need spring rate help

[Guy G]

Hello all
Need some help
Gen 2 HR, IRS, SBC
Current spring rates...400 LB front, 8"
300 LB rear, 8"

Very stiff ride
Aware of benefits of QA1's, Just want to keep the budget in check

Should I be looking at lower spring rates and longer springs? IE 10", 200 lb rear and maybe 10" 300 lb fronts?

Thanks

[progmgr1]

The following are copies of various Forum threads about spring rates for the '33. I haven't verified anything, and the prices shown are probably obsolete. Some threads are for rear ends other than the IRS, but you can see the general trend. I got my springs and shocks from Dan Ruth and don't know the spring rate. One of these days I'll measure and calculate the rates, but not today.

1) I'm using a variable rate spring from QA1 (175-350 #/In range) which gives a bit softer ride in a straight line but is progressive as the car corners (much like an anti-sway bar). I think the best ride/comfort/handling would come from less spring rate at all four corners and the addition of front/rear anti-sway bars

2) New configuration - The car is at the same height. Rear Shocks - QA1 DS702, ($170 @ Summit)16" ext ( within recommended envelope), 12" 200 lb/in springs with 1" spacer. The spacer helps clear the shock mount on the axle. Front Shocks - QA1 US 502 13 1/2" ext ( only 1/4" shorter that recommended envelope) , 10" 325 lb/in springs. The shocks are all set 4 clicks from softest at this time. The ride is still very firm, but it handles the frost strips, shallow potholes and pavement undulations very well at all speeds. It leans a little in the corners, but not much and is very acceptable for spirited street driving. The car launches, corners and stops better also.

3) Thread on springs / shocks for the '33: https://thefactoryfiveforum.com/showthread.php?40563-Koni-Shock-Spring-Rates&p=465442#post465442 (IIRC, this was a recent thread that got inputs from a lot of builders, some with the IRS)

4) I have the IRS and have left the rear springs stock; believe they are 300. The front went down to 250. Really happy with the result for cruising.

5) I switched to different spring rates & adjustable QA1 shocks on the 33 a couple years back and do not regret it at all. I'm running 9" 300# springs in the front with dual adjustable (rebound & compression) PromaStar shocks in the front (inverted for easy adjustment) and in the rear I'm running 12" 150# springs (recently changed from the 12" 300# I was running) with single adjustable (compression) PromaStar shocks.

6) Kim @ MCBParts.com sold me QA1's cheaper than anyone else. kim@mcbparts.com (If you try softer springs and still aren't satisfied)

HTH Keith HR #894

[Guy G]

Thank you for the insights. I think they will get me in the right direction!

[Dgc333]

FWIW, my 33 Speedstar has a 3 link solid axle. The stock rear springs were 250 lb/in. I found them to be jarringly stiff over anything but glass smooth roads. I dropped down to 175 lb/in springs, these made a very noticeable improvement but are still stiff. I also went from the stock 8" long springs to 10" long springs. I have 305/35-20 tires in the back and with the 8" stock spring to get adequate ride height the preload was getting close to the top of the adjustment range. I went with the longer softer spring to ensure I wouldn't run out of preload adjustment.

I have a heavy iron block Gen 3 Hemi in my car, the stock 400 lb/in spring is not jarring so I have not been motivated to change them.

I also have the standard chrome Koni shocks. These are adjustable but require removing the eyelet and bump stop to allow the shaft to be compressed in far enough to engage the adjuster. I plan to take them off this winter figure out where they are set and go softer on the setting.

My car is a cruiser so ride comfort is much more important than handling. Dave Smith had told me they have Koni set them up for handling.

[Guy G]

I guess with the research I have done, and the help from this forum, The longer springs are in my future along with significantly dropping spring rates.
Thanks for the help!

Guy
HR 1358