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Old 09-27-2013, 12:06 PM   #1
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Default Increasing rear grip...options?

Coming out of a corner getting on the gas my car feels loose. 28 front bar and 12 rear 550/325 springs. Otherwise the car feels pretty good. I could add 3mm packers to the front shocks...would that improve weight transfer to the rear? I could add the 3mm packers to the rear which would increase spring rate as the rear springs compress but I think that would increase oversteer. I could add a bit toe in at the rear at next alignment and I could increase the rear negative camber. Does increasing the rear negative camber increase rear grip? On my street car I've got .5 degree more negative camber at the rear vs the front and the car feels more stable on track.
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Old 09-27-2013, 12:12 PM   #2
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Try removing your rear bar.
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Old 09-27-2013, 12:22 PM   #3
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remove rear bar winner!

suspension tuning 101:
softer = more traction
harder = less traction

you can either make the grippy end less grippy or make the slippery end less slippery.

Note that in more advanced lessons, this does not always apply.
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Old 09-27-2013, 01:03 PM   #4
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Differential. OMFG my green car hooks on exit.
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Old 09-27-2013, 02:03 PM   #5
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Less rear ride height, less front rebound. Don't bandaid it with toe changes. When was the last time the car was cornerweighted and/or aligned? What does the tire pyrometer say?
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Old 09-27-2013, 02:17 PM   #6
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Quote:
Originally Posted by Savington View Post
Less rear ride height, less front rebound. Don't bandaid it with toe changes. When was the last time the car was cornerweighted and/or aligned? What does the tire pyrometer say?
Ride height at the pinch welds is pretty much even front and rear about 5 1/4 inches, I know lower is better but I have to be able to get it in my trailer. Shocks are SD Bilsteins so no rebound adjustability.

I'm not sure it's a differential issue as the 1.8 track car has a VLSD and the street car has a 1.6 with an open, granted, the 1.8 has gobs more torque.
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Old 09-27-2013, 02:21 PM   #7
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With those spring rates you might actually be on the bump stop with the outside rear in the corner, giving you an artificially high spring rate at the rear. Check the travel with the zip tie method before changing a bunch of things.
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Old 09-27-2013, 02:39 PM   #8
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Bump the power down.
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Old 09-27-2013, 03:01 PM   #9
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Quote:
Originally Posted by Dunning Kruger Affect View Post
Bump the power down.
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Old 09-27-2013, 03:42 PM   #10
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Quote:
Originally Posted by wannafbody View Post
Ride height at the pinch welds is pretty much even front and rear about 5 1/4 inches, I know lower is better but I have to be able to get it in my trailer. Shocks are SD Bilsteins so no rebound adjustability.

I'm not sure it's a differential issue as the 1.8 track car has a VLSD and the street car has a 1.6 with an open, granted, the 1.8 has gobs more torque.

The Viscous LSD is the 1.6 LSD. Are you sure you have two failboat diffs in your car? Or do you have a torsen in the 1.8 race car?

There's a little table I posted long ago from a book I read even longer ago about oversteer and understeer. Basically what the others have said, but it includes tire pressure, tire grip, spring rates, sway bar rates, downforce, and other things, and whether or not they increase oversteer or understeer when you increase/decrease them. Hopefully that sentence made sense.
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Old 09-27-2013, 08:49 PM   #11
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Quote:
Originally Posted by sixshooter View Post
With those spring rates you might actually be on the bump stop with the outside rear in the corner, giving you an artificially high spring rate at the rear. Check the travel with the zip tie method before changing a bunch of things.
This idea occurred to me as the track car has NB mounts and the street car has 1 inch ISC mounts.

The track car has a 99 1.8 swap with the stock 4.3 VLSD and the street car has the open diff.
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Old 09-27-2013, 10:35 PM   #12
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Better throttle control. Oh, and no rear bar.


INB4 datalogs.
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Old 09-28-2013, 12:43 AM   #13
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After crawling under the cars it's obvious that the street car with ISC top hats has more shock travel before contacting the bumpstops, probably 3/4 of an inch more. Since the setup is basically the same between both cars I'm going to try different top hats in the rear of the track car and see if that solves the issue.
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Old 09-28-2013, 07:22 AM   #14
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You can effectively get the feel of no rear bar by disconnecting one end of one end link and tying it out of the way. I would do this before anything else as it is a very easy experiment.
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Old 09-28-2013, 09:37 AM   #15
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Check the sag like you said. If the bump stops are hitting on corner exit (and the fronts are not hitting at the same time) the rear will get loose, maybe very loose depending on the stiffness of the bump stops. If this is what is going on, you need to fix the sag before you try anything else. Removing the rear sway will not help.

If it is the bump stops, I have seen this before and you will go nuts trying to correct this until you increase the sag.
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Old 09-28-2013, 10:37 AM   #16
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^He's right. Less rear bar would make it much worse if you are hitting the stops. More rear spring or more rear bar is the answer if you can't readily add travel.

My car is pretty neutral with 550/350 and FM sways (25mm full stiff/17?mm full soft) and ISC hats. You have more front bar, less rear bar, less rear spring, and less travel. I could see where you would get enough body roll to get hard against the stops.
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Old 09-28-2013, 05:58 PM   #17
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The bumpstops came with the shocks. They were cut down to 36mm. I'm guessing that they ramp up much faster than the 46mm ones on the street car.

Also, I crawled under the car and with NA Bilsteins I can slip one finger between the top of the front shock and the bumpstop so the amount of lowering left at the front is very little. Since I'm running at a very rough track any more lowering at the front probably isn't a good idea.

Last edited by wannafbody; 09-29-2013 at 07:18 PM.
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Old 10-04-2013, 03:11 AM   #18
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It's like he's not even listening.
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Old 10-04-2013, 09:44 PM   #19
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More rear bar won't work as I already had a 15mm rear swaybar and it was even looser than with the 12mm swaybar.

The front bumpstops should be engaging before the rear bumpstops as I have a 3mm spacer up front.

Last edited by wannafbody; 10-04-2013 at 10:30 PM.
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Old 10-04-2013, 10:53 PM   #20
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Pretty sure most of the people posting in this thread are telling you LESS rear bar, not more.
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