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How the nut behind the wheel affects how B15s handle...

36K views 91 replies 21 participants last post by  lossweight 
#1 · (Edited)
There have been alot of threads about what suspension to use and what springs are best etc. etc. to make our cars handle...but what can we do to change the way the car behaves???

For thoe who don't know (and those that do just be patient) my car has JIC B15FLT-A2s with 7k/6k springs, a NISMO rear bar and the NISMO bushing kit. This is my particular setup, now lets see how it does. I've autocrossed the car extensively but not until I installed an in-car camera could I dissect my mistakes and correct them later on.

First off, the facts...rear beam suspensions don't like quick transitions. They're too heavy and too slow to react properly. But, its what we have, so we have to live with it. Now, once its planted and set in a corner, the amount of grip it can develop is pretty damned good...so how can we improve the transitions? This is where you, the driver, the nut behind the wheel comes into play.

I cannot emphasize smoothness enough. Example, last month I was autocrossing, came through a slalom on my first run and the rear came loose. Luckily I caught it and managed to finish without knocking down any cones...only scaring a few course workers. The rest of the day went without incident. So what was the difference??? Upon watching the video, I realized that on my first run while I was feeling out the course, I was going through the slalom in second at about 6K rpm. I let off of the throttle and the tail swung right, then left, then I mashed the gas and straightened it out. On the next run I was more familiar with the course so I was going about 5MPH faster through that section, in 3rd now, and the car just stuck and I dropped 2 seconds off of my time. Lesson learned, since working the throttle in 3rd unsettles the car less, the car maintained its line and stuck. Now, this doesn't mean you should go through all slaloms in third, but rather if you are in second, be smoother applying and getting out of the throttle so that weight transfer is minimized.

On to the track. I'll be honest, I was afraid that my car would be a handful due to its tail happy nature when i was autocrossing. I contemplated removing the rear sway bar but decided to run the car as is because it was the way that I was accustomed to running the car. I made the correct decision.

On a track, driving styles are very different from an autocross course and smoothness is extremely important. Pushing this Sentra to its cornering limits at 100+ MPH was almost easy, it cornered flat without threatening to swap ends or resorting to terminal understeer. By giving smooth, measured inputs at the correct moments the car was transformed to a neutral handling machine that exhibited more grip than I thought it ever had.

So, keep in mind while you're hacking at the wheel...slow the hands down...think ahead...look ahead...and keep those inputs smooth (brake, throttle and steering)!
 
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#77 ·
Simmons-Racing said:
I had 500/550 springs on my Spec-V. The car seems to understear mid corner and corner exit. I just installed 600/732 springs, and I want to try a 215 rear tire instead of the 245. What do you think?

What the hell are you doing running a 245 tire?
 
#81 ·
Simmons-Racing said:
I had 500/550 springs on my Spec-V. The car seems to understear mid corner and corner exit. I just installed 600/732 springs, and I want to try a 215 rear tire instead of the 245. What do you think?
i considered this - but i never had issues with rotation. i *highly* recommend you get your rear beam bent to 0 toe - it did wonders for my car.

keep in my mind, this was all on a GS-legal car. when i ran STX, i had a very neutral car with very little understeer (and no bent beam). but i also wasn't running a max prepped car either (nismo s-tune shocks/springs - i was a total n00b, lol). bend the beam, and see what it does for ya, and go from there.

you used to have a dude on the east coast, but he moved to colorado. i can vouch 100% for darin nishimura in gardena though [but he's on the wrong coast].
 
#82 ·
boardkat said:
i considered this - but i never had issues with rotation. i *highly* recommend you get your rear beam bent to 0 toe - it did wonders for my car.

keep in my mind, this was all on a GS-legal car. when i ran STX, i had a very neutral car with very little understeer (and no bent beam). but i also wasn't running a max prepped car either (nismo s-tune shocks/springs - i was a total n00b, lol). bend the beam, and see what it does for ya, and go from there.

you used to have a dude on the east coast, but he moved to colorado. i can vouch 100% for darin nishimura in gardena though [but he's on the wrong coast].
Is that "Legal" in STX? If so where do I get it done?

Thanks
 
#83 · (Edited)
Simmons-Racing said:
Is that "Legal" in STX? If so where do I get it done?

Thanks
some would call it a "gray area", but really, if you're keeping your rear toe within FSM specifications, there will be no issues (and 0 toe is within spec). there's a thread on sccaforums that discusses the legality from a few years back, but i can't get to the site at the moment for some reason. i'll edit and include the link when i can.

EDIT: found it. you'll notice that guru andy hollis was very specific about what constitutes legal - "if its bent within manufacturer's specs (see the frame chart,hopefully wthin the FSM), its legal even in Stock"

http://sccaforums.com/forums/thread/26253.aspx

98sr20ve (steve foltz) made a jig to do it, not sure if he's on this board anymore, but i think he still frequents sr20forum. he used to live in your neck of the woods, but i think he moved to colorado. i've heard he'll still travel for "bending parties" if you can get enough people together to make it worth his time.

http://www.b15sentra.net/forums/showthread.php?t=58292

otherwise, darin nishimura @ west end alignment in gardena, ca.

 
#84 ·
IMHO, if the car is pushing mid corner and exit there is a set up issue. Whether it be spring rate, alignment settings...something needs to change.

The spring rate change you mentioned should help, but if the alignment specs aren't up to par, then they won't matter. If you can't get the front tires to grip...the car will push. I was running more than -2.5 degrees of camber on my SE when it finally started to handle decent. If I would have been allowed to open up the strut tower hole in STS I would have run more...crash bolts could help get you there though.

Staggering tire sizes is another way of affecting the balance of the car. A narrower tire in the rear will reduce rear grip and should help the car rotate better. Now, keep in mind that with the solid rear beam the B15 tends to slide the rear end rather than rotate it. You may need to keep an eye on outer edge temps of the narrower rear tire because you "may" start to over heat the outside edge of the tire from sliding the rear around.

Good Luck! :D
 
#85 ·
2000SR20 said:
IMHO, if the car is pushing mid corner and exit there is a set up issue. Whether it be spring rate, alignment settings...something needs to change.

The spring rate change you mentioned should help, but if the alignment specs aren't up to par, then they won't matter. If you can't get the front tires to grip...the car will push. I was running more than -2.5 degrees of camber on my SE when it finally started to handle decent. If I would have been allowed to open up the strut tower hole in STS I would have run more...crash bolts could help get you there though.

Staggering tire sizes is another way of affecting the balance of the car. A narrower tire in the rear will reduce rear grip and should help the car rotate better. Now, keep in mind that with the solid rear beam the B15 tends to slide the rear end rather than rotate it. You may need to keep an eye on outer edge temps of the narrower rear tire because you "may" start to over heat the outside edge of the tire from sliding the rear around.

Good Luck! :D
The car is Maxed out at -2.5 camber. Any more and the tires hit the struts. I set front toe to 1/8 out. I think the narrower tires should help?
 
#86 ·
BTW for all you guys commenting, Eric (Simmons-Racing) has my old car. :D

I know we've talked about it a bit before, but I think the new spring rates combined with a 215 or 225 tire in the rear should really help out. I know last I drove it with you right after the higher rear springs, the car felt really good to me...but I don't left foot brake, which I think is one of the things making the issue worse for you than me.

Another thought may be to put a 5mm spacer on the front to widen the track and also allow for more adjustment in camber to something a bit more aggressive, that is if the smaller rear tire size doesn't work.

As far as beam bending, yes it's a very gray area. The problem is finding someone to do it correctly. Essentially you have to bend the beam within the beam at the same time you bend the outside. Perhaps we can get with Aaron and design a jig to make it work, and then head up to Bimmerworks and get Steve to let us use the alignment rack...except that I think you have access to one, so scratch that. :D Either way, I'm sure Aaron wouldn't mind having his done as well, and if we can perfect the method then there's a money making opportunity there. ;)
 
#88 ·
With the spacers pushing the center out, and if you dial in a bit more camber to pull the top in, there shouldn't be any rubbing on the outer edge. If you keep camber the same, you would have more room between the strut and tire and still shouldn't have any rubbing on the outside at the fender.
 
#89 ·
piknockout said:
With the spacers pushing the center out, and if you dial in a bit more camber to pull the top in, there shouldn't be any rubbing on the outer edge. If you keep camber the same, you would have more room between the strut and tire and still shouldn't have any rubbing on the outside at the fender.
Anything to get more camber up front will help...to an extent. If youhave a pyrometer check if you're roasting the outside edges of the tires. If the temps are relatively even then you shouldn't need more camber. BUT, from my experience, -2.5 is not quite enough. hell, I'm running -3.0 up front on a double wishbone car that has camber gain in its travel unlike a mcstrut car. The limiting factors are physical room with that wide of a tire and the fact that braking and accelaration will begin to suffer as you add more camber...its a balance.

The narrower rear tires will help the car rotate for sure. Just budget the fact that the fronts (which you now can't rotate to the rear) will get chewed up quick and the rears will heat cycle to death before they are worn out. Something that i've done with a friends AWD SM car is to have different width rear tires to "tune" the cars attitude with tire width. Normally he runs 315 fronts and 275 rears...but can use 285, 305 or 315 rears as well.
 
#90 ·
Seeing as this is for autocross use and being setup to win, I don't think tire wear is a huge issue. I think.

Agreed, too much camber and braking and acceleration start to be hindered. I know Eric was saying there were wheel spin issues, so perhaps a bit more camber, higher spring rates in front, and softer bar will help that, then dial in a bit more camber and the smaller tire size in the rear and it may be good.

As far as tire temps, when Eric and I ran it at the last event, the driver's side showed the inside tire temp a bit hotter (barely - 5 degrees or so), but on the pass side the outside tire temp was about 20-25 degrees hotter I think. A left turn intensive course...of course. :D
 
#91 ·
piknockout said:
Seeing as this is for autocross use and being setup to win, I don't think tire wear is a huge issue. I think.

Agreed, too much camber and braking and acceleration start to be hindered. I know Eric was saying there were wheel spin issues, so perhaps a bit more camber, higher spring rates in front, and softer bar will help that, then dial in a bit more camber and the smaller tire size in the rear and it may be good.

As far as tire temps, when Eric and I ran it at the last event, the driver's side showed the inside tire temp a bit hotter (barely - 5 degrees or so), but on the pass side the outside tire temp was about 20-25 degrees hotter I think. A left turn intensive course...of course. :D
Point taken about setting the car up to win...just laying out all the information I can. I originally set up my Civic (road racing) with spring rates, etc. to support staggered tire sizes in order to get all four tires to heat up evenly...225 fronts and 205 rears. THe rears would heat up at the same pace as the fronts allowing me to be more aggressive on opening laps and having a more consistent car. The downside...5-6 races and the fronts are down to the cords and the rears are still relatively new but hard as a rock. Were I to be running even tire sizes I could rotate and likely get 8-9 races out of a set of tires. Just an example.

Another thought...lower tire pressures will aid grip (accelaration and braking) when using more extreme camber angles. Be sure to play around with this as well.

A 15 to 20 degree spread from inside to outside is not that bad...but will always be course dependant. If you're going to make changes, try and do so on a test and tune day where you can run the same course to have more concrete measurements.

Front wheel spin issues can also be cured with a softer front roll rate (combination of springs + roll bar)...but the softer front roll rate will also numb turn in so its always a compromise. Damned FWD. I have always preferred to have the crisper turn in which helps the rear come around followed by immediate throttle to control the amount of rotation.
 
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