97-98 Q 45 rear stabilizer bar upgrade

[Chrisfrend]

I recently had the opportunity to see whether the 99 Q45t rear stabilizer bar was thicker than that of the 97 Q45t. Visually, the 99 bar looked significantly thicker.

Using a wrench and metric ruler, I measured the width of the 99 bar right next to the bushing at about 21 mm; the width seemed to the the same at two other locations. My 97 rear bar seems to be about 18 mm.

If this is correct, it would seem possible to buy a bar for a 99t and install it on the 97 model, along with a larger bushings and brackets.

When I test drove some 99 Q45ts several months ago they seemed to have firmer suspensions than I found to be the case with the 97 Q45t I ended up buying. My car does not have the adjustable shocks that may explain some of the difference, but the thicker rear stabilizer bar might also be a factor.

The 99t bar would seem to be an easy and inexpensive improvement to make -- I wonder if there would be any unexpected complications.

Chris

[97Q45t]

Good find Chris,Just to let everyone know, the sway bar for 99-01 Touring is only $118.

[maxnix]

When I test drove some 99 Q45ts several months ago they seemed to have firmer suspensions than I found to be the case with the 97 Q45t I ended up buying. My car does not have the adjustable shocks that may explain some of the difference, but the thicker rear stabilizer bar might also be a factor.

It will account for a lot of the difference if they were not switched off.

[Q45tech]

The 18 mm rear bar might have a wheel rate of say 18 pounds per inch and the 21 mm about 53 pounds per inch.

Still in the safe range with 120-130 pound inch rear springs.

Educated guesses based on the similar shape and convolutions to a measured 20mm rear bar on 90-95Q..........the 97 and later is a 1" narrower bar because the rear track is narrower. Above should be accurate within 5%.

The key to Q rear bars is limiting the slop in compressing the rubber end link bushings..........which may limit the bar to 2/3 of total calulated stiffness transfered to wheel.

[Chrisfrend]

This is odd: Today I had a chance to measure a non-touring 97/98 Q45 real stabilizer bar. What got me interested in this subject was an old Auto Week review suggesting that the standard model had a thicker bar than the touring version, which doesn't seem very logical. Visually, the standard 97 Q45 bar did look thicker than the one on my car.

Although it did not seem to be not quite as thick as Auto Week suggestion of 24 mm, the nontouring Q45's bar was about 20-21 mm (14/16 of an inch on the only ruler I had with me), about the same as the 99 Q45 touring models. So it appears that going with the 97 standard model stabilizer bar might offer similar benefits as a 99t bar, and perhaps eliminate any possible fitment issues. It does seem strange that the 97 standard and 99t rear stabilizer bars seem to be more similar to each other than to the 97t bar.

Chris

[DAEDALUS]

How do the wall thicknesses of the bars compare? Outer diameter only tells part of the story unless the bars are solid.

[Chrisfrend]

That is a good point about the wall thickness of these bars. I don't even know if they are hollow or solid.

[Q45tech]

A properly designed equi diameter hollow bar will be only 5-10% less stiff than a solid bar design.

http://www.hotchkis.net/pdf_fi...D.pdf

The normal method is to bump the design 1 mm over a [x] mm solid bar calculation.

[Chrisfrend]

After measuring the 97/98 Q45 standard rear stabilizer bar with a better tool, it appears to be even thicker than does the 99t model, about 24 mm as indicated in Auto Week years ago. According to another article, the 97 Q45t has stiffer rear springs than does the standard model. Since Infiniti regarded the thicker bar as suitable and safe for the standard 97 model, I wonder if this means it would also be safe for the 97 touring model, assuming it does have stiffer rear springs as reported.

I have contacted Infiniti USA about this several times but they have surprisingly little, actually no, information about the suspension differences between these models. I was told that all of their technical information of this kind was discarded because these cars are now so old.

If use of the standard rear bar in the 97 t is safe, this would seem to be a good modification to tighten up the suspension somewhat.

Thanks to Q45tech, and the others who offered comments about this idea.

[maxnix]

I have contacted Infiniti USA about this several times but they have surprisingly little, actually no, information about the suspension differences between these models. I was told that all of their technical information of this kind was discarded because these cars are now so old.

Yeah, at least 3 years. Good work, Chris.

Any luck on inventorying the part numbers? Might be the best guide.
Modified by maxnix at 11:27 AM 10/6/2004

[shadedoc]

My sugestion to you would be to look into increasing the rate of the stbilizer bar bushings. You can probably find somthing that would fit made for another application. Given that the Q is a luxury flagship, the vehicle has significant efforts put towards the suspension & chassis components to improve ride comfort and isolate vibrations. The Q uses natural rubber bar bushings, which for a modest price could be replace with higher shore bushing (NR or urethane). Net result would be an equavelent increase in bar diameter. You would make some compromise in the ride comfort & NVH, but most of us are well down that compromise road with tires, tokico blue's, solid tension link bushings (gasp!)

[Chrisfrend]

Stiffer bushings would tighten the suspension up quite a bit, but I have a daily commute into an urban area with terrible roads and many potholes. The NVH implications make me hesitate. I'm hoping that the standard 97 23-24 mm rear stabilizer bar would stiffen up the suspension on curves without greatly diminishing straight line ride comfort. According to a number of posts, including those of Q45 tech, the stiffness of the bar rises geometrically with the width. It seems logical to think that if Infiniti would have a 23-24mm rear bar in a standard model 97 Q45, this bar wouldn't be exessive on a 97 Q45t, but since the rear springs of the touring model are slightly stiffer maybe that makes a difference. At least I, and any owner of the 97 touring model, can choose between the 21 mm rear bar of the 99 touring model, or the 23-24 mm bar of the 97 standard model, since there aren't any aftermarket stabilizer bar options for us.

[shadedoc]

OEM's select stabilizer bars are in conjunction with many other variables (springs, tires, bushings, absorbers, etc.). Essentially, the bar adds to the wheel rate when the vehicle goes around a corner (as does a stiffer spring). The difference is the spring always adds to wheel rate, the bar only with cornering, or single wheel inputs. If the roads you typically drive are smooth, or bumps act on both wheels at the same time, the larger bar should not effect the ride significantly. If you drive where there are single wheel bumps, stay away from the larger bar. As for the handling aspect, I'm sure you are aware that adding more wheel rate in the rear of the vehicle will decrease understeer. Word of caution: Depending on what your vehicle setup is, you can create an unstable vehicle that may snap-oversteer. With that said, are you looking to flaten the vehicle through the corner or quicken the yaw response? If you don't like the oversteer/understeer balance of the Q, you can add rear bar. You can also look at slowing the roll rate down with absorbers. I've read that many people like the combination of std absorbers in front & Tokico "blues" in the rear. I prefer the balance of the Tokico "blues" on all four corners (the vehicle sets & turns in quicker), but at the cost of input harshness.

[Chrisfrend]

Thanks for your comments. I'm looking into a larger rear bar because the understeer in my car seems fairly extreme, and also because there is some yaw and a slightly boat-like feeling around some sharp curves. In general, the body doesn't seem to be tied down quite firmly enough to the suspension for me. However, it appears that some other manufacturers also put smaller rear stabilizer bars on touring models with stiffer springs. From some of Q45tech's posts, it seems as if there may be some potential danger in an overly stiff rear stabilizer bar depending on the stiffness of the springs. Since I don't understand much about how the suspensions are engineered, this gives rise to a concern about putting on an excessively stiff bar if this could induce dangerous snap oversteer. The 23-24mm standard 97 Q rear bar might be overdoing it, but I don't know since Infinity doesn't have a problem using it on this model. However, I will probably choose to play it safe with the 21 mm bar from the 99 touring model instead.

[Chrisfrend]

Joe at Scottsdale Infinity received the 97 standard model Q45 rear stabilizer bar and confirmed that it is about 24 mm, or 7/8" in diameter. Although it does not seem to make sense that the standard 97 Q45 bar is thicker than the touring model bar, it is. I've gone ahead and ordered it and will report back after it is installed. An earlier post mentioned that the touring bar was $118; this also is about the same price as the much thicker standard model bar. It all seems very odd but I'm just glad that a thicker bar is available after all. For anyone who is interested, this thicker rear bar would be available for 97 or 98 Q45 touring models at a very reasonable cost.

[maxnix]

Should fit on the later (1998-2001) FY33 also. Did you record any part numbers for the various bars? It would be interesting to see if the front bar on the t was downsized like it was on the G50 t and a models.

Modified by maxnix at 11:28 AM 10/6/2004
Modified by maxnix at 11:29 AM 10/6/2004

[Chrisfrend]

No parts numbers were provided for the bars, although Scottsdale would have given to me had I asked. I'll post the parts number for the rear standard bar if it is provided on the invoice when I recieve my order next week. I looked at the front bar on my 97 Q45t before ordering the rear bar, and it seemed huge, appearing to be much thicker than the rear standard bar measured at 24 mm. I don't know if the touring and standard front bars are different.

[Chrisfrend]

The standard model 97 Q45 rear stabilizer bar arrived today. According to the Scottsdale Infiniti invoice, the part number is INF 56230-6P014. It is 24 mm in diameter, quite a bit thicker than the 18 mm bar on my 97 touring model, and seems to be hollow. It also appears to be at least slightly larger than the rear bar on the 99 touring model. In any event, it should fit on the 97/98 touring models, and perhaps on the 99-01 touring models as well.

[maxnix]

Did Joe send new bushings in the appropriate size also?
Modified by maxnix at 11:29 AM 10/6/2004

[BadQ45t]

Well post what happens, I have a 97' Touring as well. BTW, if you're on the tall 60 series tires and 16' rims, dump those. I put on 17x8 rims and 245/45 17 Yoko ES100's and the boat feeling was gone immediately. I can now whip the car into turns much harder and those big paws do not want to let go I'd still rather have my tuned 84' 300ZX in real twisty roads, but much improved with the new tires and rims.

[Chrisfrend]

New bushings for the 24 mm rear bar are necessary: part number is INF 54613-04F02. Brackets for these bushings are also needed: INF 56233-01P10.

New wheels and tires would be nice but I got new tires to replace the bad ones that were on the car when I bought it three months ago, and another replacement would be too expensive at this point. When these wear out I'll be ready to experiment with different tire sizes.

[Chrisfrend]

The new 24 mm rear stabilizer bar has been installed and it has firmed up the rear suspension very noticeably. There is much less body roll, as well as side to side and front to back rocking motions in sharp corners and over major bumps. The car feels lighter and smaller. The understeer remains, but is less extreme. Ride comfort might have been affected to a miniscule degree. The combination of the stiffer rear touring springs and the thicker bar seems to work so well that it makes me wonder if some non-US versions could have been designed this way. I'll never know, given the lack of even basic information on the U.S. models.

The only catch was that the shop claimed they had to remove the exhaust system to install it, but still the installation was only about $120. Total cost with bushings and brackets was around $250, and well worth it.

[BadQ45t]

Thanks for the report. I think this is somethign worth doing when I upgrade the exhaust to the Stillen Exhaust.

[Q45tech]

I used a 24 mm rear bar on my 90 Q [very close suspension design [90-01] except for the 1" rear track differences in 97 models.

The solid 24mm bar with urethane was installed in Florida and used on Georgia's smooth roads for 3 years. When I had to drive weekly in NC it beat me to death on their rough roads......I made some rubber bushings and tried every combination of rubber.

Finally settled on the 20 mm [active bar] with harder rubber bushings [compressed to almost solid]...........ideally I would like a 22 mm hollow bar with the Eibach lowering springs maybe a 23 mm with oem springs.

24 mm was probably found to be too rough on many US roads even with rubber bushings........so they downsized in subsequent years..........it is always confusing tthe lack of detailed info and Japanese thought processes.

Since the rear springs are always nearly the same [give or take 10%] based on weight from 90-01............the IDEAL rear roll stiffness will be the same give or take 10%.

Individuals tolerance for bumps varies widely as do the roads around US.

So you select what you can tolerate .............the major problem is that the shocks were not designed to control the sway bar and you can get significant oscillation on certain roads when the bars are coupled with urethane..........EXPERIMENT.........you can mix and match rubber and urethane JUST make sure you mirror the mixture side to side so the car tries to handle the same turning left or right.

The problem is the passenger side of the road is always rougher [truck ruts]!

[Chrisfrend]

Q45tech, thanks for your comments. I was uncertain about how much road comfort would deteriorate with a 24 mm rear stabilizer bar replacing the thinner bar on my 97 Q45 touring model. The suspension is now taut as opposed to somewhat mushy, so the ride is firmer. Today the new bar got the ultimate comfort test in a commute into the crummy roads of our nation's capital. Since harshnesss and vibration are irritating, I am glad that the new ride is firm but supple over potholes, wide expansion joints, and bumps, and still very comfortable. Perhaps the softer suspension on the FY 33 permits the use of the thicker bar without punishing deterioration in ride comfort. The handling improvement is very significant and more in line with what I expected in buying the touring model initially. It seems to me Nissan made a major design and marketing mistake by reducing the width of the touring bar so much in the 97 Q45 touring models.

[airman]

Thanks, Chris. I might do the same later on. Please post updates as you drive more with this setup.

[airman]

Q45tech, thanks for your comments. I was uncertain about how much road comfort would deteriorate with a 24 mm rear stabilizer bar replacing the thinner bar on my 97 Q45 touring model. The suspension is now taut as opposed to somewhat mushy, so the ride is firmer. Today the new bar got the ultimate comfort test in a commute into the crummy roads of our nation's capital. Since harshnesss and vibration are irritating, I am glad that the new ride is firm but supple over potholes, wide expansion joints, and bumps, and still very comfortable. Perhaps the softer suspension on the FY 33 permits the use of the thicker bar without punishing deterioration in ride comfort. The handling improvement is very significant and more in line with what I expected in buying the touring model initially. It seems to me Nissan made a major design and marketing mistake by reducing the width of the touring bar so much in the 97 Q45 touring models.

Chris,I'm about to install stabilizer bar you have. Any updates on ride comfort and handling? I wonder if this along with new struts I'm putting at the same time is going to kill the ride comfort that my rear occupants like so much

[Jeff Williams]

I had to loosen my entire exhaust system, but did not have to remove it. I just removed al lthe mounting brackets, from the transmission back, and that gave me enough room to snake the bar it. It added about 15 minutes to the 25 minute total install.

I have the "tiny" 18 mm bar on my rear, and I like it a lot, over the standard model, that had none. I can kick out the rear, more predictibally, now. And, once it is loose, I can rain it in, without scrubbing off too much speed. I don't drive like that very often, but once or twice a year, I like to let loose. (Pardon the pun).

[Q45tech]

The nice thing [or the disaster] with nissan rear suspension is you can adjust bar with bushing hardness and thickness, as you have 4 bushings per side [on end link].

Remember the motion ratio of bar is 1/4 of the wheel rate.........if the wheel moves 2" the bar only move 1/2".................hopefully you see that 4x2 or 8 bushings can compress a lot before the bar even begins to do anything.

Perfection to horrible can be a 1/4 of a turn on the end link nuts...........will give you weeks of potential fun in minute adjustments. Then the rubber bushing will wear and change frequently.

[airman]

So you prefer thinner bar with compressed bushings over thicker bar with regular bushings so it kicks in earlier and you get overall quicker response. May be improvement that Chris felt actually was from new bushings rather than from new bar. Cause to make it working would require go over fairly large bumps. I wonder whether it works in turns then.