To section or not to section? (have read FAQ)

[BrandenZ]

My understanding is that if I do not intend to lower my car more than 2 full inches of suspension travel (as opposed to ride height), I probably don't have to worry about sectioning my struts. I've taken several measurements and combined them with some guesstimates, and wanted to post them to ensure correctness and also to gather opinions from those more seasoned than myself.

 

*All rear of the vehicle

Previous configuration:

Stock springs, stock struts, 215/60/14s

 

Future configuration:

10" Hypercoil springs, 250in/lbs, Tokico Illuminas, MSA Coilover kit, 245/45/16s

 

Presumptions:

14" factory springs, estimated 125 in/lbs, 2300lb car, 575 lbs per corner, yielding:

14" no tension

9.4" compressed

using factory perch

 

New configuration:

10" no tension

7.7" compressed

given that the lower adjustable perch (not the welded perch) sits exactly where the factory perch used to sit

 

This equates to essentially 1.7" lower than stock at the same relative perch height in regards to suspension travel.

 

Factoring in the new tires/rims, which are 1.25" heigher than the previous rims, this yields a literal ride-height difference of ~1.025" lower than the previous configuration.

 

If all of my faux-math works out, I believe this will be an ideal ride-height for this set of parts. What I'm concerned about is the 1.7" of reduced suspension travel and whether or not I'll be at a risk for binding / bottoming issues. I do intend to track and autox the vehicle.

 

Please feel free to chime in and bash any of my estimates. Unfortunately I did not do any sprung or unsprung measurements prior to disassembling the entire rear. My gut tells me I should likely section the struts at least 1-1.5", but despite having a buzzsaw and welder at my disposal, I'm still rather uncomfortable with the idea of doing it to all 4 corners. However, I'd rather attempt it as opposed to losing my car at 100mph due to suspension travel issues.

 

Thanks in advance for any and all advice!

[johnc]

What I'm concerned about is the 1.7" of reduced suspension travel and whether or not I'll be at a risk for binding / bottoming issues. I do intend to track and autox the vehicle.

 

The stock shocks and most aftermarket shocks that work in the 240Z strut tubes have 5 to 6" of total travel. At static ride height the shocks are typically in the middle of their range of travel which gives 3 to 3.5" of bump travel. If you're losing 1.7" of that, by your math, you will have (at best) 1.8" of total bump travel assuming no bump stops.

 

IMHO, that's right on the border of needing to shorten the struts for a street driven car. You will need to run a bump stop of some kind which means you'll end up with .3 to .8" of free bump travel before you're into the bump stop. It they are the nice, progressive Koni bump stops, you'll be OK. If they are the standard urethane bump stops its going to suck when you hit a medium sized bump.

Edited January 11, 2010 by johnc

[BrandenZ]

Thanks John! I'll look into the Koni progressive bumpstops, and also measure the Strutmates replacement bumpstop that I have on the ready. Based on what you mentioned, it sounds like sectioning is going to be the safer route to take, regardless of how much I fear having to source a 240z hub and strut tube assembly if it doesn't go well!