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View Full Version : TR2/3/3A Toe In on TR3



martx-5
04-10-2009, 03:45 PM
Yesterday I set the toe-in on my TR3. I was going to use Randall's (TR3driver) method of the 2x3 and a couple of pieces of masonite, but I didn't have a board long enough. I therefore opted for the string method. I won't go into how to set up the strings, as that can be found elsewhere.

What I did do however, was measure the toe-in from the edges of the rims, as this was very easy to do and I have new rims from Hendrix Wire Wheel, so I know they are true.

I have a couple of questions.

1. I assumed that the toe-in of 1/8" as given in the book is TOTAL toe-in. Is that correct??

2. Since I was measuring from the rims, I set the toe-in at 1/16". Since the rim diameter is 15", and the tire diameter is 25.2", I calculated the toe-in if measured from the outside of the tires using the following relationship, looking for "x", the toe-in at the outside of the tires:

x/.0625" = 25.2/15
15x = 1.575
x = 0.105" ...0.020" shy of 1/8"

Is this logic correct?? Or am I missing something here??

prb51
04-10-2009, 04:41 PM
Art,
Toe in for bias ply's is 1/8th in. for radials 0 toe in. I always err on the side of toe in and have mine about 0 to 1/16th". Driving a bit tells the story.

TR4nut
04-10-2009, 04:49 PM
Art-

Never worked it out, but I think your math makes sense. Toe-in is total toe-in, also measured from tire edge so the correction makes sense. Minor concern would be if you are doing all this with bare rims in the air, I thought it made a difference to have the suspension fully loaded on the ground.

Randy

martx-5
04-10-2009, 06:09 PM
I have the car on the ground. It just seemed that the rims would be a more accurate place to get a reading from then the edges of the tires that have all sorts of stuff going on. Besides, that still doesn't get you to the middle of the tread of the tires where these readings are supposed to be made from.

aeronca65t
04-10-2009, 06:14 PM
Your logic seems correct to me (your math is right too).

But don't forget it's harder to be accurate as you measure closer to the axle-center (the longer, outer radius of the tire magnifies the relative position). But if you're careful, it'll work.

I agree that with radials, you can run zero degrees toe (or very, very near to that).
At some slower, twisty tracks, I run toe-out with my race radials.

Also, while you're at it, be sure that you are setting toe from the mid-point of the steering box.
Turn the wheel all the way to the left.
Then turn all the way to the right and count the number of turns.
Finally, turn *exactly* half way back to the left and fix the steering wheel in that position.
Set toe-in from that postion.

This way your maximum turning angle will be equal both left and right.
And, more importantly, your turning geometry (ie-"toe-out on turns") will be correct.

martx-5
04-10-2009, 06:22 PM
Good point of getting at the middle of the rack... I didn't do that. I still have the strings set up, so I'll center the rack and re-do to get closer to zero degrees.

Thanks for the input. :cheers:

TR3driver
04-10-2009, 06:35 PM
Art, not sure what's wrong with your math, but mine doesn't agree. I computed 1/8" times 15/25.2 to get .0744.. which is just a bit over 1/16" Conceptually this makes sense to me, as 15 is almost half of 25.2.

But there are some other problems. As noted, the book setting for radial tyres is given as parallel (0) to 1/16" toe. Also, if you are measuring from the outermost lips of the rim, they are more than 15" apart, closer to 16". Since I have Nylatron bushings, I just set mine to parallel and let it go at that.

BTW, it's not important that the measurement be taken from the center of the tread, only that that front & rear measurement points are in a plane perpendicular to the axis of rotation. That's why you can measure at the outside edge of the wheel (assuming it's true to rotation) and still read actual toe. My method of spinning the tire and marking it ensures that the reference points are in the proper plane.

Nial, on a TR3, equidistant between the stops is not guaranteed to be the center. The stops are located on the front suspension, and are separately adjustable. I prefer to use the steering position that makes the car drive straight as a reference point.

martx-5
04-10-2009, 06:56 PM
Art, not sure what's wrong with your math, but mine doesn't agree. I computed 1/8" times 15/25.2 to get .0744.. which is just a bit over 1/16" ...

Well, it doesn't agree because I computed the toe-in to be <span style="font-weight: bold">0.105"</span>, NOT an 1/8". If you substitute 0.105" times 15/25.2, you will get 0.0625" (1/16"), NOT 0.0744!

Edit: Either way, I will pull out some of the toe-in to get it pretty close to zero. :thirsty:

aeronca65t
04-10-2009, 08:10 PM
Nial, on a TR3, equidistant between the stops is not guaranteed to be the center. The stops are located on the front suspension, and are separately adjustable. I prefer to use the steering position that makes the car drive straight as a reference point.

Ahh, I didn't know that! (and I used to own a TR3).

But if stops are adjustable, wouldn't it still be best to set both stops the same and then find center as I described?

Otherwise, the car may be fine in a straight line but could be a pig in the turns (if toe-out compensation is incorrect).

aeronca65t
04-10-2009, 08:38 PM
By the way, I just drew a little vector diagram in AutoCAD (because I was too lazy to trig this out).

For 25.2 diameter wheels to be set at 1/8" total toe-in, the front wheels are each at an angle of 0.142 degrees.

If I draw a 15" diameter wheel at the same angle (0.142 degrees) I end up with 0.0744" of total toe-in.

Obviously, the difference between .0625 and 0.0774 ain't much, so we're really splitting hairs anyway. <<GRAEMLIN_URL>>/grin.gif

Since it looks like you have radials, I think your idea of setting things close to zero toe is a good idea. :thumbsup:

martx-5
04-10-2009, 09:22 PM
By the way, I just drew a little vector diagram in AutoCAD (because I was too lazy to trig this out).

For 25.2 diameter wheels to be set at 1/8" total toe-in, the front wheels are each at an angle of 0.142 degrees.



Yeah, but that's where you're missing what I did. I took a stab at setting the toe to 1/8" and set the toe by the rims at a 1/16" and wound up with <span style="font-weight: bold">0.105" not 0.125"</span> If you work backwards from <span style="font-weight: bold">0.105"</span> with your vector diagrams, you will wind up back at 1/16" (0.0625") that I set at the rims...

Everyone keeps mentioning 1/8" toe-in...I NEVER SAID THAT THE TOE-IN WAS 1/8"...I said it was <span style="font-weight: bold">0.105", 0.020" shy of 1/8"</span>.

Edit: All I did was guestimate at what I should measure the toe-in at the rims. I figured that 1/16" (0.0625") whould get me in the ballpark if I had measured from the diameter of the tires. Well, I figured that some math would help me out in knowing what the toe-in would be if I actually did it from the outside of the tires. Well, the result I came up with said that the toe-in was <span style="font-weight: bold">0.105"</span>, which is I what I said it was. For me, that was close enough to 1/8". I never mentioned that I had a toe-in of 1/8". I may have been looking for that, but settled on a slightly lower figure.

TR3driver
04-11-2009, 12:49 AM
Well, it doesn't agree because I computed the toe-in to be <span style="font-weight: bold">0.105"</span>, NOT an 1/8". Ok, my apologies. Mis-read your post.

TR3driver
04-11-2009, 01:10 AM
But if stops are adjustable, wouldn't it still be best to set both stops the same and then find center as I described? Honestly, I don't know. But I don't think so. If both methods wind up setting toe with the steering where the car goes straight, then they are equivalent, obviously. But IMO accurate toe is more important for driving in a straight line, less so for turns, so it's best to set it at "straight ahead" even if that is not centered. (Best of course is when they are the same.)

There is even some disagreement as to whether Ackerman got it right; as the outside tire in a hard turn is more heavily loaded and so can run with a larger slip angle than the inside tire before breaking loose. Having a perfect Ackerman angle is not taking full advantage of the outside tire's increased adhesion.

Most likely, it makes no noticeable difference which method you use.

Besides, I don't see how to set the stops "the same" without equipment I don't have. I just set mine so the tires don't rub the sway bar, but I doubt that's exactly the same on each side.

martx-5
04-11-2009, 11:26 AM
This morning I reset the toe. I first checked the strings, made a minor adjustment, checked the strings several more times and then proceeded to redo the toe to get it close to zero.

After several times messing with the numbers, I finally settled on 0.020" toe in measured from the rims. I had to use a digital caliper at this point. If I use the same math I used above, that would give me just a bit more then 1/32" (.034").

I'll leave it there for now and see how she drives.