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Rear lowering Springs w/perch vs. coilover spring/shock


Kevin Patten
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Now that we've discussed the torque arm vs. UCA setup anyone interested in/or have a true rear coil over set up ( Griggs or CorteX or ? ) and want to discuss the difference in that verses a rear lowering spring with an adjustable collar ( in the stock location / on the axle ). I understand most do not go past having just a lowering spring but it is nice to have an adjustable height suspension and the ability to adjust/set the vehicle corner weights that take chassis set up a step further to optimize the cars handling characteristics for street and/or track use.

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  • 2 weeks later...

When going over to a full true coil over set up I have found that most are using a Koni shock ( single adjustable ) . Griggs Racing on their SS package uses a 380lb. rate front spring and a 250lb.(with a torque arm )or optional 275lb rate rear spring . The FR500S used a 500lb. rate front spring and a 300lb. rate rear spring ( with a rear sway bar ) while the CorteX /SPP Track Pack set up is a 500lb.rate front spring with a 425lb. rate rear spring ( they recommend NO rear sway bar ) or an optional 600lb. front with a 450lb. rate rear. I know from past experiences that on the Fox body cars and SN95's that 400lb. rate fronts and 300lb. rears worked well (on track cars ) and Maximum Motorsports really had done their homework with those cars/chassis but have not seen anything as of yet from them for the s197 as far as coil over set ups. I would think that the fronts are pretty straight forward but on the rear it going to be a little more of a challenge because you will be changing the location of the spring from on top of the axle to being mounted behind the axle and moving outboard to the ends of the axle housing ( which is a better location ). I don't mind having to buy an extra pair of springs to get the ride quality I want but I hoping only to buy one or two pairs - not trying to buy a collection of unwanted springs.

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  • 1 month later...

Received my front coil overs and have the torque arm from Griggs now and have had to make mods to the front coil overs . If / when I get a break from buying parts for the SGT then I'll order the rear coil overs and start re-modding the GT500 . I'll also be replacing the BMR front lower arms with factory front LCA's but with Steeda X-5 LBJs and different bushings along with the FRPP extended tie rod ends.

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  • 2 weeks later...

Albino,

What "mods" did you have to make to the fronts? Was it a fitment issue or just something you wanted to do differently?

My car is about to undergo transformation from garage queen to a track machine capable of being driven to/from the track while beating up on my friend's Porsche GT3RS & the collection of smug BMW "M" guys on the course. Most of my experience has come from drag racing, so I've got the HP mods covered for this track, but the first time around the course I learned that the car handled like a supercharged brick - hence, it's time to teach the car (and me) to turn.

I am pretty handy with a wrench and not afraid to modify the car and then put my work to the test, plus I learn from my experience and mistakes what works and what doesn't. Like most people though - I get exasperated when I pay good money for something that doesn't fit right & I have to fix it or send it back.

I already have BMR rear LCA's & adjustable UCA - I was looking at just getting the whole Shelby "track pack" setup since it includes coilovers, then read good things about the Eiback R2's - so now am thinking the R2s plus the Shelby/Fays Watts link will be a good foundation that will allow for future flexibility while retaining streetability. Your thoughts?

I know Griggs makes a great setup, but my only rule in modding this car is no welding on any of the factory parts of the car - so going full Griggs is probably not for me.

Sorry for the long winded post & I don't mean to hijack, but I figure there is good info to be shared here. :shift:

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As far as 2007-2010 GT500's go I have found that on the front of the car the best combo for track/street perf. ( not counting SLA setups ) is going with the CorteX Racing's single adjustable Koni coil over strut with a Hypercoil 400lb rate spring with a Maximum Motorsports Caster/Camber plate and MM5C0-8 kit -this will allow articulation at the top of the strut which is not there with the GC poly top C/C plate . The strut is hollow for the adjusting rod to run down to the valve and needs to be free to articulate or unnecessary side loads are applied to the shaft and /or shock piston . It is similar to the Griggs / Ground Control but with the offset allows the use of a 10.5" wide wheel / tire combo Also use a Steeda X5 or Howe Racing extended (19.2mm) lower ball joint along with either a FRPP M-3130-R2 outer tie rod end or adjustable bump steer kit ( which takes more to dial in and wears out faster due to heat from the brakes ) . I'm finding that Prothane front lower control arm bushings work well but need to be fitted properly and right now I'm really impressed with the Whiteline anti-dive rear bushing kit for the rear position of the front lower control arms . The most common problem I run across is finding the front sway bars bound up in their frame bushings . Adjustable S/B end links are not needed but I recommend upgrading to the 2011-2013 ones because they are ribbed and flex less than the ones that come stock . ( all you have to do is have the car on a rack and loosen the frame bracket nuts and slide the sway bar up/down to relieve the preload and then retorque ) . As far as the rear coilovers here again the CorteX Racing ( NO welding ) has a matching rear single adjustable Koni and I would suggest a Hypercoil 275 lb rate spring . I am a FIRM believer in the Fays2 watts linkage set up and using a Steeda spherical joint at the top of the differential to use with the BMR LCAs ( poly front / spherical rear ) and relocate brackets . Having the spherical joints at the axle pivot points instead of the frame pivot points makes for better articulation of the axle . There's more but that should be more than enough to wet your whistle and stay on topic ( that's 5 years of S197 testing and 1,000's of dollars experience shared ).

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Albino,

Thanks a TON for the well thought out reply and experience behind it! Looks like I have some more research to do before I plunk down the coin on a pre-packaged "kit". The thing I love about doing my own research & doing most of the work myself is understanding how all the pieces should work when they go into the car. It makes it easier to understand feedback I'm getting from the car on the track & make the proper adjustments without relying on someone else's interpretation.

The vast majority of what I've read about the Fays2 setup has been positive & I'm sure with good reason, so that looks like where I will base the start of my build. That and proper coilovers at the corners (will read up on the CorteX) should get me pointed in the right direction as I learn more about what the car likes. After many years of racing 1/4 mile at a time with other muscle cars I'm confident this GT500 will soon earn the respect of the 911 & BMW crowd at my local club.

I hope you wont mind if I pick your brain some more via PM in the future.

Cheers!

Tim

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