I have ordered a rear sway bar for my 94 Q45 base model which had no stock bar. I seem to remember that Dennis recommended that the front springs need to be changed if a bar is added. How important is it?
I just got my car where I can enjoy it and don't really want to have to tear down the struts again to change springs if I don't have to. And I guess I would have to have it aligned once again.
How about it, can I use the rear bar without changing the front springs without problem?
Q45 - Add swaybar without changing springs?
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maxnix
- Posts: 22627
- Joined: Mon Jul 22, 2002 8:11 pm
- Car: 1995 Infiniti Q45
1995 Infiniti Q45t
2000 Infiniti Q45
Stock Front Springs
All the springs are the same on non-a models.
No need to change springs.
Go to http://www.infinitipartsusa.com to view diagrams and part numbers.
No need to change springs.
Go to http://www.infinitipartsusa.com to view diagrams and part numbers.
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Q45tech
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- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
In the case of small diameter rear sway bars, the name is probably a misnomer since an EXTRA 40 pounds per inch of resistance tacked on to 123 lbs per inch SPRINGS is only 1/3 stiffer.Instead of a max of 4" of rear body roll the same G force would still roll the rear 3" with rigid bushings and 3.3" with rubber ones.
What the factory does is change the existing front sway bar to a smaller size 29>28mm which increases the front sway by 13%/2 or 6.5% reducing the tire slip angle [load] on the front by roughly half that amount.The rear has less weight on the tires [they are not being overloaded like the front] so the rear bar increases the rear load by some amount and the smaller front bar decreases the front load.
The ideal situation is for all 4 tires to have the same load [weight pushing down adjusted for the differences in static weight distribution.
The Q unlike most cars has an agressive camber curve control which attempts to keep the tires [the tread part] perpendicular no matter how much the body rolls.With this taken care off by the upper links one can concentrate on balancing the load induced by turning [not really trying to minimize sway per se].
The front sway bar [is so big] to reduce the traction on the front tires making the Q progressively increase its understeer.
Wish there was another common name for sway bars which better described what we are trying to do!
What the factory does is change the existing front sway bar to a smaller size 29>28mm which increases the front sway by 13%/2 or 6.5% reducing the tire slip angle [load] on the front by roughly half that amount.The rear has less weight on the tires [they are not being overloaded like the front] so the rear bar increases the rear load by some amount and the smaller front bar decreases the front load.
The ideal situation is for all 4 tires to have the same load [weight pushing down adjusted for the differences in static weight distribution.
The Q unlike most cars has an agressive camber curve control which attempts to keep the tires [the tread part] perpendicular no matter how much the body rolls.With this taken care off by the upper links one can concentrate on balancing the load induced by turning [not really trying to minimize sway per se].
The front sway bar [is so big] to reduce the traction on the front tires making the Q progressively increase its understeer.
Wish there was another common name for sway bars which better described what we are trying to do!
Dennis,I ordered the "anti-sway bar" from Infiniti Scottsdale. I believe it is the bar that comes with the "active suspension" model. Joe said he thought it was a "big" bar, whatever that means.
Trying to decipher your technical explanation of the camber changes under load..............I know from experience with my Porsche 911, that a strut tower brace helps to keep more of the tire print on the road during cornering. Is the Q45 suspension trying to do the same? Does a strutt tower brace help with the Q?
And I guess you have answered my question in that adding the rear bar without changing either front bar or springs will not be a problem? Is that correct?
Thanks,Jerry
Trying to decipher your technical explanation of the camber changes under load..............I know from experience with my Porsche 911, that a strut tower brace helps to keep more of the tire print on the road during cornering. Is the Q45 suspension trying to do the same? Does a strutt tower brace help with the Q?
And I guess you have answered my question in that adding the rear bar without changing either front bar or springs will not be a problem? Is that correct?
Thanks,Jerry
fasride wrote:Dennis,I ordered the "anti-sway bar" from Infiniti Scottsdale. I believe it is the bar that comes with the "active suspension" model. Joe said he thought it was a "big" bar, whatever that means.
Trying to decipher your technical explanation of the camber changes under load..............I know from experience with my Porsche 911, that a strut tower brace helps to keep more of the tire print on the road during cornering. Is the Q45 suspension trying to do the same? Does a strutt tower brace help with the Q?
What a well designed suspension should do is to add negative camber (tilt the top of the tire "in" toward the car) as the suspension compresses (commonly called the camber curve) to offset the positive camber that is generated as the car rolls (think of what happens if you tilt a toy car without a suspension. The car rolls up on the outside edge of the tire). That's why when you see slammed Honduhs, their tires are tilted inward so much. The suspension is effectively compressed quite a bit, and the suspension has added negative camber. It works well for cornering when when the suspension is left at a reasonable ride height, but looks ridiculous and wears out tires very fast when the car is lowered too much. Good suspensions like those with a short long arm (SLA) design can add a significant amount of camber, and some like strut suspensions don't do a very good job of it. The goal as Q45tech mentioned is to keep the tire relatively flat on the ground when the car is cornering (actually a slight amount of negative camber while cornering is desirable with radial tires for maximum grip)
However, because of a variety of reasons, you can't fully compensate for the positive camber gain from the car rolling with suspension design alone, so you have to dial in some static negative camber (negative camber while the car is at rest), which is kind of a "head start" on negative camber while the car is cornering. Since a strut type suspension has an inferior camber curve, they need more of a head start (static negative camber) than one with a more sophisticated suspension. The problem with too much static negative camber is that it wears the inside edge of the tire quickly, and reduces traction for accleleration and braking.
In short, to make a car handle well, you have to make sure the tire is staying relatively flat on the road as the car rolls and the suspension compresses. You can do any of three things to make it happen:
1. Increase roll stiffness so that the positive camber gain from rolling is reduced. Sway bars do this as well as increasing spring rate. You can't go too far here though or the ride become unbearable, and the suspension loses compliance over rough pavement, which hurts handling on less than perfect roads (or racetracks).
2. Design a suspension that adds negative camber as it compresses. This one is beyond the control of the car owner except to the extent that adding additional caster improves the camber curve when the wheels are turned.
3. Add static negative camber to get a "head start" on adding negative camber as the suspension compresses. Some static negative camber is needed even with the best suspensions that are MUCH better than anything than anything that appears on a road going car. Look at the tires on a Formula 1 or CART car sometime while the car is at rest. You'll see that the tops of the tire are tilted "inward" quite a bit, indicating lots of static camber.
Even with the best suspensions, -2 or more degrees of static camber is needed. I've never measured tire temperatures on a Q45, which is how you setup camber, but I'd guess you'd need close to -3 degrees for optimal handling. Tire wear would be a big problem with that much camber though. Camber isn't adjustable from the factory on a Q45, but can be made adjustible with aftermarket uppper suspension links. However, the -.7 or so that comes stock on Q45s is a good compromise between tire wear and handling.
Strut tower braces are alleged to help with camber, but I've seen suspension analysis by people who do suspension design for a living, that says it may actually hurt camber while cornering rather than help it. Either way, they don't do anything for camber on a car like a first generation Q45 that doesn't have struts, and the benefit if any, is to make the car feel slightly stiffer.
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Q45tech
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1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
The problem or solution on the 90-96 Q is that it has MacPearson struts and angled upper link in PARALLEL in the front.The angled upper link creates a SERIOUS camber curve even greater than a short/long upper lower A arm type systems....roughly~~~0.8 degrees extra negative camber per degree of suspension compression or lowering.......so a 1" lower Q has negative 1.5 degrees static camber [on front] or the nominal amount that would be found in a 1 inch body roll.
The same amount as if the car was always turning a corner at 0.25-0.30 G's.
Excess negative camber [more than what was designed] in the straight ahead mode is very bad because when you panic brake the front dips [compresses] 3-3.5" due to the aft fore weight shift and the inside tread edges receive much much more load than the outside tire edge.
The small [relatively] 20 mm rear active sway bar provides 40 pounds per inch against the stock rear springs [which are 123 pounds per inch]........ the ratio is what's important, the new 123 +40= 163 vs the old 123........vs the front 146 + [zero to 146 for the front bar depending on how much front suspension rubber is compressed......the sway bar mounting slack].
The front sway bar may be providing anywhere between zero [1/8" side to side slack in all the bushings and say half or 73 pounds progressively in the first inch of body roll........hopefully the second inch has used up all the slack and the FULL 146 pounds per inch is available.So each Q is slightly different depending status of sway bar mount bushings and sway bar end link bushings......this is the complicated part ......the Critical part......the factory made it impossible to over tighten the sway bar end links by limiting the bolt threads! So the failure [or worn mode] is to have less understeer [BUT MORE SWAY] as the bushing wear vs brand new.
We check this with a big pry bar [trying to subjectively measure the slack in where the bar /endlink mounts to the lower arm].
An 1/8" of wiggle vs a 1/16" of wiggle is very subjective as is each techs amount of force applied to the bar......so it is a test designed to show total failure vs incremental failure.
Why I recommed changing out all front sway bushings every 3-4 years every 60k. It takes less than an hour and cost less than $150.
As to the strut tower brace the Q is relatively soft and flexible, it was not designed as a race car so the strut tower do move in and out as the load shifts in cornering..........it is quite feelable and easily measured with a strain gauge as a load change of 50% is significant.......the strut tower may have 1100 pounds on it sitting still and 1600 or 600 pounds depending on whether it is the load or unloaded wheel side in a turn!........it doesn't move much maybe an 1/8" but this is enough to change the camber a little less than 1.0 degrees from what it would have been if no movement occured. The inner tire moves in and the outer [unloaded] moves out. This is the source of some of the instability as you get near the full capabilities of the Q [non predictability].
With weak tires you may not feel this movement because the tires are already giving up and you have had to back off anyway.
Each tire is different so each requirement is different as is each drivers demands on the car. Thus the great variance in feel when we do a test drive.......we has a serious test track in a city industrial road right next to shop: curves, straights, railroad tracks, curves....relatively protected areas where we can do zero to 80 tests across a long bridge where you can see if anyone approaches and no one can turn in front of you......milestones from previous tests......plus an interstate where 80 mph is common and blast to 100 mph are do-able in decent safety. Plus reasonably tolerant local Police who give us bad looks but don't move......they flash their lights which means road testing is over for a few hours!
The same amount as if the car was always turning a corner at 0.25-0.30 G's.
Excess negative camber [more than what was designed] in the straight ahead mode is very bad because when you panic brake the front dips [compresses] 3-3.5" due to the aft fore weight shift and the inside tread edges receive much much more load than the outside tire edge.
The small [relatively] 20 mm rear active sway bar provides 40 pounds per inch against the stock rear springs [which are 123 pounds per inch]........ the ratio is what's important, the new 123 +40= 163 vs the old 123........vs the front 146 + [zero to 146 for the front bar depending on how much front suspension rubber is compressed......the sway bar mounting slack].
The front sway bar may be providing anywhere between zero [1/8" side to side slack in all the bushings and say half or 73 pounds progressively in the first inch of body roll........hopefully the second inch has used up all the slack and the FULL 146 pounds per inch is available.So each Q is slightly different depending status of sway bar mount bushings and sway bar end link bushings......this is the complicated part ......the Critical part......the factory made it impossible to over tighten the sway bar end links by limiting the bolt threads! So the failure [or worn mode] is to have less understeer [BUT MORE SWAY] as the bushing wear vs brand new.
We check this with a big pry bar [trying to subjectively measure the slack in where the bar /endlink mounts to the lower arm].
An 1/8" of wiggle vs a 1/16" of wiggle is very subjective as is each techs amount of force applied to the bar......so it is a test designed to show total failure vs incremental failure.
Why I recommed changing out all front sway bushings every 3-4 years every 60k. It takes less than an hour and cost less than $150.
As to the strut tower brace the Q is relatively soft and flexible, it was not designed as a race car so the strut tower do move in and out as the load shifts in cornering..........it is quite feelable and easily measured with a strain gauge as a load change of 50% is significant.......the strut tower may have 1100 pounds on it sitting still and 1600 or 600 pounds depending on whether it is the load or unloaded wheel side in a turn!........it doesn't move much maybe an 1/8" but this is enough to change the camber a little less than 1.0 degrees from what it would have been if no movement occured. The inner tire moves in and the outer [unloaded] moves out. This is the source of some of the instability as you get near the full capabilities of the Q [non predictability].
With weak tires you may not feel this movement because the tires are already giving up and you have had to back off anyway.
Each tire is different so each requirement is different as is each drivers demands on the car. Thus the great variance in feel when we do a test drive.......we has a serious test track in a city industrial road right next to shop: curves, straights, railroad tracks, curves....relatively protected areas where we can do zero to 80 tests across a long bridge where you can see if anyone approaches and no one can turn in front of you......milestones from previous tests......plus an interstate where 80 mph is common and blast to 100 mph are do-able in decent safety. Plus reasonably tolerant local Police who give us bad looks but don't move......they flash their lights which means road testing is over for a few hours!
Very interesting lessons on suspensions. I'm going to give them a try on my simulator (aka Playstation "Gran Turismo"). This game enables you to adjust cambers, add or remove different sway bars (stabilizers) and change shock dampening, spring rates and ride heights. In my experimenting, this game does effectively reproduce the charateristics one would expect from altering suspension setups including tire wear. Too bad it doesn't let you test out name brands for tires, etc. and unfortunatly there is no programmed J30 (or Q45) equivalent for the Nissan models available.
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Q45tech
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1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
When you add a camber control arm [upper link] to a Maccy P it becomes a coil over strut suspension. Doesn't matter what you call things its how well they work that counts.
By the way the 97Q has about negative 0.4 vs negative 0.7 on the 90-96..............an LS430 uses negative 0.1 as optimum and camber gain half that appropriate for the roll and typical tire.If you lower an LS430 [1"] and put real tires on it and set the camber to negative 1.0-1.3 the whale really handles as well as the best Q and the ride gets no worse [relative to the Q].
The weight of the vehicle is [85%] of what's possible tires and suspension tweeks make up the other 15%. All the engineers know what the other engineers know and there are only a few things possible with stardard suspensions [non actives] and each envolves trade offs............unfortunately any improvements over the oem design probably wear tires and suspension parts faster....what I want is one that wears tires more than suspension parts................just like wearing brake pads faster than rotors..........or oil more than engines.
By the way the 97Q has about negative 0.4 vs negative 0.7 on the 90-96..............an LS430 uses negative 0.1 as optimum and camber gain half that appropriate for the roll and typical tire.If you lower an LS430 [1"] and put real tires on it and set the camber to negative 1.0-1.3 the whale really handles as well as the best Q and the ride gets no worse [relative to the Q].
The weight of the vehicle is [85%] of what's possible tires and suspension tweeks make up the other 15%. All the engineers know what the other engineers know and there are only a few things possible with stardard suspensions [non actives] and each envolves trade offs............unfortunately any improvements over the oem design probably wear tires and suspension parts faster....what I want is one that wears tires more than suspension parts................just like wearing brake pads faster than rotors..........or oil more than engines.
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greg_atlanta
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Re: Q45 - Add swaybar without changing springs?
fasride wrote:How about it, can I use the rear bar without changing the front springs without problem?
Yes! Just do it.
Springs are more for looks than performance. Too harsh for everyday driving.