Paging all Wheel Alignment Math Geeks
Thread Starter
Drifting
Joined: Nov 2002
Posts: 1,688
Likes: 200
From: Loveland, CO
Paging all Wheel Alignment Math Geeks
I just got my 73 big block back from alignment and need help on the toe readings. Everything I have read recommends about 1/8" front toe settings (1/16 on each side). The results printout I got reads in degrees.
Left frt. 0.27 degree, Rt. frt. 0.19 degree. (their spec. 0.13 to 0.38)
Left rear 0.17 degree, Rt. rear 0.12 degree. (spec. 0.06 to 0.19)
How do these reading relate to inches? Does wheel diameter matter?
Also, is it possible to adjust front toe by knowing how much each turn (or portion thereof) of the adjuster tube relates into change at the wheel? I'd like to get my left front toe closer to my right front toe reading.
FYI, on front camber, I noticed in Chris Teague's article in the FAQ Forum that the big shims (assume 1/8") are worth about 0.25 degrees (roughly). So, one can easily play around with the camber settings.
Thanks.
Left frt. 0.27 degree, Rt. frt. 0.19 degree. (their spec. 0.13 to 0.38)
Left rear 0.17 degree, Rt. rear 0.12 degree. (spec. 0.06 to 0.19)
How do these reading relate to inches? Does wheel diameter matter?
Also, is it possible to adjust front toe by knowing how much each turn (or portion thereof) of the adjuster tube relates into change at the wheel? I'd like to get my left front toe closer to my right front toe reading.
FYI, on front camber, I noticed in Chris Teague's article in the FAQ Forum that the big shims (assume 1/8") are worth about 0.25 degrees (roughly). So, one can easily play around with the camber settings.
Thanks.
Race Director
Joined: Sep 1999
Posts: 11,360
Likes: 382
From: Plano TX
Toe is measured at the edge of the tire, so converting it to inches will depend on your tire diameter. If you have stock tires they are 27" diameter. So some trig shows us that 0.27 dgr at 27" is 0.127" (Sin(0.27)*27). I think I got the math right????
Looks like they used quite a bit of toe-in. Other side is 0.089" for a total of 0.216" or over 3/16".
The minimum spec they show (0.13 dgr) works out to a total toe-in of 1/8".
As for front camber I have done my own alignment and 1/8" shim will change it much more than 0.25 dgr. A 1/16" shim will do about 0.3 dgr.
Looks like they used quite a bit of toe-in. Other side is 0.089" for a total of 0.216" or over 3/16".
The minimum spec they show (0.13 dgr) works out to a total toe-in of 1/8".
As for front camber I have done my own alignment and 1/8" shim will change it much more than 0.25 dgr. A 1/16" shim will do about 0.3 dgr.
Instructor
Joined: Sep 2004
Posts: 168
Likes: 0
From: Houston Texas
For degrees to inches for toe in you need to reference your shop manual. The following is some info I worked up aligning my 79.
Front Camber: .2 " shim thickness = 1 deg camber (this is rough and needs to be refined)
Front Caster: Turn wheel/tire 20 deg left and take camber reading. Turn w/t right 20 deg and take camber reading. Add the camber readings and multiple by 1.5 to get caster.
Front toe: 1 turn of both tie rods = 1 " total toe change.
Rear Camber: One turn of the strut rod = 1 deg camber change
Rear Toe Toe change per wheel = shim thickness change times x .66.
Wheel/tire diameter makes a difference. These figures are for a wheel/tire approximately 27" tall.
Front Camber: .2 " shim thickness = 1 deg camber (this is rough and needs to be refined)
Front Caster: Turn wheel/tire 20 deg left and take camber reading. Turn w/t right 20 deg and take camber reading. Add the camber readings and multiple by 1.5 to get caster.
Front toe: 1 turn of both tie rods = 1 " total toe change.
Rear Camber: One turn of the strut rod = 1 deg camber change
Rear Toe Toe change per wheel = shim thickness change times x .66.
Wheel/tire diameter makes a difference. These figures are for a wheel/tire approximately 27" tall.
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
IF the forum search function is working you can find a referance to a page that gives the specifics on just how much you read off a carpenter's level for any given wheel diameter and desired degrees....so a 15" wheel is say 1/8 inch out of vertical, but on a 17" wheel it's say X amount, and so that's translated into degrees via the table....simple , really....that's how I align my car...course I got disgusted with various alignment shops down here in North Florida and decided I can do better than they can...and so far over the last...nearly 2 years +-, I have proven myself right.....should have done this decades ago...
with help/encouragement from Pete79L82? and Norval, among others it became a snap....
GENE
with help/encouragement from Pete79L82? and Norval, among others it became a snap....
GENE
Racer
Joined: Jul 2004
Posts: 286
Likes: 1
From: Mesa az
The toe-in is measured from center of tread to center of car. The "trig" should use half the actual tire diameter times the "sine of the angle" because the angle is through the center of the tire/axle. The 0.27 degrees for a 27" diameter tire is about 1/16" toe-in if the actual diameter is really 27".
Andy
Andy
Race Director
Joined: Sep 1999
Posts: 11,360
Likes: 382
From: Plano TX
Andy: That's what I thought also, but multiple sources on the web showed the toe measured as the difference between the front of the tread and the rear of the tread making it the full diameter of the tire.
Racer
Joined: Jul 2004
Posts: 286
Likes: 1
From: Mesa az
Several folks do it from front to back, but then you have to double the measured value, since the front of the tires move closer together and the rear further apart. The main problem with this is you can get the correct "difference" but have a really, really bad alignment. The toe is measured as offsets from the center line of the chassis on each wheel, and this center line is hard to establish for beginners without equipment. Do-able, but hard. You have to work from the center of either the lower steering knuckle, or center of the wheels. The center of the chassis is half way between these two points, both front and rear. Shop equipment use the distance/centers of the wheels. This is the method shown in the GM Assemble Manuals.
All this adds up to what every shop should tell anyone getting an alignment. If ANY of your steering/suspension parts are worn/loose or the frame/suspend has been bent/distorted, the alignment means absolutely nothing. Go burn the money and not waste the time.
Andy
All this adds up to what every shop should tell anyone getting an alignment. If ANY of your steering/suspension parts are worn/loose or the frame/suspend has been bent/distorted, the alignment means absolutely nothing. Go burn the money and not waste the time.
Andy
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Thread Starter
Drifting
Joined: Nov 2002
Posts: 1,688
Likes: 200
From: Loveland, CO
Thanks guys for all the input. This gives me enough to think about for a while.
Markus, I think you are correct if you use the front to rear of tread measurement method. If you have the degree angle already, I think you would only use the wheel pivot point (or 1/2 wheel diameter) to convert to toe inches.
Andy, so if 0.27 degrees is about 1/16 inch, I am just about where I need to be. Or, I could tweek the right front in just slightly to have it get closer to the 0.19 I have on the left front?
I think I will aim at 0.0 camber on both front and rear. I will use the bubble level method on the rim and just center bubble reading. On front, I'll just keep adding shims until I get a level bubble. On rear, I'll just adjust camber bolt to get the bubble level reading also. I notice that the 0.0 camber is Vette Brakes recommendation for a "Daily Driver".
Thanks again. Ralph.
Markus, I think you are correct if you use the front to rear of tread measurement method. If you have the degree angle already, I think you would only use the wheel pivot point (or 1/2 wheel diameter) to convert to toe inches.
Andy, so if 0.27 degrees is about 1/16 inch, I am just about where I need to be. Or, I could tweek the right front in just slightly to have it get closer to the 0.19 I have on the left front?
I think I will aim at 0.0 camber on both front and rear. I will use the bubble level method on the rim and just center bubble reading. On front, I'll just keep adding shims until I get a level bubble. On rear, I'll just adjust camber bolt to get the bubble level reading also. I notice that the 0.0 camber is Vette Brakes recommendation for a "Daily Driver".
Thanks again. Ralph.
Race Director
Joined: Sep 1999
Posts: 11,360
Likes: 382
From: Plano TX
You don't want 0 camber. I'm wearing the outside edge on my front tires with -0.2 dgr so I had to increase it. Changed it to -0.8 and that should take care of it. In the rear I'm running -0.5 and the wear is perfectly even.
To get -0.5 dgr you can still use a bubble level. You need to tape 2 sockets that are the exact same length to the level so that one socket contacts the lower lip on the rim and the other the upper. Then insert feeler gauges until the bubble is centered.
To get -0.5 dgr you need 0.140" in feeler gauges between the upper edge of the rim and the corresponding socket (attached to the bubble level). This is assuming you have 15" rims.
To get -0.5 dgr you can still use a bubble level. You need to tape 2 sockets that are the exact same length to the level so that one socket contacts the lower lip on the rim and the other the upper. Then insert feeler gauges until the bubble is centered.
To get -0.5 dgr you need 0.140" in feeler gauges between the upper edge of the rim and the corresponding socket (attached to the bubble level). This is assuming you have 15" rims.
Racer
Joined: Jul 2004
Posts: 286
Likes: 1
From: Mesa az
First I have to say "I made a mistake, or misleading statement and hope it didn't cause too much trouble". That being said I'll try to correct my error.
The math of .28 degrees is correct for the 1/16 inch offset of the front of the center line of the tire to the center line of the car. The error was that the toe in spec is the difference between the distances from the center-line-of-the-front-of-the-tire to center-line-of-the-car and the distance from the center-line-of-the- back-of-the-tire and the center-line-of-the-car. This was the confusion I was trying to clear up. Measuring between the center lines of the front tires and then center lines of the back tires and subtracting is not correct. But since the back of the tire moves out as far as the front moves in the calculated number should be doubled. So .28 degrees equals a toe in of about 1/8", still in spec by my '69 numbers of 1/32 to 3/32. Again both tires have to be set to center line.
The picture in the Assembly Manual helps alot.
My response was delayed a bit because the hard drive in my home PC failed and I'm having to do this on another PC.
Hope this clears things up and helps.
Andy
The math of .28 degrees is correct for the 1/16 inch offset of the front of the center line of the tire to the center line of the car. The error was that the toe in spec is the difference between the distances from the center-line-of-the-front-of-the-tire to center-line-of-the-car and the distance from the center-line-of-the- back-of-the-tire and the center-line-of-the-car. This was the confusion I was trying to clear up. Measuring between the center lines of the front tires and then center lines of the back tires and subtracting is not correct. But since the back of the tire moves out as far as the front moves in the calculated number should be doubled. So .28 degrees equals a toe in of about 1/8", still in spec by my '69 numbers of 1/32 to 3/32. Again both tires have to be set to center line.
The picture in the Assembly Manual helps alot.
My response was delayed a bit because the hard drive in my home PC failed and I'm having to do this on another PC.
Hope this clears things up and helps.
Andy
