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Post by cr89x on Apr 21, 2009 15:40:03 GMT -5
Hi guys and thank you ahead of time for the help.
If you have never driven a CRX before, they are very light in the rear and have virtually NO grip. I believe I have fixed this issue tho. Still in my curiosity I will ask.
I know front alignments should have slight toe-out and negative camber. Curosity, how much toe-out and negative camber would be reccomended? Streetability is not an issue. I can change alignment and I trailor the car to events anyway.
My main question is in the rear. I have NO idea what to do with the alignment back there. I just took it to factory spec tho. -1.4 degrees camber and very slight toe in.
My main question, what tire pressures would be reccomended?? I have one pair of crappy tires, going to the rear now, and one pair of decent Sunitomo HTR II's.
Hoping I can get the car to turn better.
Thank you all in advance. Sorry for the length. Just trying to give the details.
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Post by stealthgtfour on Apr 28, 2009 17:18:23 GMT -5
big rear bar and 0-0.1deg. total toe out in rear
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Post by cr89x on May 18, 2009 9:24:55 GMT -5
Ok mark. Appreciate that.
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Post by spdracer22 on May 20, 2009 22:37:37 GMT -5
I agree with Mark on the bar and the toe out. The best bar used to be something like a 32mm from ASR, but I haven't looked into them in a couple years. You're going to have an easier time getting the car to rotate if you lift up the inside rear tire, so if you're not doing so already, add bar until you do. You don't need to stuff the tire up in the wheel well, but it should be off the ground. Search for some pictures of the FWD SCCA World Challenge Touring cars...Realtime Acuras and the like.
I always found that the toughest time in my Civic was getting it to rotate in the middle, so I preferred to get it loosened up on entry. If I could get to the point where I was starting to unwind the wheel slightly before mid corner, I was good.
If you take a look at the rear geometry, the rear tires will toe in with bump, so the car will get tighter as you go from entry to middle to exit. I would aim for getting the car loose on entry and neutral from the middle off. So, since you trailer the car, I would keep cranking in some toe out until it gets sketchy at turn in, then go back a touch and leave it.
As far as pressures go: at first, I was told to add pressure to loosen up the car. This worked ok, but I found that the car ended up being 'snappy-loose', where I would lose all of my grip at once, versus a progressive slide. After doing some more research (and going through engineering classes in school) I started to rethink this idea, and started letting pressure out. I was already lifting up the inside tire, so I was transferring as much weight to the inside front tire as I could, so any extra spring rate from the loaded rear tire wasn't doing much. Also, I started tracking tire temperatures and found that I had a tough time generating any kind of heat in the rear tires, no matter what the pressure. So, with that info, I started running lower and lower pressures, and ended up with a 10-15psi split front to rear.
So, I would recommend starting with around 35 in the front and 30 psi in the rear and dial in the front pressures first, based on tire temps and feel. Then, I'd get the balance right with the rears.
Oh, and you asked about cambers. I ran somewhere around -2.5 degrees front, and -1.5 rear, and it seemed to work ok. Again, check tire temps. If you're getting about 10 degress hotter on the inside than the outside, you're good, otherwise adjust camber accordingly; that should get you a good starting point.
The key will be to get yourself in the ballpark, then fine tune from there.
If you don't mind posting them, what springs rates are you running? Oh, and what class?
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Post by spdracer22 on May 20, 2009 22:50:05 GMT -5
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Post by cr89x on May 21, 2009 13:16:00 GMT -5
That picture is CRAZY!!! Thanks for the wisedom. Now I would be led to believe that lifting that tire up would be due to too much speed and also that in doing so it would limit grip. Very suprising if my thinking is wrong.
I've finally got negative camber in the front, 2 degrees, but a little worried for this weekend. This CRX is a hybrid car. It's got a 3rd gen Integra rear on it. So my disc brakes are almost identical in size all four corners. I had upped my front rotors but couldn't get any negative camber out of the different knuckles. I'm going to keep trying stuff though. Definately going to look into a rear bar now and next time I put the car on the rack, which unfortunately won't be in time for this event coming, I'll play with the rear toe.
Thank you very much on tire pressures, i'll try them out and try to tune in a loose entry. Greatly appreciate that good information. I know I have the correct loose nut behind the wheel of the cars i've been driving, but just nothing on the otherside of the wheel to back it up.
I run in SSM so it's a d16a6, stock for the Si, with a t28 turbo going to 16G. It adds a good 150lbs. up front would be my guess. Spring rates, i have no clue!! or i would help. Want to look into that also tho. What I have suprisingly does ride good on the streets to me but they are stiff.
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Post by spdracer22 on May 21, 2009 21:59:41 GMT -5
Well, you are limiting grip in the rear, but there's not much load back there anyway...the rear tires just sort of hold the truck up... Anytime you make a tire do more than one thing, it's not going to be able to do it as well as if it only had to do one thing at a time (pure lateral/longitudinal, versus combined loading). So, it ends up being better to try to load the front tires more evenly (ie more inside tire load, which has more grip potential than increasing outside tire load), and the way you do that is by increasing rear roll stiffness. Now, you get to a point where you can't really add much more inside front load, and that's usually when you start picking up the inside rear tire.
If you don't have a bar at all right now, you could start with a stock ITR or GSR bar, something around 19-20mm. That will get you closer, and you should start to see a bigger difference at mid corner. If you go with a stiffer bar, it will carry the tire off the ground longer, so it will make the car looser in and looser out.
And definitely take good notes - even if they're on post-its that you throw in the glove compartment after every run - and review them after the event; you'll eventually start to see trends and know whether you're moving in the right direction or not.
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Post by cr89x on May 22, 2009 9:18:48 GMT -5
I got thinking about it later yesterday and consulted with some physics people, because we get bored and like contimplating racing. Basically your saying transfer weight to the front for more front grip and the car won't push ... as bad lol. correct?
I like the note reference. I'll definately be more aware of what the car is doing this weekend.
Thank you for your help. Gives me a new perspective now.
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Post by spdracer22 on May 22, 2009 10:29:29 GMT -5
Yes, transfer load from the inside rear to the inside front. (well...sorta)
What's happening is load is being transferred from the corner that is being unloaded (inside rear) and distributed to the other three tires; the roll/pitch stiffness (depending on lat, long, or combined cornering) determines how that load is distributed between the three loaded tires.
Remember, too, that an equally loaded axle is going to produce more grip than an unevenly loaded axle.
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