Wheel Alignment Perfect; car still does not go straight

[eastla]

Your other and more concerning problem is that it tracks differently when you accelerate and brake.

I may have not explained this properly.
Under acceleration it goes pretty straight; eventually it starts to pull a little to the left though.
Under braking the car is dead straight.
When I come off light throttle the weight transfers forward and it can send me a little left.
It is not a dramatic thing; just seems to speed up the rate it veers to the left.

[Sasso]

JBT, So where is the MM of toe measured from? I thought it was the difference between the front of the wheel and the back measured from a line parallel to the car. If you have bigger wheels, the same number translates to less angle, and angle is not ambiguous in this case, you don't measure camber in mm.
If its combined toe then I have 3mm on each side making 6mm total, but on a 14"wheel, may be a bit much but its so hard to do by yourself, , would have liked 4mm total, but the car handles well so I'll leave it.

Your other and more concerning problem is that it tracks differently when you accelerate and brake.

I may have not explained this properly.
Under acceleration it goes pretty straight; eventually it starts to pull a little to the left though.
Under braking the car is dead straight.
When I come off light throttle the weight transfers forward and it can send me a little left.
It is not a dramatic thing; just seems to speed up the rate it veers to the left.

Ok rule out the brakes then. The fact that weight transfer makes the car pull says that something is not even left and right, could be alignment or shocks or springs even. Your alignment is pretty damn close left and right but you could always try, not forgetting that once you sit in the car you completely change the numbers. Too little rear toe in is still my suggestion.

[eastla]

JBT, So where is the MM of toe measured from? I thought it was the difference between the front of the wheel and the back measured from a line parallel to the car. If you have bigger wheels, the same number translates to less angle, and angle is not ambiguous in this case, you don't measure camber in mm.
If its combined toe then I have 3mm on each side making 6mm total, but on a 14"wheel, may be a bit much but its so hard to do by yourself, , would have liked 4mm total, but the car handles well so I'll leave it.

Your other and more concerning problem is that it tracks differently when you accelerate and brake.

I may have not explained this properly.
Under acceleration it goes pretty straight; eventually it starts to pull a little to the left though.
Under braking the car is dead straight.
When I come off light throttle the weight transfers forward and it can send me a little left.
It is not a dramatic thing; just seems to speed up the rate it veers to the left.

Ok rule out the brakes then. The fact that weight transfer makes the car pull says that something is not even left and right, could be alignment or shocks or springs even. Your alignment is pretty damn close left and right but you could always try, not forgetting that once you sit in the car you completely change the numbers. Too little rear toe in is still my suggestion.

A friend of mine DavidM who has quite a bit of experience drove my car and seems to think it is pretty close to perfect.
He thinks I am crazy to try to change things.

Im off to Winton on Sunday; I think Ill see how things go and consider this problem afterwards if it still is bugging me.

Thanks to all of you again for all the pointers.

[JBT]

JBT, So where is the MM of toe measured from? I thought it was the difference between the front of the wheel and the back measured from a line parallel to the car. If you have bigger wheels, the same number translates to less angle, and angle is not ambiguous in this case, you don't measure camber in mm.

It can be given in degrees, mm or inches. Yes, degrees is a constant but what is a typical setting in degrees? 0.15 degree? 0.25 degree? The wheel size doesn't matter (for lineal measurement) as long as you don't change the rolling diameter for a particular vehicle.

Most wheel aligners show the toe result in mm or (in the past) inches. I don't think I've ever seen one in degrees.

If its combined toe then I have 3mm on each side making 6mm total....

It is combined. 6mm is far too much IMHO. You'll be chewing out tyres.

[Sasso]

JBT, So where is the MM of toe measured from? I thought it was the difference between the front of the wheel and the back measured from a line parallel to the car. If you have bigger wheels, the same number translates to less angle, and angle is not ambiguous in this case, you don't measure camber in mm.

It can be given in degrees, mm or inches. Yes, degrees is a constant but what is a typical setting in degrees? 0.15 degree? 0.25 degree? The wheel size doesn't matter (for lineal measurement) as long as you don't change the rolling diameter for a particular vehicle.

Most wheel aligners show the toe result in mm or (in the past) inches. I don't think I've ever seen one in degrees.

If its combined toe then I have 3mm on each side making 6mm total....

It is combined. 6mm is far too much IMHO. You'll be chewing out tyres.

My RC car runs 2 degrees toe in on the rear each side, I'd have to calculate the angle for the 5 but its not too difficult if you have a ruler and calculator.

Hang on how won't the wheel size affect it? How do you measure toe, do you have a diagram? Maybe I'm measuring the wrong thing.

[JBT]

From the Whiteline website:

Toe is the difference in distance between the front and rear of the tyres. Historically front toe was the only thing that could be modified as rear wheel drive vehicles using a rigid axle had fixed rear toe, usually neutral. Many modern front wheel drives have rear toe adjustment as standard which is critical to their handling.

[Sasso]

Why would you measure off the tyre, I measure off the wheel which is much more stable, the tyre can deform. Racing cars go off the wheel and use strings. Doesn't an alignment machine hang off the wheels though? That would mean different sized wheels gives different results. Also doesn't the NC have bigger dia tyres than an NA or NB?

[JBT]

The measuring instruments attach to the wheels but the measurement is given in mm. Maybe the computer calculates a rolling diameter. The NC wheel/tyre size is 205/45 17\" which is much bigger than NA.

[Sasso]

So point is that 1mm on an NC is most probably very different to 1mm on an NA, and less at that. So most likely the instability is caused by too little rear toe.

[JBT]

No, I think the rear toe is fine. I think it is a problem with his front setting. It is set to zero which will be toe out (undesirable) when moving.

Mine is running:

Front

2.5 mm total toe in
0.5 - 0.75 degrees negative camber
5.5 degrees castor

Rear

2.1 mm total toe in
1.25 - 1.5 degrees negative camber

It runs dead straight with no instability and handles very well indeed.

[eastla]

No, I think the rear toe is fine. I think it is a problem with his front setting. It is set to zero which will be toe out (undesirable) when moving.

Mine is running:

Front

2.5 mm total toe in
0.5 - 0.75 degrees negative camber
5.5 degrees castor

Rear

2.1 mm total toe in
1.25 - 1.5 degrees negative camber

It runs dead straight with no instability and handles very well indeed.

Looking at your front alignment I would have expected it to have more understeer than I like.
With toe in and such little neg camber etc.

I had a similar alignment to that when I first got the Tein's installed.
It handled excellent!
But I could not get the back out no matter what I tried.
Also, it did not turn into corners as quickly as I wanted.
I never took notice if it went straighter or not though?

The current setup I have is MUCH closer to my perfect setup as far as handling goes.
Turns into corners much faster than before with less steering input.
Still very stable under brakes.
Still pushes its nose under extreme cornering mid corner which I like; does not feel snappy.
My tires now have approx 6000km on them which could also explain a bit of the difference in characteristics.
But when pushing very hard on power early I can slide the back out slightly mid corner now. That is what it should do IMO.

I am presuming that your car is pretty stock?
Your alignment from memory is pretty much to Mazda spec so I am sure it is going to handle brilliantly. After all its an MX5

Its just that the handling characteristics can be changed and in my opinion improved with the right alignment.

Obviously I still have a slight problem; the slight veer to the left. But this does not negatively impact on the handling around corners.
Seems to steer brilliantly left and right and is AWESOME fun to punt around slow and fast corners.

[Sasso]

No, I think the rear toe is fine. I think it is a problem with his front setting. It is set to zero which will be toe out (undesirable) when moving.

Mine is running:

Front

2.5 mm total toe in
0.5 - 0.75 degrees negative camber
5.5 degrees castor

Rear

2.1 mm total toe in
1.25 - 1.5 degrees negative camber

It runs dead straight with no instability and handles very well indeed.

He has much more camber and castor than your car, that alone would make the car completely different, you can't then compare toe settings.
Those numbers might be fine for a road setup but a track setup is different. On the road you are never near the limit and care about tyre wear and fuel consumption. On the track though you'll want more camber and toe in on the rear, but the front you want zero or toe out where toe in is for stability rather than response.
Rear toe in might just be what his car needs. Might not, but gotta try, the other settings seem fine (castor is a bit much for my liking but that's irrelevant).

I run zero toe on the front and have no tracking problems. Why would it go toe out when you're moving?

[JBT]

Turn in is just right for me and effortless IMHO. Stuff all understeer. Goes around corners like it's on rails - better than my koni/king NA ever did. Yes, the car has stock suspension but it's nowhere near factory settings, which were positive front camber and 6 mm toe in, all of which were changed within 24 hours of ownership. I have trouble getting the back out too - damn DSC/TC always seems to fix that if I get too ham fisted.

It'll be out on a track day on Thursday and should run just as well as the previous NC did with those settings........and the DSC/TC will be off.

I'm glad to see that you've gone from having an alignment problem to having no problem now.

[JBT]

Why would it go toe out when you're moving?

Forces. Ask an alignment specialist or do a Google search. Here's one.

[eastla]

I'm glad to see that you've gone from having an alignment problem to having no problem now.

LOL!

It is one of those problems that may be in my head?
As far as VDC/TC; mine is always fully switched off so all of the comments I made are based on that.

Can you get the back out with your VDC/TC switched off?

I have a mate with a stock NC who seems to be able to now that his tires are a little worn in.

Seems like the characteristics change significantly with tire wear.

Have you ever tried a more agressive alignment?
I wonder if you would think its better or worse?