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R-springs on GT350

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@bpracer any update on the spring measurement?
 
492
387
DFW, TX
So... June 30th my car will go in to Vorshlag to get camber plates and we'll check out the track pack springs before I decide whether the R springs will go in. They had some delays with outsourced plating IIRC. I think their camber plates will be worth the wait.

I've done three tracks days now with the car. When I'm really pushing hard, the front tires shudder a bit. It could be bushings, dunno right now. The tires have held up OK. Modest understeer is all I've experienced. The car will be properly aligned with the camber plate install.

I got the brakes hot enough (Hallet in OK, reasonably hard track on brakes) for them to be a bit spongy to the point my heel-toe position was depressing the gas pedal too much. I have SRP pedals. It's fine on the street but for the track I may have to space the brake pedal out a bit. I have not put on the Ti brake shields yet.

Anyway... The car is awesome. My last track day was at Hallet was before the Mid-America Ford meet, about 106 degree heat index, high 90's actual temp. It was school event that I helped with instruction. The car was holding up better than the driver. Towards the end of the day I easily passed a Focus RS and was catching an R model with some Ford guys on-board but the gas gauge was saying 2 miles until empty... The R was motoring around pretty good but I have no idea who they were, but it did my ego some good ;)

More after the 30th about the springs.
 
492
387
DFW, TX
098ec57835922ec396907c62cbc6cf30.jpg

Track Pack spring

Jason at Vorshlag provided the info. The car was still on the lift so I'll get it tomorrow when it's aligned with their new camber plates. It should sit lower but we'll have to wait for tomorrow to know how much.
 
492
387
DFW, TX
Though the springs are shorter, they are telling me there is no measurable difference in ride height before and after. That seems to go along with the SC2 tires on the R being shorter causing the only ride height difference.


BTW, the drivers side, outboard CV joint/assy failed in some manner and has put grease all over the suspension and the inside if the wheel. 2400 miles...

Back to the Ford dealer next week.
 
179
1
Great info. yeah looks like its shorter but much more linear in rate. The track pack spring looks like a relatively progressive rate so has more compression when static. Makes a lot of sense if very little ride height delta is seen
 
Thanks for posting the information. While I wouldn't mind lowering my car just a bit what I'm wondering is how the front R springs will respond on track. The track pack springs felt fine with my stock tires during my track day and at TA. My concern is when I add the sticker Cup2 tires will I get more nose dive? If so maybe the R front springs will be the way to go. Thoughts?
 
1,246
1,243
In the V6L
VoodooBOSS said:
Thanks for posting the information. While I wouldn't mind lowering my car just a bit what I'm wondering is how the front R springs will respond on track. The track pack springs felt fine with my stock tires during my track day and at TA. My concern is when I add the sticker Cup2 tires will I get more nose dive? If so maybe the R front springs will be the way to go. Thoughts?

I wouldn't mess with it until you've tried it with the RComps and the stock springs. If you've got data acquisition, it'll tell you how much grip you're getting, and if it's easy to drive and you're pulling north of 1.1g's, I'd be tempted to leave it as is.

The challenge with changing springs is that the R springs are softer at the rear than the TP, and stiffer at the front. That increases loading on the outside front tire in a corner and increases the tendency to understeer. To compensate, the R has a stiffer rear sway bar (same bar, shorter arm length) that presumably restores balance. And of course, we don't know how the mag ride programming figures into this. McLaren implemented four-corner linked damping using hydraulics in the MP4-12C suspension. I think Ford did the same using electronics on the mag ride GT350. The linked damping regime improves handling by managing roll and pitch, something regular independent four-wheel spring and passive damper suspensions can't do. But, in doing that, the dampers become an dynamic part of the weight transfer process on corner entry and exit. What we can't know is how sensitive the mag ride calibration is to changes in spring rates. Could be a little, could be a lot.

So, as I said, I wouldn't mess with it until you've actually tried the RComps and the stock springs.
 
JAJ said:
I wouldn't mess with it until you've tried it with the RComps and the stock springs. If you've got data acquisition, it'll tell you how much grip you're getting, and if it's easy to drive and you're pulling north of 1.1g's, I'd be tempted to leave it as is.

The challenge with changing springs is that the R springs are softer at the rear than the TP, and stiffer at the front. That increases loading on the outside front tire in a corner and increases the tendency to understeer. To compensate, the R has a stiffer rear sway bar (same bar, shorter arm length) that presumably restores balance. And of course, we don't know how the mag ride programming figures into this. McLaren implemented four-corner linked damping using hydraulics in the MP4-12C suspension. I think Ford did the same using electronics on the mag ride GT350. The linked damping regime improves handling by managing roll and pitch, something regular independent four-wheel spring and passive damper suspensions can't do. But, in doing that, the dampers become an dynamic part of the weight transfer process on corner entry and exit. What we can't know is how sensitive the mag ride calibration is to changes in spring rates. Could be a little, could be a lot.

So, as I said, I wouldn't mess with it until you've actually tried the RComps and the stock springs.

How do you figure the R springs are softer in the rear then the track pack? That tiny bit could be between one spring to the next.
 
JAJ said:
I wouldn't mess with it until you've tried it with the RComps and the stock springs. If you've got data acquisition, it'll tell you how much grip you're getting, and if it's easy to drive and you're pulling north of 1.1g's, I'd be tempted to leave it as is.

The challenge with changing springs is that the R springs are softer at the rear than the TP, and stiffer at the front. That increases loading on the outside front tire in a corner and increases the tendency to understeer. To compensate, the R has a stiffer rear sway bar (same bar, shorter arm length) that presumably restores balance. And of course, we don't know how the mag ride programming figures into this. McLaren implemented four-corner linked damping using hydraulics in the MP4-12C suspension. I think Ford did the same using electronics on the mag ride GT350. The linked damping regime improves handling by managing roll and pitch, something regular independent four-wheel spring and passive damper suspensions can't do. But, in doing that, the dampers become an dynamic part of the weight transfer process on corner entry and exit. What we can't know is how sensitive the mag ride calibration is to changes in spring rates. Could be a little, could be a lot.

So, as I said, I wouldn't mess with it until you've actually tried the RComps and the stock springs.
Yep. I want to install the springs when I install the CC plates but I'll probably wait. I'm also hopeful that Ford Performance has their springs ready to roll by fall and they split the difference between the stock and R springs and they work well with the stock damper calibration.
 
492
387
DFW, TX
The R springs are stiffer at both ends. The rear springs sets are not a constant wire diameter and they are a variable rate. The R springs are stiffer initially and end up about the same as the TP springs with the TP spring being the more variable of the two. The R spring free height is 1/2 shorter but the ride height is the same.

The front spring is 10" free height for the R vs 11.25" for the TP.

I'll have to overlay the two charts and take in to account the free height difference, but its been long week...
 
I wouldn't bother waiting for a half-way spring. The "R" spring IS the half-way spring, and on paper at least, looks very good to me and addresses the unbalanced spring setup that the GT came with. The GT350 is a step in the right direction (for spring rates), but the GT350R looks like the best factory set of springs.

If you want a car with street manners, this is most likely the best spring set for that.
 
1,246
1,243
In the V6L
bpracer said:
The R springs are stiffer at both ends. The rear springs sets are not a constant wire diameter and they are a variable rate. The R springs are stiffer initially and end up about the same as the TP springs with the TP spring being the more variable of the two. The R spring free height is 1/2 shorter but the ride height is the same.

The front spring is 10" free height for the R vs 11.25" for the TP.

I'll have to overlay the two charts and take in to account the free height difference, but its been long week...

The numbers in the data table on the two graphs indicate that once the line straightens out, the rear R spring is in the 800's and the rear TP spring is in the 900's. I graphed the spring lengths (not deflection) vs load and the length graph shows that the springs are the same length at around 500#, with the R spring is about 0.3" shorter at 2100 pounds. With rear axle sprung mass of (let's guess at) 1600 pounds and a motion ratio between 1.5 and 2, the static load on each rear spring will be somewhere around 1200# to 1600#. The graph says that the springs lengths will differ by about 2/10" at that load, giving a difference in chassis height of about 3 or 4 tenths of an inch. We're not seeing a difference at all when Vorschlag does the measurements, so something isn't quite adding up.

The bottom line though is that the rear springs are so similar that there's little to gain from changing them. The R fronts are about 10% stiffer than the TP springs - again the question becomes "is there enough difference to make a difference", especially if you're not able to reprogram the mag ride, which is where the real magic happens.
 
492
387
DFW, TX
The rear TP spring is 12.375" (same as "R") not 12.675" as close as I can measure it so maybe a number was transposed. See how that makes the math work.
 
1,246
1,243
In the V6L
bpracer said:
The rear TP spring is 12.375" (same as "R") not 12.675" as close as I can measure it so maybe a number was transposed. See how that makes the math work.

Fascinating - so the two springs are the same length when free and again when loaded to 2130 pounds. The curve for the TP spring starts out flatter up to about 300 pounds, where the initially softer TP spring is about 0.3" more compressed than the R spring. From there the TP spring stiffens up and because it has a higher spring rate than the R spring, the two curves start to converge until both springs are the same length again at 2130 pounds.

The TP curve is a classic "tender-spring:main-spring" setup. If the spring was wound as a linear spring to deliver the rate and ride height spec, it would be too short to stay in place at full droop. So they wind it with a few low rate coils to fill the gap that would form at full droop. Once those coils have become coil bound, the higher working rate coils take over for the rest of the travel. The slightly lower-rate R spring doesn't need the curve at the bottom - even when wound as a linear spring, it's long enough to stay in place at full droop.

Over the working range of the springs under load, the TP spring is marginally (11%) stiffer than the R spring. Up front, the reverse is true. Both springs are basically linear, with the TP spring 22% softer than the R spring. The TP spring is longer in order to get the necessary preload to put the static ride height at the right level.

So, going back to the start of all this, the R springs give you a stiffer front end by about 22% and a softer rear end by another 11%. The rear swaybar has shorter arms (not links) to make it stiffer. I'd be curious if the front sway bars were different as well - does someone know?

Note: I edited this post to reflect actually computing the spring rates in the working ranges of the springs. These are they:

R - Front - 264 pounds per inch
R - Rear - 836
TP - Front - 216
TP - Rear - 931
 

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