pll

I just got my car aligned to my specs and I have a question about the toe-in number. I told the tech to give me 0.25" toe in on the rear. The printout shows 0.22 degrees total toe in on the rear. Right next to that number is a "Specified" toe in of 0.32 degrees which I'm assuming is the stock setting. Did the tech set the toe in correctly? How do I convert from inches to degrees? Thanks.

RT

[QUOTE]Originally posted by gilcwong
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Did the tech set the toe in correctly?

CoralDoc

I just had my car aligned by a technician using a Hunter machine that gives readings in degrees. According to the Helm service manual, the specification for rear total toe is 6 +/- 2mm or 1/4" +/- 1/16". The specification listed in the Hunter database for the S2000 is 0.48 +/- 0.16 degrees, slightly less than the 0.58 deg. value calculated by RT (nice math, BTW ).

If the 0.22 deg. value on your car is for total toe, it is less than the range specified by Hunter (0.32 - 0.64 deg.) and less than RT calculated. If it's for one side, and if both sides are the same, you're spot on (total toe would then = 0.44 deg.).

I'd check back with the technician that you worked with to determine if a re-alignment is in order. I'm running my rear total toe setting at the low end of specificatoion at 0.36 deg. but I have heard of some people that run close to 0 toe. From my little understanding of the matter, less toe makes the rear end feel "twitchy", but allows more effective rear steering under loading, and reduces rear tire wear due to scuffing.

pll

Thanks guys! Yeah, they were using a hunter machine to align the car. Luckily, the alignment shop has a 1 year free alignment warranty. I'll have them redo it.

Mike Schuster

CoralDoc:

The Hunter angle spec of 0.48 degrees total or 0.24 degrees per side may be slightly incorrect. [URL=http://www.hondanews.com/Forms/honda/S2000/*ws4d-db-query-Show.ws4d?*ws4d-db-query-Show***000531***-wieck_media***-***honda(directory)S2000(directory)***.ws4d?honda/S2000/results

RT

Mike, thanks for confirming the numbers/method
Technically Sin is the right function because the wheel is the hypotenuse not the adjacent side but agreed Tan works fine too because of the small angle.
The real interesting thing is that when the toe is dialed in on a linear scale, the front of the tire is moved in only about 1/4 of the total toe number (1/16" in this case) because the trailing edge moves out (~1/16") as the assembly yaws about the ball joints.
So the equation is like this (another form of my first equation):
ArcSin[1/4 of the total toe/tire radius] = ArcSin[(1/16")/12.35"] = 0.29 degrees
Which yield the same answer, just a more accurate depiction of what's really happening (two small triangles instead of the one bigger one).

God, what the hell am I doing? I hated trigonometry then (over 20 years ago) and I still hate it now

CoralDoc

I think I better turn this thread over to the math professor in the office next to mine .

Specifications are a nice place to start, but the bottom line here is what you want from your car. For example, additional camber will help your car take a set and perform well in turns at the expense of increasing wear on the inboard sides of the tire. The first model year (or two?) of the NSX had pretty high camber specs, and tires were wearing out pretty quickly. If your think SO2s for our car are expensive, try putting new rubber on an NSX! Since owners complained, the "specifications" were changed. All that this means is that people that want their cars to perform at a high standard must sacrifice even tread wear.

Additional toe-in will help your car track straight, but will diminish turn-in. Not enough toe-in (or toe-out!) can make the car feel "darty". These are not absolutes, but gradients along a performance range.

pll

Ouch. That's more math than I was expecting. Thanks for the explaination. It looks like my toe in is a bit low, but the car feels ok. The rear end feels a little light at the moment when going over bumps, but that could be due to the fact that I have unshaven Toyo RA1s. I'll put on some more miles and see what happens and I'll adjust the alignment as necessary. Thanks again everyone!

jays2000

So what i have to tell the alignment shop to adjust the toe. I using the 255/35/18 thank you

Mike Schuster

jays2000,

I suggest sticking with factory settings even with non-factory tires to start with. As with factory tires, expect more tire wear in the rear than in the front due to larger toe and camber settings in the rear. Later, if you want to make handling or tire wear adjustments you can try some changes.

In my case with factory tires I dislike my car's tendency to understeer with the factory settings and so I am experimenting with different settings to reduce this tendency.