Plaid DIY measure rear toe

[Zuikkis]

Hi,

I'm about to install rear camber shims. I figured I'd do at least some initial toe adjustment myself. I have done it before on my earlier P85+ using strings, but now I had bought a chinese laser to make it easier.

I figured I'd measure my current setup first, before installing the shims.

First I measured camber with water level, it's pretty easy. I have about -1.5 degrees per side, with car in Low.

Then the toe. Here's my top notch laser setup:

The laser is this one from aliexpress:

https://www.aliexpress.com/item/1005005860116174.html

Then I measured the beam distance to the front wheel cap, and also to the rear wheel cap. Front right was 120mm, front left 115mm, rear 78mm+20mm=98mm.



Now there was an issue that I did not know how much more inside the front wheel is. It obviously is a bit. Tesla claims that track width is 1690mm both front and rear, but even then there is the issue that front wheels have offset of 45mm and rear only 40mm.. Track width is measured to the middle of the wheel, so offset difference of 5mm would mean that the front hubs would need to be 5mm OUTER than the rear, which doesn't make sense and must be incorrect. Edit: Turns out offset is 45mm rear and 40mm front, so with same track width front hub would be 5mm inwards which does make more sense.

This site lists 1662-1700mm for the front:

https://www.car.info/en-se/tesla/model-s/model-s-s-2023-35295650/specs

Still not very helpful that gives a hint that there is some "tolerance" in the front track..

I decided to add marks to front and back of car so I could accurately measure toe without relying on the front hub location.

The boxes at rear are positioned exactly between the laser lines, and then there's plywood plates at front where I marked the laser location with a pen.

Distance between laser beams at front = 212.5cm
Distance between laser beams at rear = 210.0cm
Distance from plywood to the box = 645cm

Then it's just math. angle = atan( ( 212.5-210) / 645 ) = 0.222 degrees of total toe out! Isn't rear supposed to be toe in? Doh.

Anyway, now that I know the actual toe, I can use that to calculate how much more inside the front hubs are. Wheelbase is 2960mm. 0.222 degrees at 2960mm distance is 11.5mm. My measurements were 120mm+115mm-98mm-98mm = 39mm, from which we deduct 11.5mm = 27.5mm. That would be 13.75mm per side. Round that to 14mm and we have 1690mm-28mm=1662mm which was the number mentioned in car.info link above..

Toe per side calculated from my original measurements:

Left 115mm: atan( ( 115 - 14 - 98) / 2960) = 0.058 degrees
Right 120mm: atan( ( 120 - 14 - 98) / 2960) = 0.155 degrees

Total now becomes 0.212 degrees, slight deviation from the original measured 0.222 but close enough and very easy to measure from the front hubs.

But still it's toe out, doh.

 

[ramirj2]

I did mine with a string, race ramp blocks and jack turrets to hold the string, after returning to stock arms for a track package installation.
I reinstalled my camber arms and adjusted both camber and toe at home.
Track is the same both front and rear if you measure from the center cap. as you mentioned offset and width on the wheels is different front and rear, so I measured at the edge of the wheels to get the Toe.
My steering wheel was off center, and the car was slightly pulling left before.
I ended up with approx. 1.5 degrees of camber in low on each corner and 0.1 of Toe in per side.
Wheel is straight, car pulls straight.
Have been twice to the drag strip and at 185 MPH on a 1/2 mile since the alignment, so I haven't had a need to take it to a professional shop yet.

 

[Zuikkis]

If track is really the same front and rear, then there must be something really wrong in my measurements...

I now installed the camber shims. Toe went noticeably in. The measurement from laser to front center cap went down 15mm both sides, which should mean about 0.3 degrees per side.

I took the car to a professional. Toe was about 0.5 degrees per side, which would mean it probably was about 0.2 degrees toe in without the camber shims. So actually quite ok!

He adjusted it to 0.19 per side. It's perhaps a bit high but quite in the middle of the recommendation by Tesla . Now my laser measures exactly 115mm per side.

Anyway now I have good base to check it again if needed, as it's just a 1min job to attach the laser and measure.

 

[itch808]

OP, you're only doing a two wheel alignment. The usual DIY 4-wheel alignment needs essentially a box around the entire car at all 4 wheels. I've done it in the past with strings/fishing line and jackstands. You'll also want turn plates to help settle the suspension with every change. Without a 4-post lift, it's very tedious and time consuming to recenter the box after every change.

 

[Zuikkis]

@itch808 sure, the title says "measure rear toe".

I have used the string method before and as you said, it is too much work. Professional alignment is not that expensive, there's no point wasting hours of you own time.

This laser trick is very fast and at least tells you instantly if anything has changed since the last time .

My first Tesla was a 2013 P85+ that had a blown bushing in the rear toe link, causing excessive toe. Annual toe check would have probably caught that earlier.