adding only rear swaybar to a S14 base model?
adding only rear swaybar to a S14 base model?
Is it a good idea to add just a rear sway bar first to a base model S14 since it has nothing back there? Just wondering if it will even help because I read that the front should always be stiffer and im not sure if a whiteline rear bar in the softest setting would still be stiffer than the stock front one. My setup is going to be H&R's with agx's if that matters at all, and the rear tires are 3 sizes wider than the front ones, not sure if that affects anything. Sorry, im trying to learn all this suspension stuff.
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Nismo_Freak
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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
Most stock Nissan front bars [across the models] are ROUGHLY equal to the front spring stiffness at the wheel, but they are isolated with rubber mounts and end links which reduce the initial engagement........the 1st inch of wheel [roll] differences to smooth normal bumps. So the total front roll stiffness might be 146spring + 15bar, then 146spring +70bar, then 146spring +146bar as the roll increases in 1,2,3" of movement.
This is designed to create a progressive under steer as the tire load gets heavier [as the weigh shift increases an indicated by the body roll].
So the car might be neutral [front /rear roll stiffness equal to weight distribution ratio] in the first 1" [+-] of body roll, then the ratio shifts from 54% front, to 60%, then 65%, 70% then 75% front roll vs rear roll stiffness as the G forces increase.
A rear bar slows the rate of increase from 54%>75% down, creating less under steer at the maximum and along the way.
Rear bars with rubber isolation/mounts end links are the same as front........the first inch of rear movement is wasted somewhat in compressing all the rubber/urethane prothane mounts.
Primarily the bars diameter is a clue but the right angle arms are important also as [2 bars = diameter, one with 8" arm the other with 6" arm are 6/8= 25% different in stiffness....the lever action of the arm on the straight or convoluted bar section].Where the bar attaches [where the end links meet the lower suspension arm] is even more important.......on the rear most Nissans attach in the middle of the lower rear A arm thus dividing the bar to wheel coupling by 4. [1" of wheel movement translates to 1/4" of bar movement.
Calculations of the bar stiffness without adjusting for the as installed isolation or mounting points are always wrong, as what you want are the REAL wheel rates.
Anyway on a 240sx [or even a Q or a 300zx] the rear springs are around 120-130 pounds per inch so a rear bar probably should not be greater than 22mm in diameter with 6" arms.........which would yield an extra 80 pounds of wheel rate.
With stiffer front and rear springs you can go for a stiffer REAR bar say a 23-24 mm [roughly = 120 pound inches].
With Eibachs I like a 20mm rear bar [adding only 40 pounds to rear roll stiffness per inch as the springs are progressive [130>160>200 pounds per inch]. Total roll stiffnes is 150, then195, finally 240 at 3"...............yielding a 59%/41% front rear roll stiffness ratio..........5% vs factory 25% ratio on my Q.
The important thing is that the actual roll stiffness on the front is greater than the rear by the weight distribution ratio plus something for safety. This safety amount depends on the weather [wet or dry] the tires equal or staggered widths, and the road friction, temperature, and roughness............most importantly the driver skill and sensivity level.
The factory might use 75-80% and an expert might be able to control the car with 58%-60% in a wet cold curve while accelerating or braking with the best tires for the situation.............lots depends on the rear toe compensation built into the rear suspension.
This is designed to create a progressive under steer as the tire load gets heavier [as the weigh shift increases an indicated by the body roll].
So the car might be neutral [front /rear roll stiffness equal to weight distribution ratio] in the first 1" [+-] of body roll, then the ratio shifts from 54% front, to 60%, then 65%, 70% then 75% front roll vs rear roll stiffness as the G forces increase.
A rear bar slows the rate of increase from 54%>75% down, creating less under steer at the maximum and along the way.
Rear bars with rubber isolation/mounts end links are the same as front........the first inch of rear movement is wasted somewhat in compressing all the rubber/urethane prothane mounts.
Primarily the bars diameter is a clue but the right angle arms are important also as [2 bars = diameter, one with 8" arm the other with 6" arm are 6/8= 25% different in stiffness....the lever action of the arm on the straight or convoluted bar section].Where the bar attaches [where the end links meet the lower suspension arm] is even more important.......on the rear most Nissans attach in the middle of the lower rear A arm thus dividing the bar to wheel coupling by 4. [1" of wheel movement translates to 1/4" of bar movement.
Calculations of the bar stiffness without adjusting for the as installed isolation or mounting points are always wrong, as what you want are the REAL wheel rates.
Anyway on a 240sx [or even a Q or a 300zx] the rear springs are around 120-130 pounds per inch so a rear bar probably should not be greater than 22mm in diameter with 6" arms.........which would yield an extra 80 pounds of wheel rate.
With stiffer front and rear springs you can go for a stiffer REAR bar say a 23-24 mm [roughly = 120 pound inches].
With Eibachs I like a 20mm rear bar [adding only 40 pounds to rear roll stiffness per inch as the springs are progressive [130>160>200 pounds per inch]. Total roll stiffnes is 150, then195, finally 240 at 3"...............yielding a 59%/41% front rear roll stiffness ratio..........5% vs factory 25% ratio on my Q.
The important thing is that the actual roll stiffness on the front is greater than the rear by the weight distribution ratio plus something for safety. This safety amount depends on the weather [wet or dry] the tires equal or staggered widths, and the road friction, temperature, and roughness............most importantly the driver skill and sensivity level.
The factory might use 75-80% and an expert might be able to control the car with 58%-60% in a wet cold curve while accelerating or braking with the best tires for the situation.............lots depends on the rear toe compensation built into the rear suspension.
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yeswepromise
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Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- 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
When you increase the FRONT diameter/shorten the arm length, you increase the front roll stiffness which INCREASES the understeer.......... but it reduces the front roll which decreases the front camber change.
When Q45 added a 16mm or 20mm rear bar the factory dropped the front bar from 29mm to 28 mm [13% reduction which with equal springs neted a 6.5% reduction in total front stiffness].
6.5% more front roll is a tiny amount as is 10% less rear roll.........think in terms of a 3.5" max roll.........0.22" -0.35" change at the same load.
My front Eibach's more than compensated for the front bar change [they are 20% stiffer] net front change +7% stiffer.
Ther rear is progressive [due to Eibachs] averaging 60% stiffer at 2" of rear roll [123>197 pounds per inch] with 20mm rear bar.
This coupled with a 10% [15.9 mm] or a 32% [20mm] increase in rear stiffness from the added bar................fine tuned the chassis towards a more neutral state at the higher G loads.
Hope I am being clear that body roll is not necessarily bad as long as the tire camber changes are compensated.
Increase the front bar stiffness only as a last resort if the rear bar size/adjustment range results in oversteer!!!!!!!!!!!
When Q45 added a 16mm or 20mm rear bar the factory dropped the front bar from 29mm to 28 mm [13% reduction which with equal springs neted a 6.5% reduction in total front stiffness].
6.5% more front roll is a tiny amount as is 10% less rear roll.........think in terms of a 3.5" max roll.........0.22" -0.35" change at the same load.
My front Eibach's more than compensated for the front bar change [they are 20% stiffer] net front change +7% stiffer.
Ther rear is progressive [due to Eibachs] averaging 60% stiffer at 2" of rear roll [123>197 pounds per inch] with 20mm rear bar.
This coupled with a 10% [15.9 mm] or a 32% [20mm] increase in rear stiffness from the added bar................fine tuned the chassis towards a more neutral state at the higher G loads.
Hope I am being clear that body roll is not necessarily bad as long as the tire camber changes are compensated.
Increase the front bar stiffness only as a last resort if the rear bar size/adjustment range results in oversteer!!!!!!!!!!!
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WongFeiHung
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yeswepromise
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