Hi,

I was looking through the handbook for my 86 vette and realized there is only one set of alignment data - doesn`t mention anything different about the Z51 - but non Z51 cars have 8.5" wheels and Z51`s have 9.5" right ?

The reason i ask is cos I got my (Z51) car aligned a while back to the handbook specs - pleased with how the car handled to b4 it was aligned. However for some reason my car has 8.5" fron wheels and 9.5" rears - I think they`re 84`s as well, cos they`re black in the middle. Tyres all round are 255-50 16". My General xp`s r pretty old on the front but taking time to wear out. So i thought i`d swap the front and back (which has fairly new Kuhmo 712`s).

The car feels so wierd with the wheels swapped round. The slightest touch on the wheel and the car changed direction real quick. Before i swapped them round the car felt pretty heavy at the front and fairly dead - but nice and stable in a straight line - but now it feels light as hell.

The problem is (I know this is a bit dumb) but i`ve never driven any other Vette appart from mine so I dunno how it`s supposed to feel. :confused:

So that`s why I ask about whether or not the 9.5" wheels would need different alignment settings. If not then I guess maybe my old general XP`s are makign the steering less responsive than it should be (I know they do have slight flat spots on).

For now I have put the wheels back the way they were cos like i say i`m not sure if the alignment was off with the wider ones on the front.

any info is really appreciated :)

Tnx,
Dom.

 

The tire size should not effect alignment.It's probaly just your tires that make it feel loose. :chevy

 

Well the guys at the alignment shop would need to know the width of the tires to get everything perfect, but unless you changed tires since the alignment it shouldnt make much difference.

 

I recently E-mailed VBP asking how to convert inches to degrees as most Hunter alignment machines use degrees, and their and others spec. alignments are in inches(toe). I was told it depends on the tire size, and they were working on a conversion. They would get back to me with the info when they came up with the figures.

:chevy

 

Yeah, my tires are the same size all round - its just the wheels that are a different width.

I have noticed the sidewalls seems much less stiff on the older tires so, I guess that may be part of it - I know wider rims should mean better handling as well but i would have thought that would only be at the limit - my car feels completely different just driven gently when i put the wider rims on the front (which have the newer tyres on).

When i finally change the older tires I`ll see how it feels and maybe get the alignment checked again as well - its just bugging me that maybe my car feels completely different to how it should, just cos its got older tyres on the front - its not like theyre bald or anything.

Hmm i might put off my stereo change and put some newer tyres on now instead of waiting for em to wear out. :rolleyes:

Tnx for your help,

Dom.

:seeya

 

I went from 9.5 to 11" on the rear and I don't know if it threw it off, but you can see more negative camber(or is it positive? The top sits in and the bottom sits out). It may be that way all the time, just more noticeable due to the extra width.

 

Caster & Camber are almost always specified in degrees, toe-in/out measurements that most racers use are almost always in inches per side.

A simple method to convert the toe-in/out angular dimensions to inches at the point the tire contacts the pavement;
(Use simple Trig to find the length of side opposite)

1) Take the length/dimension from the spindle center to the tire contact patch/outside radius of tire (= side adjacent)

2) The angular dimension shown on the alignment machine (=angle)

3) Find the Tangent of that angle (scientific calculator/chart)

4) Multiply the length of the side adjacent found in step# 1 above X Tangent of the angle

5) This figure is the length of the side opposite, or simply put the distance from the tire if it were perfectly straight, no toe-in/out to the new point it contacts the pavement with toe-in/out now shown in inches.

If you want to IM me the angle I will give you the tangent so you can do the math.

 

It's actually pretty simple. This works for single or both wheel toe. Just be sure you don't mix single and double measurements up in the same calculation.

Toe degrees = (Toe inches) / (Tire diameter x 0.0174)

Toe inches = (Toe degrees) x (Tire diameter) x 0.0174

That's accurate to 3 places up to 6 degrees which covers most realistic toe angle.

It works because angle in radians = sin of the angle to 3 place accuracy for up to about 6 degrees. The 0.0174 converts between radians and degrees for small angles.

 

Very nice..... ;)

 

Besides the difference in the tires (newer and older) front and rear, you have also changed the geometry of the tires themselves. The same width tire on a wider wheel will have pulled the sidewall out and made it less flexible.

Less flex in the sidewall converts to more feel of the road. What you are feeling is close to what the later C4s with 275x40-17s all around felt. The tires want to follow the road contours.

I would also be willing to believe that the wider tire did change your camber and your toe-in marginally.

 

Hi All,

I have always done my own alignments and in my opinion the size of the tire or wheel will not change the alignment settings!!! However, depending on size (of tire/wheel)the vehicle would probably handle differently.

Also (I'm not being a wise guy) but check to see if you have the tires going in the right direction.

Steven

 

I've thought about this too. I asked a friend who owns an alignement shop and does both my cars regularly. He says that wheel width does not make a difference. Alignment settings are relative to the hub - plane of the point where the wheel mounts. Just my $.02. :flag

 

That was my thinking too, with one exception. Wheels that moved the center of the tire in or our out could cause the suspension to sit at a bit different height whoich would have some effect on alignment.

Also, differenet tires or wheels -could- have different optimum alignment numbers, even though the wheels didn't change the actual alignment.

Dick