Spring rate matching

[noneofyourbusiness]

If one were to be running front and rear coil over kits on their 510 2 door, would one want the spring rates to match front to rear or would the rears be different? Different higher or lower?

I'll be running GC fronts with kyb agx inserts and T3 rears with the AGX shocks.  Intended use is daily driver on a twisty road, daily driver period and some auto crossing. 

TIA

[Kelvin Dietz]

Coilovers are slightly different, front to back.  The back is usually lighter rate by maybe 25#.  I forget the math, but the location of the shock mount in relation to the wheel makes this work. 
Of course, this is a assuming you don't have a fat motor up front.  My VG30 ran 225 up front and 175 in the rear.  Adjustable Quickor rear bar let me tune it.

If you ran identical springs you might find a bit too much oversteer.  Also might be something you could tune out with sway bars adjustment and tire pressure. 

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[Jordan B]

250# in the front 275# in the rear. Rear sway bar disconnected. I haven't tried AGX, hopefully they are good, all the other KYB I ever tried rode like generic parts counter shocks. Koni race inserts are my favorite.

These rates are actually pretty soft compared to what most "modern"  sporty cars run. It's all about having a good shock to control the movement, I have ridden in a 510 with 350# coilovers in the back, it wasn't bad either.

Low cars don't have much travel, and bottoming out the suspension can make for a wild ride. 

Jordan B

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[Gary Savage]

The biggest issue is shocks that can handle the spring rates.  The Tokico Illuminas are said to only be good for about 250# and that is maxed out.  The Koni Sports are good to 300#.  I just took out the Illuminas and installed the Koni Sports with 250 F/R on my 2600 lbs 280Z because I didn’t care for the ride with the Tokicos.  I only have a couple trips up & down the road, so not much drive time, but the ride is better with the Koni shocks so far.  If you go near or over 300#, then the high dollar Koni race shocks are required.  Of course, a 510 is 20% lighter, so you can go with lighter springs and modern sports cars often weighing a good half ton more than a 510 would require higher rates.  Also, a coilover on a 510, because the shock sits farther out than the axle line, you add 20% more to the spring rate to get the actual wheel rate, unlike the fronts that are actual.  

Gary Savage

On Sep 1, 2021, at 11:06 AM, Jordan B <vg30...@gmail.com> wrote:



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[noneofyourbusiness]

No idea if the AGX are any good relatively. I have been running KYB GAS ADJUST shocks and struts on my everything and have been very happy with them. AGX being their higher end products I am HOPING they are even better than the GAS ADJUST product line.  This is all of course, relative. What one person likes, another person hates.  Mostly I was looking for a starting point on spring rates for the rear coilover conversion. I do have a 3 way adjustable rear bar that I am planning on running as well in the hopes of not having to run a super stiff spring to get the same results.

[Kelvin Dietz]

If you're serious about getting the rates close you need to weigh your car, front and back.  Sprung weight and wheel base are where you start.  The, as Gary said, the front springs are directly over the wheels so that's a 1:1 ratio. 

The rear mount is behind the wheel so I remember it being 90% of the front.   Gary suggests 80% of the front. 
It's been 25 years since I've done these calculations.  I'm not a math guy but I worked with math guys.  When all was said and done the Smurf with a VG was the best handling street car I ever had. 

Later I applied all this data to a L18-powered 2dr - and then THAT was the best handling car I ever had. 
2100# for the L18 car.  #2450 for the Smurf. 

https://www.drtuned.com/tech-ramblings/2017/10/2/spring-rates-suspension-frequencies

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[Ted Hedman]

Both of my 510s run 225# fronts, and rear wheel rates are ~200# on the L20b car and ~225 on the SR20DE car. Not running coilovers in the rear of either car, but for comparison purposes, it's wheel rates that matter.   Koni Sports all around on both cars, and both have Quickor adjustable rear bars. The L20b car has a 7/8" front bar, while the SR car has a 1" front bar. 

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[Kelvin Dietz]

I am a big believer in a 7/8" front bar on an L-series power car.  I've hoarded them for years but I think I'm fresh out.  And nobody makes them anymore.  I'm almost positive I found an 7/8" OEM bar on a wagon, though. All the bits looked very stock.

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[noneofyourbusiness]

Yeah I figured as much but I need a starting point. I can fine tune from there.

Thanks to everyone so far!