Rear Wheel Toe in
- Thread starter prre
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flatchat(Chris)
Supporter
Oooh! /ubbthreads/images/graemlins/blush.gif 1mm toe in should be OK-------1 deg represents about 11mm toe in
Ross Nicol
GT40s Supporter
Hi Paul
What you are referring to is a static setting of Toe.These cars however with classic 60's race car suspension can have a problem ( if not set up correctly ) with the rear wheels toeing out when the suspension changes attitude, in a corner for instance.Any toe out is bad, and is actually steering the car in a direction you will not be wanting to go, usually countering the steering your applying to the front wheels.If your setup is really bad you can apply a lot of static toe in, to counter the dynamic toe out tendency, but of course when your travelling straight down the road the tyres will be
scrubbing and wearing out the expensive rubber,not to mention slowing you down.
It is possible to set up the rear suspension so that no toe change occurs under dynamic conditions and you are able to set your static toe to zero or a small amount of toe in if you have rubber or urethane suspension mounts.Lesson over.
Ross
What you are referring to is a static setting of Toe.These cars however with classic 60's race car suspension can have a problem ( if not set up correctly ) with the rear wheels toeing out when the suspension changes attitude, in a corner for instance.Any toe out is bad, and is actually steering the car in a direction you will not be wanting to go, usually countering the steering your applying to the front wheels.If your setup is really bad you can apply a lot of static toe in, to counter the dynamic toe out tendency, but of course when your travelling straight down the road the tyres will be
scrubbing and wearing out the expensive rubber,not to mention slowing you down.
It is possible to set up the rear suspension so that no toe change occurs under dynamic conditions and you are able to set your static toe to zero or a small amount of toe in if you have rubber or urethane suspension mounts.Lesson over.
Ross
Ross Nicol
GT40s Supporter
I think I should have summarized.You can set your static rear toe to zero, only if you can be sure no toe out wll occur with suspension travel.In other words check for toe change with suspension travel (easy to do ) Then reduce toe change with suspension travel to a minimum , (zero ultimately) and after this set static toe.It's important to do adjustments in this order because static toe settings mean nothing by themselves, when you consider that more toe in is required for cars with a toe out tendency during suspension travel.Also cars with rubber or nolathane chassis connections only because the alignment changes during cornering.You may find Paul, that you are unable to set your toe to zero for the reasons I have explained even though you have rose jointed suspension.Hope this helps harder to say than to do.
Ross
Ross
You can check the static toe and then use a "bump steer gauge" to check for changes in toe with suspension movement. See this TECH ARTICLE
You can buy gauges like THIS ONE
You can buy gauges like THIS ONE
Hi Paul,
I hope it is ok for me to add some questions to your thread.
I will be getting to alignment on my car within the month and I am really enjoying this and other threads that are now dealing with alignment and bumpsteer issues. Gary's reference article about understand and setting bumpsteer is clear and to the point.
The more I read the more I have realized that measuring and readjusting bumpsteer is a exercise that requires good technique and repeatability. Controlling and/or keeping independent variables from changing while at the same time allowing only the dependent variable to change is really a highly detailed job, especially since 0.050 of an inch is the whole ballgame.
I have been looking for methods that eliminate some of the pitfalls. For example, raising and lowering the car off the ground, making baseline measurements, removing suspension components, and then raising and lowering the uprights to the baseline position all add error to the before and after measurement process.
An analogy would the difference in the precision of measuring a one foot distance with a one foot ruler in one step or measuring the same distance with a 1 inch ruler in 12 steps. In all probability the one foot ruler would always produce a more accurate measurement. I think the same is true for bumpsteer procedures. Everytime the measurement instruments are relocated, or go off centerline, more error and complexity are introduced into the process.
Everyone on the forum seems to focus on holding the chassis at a fixed position while raising and lowering the suspension. Raising the car off the ground with the wheels and some suspension parts removed is obviously convenient especially if control arms are being moved around to find the best pick-up points. However raising and lowering the hub also is raising and lowering the point where the measurements are being taken. It is my understanding that toe-in for example, should be measured in a horizontal line through the center of the hub. Having to relocate the position of the forward and rear dial indicator back to level with the hub each time it is moved adds error to the procedure.
Another method is to leave the wheels on the ground and raise and lower the chassis. I recently found an article about this method on the Pantera website. This method keeps the wheels on the ground and the dial indicators never have to be moved or repositioned. See:
http://www.panteraplace.com/page135.htm
This methods seems to be more direct, easier to do in a home shop. Gary, Howard and Ross, et al., do you guys have any pro and con comments on the two methods?
I hope it is ok for me to add some questions to your thread.
I will be getting to alignment on my car within the month and I am really enjoying this and other threads that are now dealing with alignment and bumpsteer issues. Gary's reference article about understand and setting bumpsteer is clear and to the point.
The more I read the more I have realized that measuring and readjusting bumpsteer is a exercise that requires good technique and repeatability. Controlling and/or keeping independent variables from changing while at the same time allowing only the dependent variable to change is really a highly detailed job, especially since 0.050 of an inch is the whole ballgame.
I have been looking for methods that eliminate some of the pitfalls. For example, raising and lowering the car off the ground, making baseline measurements, removing suspension components, and then raising and lowering the uprights to the baseline position all add error to the before and after measurement process.
An analogy would the difference in the precision of measuring a one foot distance with a one foot ruler in one step or measuring the same distance with a 1 inch ruler in 12 steps. In all probability the one foot ruler would always produce a more accurate measurement. I think the same is true for bumpsteer procedures. Everytime the measurement instruments are relocated, or go off centerline, more error and complexity are introduced into the process.
Everyone on the forum seems to focus on holding the chassis at a fixed position while raising and lowering the suspension. Raising the car off the ground with the wheels and some suspension parts removed is obviously convenient especially if control arms are being moved around to find the best pick-up points. However raising and lowering the hub also is raising and lowering the point where the measurements are being taken. It is my understanding that toe-in for example, should be measured in a horizontal line through the center of the hub. Having to relocate the position of the forward and rear dial indicator back to level with the hub each time it is moved adds error to the procedure.
Another method is to leave the wheels on the ground and raise and lower the chassis. I recently found an article about this method on the Pantera website. This method keeps the wheels on the ground and the dial indicators never have to be moved or repositioned. See:
http://www.panteraplace.com/page135.htm
This methods seems to be more direct, easier to do in a home shop. Gary, Howard and Ross, et al., do you guys have any pro and con comments on the two methods?
Attachments
You can use 2 dial indicators - then you do not need to relocate them at each stage of suspension movement. It doesn't matter that the camber changes during the travel, you will still get a toe-change measurement that has at least as good precision then any other bump steer setup you will make or buy. That is because there are 2 dial indicators being used. It is NOT difficult to see two at the same time. Besides, you don't need to see them at the same time according to the procedure in that article - he tells you to stop at given intervals, so what if there are 2 indicators?
I looked at that Long-Acre bump steer gauge - neat idea. But you can make one for far cheaper. A plate bolted to the hub with horizontal lines drawn every 1", and a stand that holds the dial indicators spread equi-distant from the axle. Keep the frame stationary and move the suspension up/down with the shock removed. Record the dial indicator readings and do the simple math. It's really not hard, and very inexpensive. Think about it - how often are you going to check it? This is the way most race shops do it and we won the 1994 Formula Ford national championships that way. It works at least as well as the Long-Acre method.
Besides - you are not looking for exact toe angles when you check bump steer. You want to keep it below some maximum value, and if you're really anal, as close to the other side as possible. Whether you make your own gauge, or buy one, you still need to get to know the equipment and figure out what readings you will accept as maximum. Then just adjust the suspension to keep it below that. Really simple.
However, I'm not saying anything negative about the Long-Acre one. My guess is that you should not have to relocate the dial indicator on their setup. That bump steer gauge must be made in a way that accounts for the hub moving in/out in an arc and also camber changes. Otherwise you DO have to relocate the dial indicator. You don't with a 2 indicator setup.
I looked at that Long-Acre bump steer gauge - neat idea. But you can make one for far cheaper. A plate bolted to the hub with horizontal lines drawn every 1", and a stand that holds the dial indicators spread equi-distant from the axle. Keep the frame stationary and move the suspension up/down with the shock removed. Record the dial indicator readings and do the simple math. It's really not hard, and very inexpensive. Think about it - how often are you going to check it? This is the way most race shops do it and we won the 1994 Formula Ford national championships that way. It works at least as well as the Long-Acre method.
Besides - you are not looking for exact toe angles when you check bump steer. You want to keep it below some maximum value, and if you're really anal, as close to the other side as possible. Whether you make your own gauge, or buy one, you still need to get to know the equipment and figure out what readings you will accept as maximum. Then just adjust the suspension to keep it below that. Really simple.
However, I'm not saying anything negative about the Long-Acre one. My guess is that you should not have to relocate the dial indicator on their setup. That bump steer gauge must be made in a way that accounts for the hub moving in/out in an arc and also camber changes. Otherwise you DO have to relocate the dial indicator. You don't with a 2 indicator setup.
The way I checked bump steer, as I did not need to be 100% accurate as I am not racing etc, was to use a laser light pointer. I placed it on the disk front and rear shining downwards and marked points on the ground and then drew a line between the two points. The disk was set at ride height and with the laser light on the disk shining at the line moved the suspension without the shock attached through the suspension travel and watched to see if it wobbled about the line. Depending on the wobble the steering rack can then be raised or lowered on each side to get rid of the bump steer.
I used a combination of the laser pointer and a digital set square from Bosch as a to set up the suspension and apart from my rear toe in being too much the handling feels very good and I am not sawing at the steering wheel in bumpy corners.
Regards
I used a combination of the laser pointer and a digital set square from Bosch as a to set up the suspension and apart from my rear toe in being too much the handling feels very good and I am not sawing at the steering wheel in bumpy corners.
Regards
Hi Bob. I have always used the "move the wheel method." Let me think about the other. Also there may be some confusion about the Longacre system as it only has one dial indicator as the other side is a fixed beam with a roller on the end. The system just leans against the plate and follows whatever arc the suspension makes (camber, etc.) It just shows you the relative motion between the front and rear points. It is nice in that it has a level to keep the fixture level.
Ross Nicol
GT40s Supporter
Hi Guys. I use the "move the wheel method" like Gary.Will helps me set up the car and we run 2 parallel string lines down each side of the car, adjacent to and in the centre of the wheel hubs. and measure back from the string to the wheel rim for Toe.I find 2 people reading the ruler is good as mistakes really mess you around.We don't reset the string line as the wheel moves up and down but we make sure no one bumps the strings.I did make myself a very effective camber gauge out of a digital level.It has 2 screws that sit against the wheel rim and you directly read camber in degrees wonderful.I'll take a pic of it if anyone is interested.If you find you have a lot of Toe change with suspension travel,try varying the castor that's my tip for the week.Be sensible about the range of suspension movement as it is less than the full travel with the coil/over removed.
Ross
Ross
