anzai

ive got bc racing coilovers (BR type) on my itr with custom 6kg/mm front and 4kg/mm rear spring rate. the car is very bouncy and the rubber scrapes the underside of the wheel arch, A LOT.

im thinking of changing to a stiffer springs for the front to 10kg/mm, but leaving the rear at 4kg/mm. in terms of handling, would this be alright? i've read somewhere that with itr's its best to have a 4kg/mm gap in between... for instance the default spring rate for these coilovers are F 10kg/mm and R 6kg/mm. just trying to save cash whereever i could. so whats the implication of having a great difference between front and rear spring rates?

here's some kitties in a mug as a thanks in advance!

Dave-ROR

Why in the world did you go from 246lb/in front rate and 246lb/in rear rate to ~336lb/in front rate and ~224 rear rate.

Didn't want your car to actually handle correctly anymore?

And those rates, probably dumped on the ground would of course make the car handle/feel like a POS.

The 4kg/mm less in the rear is nothing but a preference of whoever you talked to. Many here run higher rates in the rear, it all depends on what you want.

10kg/mm front and 4kg/mm rear will take one of the best handling FWD cars ever sold and turn it into a car that handles worst than a base Dodge Neon on 8 year old all season tires with no rear sway bar and an upgraded front sway bar.

Sorry.

B serious

iTrader: (1)

I think tangible handling issues onlly surface when BOTH these situations exist:
-you track the car
-you have the ability to actually look for and find tangible handling issues.

Otherwise, even $40 eBay coilovers make the car "handle great".

Not sure the OP cares about tracking the car or finding out the finer points of handling. So....no, he probably won't notice what happened to the car with 10Kg front springs and 4Kg rear springs. As a matter of fact, in the stop light grand prix, the car will feel like it turns in a bit sharper.

You can't (really shouldn't) push the car hard enough on the street to induce the long term, noticeable hopeless mid-corner understeer that the spring combo would have induced on the track.

The OP COULD raise the car up to make it stop scraping? Or get wheels that dont stick out as much?

But If you're not tracking the car, it really doesn't matter how it handles, does it? For street driving, it'll still "handle" just fine anyway with the 10k/4k combo.

As long as it's not unsafe (it's not)...people don't care how their just-for-looks street car handles. It's not important.

anzai

well most people i know who has an itr runs F 10k R 6k, and they have not complained, some takes the car to the track even. but if you could elaborate on your claim as to why F 10k R 4k would kill the handling on my car. and what would then be a good combination for street and occasional track, in your opinion?


i will be tracking the car in november this year, so i'm looking for a good spring rate combination to be used on both the street and track.

the scrubbing is not caused by the wheels being too wide, im running jdm 16'' +50 but the previous owner ran 205/50r16 and it came with the car when i bought it. a few people told me these are too big and im better off with 205/45r16 to avoid scrubbing, but im only scrubbing when hitting a pot hole, so i believe its the soft spring rate thats causing this more than anything.

what do you think is a good combination for street and track?

Todd00

Hate to break it to you, but you bought rather poor coilovers. And you're probably making the problem worse by jacking around with the springrates and running the car lower than it should be.

Raise it up, put the original springs back on the coilovers and drive the car. In the meantime, save up for something better. Hopefully you haven't "blown" the shocks out yet, but I woulnd't bet against it.

Dave-ROR

Well first let's convert the spring rates in question.
10k = ~560lb/in
6k = ~336lb/in
4k = ~224lb/in
OEM Front = ~246lb/in
OEM Rear = ~246lb/in (but progressive).

So, from the factory the front and rear rates are equal once the suspension is working, which plays a role in the car's neutral handling that we love. It's far from the only factor, but since it's the only factor we are changing in this conversation we assume everything else stays the same.

Leaving the rear OEM and no ride height changes would mean that increasing the front rate will make the car have a tendency to push, or understeer. Lowering the front rate would have the opposite effect.

Leaving the front OEM and no right height changes would mean that increasing the rear rate would make the car oversteer, lowering would make it understeer.

Effectively, 560lb/in springs up front with 224lb/in springs in the rear (higher rate than OEM up front, by more than double, and lower than OEM rates in the rear) will make the car understeer. A lot. 10kg/6kg would reduce the effect, but without alignment changes, smaller width tires in the rear, etc I'd personally hate that combination. I prefer a stiffer rear rate myself.

To keep the car's handling neutral you can just increase both rates to the same rate, or even go with a little less or more rear rate. 450 front, 400 rear for example. or 450/500, etc. Of the same, 450/450.

The lower you go the stiffer rates you'll need, and the dampers need to be better to handle higher rates.

On the flip side, many people wreck these cars because of their neutral handling, so 10kg/4kg rates is "safer" if you are prone to lift throttle oversteer or have a tendency to hit the brakes mid corner near the limits of adhesion.

I have no idea how low your car is, but I'd suggest increasing the rates to somewhere in the 400-500lb/in range (7.5-9.0kg/mm range if you prefer) and raising the car some if the rates don't help.

I have no personal experience with the BC (taiwanese) stuff but I haven't seen any great comments about them either so I have no idea how long they'll handle the higher rates. I'd hope that the front dampers can since you said they are normally 10/6 setups..

B serious

iTrader: (1)

The rear rates are not actually equal to the front rates. They're 250lb PROGRESSIVE springs, not linear springs. So the highest rated part of the spring is 250lbs. Progressive springs are difficult to "rate" since there's not much data on how soft the softest part of the spring is and how active each part of the spring is. Plus...the spring is different rates at different points of compression.

I agree that the stock ITR does handle pretty nice and neutral with a hint of understeer, however. Not to say that there isn't room for improvement.

On track, setup is much more important than equipment brand. Someone who knew how to set up a car with Megans could crush some fool with Motons simply based on setup.

That being said, the 10k/4k spring rate will produce bad understeer at the limit. The limit will most likely arrive sooner than it should. You can probably mitigate some of it with left foot or trail braking...but you'll be doing violent stuff to get it to stop the initial understeer. Corner exit will still be an issue.

It's a bad idea for a FWD car that's going to see the track, basically. With this particular chassis, it seems that a linear equal rate works well (450/450, for example). Or even slightly heavier rates out back. I had a 360/380 setup laying around so...that's what I'm doing after I track the car stock on Sunday to get a base line.

As far as tire sizing goes, the 205/50/16 is pretty damn tall. That's way too much sidewall. 205/45 is better, but I think that 215/45 is a good compromise of sidewall height and contact patch.

an2ny888

i'm looking for some enlightenment here, anybody care to give their opinion on why most japanese coilovers for the dc2 feature much stiffer front rates than the rear? for example the ohlins dfv coilover comes with 14k fr and 6k rear springs. Again i'm just looking for opinions, i'm not saying that what they did was right

Dave-ROR

B Serious: I noted that they were progressive, but once compressed there aren't many of the softer coils uncompressed...

Ultraspeed DC2

You can always compensate by lowering the front more as noted above. There's a video I have of Orido from BMI showing this example.

However, 10 and 4 are a long way away.

I like it slightly stiffer up front, as you should remember most of the weight is in front anyways. In that sense, the rear is proportionally stiffer than the front.

My personal settings are 500f, 450r. My front end measured at the top of the wheel arch is at least 1/4-1/2" lower than the rear. I play with the height difference alot and you can tune out the understeer that way.

....offset by my 26mm Mugen rear sway bar :-)

My car usually breaks the rear end out first if anything. My last 2 events were in the rain and I had no problem with front traction. I took out a R35 GTR (bad driver) and 3 Evos (2 times each) on video.

Todd00

You have to look at the entire setup...not just the springrates.

Many of these "JDM" cars also run a larger rear swaybar and a staggered tire setup (225 front, 195 rear).

Also, they come this way for safety reasons, somewhat.

anzai

thanks for the thorough explanation. you learn something new everyday! im now leaning towards F 9k, R 6 or 7k, depending on what's available. i found out cusco zero 2's has the 9/6 setup as well therefore i might try it out..

the car isn't overly low, but somehow low enough for it to scrub...
here's how its sitting at the moment:



unfortunately the $$$ is not on my side, so i dont have the luxury to be able to try out different setups... once i change it i'd probably leave it as it is until its absolutely necessary to change it again.

205/50r16 is quite tall, i am saving up for 205/45 as they are quite affordable, however 215/45 is out of question as these are about $100/tire more..

you sound like a pro track drive would you mind posting the link to orido's clip? thanks

Ultraspeed DC2

Got it:
http://video.google.com/videoplay?do...97&q=jond1492#