High spring rates

[Jean]

Is it J-Spec that's the next step up from H&R race in terms of what spring rate they use for e30 chassis? Can someone list rates that some of these high spring rate sets use?

I am ordering new suspension for my 325i and want to get an idea on what spring rate to go with. Thinking 650front/900-1000 rear? Will be used with custom valved Koni DA inserts, and Dot R tires..

[rsafier]

Depends on what you want to do. For autocross I think that is a bit too high to deal with unsmooth lots. I had a lot of luck with 500f/600r with a 25mm front sway, no rear on the old SM car. Same basic rates as a number of national level DSP cars.

[Bavarian3]

Koni should be able to match the valving to the spring rate combo...

The next step up from HR race is the J-Stock springs... After that, you have Gruppe N springs (non-coilovers); that is if you can still find them..

I don't have the rates handy right now but will find them.

Edit:

I have heard J-Stock came in different rates... I believe they are at 680/1025 which is a copy a set of Gruppe N.
I believe HR race is around 350/550.

[DSP74]

Why give up mechanical grip with an ultra high spring rate.......The car only needs to be stiff enough to keep it from bottoming, make the car responsive, and control camber loss.
Based on the size tires most folks use, and the weight of these cars, I think that's way to stiff....500/600 is probably a pretty good starting point, and it's apparently a pretty know commodity. But I'm going 400/500. And before I get the car on course I may even go with a 450/500.

Sure that may seem soft, but that's because some of the track guys quote rediculas spring rates. Sure REAL race cars use rediculas rates but they are super smooth tracks, REALLY low, and are dealing with measureable downforce. All of which we aren't dealing with. And by we I mean even the track guys.

With a less favorable motion ratio, my Camaro only had 600lb front springs. Granted with a 35mm hollow front bar. And the car was very wide. But it also had 315 front tires, and weighed close to 3600lbs with me in it. It did NOT have excessive roll, even with a much more inclined roll axis than what the BMW has. Good camber control, and Sam Strano has won a couple National Championships with the exact same setup.

Our cars have a more favorable motion ratio, are considerably lighter, a higher front roll center, and a less inclined roll axis. On top of smaller tires. ALL working to make this car roll less. Working against it are a much narrower width, and a smaller front sway bar. And that's it.

And this is my reasoning for the softer rates. If for whatever reason I don't think the car is responsive enough I can always add rebound damping.


One thing will become obvious as I get to know some of you guys....I'm no damn engineer. But some common sense practices, and logical steps to accomplish what I (we) want goes a long way towards a pretty darn good setup.........Because ultimately the car has to work. Not the paperwork, or math, or any other engineering bs. The car. Even with multi million dollar engineers formula 1 teams resort to some level of trial and error.

[JGood]

Why give up mechanical grip with an ultra high spring rate.......The car only needs to be stiff enough to keep it from bottoming, make the car responsive, and control camber loss.
Based on the size tires most folks use, and the weight of these cars, I think that's way to stiff....500/600 is probably a pretty good starting point, and it's apparently a pretty know commodity. But I'm going 400/500. And before I get the car on course I may even go with a 450/500.

Sure that may seem soft, but that's because some of the track guys quote rediculas spring rates. Sure REAL race cars use rediculas rates but they are super smooth tracks, REALLY low, and are dealing with measureable downforce. All of which we aren't dealing with. And by we I mean even the track guys.

With a less favorable motion ratio, my Camaro only had 600lb front springs. Granted with a 35mm hollow front bar. And the car was very wide. But it also had 315 front tires, and weighed close to 3600lbs with me in it. It did NOT have excessive roll, even with a much more inclined roll axis than what the BMW has. Good camber control, and Sam Strano has won a couple National Championships with the exact same setup.

Our cars have a more favorable motion ratio, are considerably lighter, a higher front roll center, and a less inclined roll axis. On top of smaller tires. ALL working to make this car roll less. Working against it are a much narrower width, and a smaller front sway bar. And that's it.

And this is my reasoning for the softer rates. If for whatever reason I don't think the car is responsive enough I can always add rebound damping.


One thing will become obvious as I get to know some of you guys....I'm no damn engineer. But some common sense practices, and logical steps to accomplish what I (we) want goes a long way towards a pretty darn good setup.........Because ultimately the car has to work. Not the paperwork, or math, or any other engineering bs. The car. Even with multi million dollar engineers formula 1 teams resort to some level of trial and error.

Agreed.

What was the wheel rate of the Camaro with those springs? Kind of hard to compare spring rates between different cars...

[DSP74]

Can't remember off hand. I gave my notebooks to the guy I sold it too. I don't even remember exact numbers for the motion ratio but it was somewhere around .69-.73
I would need that notebook. It also had the spring inclination angle too.

Even with spring wheel rates a little hard of a comparison as the swaybar is hard to get an actuall wheel rate, because of all the bends. A splined race bar would sure be easier!

I'm no engineer. All that stuff I had on that car took a long time for me to gather up.

[Jean]

Appreciate all the input / suggestions!

The 500/650 rates worked ok for me, but I figure since the next car will be heavier (84 318i with no a/c or power options and minimal sound deadening VS. 89 325i with power everything, 6cyl) and the fact that one car will have more tire grip with at least 225 wide dot r tires (I am going to pull the fenders and see if I can fit 245s) would lean even more.

Here is my 318i on a set of bilstein sports, 195 rt615s, 500front/650rear springs, no rear sway through a 90 degree corner, notice the roll. Am I wrong to think it will roll even more with wider/stickier tires in a heavier chassis?



I know it's a lot of trial and error, and some lots will favor one set over another (I'll have two rear diffs to play with for this reason as well), but I wanted to get an idea what front/rear rates some of the well known sets come with. I might just up the rates to 600front/850rear and it's easy enough to swap the springs if they end up being too stiff.

[DSP74]

Wider stickier tires will make the car roll more. And heavier will too. However that car is pretty damn flat. What swaybar are you using in the front.....


Obviously I need to get this car on a course, but rear swaybar's have been on my mind a little lately. Lots of guys drop the rear bar entirely to eliminate the rear wheel lift. But I think that maybe with a bar in the back (small-maybe stock converted to adjustable) the ruduced roll angle in the rear would eliminate the rear wheel lifting. Counter intuitive sure....But something I'm going to try.

A couple quick things as a reminder. A lower ride height is going to lower roll centers which will increase roll angle. How that works out when compared to the decrease in weight transfer due to a lower CG I don't know. And also a car with either 275-15's or 285-18's will roll less due to the increased track width.

[Jean]

Front sway is stock with just new hardware, and there is no rear sway. I don't plan on lowerng the car too much, in fact I ended up raising my 318i up about 3/4" after a couple of events and it bounced way less and was easier to drive at the limit. Also another reason why I am going with different shocks for stiffer springs.

[DSP74]

Maybe the housings needed to be shortened, shortened insert, and appropriate bump stop installed? To maintain travel at that height.


The sway bars do ALOT of the work and a 25mm front bar with M3 style links would probably be all that is needed with those rates, and the bigger tires/car.

[DSP74]

One other thing I forgot to add about my last Street Prepared car the Camaro. The car had the nice long Koni type bump stops and I'm almost certain the car did use them regularly over bumps.
But that is what you want. And because of the non hysterisis properties, they don't become a shock tuning nightmare.

I plan to shorten the housings about 2" but I also plan to USE those nice long progressive bump stops. As a non rebounding progressive spring of sorts....It helps the car to really absorb bumps on crappy lots.

[joshh]

Looks like we have some good answers.
With my Integra while running 225's in front and 205's in the rear at Packwood WA (National tour site) I'm using 450lb springs in front and 500 in the rear. The car could use a bit more spring and more shock but it's very close to being just right as it is now. The surface is also pretty smooth overall with some "humps". Anything rougher and I'd want softer springs.

The only other thing I'd add is having such a large difference in springs front to rear might cause some more oversteer than you want, depending on the size of the rear swaybar.

[Jean]

Maybe I'll just have to have a couple different sets of rear springs as they are easy enough to swap, but keep the front static. Most likely will not run a rear sway, I'll give it a shot as it's already on the car though.

[DSP74]

Maybe I'll just have to have a couple different sets of rear springs as they are easy enough to swap, but keep the front static. Most likely will not run a rear sway, I'll give it a shot as it's already on the car though.

That's the way to go. And TnT events are great for this if you can find them.

I still think I'd go to a bigger front bar. The bar does alot of work, and will make a big difference in roll angles.

[Jean]

That's the way to go. And TnT events are great for this if you can find them.

I still think I'd go to a bigger front bar. The bar does alot of work, and will make a big difference in roll angles.

I will, the stock bar is on the 318i, 325i is the car i am building :)