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Discussion Starter #1 (Edited)
I have been chasing a ghost... 2 cars handle a bit different although they are almost identical. 1991 Turbo cars, TTop(handles better) and Hardtop.
First car (TTop), handles like on rails. I would not hesitate to take it to the limit it feels so stable it amazes me. The only difference it has Eibah Pro springs, smaller steering wheel and power steering.
Second car(Hardtop), it is stable but not as the first. I mean nothing rattles, but I would not be comfortable taking a corner with this car at the same speed as first one. Again no funny noises, nothing that would tell you something is wrong. I do not know how to describe it. It feels like the front is lighter and it does not grip the road as good. It has TRD springs and larger steering wheel.
All other factors are identical. Same tires/rims (swapped it back and forth), TRD swaybar with adjustable endlinks. Stock strutbars. Koni yellows at full firm mode. 93 + crossmember. Alignment done at the shop.
What am I overlooking? Steering wheel size? Something in the steering column? Can't be springs can it? Koni yellows installed by previous owners. They rebound the same, no leaks but could it be bad or going bad on the car with "lesser" steering? Puzzled.
 

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Same spring rates? Spring rates will affect handling, particularly in corners.

Also, do you have the alignment reports? Done by the same shop does not guarantee that they are identical.
 

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Discussion Starter #3 (Edited)
Same spring rates? Spring rates will affect handling, particularly in corners.

Also, do you have the alignment reports? Done by the same shop does not guarantee that they are identical.
I added some info in the first post. Springs are different.
BTW both cars MKII 1991 Turbo cars. The better handling one has Eibach Pro, the other TRD srpings - I do not know the spring rates. Konis rebound on both cars and have no leaks but that is the only thing I did not swap and probably could do that over some weekend.
Even if you take a car on the straight and do like those racing cars do before they start racing - sharp turns left and right at low speed - one is like glued to the road and another I would say - "nothing special".

Alignment is done by the same shop, I should be able to get reports on both cars. Will scan them when I get them.
 

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The TRD springs are 29.4N/mm or 168ib/in front and 53.9N/mm or 307lb/in.
The Eibach Prokit are 17.5-36.7N/mm or 100-210lb/in front and 24.5-53N/mm or 140-303lb/in rear.

TRD do have a stiff rear spring at 60.8N/mm or 347lb/in.

The Eibach is quoted as progressive but I wouldn't think you use much of the low end spring as the weight of the car takes up those coils.

TRD springs are one rate due to this. See attached images. These are in fully compressed form. I found that the stiffer the spring the faster the response in steering and stability on flat ground.
 

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The ratio of the rear to front spring rates will determine the vehicle stability. From the information above, the TRD set appears to have a greater R/F ratio, and that would make the car oversteer. That might account for your reduced confidence in the car during hard cornering.
 

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Discussion Starter #6
Thank you for your comments.
So if I understand correctly , Eibach pro is a bit stiffer and more balanced (Front Rear) vs TRD set which could be mismatched (rear are stiffer and front is softer)? Now I am definitely going to try swapping the springs and see if that helps... The hardtop is predictable for sure and I guess part is getting used to the car the way it drives. I just expected both cars to handle the same.
 

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The TRD springs are 29.4N/mm or 168ib/in front and 53.9N/mm or 307lb/in.
The Eibach Prokit are 17.5-36.7N/mm or 100-210lb/in front and 24.5-53N/mm or 140-303lb/in rear.

TRD do have a stiff rear spring at 60.8N/mm or 347lb/in.

The Eibach is quoted as progressive but I wouldn't think you use much of the low end spring as the weight of the car takes up those coils.

TRD springs are one rate due to this. See attached images. These are in fully compressed form. I found that the stiffer the spring the faster the response in steering and stability on flat ground.
The spring rate ratio front to rear makes a big difference in how the car handles. I have found that I like a ratio in the .7 to .8 range, and even with the front that stiff relative to the rear, I don't run a rear sway bar on my car. The TRD springs for comparison have a ratio of .55, and the Eibach's are .69. That will make a big difference. It doesn't surprise me at all that you find the car with the Eibach springs to be more stable and confidence inspiring.

Also, all aftermarket springs are progressive. If they weren't, they wouldn't lower the car while also being stiffer than stock. The fact that some of the coils are fully compressed doesn't necessarily make it not progressive, as those coils will unload when that side of the suspension unloads (inside of the corner due to body roll).

The inside spring has as much effect on body roll as the outside spring (I know this sounds counter intuitive). Consider this: Two cars, identical, except one has 100lb/in springs and the other has 500lb/in springs. Walk up to the fender, grab it, and try to lift the car. The softly sprung car will require 100lb of lift to raise it 1". The stiffer car will require 500lb of lift to raise it the same 1". The same happens during cornering as the body roll tries to "lift" the inside edge of the car while compressing the outside. The outside is able to resist that compression because it is operating in the stiff section of the progressive spring. The inside is less able to resist the lifting, because as it lifts it gets into the softer section of the progressive spring.
 

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The spring rate ratio front to rear makes a big difference in how the car handles. I have found that I like a ratio in the .7 to .8 range, and even with the front that stiff relative to the rear, I don't run a rear sway bar on my car. The TRD springs for comparison have a ratio of .55, and the Eibach's are .69. That will make a big difference. It doesn't surprise me at all that you find the car with the Eibach springs to be more stable and confidence inspiring.

Also, all aftermarket springs are progressive. If they weren't, they wouldn't lower the car while also being stiffer than stock. The fact that some of the coils are fully compressed doesn't necessarily make it not progressive, as those coils will unload when that side of the suspension unloads (inside of the corner due to body roll).

The inside spring has as much effect on body roll as the outside spring (I know this sounds counter intuitive). Consider this: Two cars, identical, except one has 100lb/in springs and the other has 500lb/in springs. Walk up to the fender, grab it, and try to lift the car. The softly sprung car will require 100lb of lift to raise it 1". The stiffer car will require 500lb of lift to raise it the same 1". The same happens during cornering as the body roll tries to "lift" the inside edge of the car while compressing the outside. The outside is able to resist that compression because it is operating in the stiff section of the progressive spring. The inside is less able to resist the lifting, because as it lifts it gets into the softer section of the progressive spring.
I can't argue with a guy who's done research and testing on multiple setups. Thanks for the explanation and information. It makes sense about the springs loading and unloading.
 

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Discussion Starter #9
I appreciate all the comments. Thank you all.
Thank you Alex for the info, I find it really useful.
 
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