Get rid of rear end bounce with BMR minimum drop springs

[SergeyMelnik]

I would like to get rid of the bouncy ride I feel at the back of the car. Its a 2015 GT PP with BMR minimum drop springs all around(SP763), stock PP shocks, Steeda IRS alignment pins, stock size Firehawk tires on stock wheels with 25mm wheel spacers. Ford performance spec alignment. Everything else is stock.

From the research I did it seems like the PP shocks should pair well with these springs however it feels under damped in the back. The front feels good. I also found out in 2016 ford changed the shocks a bit on the pp cars and added more damping. My idea was to try out the rear pp shocks off a 16 or 17 car and then possibly add the steeda shock mounts if theyre still needed to smooth it out even more. Would this be a good idea or is there a better solution?

Also the part numbers are a bit confusing to me. Looking at the current part numbers for the rear pp shocks they go like this FR3Z-18125-W. The last letter can be a few different letters like FR3Z-18125-N. I would like to know what exact part number I would have to get if I go with these shocks. My 15 pp shocks have totally different part numbers but the left one is different than the right one. The dealer changed the left one out when it started clicking. The right one is FR3C-W002. Left one is FR3C-18080.

So basically I need help on the best way to get rid of the slight bounce in the back.

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[BmacIL]

BMR CB005 and Steeda shock mounts. The first to control the IRS and secure it to the body (right now it can just bounce around undamped, and prevents the shocks from working to their full capability), and the second to remove bind from the suspension and further let the shocks control the body, particularly from higher frequency but lower displacement inputs.

Can you post a picture of the two shock part numbers?

 

[SergeyMelnik]

 

[BmacIL]

Well the good news is that they're both K suffix, so they're both GT PP tuning of that year. I don't see 18080 base part anywhere in the full BOM of my car, only 18W002. That is very odd. The 2016+ PP dampers have additional rebound control compared with 2015, but it doesn't make sense to buy those.

 

[SergeyMelnik]

Why doesnt it make sense to buy them? People sell them here all the time for cheap and I can sell my current ones. Is it because its not gonna be a big enough difference? Is there an aftermarket shock that would be better?

 

[BmacIL]

Why doesnt it make sense to buy them? People sell them here all the time for cheap and I can sell my current ones. Is it because its not gonna be a big enough difference? Is there an aftermarket shock that would be better?

I suppose if you can get them cheap, its worth it. Yes there are several aftermarket shocks that will perform better.

If you go that route, my recommendation (individually sold):
https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/222447569684

 

[TheLion]

Wouldn't the added dampening of the PP Track struts make the reaction of the suspension "lazy" on rebound and "slow" on compression? The springs are going to move less as the damping is higher, so yah that would reduce the "bounce" of the stock PP setup. However the stock spring rates are quite a bit lower than what those dampers were designed to be used with.

Thanks to you @BmacIL we know the FP Track Struts use GT350 valving. The GT350 valving was tuned for a 240 lbs/in front and 914 lbs/in rear spring rate, not the stock 165 lbs/in front and 735 lbs/ in rear PP spring rates. I don't seem to have any "bounce" per say with my SP080 springs and stock 2016 PP struts.

 

[BmacIL]

Wouldn't the added dampening of the PP Track struts make the reaction of the suspension "lazy" on rebound and "slow" on compression? The springs are going to move less as the damping is higher, so yah that would reduce the "bounce" of the stock PP setup. However the stock spring rates are quite a bit lower than what those dampers were designed to be used with.

Thanks to you @BmacIL we know the FP Track Struts use GT350 valving. The GT350 valving was tuned for a 240 lbs/in front and 914 lbs/in rear spring rate, not the stock 165 lbs/in front and 735 lbs/ in rear PP spring rates. I don't seem to have any "bounce" per say with my SP080 springs and stock 2016 PP struts.

The 2015 PP dampers had too much compression and too little rebound. They addressed this for the '16MY, though not enough, IMO. The car as a whole, even with the 2016/2017 PP dampers, is still a bit underdamped for a performance car, on stock or even SP080/SP763 springs. It rides pretty well but is craving more. For most, the stock PP dampers are perfectly fine with those springs, but that's not to say there's not a better match. There are a few handful of folks who've done FP Track with SP080 or SP763 and love the ride and handling. @SVT-DADDY @udcvsean come to mind.

 

[Norm Peterson]

Wouldn't the added dampening of the PP Track struts make the reaction of the suspension "lazy" on rebound and "slow" on compression? The springs are going to move less as the damping is higher, so yah that would reduce the "bounce" of the stock PP setup. However the stock spring rates are quite a bit lower than what those dampers were designed to be used with.

With firmer damping the movement is going to be slower but the development of damper force higher. I think what's happening is that the car taking a set depends more on the forces involved getting closer to a constant total (spring and bar forces on the outside wheel always increasing, shock/strut forces increasing then decreasing). More damping - higher %critical damping - should make the damper contribution peak a little sooner.


Norm

 

[BMR Tech]

I would like to get rid of the bouncy ride I feel at the back of the car. Its a 2015 GT PP with BMR minimum drop springs all around(SP763), stock PP shocks, Steeda IRS alignment pins, stock size Firehawk tires on stock wheels with 25mm wheel spacers. Ford performance spec alignment. Everything else is stock.

From the research I did it seems like the PP shocks should pair well with these springs however it feels under damped in the back. The front feels good. I also found out in 2016 ford changed the shocks a bit on the pp cars and added more damping. My idea was to try out the rear pp shocks off a 16 or 17 car and then possibly add the steeda shock mounts if theyre still needed to smooth it out even more. Would this be a good idea or is there a better solution?

Also the part numbers are a bit confusing to me. Looking at the current part numbers for the rear pp shocks they go like this FR3Z-18125-W. The last letter can be a few different letters like FR3Z-18125-N. I would like to know what exact part number I would have to get if I go with these shocks. My 15 pp shocks have totally different part numbers but the left one is different than the right one. The dealer changed the left one out when it started clicking. The right one is FR3C-W002. Left one is FR3C-18080.

So basically I need help on the best way to get rid of the slight bounce in the back.

Just to confirm - did you trim your rear bumpstops down when installing the SP763 springs?

 

[BmacIL]

Just to confirm - did you trim your rear bumpstops down when installing the SP763 springs?

I should've asked this first, but always assume people do it

 

[SergeyMelnik]

Just to confirm - did you trim your rear bumpstops down when installing the SP763 springs?

Yes I trimmed the bump stops on the front and rear shocks. I was watching I believe a CJ Ponyparts installation video as I was doing the install. I used a measuring tape too.

The bounciness is not that bad and after spending some time in the car its not a major issue. However after I drive my 328i sport and getting back into the mustang I notice the bounce immediately. Its at the end of the shock movement. Its like the rear end sort of slowly "shakes" up and down after the initial compression and decompression. I used to race rc short course trucks and I understand the basics of adjusting a suspension. If I had this problem on my RC truck I would either use a lighter spring or switch to a slightly heavier oil.

So I see BmacIL you mentioned the Ford track shocks. I noticed conflicting information on whether or not these can be paired with my springs. Im ok with a slightly stiffer ride even though its not my goal but wont these have too much dampening? And what about the front? Will I have to switch out to the ford track shocks there as well if I do the back?

 

[BlownGP]

Following this thread since i'm about to install those springs and still undecided on what shocks/struts to get.

 

[JOKER M1]

I’ll throw in my 2 cents worth and I know nothing compared to the other guys that have already commented. I installed the BMR 763’s with 16’ PP shocks (I received these free from a friend) and lost all confidence in cornering and I just didn’t like the ride, very disappointing. I purchased the steeda shock mounts to help solve my issues and during that process I noticed both my rear shocks blown out so I’m not completely sure when they blew out. I’ve since installed the Ford Racing Track shocks and struts and I couldn’t be happier, I should also mention I have the GT350 front & rear sway bars.

 

[SergeyMelnik]

I’ll throw in my 2 cents worth and I know nothing compared to the other guys that have already commented. I installed the BMR 763’s with 16’ PP shocks (I received these free from a friend) and lost all confidence in cornering and I just didn’t like the ride, very disappointing. I purchased the steeda shock mounts to help solve my issues and during that process I noticed both my rear shocks blown out so I’m not completely sure when they blew out. I’ve since installed the Ford Racing Track shocks and struts and I couldn’t be happier, I should also mention I have the GT350 front & rear sway bars.

Thats odd, Ive seen the BMR763s recommended with PP shocks many times here. What exactly did you not like about this combination? What changed with the ford track shocks? Is it noticeably harsher for cruising?

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