Minimum spring rate for 1 inch drop = prokits are a bad idea?

[hsk8te2006]

Ok, so I've read that it's important to make sure that if you lower the car, you increase the spring rate by at least the ratio of the old suspension travel to the new, so that it still takes as much force to hit the bumpstops.

Not being able to find or easily measure my suspension travel right now, I'm estimating with the distance between the top of my tire, and the bottom of my fenderwells.

1) Is that an ok way to estimate current versus future suspension travel limits?

Assuming that is true, and assuming that the stock 2g spring rates are approx. 260/173 (FWD), then a 1 inch drop would require minimum spring rates of 390 Front/ 260 rear.

2) Considering that Eibach prokits lower the car 1.3 inches, and only have spring rates of 330/260 (instead of the 450/300 needed for a drop from 3 inches travel to 1.7 inches travel), am I correct to say that the pro-kits are a bad idea?

Also... I read ina thread that the H&R OE sports are around 15-20% stiifer than stock, however with a 1 inch drop, they would be nowhere near the 50% increase of spring rate needed, so would the same argument hold?

 

[asian312]

Can't help you on the math, but I know the H&Rs work just fine both on the street and just fine. With the stock sized tires and wheels I never had any issue of bottoming out. Also your suspension has bump stops for that very reason. They are there to stop the travel in the event there is too much.

 

[hsk8te2006]

My point is I am trying to keep my car off the bumpstops, and I would like to make sure that whatever spring I get makes it just as hard for me to hit my bumpstops as it was stock.

 

[wret]

Your math makes sense, which is why most would trim the bump stops. Both the Pro-kit and H&R OE Sports are well-proven. They are probably the #1 and #2 most often used lowering springs for street DSMs.

 

[hsk8te2006]

How hard is it to trim the bumpstops?

Is it just safer to go with a stiffer spring coilover sleeve?