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There are differences between GT and Pony (V6) springs. The springs are slightly taller and have a higher spring rate because of the weight. Remember, a spring will compress when installed, known as the installed height. So, if the same spring from a Pony were installed onto a GT, it will compress more.
As far are reputation goes, I've had nothing but good things with Eibach (so far). Almost all of the decent spring companies guarantee the springs to NOT change (drop or spring rate) more than 10% from their new condition.
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Here is some data to update your chart with. I lost a notebook full of other S197 type springs by H&R and Eibach Sportlines. Oh well I still have these numbers. These were all tested using a very good digitalload cell based spring tester made in Germany for H&R springs.
Name- (part number)- lowering amount- spring rates
Stock/Factory GT springs (Tags= Yellow, Orange) - front: 136lb/in / rear: 142lb/in, I have confirmed all of these rates using a 0.000000Nm German spring tester, very soft with lots of roll and moderate understeer
Eibach Pro-kit (pn 35101.140) / Ford Racing (K-springs) (pn M-5300-K) 1.5/1.7 -, These are progressive rate front springs with a starting rate of 173lb/in a working rate of 239lb/in and max. rate 247.6lb/in at coil bind, good spring rates but ride height is a bit too low, will easily bottom out all the time with harsh ride due to the rear axle living on the bumpstops all the time due to excessive lowered ride heighting with potential to snap over steer on rough roads with suspension loaded up.
At the rear measurement & testing verified that the spring rates are progressive rate springs starting at 195lb/in, with a working rate of pprox. 203lb/.in and 236lb/in near coil bind. The Eibach Sport spring set had the best rates for the street but are too low to use all the time as a DD without bottoming frequently which kill the ride.
Eibach Sportline (pn 4.10135) 1.6/2.0 - tested, lost data but these spring rates are extremely high and are IMO unsafe due to almost zero rear travel before going solid and into snap oversteer, these are poser springs
Steeda Ultra-lite (pn 555-8206) 1.25/1.5 front: 195lb/in / rear: 175lb/in, Testing verified, front measure 198lb/in, rear measure 167lb/in and both are linear rate springs.
Steeda Sport (pn 555-8216) 1.0/1.25 - front: 200lb/in / rear: 175lb/in, Testing verified, front measure 205lb/in, rear measure 168lb/in and both are linear rate springs.
Steeda Competition (pn 555-8241) 1.0/1.25 - front: 225lb/in / rear: 185lb/in, Testing verified front measure 231lb/in, rear measure 172 and both are linear rate springs.
HTH!
Cheers/Chip
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2005 Mineral Grey Mustang GT Coupe, Premium, M5, ICAP, IUP, Active Anti-theft, LoJack
Mods: Gave up trying to make it all fit, but ask if interested!
I actually spoke with the General Manager from H&R for a while, and I listed the approximate rates as he did. They don't want to list exact rates because (according to him), 1) other companies do NOT use realistic or reliable tests to determine their rates [IE springs are not tested at the installed height and in the normal range of suspension travel], 2) the actual spring rates can end up being slightly different depending on the car setup, weight, and damper size and 3) the exact same spring rates can act differently depending on the rest of the suspension setup. Simply put, there are too many variables. I will say that H&R knows their stuff and it was very refreshing to have an in-depth conversation with a suspension company. Plus, they make everything in house- which is something I've learned recently about other companies.
If your car has not been lowered you look at at from the side on level ground you should be able to see that the back sits higher than the front
correct; there are a couple things that contribute to the appearance of the back sitting up higher; the car body itself is a little taller in the back, and the space between the rear wheel and the fender well is quite a bit more on the back than the front, however if you measure the distance from the bottom of the rocker panel to the ground, right behind the front wheel and ahead of the rear wheel, the distance on the back is only 1/2" or less greater than the distance in front.
given this, if you lowered the back more than 1/2" more than the front, the visual line of the rocker panel relative to the ground would slope down towards the back, instead of sloping down slightly towards the front, as it does on stock models. lowering the back somewhere in the range of 1/2" more than the front will "level" the car as much as possible.
anybody know anything about "Rousch extreme lowering springs? i don't see much definitive info on them so far in this thread. i notice that on their website they say that they are designed to be used with the stock mustang shocks (they lower the front 1" and the back 1.25"). my question is, how is this possible, if the springs are shorter than the stock ones, they must not have the same spring rate, so how can they be used with the original shocks?
anybody know anything about "Rousch extreme lowering springs? i don't see much definitive info on them so far in this thread. i notice that on their website they say that they are designed to be used with the stock mustang shocks (they lower the front 1" and the back 1.25"). my question is, how is this possible, if the springs are shorter than the stock ones, they must not have the same spring rate, so how can they be used with the original shocks?
Because it's what they want you to believe, and most don't know any better. Makes it a lot easier to sell springs if folks think what they have already is fine for the job....
Sad, but true--and the fact I won't do that is a good part of the reason I'm not rich. Damn-it.
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Strano Performance Parts www.stranoparts.com
814-849-3450
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SCCA ProSolo Overall Champion 2009
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