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Discussion Starter · #1 ·
My wife and I bought a Fortwo about 4 months ago and have proceeded to rack up miles. I noticed that the car seemed to wander a bit while going down the road. Back in college I drove a Fiat 850 - a wonderfully small car with some similarities to a Smart - rear engine, rear drive, and small. I found, in driving my 850 over Colorado mountain passes that the front alignment cared how the car was loaded - one person vs two, and how much was in the front trunk. What this did was make me very good at recognizing when the little thing was out of toe-in alignment - the steering felt like it was sort of skating from one tire steering the car to the other. That is the way our Smart felt.

So, I checked on the alignment specifications - 0.1 to 0.2 inch toe in. For those that don't know, toe in is a measure of how much the front tires "Toe in", or how much the front edges of the tires are closer than their back edges. My experience has taught me that 0.1 to 0.2 is not bad, for a full sized car. But it seemed excessive for a car with really small rims.

So, I checked the toe in - this is something one can do with a tape measure. The tires were towing in 1/8 of an inch, or 0.125. Well within spec. But, gads, that is still a lot of toe-in for a small tire.

I also read on various forums that the front tires on these cars wear out before the rears. No way that should be possible on a rear-engine, rear-drive car, unless the alignment is messed.

Why do the tires toe in? Because, when the car is rolling down the road the "rolling resistance" of the tires pull them back just a little bit - toes them out - which acts to spread the front of the tires just a little bit. The goal is to set the toe in such that the tires roll down the road parallel to each-other. Toe in should match the amount of "give" in the steering rack, tie-rod ends, and various other components. But, looking under a Smart - that all looks pretty tight. I really don't see how the front tires could get 0.2 inches of toe-out while rolling down the road to negate the toe-in specified.

So, I reduced the toe-in on our Smart to 0.06 inches, or 1/16 of an inch. The next day my wife drove the car and couldn't believe the difference. She had been harboring thoughts that the car had to go - suddenly it was everything she wanted.

I have also put on miles, the front end now feels planted on the road. It is a completely different feel - one that feels right.

So, I thought I'd make my first posting on this - see if others have any comments.

If folks like I can also post how to check and adjust ones own toe in - it is very simple and requires very few tools.

Stephen
 

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Discussion Starter · #4 ·
How to check toe-in

Toe-in is the difference in the distance between the front and back of the front tires: Rear distance minus front distance. The opposite is toe-out - which is what front-wheel drive cars need, since the front tires tend to toe-in when they are under power, making up for the static toe-out setting.

OK, back to toe-in. The first step is to get the car on a flat surface with the wheels pointed straight ahead. One way to achieve this is to drive into your garage with the wheels straight ahead. If you use the brakes to stop you will toe the tires out a bit on stopping. Probably doesn't matter, but none the less I either shift out of gear and coast to a stop, then set the emergency brake, or use the emergency brake to stop so the back tires are the ones doing the stopping and the front tires come to rest in a very neutral position. The goal is to not use the brake pedal to stop. But, once stopped, be sure the car is left in park with the emergency brake set.

Next I measure, with a tape measure, the distance from one of the grooves between treads on one front tire and the same groove on the other front tire. In the best of all worlds you would do this on the very front edge of the tires. But, the body gets in the way. So, I measure about 4 inches off the floor - or as high as I can and still have the tape measure not touching the bottom of the car.

I then go to the back of the tires and measure between the same two tread grooves. I then go to the front and measure again, now that I have figured out how tight to stretch the tape measure. And do the backs again. I keep doing this until I am confident I know the two dimensions.

It helps to have a helper while doing this. Or some tape to hold the end of the measuring tape to the tire.

In my case the difference between the two dimensions was 1/8 inch. Or 0.125 inches.

Next I crawled under the car and looked at the tie-rods. The tie-rods are shaped with 6 sides - like the head of a bolt - only these are rods. They are locked in place in the tie-rod end by a locking nut. If you check you will find that the threads on the tie-rods are roughly 16 per inch.

Since we are trying to change the distance between the front edges of the tires it would be neat if we had some idea of the impact of one turn of the tie-rod. Laying in front of the car I took out my tape and estimated the length of the control arm (the lever that the tie-rod end bolts into). I figured 3.5 inches. OK, and the radius of the tire - about 10 inches. Or, about 1 to 3. I’m an engineer so I pretty much think in whole numbers so I can do the math in my head while laying on the ground if front of cars.

So, 1/16 movement on the control arm would be about 3 times as much movement on the front of the tire. And, given that moving the front one way results in the back of the tire going the other way, the change in toe in for 1/16" movement on the control arm is 6/16" on the toe-in.

A very small change in the tie-rod is all that is needed to get 1/16" change in the toe in. Interestingly, if one turn of the tie-rod in the tie-rod end is 1/16 inch, then turning only 1 flat on the tie rod (as in 1/6 of a turn) will result in a 1/16" change in the toe-in of the front tires. It's true - check the math.

That is what I did. First I used a Sharpie to mark on the tie-rod and on the tie-rod end so I would know where they were originally set. I then backed out the tie-rod by 1 flat of the 6-sided tie-rod. This requires that you hold the tie-rod with a wrench so it does not move while you back out the tie rod. Then, tighten up the locking nut without moving the tie-rod in the tie-rod end and you are done.

You will need to figure out how many flats to get around 1/16” toe in. For instance, if you measured the toe-in as 0.2 inches, at the max recommended for the car, you would want to turn the tie-rod just over 2 flats.

Of course you should check your work, so back the car up a bit, pull forward and either coast to a stop or use the emergency brake. Make sure the car is in park with the emergency brake set. Then measure the distances again and verify that the distance is what you expected. On mine, the 1/8 inch decreased to 1/16 inch, or 0.06 inches.

SAFETY: Make sure you tighten up the locking nut that locks the tie-rod end to the tie-rod. Then check again that it is tight.

Make sure the car is in park with the emergency brake set before you lay down in front of it. If you have kids – lock the car and hide the key in your pocket – never know with those little tykes…

I found there was no need to jack the car up to change the toe-in - just turn the steering so the front tires are all the way to one side. This opens up enough space between the front of the tire and the body to reach in and make the adjustment.

CAVEAT: For this procedure to be effective your front rims need to be true - as in they don't wobble when spinning. We have alloy rims and they are wonderfully straight. I checked by jacking each up and spinning them with a piece of wood held near the outer flange on the rims. They had no wobble to them. So, totally reasonable to measure front and rear. If there is any wobble you would want to mark the spots on the front of the two tires where you do the first measure, then gently roll the car forward till the marked spots are the same height from the floor, but on the back of tires, and measure again. This assures you are getting the most accurate measure.

I hope this helps. As I pointed out in my original text - this took a pretty squirmy-feeling steering to a very solid one.
 

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One should note that adjusting the toe on one tie rod only can cause the steering wheel to go off center...
Also, it's possible the toe may be off one side or the other and not knowing what angle (relationship) the front wheels are to the car you may end up adjusting the wrong wheel or both...
Doing toe alignment this way can create problems...Like dog tracking and steering wheels cocked...
That's why there are professional alignment machines to do this...:)
The only thing you have to worry about then is if the alignment operator is competent...:rolleyes:
 

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Discussion Starter · #6 ·
Front end alignment

I thought about the concern that an adjustment on only one side might shift the wheel to one side - but the reality is that shifting by the very small amount I am talking about did not have a perceptible impact on the steering wheel. If this is a concern, then one could divide the change between both sides. In truth, being a clock and watch restorer I am good at doing small things, but the thought of changing both sides by turning just one half flat is a bit interesting.

The second comment, that toe might be off on one side or the other is sort of missing the point of how toe-in works. Adjusting one wheel changes the dimension for both - you can't have toe-in off on just one side. And, given the very small changes involved, as I said above, impact to the wheel is negligible. Changing toe-in on the front of a car is not the cause of dog-tracking, though a large change in toe in can shift the steering wheel from center.

I'd suggest trying it, but only after making sure one makes marks to show exactly where the bits were before making changes, so it is easy to go back to where one started. Or, take it in to a professional and have them set the toe in to 0.06 inches. Either way, I suspect the change in the feel of the front end will be striking. And it should eliminate the excessive wear that is reported for these cars.
 

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With rack & pinion steering it is quite possible to have front wheels misaligned from side to side in relationship to the chassis centerline and having a centered steering wheel...:wink:
 

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Discussion Starter · #8 ·
Miss-aligned front wheels

Barney O. - thanks for the great comments. I guess I am just not as smart as I thought I was. Not to worry, my wife has been telling me this for years.

Barney O. suggest in his post that rack and pinion allows for a miss-alignment not possible in other forms of steering? I am confused I guess.

Doglegs are due to the rear tires being out of true with the center-line of the car - as in the back axle (or a line between the rotational center of the tires) not being perpendicular to the center-line of the car. Hence the back tires tracking on a separate line from the front tires. But, in truth, I really don't see how front tires can achieve this. Unless of course the back end is out of alignment. If interested, check out http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=4 under "Thrust Angle" or even better, check out this youtube video.

Doglegs could also be caused by the front or rear tires being offset to one side of the vehicle - but I have never seen or heard of this except in situations where the frame of the vehicle is severely bent. Or a live back-axle being installed too far to one side of a vehicle.

Just trying to cover all the possibilities here - and trying to make sure I don't miss something.

None-the-less, as the kids of today say, whatever. I'd suggest that folks try a toe-in of 0.06 inches and see if it doesn't make these lovely little cars easier to drive. Face it, there is no legitimate reason why the front tires on a Smart car should wear faster than the rears, unless there is a problem with the alignment.

And, whether you make the 0.010 to 0.020 inch change in tie-rod length on one side or split it between both sides - well, I suspect that is up to you. But I know that experienced front-end men would giggle a bit if you suggested that they make a 0.005 inch change in tie rod length to both sides of the car rather than a 0.010 change on one side. These changes are insignificant when it comes to steering wheel alignment.

For what it is worth I am an engineer with 40 years experience, 6 patents, and the ground-up restoration of a number of cars under my belt. I do all my own alignment work. Early on I had my alignment work checked buy alignment shops and was told I was spot on. Any more I just do what I do and enjoy driving my cars.

Flip side, if all this makes you nervous, well, keep on trucking - you still drive a great little car!
 

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Well there you have it... Engineer with patents trumps machinist that has built custom cars most of his life...:D
 

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Most of the vehicles that I have seen that dog track or crab are trucks with the centering pin broke on the leaf spring. When the truck is under power, that side of the axle can shift forwards and cause it to dog track by actually steering the rear axle.
 

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Discussion Starter · #11 ·
Dog legging

Barney - again, thanks for your gracious reply. I suspect you might be surprised how much mechanical know-how it takes to be a good engineer - one that builds things that work. I credit the little bit of success I have had as an engineer to starting my first car rebuild at 14. Only wish I had more time now to play with cars.

None the less, I do not in any, any way want to denigrate your experience, and in fact I find I learn the most from folks just like you. But, well, even I have to admit I am wrong when the references weigh against me. Well, that is not totally true, hence some of my patents. But that is another story or two.

Just trying to help folks make these great little cars even better, not step on experienced folks toes.

And hey Stretchmobile - thanks for weighing in - yup, that will make a truck dog track, dog leg, crab, or whatever one wants to call it!
 

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Yep, we work for good and bad engineers everyday, same holds true for machinists too..:)
As for dog tracking I was referring to the front wheels having the correct toe dimension but both wheels could be aimed right or left ... I apologize for not making that clear.

FWIW : When you hold the steering wheel off center to travel straight down a highway, be it from wind or misaligned front wheels can be considered dog track'n...
 

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Thanks for the detailed instructions and details on the theory both were well articulated. I adjusted my front end to +1/16" (it was quite off) and the car drives much better now.

I also just replaced tires - at 27K my original OEM Continentals and now at 56K a new set of Kumhos - both suffered from excessive inside wear on the front tires and low tread on the rears. (In Michigan we need plenty of tread for winter driving in snow - and I like the Conti ProContact better for this) I will let you know if this resolves the excessive wear on the inside edge of the front tires.
 

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Discussion Starter · #14 ·
12,000 miles later

Since changing the alignment we have put 12,000 miles on a new set of Bridgestone Blizzak's - great winter tires, and also great in the rain, but not long life tires. But, with a starting tread depth of 11/32, we now show 7 uniformly across both front tires. So, the 1/16" toe-in is giving even wear. That's about the best I can hope for.

I am glad my comments did you some good!

Stephen
 

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Great information. Great thread. Can someone please explain to me why less toe-in is making the 451 "drive better," especially such a small decrease? I've read through the posts and it's the one thing I don't see mentioned.
 

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Discussion Starter · #16 ·
The reason for "toe in" is so that, when the car is rolling down the road the tires end up running parallel to eachother. As your car goes down the road there is force exerted on the tires to push them back - which results in the tires turning a bit out. The goal is to have the front tires "toed-in" just enough to balance the amount the tires "toe out" when rolling down the road. Of course, there is a different amount of toe out depending on the speeds you drive, but the initial toe out that starts as soon as you start moving is the biggest part that you need to worry about. The toe in specified by the factory is too much (IMHO) and the tires end up toed in even when running down the road. Which generates a very recognizable feel in the steering - like the car is shifting from one tire to the other. Unless the toe in is too great - which results in the equivalent of a skiers snow plow. NTL, the best thing is to have the tires rolling down the road parallel to eachother - which 1/16 inch seems to give.
 
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