How much is too much?

ExSRT8Guy

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I don't know off the top of my head what the "P" rear spring rates are, but I'll bet they're at (or under) 200lb/in. With 3/4" static clearance between the frame rails and the bump-stops, that would allow you less than 150lbs of load transfer to that spring before you're on the bump-stop and go to effectively infinite spring rate (simplified) and that certainly WILL create a "non-linear" handling characteristic. Same will happen if you bottom out the shock on that corner as well...

When you say "the back end started to come around," do you mean that you experienced SOME oversteer, or that you suddenly snapped around? big difference in the diagnostics tree. Also, how much experience do you have on track? If you're timing laps, what is your typical time spread on clean laps? 0.1 seconds? 0.5 seconds? 1 second?

I'm inclined to look at driver input rather than hardware first...

Maybe it's an inch. Didn't measure; just guessed from the visual. But I get your point. That said, there's a measurable amount of compression in the untrimmed bump stop before it goes "solid", right?

Snap oversteer is what we used to get when we lifted throttle mid-corner in a pre-'64 Corvair, or an early 911. Compared to that, this was "some" oversteer. I steered into it, let off, got it straightened out, and kept going. Nothing overly dramatic, but definitely not the quickest way through that corner.

I have no idea what my lap times are. I'm just out there to have fun in a controlled environment, hopefully without thrashing one of my street cars too badly :waytogo:
 

2013DIBGT

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Maybe it's an inch. Didn't measure; just guessed from the visual. But I get your point. That said, there's a measurable amount of compression in the untrimmed bump stop before it goes "solid", right?

One fairly easy way to test the theory would be to grease up the top of the rear bump stops with something like that silver disk brake quiet/Anti seize crap that seems to find its way all over the place just by opening the lid. Slop up the bump stops before your next session and then check for signs of it on the frame rails after the session.

Then again you could just lop them off at the half way point just in case and forget the silver grease but its probably worth the effort to find out anyway because in doing so it will tell you if more rear spring rate or better shock is needed.
 
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ExSRT8Guy

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Tire compound is more important than tire size. I ran some good laps on 245/47/17 NT01s. Then I ran my 275/40/18 NT555s and they were definitely slower, less grip. Ok to have fun on, but I prefer the sticky rubber. :)

I get it. Trying to justify a second set of wheels/tires for the too-infrequent track days I attend. Maybe it'd be incentive to go more often!

One fairly easy way to test the theory would be to grease up the top of the rear bump stops with something like that silver disk brake quiet/Anti seize crap that seems to find its way all over the place just by opening the lid. Slop up the bump stops before your next session and then check for signs of it on the frame rails after the session.

Then again you could just lop them off at the half way point just in case and forget the silver grease but its probably worth the effort to find out anyway because in doing so it will tell you if more rear spring rate or better shock is needed.

Good idea. And based on Dave's input, I'll likely cut off the top section, anyway.
 

Norm Peterson

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Maybe start by trimming only half a convolution off the stops. You can always cut more off if you find that's not enough.

After cutting, it may be worth "countersinking" the hole in the middle with a rotary rasp or a step-drill in order to regain a little initial compliance for the times when you will hit them.


Norm
 

ExSRT8Guy

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Maybe start by trimming only half a convolution off the stops. You can always cut more off if you find that's not enough.

After cutting, it may be worth "countersinking" the hole in the middle with a rotary rasp or a step-drill in order to regain a little initial compliance for the times when you will hit them.


Norm

:waytogo:
 

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