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

[ShatterPoints]

from everything you stated I gathered the following information in short:

1. the 565 lb/in for performance springs were engineered that way to return to equilibrium slower (on time I guess) to prevent bounce on the road courses to keep the rear end more stable, for better traction. Which will mean less bounce on the street at lower speeds and sharp bumps. Allowing them to get progressively stiffer at faster bumpe. Effectively removing sloppiness or bounce. Pretty much trying to eliminate anything that would not allow full control or traction of the rear.

2. ford should have use these springs in the cars oem setup but didn’t do so to make extra money and they sit to low due to warranty claims.

Close...

1. Springs oscillate at a given frequency which depends on the weight of the vehicle and the rate of the spring. A softer spring oscillates faster, and since the spring's job is to reset the suspension to static ride height all it does is allow the suspension to move as it compresses and extends. The SHOCK is what controls the amount of time the sprung system returns to equilibrium. The shock RESISTS compression and rebound and so the more of each you have the slower the shock is. The best way to think of it is, springs control HOW MUCH weight is transferred and shocks control HOW FAST that weight is transferred.

2. The OEM springs are setup so that the front end has a lot of mechanical grip in relation to the rear (the more front grip the less understeer) the OEM shocks are designed to match that design. The FP springs will solve the bounce you are feeling but in an incomplete way and will cause the car to pitch much more than it does now. You will encounter low speed understeer with the FP springs on the car. At higher speeds it will be fine, typically you want a car that oversteers in low speed and understeers slightly or is neutral balanced at high speeds. Though there are plenty of people happy with whatever works for them.

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[Driveway Demons]

Close...

1. Springs oscillate at a given frequency which depends on the weight of the vehicle and the rate of the spring. A softer spring oscillates faster, and since the spring's job is to reset the suspension to static ride height all it does is allow the suspension to move as it compresses and extends. The SHOCK is what controls the amount of time the sprung system returns to equilibrium. The shock RESISTS compression and rebound and so the more of each you have the slower the shock is. The best way to think of it is, springs control HOW MUCH weight is transferred and shocks control HOW FAST that weight is transferred.

2. The OEM springs are setup so that the front end has a lot of mechanical grip in relation to the rear (the more front grip the less understeer) the OEM shocks are designed to match that design. The FP springs will solve the bounce you are feeling but in an incomplete way and will cause the car to pitch much more than it does now. You will encounter low speed understeer with the FP springs on the car. At higher speeds it will be fine, typically you want a car that oversteers in low speed and understeers slightly or is neutral balanced at high speeds. Though there are plenty of people happy with whatever works for them.

So at slower speeds the FP springs will be harder to turn or just require more effort? IT will be the same at higher speeds? I take it from this that means that it will increase speed through turns as instead of oversteering and having the stiff rear bounce and lose traction (rear end spins out or lose control) the soft rear will help keep the traction and enough understeer so that even tho more effort is required to go through the turn speed can be maintained and increased thus lowering lap times.

 

[ShatterPoints]

So at slower speeds the FP springs will be harder to turn or just require more effort? IT will be the same at higher speeds? I take it from this that means that it will increase speed through turns as instead of oversteering and having the stiff rear bounce and lose traction (rear end spins out or lose control) the soft rear will help keep the traction and enough understeer so that even tho more effort is required to go through the turn speed can be maintained and increased thus lowering lap times.

Steering effort is 95% alignment related (Camber, Caster, Toe). You will have some understeer at lower speeds so you will feel the car pushing a little bit. I would suspect it would be a small amount at turn in and then towards the apex you will push wide, in order not to you would need to slow down. At high speeds it would more or less feel exactly as it does now. The total change in spring stiffness between OEM, FP, and BMR will not result in an appreciable lap time difference for you. It may by way of feedback give you more confidence to drive the car closer to the limit and so in a somatic sense you will be faster. Mechanically the car's capability is not changing when you only change the springs.

 

[Driveway Demons]

Steering effort is 95% alignment related (Camber, Caster, Toe). You will have some understeer at lower speeds so you will feel the car pushing a little bit. I would suspect it would be a small amount at turn in and then towards the apex you will push wide, in order not to you would need to slow down. At high speeds it would more or less feel exactly as it does now. The total change in spring stiffness between OEM, FP, and BMR will not result in an appreciable lap time difference for you. It may by way of feedback give you more confidence to drive the car closer to the limit and so in a somatic sense you will be faster. Mechanically the car's capability is not changing when you only change the springs.

Ok thanks so much. Would you think that the FP would be the better way? I do like the feeling of slight oversteer. Thats why I was thinking about the OEM GT350 R springs as they are the same as FP up front but instead of progressive 565 ln/in to 765 ln/in rear the R springs are 914 lb/in.

I feel that I may like the R better but not sure and don't want to do this twice LOL

 

[ShatterPoints]

Ok thanks so much. Would you think that the FP would be the better way? I do like the feeling of slight oversteer. Thats why I was thinking about the OEM GT350 R springs as they are the same as FP up front but instead of progressive 565 ln/in to 765 ln/in rear the R springs are 914 lb/in.

I feel that I may like the R better but not sure and don't want to do this twice LOL

I'd want to find out what the rear motion ratio of the car is to best answer you. However I'd assume that the rear wheel rate is higher than the front which is a good thing and supports the small amount of oversteer you like. I would say the R springs are what you want, and in order to totally solve the handling behavior you do not like, you would need to change all 4 shocks as well.

I can try and grab measurements for the MR and give you an answer by this weekend if you'd like.

 

[Driveway Demons]

I'd want to find out what the rear motion ratio of the car is to best answer you. However I'd assume that the rear wheel rate is higher than the front which is a good thing and supports the small amount of oversteer you like. I would say the R springs are what you want, and in order to totally solve the handling behavior you do not like, you would need to change all 4 shocks as well.

I can try and grab measurements for the MR and give you an answer by this weekend if you'd like.

you mean the bouncing rear? Mine doesn't bounce much now at all. I thought I could get away with the OEM R springs since they share shocks with the GT350.

I guess I could install the FP springs since they are here now and see how I like them and if I want more stiff in the rear I could install BMR rears only since they are -0.55 drop and 950 lb/in I believe. The FP is -0.78 drop so essentially with FP up front and BMR rear would be -0.78" front and 0.55" rear drop with 250 lb/in front and 950 lb/in rear spring rates and that is pretty good sweet setup.

 

[Venom52]

I would also add the sway bars add stiffness to the ride as well. When i did mine it was the complete package springs and sways the car stiffened up nicely and stay flat in corners with the slight understeer as mentioned. I dialed that out by running a square setup and now it's neutral to me pretty much point and shoot now.

 

[Driveway Demons]

I would also add the sway bars add stiffness to the ride as well. When i did mine it was the complete package springs and sways the car stiffened up nicely and stay flat in corners with the slight understeer as mentioned. I dialed that out by running a square setup and now it's neutral to me pretty much point and shoot now.

My owners supplement says I have the same rear sway as the R but thicker front sway.

should I eventually look to ford performance bars you mean?

I love the look of the FP springs but love the oversteer. I guess putting the R front sway on and rear ford performance which would stiffen the rear and loosen the front could fix understeer right?

 

[Venom52]

My owners supplement says I have the same rear sway as the R but thicker front sway.

should I eventually look to ford performance bars you mean?

I love the look of the FP springs but love the oversteer. I guess putting the R front sway on and rear ford performance which would stiffen the rear and loosen the front could fix understeer right?

Correct the FP Rear bar seems to me just a stock R bar with an extra hole in it However, when matched with the FP springs brings performance up or a fraction better than the R. It really depends on the use of the car for instance i just track mine so i went lighter wheels sticky tires and stiffer suspension which brought me neutrality finally.

I would recommend put the springs in and see how you like it and go for there since you can always go back to stock.

 

[sk8ermoo]

Talk about analysis paralysis. Spring sets are cheap. Buy them, try them, swap them if your not happy.

Where's the paralysis? You don't like backing up decisions using data? When you hang photos on a wall, do you just slap them up there and eyeball it? Screw measuring! Just keep trying until you visually like it. Don't mind all the holes in the wall.

 

[ShatterPoints]

My owners supplement says I have the same rear sway as the R but thicker front sway.

should I eventually look to ford performance bars you mean?

I love the look of the FP springs but love the oversteer. I guess putting the R front sway on and rear ford performance which would stiffen the rear and loosen the front could fix understeer right?

Stiffer = less grip

Which ever end experiences the least amount of grip FIRST will begin to slide. A stiffer front bar causes understeer since the front loses grip. A softer rear bar ADDS grip to the rear and reduces oversteer.

Moving to 305/35/19 fronts will add track width and therefore ADD more total grip to the front which is how Venom52 dialed out his felt understeer.

The OEM front bar is good, I would not change either the front or the rear. In total the roll bar's contribution to roll resistance is not very much compared to the springs. The roll bar is a nuanced tool and you typically want to use as little as absolutely necessary. For instance it's common for Auto crossers to completely disconnect one or both sway bars.

I would say the FP fronts and the BMR rear springs are a good combo. The final piece to all of this is to modify the shocks at some point. They have more to do with changing what you feel when driving than the springs do.

 

[Driveway Demons]

Stiffer = less grip

Which ever end experiences the least amount of grip FIRST will begin to slide. A stiffer front bar causes understeer since the front loses grip. A softer rear bar ADDS grip to the rear and reduces oversteer.

Moving to 305/35/19 fronts will add track width and therefore ADD more total grip to the front which is how Venom52 dialed out his felt understeer.

The OEM front bar is good, I would not change either the front or the rear. In total the roll bar's contribution to roll resistance is not very much compared to the springs. The roll bar is a nuanced tool and you typically want to use as little as absolutely necessary. For instance it's common for Auto crossers to completely disconnect one or both sway bars.

I would say the FP fronts and the BMR rear springs are a good combo. The final piece to all of this is to modify the shocks at some point. They have more to do with changing what you feel when driving than the springs do.

do you mean as in getting aftermarket shocks? When I spoke to the Ford performance tax he said the springs were designed for my stock shocks and that I wouldn’t have to reset them or re-calibrate them everything would work appropriately.

 

[Inthehighdesert]

Your reaching. Springs on cars are subjective. What you feel and what I feel driving the car can be completely different. At some point you have to make a decision and establish a baseline based on your own observations. And I’m a GC, So your analogy is pretty humorous to me. My eye is better then most with a tape measure and a level in most scenarios. Springs are inexpensive and less then a couple hours to swap out. It’s not a big deal to try a few to get exactly what you want to achieve.

Where's the paralysis? You don't like backing up decisions using data? When you hang photos on a wall, do you just slap them up there and eyeball it? Screw measuring! Just keep trying until you visually like it. Don't mind all the holes in the wall.

 

[Driveway Demons]

also I’m curious if running -1.2 camber front and -0.75 rear would help provide more oversteer?

 

[ShatterPoints]

Your reaching. Springs on cars are subjective. What you feel and what I feel driving the car can be completely different. At some point you have to make a decision and establish a baseline based on your own observations. And I’m a GC, So your analogy is pretty humorous to me. My eye is better then most with a tape measure and a level in most scenarios. Springs are inexpensive and less then a couple hours to swap out. It’s not a big deal to try a few to get exactly what you want to achieve.

Springs are not subjective, your experience of them is. We can all agree a 5lb spring is way to soft and we can all agree a 2000lb spring is wayy too stiff. So in that sense you can figure out the natural frequency the spring rate you choose oscillates at which is what will tell you if the car is setup for bumps or more of a flat track. Or if you are mechanical grip dominate or aero dominate. You are right though springs are super cheap by comparison and so there is not a huge amount of harm in swapping springs as its usually quick and easy.

also I’m curious if running -1.2 camber front and -0.75 rear would help provide more oversteer?

The closer to 0 camber the larger your contact patch is and so you will reduce oversteer. However during a turn you will experience a change in the camber as load on a wheel changes. Suffice it to say the track you are running on is what dictates the amount of camber you need. To provide more oversteer you'd want more toe in (negative toe) in the rear, which to you will be power oversteer.

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