Using a Laser Level to Set Rear Toe-In

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Apr 17, 2013 | 05:11 PM

robrob

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From: West Virginia

Using a Laser Level to Set Rear Toe-In

I recently had my car professionally aligned and wanted a more precise way for me to set the rear toe than stringing the car. Since I had a known starting point for the alignment settings I calibrated my ebay special laser level to inexpensively and accurately adjust rear toe. Using this method allows me to play with rear toe settings to tune the handling of the car. This is basically cut and pasted from my website's alignment page.

Using a Laser Level to Set Rear Toe

24" Digital Laser Level

This $55 ebay 24 inch digital laser level can be used to project a laser dot to help set the toe. It projects a laser dot out of one end and it has a digital level display accurate to 1/10 of a degree so it can also be used to set camber and caster too. I compared this level to my SmartCamber digital camber gauge and it was within 1/10º. You need to start with a known alignment to calibrate your measurements so get the car aligned at a shop then come home and take measurements with a laser level and you'll then be able to accurately set rear toe.

Checking Camber 90º - 87º = 3.0º negative camber

You can adjust the laser's internal alignment by removing one screw on the end of the level, removing the plastic end cap and adjusting the three hex screws that aim the laser. I also put small rubber bumpers on the backside of the level so they would make contact with the wheel rim lip instead of the tire.

Rubber Bumpers for Wheel Rim Contact

To give your laser an accurate target you can attach a magnet to a metal 6 or 12 inch ruler and place it on the hub center extending outward. I attached a magnet to a 12" precision metal ruler and stuck it to the front hub (you may have to pop your wheel center cap). A 6" ruler will work too. A tape measure can also be used.

Magnet Holding Ruler to Hub

You then place the laser level across the center of the wheel as shown above and shine the laser on the tape measure at the front hub. For hands free lasering you can use a bungee cord to hold the laser level to the wheel.

Hands Free Laser for Toe Adjustment

Laser Dot on Ruler

I took good rear toe readings with the car on the ground then raised just the rear of the car so I could get under it and make adjustments. If you jack the front of the car too the front hubs will move as the front suspension droops. With the front tires on the ground and the rears in the air I took toe readings. My Megan Racing rear bump steer correcting link must be working because at full droop the toe reading didn't change by more than a couple of hundredths of an inch at the front hub. My right rear camber adjuster had slipped a little during my last track day and threw off the toe so I knew its toe was off. I adjusted the right rear camber adjuster to match the known good left rear toe. When I put the car down and rolled it back and forth to allow the suspension to unbind I verified the toe-in settings still matched.

Here's the correction factor for measuring toe at the opposite hub:

We know 0.25" of total rear toe is equal to 0.0625" at the leading edge of the tire (total toe / 4)

The distance from the center of the wheel to the tire edge is 12.3" (24.6" diameter for stock tires)

The S2000's wheel hubs are 94.5" apart (wheel base)

Therefore you can divide 94.5" by 12.3" to get a Rear Tire to Front Hub Correction Factor of 7.683

0.0625" measured at the rear tire is equal to 0.0625" x 7.683 = 0.48" measured at the front hub.

If you want to make a 0.1 inch change to the toe you would move the laser dot 0.77" (0.1 x 7.683).

Measuring toe at the front hub is much, much more precise than trying to use string and measure the difference between the leading and trailing wheel rim lips.

I calibrated my laser measurements after a shop alignment. With a known setting of 0.14" total rear toe (0.07" per rear tire), my laser projected a dot at 5.48" out from the hub on the ruler. The laser level's alignment and rear wheel size and offset will affect this measurement so the 5.48" figure only applies to my laser level and CE28 17 x 9 rear wheels and 0.14" total rear toe-in.

Rob Robinette

Apr 22, 2013 | 04:46 AM

robrob

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Joined: Jul 2005

Posts: 4,634

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From: West Virginia

You can use this laser level to quickly and accurately verify front and rear toe settings. If your toe settings are the same as a known good setting then you know the caster and camber settings are the same too because if an alignment adjuster slips it will change the toe--this is true front and rear.

I used the laser level to very accurately set and verify my front and rear toe settings. You simply place the laser level against the wheel and project the laser in front and behind the car for a more accurate toe measurement. In my garage I can separate two tape measures by 272 inches, one in front of the car and the other behind it. Since the front wheel track is narrower than the rear I had to put the laser level with its narrow edge against the tire to get the laser to clear the rear tires and hit the rear target.

I started by converting my desired toe-in in inches to degrees. I used my Convert Toe Inches to Degrees web page and plugged in my desired 0.16 inch total toe-in and 24.6 inch tire diameter to get the equivalent degree for one wheel of 0.186 degree. I then went to my Convert Toe Angle to Toe Inches web page and plugged in 0.186 degree and 272 inches for the tire diameter (this is the distance between the two tape measures). This gives a total toe of 1.77 inches so that is the measurement difference between the front and rear laser targets I was looking for--0.16 inch of total toe measured on the tire tread is equal to 1.77 inches at the tape measures.

To make things a little easier for me instead of using a tape measure I put inch marks on my 8 foot long level and used it as a laser target. I placed it in front of my car as far forward as my garage space would allow. I put the level on a box to get it up to wheel hub level. I then shot the marked level from all four wheels and noted the readings. I then moved the marked level to the rear of the garage and measured the distance between the front and rear laser targets. For me it was 272 inches. I then took laser measurements at all four wheels. The difference between the measurements taken at the front and back of the garage is the total toe--just like measuring toe on the tire tread itself.

I also took laser readings using a ruler at the opposite wheel hub so I could keep the toe settings equal on both wheels. I then adjusted the rear toe until I got 1.77 inches of difference between the two laser measurements and equal measurements at the opposite wheel hubs.

Once you get the alignment set note the readings on the hub rulers for future reference. You can then verify your alignment settings in about two minutes at the track using the laser level and magnetic ruler.

These were my hub ruler readings:
Rear total toe of 0.16" = 4.5" out from each front hub
4.31" = .06" MIN, 4.68" = 0.25" MAX
Front 0 toe = 2.1" out from rear hub

How to measure total toe: