What Spring Rate Do I Need? | Suspension Setup

How to choose spring rates.
Getting your spring rates to a sensible starting point for you car and application is something we all struggle with when starting out. This lesson, taken directly from the Suspension Tuning and Optimisation course, will hopefully help make it a little bit easier for you.
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🙋‍♂️ Take $25 USD off ANY HPA course with coupon code: KZbin25
Enroll now: hpcdmy.co/25offyt
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Using a mechanically biased RWD road legal circuit car for the example, Tim runs though the calculations used to work out our spring rates for the front and rear of the car noting along the way some differences in doing so for a race application vs road use.
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0:00 - One Module From A Full Course
0:45 - RWD Circuit Racing Coupe Example
1:21 - Key Information
1:31 - Total Corner Weights or Weight Split From OEM
2:03 - Pro Tip: Unit Consistency
2:25 - Back To Weights
3:00 - Sprung Mass Only
3:48 - Our Example Continued
4:18 - Motion Ratio
5:52 - Purchasable Spring Value
6:10 - Rear Axle
6:50 - Rear Vs Front Frequency Race Use
8:00 - Simplified Calculation
8:45 - Suspension Tuning
9:18 - Lateral Load Video - Linked Below
9:35 - Just One of 37 Modules
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LINKS:
Lateral (FREE) load module: hpcdmy.co/lateralloadyt
🔧 Interested in learning how to do your own wheel alignment for the track or street? Start with a free alignment & suspension 101 lesson now: hpcdmy.co/aljyt
Check us out: hpcdmy.co/hpa
Have a listen: hpcdmy.co/podcast
Steal our wardrobe: hpcdmy.co/merchy
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#highperformanceacademy #suspensiontuning #springrates #suspension #springs #racing #datanerd #gofasterwithdata #racecraft #learndriveoptimise #motorsports

[@hpa101]

Take $25 USD off ANY HP Academy course with this coupon: KZbin25 Enroll now: hpcdmy.co/25offytc - Taz 👨🏻

[@InitialDIYmods]

I can't like this video enough. Great job mate. Once I'm done with the engine setup at HPA, I really need to get the suspension settled 😁👍

[@ther1kid]

Okay! okay! Ill buy the courses! Well done.

[@hpa101]

haha cheers mate! Even if you don't our aim is to please, but appreciate the support nonetheless and hope you enjoy a deeper dive! 😎 - Taz.

[@michaelblacktree]

Perfect timing! I need to select spring rates for my project car. 👍

[@hpa101]

Perfect!

[@s4060]

Great video, you really explain things very easily! I’ve been racing for a good long while and it time to develop the suspension for the race car. Out of curiosity, what spring rate did you finally end up with on the SR86? Was it close to the ball park the calculations got you?

[@SLU2MOVIES]

You guys are nailing the course ☺️ Some day I'll go through them all In the mean time 😂 I'll slap my airbags on my tein suspension with edfc 😂 and hope for the best

[@hpa101]

#sendit haha We'll be here when you're ready! We all start somewhere 😎 - Taz.

[@zaydabbas1609]

Damn this course is legit, we use the same quarter car model in my control systems class

[@hpa101]

Cheers Zayd, hope you're enjoying your class too! What degree are you doing? Tim has drawn on resources here from his own studies at university as well as on the job as a motorsport engineer and packaged them into this specific course for ease of accessibility and reference 😎 - Taz.

[@zaydabbas1609]

@@hpa101 Thanks! I’m doing electrical engineering, having (not so much) fun with the closed loop tuning stuff, but it’s awesome to see the real deal in videos like these!

[@forgottenautos8461]

The angle of the shock can change the appropriate spring rate needed. Two cars that have the same weight ratios can have wildy different spring rates. Just something to think about in case you have a car that has a very high angle spring (0 degrees being vertical).

[@Owen-wg1md]

How did you find the frequency of the system?

[@akioasakura3624]

From where do the base frequencies come from? Why was 1.5-2.5 chosen for the low aero circuit car? I want to get to the root of the issue if you get me. Good video, thank u for uploading

[@gordowg1wg145]

Excellent introduction. With the spring rates, if one cannot find what one needs, two shorter springs can be combined to get what is required.

[@TranceFur]

Really? I’ve literally never seen a setup like that.

[@charlesshamseldin9555]

Fantastic

[@hpa101]

Cheers Charles! Glad you enjoyed this one - Taz.

[@charlesshamseldin9555]

@@hpa101 I'm a bit of a loon running race rates on the street 512/in fr 468/in rear but I prefer a stiffer set up; in addition to linear rate springs vs the more common progressive setup on the street

[@peejay1981]

This is giving me nightmares from uni calculating the undamped natural frequency of a system :-)

[@hpa101]

Sorry for the flashbacks haha Pain was worth the gain though hopefully! - Taz.

[@GP-fc7jv]

It looks like you are using a 86/BRZ for your example am I right?

[@johnterpack3940]

Wait, wait, wait... you can't just go putting up car videos that have actual numbers and engineering in them. You're supposed to talk about "fitment" and stuff. The way you're going, somebody might accidentally learn how cars work. Where would F&F be if the Vin Diesel fan club realized everything they grew up believing was wrong?

[@nathancupp1361]

Bro sounds so close to the guy who usually does these. I wasn't looking at the screen and thought he just had a cold.

[@hpa101]

hahaha. Gottem! Tim does the suspension and data analysis course content and as you can tell, he has a pretty thick Kiwi accent like Andre too 😅 Hope you enjoyed this one! - Taz.

[@enjoying_life49]

Great Video! I did not find the link for the cheat sheet. Can you help me find it?

[@rollingfilms1596]

www.hpacademy.com/assets/Course-Content/Suspension-Fundamentals/655e37b440/Suspension-Formula_CheatSheet_03.pdf

[@CallToGrid]

Googled for it and found it. Here it is. www.hpacademy.com/assets/Course-Content/Suspension-Fundamentals/655e37b440/Suspension-Formula_CheatSheet_03.pdf

[@Malficion]

I knew the ideal was 8kgf/mm F & 6kgf/mm R 😮 12kfg/mm F & 9kfg/mm R is way too high for a street car.

[@elitecol69]

When are you doing the g25 660 comparison?!

[@hpa101]

Mid 2022 Andre hopes 🤞 - Taz.

[@justinguarino201]

So if we are accounting for the driver being in the vehicle thus making the driver side weight more, does that mean I need to get 3 different spring rates? One for the driver side, one for the passenger, and then 2 of the same for the back? Don’t springs come in pairs? So I will end up with to extra spin tha both at a different spring rate? After my calculations, assuming I didn’t miss anything (using the 1.1 and 1.3 motion ratio, since I can’t find that anywhere on forums or dealer info for my car… a ~2800lb car is 900lb front driver wheel, 700lb passenger front wheel and 120lb rear. Now that doesn’t sound right because of the drastic difference from front to rear. Then again it’s about a 300lb difference from front to rear so maybe that’s why? Thoughts? From this, it makes it seem like my front will be stiffer than the rear. Is this because it would be front wheel drive?

[@hpa101]

No, you don't mix spring rates like that. Corner balancing is what you will do noting it is hard to get it perfect without building a car from scratch and physically mounting things correctly to offset weights side to side and front to rear. Even then, you pop a heavier or lighter drive in and its different again which leads to the fact that every single part and setup choice comes with some sort of compromise - Taz.

[@justinguarino201]

@@hpa101 Okay, I appreciate the response. After some research and feedback from others in the same platform using a similar type of driving that I will be (autox and daily/canyon driving), I am going with a 12k front and 16k rear (currently on a 7k front and 8k rear), so hopefully this will be much better moving forward.

[@__dm__]

4:41 -- omega is the angular frequency, not regular frequency, so the symbol should be "f"

[@hpa101]

The symbol Omega is used in the calculation of natural frequency (ω = √k/m) and we’ve carried the symbol through our calculations to represent natural frequency for consistency throughout the course. But you are right, we’ve converted from rad/s to Hz in the equation so we could have denoted that as f.

[@zaydabbas1609]

Ahh thanks, i was wondering the same thing

[@learysinsight9617]

Does 'un-sprung' include control arms and associated equipment?

[@johnterpack3940]

Roughly half-ish. Honestly, there's a bit of voodoo involved in deciding what is or is not un-sprung.

[@natansabillon9847]

Can I request your help to modify the shock absorbers for 1998 Mitsubishi SpaceGear?

[@hpa101]

If you think the suspension course applies to you and your application, sure. What form of motorsport are you racing your SpaceGear in though out of interest? 😎 - Taz.

[@mastercricket7626]

Ha ha I just always wne t for the stiffest possible and beefy swey bars and cage ect so as lil body roll as possible 😉 but that is also a good way to spin out constantly if not usta it lol ask me how I know 🤣💪🏽✌🏽 peace n love all stay safe build on and keep it radical

[@Bigelboe]

Why is the spring rate multiple by the MR squared, and not just the MR?

[@200mphgt40]

Because the travel of the suspension at the springs is reduced by the MR and also the force acting on the springs is increased by the MR. So you get two effects for the price of one, meaning you account for it twice by squaring the MR.

[@Bigelboe]

@@200mphgt40 thanks, great explanation

[@ttt69420]

Because it's a wave function. It "accelerates" and "decelerates" over an area of time. Like displacement, it's squared. All wave functions are squared whether in respect to time, or probability, or any other area that they displace. The short of it is that's what makes the math work. The long of it is explained in pre-calc / calc.

[@VinRZ]

Whats the effect on higher front frequency than rear? For example 2.2Hz front and 2.0 Hz rear

[@oxen8086]

like he said in the vid ur car will pitch(if u don’t know just look it up super easy) typically u want a flat ride set up which is rear Hz is higher then front, i use this for aggressive mountain driving an autocross helps the car settle better :) hope this helps

[@VinRZ]

@@oxen8086 Thank you man! Since I put in this comment 2 months ago, I started to do research on my own (Since HPAcademy didn't answer my question lol). Came to the conclusion that Flat Ride is great for street driving and track driving, fast settling etc. But I just started doing research on drift setups, drift bois tend to run the pitch setup, which it still baffles me.

[@oxen8086]

@@VinRZ also something to keep in mind is FRC% (front roll couple) i think higher the more over steering is an lower is more understeer,FatCatMotors has a vid on it with suspension answers as well 👍🏽

[@VinRZ]

@@oxen8086 Thanks! I have watched some of his videos. Though not 100% of his information is correct. I did get my hands on an excel spread sheet that will calculate my roll couple!

[@DehBassman]

Doesn't a motion ratio above 1 mean that the wheel has less than a direct moment of leverage on the spring? Wouldn't the equation need to be dividing by 1.1sq?

[@3.8gen]

ah so this is why I needed to take math classes

[@hpa101]

Might have been a bit more exciting if they used examples like this too 😂 - Taz.

[@3.8gen]

@@hpa101 yes XD

[@JasonHam41]

@@hpa101 ain’t that the truth, if my teacher had started talking about anti squat and roll axis rather than X and Y I’d have shown some interest.

[@geocell748]

I appreciate this video but your unspring weight was off by 1kg. 380 - 43 = 337 😆

[@DehBassman]

761.5/2 is 380.75. 380.75 - 43 = 337.75 then they rounded up to 338. Idk why they didn't just put the .75kg into begin with considering they showed the .5kg over both axles for the front total weight.

[@funkyd04]

Professionals don't use ride frequency to design race cars. Not since the 60's or so. Not even as a starting point.

[@akioasakura3624]

How do they do it? I want to learn

[@funkyd04]

They start with roll gradient. (degrees/g) And that can only be decided after you pick a tire. The tire is the 1st design consideration, everything comes after. @@akioasakura3624

[@ttt69420]

If she bottoms, she needs more spring. Simple as.

[@hpa101]

Actually you might be interested to learn that some setups will ride the bump stops, and you tune those as well 😉 Things that seem so simple have a way of not actually being all that simple at all. - Taz. www.hpacademy.com/blog/do-you-need-to-tune-your-bump-stops/? PS: This podcast with Andrew Wojteczko talks a bit more about some of the reasons behind bump stop tuning in class racing with fixed suspension restrictions: www.hpa-tunedin.com/1755412/9568537-015-squeezing-more-performance-out-of-your-race-car-with-awa-racing

[@ttt69420]

@@hpa101 I was merely jesting

[@hpa101]

ahh sorry! We get all sorts of comments that are serious so I err on the side of caution haha That said, still good links to check out if you haven't already anyway! - Taz.

[@ClaytonYatescarenthusiast]

I just want to say. This is good information but is useless for about 98% if not more people. I'm a very hard core time attack racer. I have corner scales and corner balance my car,do my own alignments and have a degree in mechanical engineering. I still don't have time to do this. Nobody is doing this.

[@hpa101]

No one is telling you that you have to do this, but for your 2% that want to, this is easily accessible information to help them. Not sure why you're upset about that and I'm sure I can find plenty of people having a crack at grassroots racing like you that would probably say the same about corner weighting. My answer would be the same regarding that as well 😎 - Taz.

[@TheDoctor46vr]

You don't know the difference in terms of lap time on track between the lowering springs and coilovers do you? I know it's a complicated question but I'm just looking for a reference point

[@hpa101]

No not something I can help with sorry, so many variables even down to the track itself. What is on your pros and cons list for both options and your application? - Taz.

[@TheDoctor46vr]

@@hpa101 application is for daily use with the occasional B road blast and track day. Lowering springs Pro •they're cheap Con •Lack of adjustment Coilovers Pro •Able to fine tune Con •The cost ps. If I went coilovers I wouldn't get fully adjustable because of the cost. Would be looking at basic ride height adjustment and camber. Something like perhaps the Bilstein B14 might be a good option but that's still $1000AUD more than springs. On a standard 1 min 30 sec lap for example (obviously tracks have more technical depth to them than an average lap time.) If it maybe gave me a second per lap quicker than mountune lowering springs on my ST180 I'd be willing, still not sure where I draw the line to be honest. I've only just started considering coilovers, I've been set on springs for months until now.

[@chinballs2]

Can anyone clear something up for me? At 4:40 is the calculation for the target spring rate, or wheel rate?