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Lowering GT350R ...is it worth it? (Eibach, FP and BMR)

ShatterPoints

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Thanks for chatting with me about this! Do you think +0.10 or -0.10 would be more stable at highway speeds? I wish I could have found out what settings my car had stock. It drove amazing.

I want to have slight oversteer and good spirited driving in the streets/mountains and highway. Do you think my specs would setup that right? Or do you think I would need more or less negative camber in the rear?

I feel like stock it was -1.1 front and -1.2 rear. But I want to compensate the softer spring rate in the rear so I figured less camber on the rear would promoted oversteer. Thats why the R came with -0.7.

These springs handle very good. Cant wait to dial it all in. You think I should leave the rear -0.7 or go -1.2? I am still deciding if I should go +0.5/0.10 or -0.5/0.10 on the front toe.
+/- 0.10 front toe will not cause instability. I would run -0.10 front toe (per side). You want more camber in the front than the rear so -1.2 or -1.5 front camber would be good. Rear camber should be between -0.70 and -1.0. That will give you a very good basic alignment that you can tweak as you see fit based on your driving style and what you want from the car.
 

Driveway Demons

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+/- 0.10 front toe will not cause instability. I would run -0.10 front toe (per side). You want more camber in the front than the rear so -1.2 or -1.5 front camber would be good. Rear camber should be between -0.70 and -1.0. That will give you a very good basic alignment that you can tweak as you see fit based on your driving style and what you want from the car.
Thanks! Rear toe +0.15 per side sound good?
 

Driveway Demons

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The shop tech said the rear camber arm will not adjust. He said it’s not elongated in the subframe. He said he didn’t remove the but but the arm wound not move and he wasn’t putting a 6ft our bar on it. Has this ever happened? He said ford when they manufactured the car maybe made a mistake on this. I call b.s. tho. Picture of the adjustment bolt in question.
A5289062-FD6E-4D7D-AA59-80174575E0B4.png
 

ShatterPoints

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The shop tech said the rear camber arm will not adjust. He said it’s not elongated in the subframe. He said he didn’t remove the but but the arm wound not move and he wasn’t putting a 6ft our bar on it. Has this ever happened? He said ford when they manufactured the car maybe made a mistake on this. I call b.s. tho. Picture of the adjustment bolt in question.
A5289062-FD6E-4D7D-AA59-80174575E0B4.png
Rear toe +0.15 per side.

Don't just run but FUCKING RUN from that shop. Dude has no clue what he is talking about. Stock parts will allow both camber and toe adjustments in the rear.
 

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Rear toe +0.15 per side.

Don't just run but FUCKING RUN from that shop. Dude has no clue what he is talking about. Stock parts will allow both camber and toe adjustments in the rear.
They did the alignment and this is what I ended up leaving with...
440BBEFC-9E81-482B-A892-C4A66761C5B9.jpeg
 

ShatterPoints

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They did the alignment and this is what I ended up leaving with...
440BBEFC-9E81-482B-A892-C4A66761C5B9.jpeg
Those before stats explain why you were experiencing issues with how the car felt. It must be way better now at any speed lol.
 

Driveway Demons

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Those before stats explain why you were experiencing issues with how the car felt. It must be way better now at any speed lol.
It’s great now yes, just worried about the rear camber lol
 

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So I went to the Ford dealership to figure out what was going on in the rear and they were able to adjust it they said it was a little stiff back there and hard to get to. They ended up not getting the front camber identical. Steering wheel is perfectly centered now.

should I try and perfect it or leave it?
09AA1CD1-2D95-48D1-9245-E25E747BBF3A.jpeg
 

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ShatterPoints

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Yes that is totally fine. Roads have crowning and there are an infinite number of things that dynamically change what your camber is at any time your car is moving. A slight variation will not be a cause for concern. As an fyi I managed to get the motion ratios of the front and rear. The front is 0.98 and the rear is 0.50, with the OEM springs this translates to a front wheel rate of ~177lbs and a rear wheel rate of ~220lbs. Giving us a 1.35hz front frequency and a 1.55hz rear frequency. Personally I plan to change my springs to 300lbs front for 1.7hz and 1283lbs rear for 1.9hz.
 

Niz55

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Yes that is totally fine. Roads have crowning and there are an infinite number of things that dynamically change what your camber is at any time your car is moving. A slight variation will not be a cause for concern. As an fyi I managed to get the motion ratios of the front and rear. The front is 0.98 and the rear is 0.50, with the OEM springs this translates to a front wheel rate of ~177lbs and a rear wheel rate of ~220lbs. Giving us a 1.35hz front frequency and a 1.55hz rear frequency. Personally I plan to change my springs to 300lbs front for 1.7hz and 1283lbs rear for 1.9hz.

And where are you getting 1283 lbs spring?
 

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Yes that is totally fine. Roads have crowning and there are an infinite number of things that dynamically change what your camber is at any time your car is moving. A slight variation will not be a cause for concern. As an fyi I managed to get the motion ratios of the front and rear. The front is 0.98 and the rear is 0.50, with the OEM springs this translates to a front wheel rate of ~177lbs and a rear wheel rate of ~220lbs. Giving us a 1.35hz front frequency and a 1.55hz rear frequency. Personally I plan to change my springs to 300lbs front for 1.7hz and 1283lbs rear for 1.9hz.
Awesome! What would my hz be with the fp springs?

also what is the advantage to 1.7 over 1.55? The only spring that will get you to those rates is steeda. The front is dual 220-350 and rear 800-1280
 

ShatterPoints

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And where are you getting 1283 lbs spring?
f = 1/(2π)√(K/M)

K= (4π²F²M)/mr²

Assuming the gt350 is 3700lbs and .53% front

a 1283lbs spring provides 1.7hz frequency (That is the target. The shock angle and possible use of a tender spring may change it slightly. I will not go any higher than a 1.7hz rate)

Awesome! What would my hz be with the fp springs?

also what is the advantage to 1.7 over 1.55? The only spring that will get you to those rates is steeda. The front is dual 220-350 and rear 800-1280
You can run stiffer springs to take advantage of better tires (especially if you track your car with good tires). This is the 'rule of thumb' I use:

0.5-1.0Hz Passenger cars, typical OEM
1.0-1.5Hz Typical lowering springs
1.5-2.0Hz Rally Cars
1.5-2.5Hz Non-Aero racecars, moderate downforce Formula cars
2.5-3.5Hz Moderate downforce racecars with up to 50% total weight in max downforce capability
3.5-5.0+Hz High downforce racecars with more than 50% of their weight in max downforce

The higher the Hz the more overall stiffness exists in the system. Too soft and you have a numb car that while has grip it is not able to transition its weight very well. Too stiff and you can cause the wheel to skip along the road surface, in both cases this reduces overall grip. So you have to find the best balance, in my 911 I ran 1.9hz front and 2.3hz rear. I decided that was a little stiff for me and so I will start a little softer with the gt350.
 

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f = 1/(2π)√(K/M)

K= (4π²F²M)/mr²

Assuming the gt350 is 3700lbs and .53% front

a 1283lbs spring provides 1.7hz frequency (That is the target. The shock angle and possible use of a tender spring may change it slightly. I will not go any higher than a 1.7hz rate)



You can run stiffer springs to take advantage of better tires (especially if you track your car with good tires). This is the 'rule of thumb' I use:

0.5-1.0Hz Passenger cars, typical OEM
1.0-1.5Hz Typical lowering springs
1.5-2.0Hz Rally Cars
1.5-2.5Hz Non-Aero racecars, moderate downforce Formula cars
2.5-3.5Hz Moderate downforce racecars with up to 50% total weight in max downforce capability
3.5-5.0+Hz High downforce racecars with more than 50% of their weight in max downforce

The higher the Hz the more overall stiffness exists in the system. Too soft and you have a numb car that while has grip it is not able to transition its weight very well. Too stiff and you can cause the wheel to skip along the road surface, in both cases this reduces overall grip. So you have to find the best balance, in my 911 I ran 1.9hz front and 2.3hz rear. I decided that was a little stiff for me and so I will start a little softer with the gt350.
The fp springs are dual rate linear (which is progressive) but it’s a lot different than a typical progressive spring. What is my hz rate at 250 front and 565/765 rear?
 

Niz55

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What I meant was where are you buying a 1200+lbs rear springs from?
 

ShatterPoints

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The fp springs are dual rate linear (which is progressive) but it’s a lot different than a typical progressive spring. What is my hz rate at 250 front and 565/765 rear?
Front is 1.55hz and rear is 1.2hz at 565lbs and 1.4hz at 765lbs. Personally I do not like when the front frequency is higher than the rear on a non aero car.

What I meant was where are you buying a 1200+lbs rear springs from?
Doesn't look like I can get one that is not the steeda spring that will fit the stock spring cups for the rear. I will have to go with an aftermarket coilover and use a 24k swift spring which ends up being 1344lbs (still less than 2.0hz) so it will work for me.
 

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