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Rear Toe alignment preferences

I am working on my alignment for summer and autocross. I have the MPP toe and camber arms, so it is super simple to adjust with my toe plate kit (note that I have had a shop alignment previously to make sure it was close and even side to side).

What toe specs are people running? Why would Tesla spec positive toe in the rear? Should I just shoot for zero?

I am measuring in fractions of inches because that is what my toe plate kit came with.

I have searched the numerous threads, but have not seen just the rear toe discussed at this level.
 
Dead-on zero toe all around is not ideal.
Read all about it on automotive racing forums.

Depending on your use and preference a bit of positive toe in the back (just like a bit of negative camber all around or upfront) is ok. And by a bit I mean even as little as 0.05, 0.125 or 0.25.
 
I’m running 0 toe all around. Rear settled in at -1.5 camber with stock arms and fronts I run at -1.2 in the front with a full shim stack in the MPP FUCA for street and whatever no shims gets me for AutoX.

Just took a 1400 mile road trip, left 2 hours after setting FTD at our AutoX event and have no complaints at all about how it drove so it must be working.
 
This is a subject I'm also curious and learning about. MPP lists their alignment specs for track and street in their project car section in mm. If using camber plates, doesn't the measurement depend on how far up the tire you measured?

Also, do you guys adjust your toe every time you swap camber shims in/out for autoX? Seems like a hassle, but maybe it's not hard.
 
This is a subject I'm also curious and learning about. MPP lists their alignment specs for track and street in their project car section in mm. If using camber plates, doesn't the measurement depend on how far up the tire you measured?

Also, do you guys adjust your toe every time you swap camber shims in/out for autoX? Seems like a hassle, but maybe it's not hard.

I do. And part of the reason I am running full shims on street and no shims for AutoX because MPP has that change listed as exactly 2 full turns of each tie rod. I got it aligned with full shims in and then used a paint marker to mark them.

I may go to just the one 8mm shim for street which they have listed as 1 full turn when going to no shims to get a little camber for street fun.
 
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pt19713

Active Member
Feb 5, 2020
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On my Y I'm running 0.20 toe in the rear. This helps eliminate the stock tendency to understeer. The rear end rotates around much easier with the positive toe in the back. I'm also running a fairly mild -1.0 camber. Those running a little more negative camber are probably running less positive toe in the rear.

It's one of those settings that you'll get a wide range of responses. Some prefer having a more neutral rear end, others prefer having it rotate more. You might also get different responses based upon tire pressure and camber settings.
 
On my Y I'm running 0.20 toe in the rear. This helps eliminate the stock tendency to understeer. The rear end rotates around much easier with the positive toe in the back. I'm also running a fairly mild -1.0 camber. Those running a little more negative camber are probably running less positive toe in the rear

More toe-in at the rear improves stability and reduces rotation speed into a corner in my experience because the outer rear wheel in a turn is always trying to straighten the car due to it’s increase in slip angle. Same with the front end, toe-in will increase understeer, but improve stability, toe-out will improve turn-in.
 

pt19713

Active Member
Feb 5, 2020
1,056
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Delaware
More toe-in at the rear improves stability and reduces rotation speed into a corner in my experience because the outer rear wheel in a turn is always trying to straighten the car due to it’s increase in slip angle. Same with the front end, toe-in will increase understeer, but improve stability, toe-out will improve turn-in.
Sorry, I just realized I typed toe in for the rear. I'm running toe in for the front, toe out in the rear.
 
Toe out in the rear is semi common in AutoX where you want to rotate quickly. It's generally a bad idea in road courses where you need more braking and high speed stability.

This is why I disagree with the "Dead-on zero toe all around is not ideal." from earlier- 0 toe can be a reasonable setting for cars that are not focused on one duty. I like to AutoX the same car I drive to work without hours of work to convert it, so I don't run toe or camber that makes the car twitchy on the street or eats tires. 0 toe is kind of that middle road in a lot of ways. Like SK360 I often do FTD at my AutoX so it's not some handling pig at 0 rear toe- in fact I find the car a bit tail happy under power.
 
Just put 5,500 miles on the car for One Lap of America. Car was understeering quite a bit on 275 Michelin PS4S with zero toe in the front and .2 degrees of toe-in on each rear tire (factory setting). We zero'd out the rear toe halfway through the event and the understeer was virtually eliminated. I think honestly this is a pretty good setting. If you added a lot of rear downforce, you would even want a bit of toe out in the rear to help the car rotate at lower speeds (and the downforce would help high-speed stability).
 
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pt19713

Active Member
Feb 5, 2020
1,056
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Delaware
Jeez, that must be scary at high speed corner entry! On my race car, I run the opposite, toe-out at the front for decent turn-in with slight toe-in at the rear for some stability.
Slightly different driving dynamics in the Y due to the extra 400 lbs of weight, so it has a bit more understeer. The toe-out in the rear helps keep the understeer in check. Plus, it's just how I like my car setup. I've owned two Miatas over the last 2 decades, started out with a 1997 Miata 1.8L built for CSP, then I moved on to a 2004 Mazdaspeed MX5. I like have my rear end rotate around, but I might have to adjust my driving style for a car that weighs over a ton more than the Miatas haha. I'll probably have to change to the more traditional slow in, fast out approach instead of the Miata mentality, balls to the wall fast in fast out and letting the rear end rotate aggressively.
 
Slightly different driving dynamics in the Y due to the extra 400 lbs of weight, so it has a bit more understeer. The toe-out in the rear helps keep the understeer in check. Plus, it's just how I like my car setup. I've owned two Miatas over the last 2 decades, started out with a 1997 Miata 1.8L built for CSP, then I moved on to a 2004 Mazdaspeed MX5. I like have my rear end rotate around, but I might have to adjust my driving style for a car that weighs over a ton more than the Miatas haha. I'll probably have to change to the more traditional slow in, fast out approach instead of the Miata mentality, balls to the wall fast in fast out and letting the rear end rotate aggressively.

I probably shouldn’t compare my Evo to a Tesla, as the suspension geometry is different, but slight toe-in at the rear and toe out at the front worked well on track at all speeds. Car also has plated diffs front and rear, and spring rates and anti-roll bars set-up for zero understeer!

I tried zero toe at the rear on my Model 3 (zero at the front too), and it felt unstable at high speed (120mph+). I’ve since adjusted slight toe-in at the rear, and it feels stable again. I also changed all the arms to MPP at the same time, so perhaps I should try zero toe at the rear again. TBH, zero toe all round would be preferable as long as it’s stable at high speed.
 
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Dangerous Fish

Pilots the Millennium Milkfloat
Supporting Member
Jul 21, 2016
2,107
4,720
UK
1mm of toe out at the front and 1mm toe in at the rear on mine.
Only shook it down yesterday with these settings along with more camber but it felt good and was no trouble to drive an hour each way to the track on various road surfaces and speeds.
With 30/70 balance on TM it's very neutral through the corners, but I can understand why Autocrossers might want a bit more rotation through tight turns by being more aggressive with rear settings.
 

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