Coil over spring question

So when I installed adjustable camber & caster plates on my XR4Ti, I also installed a set of 350 lb / 9" coil over springs. I previously had a set of 275 / 10" springs.

Well, for the roads here in the Chicago-land area, it's a bit rough. Not semi truck rough but rougher than I would like it to be.

So would I notice a difference dropping back to 325 springs or should I go down to 300 lbs springs? Can you tell a difference by making a 25 lb change in the springs? I went to the 350's to combat body roll during autocross but am now second guessing myself. It does corner much nicer but hitting the frost heaves and potholes has my fillings coming loose.

I use the car as a daily driver in the summer and also autocross it.

Did you change shocks when you changed springs? If not, you're underdamped now, plain and simple. Getting shocks with the damping to match the new spring rates could help a lot.

350# springs are really not THAT stiff. Especially on a 3,000 pound car. GameboyRMH is right, sounds like shocks are needed.

I've got Koni Yellow strut's on it and increased the rebound to compensate for the stiffer springs but there is no comp adjustment on them.

Well then! I recommend you move south.... no frost heaves. But we do have this when the weather forecast calls for snow......

https://www.youtube.com/watch?v=i6zaVYWLTkU

A 25# change in spring will not make much difference in ride quality.

25# increments will make a difference when you are dealing with spring rates that low. Sometimes you need to circle the wagons to find what you are happy with. 300 to 325 is going to seem like a bigger jump than going 900 to 925. I have several TR8s with spring rates between 200 and 300. Huge differences between them.

^^Yep--consider the % change more than the absolute number. Why not just have a "winter" set (in the 200s) and a "summer" set (in the 3-400s)?--that is the beauty of coilovers.

Ok, I'll look into getting another set of springs. Maybe get some 300's and toss in the slightly larger front anti-sway bar.

No winter driving for this car. Took too long to find a rust free one and I'd like to keep it that way.

We run 250s x 7in in the front of our XR4Ti on old koni reds and 600lb x8.5in in the rears and drive on the street to and from autox and road racing, its very nice on the street but a bit soft on track handling hard transitions. Stock is like 100-125 up front...

So will the length of the spring make a difference? Like a 250 x 7 will be stiffer than a 250 x 10?

I know it shouldn't matter but I wonder if it does?

Length can only make a difference in ride quality if you're bottoming out/hitting droop limit, or if the shocks have different damping at different points of travel (usually only high-end offroad shocks have this).

I'll throw this in; I subscribe to the mindset off softer springs bigger bars. Because I pound over the kerns on track I prefer to keep the suspension compliance but that of course leads to the dreaded body roll.....hence the stiffer anti roll bars. For me seems to be the best of both worlds.

    Tom

Tom1200 wrote: I'll throw this in; I subscribe to the mindset off softer springs bigger bars. Because I pound over the kerns on track I prefer to keep the suspension compliance but that of course leads to the dreaded body roll.....hence the stiffer anti roll bars. For me seems to be the best of both worlds. Tom

I wouldn't say it's the best of both worlds (it does nothing for dive/squat, for one) but it's definitely a great compromise between comfort and performance.

From a pure performance standpoint, hard as hell springs + no bars is theoretically best, but in practice it's usually stiff-ish springs + soft/medium bars because otherwise the driver's teeth won't stay in

FRICS is the best of both worlds. You can tell because it costs all the money

You mention going to colilover springs. Does that mean the springs were previously offset? If so, don't forget that the effective spring rate can change quite a bit when going from an offset perch to a coilover.

Edit - sounds like this is front so probably not.

My money would be on changing to a better shock. I like the soft springs/big bar thing as well but some cars don't respond well to that technique.

@GameboyRMH on our D-Sports the car had no anti roll bars, the car was 72" wide the chassis was maybe 18" wide but the A arms radius rods etc. were quite long; we'd run the car as soft as possible because anything lost due to the dive under braking was gained back because of the suspension compliance. You can tune the shocks to work with the set up. Note the car pulled 3Gs on the brakes and I set the lap record with it, so you can make this work very well. By virtue of instructing I have hopped in a lot of cars that are rock hard, yes they give instant feedback but they tend to be skaty and give up grip earlier than softer sprung cars. Driving style does factor into this as well, if you slap on the brakes like you are in a winged single seater than the stiffer springs will work better but (personal opinion) that doesn't work so well in door slammers. I have driven some cars that work well sprung like a kart but 90% will turn faster lap times if you run them towards the soft side. When I say soft with bigger bars I am talking 275# springs versus 315# and bigger bars being 25mm versus 23mm etc. As an example on my road race Datsun 1200 front springs are 225 rears are 135 with front /rear bars being 7/8ths & 5/8ths. The car is 1830lbs (I'm 140) and belts out a whooping 95-100 whp. The set up is straight out of the Nissan Comp manual. With all that said the set up has to work for the driver, my motorcycle road racer background tends to bias me toward a car that oversteers. I have raced against people who prefer a car with ever so slight understeer and go figure we set identical lap times. OK back on the topic of said Merkur, I would go with the slightly softer spring and get some dampers that you can adjust both compression and rebound, in day to day driving you can run them full soft then adjust the clickers when you get to autocross.

  Tom

I've got a bike road race back ground also. Adjustable struts & shocks for an XR4Ti aren't all that common.

GPz11 wrote: So will the length of the spring make a difference? Like a 250 x 7 will be stiffer than a 250 x 10? I know it shouldn't matter but I wonder if

It would depend on the number of coils.

More coils=softer spring.

You need to look up how to figure wheel rates for your car. IIRC the XR4Ti has a true Macpherson strut which will have the same wheel rate as the actual spring. If the strut is mounted inboard at the bottom then there is a multiplier necessary to figure the wheel rate. For instance, on my Jensen it's necessary to run an 800 inch pound front spring to achieve a 325 pound wheel rate. On the rear, since the shocks are mounted differently the spring rate is the actual wheel rate.

To me, 350 does not sound excessive for that car either. So I'd go check for binding suspension parts first.

GameboyRMH wrote: Did you change shocks when you changed springs? If not, you're underdamped now, plain and simple. Getting shocks with the damping to match the new spring rates could help a lot.

Or overdamped, if the strut force was being used to compensate for too-soft springs.

GPz11 wrote: I've got Koni Yellow strut's on it and increased the rebound to compensate for the stiffer springs but there is no comp adjustment on them.

Try going the other direction with your adjustment.

If I go softer on the rebound damping, the front end bounces like crazy.