I know this sounds stupid, but do I have to use the same size wheel, tire and offset when I go get the alignment as I use on track? Since alignment is all about angles, I would assume none of this changes with wheel dimensions an offsets, right?

 

correct.
sketch it out on a peice of paper, the basic (and most important) angles will be unaffected, although offsets can affect some of the more obscure angles such as scrub radius and toe out on turns.

 

Hello Civic44,
You wrote;
"do I have to use the same size wheel, tire and offset when I go get the alignment as I use on track?"

If you are smart you will use the same size tire and wheel. Wheel offset will affect wheel rates and therefore camber and toe settings.


[Modified by DB1-R81, 3:26 PM 3/31/2003]

 

To me, it would seem more accurate, or exact, readings can be found with a really large diameter wheel. But, maybe not.

 

To be clear, changing wheel offset will not change your actual toe or camber measurements but it WILL change the way your car behaves with those settings. Changing tire outside diameter will change your actual toe measurement (since it is typically in in. or mm rather than degrees).

Kirk

 

It will also effect ride height if you are using a PLUS size tire that is not exactly a PLUS combination from your original, which WILL give different readings when performing a caster sweep, also throws off SAI (steering angle) slightly (doesn't really make sense why, but for some reason it does)..

If you have a car with radius rods, you can adjust caster (if needed/wanted) so these readings could be important..

As previosuly stated, best to just put on the wheels that you plan on running..

Also more importantly, use these same wheels for re-alignment if you plan to make changes to the alignment settings(more toe/ less toe) This way you can chart the progress of your changes. The more variables you remove, the more feedback you will aquire from each adjustment..

Jeff

 

would you mind explaining that? Since Steering axis inclination is just caster viewed from the front, I cant really place why offset and wheel width would affect readings.

 

if you mean to ask "will the car still go straight when i put a different size or offset tire on" then yes, it wont affect alignment. if you mean to ask "will it affect car behavior?" then yes, the amount of total toe or camber or whatnot should be reoptimized. but it wont matter anyway if it wasnt optimized anyway, or if you have no idea how to drive and tell it is optimized.

 

The tire diameter affects the height of the wheel sensor as it is mounted on the vehicle, and this slightly affects the caster sweep readings. In a comparison I did with 195/60/14 full tread tires compared to 205/50/15 tires (both on 6" wide rims both with the same 40 offset), the steering angle was off by 0.03 degrees and caster off by 0.14 degrees. Not that it was out of spec off, but differed between the 2 measurements. Car stayed on lift, just jacked up front and rear and changed tires, remeasured and compared the 2 readings (before and after). Camber and toe readings changed slightly also.

So basically since the tire DIAMETER affects toe and camber readings, it will ALSO affect SAI and caster sweep. Offset and width have really no relation.

Jeff
[edit for content]


[Modified by jasyatz, 9:03 AM 4/1/2003]

 

I hate to steel your post, but will 15x6 in 195-50- 15 replaced with 205-50-15 on 15x7 will it change the car's allignment. I have already noticed that it raised the car and it reduced the camber overall(only visual not sure if its true).

Thanks in advance!

Rado