Cage match: RPM Sport Springs vs. 3-fat-asses

[speedie6]

Not sure if the silly thread title will help or hurt responses... Here's what I'm really trying to say. I've got RPM Sport springs on my car with Bilstein shocks. I like them very much. I just bought some 225 wide tires, 7.5" wheels, 48 offset. I hadn't noticed any rubbing, but, I'm probably going to get fenders rolled. Well, to be more specific, I hadn't noticed any rubbing until yesterday. I'm not a little guy, around 225 lbs. I had two passengers yesterday. They are real fat asses, in the 275 lb range or so. So, we're talking 750lbs+ in passengers.

So, I start to drive off, and, something is dragging. I thought my brakes were screwed up and dragging. So, the other two guys get out, and no problem. It seems that the weight caused the tires to rub the fenders. Now, I know that's a lot of weight. But, with nobody in the car, the Sports don't lower the car much from stock and there is still several inches of clearance from the tire to the fender if the car is just parked. If I get in it, just by myself, I don't seem to compress the springs too much. Still looks like lots of room. So, I was surprised that the additional 550 lbs or so of the other two guys would compress the springs so much that the tires would hit the fender.

So, for one, while I don't mind getting my fenders rolled, I'm a bit surprised I need to. I thought that the specs I gave (225 tires, 7.5" wheels, 48 offset), I didn't think there would be a fitment issue. But, the primary question for this particular post is, should the RPM Sport springs have compressed that much with the weight I'm talking about? Sure, with that much weight, I can imagine the springs compressing a lot whenever hitting a bump. But, just pulling out of a parking space, I didn't expect that much compression. Or are we just too damn fat?

[fireguy1578]

Roll the fenders. That wheel and rim combo along with your springs will cause you to rub with a lot of wieght or big bumps.

[falcontx]

Yeah, ultimately, this has nothing at all to do with the springs. When installing new rims/tires, you should check to ensure that they can travel throughout the entire range of the suspension without hitting anything. If they can not, then it will just be a matter of time before you have problems, regardless of the springs/shocks you are using.

[speedie6]

I was just a little surprised that the springs compressed that much. But, no biggie, I'll roll the fenders. Thanks for responding falcon & fireguy.

[falcontx]

QUOTE (speedie6 @ Sep 9 2008, 04:27 PM)

I was just a little surprised that the springs compressed that much. But, no biggie, I'll roll the fenders. Thanks for responding falcon & fireguy.[/b]

Well, you can use the spring rates to determine what should happen, in theory, when the weight is added. The rear springs have a spring rate of 250 lb/in, which means that they will compress 1 inch for every 250 lbs that they have to support. If you placed 750lbs in the very center of the car, that weight would be equally distributed among the 4 springs, so each spring would be supporting 187.5 lbs. 187.5 divided by 250 is 0.75, which means that the rear spring would compress 3/4" with all 3 of you.

Now granted, your weight is probably not exactly centered between the 4 springs, but this should give you an idea of what to expect.

[speedie6]

QUOTE (falcontx @ Sep 10 2008, 01:59 PM)

Well, you can use the spring rates to determine what should happen, in theory, when the weight is added. The rear springs have a spring rate of 250 lb/in, which means that they will compress 1 inch for every 250 lbs that they have to support. If you placed 750lbs in the very center of the car, that weight would be equally distributed among the 4 springs, so each spring would be supporting 187.5 lbs. 187.5 divided by 250 is 0.75, which means that the rear spring would compress 3/4" with all 3 of you.

Now granted, your weight is probably not exactly centered between the 4 springs, but this should give you an idea of what to expect.[/b]

Okay, well, based on that, we should not have come anywhere near compressing the springs enough to hit the fenders. With nobody in the car, there is at least 2 inches between the tire and the fender. I guess I need to rerun the experiment. Perhaps something different happened. I just kinda figured it had to be the fenders rubbing given that as soon as they other guys got out, the drag went away.