Wierd side to side movement
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DenverQ
- Posts: 396
- Joined: Mon Jul 22, 2002 1:23 pm
- Car: Tryin to make a living, Driving/Fixing my Q and my Beautiful Baby girl =)
Wierd side to side movement
I was wondering should I be able to move the car side to side? In the back end I can push on the side and get it rockin but in the front I cannot. Is this due to bad subframe bushing? The front harly sways/moves at all. any input would rock!!!
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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
Rear springs are only 123 lbs per inch of compression and the stock rear 15.9 mm sway bar adds only 12 pounds per inch........with shocks having more than 40,000 miles, easy to get the rear rocking.........even with a good rear subframe.
The front shocks out last the rear and the 146 lb/in springs and the 130 per inch front bar make it nearly impossible to depress the front very much.
The front is twice as stiff as the rear when depressing a single corner: 276 vs 135.............once the front sway bar bushings are compressed.
Rear sway is proof of weak rear shocks!
The front shocks out last the rear and the 146 lb/in springs and the 130 per inch front bar make it nearly impossible to depress the front very much.
The front is twice as stiff as the rear when depressing a single corner: 276 vs 135.............once the front sway bar bushings are compressed.
Rear sway is proof of weak rear shocks!
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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
The Eibachs are actually the same or a little softer in the first half to 3/4" of compression, then each inch gets progressively stiffer [120,150, 185, 200] necessary to reach the greater than 500 TOTAL POUNDS in the reduced spring travel. So highway bumps are not a jarring!
The stock springs had 3.75" of possible compression, the lowering spring have only 3.15".
Study the shock absorber shaft length [=7.5" MAX...+- 3.75"].
IRS [independent rear suspension] have a very high roll center and high rear center of gravity [gas tank]. 23" front 28" rear.....22% more rear roll couple yet 15% less weight [depending on gas tank level].
Rear Roll is not a problem [other than feeling it] as the suspension has enough camber gain to control the tire if set negative 1.1 degrees [static] and the tires are oem equivalent.
The body has to roll on the springs or the springs have to be twice as stiff [just to cut roll in half] or the sway bar has to be as stiff as the springs.......[even the 20 mm bar 40/163=0.245 only reduces the sway by 25% or 1.0" at best....whereas the stock t [15.9 mm is only 12 pounds per wheel inch adding only 8.8% roll stiffness reducing total roll by 0.33" at best!
Lux cars have soft springs to make them ride luxuriously.
Be careful about lowering springs as the 3.3% improvement in roll [lowered C of G]...less weight transfer is only 48 pounds or 10% at max compression......about 0.32" less total at BEST probably more like 0.25" and nothing if not worse in the first inch!
The 4300 pounds has to go somewhere if you stiffen the springs the forces just transfer to the tire sidewall or temporarily bend [twist] the car frame.
The rear roll is to warn you to slow down before the rear tires lose grip.
The stock springs had 3.75" of possible compression, the lowering spring have only 3.15".
Study the shock absorber shaft length [=7.5" MAX...+- 3.75"].
IRS [independent rear suspension] have a very high roll center and high rear center of gravity [gas tank]. 23" front 28" rear.....22% more rear roll couple yet 15% less weight [depending on gas tank level].
Rear Roll is not a problem [other than feeling it] as the suspension has enough camber gain to control the tire if set negative 1.1 degrees [static] and the tires are oem equivalent.
The body has to roll on the springs or the springs have to be twice as stiff [just to cut roll in half] or the sway bar has to be as stiff as the springs.......[even the 20 mm bar 40/163=0.245 only reduces the sway by 25% or 1.0" at best....whereas the stock t [15.9 mm is only 12 pounds per wheel inch adding only 8.8% roll stiffness reducing total roll by 0.33" at best!
Lux cars have soft springs to make them ride luxuriously.
Be careful about lowering springs as the 3.3% improvement in roll [lowered C of G]...less weight transfer is only 48 pounds or 10% at max compression......about 0.32" less total at BEST probably more like 0.25" and nothing if not worse in the first inch!
The 4300 pounds has to go somewhere if you stiffen the springs the forces just transfer to the tire sidewall or temporarily bend [twist] the car frame.
The rear roll is to warn you to slow down before the rear tires lose grip.
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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
The 15.9mm rear sway bar shouldn't be called a sway bar and neither should most since they are not large enough to actually reduce sway!!!!!!!!!!!!!!!!!!!!!The front SWAY BAR actually does something in the front by reducing sway close to 100% as the 29/28 mm bar is 9-10 times stiffer than the rear bar.
If you reduce the front sway it just travels to the rear [via chassis].......if you stiffen the rear as much as the front the chassis bends in the middle.
A 24 mm rear bar was available and was 109 vs 123 springs.
The ratio of front to rear TOTAL stiffness should always exceed the weight distribution by 8- 10% or you get oversteer [the moment the road gets wet or power is applied]62- 64% front 38-36% rear is the hairy edge of instability.4300x 0.36= 1548/2=774 pounds of total rear roll stiffness per rear wheel vs 462 stock at 3.75" roll
You must consider the progressive nature of the Eibach lowering springs.......at full compression with a bigger than 20-22 mm bar it is possible to get close or exceed the rule.
As to whether a t car rear bar bushing is tight or lose not sure you could feel it.........zero to only 10% reduced rear sway vs the 20 mm which would be zero to up to 25% reduced sway with urethane bushings
If you reduce the front sway it just travels to the rear [via chassis].......if you stiffen the rear as much as the front the chassis bends in the middle.
A 24 mm rear bar was available and was 109 vs 123 springs.
The ratio of front to rear TOTAL stiffness should always exceed the weight distribution by 8- 10% or you get oversteer [the moment the road gets wet or power is applied]62- 64% front 38-36% rear is the hairy edge of instability.4300x 0.36= 1548/2=774 pounds of total rear roll stiffness per rear wheel vs 462 stock at 3.75" roll
You must consider the progressive nature of the Eibach lowering springs.......at full compression with a bigger than 20-22 mm bar it is possible to get close or exceed the rule.
As to whether a t car rear bar bushing is tight or lose not sure you could feel it.........zero to only 10% reduced rear sway vs the 20 mm which would be zero to up to 25% reduced sway with urethane bushings
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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
Making sure the rear tires are wider or softer [both is better] than the front is the usual method to rein in the changes in roll stiffness caused by bigger bars and stiffer springs on the rear..........at least in lateral step outs [power oversteer in wet].
Unfortunately almost imposible [impossible] to buy a soft 15" performance tire any longer after the last of the AVS I 225/60/15 are gone............we are stuck with wider 235/60/15 Pilot H4 with their 400 rating.
Unfortunately almost imposible [impossible] to buy a soft 15" performance tire any longer after the last of the AVS I 225/60/15 are gone............we are stuck with wider 235/60/15 Pilot H4 with their 400 rating.