Cutting Coils: Let the hate flow....
 

My goal is to lower my BRZ about 1/2 inch, increase spring rate slightly and increase dampening dramatically.

Bilstein B6 Shocks will take care of the dampening and work fine with a drop of less than one inch.

There doesn't seem to be any springs on the market that fit my goals. I'm thinking about cutting stock springs to achieve this very modest change.

I don't see any issue with the result, as I will be cutting the free end of the coil and uprating my struts.

My question is does anyone have access to a good calculator and/or the dimensional specifications of the BRZ springs?

(Also I expect plenty of "Go by a '92 Civic if you want to cut coils")

:thumbdown:

just get TRD springs then

wait.. Yeah. If you only want to go about a 1/2 inch lower from stock then why not go TRD or Eibach? Eibach has good ride quality. My tein s-techs lowered me about an inch or so.

Alternatively buy lowering spring and find/make/commission a 1/2" spacer to reduce the drop, cutting the spring isn't going to significantly stiffen it as I do not believe they are terribly progressive.

There are easily 20+ spring kits on the market, keep searching. Cutting the spring will just make you bottom out a lot easier.

If you really want to cut the spring, just cut one coil and be done with it. No calculator needed.

The JDM STI springs would work well for you. 15mm drop.

- Andrew

cutting springs also weakens them near the cut and makes them prone to snap near the cut

That was the road that I was going down initially, but then I started to think why buy something to lower and then buy a spacer, when modifying the existing spring for free would help me achieve my specific goal?

umm maybe safety? but hey if you like living on the edge go for it. I just hope our insouciance doesn't go up if you crash

Thanks for your input Andrew. I really respect anything coming from you or Myles.

Can you tell me why a well measured cut of the factory spring wouldn't be a cost effective way of achieving my specific goal?

Can you explain in what way cutting the springs will weaken them?

I understand that the lower you go, the higher the spring rate needs to be in order to prevent the suspension from bottoming out. If you go too low the increase in spring rate may not be appropriate for the ride height, but for what I'm doing that should not be an issue.

Are you referring to action of heating stock springs to lower? That can cause issues, but I wouldn't go that route.

you will be heating the metal up when you cut it and that will weaken it near the cut point. Is it likely going to fail... no, but there is a greater chance and why take that risk?

You ride will become much softer and bouncy and to boot you will ride on your bump stops a lot during hard cornering and this will upset the car and lead to unstable (possibly unsafe) cornering. You really should just buy some used spring if you are looking to save a buck.

Edit: its not hard to hit the OEM bumpstop with everything stock

Strongly disagree.

Bone stock the suspension spends a lot of time riding the bump stops. That's fine because it was designed that way. A cut spring is only marginally stiffer, this sample calculation (https://www.eatondetroitspring.com/c...-calculations/) shows a gain of ~18lbs/in (and remember, rear motion ratio is under 1 - if you don't know why that matters, stop here, do not pass go, do not cut your springs).

That sort of rate gain is in no way going to make up for 0.5" less travel. You will spend more time on the bump stops and go deeper into them (past the progressive zone and straight into the hard bump stop), resulting in a much harsher ride. A basic set of drop springs with appropriately sized bump stops is going to be much nicer than what you're trying.

Next Thread: Baby stomping!


but seriously, there are many many very affordable ways to drop the car

I hear what your saying, but we're being speculative here and that's why I'm looking for a calculator.

Stock BRZ rates are 153/195

Swift Sport Springs Drop 1" and are 212/252

If I calculate the stock .5" cut rates and come up with something like 185/225 it may be a reasonable experiment. If I come up with 158/200 I could expect to spend a lot of time on my bump stops.

Like many things in life there are handful of good options and bucket load of bad ones.

I am genuinely interested in exploring the topic a little a further and I hope anyone who checks in here is on the same page. There are tons of myths and anecdotes about how horrible the idea is, but ultimately there is a right and wrong way to do it. The point of this thread is to see if cutting the correctly measured amount can create an acceptable spring rate for my goals.

I'm sure everybody knows a kid who dropped his 93 accord 4" on the stock struts by cutting the coils and had a bad time.

The cut is at the very end, and the coil is "dead" there. I'm not sure how a properly cut coil would fail. Heated yes, that weakens the spring by annealing it, but cutting only heats the very end, if that. I suppose if you cut it really slow, with a torch, you could cause it to anneal farther up the winding, but in general terms, properly cutting a coil is perfectly safe.

fwiw Herb Adam's even suggests it in his book, "Chassis Engineering".

To be totally honest I am no expert in the field, I was always taught cutting spring weakens them and thats the only logical way they could be weakened, but your probably right that at the ends its a "dead zone"

Question for OP how will the spring sit on the perch once they are cut? I thought they do a near full rotation at the base/top before beginning to coil up/down??

Funny, in that case you heat the end, and form it back to a full rotation at the end, but again, that is all dead coil.

From Herb's book:
http://farm9.staticflickr.com/8291/7...0750e3f2_z.jpg

Neat. This herb guy sounds like a good time hahaha!

I've never met him, but I bet he has cool stories!

http://blog.caranddriver.com/50-year...sa-sports-car/

Yup he sounds like my kinda guy hahahaha!

Made this little article like 5-7 years ago about this very subject. I haven't verified it since, but it's probably not too far off from reality:

http://craig.backfire.ca/pages/autos/cutting-springs

I'm sure this was a great book to have back in 1992. A lot has changed since then such as, research, tech, new manufacturing techniques, and materials just to name a few. Seems a little outdated for our application IMO. Back then we cut or heated springs because it was one of the few options we had in order to lower our cars, now we have tons of options, affordable options. Over the years I've heard "springs are springs and they all come from the same German manufacturer no matter what brand of spring you buy". How much, if any truth to that I cant say. CUT EM, Take pics, let us know how it goes, its your car.

Just for the heck of it, here is Paul Haney's article on springs. Good info, and math, if you want to crunch numbers.

http://insideracingtechnology.com/eibach1.htm

I agree. Although there is nothing wrong with cutting your stock springs, you should look at all the options available to you. In the end, if you factor in the value of your time, you will probably come out ahead buying the correct spring kit. As Jedi said, back in the day, it was a necessity to cut springs for a street car. The only other option was to adapt full-on race Koni coilovers and custom springs that could cost around $1,000 EACH and that is in 1970's dollars. :confused0068:

I think since the spring is progressive, cutting the spring will change it's rate in a way only toyota(or Subaru) can know. Letting springs are dirt cheap, there is really no reason not to just get them. They also won't severely devalue the car. Have fun trying to sell it with "chopped"springs. If you can't afford $300 for springs, you shouldn't be making payments on a 3 year old car.

Additionally I asked Stance once about increasing preload on my springs instead of getting a stiffer set of springs and they told me it would have unforeseeable affects on the spring rate

The springs need to have one open end and one closed end. You cut the open end and rotate it on the closed end. In this case there's no issue with how the spring will sit in the perch. If both ends are open, you need to be able to rotate at least of the perches to have the spring seat properly.

Okay makes sense.

I am now legitimately interested to see how this turns out now.

As far as I can tell based on data I've found and looking at the springs themselves, they are not progressive. Where did you get information that suggests they are?

I'm not interested in the residual value of my vehicle, I am interested in customizing it to exactly the way I want it to perform on the streets that I spend most of my time driving on. One of the nice things about there being so many affordable out-of-the box solutions, is that there are tons of oem springs floating around for free or next to nothing. I have a free standing spring compressor and a garage, so swapping springs doesn't take me much time and I could easily go back to the stock suspension prior to sale if I wanted to.

I guess honestly I just assumed they were progressive. Thought all shock springs were, that's why companies sell Swift springs right? Anyways, I commend your attitude on personalization as I do things the same way.

EDIT: You also make a good point about cheap springs and having a place to work on them. But really, why not just buy a set that's already stiffer and engineered to work properly? If the springs AREN'T progressive your ride heightwill be lower but your spring rate won't be higher, you will bottom out more and put excessive strain on your shocks

So I found some good info ( http://www.bluecoilspring.com/rate.htm ) and created a calculator in Excel. Using pictures of the stock springs and the known values published about them, I was able come up with reasonable estimates and tweak it to produce the factory specs. Then I'm able to "remove" coils and get the new spring rates.

What I found was that cutting .5 coils off the front will increase the spring rate from 153 to 170 and cutting the same of the rear will increase from 195 to 215.

Ideally if I could figure out how much coil to cut to achieve my targeted ride height, then I could plug that amount in and find my spring rate. Unfortunately it seems like it would be incredibly difficult to accurately calculate that and it would probably be better to start experimenting if I want to move forward.

The utility of progressive springs is one of the arguments for buying springs. I like the feel of a stiff dampener combined with a progressive spring, it allows for good handling on less than perfect road surfaces.

Spring rate does go up as you remove coils, the question is whether or not the spring rate will increase enough at the desired height

Compare your calculations to other aftermarket options

I definitely will, I would just need to figure out the ride height change to have the complete picture... I know what cutting half a coil will due to the spring rate, I don't know yet how much drop it will yield.

So cut off .25 and see where it sits?

That's a good starting point. Also I'm not driving my BRZ in the winter, so I have plenty of time to play and tweak.

Go find a local giving away or selling their springs cheap so if you mess it up you got a fall back

FWIW, the book "Race Car Vehicle Dynamics" by Milliken and Milliken was written in 1995, and is still considered the suspension 'bible'.