Some coil over questions

[Nguyen Nguyen]

Hello,

Hopefully you guys don't mind a couple of "dumb" suspension question. I am looking at a couple of coil-over and lowering options. Some shocks has built-in threads on the outer body. This allows an adjustable ring to which the coil rests on. Other shock has a threaded sleeve fit over, then the ring screws onto the sleeve. How is this sleeve stay secure to the shock with 1/4 of the weight of the car rest on it? Is there any wobbling with this set-up? Lastly, what is the down side of cutting the OEM spring just to lower the car? THanks.

- Nguyen

 

[nsxtasy]

Originally posted by Nguyen Nguyen:
what is the down side of cutting the OEM spring just to lower the car?

I've heard that this is a very bad idea because it gives you very little control regarding the progressivity and rebound rates, etc.

 

[matteni]

Originally posted by nsxtasy:
I've heard that this is a very bad idea because it gives you very little control regarding the progressivity and rebound rates, etc.

Ken is again right!

I would recommend filling the trunk with cement before cutting springs on a NSX. The best way to lower your car would be with shorter springs but that does not mean yanking them from under the car and cut 'em off with a torch. When a spring gets shorter, the rate will decrease, meaning that the spring will be "softer". The general rule is the spring rate should be increased 15 percent for every inch of drop.

So if the stock springs are rated at 300 lbs/in and you shoot for a 2 inch drop the new spring rate should be 390 lbs/in (roughly). You would also have a problem with the suspension bottoming out.

I would also recommend from personal experiance against getting engineered lowering springs without changing to a better matched set of shocks that can keep up with them - or again - you will not be able to effectively control dampening of the springs and you will be bouncing down the road!

Good luck!

------------------
Nick M

91' Red/Black with Many Mods
99' Honda Odyssey with Many Kids

[This message has been edited by matteni (edited 18 March 2003).]

 

[sjs]

OK, it's been a long time since I had to resort to cutting springs on an old Datsun and I’m no mechanical engineer, but I think the bit about a spring getting softer when cut is misleading. Ignoring progressive rate springs for a moment, if you cut off a few coils then your effective rate should probably go up, not down. Try pressing on the top of a spring and see how much you can compress it. Then slide something through the coils a couple turns up from the bottom and apply the same force. I think you will compress each of the remaining coils the same amount per coil, and therefore less total compression. In other words, it seems stiffer because the same force moves it less. No? With progressive rate springs it would depend on the specific design and where you cut.

As for the advisability of such approach, I would agree that it just doesn't make sense given how affordable replacement springs are. One of the risks of shorter springs is bottoming out a shock and damaging it, so even if handling isn't high on your list of priorities it is important to correctly match springs and shocks.

 

[RyRy210]

I would just lower it with bilstein shocks and keep the OEM springs. It has the option to lower the car 0.8 inches on the lower perch. You can also have bilstein machine in extra perch grooves at $10 per groove. It can only be done in 10mm increments (.4 inches).

Shocks is something you have to eventually change out anyway, so why not change them to a performance shock that offers height adjustment and a lifetime warranty? Why resort to cutting or doing something that could be potentailly dangerous and/or harmful to your car?

Just my 2 cents.

 

[matteni]

Originally posted by sjs:
OK, it's been a long time since I had to resort to cutting springs on an old Datsun and I’m no mechanical engineer, but I think the bit about a spring getting softer when cut is misleading.

I agree - now that I read my post again that it is misleading that "softer" = spring rate.

The important things are the mismatch you would create between the spring rate and the shocks, putting the suspension out of geometry (can you say "bump steer"), and the cars reduced ability to keep from bottoming out.

Wasn't my intention / thanks for pointing that out.

------------------
Nick M

91' Red/Black with Many Mods
99' Honda Odyssey with Many Kids

 

[Nguyen Nguyen]

Many thanks you guys. Just a couple more questions ;-).

Bilstein and stock spring: For this combination, do the spring move around as the car goes over pot holes and curb? Is this what helper spring do (keep the main spring from moving around)?

Bilstein and Eibach: Same question for this combination.

Many thanks again!

- Nguyen

 

[matteni]

Originally posted by Nguyen Nguyen:
Many thanks you guys. Just a couple more questions ;-).

Bilstein and stock spring: For this combination, do the spring move around as the car goes over pot holes and curb? Is this what helper spring do (keep the main spring from moving around)?

Bilstein and Eibach: Same question for this combination.

Many thanks again!

- Nguyen

I am not sure what you mean by "helper spring"? There is a shock and a spring. The springs are progressive and have been engineered so that part is "thicker" then other parts - but I don't know of any that work with 2 springs. I have used stock, H&R, and eibachs.

 

[Larry Bastanza]

Nguyen,

Helper springs are not required for the Bilstein/OEM spring setup. Helper springs are normally used with very stiff main springs that are short. Therefore when the suspension is in full droop, there is actually a gap between the spring top and the upper spring perch (the spring is loose). This will make them slap around in there. The helper spring is a very light spring just to take up the slop in this type arrangement.

This is typically seen is race suspensions with extremely stiff springs like the Comptech Pro Kit. I think there is a good picture on at www.comptechusa.com if you want to see these.

In regard to your question about the threaded body vs. an add-on threaded sleeve, go here: http://www.daliracing.com/v666-5/catalog/index_browse_part.cfm?focus=715 and look at the lock screws at the top of this setup available from Mark Johnson.

I would keep in mind that this setup would be used ONLY if you really want to corner balance the car, as in race setup, where you are trying to gain 10th of a second off your lap time, as an example. Also the car will need to go on scales to have the height adjusted properly. The NSX is pretty well balanced as is for the street, even aggressive street.

I would spend a lot more time and money on driving school, before I would spend on adjustable suspension, unless of course you are keeping up with the likes of Andrie and others in the OTC race team

.

HTH,
LarryB


[This message has been edited by Larry Bastanza (edited 20 March 2003).]

 

[Nguyen Nguyen]

Ooops, I post before seeing your post. Thanks Larry & Nick.

- Nguyen

Hi Nick,

I found an FAQ thread about suspension and I THINK it confirms that the helper spring keeps the main spring in place whenever the suspension unloads.

I just thought of another question, does coil over set-up enables corner balancing easier?

Thanks.

- Nguyen



[This message has been edited by Nguyen Nguyen (edited 20 March 2003).]