Thread: Front vs Rear Spring Rates

Now, does this only apply to the B14-15 with the rear beam? If you have IRS is this not true? I think the weight distribution of the car has something to do with this as well, once all of the other hindrances are fixed.

Say we have a car that is 60F/40R weight distribution, now you went with a street-able 400lb front spring, would you want a 600lb rear spring? I took 400/40=10 then 10*60=600. Would this help offset the weight distribution and keep the car balanced assuming all of the other items are equal? This comes out to the rears being 50% stiffer.

This creates the formula (Front Spring Rate/Rear Weight Distribution) * (Rear Spring Rate/Front Weight Distribution)

If you apply the above formula to the B15 SpecV and Nismo springs you get a 62%F/38%R weight distribution.

The stiffer i go with the shock setting in the rear of my P10 the more it likes to rotate. So if i increase the rear spring it should do the same.

Mikes suggestion was definitely towards the OUR rear beam with horrible roll center, but I think it can apply to any FWD vehicle that understeers a lot.

Something to consider... P11 and P10 stock spring rates:
P10 Stock: 90-100F / 112R
P11 Stock: 123-134F / 190-212R

Now if you look at Sarah's quote, she says that multilinks have 0.7:1 motion ratio... that means the realistic spring rate for both is, now Macpherson struts have about a 0.96:1 motion ratio, hence P10 rear is a little lower on the rates.
P10 Stock: 63-70F / 108R
P11 Stock: 86-94F / 190-212R

In which case, maybe Nissan designed the P10's to have a much lower spring rate front compared to rear for a reason, maybe the stiffer P10 chassis required it?

So i think we have concluded that the rear should be more stiff, even once the under steer condition is fixed based on Mike's work. This also leads back to why do some of the aftermarket springs/coilovers use stiffer springs in the front?

Well I don't think the P10 will suffer the same 12" roll center as the Scott Russel rear beam Nissan's suffer. All of Mike's work was to combat the awfully high roll center really. One thing I don't see him mentioning is the beam shift, basically when you lower a beamed car, the link needs to be shortened or the whole beam slops to left or right side. On my B15 with about 1.5" drop in the back, the beam shifted 1/4" to the passenger side, add on toe in and you got a perfect dog tracker.

What I find interesting is, simple drop in lowering springs actually followed Nissan's standards, ~40% stiffer rear, this could be because they didn't want to R&D with different spring rates. But I do find it interesting that coil over spring makers, which should spend more time R&Ding setups per car, just default to industry standard rates. Either way if you go with a decent coilover company you can do custom rates and you should be golden.

I have 400lbs front and rear right now and the car does still understeer a bit. I'm going to try softer front springs, going with SWIFT 5kg's (280lbs), little more then 30% softer front. This should make the car more drivable on the street too, we'll see what it does with understeer/oversteer.

The scott-russell beam is interesting. Tuning the spring rates on one doesn't seem to follow the same rules as an independent suspension. I can't quite figure out why the wheel rate calculates out to be so high, Nissan probably doesn't put a lot of priority on handling for a standard QG18 sentra such that it would need a racecar stiff 1.72Hz rear freq.



That's the difference between a factory tuner like Nismo, and a one-size-fits clone like BC.

That beam is definitely interesting, I really wonder why Nissan just didn't go with Watt's or a much simple panhard...



Agreed, but the drop in springs are only as good as the shocks/struts that they go on. AGX's plain out suck, if your not putting those drop in springs on better shocks your not going to get good results.

I vouche for BC's because of the features to price point you get from them, and they don't mind at all when you go custom spring rates (like I did).

It will be a smoother ride on the street, no doubt. When you push it hard with softer springs in the front, you're going to really notice the car pitching up and to the outside wheel. With that roll center so high in the rear, anything you do, outside of the panhard conversion, is just a bandaid.

Cheaper = better when it comes to mass production!

I'm pretty sure the gain in trunk space had a lot to do with it? I read that somewhere...

Boom! Correct Ben

Packaging a double A-arm setup like the Honda's rob ALOT of trunk space!

P.S One thing Mike didn't speak about when strengthening the rear end is a (true) weld in 4 point roll bar/cage . Two birds with one stone