alignment bar
02-17-2010, 06:33 PM
#1
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alignment bar
i've borrowed a bar used for toe alignment from the shop at which i work from time to time. i could spend several paragraphs describing it, but i think i can just get by with some basics.
it's going to measure the rim (front and back obviously) about 6 inches off the floor. that will give me a measurement of difference, but it won't give me "total toe", by my understanding of the term. for that i'd have to measure half way up the hight of the wheel/tire combo. i hope i'm explaining this ok.
roughly illustrated:
i will be measuring at the red marks instead of the blue marks, which would be easier. though, if i can figure out what the difference will be, this bar will allow me to do it much more accurately than would whatever method i come up to measure at the blue marks.
so... does anybody have any idea how to translate 1mm or whatever is the spec of total toe at the blue marks into what the toe should be measured from any given lower point on the wheel?
it's going to measure the rim (front and back obviously) about 6 inches off the floor. that will give me a measurement of difference, but it won't give me "total toe", by my understanding of the term. for that i'd have to measure half way up the hight of the wheel/tire combo. i hope i'm explaining this ok.
roughly illustrated:
i will be measuring at the red marks instead of the blue marks, which would be easier. though, if i can figure out what the difference will be, this bar will allow me to do it much more accurately than would whatever method i come up to measure at the blue marks.
so... does anybody have any idea how to translate 1mm or whatever is the spec of total toe at the blue marks into what the toe should be measured from any given lower point on the wheel?
Last edited by KasbeKZ; 02-17-2010 at 09:52 PM.
02-18-2010, 10:05 PM
#3
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you should be able to do this with basic geometry... why should we do this for you? 1mm toe in is not much at all, just give it 1mm at the blue marks. I highly doubt you'll notice any difference between the true 1mm at the red and 1mm at the blue.
(in case you didn't know - not sure if you did or not from your original post or not - take the back measurement, subtract the front measurement and divide by 2. That's your toe-in.
(in case you didn't know - not sure if you did or not from your original post or not - take the back measurement, subtract the front measurement and divide by 2. That's your toe-in.
02-19-2010, 03:03 PM
#5
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Holy **** dude I thought it was gonna be a basic question like "my alignment shop couldn't get this within spec, what should I do?" not "how do I use geometry and trigonometry to adjust for measuring at a different height?" I'm in the middle of packing for a trip to Chicago right now, I can't dedicate this much time at the moment. LOL
First, why do you desire to do things differently?
Second, how are you measuring the toe to begin with? I've never done my own alignment (don't have the space nor equipment), but if you tell me how you're measuring it, I can answer it.
With that said, my understanding of toe measurements is to basically measure the angle of the wheel relative to the straight-forward position of the vehicle. As such, the measurement at ANY point of the wheel is the exact same. The reason they recommend doing it at half the height of the wheel is to avoid miscalculation due to tire bulge.
And as a matter of interest that may help, the shop that did the alignment on my Blazer couldn't get the toe on the front passenger wheel right... my solution will be to get underneath the car and measure the distance between two opposite points of the front wheels and adjust the passenger's side wheel until the lengths are equal (with toe out, which is what I have, the front distance will be greater than the rear). I know that doesn't provide insight on "zeroing" the wheel to begin with, but it may provide some idea.
First, why do you desire to do things differently?
Second, how are you measuring the toe to begin with? I've never done my own alignment (don't have the space nor equipment), but if you tell me how you're measuring it, I can answer it.
With that said, my understanding of toe measurements is to basically measure the angle of the wheel relative to the straight-forward position of the vehicle. As such, the measurement at ANY point of the wheel is the exact same. The reason they recommend doing it at half the height of the wheel is to avoid miscalculation due to tire bulge.
And as a matter of interest that may help, the shop that did the alignment on my Blazer couldn't get the toe on the front passenger wheel right... my solution will be to get underneath the car and measure the distance between two opposite points of the front wheels and adjust the passenger's side wheel until the lengths are equal (with toe out, which is what I have, the front distance will be greater than the rear). I know that doesn't provide insight on "zeroing" the wheel to begin with, but it may provide some idea.
Last edited by ZLover4Life; 02-19-2010 at 03:05 PM.
02-19-2010, 03:10 PM
#6
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the bar spans the width of the car and measures the distance the distance between the rears of the front wheels, and the distance between the fronts of the front wheels, and i'll take that difference to calculate toe. i'll be measuring at the rim, so tire bulge is no issue.
i desire to do it that way because i have the bar, and i believe that i can get an accurate measurement with it for the time being to get the car back on the road while saving for more suspension parts. i paid for an alignment a few years ago, i need one now, and i'm going to need another when i get my tension rods in the summer.
if you're referring to why i want to measure at the red marks and not the blue ones, the answer is that i don't, but that's how my tool works. i'm sure you're wondering what the hell kind of tool this is, but it's legit, purpose built, and i'm pretty sure it was the standard for alignments at some time or another.
does that clear it all up? thanks for the reply.
i desire to do it that way because i have the bar, and i believe that i can get an accurate measurement with it for the time being to get the car back on the road while saving for more suspension parts. i paid for an alignment a few years ago, i need one now, and i'm going to need another when i get my tension rods in the summer.
if you're referring to why i want to measure at the red marks and not the blue ones, the answer is that i don't, but that's how my tool works. i'm sure you're wondering what the hell kind of tool this is, but it's legit, purpose built, and i'm pretty sure it was the standard for alignments at some time or another.
does that clear it all up? thanks for the reply.
Last edited by KasbeKZ; 02-19-2010 at 04:57 PM.
02-22-2010, 02:35 AM
#7
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In that case, the toe angle at any point of the wheel should be identical, thus no calculation is required. (If the face of the wheels is flat, which it should be, the angle at the top of the wheels should be the same as the angle at the bottom or the center [assuming the bar is held perpendicular to the ground, which it would need to be in order to measure toe].)
02-22-2010, 08:13 AM
#8
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but this bar doesn't measure angle, it measures distance.
http://www.chicagolandmgclub.com/mem...alignment1.jpg
it's similar to that, but not quite. so picture the difference between the wheels at 3 o'clock and at the lowest part of the rim. if they are toed in or out, the measurement will be different. yeah, i'm talking about really small differences, but so is 1mm of toe.
in other words, i'm measuring the wheels in reference to each other, not the wheels in reference to the car.
i'd look pretty stupid if you already understood that, but i hope we're both clear now. thanks for the reply.
http://www.chicagolandmgclub.com/mem...alignment1.jpg
it's similar to that, but not quite. so picture the difference between the wheels at 3 o'clock and at the lowest part of the rim. if they are toed in or out, the measurement will be different. yeah, i'm talking about really small differences, but so is 1mm of toe.
in other words, i'm measuring the wheels in reference to each other, not the wheels in reference to the car.
i'd look pretty stupid if you already understood that, but i hope we're both clear now. thanks for the reply.
02-22-2010, 12:48 PM
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You don't need to know the angle to be able to adjust it to spec, and I thought all you were trying to do was adjust it (to be 0, as it should be). If you have 0deg toe on each wheel, the distances between the front and back of each opposite wheel is equal (remember I mentioned above how I was going to adjust the toe on the Blazer by measuring the distances between fixed points on opposite wheels?)... if you just want to correct it, simply adjust the toe until the front and back distances are equal.
But if you want to know the actual toe of your car based on these distances, you're using trigonometry. Are you using one bar on each side simultaneously? (I assume so, since you talk of "total toe" which seems to be the sum of the toe of the front two wheels... but I have to warn you, that's useless... what if the driver's side wheels is +2deg, the passenger's side is -2deg... then your total toe is 0 and you'll think it's aligned... but the car will pull to the right because the front wheels aren't aligned with the chassis. I address the proper way at the end.)
If the bars aren't parallel, then if we extended them to be indefinitely long, they would at some point intersect on one side of the car (the side with the shorter distance, of course). Think of that as the tip of a triangle, and you can think of the distance the bars are apart at the other end as the base. Given the way you're calculating (your "total toe" with this method), we must assume that we have an isosceles triangle (since we will have no idea if either wheels is more out of spec than the other). To use trigonometry, we need right triangles, so we'll have to bisect the isosceles triangle to be two right triangles, calculate the angle we want, and then double it for total toe. First we have to know another length, though, for which we will use similar geometry.
We know the length of the bar, we know the length of the base of our right triangle (half the base of our isosceles triangle), and we know half the distance between the closer ends of the poles. So we can use the fact that similar shapes maintain ratios. For simplicity, let's define some variables (and I'll keep it in terms of your known distances so you can just plug **** in).
Let:
a = shorter distance between the poles
b = longer distance between the poles
c = length of the poles
x = hypotenuse of our right triangle (unknown)
(x-c)/a = x/b
b(x-c) = ax
bx - bc = ax
bx - ax = bc
x(b-a) = bc
x = (bc)/(b-a)
The lower your toe, the larger x will be.. And remember, once you start going to decimals, you risk losing information... so if you get an irrational number (like 481/3 for example), leave it like that unless you absolutely have to convert to decimal.
Then to find our angle, since we have the opposite and hypotenuse, we shall use sine. But since we don't know the angle, but rather the distances, we must use inverse sine (will show up on the calculator as sin^(-1) and will type as invsin(y)).
Your total toe is 2*invsin((b/2)/x).
If you want to know the toe for a specific wheel, do this same process with one wheel and a bar (or string) drawn underneath the car directly down its center. If a = minimum distance, b = maximum distance, c = length of bar, x = hypotenuse, we still use
x = (bc)/(b-a)
but the angle becomes
invsin(x/b)
Hope that's what you wanted.
But if you want to know the actual toe of your car based on these distances, you're using trigonometry. Are you using one bar on each side simultaneously? (I assume so, since you talk of "total toe" which seems to be the sum of the toe of the front two wheels... but I have to warn you, that's useless... what if the driver's side wheels is +2deg, the passenger's side is -2deg... then your total toe is 0 and you'll think it's aligned... but the car will pull to the right because the front wheels aren't aligned with the chassis. I address the proper way at the end.)
If the bars aren't parallel, then if we extended them to be indefinitely long, they would at some point intersect on one side of the car (the side with the shorter distance, of course). Think of that as the tip of a triangle, and you can think of the distance the bars are apart at the other end as the base. Given the way you're calculating (your "total toe" with this method), we must assume that we have an isosceles triangle (since we will have no idea if either wheels is more out of spec than the other). To use trigonometry, we need right triangles, so we'll have to bisect the isosceles triangle to be two right triangles, calculate the angle we want, and then double it for total toe. First we have to know another length, though, for which we will use similar geometry.
We know the length of the bar, we know the length of the base of our right triangle (half the base of our isosceles triangle), and we know half the distance between the closer ends of the poles. So we can use the fact that similar shapes maintain ratios. For simplicity, let's define some variables (and I'll keep it in terms of your known distances so you can just plug **** in).
Let:
a = shorter distance between the poles
b = longer distance between the poles
c = length of the poles
x = hypotenuse of our right triangle (unknown)
(x-c)/a = x/b
b(x-c) = ax
bx - bc = ax
bx - ax = bc
x(b-a) = bc
x = (bc)/(b-a)
The lower your toe, the larger x will be.. And remember, once you start going to decimals, you risk losing information... so if you get an irrational number (like 481/3 for example), leave it like that unless you absolutely have to convert to decimal.
Then to find our angle, since we have the opposite and hypotenuse, we shall use sine. But since we don't know the angle, but rather the distances, we must use inverse sine (will show up on the calculator as sin^(-1) and will type as invsin(y)).
Your total toe is 2*invsin((b/2)/x).
If you want to know the toe for a specific wheel, do this same process with one wheel and a bar (or string) drawn underneath the car directly down its center. If a = minimum distance, b = maximum distance, c = length of bar, x = hypotenuse, we still use
x = (bc)/(b-a)
but the angle becomes
invsin(x/b)
Hope that's what you wanted.
02-22-2010, 01:22 PM
#10
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yeah i'm pretty sure that's what i need. i'll need to read it about 5 more times before i've got a full understanding.
0 toe? fsm says 1-2 mm toe in. this is to compensate for the wheels swinging back a little at speed i've been told. is this not the setting you're familiar with?
0 toe? fsm says 1-2 mm toe in. this is to compensate for the wheels swinging back a little at speed i've been told. is this not the setting you're familiar with?
02-22-2010, 01:51 PM
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ok, two quick questions. the term pole refers to the points on the wheel that the measuring tool is touching? and "length of poles/c" is the average between front and back measurements?
and this: "with one wheel and a bar (or string) drawn underneath the car directly down its center". no idea on that one.
this tool has a solid point on one end that can contact the outside of the rim and a slide-able point on the other end to slide into the rim once the other point is set. the sliding part has a ruler on it.
and this: "with one wheel and a bar (or string) drawn underneath the car directly down its center". no idea on that one.
this tool has a solid point on one end that can contact the outside of the rim and a slide-able point on the other end to slide into the rim once the other point is set. the sliding part has a ruler on it.
Last edited by KasbeKZ; 02-22-2010 at 02:15 PM.
02-22-2010, 01:52 PM
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Weird... I remember typing out that I've never done my own alignment on a Z32, but I guess I replaced that text with something else (perhaps the story of how I'll get the toe on my Blazer in spec). Nonetheless, the math doesn't change (and that's what I was here to provide), just the target. Go by the specs, I simply assumed it should be ~0.
02-22-2010, 02:14 PM
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judging by the pattern of our posts, i'd say it's likely that you missed my follow up questions 4 posts above. again, not pestering, you always have the right to refuse! thanks for taking the time to answer this stuff. there are not many people that can answer stuff like this, let alone that are willing to.
also, you never included a hight measurement did you? it seems to me though that using those equations, it's all about the differences in measurements of the front vs. the rear rather than the actual length measurement between the (poles?) of the wheels. you do agree that the length measured between the blue marks (see first post pic) of each wheel will be different than the lengths at the red marks?
also, you never included a hight measurement did you? it seems to me though that using those equations, it's all about the differences in measurements of the front vs. the rear rather than the actual length measurement between the (poles?) of the wheels. you do agree that the length measured between the blue marks (see first post pic) of each wheel will be different than the lengths at the red marks?
02-22-2010, 02:39 PM
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I have no idea what this tool looks like or how it works from your description. I assumed you were doing this the normal garage-mechanic way... you basically have a tool that sits flush on the face of the wheel and protrudes a bit, with a rod that extends partway down the length of the car (parallel to the face of the wheel). The further it extends, the more noticeable any variation in toe becomes... if that's not what this device does (and it seems it's not), then ignore everything I've said and talk to an expert (or do what 99.9% of all people do... take your car to a shop with an alignment machine... even the morons at the shop can't **** it up when the machine reads the car's specs and tells them what to adjust).
The height makes no difference, what matters is the length of the part you're measuring and you have not provided sufficient information for me to answer your question (6" up the floor places you at different lengths depending on aspect ratio and tire wear - you can't account for that accurately). If you do not measure it at exactly opposite ends of the wheels parallel to the ground (i.e. the blue dots), you WILL have this error due to approximation.
If you still insist on trying it yourself, and if this gauge measures mm of toe (and not degrees as I was doing before), you will use similar triangle geometry once again. You need to measure the distance between those red marks (good luck being as precise as the measurement for the diameter of the wheel, which is used for a real alignment), measure the toe (however this device does so), and then (measured toe)/(distance between red marks) = (actual toe)/(wheel diameter) [I assume this tool requires wheel diameter for its calculation, hence why you're *supposed* to measure at the blue dots].
The height makes no difference, what matters is the length of the part you're measuring and you have not provided sufficient information for me to answer your question (6" up the floor places you at different lengths depending on aspect ratio and tire wear - you can't account for that accurately). If you do not measure it at exactly opposite ends of the wheels parallel to the ground (i.e. the blue dots), you WILL have this error due to approximation.
If you still insist on trying it yourself, and if this gauge measures mm of toe (and not degrees as I was doing before), you will use similar triangle geometry once again. You need to measure the distance between those red marks (good luck being as precise as the measurement for the diameter of the wheel, which is used for a real alignment), measure the toe (however this device does so), and then (measured toe)/(distance between red marks) = (actual toe)/(wheel diameter) [I assume this tool requires wheel diameter for its calculation, hence why you're *supposed* to measure at the blue dots].
Last edited by ZLover4Life; 02-22-2010 at 03:02 PM.
02-22-2010, 06:08 PM
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the only difference is that mine does the reach around allowing it to measure at the rim instead of on the tire. also, it touches the ground at two places, so that it stays level
02-22-2010, 06:22 PM
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oh haha sorry.
http://wb7.itrademarket.com/pdimage/...augementah.jpg
here's a different one. it's just about like that, but again, mine does the reach around instead to measure the rim.
http://wb7.itrademarket.com/pdimage/...augementah.jpg
here's a different one. it's just about like that, but again, mine does the reach around instead to measure the rim.
02-23-2010, 11:08 AM
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... final thought... you could always stack some blocks of wood (and other flat surfaces) underneath the device to raise it to the height needed to measure at the entire diameter of the wheel, thus negating needing to do any calculation at all. Just make sure the surface you construct is level.
Last edited by ZLover4Life; 02-23-2010 at 11:31 AM.
02-23-2010, 12:13 PM
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I was in for my birthday. My spring break begins on March 12th, and it will make a road appearance that week (brakes and tires first, then driving it over to my friend's house to complete other work).
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