coilover spring rate question

[Victor Newman]

i'm thinking about getting coilovers as my next mod, and i want to make an informed purchase with spring rates in mind. i want dampening adjustability, but there are a few selections out there that include damping adjustment, so i think the decision will come down to what spring is going to be the best stiffness. i ran across this:

http://dreamingin302ci.blogspot.com/2014/09/suspension-data-b8-platform-spring.html?m=1

and is it true that most coilover kits have a softer rear spring than stock? am i reading that right? i'd like to stiffen the rear to reduce understeer (along with rear sway bar upgrade), and not over-stiffen the front. looks like our rear oem springs are somewhat stiff, and that the fronts are only 10% stiffer, while some nice coilover kits have a notably lower rate in the rear. am i missing something? thanks for help

[Victor Newman]

bump

[SportVier]

Interesting. Thanks for bumping this.

Was thinking about the PSS10 but kind of surprised the rear rate is so soft (relative to the front and stock...) Hmm...

[jran76]

boro92 covered this in more detail on the "other" forum (AR). I can't link posts from there, but if you go to the B8 S4 section on Audi Revolution, there is a post titled "B8 S4/S5 Suspension Thread" started by boro92. It's a good discussion, and more than you'll probably get here. To answer your question, yes, most aftermarket rear springs are softer than stock; although the spring rate he is basing that off of is from the S5 I believe, so the actual rate for the S4 may be slightly different. Also consider that progressive springs aren't exactly cut and dry in terms of their springs rate as they change (stiffen) as they are compressed.

My personal recommendation would be the H&R RSS+ that would allow you to change the springs to anything of your liking. They use off the shelf linear race springs from H&R.

[boro92]

Hey guys! I'm still around :)

Thanks jran for chiming in as usual.
You can't just look at spring rates at face value. How a spring is mounted, and the geometry of the suspension arms place a sort of lever mechanism on the spring. This results in a spring which can be softer at the wheel (called wheel rate). So just like how you can measure HP at the wheels, you can also measure spring rates at the wheels.
With the B8 chassis, the front suspension is double wishbone, and based on how the spring is mounted, you get approx 60% of the spring rate at the wheel. However, for the back, you are closer to 95% due to the spring being mounted right on the knuckle (thereby ensuring that the full stiffness of the spring is utilized by the wheel).
So although you may have a coilover spring rate that is like 590f/298r, when you calculate the wheel rates, they are very close to being equal.

One correction which i never made on my blog is that the S5 spring rates (obtained form Stasis literature) are incorrect. The rear rates are reported really high, and that's not the stock rate. The stock rear springs are signficantly softer than the fronts--just like the coilovers. They had miscalculated their numbers. Do not base anything off the Stasis reported stock spring rates for S5.
I write more on wheel rates here: http://dreamingin302ci.blogspot.ca/2013/10/wheel-rates-vs-spring-rates.html

+1 on jran's recommendation for RSS coilovers. If it were up to me, I'd pick those for serious track use. It's a very proper setup.
If it's a mix of street and track, Bilsteins are fantastic.

It should also be noted that there is much more to a coilover than the spring rate. There is the shock performance - and that is much more important...and where your money is going.
Let's not also forget that you can tune handling balance by adjusting rebound, or bump, or both.

[SportVier]

How a spring is mounted, and the geometry of the suspension arms place a sort of lever mechanism on the spring. This results in a spring which can be softer at the wheel (called wheel rate). So just like how you can measure HP at the wheels, you can also measure spring rates at the wheels.
With the B8 chassis, the front suspension is double wishbone, and based on how the spring is mounted, you get approx 60% of the spring rate at the wheel. However, for the back, you are closer to 95% due to the spring being mounted right on the knuckle (thereby ensuring that the full stiffness of the spring is utilized by the wheel).
So although you may have a coilover spring rate that is like 590f/298r, when you calculate the wheel rates, they are very close to being equal.

Thanks for posting up the info and sorry for the ignorance on this, but...

If stock rear spring rate is 440 and RSS is 343, and both are mounted identically, you still end up with a large difference between the two, right?

95%*440 = 418
95%*343 = 309 (26% softer)

And this while increasing the front spring rate from 480 to 686 (43%!) No matter how you cut it, that is a huge change in relative F/R rates, right? But it also looks like almost all the aftermarket kits go the same general route on spring rates.

Did Audi just got it wrong? Hard to believe because the set up feels pretty good to me, and balance mid-corner is not bad at all for such a nose-heavy car.

[boro92]

Thanks for posting up the info and sorry for the ignorance on this, but...

If stock rear spring rate is 440 and RSS is 343, and both are mounted identically, you still end up with a large difference between the two, right?

95%*440 = 418
95%*343 = 309 (26% softer)

And this while increasing the front spring rate from 480 to 686 (43%!) No matter how you cut it, that is a huge change in relative F/R rates, right? But it also looks like almost all the aftermarket kits go the same general route on spring rates.

Did Audi just got it wrong? Hard to believe because the set up feels pretty good to me, and balance mid-corner is not bad at all for such a nose-heavy car.

So that rear spring rate is wrong (for the s5 rate - 440 is not the stock rear spring rate...it's more like half of that). Do not compare to that.
Also, using dirty math if we convert the RSS spring rates to wheel rates, you get: 411 front, 325 rear (front is 0.6, rear is 0.95). It's quite close.
Ultimately on the S4, you have the entire motor ahead of the front axle. You're going to want firmer front rates. The balance for the rear of the car can be tuned with sways, tire pressures and alignment. Let's not also forget the sport diff - so you wouldn't over spring the back. You want to use the advantage of the differential to proportion power between the 2 rear wheels. So it's going to need sufficient grip back there to do its job.

You may have seen this already, but the alignment which really transforms the S4 which I've found works tremendously well on track is as follows:
Front
-3deg Camber
5.5deg Caster
-0.12deg Toe (1.5mm total toe out)
26in FTG

Rear
-2deg Camber
0.15deg Toe (1.8mm total toe in)
25.5in FTG


The car is very fun, very tossable and drives nothing like any factory audi with those numbers. There is enough slip angle on the rear axle on the entry of a corner for people behind you to be a little worried, as it can look like you're going to lose control of the car. When in reality, it slides gracefully if you ask it to.

[SportVier]

So that rear spring rate is wrong (for the s5 rate - 440 is not the stock rear spring rate...it's more like half of that).

Ah, ok, thanks. That explains everything.

Looks like you corrected the rear rate for the H&R OE Sport - was 480/440 now 480/200.
What about H&R Street? Assuming that is more like 450/190, not 450/450.

The internet never forgets... [;)]

[boro92]

Ah, ok, thanks. That explains everything.

Looks like you corrected the rear rate for the H&R OE Sport - was 480/440 now 480/200.
What about H&R Street? Assuming that is more like 450/190, not 450/450.

The internet never forgets... [;)]

Whoops missed that. Yes H&R street rear rates would come down. To 200.
The fronts at 450 are accurate (they kept the same spring rate as they did for the B7 for the fronts).

[eurotic]

boro92 is an invaluable resource when it comes to suspension on the S4. He saved me a lot of grief by educating me on this very topic just before I pulled the trigger on a different solution (B12 Pro-Kit).

After seeing that I was ultimately softening the suspension with the B12 I was considering the RSS+ and PSS10 kit and struggled with the choice. However I think I was leaning toward the PSS10 as the car is my daily driver and there was some talk of the lowering on the RRS+ being quite low even at maximum setting and that the spring rates were even firmer than the PSS10 which might make daily driving on not the best roads annoying. Unfortunately I had to back out at the last minute on purchasing anything (unexpected very large veterinary bills) that took priority from the car mod fund. Hopefully in the new year I can pull the trigger.

Oh and props to Tam at SupemePower for working with me and understanding my change of circumstance...they will be getting my business when the time comes.

[Victor Newman]

No matter how you cut it, that is a huge change in relative F/R rates, right? But it also looks like almost all the aftermarket kits go the same general route on spring rates.

That's exactly what I was worried about. Spending $$$ to end up with balance worse than OEM.

Huge thanks boro for clearing that up with the rear spring rate correction. I read your blog about wheel rates, but it still wasn't adding up that going from a 400 rear spring to a 300 rear spring was going to help (assuming the front spring gets stiffer). Knowing the stock rear spring is closer to 220 or so makes much more sense.

Thanks for sharing your wealth of information on the suspension and alignment setup for this platform.

[boro92]

Good stuff. Glad to help guys. I nerd out on this stuff way too much - I'm happy to share the info.
Victor Newman, what setup were you considering?

[Victor Newman]

Good stuff. Glad to help guys. I nerd out on this stuff way too much - I'm happy to share the info.
Victor Newman, what setup were you considering?

Was looking at H&R, but need to go back and research more. The Ksport ones are super cheap, but everyone hates them, so probably not going to try it. This is my "test" S4. I'm going to go all-out when I upgrade to a used 2016, but wanted to dabble with the B8 for now.

[eurotic]

Was looking at H&R, but need to go back and research more. The Ksport ones are super cheap, but everyone hates them, so probably not going to try it. This is my "test" S4. I'm going to go all-out when I upgrade to a used 2016, but wanted to dabble with the B8 for now.

Some of what I found out about the RSS+ that I considered cons are:
- The adjusters are somewhat vague when it comes to setting them (the clicks are not very positive) and no visual indicator of what they are set to so you have to count clicks
- The rear sits quite low (like the H&R Sport Spring - not the OE sports) when at the highest setting
- Spring rate might be a little harsh for daily driving if you have poor road
- This is a quote from another user that had the RSS+ coilovers "The biggest issue I had with the coilovers was the install. I was told by my installed the springs didn't mate well with the stock rubber bushings that are built into the metal strut mounts on our cars. They called H&R and they said to not use the rubber bushings and let the springs sit directly on the metal strut mount. They ended up cutting out the rubber bushings and installing per H&R. No issues with spring creaking or popping but it did seem a little strange. Bad news is when I went to install stock springs I had to buy brand new strut mounts because the rubber bushings are BUILT into the mounts."

That said he did say that the coilovers were fantastic on the track and that his lap times dropped significantly. For me this still ahs me thinking that for a year round daily driver that gets some hotlaps in and lots of autocross that maybe the Bilstein PSS10 is the better choice.

Hope this information is useful.


Shawn

[boro92]

Ah yes, the RSS sits quite low. A member on AZ has them on an RS5 and his car is slammed (despite being at max height or near it!).
I wouldn't go ksport. The shocks cannot handle the spring rates, and no shock worth their weight has like 27 clicks of adjustment. Many of the clicks simply aren't doing anything.
For street, it's fine. For track on a 4000lb car, nope. You want the best shocks you can buy. For an off the shelf coilover, PSS10 is likely the most economical choice (before you jump into JRZ, AST, Ohlins et al).

[Victor Newman]

Thanks Shawn. I keep going back and forth between more extreme, and less extreme. One day I'm committed to getting a $2,500 set of nice coilovers, and the next day 4-way adjustable Koni's and OE Sport springs for $750 total sounds really appealing, especially since I have a long mod list and also need to budget for a clutch replacement in the next year or so.

Right now, I'm leaning toward going with Konis and springs to get my feet wet, and years from now when I pick up a 2016 and don't have such a long mod list, dump $2,500 on quality coilovers. Adjustable Konis and springs might be good training wheels while I figure out what I really want in an ultimate suspension setup.

[Victor Newman]

Ah yes, the RSS sits quite low. A member on AZ has them on an RS5 and his car is slammed (despite being at max height or near it!).
I wouldn't go ksport. The shocks cannot handle the spring rates, and no shock worth their weight has like 27 clicks of adjustment. Many of the clicks simply aren't doing anything.
For street, it's fine. For track on a 4000lb car, nope. You want the best shocks you can buy. For an off the shelf coilover, PSS10 is likely the most economical choice (before you jump into JRZ, AST, Ohlins et al).

Got it, thanks a bunch. I'm not going to bother with the Ksports.

If I was really going to cheap out, do you think the Konis and springs would be good enough for the time being, and make up the difference with sway bars and alignment? I use my car 99.9% on the street, but want to do a couple of trackdays a year starting next year. If that setup is OK, i read that they have 4 damping adjustment levels. 0 (standard comfort), 20%, 50%, and 100%. Any idea what would be best to set them on front / rear with say, OE Sport springs? Also, should I go with OE Sport or Sport? Are Sports any stiffer than OE Sport?

[SportVier]

@Victor I can see some OE Sports and struts in my future also. Just curious, why are you thinking Koni and not Bilstein?

[Victor Newman]

i could be wrong, but it doesn't look like the bilsteins are adjustable, but i found where the konis are. i don't want to run into what boro said on his blog, that the damping isn't tuned differently between the s4 and a4, so it would be under-damped for our slightly heavier engines. if that's the case, i'd like to have the slight adjustability of the konis to go slightly stiffer in the front relative to the rear for good turn-in at the front, and use a stiffer rear sway bar to add rear stiffness for balance

[eurotic]

i could be wrong, but it doesn't look like the bilsteins are adjustable, but i found where the konis are. i don't want to run into what boro said on his blog, that the damping isn't tuned differently between the s4 and a4, so it would be under-damped for our slightly heavier engines. if that's the case, i'd like to have the slight adjustability of the konis to go slightly stiffer in the front relative to the rear for good turn-in at the front, and use a stiffer rear sway bar to add rear stiffness for balance
Just be careful. On my B6 S4 I had the Konica yellows and they were only adjustable off the car which totally defeats the purpose in my eyes.

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[Victor Newman]

Just be careful. On my B6 S4 I had the Konica yellows and they were only adjustable off the car which totally defeats the purpose in my eyes.

Sent from my SM-G930W8 using Tapatalk

yep, that's how these are too. i'm hoping to luck up and get it right the first time, or at least only have to make one change, and leave it alone permanently. i don't need to adjust back and forth from street to track. i just want a more aggressive street setup that will work a couple of times on the track per year

i'm thinking of starting full stiff in the front, and third setting out of four in the rear, and only having to adjust up or down one time if needed

[eurotic]

Ah yes, the RSS sits quite low. A member on AZ has them on an RS5 and his car is slammed (despite being at max height or near it!).
I wouldn't go ksport. The shocks cannot handle the spring rates, and no shock worth their weight has like 27 clicks of adjustment. Many of the clicks simply aren't doing anything.
For street, it's fine. For track on a 4000lb car, nope. You want the best shocks you can buy. For an off the shelf coilover, PSS10 is likely the most economical choice (before you jump into JRZ, AST, Ohlins et al).

Yeah I was going to look at the JRZ based on the AR thread but I didn't like all the collateral changes (like cutting a hole in the shock towers) required to get to the adjusters. I think that is more what I would do if I were to decide that the S4 was going to become racecar.


Thanks Shawn. I keep going back and forth between more extreme, and less extreme. One day I'm committed to getting a $2,500 set of nice coilovers, and the next day 4-way adjustable Koni's and OE Sport springs for $750 total sounds really appealing, especially since I have a long mod list and also need to budget for a clutch replacement in the next year or so.

Right now, I'm leaning toward going with Konis and springs to get my feet wet, and years from now when I pick up a 2016 and don't have such a long mod list, dump $2,500 on quality coilovers. Adjustable Konis and springs might be good training wheels while I figure out what I really want in an ultimate suspension setup.

Sounds like you and I have the same struggle. I was dead set on the B12 kit until boro talked some sense into me. I too have a long list of things that I want to do and need to just be cognizant of the fund allocation. As much as my wife fully supports me buying car stuff, we aren't independently wealthy and the Audi tax is significant.

[boro92]

The PSS can be adjusted on car.
Actually, I had KW's and they could also be adjusted on car.
BUT I did drill my shock towers for that...and the rear required u to adjust it blind, but it's doable.
PSS is better, as the adjustment is underneath (it faces the ground). You just need to go under and turn the knobs.

I would not go full stiff on the front on PSS - it will drive reallllllllly badly.
Rear, maybe. Front...not so much.

[SportVier]

The PSS can be adjusted on car.

Yeah, but I think Victor was saying that the Bilstein struts (B8) are not adjustable, while the Konis are.

[boro92]

Yeah, but I think Victor was saying that the Bilstein struts (B8) are not adjustable, while the Konis are.

Whoops. Yes this is true.

[Jay@JXB]

This is a cool thread that should stay at the top! I have H&R RSS+ currently but will end up with some custom 3-way setup down the road (likely from Stance Suspension in Chicago). Here's my current corner balance, with all the weight removed in the rear I've been softening up the rear shocks to stop it from getting skittery upon corner exit and over parking lot bumps and undulations (autocross use).

https://uploads.tapatalk-cdn.com/20170906/6f8437b464a0a3d8598e2b682907dc35.jpg

https://uploads.tapatalk-cdn.com/20170906/da62cfa87067543135d622c3d409024d.jpg


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