Horrible understeer

[TeeLew]

@TeeLew, I have 2019 PP1 Magneride, and GT350R bars front & rear. I am unsure of the OEM spring rates. The spreadsheet in the 6g sticky thread is getting rather dated. If it is correct for my car then I am at only 165#/inch front rate, and 728 rear.

The M1 owner's manual publishes (page 339) 211#/in front and 742 rear for the handling package. So the rear is already pretty close between the two cars.

I switch several things converting my car from street to track and back again. So inserting spring rubber donuts would be easy enough to add.

Which hardness donut do you recommend for me to attempt to mimic the M1 front spring rate? Which sets if I ordered two pairs of different hardness?

Would be nice if there was a chart to help choose which donuts.

I think those rates are correct. It's about the best info we have.

The spring rubbers will act a little different in each spring, so the only way to really know is a test with a spring rate machine.

For a back-of-the-envelope guess, count the coils of the spring. 1 spring rubber partially cancels a coil.

If you have 6 coils in a spring and cancel one, then only 5 are left deflecting and "active". The math works like this:

New rate= old rate x (coils/active coils)
K = 165 x (6/5) = about 198 #/in

The stiffer the spring rubbers are, the closer this estimate will be, but the really stiff ones can be tough to fit on certain springs. Shore 70 hardness is a good compromise.

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[GTP]

I think those rates are correct. It's about the best info we have.

The spring rubbers will act a little different in each spring, so the only way to really know is a test with a spring rate machine.

For a back-of-the-envelope guess, count the coils of the spring. 1 spring rubber partially cancels a coil.

If you have 6 coils in a spring and cancel one, then only 5 are left deflecting and "active". The math works like this:

New rate= old rate x (coils/active coils)
K = 165 x (6/5) = about 198 #/in

The stiffer the spring rubbers are, the closer this estimate will be, but the really stiff ones can be tough to fit on certain springs. Shore 70 hardness is a good compromise.

This ^
Is EXACTLY the logic that I had come up with! All of it! (Engineering mind.)
And thanks for confirming my genius-ness.

Okay so I'm picking up some new street wheels and tires tomorrow. When I change them out I'll count the coils on the struts and confirm the diameter and spacing and then order those spring rubbers. And thanks for the tip on the hardness. That part I hadn't predicted.

 

[TeeLew]

That's the one!

 

[galaxy]

Wonder why they don’t have a kit with a MR upgrade for the 350? It uses the same springs.

 

[TeeLew]

Wonder why they don’t have a kit with a MR upgrade for the 350? It uses the same springs.

If you ask me, this package would be an upgrade for a 350, but you probably wouldn't do the flash.

 

[galaxy]

https://performanceparts.ford.com/part/M-5700-N

Darn near same kit. W springs, same sway bars, no flash, listed for the 350. Guess someone determined the 350 MR was good enough! Minus the ‘debatable’ rear springs being too soft.

 

[Radiation Joe]

The only way a hubcentric spacer will fail is if they are not torqued properly, and never checked thereafter.

There is some truth to that, however, not all spacers are created equal. 12mm hub-centric spacers exist that have a very thin section between the body and the hub extension. Theoretically, with enough torque, they will hold up. In practice ... not guaranteed (especially if they are anodized). I'm running 15mm spacers up front and am not worried about them. I am anal about torque and impact loads. If I hit something hard, my wheels will come off to check. I accept that I can break them and might have to replace. Bottom line is that you are not going to crash because a wheel spacer failed ... unless you are an idiot and can't recognize the symptoms of a horrendous vibration.

 

[TeeLew]

https://performanceparts.ford.com/part/M-5700-N

Darn near same kit. W springs, same sway bars, no flash, listed for the 350. Guess someone determined the 350 MR was good enough! Minus the ‘debatable’ rear springs being too soft.

I don't think it's an accident that both the W springs and the Mach 1's have much softer rear springs than the 350/350R. It's a philosophically different approach. There must have been a chassis engineer that fell in love with rear spring early on in S550 development who isn't there any more.

 

[K4fxd]

What are the Mach 1 spring rates?

 

[TeeLew]

Wonder why they don’t have a kit with a MR upgrade for the 350? It uses the same springs.

Because they don't want to pay for the development costs and the existing calibration works well.

 

[TeeLew]

What are the Mach 1 spring rates?

Let me see if I can find them, but from memory...

Std. ~200#F/675#R
HP ~220#F/725#R

 

[K4fxd]

I wonder if my 800# rear springs are too much?

 

[luc]

Let me see if I can find them, but from memory...

Std. ~200#F/675#R
HP ~220#F/725#R

Just curious, do you know the numbers for the ford racing track kit that i have on my 17. Pp1 ?

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