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Thread: Front vs Rear Spring Rates

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Posts: 11-20 of 53
2013-03-03 22:57:21
Originally Posted by Vadim
Tell me then, why do coilover manufacturers are putting much softer springs in the rear, while drop in lowering springs got it correct like OEM Nissan did?

Because the vendors selling the various generic "36 way adjustable" coilovers from china don't really understand suspension tuning?

Now I haven't really studied the rear beam cars, but based on the rates used, the rear probably has more motion ratio than the front. Differences in suspension geometry are why one needs to calculate ride frequency, rather than just arbitrarily pick a spring rate based on what someone uses on a different chassis.
Last edited by MCarp22 on 2013-03-03 at 22-59-49.
2013-03-03 23:33:11
Originally Posted by MCarp22

Because the vendors selling the various generic "36 way adjustable" coilovers from china don't really understand suspension tuning?

Now I haven't really studied the rear beam cars, but based on the rates used, the rear probably has more motion ratio than the front. Differences in suspension geometry are why one needs to calculate ride frequency, rather than just arbitrarily pick a spring rate based on what someone uses on a different chassis.

That's actually what I'm thinking, I'm thinking they are just doing following a generic method for all cars, not knowing that Nissan Rear beams require a different method.

Here's a part out of Sarah's book. Interesting about P10's/P11's. It explains why the car still feels nicer even with stiff springs compared to my old B14.

Last edited by Vadim on 2013-03-03 at 23-38-10.
2013-03-04 00:23:12
Chassis weight and motion ratio of the suspension at hand as @MCarp22 touched on. I, unfortunately, cannot tell you why any manufacturer choose the springs rates they do but knowing a nose-heavy car such as all FF chassis tend to be, should get some heavier springs in the front vs rear.

EDIT: That is what manufacturers choose. That is not what is optimal for handling. Nice try @Vadim.
Last edited by Kyle on 2014-03-09 at 15-09-51.
2013-03-04 01:35:34
How much R&D do these companies do? For the stock type springs do they just lower by what ever and then stiffen the factory rate by some percentage and call it good? maybe put it in a car to make sure it doesnt blow up and start shipping them. I would expect the coilovers to go though some testing but i could be wrong. Even the GC coilovers are stiffer in the front than the rear.
2013-03-04 02:17:39
My RM's for the B15 are 360fr/350rr. Someone may have done some research lol
2013-03-04 20:11:31
Been doing some searching, Keo pointed me to the Mike K quote, which led me to find some good posts.

From Steve that explains the old method of thinking: Post 132
Originally Posted by 98sr20ve

I think that the reason you see the 300/200 kits for the b14 is because no one had the nerve back in 1995 to suggest higher rear rates on our cars (not including cars that have leverage type suspensions that need higher rear rates due to leverage). Plus, the rear toe issue was not known at that time to most people. Once they tried the 300/200 for a while people started complaining and the B15 came along. Then the even rates front to back started to get some attention. Keep in mind that these people are not developing kits for autocrosses only. They are looking at road racing and general use as well. On my car with the even rates it is imperative on the high-speed corners to hit them with the gas down. It makes the car fast but most people don't drive like that. On the street it is a non-issue because you don’t drive 100% at 100mph+ on the street. Auto crossing requires a very unique setup depending on the course. A road racing setup will simple not be a great setup for auto crossing. It can be good but not great. I went from full stiff on my rear bar while auto crossing to full soft and I still would have preferred a stiffer rear setup on the autocross. Fortunately it is relatively easy to swap rear springs on B14/15 and I think that is the way to go on a dual-purpose car.

Post 133

Originally Posted by Dangling
Regarding higher rates in the rear vs front, I asked the same question to smartbomb back in July:

Higher spring rates in the front of our b15s seems to be the consensus when looking at coilovers or other high end pieces. You seem to recommend 700f/600r for a track only car. This mirrors the coilovers that allow daily driving, like the Tein SS default at 336f/280r, and those who recently bought JICs went with 392f/336r.

So why do all b15 stock springs, lowering springs and the NISMO suspension kit have higher rates in the rear? Does this have to do with progressive vs linear springs? Are higher front rates preferred simply because we have a 62f/38r weight distribution?

Here's his response:

Strangely with the stock trailing arm bushings, I run stiffer rear springs as well. The stock bushings are so gushy, they don't allow the rear bar, including the stock one inside the twist beam to couple well. Once you get rid of the squishy rubber, man does the understeer go away. To me, its like a couple hundred in/lbs difference in spring.

So I would run the Tein/JIC rates most likely as a starting point in a car with urethane trailing arm bushings.

The other reason is that when you start getting stiffer and lower, the transition to oversteer gets more dramatic so a rear biased spring rate gets too snappy for all but the most skilled to handle. Not that the RTR World Chalange Spec V has 1200 in/lb rear and about 900 in/lb front springs. Peter Cunningham likes a lot of oversteer, his car is set up so you hardly have to turn the wheel, you just control the car in the turns with throttle.

A softer stock or street car likes more rear to help the car rotate.

Another great post about bushing softness, #135

Originally Posted by Dangling

Here's some more info I dug up searching:

I have been building and racing B14's for quite a
while and have never quite been able to get all of the
understeer out of the chassis and to make the car
respond crisply to attempts to get it to rotate. I
have gotten them to where they rotate slowly with
bending the beam and with ridiculose spring and rear
bar rates but they will still have terminal understeer
if driven in a ham fisted manor.

The B14 is also sort of squirmy under trail braking
and turn in and also has a vauge feeling in the rear
while taking a set.

Well I was looking at the trailing arm bushings and
noted that they were made of really gushy rubber and
had large windows cut out in them for additional flex.
I figured that these bushings were allowing the axle
to walk around giving the unsecure feeling in the back
and also decoupling the antisway bar and the torsion
bar of the rear axle.I had Energy make me a set of
urethane solid bushings to replace the rubber.

The results are oh my god! The car is now so
responsive I spun it on the track on my first lap,
just warming up the tires. The car was way too loose,
a first for a B14. After some shock and tire pressure
adjustment, it was a lot better but still quite loose
and I managed to spin in the race when I had to take a
turn off line to avoid spinning cars.

I feel that this will make a big breakthrough in
B14-B15 handling, i just have to resort my car to take
advantage of the better response but reducing
oversteer a little. I am going to soften the rear bar
and perhaps the rear springs.

These bushings are like going up 300 in/lbs in rear
spring rate! They make a bigger difference in chassis
balance than anything I have done so far. They also
eliminate the squirm and weird feeling out back.

Energy should have them for sale soon. As a warning,
although they should be nice on a street car, if you
have an already on the edge tuned race car, its going
to knock you into wild oversteer.

Bushings aside here are a few good quotes which starts making more sense on why coilovers have stiffer fronts.
Source thread

Originally Posted by RobertspecV

Incidentally, when you lower the car you need more front roll stiffness, either through springs or ARBs. It's long and complicated to explain, but basically the front roll center drops further than the rear rc for the same amount of lowering. This = more roll in the front than rear for a given drop since roll is a function of weight being transferred and the distance between the roll center and center of gravity. This will tend to loose front traction and give you a push all else being equal. This is part of the reason that all lowering kit springs have a higher rear bias in spring rate than stock.

Originally Posted by Dangling

I gotcha, more rear and less front traction means a lot of understeer. This is a good explanation of why stock spring rates and aftermarket lowering springs have higher rear rates.

Interestingly enough, once you start using much higher spring rates all around, add damping adjustability and go from progressive to linear, you begin to notice that the recommended settings of products like high end coilover systems have higher rates up front vs rear, or even identical in one case:

336F/336R Tein Basic
336F/280R Tein SS
392F/280R JIC FLT-A1
392F/280R JIC FLT-A2

There are other factors. What happens when you install the rear beam pieces of the Nismo bushing kit? That increased durometer rubber acts as a higher spring rate, and Kojima himself contends in a older post that the rear on his b14 would come out at will with harder rubber bushings installed in the rear beam. There are many things to consider in suspension tuning that it's hard to keep track of sometimes.

After all of that reading squirlz was on the right track, but not quite there. Lowering springs are meant for people that leave the rest of the car stock, while Coilovers are meant for people that are serious about handling, which means they will have other mods that stiffen the rear up already.
2013-03-05 01:46:00
Thats some good info. Thank you for putting it together. Although it is of no use to me but it will be for lots of others. @Shawn B, Most of this info should go in the suspension thread for people who are concerned about improving their handling rather than just dropping the car.
Last edited by squirlz on 2013-03-05 at 01-47-46.
2013-03-10 15:38:42
Originally Posted by Vadim

Tell me then, why do coilover manufacturers are putting much softer springs in the rear, while drop in lowering springs got it correct like OEM Nissan did?

In the early 90's many of the FWD pro racers started playing with bigger rear spring rates than the front. Increasing rear stiffness helped keep both ft wheels planted by reducing roll. That set-up works because on road courses the throttle is typically mashed most of the time so weight transfer to the rear needs to be avoided with FWD (but the opposite for RWD). Race cars can get away with extreme rear stiffness because the tires are so sticky the car is usually controllable even with one wheel off the ground.

For street there is no reasonable way to be on the gas all the time, tires are not as sticky and pavement is typically not smooth like a track. A convetional medium rate ft and lighter rear spring works because that matches the weight distibution on a FWD car. Softer springs that follow the pavement better are faster on street that stiff race setups. And yes I have confirmed this with my track B13 that still has tags.
2013-06-14 21:20:24
Originally Posted by Keo
Mike K made a article about it

Yes, I'm glad you pointed me to it just recently, it's an awesome article.

Mike Kojima's Post about Making Beam Axle Handle Well
Originally Posted by choaderboy2

I think I finaly get the beam axle to really handle well

For not much money.

So I have been inadvertantly experimenting with a cheap way to get the B14 to handle correctly. I have been struggling with this ever since I started to race one of these things. I think I am finaly on to how to get one of these to turn right.

In my development of the B14 I have struggled to fix a couple of handing issues that were very stubbon. The first is a vauge rubbery feeling in the back with some unpredictableness in how the rear end responds. One, this feels bad, espicaly on high speed turns, two, it is unpredicable and not consistant when oversteer will finaly happen.

The second is a nearly relentless tendancy for grinding low speed understeer, unless tricky driving is done (like lots of trail and left foot braking). This is caused by the car falling over on its outside front wheel in hard turns which I think is a roll axis location issue. The falling over causes it to loose camber and contact patch and thus grip.

I have been working on different ways to fix this without hurting the B14's good points, which is really forgiving and self correcting recovery from real sideways. All of my fixes have been high dollar and custom parts, not what your average guy can come up with.

A lot of the problem is around the rear axle. This rear axle is really quirky but highly engineered so it is real hard to get a good understanding on how it works and how to fix it for high performance. I spent a good amount of time going backwards until I hit the nail close to the head.

First I bent the beam for zero toe. This is critcal as the B14 handles like utter dogsh*t unless you do this. It has 1/4" of toe-in stock and you just can't overcome that with suspension turning. 1/4" of toe make it push like a pig and suddenly let loose if you try the normal bar and spring thing to fix the push. YOU CANNOT MAKE A B14 handle without this. See Steve, he will fix you up unless you dick him around. DON'T DICK STEVE AROUND AND GET HIM MAD. For most of you he is your only option for beam bending. The other option is that you can ship your car and lots of money to me and I'll do it for you.

Next I installed hard urethane bushings in the trailling arms of the suspension. This made a pretty big difference as the soft rubber bits actualy damped out the effect of bar and spring rate change due to the 1/2" of gush they have. Now the car was more preditable in trail braking but still was nothing great. You get these bushings from Global Performance Products. The car was now sort of ok but no B13 and certainly no Honda. I raced the car like this for many years, it still won lots of races, sat on poles, did ok at time attacks and held a few lap records.

After building the Dog III, I had a spare B15 Spec-V Scott-Russel linkage lying around. Looking at the B14 linkage I noted big mushy busings and a pretty wimpy stamping holding it all together.

The Spec v part is way more substantial, has a forged aluminum link and smaller harder bushings. I had to drill out one of the steel sleeves to 12 mm or something to get it to fit on the B14 but it was mostly a bolt on.

Whoo wee I thought, this would fix the remaining vaugeness of the rear end. I was wrongo. The rear of the car felt much more planted and stable, really good in fact but the car pushed like a pig, like back to square one.

I did some thinking and figured out the the stock beam depended on the flex in the scot-russel link to give the back of the car toe steer to make it turnable. You see the Spec-V is an evolution of this car and it has only about 1/16"-1/8" of toe in the beam stock with less toe steer in the linkage

I then took a careful look at the motion ratio of the rear suspension and figured that it was greater than the B13 as the shocks are way inboard, forward and at an angle inward. Much stiffer springs were in order. I started to up the rear rate and found the car working better and better. With the Spec-V rear link, I ended up at 25% stiffer rear springs, for my race car this means 600 front and 800 rear. Hummm, the spec-v comes with stiffer rear than front springs stock....

I mean I am thinking of going even stiffer in the rear but your average guy might not find this much oversteer to his liking and the suspension harmonics numbers start going away. I am going to experiment with getting more front grip instead.

Now the car has been transformed, the understeer is gone unless your really hamfist it. With trail braking or lift throttle the car pivots around the nose, infact the rear tires wear faster than the front! At high speeds it four wheel drifts with the front leading slightly. The rolling over on the front feel is mostly gone and pictures of the car cornering show this as well.

The rear slides nice and is solid and predictable feeling. So this gets rid of all of the B14's weak points over the B13 and makes it feel almost like a Honda. The dog car feels almost as good as my buddys H4 DC2 Integra now.

The progress bars are full stiff in the rear and middle in the front. Future tweeks will be to revalve the shocks for more rear rebound and more lowspeed front rebound damping and it should be real good. Maybe a little more rear spring.

So what did I learn that you can copy?

Bend rear beam to zero toe
Urethane rear trailing arm bushings
Spec-V Scott-Russel linkage
25-30% more rear than front spring rate

Kick some ass.
2013-06-14 21:33:00
With that in mind if we look at stock spring rates, we will see that Nissan acknowledged that their beam has issues and that they should increase rear rates to make the car handle better.

B15 SE/SE-R: 134F/212R - Rear 37% Stiffer
B15 Spec-V: 154/247 - Rear 38% Stiffer
B13 SE-R: 123F/112R - Front 10% Stiffer

Drop in Springs:
Eibach Pro-Kit: 180F/300R - Rear 40% Stiffer
Tein S-Tech: 170F/270R - Rear 37% Stiffer
Tein H-Tech: 154F/246R - Rear 37% Stiffer

BC Racing: 336F/224R - Front 50% Stiffer
Tein Basic: 336F/336R - Front 0% Stiffer
Tein SS: 336F/280R - Front 20% Stiffer
Nismo S-tune Kit: 185F/300R - Rear 38% Stiffer

With that in mind, brings me back to why I started this thread to begin with. I was curious on who was more correct, Nissan and Aftermarket manufactures with drop in springs or aftermarket coil over manufactures. Seeing Mike's post reassured my suspension that coil over manufactures just follow the industry standards for spring rates instead of tailoring them to a specific car. Now some of you said that the reason for that could be because people that get coil overs usually have other mods done. That is true too, but referring back to Mike K's post, even a fully modded race car like his needed the 25%+ stiffer rear to handle better.

The only time I think we can rely on the standard front springs stiffer then rear springs standard is if we do the panhard conversion, but even then that might not be enough.
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