BD Race Springs - Rear Rate

TimeForACobra · #1 (**permalink**) 02-20-2014, 07:40 AM

Good Morning,

Does anyone know the rate of the rear Backdraft Racing Race springs?

Thanks,
Keith

Kobura · #2 (**permalink**) 02-20-2014, 01:37 PM

I think that my BDR springs, front and rear, are too stiff maybe because of the (relatively) small engine in my build. Admittedly, the handling through curves is great, like the car is on rails, but not so great if the road surface is bumpy. So, I attempted to find out what the stock spring rates are but came up with nothing. Therefore, I don't think anyone would know what the race spring's rate is. I have gotten a pair of softer coil springs for the front on the assumption that the stock spring rate is about 300 lb/in, but have not installed them, yet. I don't think that there are any softer springs for the rear as I believe the stock ones are the same as for the BMW 3 Series 318i. If anyone has spring rates for BDRs, front or rear, stock or race, it would be nice to know.

TimeForACobra · #3 (**permalink**) 02-20-2014, 02:57 PM

Thanks Kobura...

I'm trying to autocross and the stock spring rates are too soft. I've been told when I am on the throttle hard the back end squats pretty low. But, I drive the car quite a bit on the road.

From what I have been able to gather, the stock front springs are 215 lbs, and the front race springs are 450 lbs.

I haven't been able to gather the same info on the rears.

Also, I've heard/read that the race springs could be too harsh for street driving. Well, at least for my preference. So, I want something in between. I'm probably going to try 300 or 350 in the front. Now, I just need to figure out the rear.

The "in between" springs from Backdraft aren't yet available, so I'm starting to research other springs. Right now, my best option is to pull the existing springs and see what will fit.

Thanks again.

PLDRIVE · #4 (**permalink**) 02-20-2014, 06:40 PM

Race springs were (2008) around 450 front and 950 rear.

Trueoo7 · #5 (**permalink**) 02-20-2014, 06:59 PM

Try Tony Martin at the factory. He helped me years ago with spring rates. Very knowledgable.

TimeForACobra · #6 (**permalink**) 02-21-2014, 04:51 AM

Thanks!

cbreez · #7 (**permalink**) 02-21-2014, 12:05 PM

Quote:

Originally Posted by PLDRIVE

Race springs were (2008) around 450 front and 950 rear.

That just doesn't sound right for the rear...seems way to stiff for a 2400 lb car...
Why don't you remove them and find a local racer with a spring checker to actually check them? Have you ever really checked your shock travel first...to see what they are doing?

pjmoore2003 · #8 (**permalink**) 02-21-2014, 07:34 PM

I have the race springs, car corners flat and rides nice over bumps... But my seats are much more padded

PLDRIVE · #9 (**permalink**) 02-21-2014, 07:42 PM

I had the springs tested . The rear springs were way toooooooooo stiff for my liking. I would not recommend them if they are still 950.

FYI Coilovers are roughly 60 to 65 % of an e36 rear spring rate ( u may have already known this.)

I run MCS double adjustable coilovers (Moton) on all corners.

wrogers55 · #10 (**permalink**) 02-22-2014, 08:13 AM

Do a search here under "Spring Help" in 2009. I was the original poster. Tony Martin replied as well as some other good info.

I have chassis 318 on 315/17 Nitto NT01s which grip enough to break things if you are not a bit careful, and I run it really, really low. To keep it off the ground, I run the race springs on the rear and standard BDR springs on the front. Probably not your perfect track setup, but works on street extremely well. The soft front compared to the rear really turns in well, but you will need some good experience to get comfortable and stay out of trouble with that kind of setup. It's a rough ride on an empty tank and driver only. Fill up the tank and put a passenger in it and you would love it.

Biggest benefit is no bottoming on the street, loaded, even with a super low ride height.

Good luck.

Kobura · #11 (**permalink**) 02-22-2014, 08:24 AM

I "measured" my stock spring rates by first jacking up the right front wheel and then the right rear wheel to unload them of the car weight and measuring the drops in the height of the fender lips when the car was lowered. The front dropped 2-1/2 inches and the rear 2 inches. Assuming that the car weighs 2400 lbs and each corner supports 600 lbs, the spring rates would be 240 lbs/in for the front coils, and 300 lbs/in for the rear springs. The springs are located between the tires and the pivots for the suspension arms, so the actual rates are much higher, maybe up to twice(?). I know, totally ballpark numbers, but at least it gave me something to work from toward softening the ride.

cbreez · #12 (**permalink**) 02-22-2014, 10:00 AM

That's very ingenious! You are very close on the weights. I have scaled my car with a tank of gas and the weights were 602 lf 635 rf 664 lr 714 rr about 47% front and 53% rear. BTW, if you put a driver in the car you will be close to a 50-50 side to side weight distribution.
I mentioned shock travel because a good rule of thumb is that you want 2 to 2 1/2 inches of travel...so if your springs get you close to that, you are close to having the correct rate in the car.
These cars will never feel like a Caddy!

Grey 65 · #13 (**permalink**) 01-09-2015, 09:10 AM

Quote:

Originally Posted by TimeForACobra

Thanks Kobura...

I'm trying to autocross and the stock spring rates are too soft. I've been told when I am on the throttle hard the back end squats pretty low. But, I drive the car quite a bit on the road.

From what I have been able to gather, the stock front springs are 215 lbs, and the front race springs are 450 lbs.

I can confirm the stock rates are 215lbs front and 450lbs rear. I had mine tested at Vorshlag Motorsports in Plano, Texas...

I am putting 450lb fronts and 650lb rears on my car.

Kevin.....

mln385 · #14 (**permalink**) 01-09-2015, 04:04 PM

Quote:

Originally Posted by Grey 65

I can confirm the stock rates are 215lbs front and 450lbs rear. I had mine tested at Vorshlag Motorsports in Plano, Texas...

I am putting 450lb fronts and 650lb rears on my car.

Kevin.....

That is quite an increase no. How do you think it will re act with those rates?

lovehamr · #15 (**permalink**) 01-09-2015, 04:40 PM

I ran the race springs on my last BDR and they handled great on smooth surfaces but it didn't seem like the shocks were up to the task of controlling them. I also don't know of any performance replacement shocks to go with them.
Don't have the race springs on BDR1311.

Because of the shock question I'd really like to see PLDRIVE's setup and cost!

Quote:

Originally Posted by PLDRIVE

I had the springs tested . The rear springs were way toooooooooo stiff for my liking. I would not recommend them if they are still 950.

FYI Coilovers are roughly 60 to 65 % of an e36 rear spring rate ( u may have already known this.)

I run MCS double adjustable coilovers (Moton) on all corners.

Grey 65 · #16 (**permalink**) 01-09-2015, 07:50 PM

Quote:

Originally Posted by mln385

That is quite an increase no. How do you think it will re act with those rates?

It will be fine. The 450lbs in the front is what the math says you should run for racing. The rear should be right at 900lbs-950lbs. But I wanted a little softer so I went with 650lbs since I drive on the street in addition to autocrossing.

There are no real struts for this setup. The closest is the BDR TD front struts which I bought and a pair of Bilstein rears which I also bought... Otherwise you have to have a special set of one offs made.

Kevin.....

cbreez · #17 (**permalink**) 01-10-2015, 04:56 AM

Please explain your "math" that you used for determining racing spring rates. We all would love to know...

Grey 65 · #18 (**permalink**) 01-10-2015, 07:04 AM

Quote:

Originally Posted by cbreez

Please explain your "math" that you used for determining racing spring rates. We all would love to know...

The lead engineer at Vorshlag Motorsports took the dim's and weights off of my car and figured it out. It is kind of his full time job....

If you took the time to read what I wrote you would see that I said "Vorshlag Motorsports".

Kevin.....

cbreez · #19 (**permalink**) 01-10-2015, 08:03 AM

I did read the post...you still haven't explained anything to all.

I think that what you portray is wrong regarding a recommended spring rate so explain it to us how that was determined other than that somebody told you something, I would like to learn...

There are many variables in determining spring rates for racing, street, autocrossing, etc.

BTW, before you convince everyone that rock hard springs are the answer to handling, which they are not, most racing folk adjust with sway bars first...

Grey 65 · #20 (**permalink**) 01-10-2015, 11:46 AM

Quote:

Originally Posted by cbreez

I did read the post...you still haven't explained anything to all.

I think that what you portray is wrong regarding a recommended spring rate so explain it to us how that was determined other than that somebody told you something, I would like to learn...

If you would like to learn you can get a job at Vorshlag sweeping the floors, then they will eventually let you work on the cars and at that point the lead engineer will give you the time of day and explain things to you. Or you can go get an engineering degree or you can just do like most of us and go pay a race engineer to figure it out for you. I don’t ask the doctor why he gives me such and such medicine to take, nor do I ask the engineer why the numbers are what they are. I give him the car and I tell him how I want to use it. He then determines what the best spring rates are for what I want to do.

Quote:

Originally Posted by cbreez

There are many variables in determining spring rates for racing, street, autocrossing, etc.

You should spend more time on reading comprehension. The original OP was looking for stiffer rates for AUTOCROSSING. I said in my posts that I AUTOCROSS. I would deduct that the proper rates quoted to me by Vorshlag Motorsports were for AUTOCROSSING and not waterskiing.

Quote:

Originally Posted by cbreez

BTW, before you convince everyone that rock hard springs are the answer to handling, which they are not, most racing folk adjust with sway bars first...

FYI: You tune for the particular track or conditions with swaybar changes or swaybar adjustments. That is once you have the proper spring rates for the type of racing you participate in and you fine tune with air pressure adjustments.

Kevin.....