Ark GT-F springs installed

[Husky]

Interesting. Good to know.
Do you know what the wire diameter of the stock and Ark springs are? (do you have some calipers to measure them?) I'd be curious to know how they compare.
I also wonder how the Eibach spring stiffness compares to stock. I haven't seen any published spring rates (lbs/inch).

 

[Slip_Angle]

Interesting. Good to know.
Do you know what the wire diameter of the stock and Ark springs are? (do you have some calipers to measure them?) I'd be curious to know how they compare.
I also wonder how the Eibach spring stiffness compares to stock. I haven't seen any published spring rates (lbs/inch).

Hmm, I may have calipers. I'll have a look tomorrow and see what I can gather.

I believe the Eibachs are progressive and the Arks are not but I don't know what the rates are.

 

[Volfy]

@Slip_Angle your post got me curious, so I did a quick search and found this thread: OEM vs Eibach vs Ark Spring Rates

Frankly, I was shocked at the Ark numbers. Lowering springs need to be stiffer to compensate for the reduced suspension travel. While the lowered spring stiffness isn't always exactly proportional to the lowering amount (% relative to max OEM suspension travel), they should be NO LESS than what is required to maintain the load handling of the vehicle, expressed as:

Max load = spring rate x max suspension travel

To that end, the Eibach's numbers (+12%F, +14%R) make perfect sense to me.

Ark GT-F's +4%F, -33% boggle my mind. I would not have believed it, but your experiences are pretty close to what I would expect spring rates like these would do to your car. 33% softer in the rear... no wonder you were bottoming out like crazy. Even the front's 4% is essentially same stiffness as stock... good lowering spring those do that make!

Even beyond simple max load calculations, which any 9th grader with at least B- average could figure out, there is also how those spring rate affect cornering attitude. Substantially softer rear springs will typically INCREASE understeer, That is not good for performance driving!

 

[Volfy]

BTW, whenever you see spring rate listed with two numbers, like:

Eibach:
front: 195 (+12%)
rear: 331-565 (+14%)

It means the spring has two sections of coils. The softer coil allows the spring to stay taut and seated between the two end caps, when the suspension is fully extended. However, it is soft enough to compress fully at static sag (the weight of car compressing the spring). Once the softer section fully compresses, it then becomes incompressible, so the car rides primarily on the stiffer coil during normal driving.

Some mfrs call this kind of spring PROGRESSIVE. Personally, I think that is a bit of a misnomer. The correct term is DUAL RATE. It's fairly commo for lowering springs.

The front spring already gets a preloaded tension, once the strut is fully assembly, so it does not need dual rate spring.

 

[Husky]

Good info. I'm surprised that the rear spring rate is more than double the front! The front number seems quite low.

 

[Husky]

So strange that Ark would make the rears much softer. Doesn't sound like a good idea.

 

[MichaelJohnson]

So... I'm thinking about removing the Ark GT-F springs and returning to stock.

Really, the only reason is that with the shock compressed, I find the suspension crashes over rough roads. Where I live, the roads are terrible. Unless I can figure out another solution to prevent it.... but I can't think of anything. These springs are fantastic in every other way but the shocks are bottoming out on occasion and I'm worried something is going to break.

For anyone thinking about these springs, don't let this post give you a negative feeling about them. They are great! Again, it's just the roads where I live and with the shock more compressed, the remaining travel isn't always enough.

I've got the GT-S springs and haven't had any issues. However, the roads where I live are great for the most part. I hate that your experience differs.

 

[Volfy]

Front springs don't typically have to deal with live loads (occupants + luggage) as rear springs do. That's why rears have higher spring rates.

You see this in trucks, to an exaggerated degree. Leaf springs are common on trucks for this reason. They are truly progressive to handle severe loads.

 

[Husky]

Interesting. I would have thought that with near 50/50 weight distribution, and the weight of the engine up front, they'd be higher, but I understand that the weight in the rear is more dynamic or subject to change.

 

[Slip_Angle]

I've got the GT-S springs and haven't had any issues. However, the roads where I live are great for the most part. I hate that your experience differs.

I know, it's disappointing... but hey if yours are working for you that great!

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[Slip_Angle]

@Slip_Angle your post got me curious, so I did a quick search and found this thread: OEM vs Eibach vs Ark Spring Rates

Frankly, I was shocked at the Ark numbers. Lowering springs need to be stiffer to compensate for the reduced suspension travel. While the lowered spring stiffness isn't always exactly proportional to the lowering amount (% relative to max OEM suspension travel), they should be NO LESS than what is required to maintain the load handling of the vehicle, expressed as:

Max load = spring rate x max suspension travel

To that end, the Eibach's numbers (+12%F, +14%R) make perfect sense to me.

Ark GT-F's +4%F, -33% boggle my mind. I would not have believed it, but your experiences are pretty close to what I would expect spring rates like these would do to your car. 33% softer in the rear... no wonder you were bottoming out like crazy. Even the front's 4% is essentially same stiffness as stock... good lowering spring those do that make!

Even beyond simple max load calculations, which any 9th grader with at least B- average could figure out, there is also how those spring rate affect cornering attitude. Substantially softer rear springs will typically INCREASE understeer, That is not good for performance driving!

Thanks for looking that info up. It really is surprising and especially since the same springs are used for the rwd and awd cars. I even question the +4% in front. The stock springs don't compress at all by hand and the Ark's did...

 

[Volfy]

The more I think about the ARK, the only way that softer rear springs would make sense is for launching a RWD car at the drag strip. It would allow the rear to squat on accel, which encourages weight transfer to the rear axle for better hookup. given how many Stinger/G70 3.3T owners seem to be into the 1/4 mile, that could potentially be a plus... albeit at the expense in other aspects. Just a big baseless wild guess, but I'm coming up empty otherwise.

 

[thatjawncrazy]

Hmm... I wonder why the discrepancy. Eibach was very specific with the trim instructions:
View attachment 48586
I have no reason to doubt Eibach. Bump stops are there for a reason. Judging by how much the drop is for my cars:

G70 2.0T RWD: 0.7"F 0.6"R
Stinger 2.0T RWD: 0.8" F 0.8"R

I'd say 20mm F and 30mm R are spot on.

This is my first time learning I was supposed to trim the bump stops. Oops.

 

[Slip_Angle]

This is my first time learning I was supposed to trim the bump stops. Oops.

Ark doesn't say you have to.. but you can if you want.