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Aggressive alignment and hard braking on a GT350R (pre-2020)

fpa1974

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So after the last round of alignment when I went pretty aggressive with front camber, I noticed some good things I expected, some bad ones that I also expected and some that I did not. The car definitely tracks better while cornering, and is more throwable., this part is good. Tramlining got worse - I expected this but it is definitely manageable. What I did not expect so much is the behavior under really hard, threshold braking when ABS is engaging but barely - the car pulls left and right like it does when tramlining but more pronounced - this is on not perfect pavement. I guess this is expected (the braking behavior) to a degree but is it really? Anything to do to tame this other than toning down the alignment?
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fpa1974

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Around -3 camber and 0 toe front with about -1.8 rear and 0.3 toe in.
 

jmn444

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I'd try .1 in up front. I have more camber front and rear and haven't had that issue, not sure what else it could be.
 
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fpa1974

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I am on Cup2s - I suspect that contributes quite a bit to it as well
 

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jmn444

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maybe, but my guess is still the toe.

Stickiest I've run is GY SuperCar 3R, but they should be similar to cup 2 and no braking issue like that so i'm not sure.
 

pilotgore

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So after the last round of alignment when I went pretty aggressive with front camber, I noticed some good things I expected, some bad ones that I also expected and some that I did not. The car definitely tracks better while cornering, and is more throwable., this part is good. Tramlining got worse - I expected this but it is definitely manageable. What I did not expect so much is the behavior under really hard, threshold braking when ABS is engaging but barely - the car pulls left and right like it does when tramlining but more pronounced - this is on not perfect pavement. I guess this is expected (the braking behavior) to a degree but is it really? Anything to do to tame this other than toning down the alignment?
By adding more negative camber you're putting the burden of traction on a smaller patch of tire while going straight, so you're losing overall traction in a straight line. The trade off is increased grip while in a turn, which is usually where we need it the most.

When threshold braking, a significant amount of weight shifts to the front tires/brakes.... and now on less of a contact patch than before. As the tire looses traction slightly and as ABS pulsates, you might feel a tendency for the car to walk in on direction or another (or tram-line). In my experience with cup 2's, what you're experiencing seems normal (usually not very bad though.) I particularly notice it as my tires become more worn on the outsides from high speed cornering, making the contact patch on the inside even smaller. Driving home from a track day with worn tires is the worst for tram lining!

For reference, I run -3.0 up front and -2.2 or -2.4 in the rear, with toe at -.1. Maybe adjust the toe and consider giving it more negative rear camber or decreasing front camber a bit.
 
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fpa1974

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That is an excellent summary and along the lines I was thinking as well. And thanks for the tips on alignment settings. I think I will for now reduce the camber a bit up front, add a little toe in in the front and see what is going on.

My initial post was also probing if this can be attributed to other things (alignment might have made things more obvious). I know the car is new and all and I maintain it properly, but theoretically can brake imbalance in the front cause this as well?
 

pilotgore

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That is an excellent summary and along the lines I was thinking as well. And thanks for the tips on alignment settings. I think I will for now reduce the camber a bit up front, add a little toe in in the front and see what is going on.

My initial post was also probing if this can be attributed to other things (alignment might have made things more obvious). I know the car is new and all and I maintain it properly, but theoretically can brake imbalance in the front cause this as well?
To a point, yes, but only temporarily. In my experience when I’ve swapped track pads on one side and not the other, heavy braking can make the car feel a bit squirrelly for the first couple laps until the pads have had a chance to bed into the old rotors. After a few laps, pad thickness won’t make any difference in feel or braking ability.

I’m using G-loc R12’s in the front, and my left fronts wear faster than my right (just like tires if I didn’t rotate then between track days.) There’s no point in trashing the front right pads when they have another track day in them!
 

jmn444

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To a point, yes, but only temporarily. In my experience when I’ve swapped track pads on one side and not the other, heavy braking can make the car feel a bit squirrelly for the first couple laps until the pads have had a chance to bed into the old rotors. After a few laps, pad thickness won’t make any difference in feel or braking ability.

I’m using G-loc R12’s in the front, and my left fronts wear faster than my right (just like tires if I didn’t rotate then between track days.) There’s no point in trashing the front right pads when they have another track day in them!
off topic, but how many days do you get out of the R12's?
 

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pilotgore

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off topic, but how many days do you get out of the R12's?
I’m currently traveling and don’t have access to my maintenance log.... but I think 5 days front left, 6 days front right, 7 days both rears. The rears I use r10’s.
It’s entirely possible all of them are one less day, but that’s definitely the order they were replaced in.
 

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-3.0 front camber is ALOT. Certainly reducing this will help with the tramlining. Depending on your Caster settings you could be picking up a significant camber gain under breaking. Camber is usually track specific, so you can potentially dial that back much more than you think.
 
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fpa1974

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I thought McPherson does not have a lot of camber gain under compression.

In any case I am planning on reducing the camber and see where that gets me.
 

jmn444

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-3.0 front camber is ALOT. Certainly reducing this will help with the tramlining. Depending on your Caster settings you could be picking up a significant camber gain under breaking. Camber is usually track specific, so you can potentially dial that back much more than you think.
I can't figure out how caster would affect camber gain under compression either... Can you explain?
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