Effect of ride height on alignment and other queries
12-09-2015, 02:05 PM
#1
Rennlist Member
Thread Starter
Effect of ride height on alignment and other queries
After some extensive [for me] work on the 928 I finally managed a test run today. I knew the front toe setting was likely to be all over the place after replacing the tie rods and I also adjusted the rear ride height on one side- everything else remained the same.
Starting from first principles, I understand that as the ride height settles the camber will tend towards more negative and the toe setting will tend to "toe out" correct me if I am wrong.
At the moment I have some more work to do at the rear end so do not want to do a new alignment until this activity is completed. Thus I want my front toe so that it will not damage the tires due to scrubbing. Today's drive was about 20km in total so I expect a fair degree of settlement from that [as seemed to be the case].
As I drove the car today it drove in a straight line and braking was OK but the steering wheel tended towards the 11 O'clock position. This told me that I probably had too much toe-in on the front left. when I returned back to the garage I parked the car parallel to the interlock tiles on the deck and noticed straight away that the front left wheel had more toe in than the front right so this evening I adjusted it until it seemed as though both sides had the same nominal amount of toe. I did this by using one eye viewed from the back of the car looking forwards and slowly changed my angle of view of the front tire until the leading edge of the wheel was eclipsed. I was still a bit outboard of the rear wheel but not by so much as I was earlier. On the passenger side I tried the same and visually this seemed to need no adjustment. I will test this tomorrow-
Query 1- does this seem a reasonable approach to stand a chance of not damaging the tire/does anyone do this prior to actually getting on the alignment rig [Mark K?].
Query 2- When my car had its annual inspection at the police their new test rig has a weight measure that reads out the weight on each wheel. Much as I expected there was a noticeable imbalance on the corner weights with the rear left and front right being the dominant axis carrying about 70kg more than the other axis. To me that sounds as though it could be significant. Whilst the car was on the jack I took a look at the shock ride heights and both fronts were about the same but there was a noticeable difference in the height adjustment between the two rears with the rear right being about half an inch lower than the rear left. As I remember this was because when setting up the car I was trying to get the corner height the same- with hindsight possibly a mistake as one should not assume the spring rates are identical [apparently Porsche spring rates are very consistent but Eibach?]. Anyway I adjusted my rear right adjuster and increased the height to the same number of threads on the adjuster as the other side to try this setting. Now this side of the car is clearly riding higher than the other side but not by a whole lot. My question is how much will this impact the current rear alignment. I was assuming this change will decrease the amount of negative camber and possibly increase the rear toe-in a bit but on the camber front to date I cannot find any apparent difference.
Any thoughts appreciated
Rgds
Fred
Starting from first principles, I understand that as the ride height settles the camber will tend towards more negative and the toe setting will tend to "toe out" correct me if I am wrong.
At the moment I have some more work to do at the rear end so do not want to do a new alignment until this activity is completed. Thus I want my front toe so that it will not damage the tires due to scrubbing. Today's drive was about 20km in total so I expect a fair degree of settlement from that [as seemed to be the case].
As I drove the car today it drove in a straight line and braking was OK but the steering wheel tended towards the 11 O'clock position. This told me that I probably had too much toe-in on the front left. when I returned back to the garage I parked the car parallel to the interlock tiles on the deck and noticed straight away that the front left wheel had more toe in than the front right so this evening I adjusted it until it seemed as though both sides had the same nominal amount of toe. I did this by using one eye viewed from the back of the car looking forwards and slowly changed my angle of view of the front tire until the leading edge of the wheel was eclipsed. I was still a bit outboard of the rear wheel but not by so much as I was earlier. On the passenger side I tried the same and visually this seemed to need no adjustment. I will test this tomorrow-
Query 1- does this seem a reasonable approach to stand a chance of not damaging the tire/does anyone do this prior to actually getting on the alignment rig [Mark K?].
Query 2- When my car had its annual inspection at the police their new test rig has a weight measure that reads out the weight on each wheel. Much as I expected there was a noticeable imbalance on the corner weights with the rear left and front right being the dominant axis carrying about 70kg more than the other axis. To me that sounds as though it could be significant. Whilst the car was on the jack I took a look at the shock ride heights and both fronts were about the same but there was a noticeable difference in the height adjustment between the two rears with the rear right being about half an inch lower than the rear left. As I remember this was because when setting up the car I was trying to get the corner height the same- with hindsight possibly a mistake as one should not assume the spring rates are identical [apparently Porsche spring rates are very consistent but Eibach?]. Anyway I adjusted my rear right adjuster and increased the height to the same number of threads on the adjuster as the other side to try this setting. Now this side of the car is clearly riding higher than the other side but not by a whole lot. My question is how much will this impact the current rear alignment. I was assuming this change will decrease the amount of negative camber and possibly increase the rear toe-in a bit but on the camber front to date I cannot find any apparent difference.
Any thoughts appreciated
Rgds
Fred
12-09-2015, 02:26 PM
#2
Rennlist Member
you cant have toe in on the "left". 
its a hard concept to initially grasp, but the tires naturally go straight. and the wheel will be shifted if that isnt set up right. now, if it pulls to one side or another, thats a set up issue with the rears vs the front, or a tire deflated, caster issue, uneven camber, uneven ride hight. etc .
after you set the caster and camber, the toe is set and you are done. you lower the car, and the camber will go up slightly and the toe will toe out. setting a litte toe in, is best, especially with a soft riding car, (stock) that might be driven hard. hard braking pushes the car down, and gives more toe out under braking, and makes the car wonder. people think its bumps steer, but its not. (if too low).. my car is at 110mm and its straight as an arrow under all conditions. no downside, but at willow springs under full compression around a 135mph turn for 8 seconds. the hanging tire points out way too far and scrubs the inside edge more than if the car was at the proper ride height. (decent trade off for the benifits of a low ride height)
back to your situation. yes, you did the right thing. if you can adust one toe adjuster .5 turn and do the other side the sam, you will straighten the wheel out. you can also change the toe by moving both wheels turned outward by lengthening both adjusters by .25 or .5 turns, depending if you have too much toe in for example.
i would be more loooking at the reason the wheels are turned one way with the sterring wheel straight. that will happen if you hit a curb real hard and bend that one side a little. i remember getting centerpunched a little at the track, and raced wtih .5" toe out for the race and all the way home . the inside edge was scrubbed clean. measured the alignment and saw that the toe was .5" toe out... moved the one adjuster inward, the wheel straightened and i was back to about 1/8" toe in. alignment shop a week or two later and proved that i did good. very small adjustment to make it all perfect again. but certainly good enough for a short period of time for racing or driving on the street with no issues.
corner balancing: if you are 140lb heavy on one corner to corner, lower those two points , giving most of the lowering to the front corner if possible
ride height is a ball park and all the corners will not be perfect, nor the springs or connetive components. if you end up with near perfect balance for what you have, you end up like what i have, and its about each corner being with in .25" of each other in front and in rear. (not comparing front to back) im 110 112 mm, and rear 135 133mm) corner balance is within 10lbs.
its a hard concept to initially grasp, but the tires naturally go straight. and the wheel will be shifted if that isnt set up right. now, if it pulls to one side or another, thats a set up issue with the rears vs the front, or a tire deflated, caster issue, uneven camber, uneven ride hight. etc .after you set the caster and camber, the toe is set and you are done. you lower the car, and the camber will go up slightly and the toe will toe out. setting a litte toe in, is best, especially with a soft riding car, (stock) that might be driven hard. hard braking pushes the car down, and gives more toe out under braking, and makes the car wonder. people think its bumps steer, but its not. (if too low).. my car is at 110mm and its straight as an arrow under all conditions. no downside, but at willow springs under full compression around a 135mph turn for 8 seconds. the hanging tire points out way too far and scrubs the inside edge more than if the car was at the proper ride height. (decent trade off for the benifits of a low ride height)
back to your situation. yes, you did the right thing. if you can adust one toe adjuster .5 turn and do the other side the sam, you will straighten the wheel out. you can also change the toe by moving both wheels turned outward by lengthening both adjusters by .25 or .5 turns, depending if you have too much toe in for example.
i would be more loooking at the reason the wheels are turned one way with the sterring wheel straight. that will happen if you hit a curb real hard and bend that one side a little. i remember getting centerpunched a little at the track, and raced wtih .5" toe out for the race and all the way home . the inside edge was scrubbed clean. measured the alignment and saw that the toe was .5" toe out... moved the one adjuster inward, the wheel straightened and i was back to about 1/8" toe in. alignment shop a week or two later and proved that i did good. very small adjustment to make it all perfect again. but certainly good enough for a short period of time for racing or driving on the street with no issues.
corner balancing: if you are 140lb heavy on one corner to corner, lower those two points , giving most of the lowering to the front corner if possible
ride height is a ball park and all the corners will not be perfect, nor the springs or connetive components. if you end up with near perfect balance for what you have, you end up like what i have, and its about each corner being with in .25" of each other in front and in rear. (not comparing front to back) im 110 112 mm, and rear 135 133mm) corner balance is within 10lbs.
12-09-2015, 02:36 PM
#3
Rennlist Member
Thread Starter
That is exactly what happened- the car was driving perfectly straight but it takes its natural balance point between the toe on both wheels with the result that the steering wheel is in equilibrium in an offset position- in my case it was at 11 O'clock and that told me I was probably out on the left hand toe as the steering had more "feel" than I normally have with the minimal toe setting I normally use.
Rgds
Fred
12-09-2015, 02:44 PM
#4
Rennlist Member
Mark.
That is exactly what happened- the car was driving perfectly straight but it takes its natural balance point between the toe on both wheels with the result that the steering wheel is in equilibrium in an offset position- in my case it was at 11 O'clock and that told me I was probably out on the left hand toe as the steering had more "feel" than I normally have with the minimal toe setting I normally use.
Rgds
Fred
That is exactly what happened- the car was driving perfectly straight but it takes its natural balance point between the toe on both wheels with the result that the steering wheel is in equilibrium in an offset position- in my case it was at 11 O'clock and that told me I was probably out on the left hand toe as the steering had more "feel" than I normally have with the minimal toe setting I normally use.
Rgds
Fred
measure the toe as i have suggested.
straight edge front of thetire, rear of the tire with a magic marker. (much more accurate than dr bob understand.. he stilll doesn't get how accurate it is.. its not the size of the magic marker pointer, its the edge against the straight edge. like if you used spray paint... the edge is very accurate.
anyway, do front and rear of the tire to the ground. 20" apart. then do the same on the other tire. then measure the front marks distances compared to the rear mark distances.
take that difference between the two distances . divide by 2... get a calculator and take that number and divide it by 20" and then push INV TAN function.
that will give you the degrees of toe in or out.. you want that mesured value to be about 1/4" (which is about 1/8 for each side)
that would be , in this example .35 degrees toe in or out. I think the stock spec is .5 degrees.
12-09-2015, 02:47 PM
#5
Nordschleife Master
There's "left toe," "right toe" and "total toe." Imbalance in the left and right makes the steering wheel off-center. You could have other things wrong, but that's what happens.
12-09-2015, 03:27 PM
#6
Chronic Tool Dropper
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Using the eyeball method looking for paralle with the rear tire is misleading at best. The track and wheel widths are different. The curve of the fender and body draw the eye and confuse it.
Earl Gilstrom shared a good DIY alignment method that can be easily implemented using strings, a tape measure, and a pocket scale. Jackstands are handy supports for the strings. I used to do this with thread instead of string so the measurements would be easier. I've since moved on to laser fixtures I made that clamp to the rims, but for at least an initial setup the strings-and-scale method work fine.
Before you do that though, get the spring adjustments even side-to-side, and your ride height pretty much where you need it. Or progressively adjust as you add miles and suspension settling. If you will be doing multiple adjustment sessions as the car settles, do yourself a favor and make a mid-car mark at the front and rear of the car at string height, maybe a pen mark on a piece of tape. With that, you'll be able to very quickly position your jackstand string supports correctly for measurement.
IIRC, the scale measurements for front toe work out to 1/32" difference between front and rear edges for each of my 17" wheels, front is narrower or further from the string for toe-in.
Earl Gilstrom shared a good DIY alignment method that can be easily implemented using strings, a tape measure, and a pocket scale. Jackstands are handy supports for the strings. I used to do this with thread instead of string so the measurements would be easier. I've since moved on to laser fixtures I made that clamp to the rims, but for at least an initial setup the strings-and-scale method work fine.
Before you do that though, get the spring adjustments even side-to-side, and your ride height pretty much where you need it. Or progressively adjust as you add miles and suspension settling. If you will be doing multiple adjustment sessions as the car settles, do yourself a favor and make a mid-car mark at the front and rear of the car at string height, maybe a pen mark on a piece of tape. With that, you'll be able to very quickly position your jackstand string supports correctly for measurement.
IIRC, the scale measurements for front toe work out to 1/32" difference between front and rear edges for each of my 17" wheels, front is narrower or further from the string for toe-in.
12-09-2015, 03:34 PM
#7
Rennlist Member
Using the eyeball method looking for paralle with the rear tire is misleading at best. The track and wheel widths are different. The curve of the fender and body draw the eye and confuse it.
Eral Gilstrom shared a giid DIY alignment method that can be easily implemented using strings, a tape measure, and a pocket scale. Jackstands are handy supports for the strings. I used to do this with thread instead of string so the measurementswould be easier. I've since moved on to laser fixtures I made that clamp to the rims, but for at least an initial setup the strings-and-scale method work fine.
Before you do that though, get the spring adjustments even side-to-side, and your ride height pretty much where you need it. Or progressively adjust as you add miles and suspension settling. If you will be doing multiple adjustment sessions as the car settles, do yourself a favor and make a mid-car mark at the front and rear of the car at string height, maybe a pen mark on a piece of tape. With that, you'll be able to very quickly position your jackstand string supports correctly for measurement.
IIRC, the scale measurements for front toe work out to 1/32" difference between front and rear edges for each of my 17" wheels, front is narrower or further from the string for toe-in.
Eral Gilstrom shared a giid DIY alignment method that can be easily implemented using strings, a tape measure, and a pocket scale. Jackstands are handy supports for the strings. I used to do this with thread instead of string so the measurementswould be easier. I've since moved on to laser fixtures I made that clamp to the rims, but for at least an initial setup the strings-and-scale method work fine.
Before you do that though, get the spring adjustments even side-to-side, and your ride height pretty much where you need it. Or progressively adjust as you add miles and suspension settling. If you will be doing multiple adjustment sessions as the car settles, do yourself a favor and make a mid-car mark at the front and rear of the car at string height, maybe a pen mark on a piece of tape. With that, you'll be able to very quickly position your jackstand string supports correctly for measurement.
IIRC, the scale measurements for front toe work out to 1/32" difference between front and rear edges for each of my 17" wheels, front is narrower or further from the string for toe-in.
thats a pretty tight measurement and im sure it works for you .. but look at all you need... lasers, strings, adapters, etc. my way, is the same. i use 20" front and rear of wheel. get that 1/4" reading between the two wheels front to back and that works out to .36 degrees where your 1/32 each wheel is .2 degrees. very close. My way is just a bit easier and just as accurate as proven by the hunter machine when i double check it. as long as you are firmly pressed against the wheel or tire to the ground, that mark, on the inside is golden! there is no variance and it is very accurate .
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12-09-2015, 03:51 PM
#8
Rennlist Member
Thread Starter
Using the eyeball method looking for paralle with the rear tire is misleading at best. The track and wheel widths are different. The curve of the fender and body draw the eye and confuse it.
Earl Gilstrom shared a good DIY alignment method that can be easily implemented using strings, a tape measure, and a pocket scale. Jackstands are handy supports for the strings.
Earl Gilstrom shared a good DIY alignment method that can be easily implemented using strings, a tape measure, and a pocket scale. Jackstands are handy supports for the strings.
I only use the rear wheel trailing edge as a reference point to tell me roughly where the [developed] virtual axis of the front wheel edge would be as it passes the rear wheel. It is not drop dead accurate but it seems to give a useful perception of where the front toe lies- the trick being to use one eye so as to eliminate any "depth misperceptions".
I also tried to use my laser levels by projecting the beams at axle height along both sides of the car- same kind of idea as the strings I suspect. Main thing at this stage is to ensure some degree of toe-in exists- far better to have too much than too little or worse, some degree of toe-out.
12-09-2015, 03:59 PM
#9
Rennlist Member
Thread Starter
Great point about eyeballing the front to the rear. impossible.especially on a 928. stringing is a great way to get it right.
thats a pretty tight measurement and im sure it works for you .. but look at all you need... lasers, strings, adapters, etc. my way, is the same. i use 20" front and rear of wheel. get that 1/4" reading between the two wheels front to back and that works out to .36 degrees where your 1/32 each wheel is .2 degrees. very close. My way is just a bit easier and just as accurate as proven by the hunter machine when i double check it. as long as you are firmly pressed against the wheel or tire to the ground, that mark, on the inside is golden! there is no variance and it is very accurate .
thats a pretty tight measurement and im sure it works for you .. but look at all you need... lasers, strings, adapters, etc. my way, is the same. i use 20" front and rear of wheel. get that 1/4" reading between the two wheels front to back and that works out to .36 degrees where your 1/32 each wheel is .2 degrees. very close. My way is just a bit easier and just as accurate as proven by the hunter machine when i double check it. as long as you are firmly pressed against the wheel or tire to the ground, that mark, on the inside is golden! there is no variance and it is very accurate .
That is also a useful approach I suspect as you can take a sensible measurement. Best way to do this would be to have a flat sheet of some kind height as from ground to wheel centre line and width as per the outer diameter of the tyre.
At least one can adjust the toe with the wheels on the ground at full lock.
rgds
Fred
12-09-2015, 05:22 PM
#10
Rennlist Member
Thread Starter
Well just went outside again now the family are tucked up in bed and set the laser beams up most carefully to project two parallel beams starting from about a metre behind the car projecting onto the white garden wall about 2m in front of the 928. I set the beams 194cm apart- the longer the beam the greater the accuracy. I then measured the distance from the front and back of the rims to the beam and the difference in distance between the two sets of measurements is the total toe- this came out to 6mm or roughly 1/4 of an inch- how about that Mark? That after adjusting by eyeball alignment! Whether or not it is correct either side remains to be seen- will take a look where the steering wheel sits tomorrow.
For the rear wheel on the side I increased the height either I wrote the numbers down back to front or the thing is now toe'ed outwards will check tomorrow.
I reckon with this laser rig I can actually measure to within about 1mm of accuracy. Tomorrow I will set it up to be absolutely parallel with the axis of the car now that I have the widths hub cap to hub cap and then I should be able to measure both left and right toe components just as accurately. I'll also do the trig to see if Mark's arithmetic is correct [ha ha]!
Rgds
Fred
For the rear wheel on the side I increased the height either I wrote the numbers down back to front or the thing is now toe'ed outwards will check tomorrow.
I reckon with this laser rig I can actually measure to within about 1mm of accuracy. Tomorrow I will set it up to be absolutely parallel with the axis of the car now that I have the widths hub cap to hub cap and then I should be able to measure both left and right toe components just as accurately. I'll also do the trig to see if Mark's arithmetic is correct [ha ha]!
Rgds
Fred
12-09-2015, 05:50 PM
#11
Rennlist Member
Mark,
That is also a useful approach I suspect as you can take a sensible measurement. Best way to do this would be to have a flat sheet of some kind height as from ground to wheel centre line and width as per the outer diameter of the tyre.
At least one can adjust the toe with the wheels on the ground at full lock.
rgds
Fred
That is also a useful approach I suspect as you can take a sensible measurement. Best way to do this would be to have a flat sheet of some kind height as from ground to wheel centre line and width as per the outer diameter of the tyre.
At least one can adjust the toe with the wheels on the ground at full lock.
rgds
Fred
Well just went outside again now the family are tucked up in bed and set the laser beams up most carefully to project two parallel beams starting from about a metre behind the car projecting onto the white garden wall about 2m in front of the 928. I set the beams 194cm apart- the longer the beam the greater the accuracy. I then measured the distance from the front and back of the rims to the beam and the difference in distance between the two sets of measurements is the total toe- this came out to 6mm or roughly 1/4 of an inch- how about that Mark? That after adjusting by eyeball alignment! Whether or not it is correct either side remains to be seen- will take a look where the steering wheel sits tomorrow.
For the rear wheel on the side I increased the height either I wrote the numbers down back to front or the thing is now toe'ed outwards will check tomorrow.
I reckon with this laser rig I can actually measure to within about 1mm of accuracy. Tomorrow I will set it up to be absolutely parallel with the axis of the car now that I have the widths hub cap to hub cap and then I should be able to measure both left and right toe components just as accurately. I'll also do the trig to see if Mark's arithmetic is correct [ha ha]!
Rgds
Fred
For the rear wheel on the side I increased the height either I wrote the numbers down back to front or the thing is now toe'ed outwards will check tomorrow.
I reckon with this laser rig I can actually measure to within about 1mm of accuracy. Tomorrow I will set it up to be absolutely parallel with the axis of the car now that I have the widths hub cap to hub cap and then I should be able to measure both left and right toe components just as accurately. I'll also do the trig to see if Mark's arithmetic is correct [ha ha]!
Rgds
Fred
but how do you know its 6mm differnce from the rear ? shining backward to some board too? or shining straight down and marking the pavement from the center of the wheel or rear edge?
12-09-2015, 06:28 PM
#12
Chronic Tool Dropper
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Fred, steering needs to be centered, best if rack is also centered, good if steering wheel is centered when rack is centered. The steering geometry includes "Akerman Effect", letting the inside wheel turn more than the outside wheel when going around a corner. Moving the steering from centered will offer toe-out relative to wheels straight ahead.
MK and I go back and forth on the available accuracy of his stick-against-the-tire method. I argue that the tire sidewall is hardly a solid place on which to base a measurement. He argues that his results match what he gets on a commercial Hunter alignment machine. I argue that getting a good even contact pressure at the tire is too subjective, and that making marks on asphalt with any kind of marker is likely inconsistent. Mark measures tire life in race sessions, and seldom drives with the wheels straight ahead with suspension completely settled, so no real testimonials (in tire life) to support measurement accuracy using his stick against the tire method. He stands by it.
Using his 20" forward of center and 20" rear of center to make marks on the pavement, the --total-- toe of 1/4 of one degree means a difference of about 3/16" narrower at front marks than rear marks. Or 3/32" per side relative to center. In my experience, few tape measures are scaled in 1/32" increments. You get to guess-terpolate between the scale marks. The string method is better iin that you can use a machinists scale to get the measurements, usually in 1/64" graduations. Hence the use of thread instead of string.
I made a couple bridges from .250"-wall 2.5" square aluminum box tubing about 24" long, with two .250"-wall 1.5" x 8" long pieces of extruded aluminum angle as standoffs. I put a layer of good plastic tape on the edges that contact the rim edges. The box tube is drilled in several places so the standoffs can be moved for different size rims. Lasers mount on the box tube with machine screws and locknuts. The latest design has a 1/4-20 capscrew through the box tube in the middle to hold the laser levels in place, with a wave washer under the bolt head to add a bit of tension to hold it in place. I made two of these, and zeroed them and to each other. You really only need the two to match each other to get a good alignment. Or just use one and move it from side to side and don't worry about matching anything.
Once you have a fixture (or two matched) with laser level mounted, sit them on te rim edges (I attach them with elastic bungee cords) and make marks about 86" apart on the floor with them, about 43" forward of wheel center and 43" behind. Do the same on both sides. I use painter's tape on the floor and a pencil. When the front marks on either side are 3/8" closer together than the rear marks, your toe is set correctly at 15' (fifteen minutes or 1/4 of one degree). The WSM suggests as much as 20' (one third of one degree) is acceptable, which corresponds handily to 1/2" closer for the forward marks than the rear marks. In the US anyway, finding tape measures that have 1/8" or 1/16" graduations is easy, and even us old blind beggars can easily line up the red laser lines on the tape measure graduations. I write the readings down of course.
Note that the only reason I ever bothered to make the laser setups was because the highly-recommended local alignment place managed to screw it up, costing a set of PS-2's in a very short while. I sat under the car with the tech as he adjusted, and the readings said everything was right on the money. Twice. It was easier and way cheaper to make my own tools than it was to sacrifice aother $500 at the Michelin store for new fronts.
MK and I go back and forth on the available accuracy of his stick-against-the-tire method. I argue that the tire sidewall is hardly a solid place on which to base a measurement. He argues that his results match what he gets on a commercial Hunter alignment machine. I argue that getting a good even contact pressure at the tire is too subjective, and that making marks on asphalt with any kind of marker is likely inconsistent. Mark measures tire life in race sessions, and seldom drives with the wheels straight ahead with suspension completely settled, so no real testimonials (in tire life) to support measurement accuracy using his stick against the tire method. He stands by it.
Using his 20" forward of center and 20" rear of center to make marks on the pavement, the --total-- toe of 1/4 of one degree means a difference of about 3/16" narrower at front marks than rear marks. Or 3/32" per side relative to center. In my experience, few tape measures are scaled in 1/32" increments. You get to guess-terpolate between the scale marks. The string method is better iin that you can use a machinists scale to get the measurements, usually in 1/64" graduations. Hence the use of thread instead of string.
I made a couple bridges from .250"-wall 2.5" square aluminum box tubing about 24" long, with two .250"-wall 1.5" x 8" long pieces of extruded aluminum angle as standoffs. I put a layer of good plastic tape on the edges that contact the rim edges. The box tube is drilled in several places so the standoffs can be moved for different size rims. Lasers mount on the box tube with machine screws and locknuts. The latest design has a 1/4-20 capscrew through the box tube in the middle to hold the laser levels in place, with a wave washer under the bolt head to add a bit of tension to hold it in place. I made two of these, and zeroed them and to each other. You really only need the two to match each other to get a good alignment. Or just use one and move it from side to side and don't worry about matching anything.
Once you have a fixture (or two matched) with laser level mounted, sit them on te rim edges (I attach them with elastic bungee cords) and make marks about 86" apart on the floor with them, about 43" forward of wheel center and 43" behind. Do the same on both sides. I use painter's tape on the floor and a pencil. When the front marks on either side are 3/8" closer together than the rear marks, your toe is set correctly at 15' (fifteen minutes or 1/4 of one degree). The WSM suggests as much as 20' (one third of one degree) is acceptable, which corresponds handily to 1/2" closer for the forward marks than the rear marks. In the US anyway, finding tape measures that have 1/8" or 1/16" graduations is easy, and even us old blind beggars can easily line up the red laser lines on the tape measure graduations. I write the readings down of course.
Note that the only reason I ever bothered to make the laser setups was because the highly-recommended local alignment place managed to screw it up, costing a set of PS-2's in a very short while. I sat under the car with the tech as he adjusted, and the readings said everything was right on the money. Twice. It was easier and way cheaper to make my own tools than it was to sacrifice aother $500 at the Michelin store for new fronts.
12-09-2015, 07:17 PM
#13
Rennlist Member
Fred, steering needs to be centered, best if rack is also centered, good if steering wheel is centered when rack is centered. The steering geometry includes "Akerman Effect", letting the inside wheel turn more than the outside wheel when going around a corner. Moving the steering from centered will offer toe-out relative to wheels straight ahead.
MK and I go back and forth on the available accuracy of his stick-against-the-tire method. I argue that the tire sidewall is hardly a solid place on which to base a measurement. He argues that his results match what he gets on a commercial Hunter alignment machine. I argue that getting a good even contact pressure at the tire is too subjective, and that making marks on asphalt with any kind of marker is likely inconsistent. Mark measures tire life in race sessions, and seldom drives with the wheels straight ahead with suspension completely settled, so no real testimonials (in tire life) to support measurement accuracy using his stick against the tire method. He stands by it.
Using his 20" forward of center and 20" rear of center to make marks on the pavement, the --total-- toe of 1/4 of one degree means a difference of about 3/16" narrower at front marks than rear marks. Or 3/32" per side relative to center. In my experience, few tape measures are scaled in 1/32" increments. You get to guess-terpolate between the scale marks. The string method is better iin that you can use a machinists scale to get the measurements, usually in 1/64" graduations. Hence the use of thread instead of string.
I made a couple bridges from ..
MK and I go back and forth on the available accuracy of his stick-against-the-tire method. I argue that the tire sidewall is hardly a solid place on which to base a measurement. He argues that his results match what he gets on a commercial Hunter alignment machine. I argue that getting a good even contact pressure at the tire is too subjective, and that making marks on asphalt with any kind of marker is likely inconsistent. Mark measures tire life in race sessions, and seldom drives with the wheels straight ahead with suspension completely settled, so no real testimonials (in tire life) to support measurement accuracy using his stick against the tire method. He stands by it.
Using his 20" forward of center and 20" rear of center to make marks on the pavement, the --total-- toe of 1/4 of one degree means a difference of about 3/16" narrower at front marks than rear marks. Or 3/32" per side relative to center. In my experience, few tape measures are scaled in 1/32" increments. You get to guess-terpolate between the scale marks. The string method is better iin that you can use a machinists scale to get the measurements, usually in 1/64" graduations. Hence the use of thread instead of string.
I made a couple bridges from ..
Bob, i dont know why you think the side wall is not sufficient for measuring. there is no runout of the side wall and we are not in the deflection area.
why do you think i drive my car around unsettled. my car is more settled and consistent than any ive seen. and the trips to the alignment rack seem to prove this.
what i measure is the distance between the two wheels front and rear. (about 20". that 1/4 is well within the limits of a common tape measure. its repeatable , many times over with near perfect accuracy. i might have to make a video to prove it to you. why dont you TRY it once , PLEASE!!
1/4" front to rear difference is very easily measured, and that means 1/8" per side / the 20" ......INV TAN.... that equals .35degrees.
the marker..... why cant you understand that the marker is not the line, its where it meets the Level (not a stick
) you can use a can of spray paint. its not the size of the spray, its where it MEETS the edge. very accurate and very repeatable. again, you need to try it. when ever i go to the alignment rack, I always start with what i think it will be... Im very close each and every time.why is that???? maybe it DOES work Bob.
good point about akerman effect. very real . need to center the rack and thats easy to do with the little hole for the centering tool
by the way Bob... ive driven 1000s of miles on RACE rubber with no adverse wear. you cant do this unless your alingnment is set up near 0 toe while you drive. not so much these days , but for many many years, i would drive to the track on hoosiers , 400 miles on the freeway, with most all the wear from the track, not the commute!
12-10-2015, 02:37 AM
#15
Rennlist Member
Thread Starter
Dr Bob's laser levels are identical to mine- the black projector or whatever it is called that the beam emits from is polarised [correct term?] in that rotating it through 90 degees creates a beam that can be oriented either vertical or horizontal [or any angle in between]. I orient mine vertical so that when projected onto the wall I see a clear vertical line.
In my situation at the moment I project two parallel beams down the side of the car sitting each laser level on top of two axle stands thus I have a vertical beam passing along the side of the car close to the wheels and then I simply measure the distance from the beam to the front wheel rims forward [9 0'cloxk]and aft [3 O'clock] at the horizontal centreline. During the setup process I ensure that the separation of the two beams is the same in front of and behind the car. You can do this referencing the laser line image on the floor or you can do it projected onto a wall. The longer the laser line length the more accurate the setup will be.
The difference between the readings for both front wheels gives the total toe. To understand the toe setting for each wheel I will need to calibrate the beams to ensure they are parallel both sides. I now know the difference between the position of the front hub caps and rear hub caps so that should be relatively easy to set up- a bit fiddly but "doable".
Rgds
Fred