coil over spring rate help

[Dallas J]

The reason I don't like NF is because it's weight dependant so the same spring will have different NF on a 2000 lbs car and on a 3700 lbs car. Which makes it very hard to know what is good or bad (Gran Turismo 7 uses NF instead of spring rates for springs and it's super stupid way to tune suspension).

Thats the reason why you SHOULD use NF. It takes into account weight and motion ratio to give a relevant effective stiffness that can be compared across platforms. Its the proper number to look at when talking stiffness. Roll rates (angle/g) would be a step higher and better but takes more math and knowledge of the full geometry and setup.

However your rear springs are way higher than the front so I'm guessing your car is oversteering a lot. For rear coilover springs your front and rear springs have almost the same MR or very close to one another with probably rears been little higher.

Vorshlag actually have spring packages that they tested and developed for MCS:

• Vorshlag's GT Spring Package is 450 #/in (2.18 hz) Front / 550 #/in (2.04 hz) Rear - This I guess is a package for a street / weekend car on street tires (PS4s, Cup 2)
• Vorshlag's GTS Spring Package is 600 #/in (2.51 hz) Front / 750 #/in (2.38 hz) Rear - This should be the experienced driver 200TW tire package so I guess this will be your best bet.
• Vorshlag's GTR Spring Package is 800 #/in (2.90 hz) Front / 1100 #/in (2.88 hz) Rear - This is the straight out slick tire Sunday racer package I find the rear a bit too high for my liking aka DHR cars don't run rear springs that high.

These were where I started. I have 450/550, with the intent to swap 550 to front and add 700 to rear if/when I wanted more. Its the same ratios of NF balance even though not exact same numbers. But I suspect the rates are better on track than AutoX where we spend FAR less time at steady state and more time in transition. Plus the torque to wheels coming out of corners in 2nd asks more of the rear than 3rd or 4th on track. But thats just a guess. Still learning mustang

This packages as a concept are what late Kenny Brown was teaching in his Speed Therapy Academy so the rates should get you there. And If I were in your shoes I would have probably go to the GTS package.

The Divorced spring location just doesn't have enough MR to get to a rear that firm which is why I think the Ohlins are just a street coilovers and not a great track coilovers though I don't want to go through the hassle of going with true coilover on the rear and they work great for a dual purpose car.

Hope this helps.

All the coilovers with divorced springs seem to be pretty soft in the rear. and TeeLew has talked about running quite a bit softer rear with success, so at least worth trying. They're cheap enough and easy enough to swap in an evening.

 

[TeeLew]

Bnight, Dallas kinda nailed it. I use Nf as a tool to be able to compare cars which are not alike. It's probably the same reason the do it in the Sim you mention. This way they don't have to do a rate calculation for every car. Even among Mustangs, the S197 guys talking about 250's and S550's talk about 1000's. Once we take weight and motion ratios into account, though, we might actually be at a similar stiffness level (no idea for real, just an example) with regard to how we should expect the car to act with a given track input.

If I'm comparing a GT3 something and a Spec Miata, then there are so many different variables that about the only way you can talk about the relative stiffness levels is by referencing Nf.

When you really start digging into it, you kind of figure out that it's all waves, wave forms and frequency. Little things...like the entire time domain...drop out of a lot of the equations.

 

[Stan Whitney]

As a data point, on my car (street weight gt500 - 4100 before driver) I've gone from steeda springs, vosrhlag mcs 600/750 and now 800/1100. On big super 200s - 325s, big swaybars, and a few hundred lbs of rear aero.

The interesting thing here is the front wheel rate % vs combined wheel rate has gone from 54% - 56% (600/750) and now back to 54% (800/1100).

The switch to mcs 600/750 was positive, but the front picked up a small to medium push, getting worse if overdriven. Still made lap time gains, but had to drive around this feature. Stiffening the rear bar made things twitchy and slower.

Switch to 800/1100, and the easy balance is back. Corner entry did not get worse, but mid to exit is more neutral, while still being able to power down. Overall grip feel is up (but data does not show this), like the car is using the tires better, and the chassis transitions from brake to turn in better. It is more confidence inspiring, so am going to keep this for now.

Wheel rate went up 30%+, so I took out about 30% compression clicks front and rear. Over the journey rear wheel rate has gone from 276-> 445->652#.

 

[bnight]

All the coilovers with divorced springs seem to be pretty soft in the rear. and TeeLew has talked about running quite a bit softer rear with success, so at least worth trying. They're cheap enough and easy enough to swap in an evening.

Yeah but the soft rear leads to the exactly opposite problem to what you have with the stiff rear. It has a ton of Understeer when you have stiff front (you need it because weight is on the front of this cars) and then the soft rear makes the car really hard to rotate in slow corners and since the rear is so soft it makes it hard to control in fast corners (rear wants to step out). Which is all problems that switching to real coilover on the back you can use softer springs but get better Wheel Rate and have more flexibility when dialling the car to liking.

 

[Dallas J]

Yeah but the soft rear leads to the exactly opposite problem to what you have with the stiff rear. It has a ton of Understeer when you have stiff front (you need it because weight is on the front of this cars) and then the soft rear makes the car really hard to rotate in slow corners and since the rear is so soft it makes it hard to control in fast corners (rear wants to step out). Which is all problems that switching to real coilover on the back you can use softer springs but get better Wheel Rate and have more flexibility when dialling the car to liking.

Just for reference and clarification, the idea for dumping rear spring rate as a test wasn't to assume it was going to be the ideal setup. As TewLew alluded to, the idea is to not make baby steps and over shoot the correction. Since my issue wasn't understeer, it was putting power down. So we wanted to see what happens with an extreme change. Does it fix at least that problem even though it may come with other issues.

I tested today at our small lot so its not the best opportunity to feel the car out at speed or steady state. Its all quick transition, short accelerations, and slow digs. But I would say the car is better though could still be better. But what the test tells me is that dumping spring rate isnt the full solution to getting more power down. But the car didnt really push because we never really sat at steady state.

 

[bnight]

Just for reference and clarification, the idea for dumping rear spring rate as a test wasn't to assume it was going to be the ideal setup. As TewLew alluded to, the idea is to not make baby steps and over shoot the correction. Since my issue wasn't understeer, it was putting power down. So we wanted to see what happens with an extreme change. Does it fix at least that problem even though it may come with other issues.

I tested today at our small lot so its not the best opportunity to feel the car out at speed or steady state. Its all quick transition, short accelerations, and slow digs. But I would say the car is better though could still be better. But what the test tells me is that dumping spring rate isnt the full solution to getting more power down. But the car didnt really push because we never really sat at steady state.

You actually had to make a correction on the long left corner because the car was pushing you wide (aka understeer). But yeah looks like it's putting power down.

 

[Anviltester]

Thats the reason why you SHOULD use NF. It takes into account weight and motion ratio to give a relevant effective stiffness that can be compared across platforms. Its the proper number to look at when talking stiffness. Roll rates (angle/g) would be a step higher and better but takes more math and knowledge of the full geometry and setup.



These were where I started. I have 450/550, with the intent to swap 550 to front and add 700 to rear if/when I wanted more. Its the same ratios of NF balance even though not exact same numbers. But I suspect the rates are better on track than AutoX where we spend FAR less time at steady state and more time in transition. Plus the torque to wheels coming out of corners in 2nd asks more of the rear than 3rd or 4th on track. But thats just a guess. Still learning mustang


All the coilovers with divorced springs seem to be pretty soft in the rear. and TeeLew has talked about running quite a bit softer rear with success, so at least worth trying. They're cheap enough and easy enough to swap in an evening.

Im not understanding how a coilover can have a divorced spring. A coilover has the spring on the shock as one unit - anything else is just a spring and a shock.

 

[TeeLew]

Im not understanding how a coilover can have a divorced spring. A coilover has the spring on the shock as one unit - anything else is just a spring and a shock.

It means you're using a damper which could accept a spring, but you've put the actual spring in the stock, divorced position.

I think if we want to put spring loads through the damper mount, we'd probably better stiffen it up first. It's not difficult to get in the situation of 'stiffen the spring but that makes the mount flex more.'

 

[Dallas J]

Im not understanding how a coilover can have a divorced spring. A coilover has the spring on the shock as one unit - anything else is just a spring and a shock.

Thats just being pedantic, coilover being just a generic term for "not" a standard spring and lowering spring. We dont call the OEM front strut a coilover..

I think if we want to put spring loads through the damper mount, we'd probably better stiffen it up first. It's not difficult to get in the situation of 'stiffen the spring but that makes the mount flex more.'

Here's my solution for that.

BMR has a steel version, but this is mine. The 3rd mount connects through the double thick sheet metal and prevents the shock mount from rocking and fatiguing then tearing the metal.

View this content on Instagram

View this content on Instagram

 

[TeeLew]

You actually had to make a correction on the long left corner because the car was pushing you wide (aka understeer). But yeah looks like it's putting power down.

I think you're exactly correct. There's a nonsense video on YouTube right now that says, "Snap Oversteer Doesn't Exist" or something like this and then it goes into fair detail for the next 15 minutes about lift-off and trailing-throttle oversteer. They never even actually talk about snap oversteer. It's kinda funny.

Snap oversteer is when the car is understeering and you're trying to get to throttle. Sometimes the car will continue to understeer the entire way to the exit and sometimes it will quickly transition to a late corner oversteer. The speed of the transition depends on how much U/S you had initially. If the car has *a lot* of understeer, then it's going to be a big snap when the rear finally frees up. That wiggle at the end of the run was just this and being a little greedy with the throttle. That wasn't something I'd really worry about.
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Dallas, does the car overall have U/S? Yes, but I think a lot of that could be addressed with footwork. AutoX can be a little tough, because *everything* is going to understeer at 30 mph with the steering at full lock. The trick is loading the front end of the car as much as possible to initiate the turning as early as possible to avoid this situation. Right now, I feel like you're a little late on getting the car rotated which means you have to ask a lot from the front later in the corner. Traction is a big deal, though, and it looks like that's pretty good. I don't have a 'before' vid, so I don't know how much of an improvement that really is. You'll have to tell us on that part.

You're nailing cone precision in terms of line and you're being aggressive with the throttle, so all good there. How much do you have to sacrifice to get the front to work better? The corner from 0:15-0:22 is kind of a 'worst case' scenario. You're rolling speed in without being able to really do much to load the front in terms of braking. We want to consciously approach the course thinking, "I want to avoid the steady-state, max lateral G condition," because our cars aren't good doing that. That's where cars like the Subu-yotas are soooooo good. They can just float through that sht.

We're good at going in straight lines, so if we split long corners up into a couple straight lines, that can sometimes help. Here an idea. You might have tried to get the car a little more to the right after the gate at 0:17 and then been as wide as possible through the gate at 0:18. This might have allowed you to straighten the car and had a blast of full-throttle for just a moment, touch the brake, pivot the car for the cone at 0:19. Do the exact same for the cone at 0:22. When you do it there, you will pass that cone at a different angle, so you're able to unwind the wheel and go to throttle earlier to gain down that shoot to the corner at 0:24. I'm not saying 100% that this would work. I'm just sharing how I think of those types of corners.

There are some corners where it's just unavoidable, but my AutoX line approach is always to minimize steady state cornering. I'll give up mid-corner rolling speed to get the car turned earlier every time.

Walk us through the change. What did you feel it do to the car? Did it allow or require you to do anything differently than what you had before?

 

[TeeLew]

Thats just being pedantic, coilover being just a generic term for "not" a standard spring and lowering spring. We dont call the OEM front strut a coilover..


Here's my solution for that.

1. Correct.
2. Looks good!

 

[Dallas J]

Dallas, does the car overall have U/S? Yes, but I think a lot of that could be addressed with footwork. AutoX can be a little tough, because *everything* is going to understeer at 30 mph with the steering at full lock. The trick is loading the front end of the car as much as possible to initiate the turning as early as possible to avoid this situation. Right now, I feel like you're a little late on getting the car rotated which means you have to ask a lot from the front later in the corner. Traction is a big deal, though, and it looks like that's pretty good. I don't have a 'before' vid, so I don't know how much of an improvement that really is. You'll have to tell us on that part.

We definitely understeer on entry and oversteer on exit. Which is gonna be probably standard for a mustang but always a gradient. This event was too tight, slow, and short to really get a feel but it did put power down a bit better though not "great". The lot here is absolutely a small car lot. Hustling CAM cars through things requires delicacy!

So far I think the best the car has felt has been 550/700 with the redrilled front bar and disconnected rear. That seemed to have the best entry grip/balance and let me get out of the corner the most aggressively.

One thought, I do have 10mm extra offset in my top hats which should account for about 1deg added caster. Its not much, but caster does cause a jacking effect unloading the inside rear at high steering angles. Maybe I'll make a plate to zero that out, or even reverse that to try a reduced caster. That's an easy one to make a couple versions and swap day to day.

You're nailing cone precision in terms of line and you're being aggressive with the throttle, so all good there. How much do you have to sacrifice to get the front to work better? The corner from 0:15-0:22 is kind of a 'worst case' scenario. You're rolling speed in without being able to really do much to load the front in terms of braking. We want to consciously approach the course thinking, "I want to avoid the steady-state, max lateral G condition," because our cars aren't good doing that. That's where cars like the Subu-yotas are soooooo good. They can just float through that sht.

I've been known to touch but not knock over a lot of cones

Throttle control is something I've been focusing A LOT on with the mustang. I've been in AWD for over 20yrs so turbo lag and grip really has a different throttle need. But, I feel I'm getting a lot smoother with it.

I agree on the line choices. This lot size doesn't leave a ton of room for positioning, but you can see in places like 0:17 where I'm trying to get right while braking where most are just diving at that cone. But typically I shoot for very late apexes to get on throttle physically early in the course.

We're good at going in straight lines, so if we split long corners up into a couple straight lines, that can sometimes help. Here an idea. You might have tried to get the car a little more to the right after the gate at 0:17 and then been as wide as possible through the gate at 0:18. This might have allowed you to straighten the car and had a blast of full-throttle for just a moment, touch the brake, pivot the car for the cone at 0:19. Do the exact same for the cone at 0:22. When you do it there, you will pass that cone at a different angle, so you're able to unwind the wheel and go to throttle earlier to gain down that shoot to the corner at 0:24. I'm not saying 100% that this would work. I'm just sharing how I think of those types of corners.

There are some corners where it's just unavoidable, but my AutoX line approach is always to minimize steady state cornering. I'll give up mid-corner rolling speed to get the car turned earlier every time.

Walk us through the change. What did you feel it do to the car? Did it allow or require you to do anything differently than what you had before?

Its hard to tell in the vid, but the asphalt changes at 0:16s. That area in the dry is about 0.1g less grip and most cars seem to push here. In the wet that part is diabolical. Seems their some oils or extra tar in it that just makes it worse then anywhere else.

The section around 0:22 I was 2/10 quicker in a different run on data. I was in 3rd and had a better backside line on the exit cone.

After this event, I would say corner exit was slightly improved but not enough for the sacrifice on the big course to understeer. I think going back to the baseline of 550/700 with redrilled front and no rear bar is the plan. Also reducing rear camber from -2.5 to -2.0, and reducing caster 1deg.

The 700lb rear spring should help corner entry, and other 3 help corner exit.

 

[TeeLew]

So far I think the best the car has felt has been 550/700 with the redrilled front bar and disconnected rear. That seemed to have the best entry grip/balance and let me get out of the corner the most aggressively.

I've been known to touch but not knock over a lot of cones

Throttle control is something I've been focusing A LOT on with the mustang. I've been in AWD for over 20yrs so turbo lag and grip really has a different throttle need. But, I feel I'm getting a lot smoother with it.

Its hard to tell in the vid, but the asphalt changes

After this event, I would say corner exit was slightly improved but not enough for the sacrifice on the big course to understeer. I think going back to the baseline of 550/700 with redrilled front and no rear bar is the plan. Also reducing rear camber from -2.5 to -2.0, and reducing caster 1deg.

The 700lb rear spring should help corner entry, and other 3 help corner exit.

By re-drilled front bar, do you mean to make it stiffer or softer?

I only ran with the rear disconnect one afternoon, but I did feel it added a ton of rear grip, entry and exit. Transitions were tricky, but I was softer (950 divorced at that point) than you. I didn't have a way to change the rear ride height with that spring, so I was stuck with the rear too high, which caused it's own problems. There very well might have been something to it.

So much is hard to tell from the video that I hesitated to say much on driving. I guess more than anything, I was trying to see what it did or didn't do for you. That course was like trying to watch someone get dressed in a phone booth (if those even exist, anymore.)

You'd talked about corner entry instability before and now we're dealing with entry U/S. At the very least, I'd say the change went in the direction we'd expect it to go. It didn't get what you want in the way you want it, which is understandable.

How about ride on bumps? Was there anything either on the course or on the road which is worth commenting?

How about brake pitch (rear lift) or squat on the throttle? Did you feel either was excessive?

Did you notice anything different on ABS intervention? It doesn't look like there was enough braking to really know.

As far as rear wheel drive throttle application, my personal opinion is that stair-stepping the input is the best approach for both handling balance of the car and consistency. It's not what books tell you to do, but it works. Most will tell you to slowly progress to throttle at the limit of traction. Not only is that a way to consistently undershoot throttle application, but it loads the chassis in a way which creates understeer. A 2-step throttle, where you abruptly go to partial with no attempt to go to full-throttle on the initial application, pause, then go full is a better overall technique, IMO. I've shared this before, but it's the best demonstration I know.