Spring Length Question - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

Captain Snooze · 09-29-2014, 06:30 AM

Hypothetical question.
What's the difference between fitting a 5 inch spring and a 6 inch spring of the same rate with the spring perch 1 inch lower?
Assumes that the spring perch has adequate adjustment and the spring is fully seated at maximum droop.
Ta.

DougW · 09-29-2014, 09:54 AM

1 inch.
DougW

Fizz · 09-29-2014, 11:10 AM

1 inch less bump travel?

Wepeel · 09-29-2014, 12:33 PM

The longer spring will provide more travel before coil bind. May or may not be an issue depending on the setup. Also the 6" spring will be marginally heavier, if that makes a difference to you.

wparsons · 09-29-2014, 12:40 PM

Quote:

Originally Posted by Wepeel

The longer spring will provide more travel before coil bind. May or may not be an issue depending on the setup. Also the 6" spring will be marginally heavier, if that makes a difference to you.

This! I doubt that coil bind is going to be an issue with either free length on these cars though, unless you're running really low spring rates.

Racecomp Engineering · 09-29-2014, 01:01 PM

Quote:

Originally Posted by wparsons

This! I doubt that coil bind is going to be an issue with either free length on these cars though, unless you're running really low spring rates.

5 inches is a pretty short spring though...I wouldn't run them on a KW for example.

- Andy

Wepeel · 09-29-2014, 01:15 PM

Quote:

Originally Posted by Racecomp Engineering

5 inches is a pretty short spring though...I wouldn't run them on a KW for example.

- Andy

Yeah, 5" is kind of short. Maybe if you had a damper with crap travel and ran super low it would work.

I was wondering this - what do you guys assume for bump stop compression? I'm assuming "fully compressed" is about 0.5" of the free length, but I'm thinking it might be longer than that.

Racecomp Engineering · 09-29-2014, 01:30 PM

Quote:

Originally Posted by Wepeel

Yeah, 5" is kind of short. Maybe if you had a damper with crap travel and ran super low it would work.

I was wondering this - what do you guys assume for bump stop compression? I'm assuming "fully compressed" is about 0.5" of the free length, but I'm thinking it might be longer than that.

Depends on the bumpstop of course and sometimes that data is available.

For the purposes of avoiding coilbind we typically assume a much larger % of the bumpstop can be compressed.

- Andy

Fizz · 09-29-2014, 01:36 PM

This thread is boring without the expert opinions of Ubersuber....

wparsons · 09-29-2014, 01:57 PM

Quote:

Originally Posted by Racecomp Engineering

5 inches is a pretty short spring though...I wouldn't run them on a KW for example.

- Andy

Because of their spring rates, or because of their shock design?

Quote:

Originally Posted by Wepeel

Yeah, 5" is kind of short. Maybe if you had a damper with crap travel and ran super low it would work.

I would think it depends more on how much the spring is compressed between free length and static ride height than anything else, which is mostly going to be driven by spring rate.

Racecomp Engineering · 09-29-2014, 02:26 PM

Quote:

Originally Posted by wparsons

Because of their spring rates, or because of their shock design?

I would think it depends more on how much the spring is compressed between free length and static ride height than anything else, which is mostly going to be driven by spring rate.

KWs have a lot of available stroke. Yes if they're slammed it's not a lot of bump travel. But at a realistic ride height you have a good amount of bump travel...probably more than the a 5 inch spring has before it binds (which is a problem).

- Andy

wparsons · 09-29-2014, 03:40 PM

Quote:

Originally Posted by Racecomp Engineering

KWs have a lot of available stroke. Yes if they're slammed it's not a lot of bump travel. But at a realistic ride height you have a good amount of bump travel...probably more than the a 5 inch spring has before it binds (which is a problem).

- Andy

Ah, gotcha. My thought was that with stiffer springs you're running less pre-load and will run out of damper stroke before running into coil bind. Guess it really depends on how much stroke you have and spring rate.

Wepeel · 09-29-2014, 09:48 PM

Yep, the kw have about 5.6" of total damper stroke in the front. With my ride height 1" lower than stock, using a 7"/7k spring, I actually only have 0.12" of margin before coil bind (spring travel left when the damper is fully bottomed), assuming 50% bump stop compression. I was surprised to see it was that close.

If I dropped to 1.5" lowered I'd have 0.5" before coil bind.

I should probably lower the car a bit.

09-29-2014, 06:30 AM	#1
Captain Snooze Because compromise ® Join Date: Jan 2012 Drives: Red Herring Location: australia Posts: 7,817 Thanks: 4,047 Thanked 9,548 Times in 4,194 Posts Mentioned: 60 Post(s) Tagged: 0 Thread(s)	Spring Length Question Hypothetical question. What's the difference between fitting a 5 inch spring and a 6 inch spring of the same rate with the spring perch 1 inch lower? Assumes that the spring perch has adequate adjustment and the spring is fully seated at maximum droop. Ta. __________________ My car is completely stock except for all the mods.

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09-29-2014, 09:54 AM	#2
DougW Senior Member Join Date: May 2013 Drives: FR-S stock for now Location: SC Posts: 160 Thanks: 3 Thanked 171 Times in 81 Posts Mentioned: 10 Post(s) Tagged: 0 Thread(s)	1 inch. DougW

09-29-2014, 11:10 AM	#3
Fizz Senior Addict Join Date: Jan 2013 Drives: 86 GT Location: Perth, Australia Posts: 1,217 Thanks: 249 Thanked 336 Times in 215 Posts Mentioned: 12 Post(s) Tagged: 0 Thread(s)	1 inch less bump travel?

09-29-2014, 12:33 PM	#4
Wepeel Senior Member Join Date: May 2012 Drives: '13 BRZ Ltd Location: PA Posts: 458 Thanks: 265 Thanked 230 Times in 117 Posts Mentioned: 8 Post(s) Tagged: 0 Thread(s)	The longer spring will provide more travel before coil bind. May or may not be an issue depending on the setup. Also the 6" spring will be marginally heavier, if that makes a difference to you.

09-29-2014, 01:36 PM	#9
Fizz Senior Addict Join Date: Jan 2013 Drives: 86 GT Location: Perth, Australia Posts: 1,217 Thanks: 249 Thanked 336 Times in 215 Posts Mentioned: 12 Post(s) Tagged: 0 Thread(s)	This thread is boring without the expert opinions of Ubersuber....

09-29-2014, 09:48 PM	#13
Wepeel Senior Member Join Date: May 2012 Drives: '13 BRZ Ltd Location: PA Posts: 458 Thanks: 265 Thanked 230 Times in 117 Posts Mentioned: 8 Post(s) Tagged: 0 Thread(s)	Yep, the kw have about 5.6" of total damper stroke in the front. With my ride height 1" lower than stock, using a 7"/7k spring, I actually only have 0.12" of margin before coil bind (spring travel left when the damper is fully bottomed), assuming 50% bump stop compression. I was surprised to see it was that close. If I dropped to 1.5" lowered I'd have 0.5" before coil bind. I should probably lower the car a bit.

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