out to Autofil for some track driving/shooting for one of their TV programmes/episodes)

I have noticed that my sway bars do not have any clips or collars preventing it to move.
If my rears are exposed to lateral forces, from grooved worn tarmac, could it be my rear moves a little due to sway bar movement ??

Trond.

 

[Hrant]

Snip ...

I have noticed that my sway bars do not have any clips or collars preventing it to move.
If my rears are exposed to lateral forces, from grooved worn tarmac, could it be my rear moves a little due to sway bar movement ??

Trond.

[/B][/QUOTE]

Trond,

All previous suggestions are worth exploring to go through the process of elimination.

But check the following first:

Make sure the sway bar brackets are tightly secured (bolted/screwed). Then get some clips to secure them from moving; I just ordered some from Al Terpak as the Comptech clips do not seem to do the job.

Also running 3mm treadwear given your tire 19" wheel size, your tire patch is wider on the wet surface so you are more prone to hydroplaning then a newer tire not to mention oem size tires .......

And I think you are confounduing the problem with your tire pressures! You noted:

"Today I tried with 32 psi in my rear tires and 34 in my front ones, and this seemed to help a little. With 40 psi in them going to the tracks, the problem seemed worse than before installing the sway bars."

32 rear with 34 front! That's the first time I have heard this combo unless you meant 32 front and 34 rear? Even then you will get oversteer. 40 psi on the track is way too much ............. by the time you heat the tires you will most likely be at 47-48 psi in the rear if not more! Many of us are become converts that on the track, the "hot" reading should be similar to the cold oem pressure; it seems to work well.YMMV based on the tires and driving style.

Finally what is the alignment setting you now have after putting the 19" wheels? What toe and camber are you running in the rear?

HTH


[This message has been edited by Hrant (edited 09 September 2002).]

 

[Trond]

Hrant:

Thanks for replying this and previous posts

The alignment was made after installing the Bilstein/Comptech suspension by Honda in Germany. So the toe/camber should be according to OEM set-up. Everything was made with the 18/19'' combo on the car.

OEM cold tire pressure is 33 psi front and 40 rear. Yesterday I just experimented with less pressure in my rears to see how this affected the rear lateral movement.
I just kept my front pressure normal level, as I know too little pressure in the front will cause more lateral front movement on grooved tarmac.

What you basically say is I should start my track session with cold tire pressure front 28-29 and rear 34-35 psi, which would equal around 33 and 40 with hot tires ?

I've only done 1 track session with the car, before this weekend, and then I felt the OEM pressures were too low. I got tire squeal and understeer in every turn....

I had a set of 17/18'' wheels (215 and 265 width) with me to the track. I filled both front and rears to 40psi cold tire pressure, and the professional driver testing the car for a car magazine, was very satisfied with the cars handling. Calling it "neutral, on the edge of boring"

Amongst the experienced track NSX drivers, the OEM difference in front/rear tire pressure (around 7 psi) is still maintained ??

How can I get hold of the collars from Al Terpak ?

Trond

[This message has been edited by Trond (edited 09 September 2002).]

 

[Hrant]

............ Comments imbedded.

Originally posted by Trond:
Hrant:

Thanks for replying this and previous posts

The alignment was made after installing the Bilstein/Comptech suspension by Honda in Germany. So the toe/camber should be according to OEM set-up. Everything was made with the 18/19'' combo on the car.

............ Did they give you a print out? Do not assume anything, check the numbers on the print out

OEM cold tire pressure is 33 psi front and 40 rear. Yesterday I just experimented with less pressure in my rears to see how this affected the rear lateral movement.
I just kept my front pressure normal level, as I know too little pressure in the front will cause more lateral front movement on grooved tarmac.

....... I don't have experience with grooved tarmac but if you lower the rear keeping everything else, the theory says you get more oversteer. Now given the size of wheel/tires you are running you may want to experiment a little. My comments are for oem size wheels/tires combo.

What you basically say is I should start my track session with cold tire pressure front 28-29 and rear 34-35 psi, which would equal around 33 and 40 with hot tires ?

I've only done 1 track session with the car, before this weekend, and then I felt the OEM pressures were too low. I got tire squeal and understeer in every turn....

........... Yes, I was at 33/40 cold for some time, as my speeds picked up started experimenting and finally seem to have converted to those who have been preaching lower psi ..... note ambient temperature will also affect what cold psi you use. With only 1 track session under your belt, I would not worry too much on tire pressures but learning the lines of the track unless you are an accomplishesd driver from some other venue. We always tells new trackers to start with oem tire pressures because their speeds and tire temps will not be same as a more advanced driver pushing the car and tires. Again your wheel/tire combo may vary.

I had a set of 17/18'' wheels (215 and 265 width) with me to the track. I filled both front and rears to 40psi cold tire pressure, and the professional driver testing the car for a car magazine, was very satisfied with the cars handling. Calling it "neutral, on the edge of boring"

......... well heck, how can I compete with a professional driver's opinion

40 psi front and rear seem not only way too high but weird; you may blow your fron tire at that pressure ..........

Amongst the experienced track NSX drivers, the OEM difference in front/rear tire pressure (around 7 psi) is still maintained ??

.......... that or at least 4-6 psi dependeing on driving style.

How can I get hold of the collars from Al Terpak ?

............. you just did LOLL! I will tell him of your interest; he is not on this forum. His e-mail address is: [email protected] (Al Terpak)he check it every other day.

Trond

[This message has been edited by Trond (edited 09 September 2002).]

 

[Trond]

"............. you just did LOLL! I will tell him of your interest; he is not on this forum. His e-mail address is: [email protected] (Al Terpak)he check it every other day."

Thanks ! seems my Honda dealer didn't bother to put on the teflon tape on my sway bars - I'll do the collars when taking care of this issue...

I have reset my tire pressures to 33/40, to see how that affects my problem...

In theory softening the rear sway will cause more understeer or oversteer ??

How do you set your tire pressures under wet conditions ??
I did some laps this weekend (really wet conditions), with way too high and equal pressure front/rear and got a taste of sudden oversteer and the sand traps

(Managed to keep the nose pointing the right way, and found my way out of there LOL)

I will have my alignment checked tomorrow towards OEM data in the instruction manual. They are the correct ones to use, right ?

Trond

 

[Hrant]

Originally posted by Trond:
"............. you just did LOLL! I will tell him of your interest; he is not on this forum. His e-mail address is: [email protected] (Al Terpak)he check it every other day."

Thanks ! seems my Honda dealer didn't bother to put on the teflon tape on my sway bars - I'll do the collars when taking care of this issue...

............ they may have put a glob of grease; samething except the grease collects dirt over time ......

I have reset my tire pressures to 33/40, to see how that affects my problem...

In theory softening the rear sway will cause more understeer or oversteer ??

.......... understeer

How do you set your tire pressures under wet conditions ??

.......... tire pressure should not change under wet or dry conditions for street driving; they are optimized based on the rubber and design. I have driven in the wet on the track (unexpectedly it rained) only once ...... since I was on oem yokos, I was just "mastering" the lines rather than getting speed ........ it was my best track event ever because I learned the lines very quickly .........

I did some laps this weekend (really wet conditions), with way too high and equal pressure front/rear and got a taste of sudden oversteer and the sand traps

(Managed to keep the nose pointing the right way, and found my way out of there LOL)

I will have my alignment checked tomorrow towards OEM data in the instruction manual. They are the correct ones to use, right ?

......... yes, but given your 19" wheels in the rear, you may not get the camber within oem spec range. Give yourself about 3-4 mm toe in the rear and on the front anywhere between 0.5 (if you want to preserve tire wear) to up to 2.0 if you are concerned about steering response for the track.

While others may have different viewpoints given your wheel/tire combo, do realize that the first step is to get the alignment right. Then the tire pressures and then play with sway bar for fine tuning.


Trond

 

[Trond]

Changed my tire pressures back to OEM and this seemed to help some. I guess I'll be experimenting some more here

I will also change my rear sway bar setting to "soft", to see how this affects general handling and this particular problem.

Do the installation of sway bars itself change the wheel alignment ?

What are the particular purposes of the CT non-compliance toe links kit and rear beam ?

Thanks !

Trond.

 

[Larry Bastanza]

Trond,

No, the sway bar will not effect the alignment. IF the swaybar is adjustable (the links that is) you will want to be sure you have no "preload". That is when the car is on the ground and settled at it's normal height, the sway bar should have no tension on it. The adjustable links alow you to adjust their length to eliminate any preload. (The stock links ARE NOT adjustable)

The non-compliance toe links and rear beam bushing mods are to eliminate rear toe change under extreme loads. If you track your car and really push it, the tail will get unstable the harder you push it. This is due to the rubber bushings in the toe link.(inside connection to the rear beam) It is also due to the bushing for the lower A-arm (where the camber gets adjusted) When you apply pressure to the rear susupension in a hard corner the rear bushings will absorb this pressure and compress, the result is the rear wheels toeing OUT as the bushings compress.

Most folks that have done this mod remark: "It is a totally different car at the limit, much more stable.

I think most would agree, this is "THE" mod for track use if you are driving fast enough.

HTH,
LarryB

 

[Edo]

One thing you might do is check the camber settings on the rear. I took my NSX out in the rain on my race specs -2.8*/side and the car would scoot over about 6 inches every time you went over a paint strip, or tried to change lanes.

Also, if you want the rear to stay planted LOWER the rear pressure. Don't raise it. Same with the Sway Bars, soften them. Tight Sway Bars+ Rain aren't a great combo.

And lastly, wide tires like to roll side to side in the grooves of the road itself. Every car I have driven with massive front tires becomes a Pain in the ass to drive in a straight line on grooved pavement, and having large 19" rims+tires on the rear wil give you the same effect..just on the rear.



[This message has been edited by Edo (edited 17 September 2002).]

 

[Trond]

Edo:
I softened my rear bar before this weeks track event, because of this problem AND because I felt I had too much oversteer.

With front sway bar to the middle position and the rear to soft, I had neutral handling when really pushing the car in corners, and my problem (exactly like you descibe when going over paint strips/small wet areas (not hydroplaning)/changing lanes) was not that significant any more.

However it's still there, and I guess I have to check my rear camber setting to see if it's too negative for street use.

Before installing the sway bars I felt the wide tires/grooved tarmac combination only troublesome on my front axle, not the rear.

The front tires will have a lesser tendency of lateral movement when having higher pressure. I assumed the same for the rear. I will definately experiment some more with tires pressures to see how this effects my rear "living its own life"

Thanks !

Trond.