Please tell me I did this right.. Math was arctan x (toe in inches/ tire dia)



If this is right please add it to the upcoming str FAQ

 

is that per side or total? i imagine total

 

Total

 

looks right to me.

 

for a shorter diameter, would that toe number be more or less in degrees?

 

So first, technically it'd be arcsin instead of arctan. This is academic though since for small numbers like what we're dealing with arcsin and arctan are effectively the same.

Next, inches of toe suck and different methods of measuring toe get different numbers. For me personally, it's toe plates. I'm assuming a lot of other people are using toe plates. All the toe plates I've seen are 24". So then if the total toe is t, then the toe in degrees at each wheel is arcsin((t/2)/24). Alignment guys think in terms of each wheel, and most machines don't add these angles together in the way you did in that table, so if you try to add the angles together you'll confuse them in most cases.

So for example 1/4" total toe measured with toe plates is 0.298 degrees at each wheel. 1/4" of total toe measured at the actual extent of the tire, which is another valid way of doing it, would be arcsin((t/2)/25) or 0.286 degrees. Luckily these aren't that different, but they are a little. So I hesitate to make a table since the numbers are kind of approximate depending on how they were measured.

 

It'll be the same. Degrees are independent of diameter, which is why alignment machines default to them. Degrees are what matter to handling. So if you have a toe of 0.25 degrees, then you get bigger wheels but want to keep the same handling, you'll still want to set it at 0.25 degrees.

However if there's a conversion somewhere with inches...if a bigger wheel and a smaller wheel have the same toe in inches, then the bigger wheel will have less toe in degrees.

 

Thanks Jon for clarifying the math. Arcsin and arctan give the same numbers btw. Here's my contributation, I think this should be listed in the str FAQ because all the stats given for the 2011 solo thread use inch toe numbers. Noobs are not going to know how to convert it and this chart makes it very easy.

 

Made this a while back...

Degrees-Inches Conversion Table

 

Nice! I've never seen that! I just went back and looked at my current toe setting. I was stuck at .18 on each side so I'm at about 5/32 or just right between 1/8 and 3/16. Next year I want the car to have between .2984 and .3730 on each side depending on driver feel. Granted I am bumping the rear springs 100lbs and dropping the front bar one notch. The toe should keep the car in check. It's still alittle looser then I want at the current setting but I got to cut off the rear arms to fix the issue. Winter project should be fun!

If class doesn't work out this simester I might be out of racing until May 5th though. I've got a A in my A&P class right now and have got 10/10 on my last 3 quizes so Hopefully I make it through. I have heard alot of people fail the last 2 test though. Our class has already dropped from 63 people to 24. So I've got a motive to finish the class so I can race as soon as the season starts up. If not It's looking like I'll have to take a sunday class which would mean I can't race until we get out for the summer. If I spent half as much time studying as I do looking at and reading about car stuff school would be cake! haha