follow ft86club on our blog, twitter or facebook.
FT86CLUB
Ft86Club
Delicious Tuning
Register Garage Members List Calendar Search Today's Posts Mark Forums Read

Go Back   Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community - FT86CLUB > Technical Topics > Suspension | Chassis | Brakes -- Sponsored by 949 Racing

Suspension | Chassis | Brakes -- Sponsored by 949 Racing Relating to suspension, chassis, and brakes. Sponsored by 949 Racing.


User Tag List

Reply
 
Thread Tools Search this Thread
Old 06-26-2012, 07:57 PM   #1
Racecomp Engineering
 
Join Date: Nov 2011
Drives: 2016 BRZ, 2012 Paris Di2 & 2018 STI
Location: Severn, MD
Posts: 5,393
Thanks: 3,405
Thanked 7,233 Times in 2,957 Posts
Mentioned: 303 Post(s)
Tagged: 9 Thread(s)
Send a message via AIM to Racecomp Engineering
Basic tech info: spring rates, rear suspension, motion ratios, and you.

I wrote this before on an EVO messageboard and it helped a lot of people figure out what to aim for and motivate them to educate themselves on suspension. I thought it would help here too so I modified it a little and here you go. Multiply 1 kg/mm by 56 to get the rate in lbs/in.

-------------------------------------------

Suspension Tech: Motion ratio and choosing spring rates

First, if you don't really care about performance or ride quality and just want a drop, close the thread now and don't sweat it too much.

But if you do care about performance and function, it helps to know what's going on! So keep reading.

Second, I'm not going to spell out exactly what are the "best" spring rates. There are many factors at play that it's impossible and wrong to say what's best for everyone and every application. Ideally you'd have a suspension tuner design a suspension for your specific set-up, needs, and preferences. It's also a little early for that IMO and many of us are still testing things out.

Third, I'm also not going to talk about specific brand names. This is just intended to be a rough guide for people looking at and comparing spring rates for springs and coilovers. Really this is one stepping stone for you to read more authoritative material on suspension.

------------------------------

We often see spring rates that are just plain wrong with several brands of off the shelf coilovers for a variety of cars. It does not necessarily mean the coilovers are bad, but the springs should be swapped out if performance is the goal.

Basics

1. Too stiff. You don't need crazy 14 kg/mm spring rates on narrow street tires. You don't have enough grip to generate enough body roll to need super stiff spring rates. You'll likely be overheating and overloading your tires very quickly. With R Compounds and sticky street tires you will end up on the firmer side of things but there is still much to test for the BRZ/FRS.

Autocross sometimes makes things a bit more interesting and firmer than usual often feels good to some people. Aero also changes thing, as does driver preference, and swaybar sizing. That's a topic for another thread.

2. Secrets. I strongly disagree with the practice of vendors or companies keep their spring rates secret. It isn't a secret sauce, it's just physics. Many get it wrong, but it's not magic and it's up to them to prove they got it right. Physics. Even if you're not a suspension nerd, non-disclosure agreements and secrecy should be a red flag. I really must know the spring rates for a set-up as it's the foundation for everything and I would refuse to purchase anything when that's not provided. Physics.


Failing to account for the motion ratio

Sometimes you see spring rates for a set of coilovers and it's something like 7kg/mm front and 5kg/mm rear. Makes sense, since the BRZ/FRS is a little front heavy right so we can make the rear a little softer? Well actually there's another factor at play.

The BRZ/FRS has a multi-link rear suspension. The rear spring is mounted inwards on the control arm just a little bit. Unlike the front strut which is mounted at the hub, a 5 kg/mm spring rate in the rear does not mean a 5 kg/mm rate "at the wheel". Essentially the rear control arm is a moment arm....placing the spring inwards towards the pivot point means it needs to be stiffer to have the same effect as it would if it were mounted at the end of the arm or at the hub. Sometimes you'll see people mention the "motion ratio." For the front BRZ/FRS with the strut based suspennsion, it's close to 1. For the rear, it's around 0.75.

To get the "wheel" rate of the spring, or the spring rate at the wheel, you multiply the spring rate by the square of the motion ratio.

So that 7k/5k is really more like 7 kg/mm front and 2.8125 kg/mm rear.


Is that bad? Well, if it's not what you were planning on then, yeah, that's not good. It has it's advantages and disadvantages. Some of these can be tackled through swaybars and alignment settings but my philosophy is to get the spring rates right first as a foundation. Softer rear rates CAN work.

Sooo....this doesn't mean that you should go stiffer in the rear, or that softer in the rear is "bad." But it's just something for everyone to understand when looking at spring rates for the various springs and coilovers out there. I'd encourage everyone to read up on what springs actually do for the car and how changes affect a car. I do plan on writing on a few more topics eventually but uh....we've been a little busy lately.


- Andrew

Last edited by Racecomp Engineering; 07-16-2012 at 11:03 AM.
Racecomp Engineering is offline   Reply With Quote
The Following 74 Users Say Thank You to Racecomp Engineering For This Useful Post:
Ammunition (10-17-2015), AreteAuto (11-30-2015), B L U E S L A T E (01-28-2013), bear89103 (09-26-2013), Calum (06-26-2012), chulooz (06-26-2012), Creole (04-09-2014), DAEMANO (05-26-2014), Dave-ROR (06-26-2012), denkigrve (07-16-2012), Dimman (06-26-2012), djdnz (07-30-2012), DrDuquette (07-30-2012), dun3 (01-07-2013), Duo (09-17-2012), Fish (06-27-2012), flippy (06-10-2015), Fly Guy (06-27-2012), Freshfrs86 (12-08-2014), FutureFT86 (12-09-2012), hachigoku (12-07-2017), Hanni_0176 (02-07-2014), iBRZ (11-24-2012), illmatic (07-27-2012), jayliu.jiayu@gamil.com (07-09-2018), Jeff Lange (06-26-2012), JMon85 (05-11-2017), Krispeee (12-01-2013), Lococholo84 (01-27-2017), manonastick (02-24-2014), mechaghost (06-26-2012), MooseWRX (11-21-2014), Nardi330 (06-27-2012), Ndgreely (07-17-2013), No Limit Motorsport (08-09-2012), notout86 (04-15-2018), oaroyale (02-07-2014), onefitz (04-17-2014), PikachuBRZ (10-17-2022), racecaresuaceb (04-09-2014), rice_classic (06-26-2012), RiskyTrousers (06-26-2012), RJasonKlein (10-26-2015), RobertPaulson (07-02-2015), rupert (06-27-2012), sandman126 (07-30-2012), sato (04-16-2018), Scargod (01-29-2022), schtebie (07-27-2012), Shneegle (03-26-2016), Slartibartfast (09-07-2012), solidONE (12-20-2013), Sugi (01-04-2015), Superhatch (06-11-2013), SVTSHC (03-12-2013), Techfl3x (11-27-2013), TemeCal (08-17-2012), timurrrr (10-17-2022), tintumz22 (04-23-2019), tnt (08-20-2012), TofuJoe (03-26-2016), TRAKRAVN (02-12-2016), Tristor (02-28-2018), TSLRich (07-29-2012), TuxedoCartman (07-27-2012), UncleFester (06-26-2012), Valentino (05-17-2015), WeaponX (12-28-2015), whataboutbob (04-22-2018), wheelhaus (08-13-2012), why? (04-16-2018), WRB-DZA-BRZ (06-27-2012), wu_dot_com (07-27-2012), ZeHeadBanger (04-28-2014)
Old 06-26-2012, 10:52 PM   #2
Jeff Lange
Senior Member
 
Jeff Lange's Avatar
 
Join Date: Dec 2011
Drives: 1986 AE86 GT-S, 2011 Lexus IS250 6M
Location: Calgary, Canada
Posts: 661
Thanks: 136
Thanked 361 Times in 161 Posts
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
So many people forget about motion ratio and try to compare spring rates between different cars (!), nevermind front/rear.

Jeff
__________________

2011 Lexus IS350 F-Sport 6MT with LSD
1986 Toyota Corolla GT-S Supercharged
Jeff Lange is offline   Reply With Quote
Old 06-26-2012, 11:10 PM   #3
rice_classic
Senior Member
 
rice_classic's Avatar
 
Join Date: Jun 2012
Drives: Nevermorange FRS
Location: Seattle, WA
Posts: 4,160
Thanks: 755
Thanked 4,200 Times in 1,803 Posts
Mentioned: 77 Post(s)
Tagged: 1 Thread(s)
Please, get technical. I always look forward to a good read.
rice_classic is offline   Reply With Quote
The Following 2 Users Say Thank You to rice_classic For This Useful Post:
blu_ (07-29-2012), Scargod (01-29-2022)
Old 06-26-2012, 11:48 PM   #4
Dimman
Kuruma Otaku
 
Dimman's Avatar
 
Join Date: Dec 2009
Drives: Mk3 Supra with Semi-built 7MGTE
Location: Greater Vancouver (New West)
Posts: 6,854
Thanks: 2,398
Thanked 2,265 Times in 1,234 Posts
Mentioned: 78 Post(s)
Tagged: 2 Thread(s)
Garage
Sticky? Or daily bump?

You guys have been unbelievably helpful on this forum.
__________________


Because titanium.
Dimman is offline   Reply With Quote
Old 06-27-2012, 09:17 AM   #5
Calum
That Guy
 
Join Date: Dec 2011
Drives: 2013 asphalt FRS MT
Location: Halifax, Nova Scotia
Posts: 4,865
Thanks: 5,058
Thanked 2,867 Times in 1,499 Posts
Mentioned: 82 Post(s)
Tagged: 1 Thread(s)
^^agreed!!
Calum is offline   Reply With Quote
Old 06-27-2012, 10:07 AM   #6
Racecomp Engineering
 
Join Date: Nov 2011
Drives: 2016 BRZ, 2012 Paris Di2 & 2018 STI
Location: Severn, MD
Posts: 5,393
Thanks: 3,405
Thanked 7,233 Times in 2,957 Posts
Mentioned: 303 Post(s)
Tagged: 9 Thread(s)
Send a message via AIM to Racecomp Engineering
Quote:
Originally Posted by Dimman View Post
Sticky? Or daily bump?

You guys have been unbelievably helpful on this forum.
Thank you.

On the EVO board there was one "tech" thread that was stickied that linked to a bunch of good threads. That might work well here.

- Andrew
Racecomp Engineering is offline   Reply With Quote
Old 07-27-2012, 12:19 PM   #7
TouchMyHonda
Vtec Jesus
 
TouchMyHonda's Avatar
 
Join Date: Jul 2012
Drives: 13 BRZ, 13 Golf R, 15 Audi S4
Location: LSD
Posts: 1,165
Thanks: 623
Thanked 243 Times in 153 Posts
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
in to read later.
TouchMyHonda is offline   Reply With Quote
Old 07-29-2012, 09:24 PM   #8
yomny
Senior Member
 
yomny's Avatar
 
Join Date: Jul 2012
Drives: 2013 FRS Whiteout
Location: MIA
Posts: 1,545
Thanks: 557
Thanked 469 Times in 340 Posts
Mentioned: 33 Post(s)
Tagged: 5 Thread(s)
This is pretty interesting, i was just coming back from a drive and felt so good driving the car, i plunged into a few corners and the car's front end just dives, it rotates so perfectly. The rear end of the car likes to go out but in a very controlled manner. What i don't really get is if its so great in stock form why don't they keep the same ratio of front to rear spring stiffness when upgrading to shorter stiffer springs.
yomny is offline   Reply With Quote
The Following User Says Thank You to yomny For This Useful Post:
KidRed (09-17-2015)
Old 07-29-2012, 10:39 PM   #9
Racecomp Engineering
 
Join Date: Nov 2011
Drives: 2016 BRZ, 2012 Paris Di2 & 2018 STI
Location: Severn, MD
Posts: 5,393
Thanks: 3,405
Thanked 7,233 Times in 2,957 Posts
Mentioned: 303 Post(s)
Tagged: 9 Thread(s)
Send a message via AIM to Racecomp Engineering
That's a great question...

A short answer is that the front and rear of the react differently to changes in spring rate. Roll centers and dynamic alignment changes play a big part here too and change differently in the front vs the rear with ride height and spring rate changes.

- Andrew
Racecomp Engineering is offline   Reply With Quote
Old 07-30-2012, 10:17 AM   #10
yomny
Senior Member
 
yomny's Avatar
 
Join Date: Jul 2012
Drives: 2013 FRS Whiteout
Location: MIA
Posts: 1,545
Thanks: 557
Thanked 469 Times in 340 Posts
Mentioned: 33 Post(s)
Tagged: 5 Thread(s)
I'm just afraid to really mess up the cars amazing handling characteristics, but it needs to be dropped lol. I'm seeing many companies coming out with 7/7,8/8 for front and rear rates and can't help but wonder if this will retain the stock character. The stock ride is nice and stiff, so maybe a set of coilovers with similar rates to stock(maybe a bit higher) would be great? I'll wait and see before choosing coilovers and spring rate, hopefully a few write up on different rates and their behaviors will come along
__________________
GTX2867R, moto-tuned , tomei op , motiv fp , Invidia Q300 ti , Rota titan 17x9 +42 , nt555 255/40 , ST coilovers w/cascam , Hotchkis sways
yomny is offline   Reply With Quote
Old 07-30-2012, 12:12 PM   #11
schtebie
Senior Member
 
Join Date: Jun 2012
Drives: CBS BRZ Limited
Location: TN
Posts: 494
Thanks: 336
Thanked 193 Times in 136 Posts
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quote:
Originally Posted by yomny View Post
I'm just afraid to really mess up the cars amazing handling characteristics, but it needs to be dropped lol. I'm seeing many companies coming out with 7/7,8/8 for front and rear rates and can't help but wonder if this will retain the stock character. The stock ride is nice and stiff, so maybe a set of coilovers with similar rates to stock(maybe a bit higher) would be great? I'll wait and see before choosing coilovers and spring rate, hopefully a few write up on different rates and their behaviors will come along
One important thing to keep in mind is the dampers play a huge role in ride comfort. Even if with higher spring rates, as long as the dampers can keep up, you could end up with a smooth, if not smoother ride than stock.
schtebie is offline   Reply With Quote
Old 07-30-2012, 01:44 PM   #12
yomny
Senior Member
 
yomny's Avatar
 
Join Date: Jul 2012
Drives: 2013 FRS Whiteout
Location: MIA
Posts: 1,545
Thanks: 557
Thanked 469 Times in 340 Posts
Mentioned: 33 Post(s)
Tagged: 5 Thread(s)
Yeah i think what contributes to the stiff feeling of the FR-S are the dampers. I read in a review that the FR-S has stiffer shocks than the BRZ. What i like is the match that the FR-S has between then dampers and the spring rates, would love to keep the same ratio/match.
yomny is offline   Reply With Quote
Old 07-30-2012, 01:45 PM   #13
blu_
Senior Member
 
blu_'s Avatar
 
Join Date: Mar 2012
Drives: SWP BRZ LTD
Location: Portland, OR
Posts: 889
Thanks: 637
Thanked 170 Times in 106 Posts
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
I believe there have been more than one independent shock dyno's which show the dampers are the same between the two cars. Only the spring rates are different.
blu_ is offline   Reply With Quote
Old 07-30-2012, 01:52 PM   #14
xwd
Senior Member
 
Join Date: Feb 2012
Drives: 2013 DGM Subaru BRZ (Subie #9)
Location: ATL, US
Posts: 2,667
Thanks: 123
Thanked 860 Times in 552 Posts
Mentioned: 32 Post(s)
Tagged: 0 Thread(s)
Quote:
Originally Posted by yomny View Post
Yeah i think what contributes to the stiff feeling of the FR-S are the dampers. I read in a review that the FR-S has stiffer shocks than the BRZ. What i like is the match that the FR-S has between then dampers and the spring rates, would love to keep the same ratio/match.
If there is any difference (and nothing has confirmed yet there is), it is small enough spring vendors are using the same springs for both cars. Most of the rates people are coming out with are somewhere in the middle between the two cars, when you look at the difference between front and rear. The North American FR-S has 40% higher spring rates in the rear, the BRZ is around 23%. Most of the aftermarket vendors are somewhere around 25-30% higher in the rear. Like Racecomp said, when you lower the car it has effects on the whole suspension so the rates may not be the same as stock for a lowered car.

Coilovers are an entirely different thing since the damping may be drastically different than stock.
xwd is offline   Reply With Quote
 
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
MotoIQ: Tech Look at FR-S Underside - Suspension, Chassis, Brakes, Differential oneday Suspension | Chassis | Brakes -- Sponsored by 949 Racing 93 09-22-2017 10:47 AM
Is anyone going to motion car show? Pekingduck Southern California 15 05-20-2012 11:46 PM
Weird GT 86 factory spring rates in GT5? Spec-Al Suspension | Chassis | Brakes -- Sponsored by 949 Racing 36 03-27-2012 02:30 PM
TRD 86 MSB (Motor Sports Basic) Race Packages Announced switchlanez Scion FR-S / Toyota 86 GT86 General Forum 49 03-27-2012 08:31 AM
Crazy idea... the Rear Seat info ? MRZ415 Scion FR-S / Toyota 86 GT86 General Forum 78 01-27-2012 12:19 PM


All times are GMT -4. The time now is 08:41 AM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
User Alert System provided by Advanced User Tagging v3.3.0 (Lite) - vBulletin Mods & Addons Copyright © 2024 DragonByte Technologies Ltd.

Garage vBulletin Plugins by Drive Thru Online, Inc.