Spring Length affect on the suspension?

[Button]

Hey guys, I finally got my fenders rolled so I can now set the proper ride height but the problem I am running in to is that when I set the height where I like it the back of the tire is hitting the bottom adjustment rings of the coilover. I currently have 10" long springs but I am pretty sure if I went with 8" long springs it will clear. My questions is assuming that they are the same spring rate what impact if anything will going from 10" to 8" spring have? I could theoretically solve my problem by spacing the wheel out about another 1/4 of an inch but I already have 1/2" spacers on there and would prefer not to have to go even wider with spacers.

Some info if it's useful.
280zx Struts (I'm pretty sure they have been shortened)
Tokico Inserts - BZ3099 (MR2)
DP Racing coilover kit
10" Eibach 250lb springs
DP Racing 1" Knuckle Risers
195/50 R15 tires
15x7 +12 wheels

I also have a bonus question if anyone has experience. With 8" Springs I believe the springs will not be tight at full droop. I am assuming I should run helper springs (fully compress under normal load) to keep tension on the main springs during full droop. Anyone have any experience with these.

Thanks.

Chris

[Byron510]

The answer is simple, the longer the spring the more linear the spring rate over the same given traveled distance. That said, many of us run such stuff spring rates that our suspension barely moves! Making sure the shock can handle the frequency of the spring is really important and often overlooked on basic suspension set ups. It is best to run the longest spring you can.
That said, the 8” spring length is quite commonly used on our 510’s for just the reason you need them, for a compact package and tire clearance.

Regarding the helper springs, I have used them in the past and they do work great, but add height. I think my 2” tall ones compressed (at 75 lbs) to 3/4” height. But they do keep tension on everything when the suspension is unloaded.

Hope that helps.

Byron

[JordanTr]

I don't run anything longer than 8" because it limits clearance at the tire.

If all the stars align on the homebuilt coilover setups, you can end up with shortened struts and inserts, an 8" spring, the correct ride height, AND some preload on the spring. This is the optimum case as Byron stated. I ended up getting the above with flukey luck but earlier versions of my coilovers were not as ideal (the springs were totally unloaded and rattley at droop so they would have benefitted from helper springs).

Chris, FWIW my setup is as follows:
M30 Struts (shortened and 5 lugged with Z31T parts)
Tokico Inserts - BZ3099 (MR2)
GC camber plates
8" Eibach 275lb springs
1.25" Knuckle Risers (roll center adjusters)
215/40 R16 tires
16x8 +30 wheels (2.5mm spacer for aggressive)

You will be happy with that spring shock combo.

HTH

[JordanTr]

Longer spring means more travel before the spring becomes "solid" aka runs out of travel. With high (stiff) spring rates, this is not much of a concern on 510s.

An 8" 250lb/in spring and a 10" 250lb/in rate spring will be an unintelligible difference to the driver since the rates are the same. 8" is better for reducing unsprung weight yet it would suffer if you were building a rally car and needed the extra travel. 8" also gives more wheel clearance.

All you need to know about springs: https://www.engineersedge.com/spring_comp_calc_k.htm
Most springs we encounter would be 11.5-12,000,000 psi modulus of rigidity so you can measure the geometry and calculate spring rates and it works out well enough if you get your hands on unmarked springs.

[Button]

Thank you for the thorough responses Byron and Jordan it is very helpful. I have heard good things about the Tokico 5 way adjustable inserts so hopefully they will be a good pairing with the springs. I am going to order up the 8" springs and see how they work. I can always get some wider spacers and put the 10" springs back on if it's an issue down the road.

On a separate note I need to get bump stops for my coilovers and the shaft of the strut is 22mm wide, and I am having trouble finding a perfect size match for the bump stops. Does anyone know if it's ok if the bump stop holes are slightly under sized and I can press them on or if they are slightly overs sized if that's ok? Summit racing sell some that have 7/8" holes which equals 22.25 mm but I assume that with that extra space it will just slide up and down the shaft. This is probably a stupid question but I have never had coil overs before. Any advice?

Chris

[bertvorgon]

Just an FYI.... I ran the Tokico 5 ways in my Toyota GTS, where I duplicated the front of my 510 with #300 lbs springs...the Tokico's worked just fine.

As we have cold winters here, only change I did was soften them up in the winter and ran them at 4-5 for summer use.

[JordanTr]

Thank you for the thorough responses Byron and Jordan it is very helpful. I have heard good things about the Tokico 5 way adjustable inserts so hopefully they will be a good pairing with the springs. I am going to order up the 8" springs and see how they work. I can always get some wider spacers and put the 10" springs back on if it's an issue down the road.

On a separate note I need to get bump stops for my coilovers and the shaft of the strut is 22mm wide, and I am having trouble finding a perfect size match for the bump stops. Does anyone know if it's ok if the bump stop holes are slightly under sized and I can press them on or if they are slightly overs sized if that's ok? Summit racing sell some that have 7/8" holes which equals 22.25 mm but I assume that with that extra space it will just slide up and down the shaft. This is probably a stupid question but I have never had coil overs before. Any advice?

Chris

Glad to help.

I've pressed bump stops onto the stanchions with no issues. They just end up living high up.

[Button]

Thank you guys.

I bought some 8" front springs and swapped those out today and it sits where I want it to now and there is no rubbing. I eventfully would like to get some helper springs because I don't have tension under full droop.

So now that I have an extra set of 225# 10" springs should I swap those out for the 175# 8" springs that are on the rear coilovers? On the back I have some adjustable AGX shocks and 7/8" sway bar. On the front I will be running a 1" sway bar.

I have looked a bit and some people seem to match spring rates front and back (assuming they have coilovers on all 4 corners)and others seem to go a little softer spring rate in the rear. Some are running 300# in the front and 1200# springs in stock location (1200/3.8 = ~315# coilover equivalent in the back) but are not running a rear sway bar.

I am looking to have a fun canyon car, and occasional auto-x and track car so I am more interested in performance than daily cruising. So what do you think 225 or 175 in the rear?

Cheers.

Chris

[Byron510]

I am looking to have a fun canyon car, and occasional auto-x and track car so I am more interested in performance than daily cruising. So what do you think 225 or 175 in the rear?

Chris

Simple Answer - go take a drive!

Other than the shock being matched to the spring - just see how it drives with both.

When I've run springs that are too soft, it was especially noticeable on sweeping corners at Auto-X's where I'd squat the rear so much on the one corner that I'd pick up the opposite front wheel in the air and just carry it off the ground through the corner. Obviously the tire doesn't do anything in the air, that's a given.

Conversely, if the rear is too stiff, it'll tend to step out on you under the same cornering condition (scary!).

And then there is the ride quality you want.... I guess it depends on how you drive and what you want from the car. You have the bits - try both and go from there.

Byron

[Button]

Good advice Byron, and thank you for the description of the driving dynamics of having the rear suspension be too soft or too hard - that is good to know.

After 4 years of working on and off on the 510 it's getting pretty close to being driveable so for now I was looking for a best guess for the initial setup. Either way it's easy to swap out the springs so I will leave the 175's on there for now and test them once I get going to the point where I can drive it hard.

Cheers

Chris

[bertvorgon]

Also, go back and read in the "suspension thread" my/our discussion of shock/spring setups.

Maybe just start on this page..my posts..might give you some insight...

http://www.the510realm.com/viewtopic.ph ... &start=180

[funwithmonkeys]

I started out with 200 and 800 on my car and went to 300 and 1100 when my suspension was set up by Andy at Specialty. I have a 1 1/8" front sway bar and no rear bar. I really did not notice a lot of difference in the ride other than the fact my suspension would no longer bottom out on bumps in hard corners. When that happens it can be a bit scarry. A good adjustable shock will let you change the feel of the car as you go between autox/canyon carving/toodling around. It doesn't take much of an adjustment on the shock to really change the feel. My suspension gets near to bottoming out as it is now with the heavy springs. I would try it with the 225s and go through some corners with some bumps. I did this a bunch when working with my front sway bar that was bottoming out. The difference when the suspension never bottoms out is amazing. You know how your car is going to react. When the suspension hits bottom you can't predict what it will do.