I have a couple questions that I hope I can find answers to:

1. Assuming a car has had the alignment set up perfectly, the tires are scrubbed in and in excellent condition, tire pressures are properly set, and the brakes aren't dragging excessively at one wheel, is it possible for the weight of a driver to cause the car to drift slightly to the left when steady-state cruising on a flat road with no crown when the hands are taken off the steering wheel?

2. If a car has it's alignment set with the driver or equivilent weight in the driver's seat, will the setup be different than if the car did not have the driver's weight in it?

The reason I ask is that I just had my '06 JCW Mini at BR Racing for some needed maintainence, and in the process, I had the lower front control arm bushings replaced and a complete alignment. They know what they're doing and they hit the numbers right on. And while I had a slight drift to the left before the work, it seems ever so slightly more pronounced now. Mind you, it's very subtle and many people would likely not even notice it.
The tires I'm running are not new, though, and I'm also aware that even new tires can produce a drift one way or another. (Toyo Proxes 4's I was forced to put on once did this fairly dramatically.)

I haven't talked with BR Racing yet about this, but I wanted to get feedback from the collective wealth of knowledge here before I give them a call.

FYI: I'm 275 lbs.

Thanks much!

 

The place I go lets me sit in the car when they align it. It's possible that your extra weight could be an issue, but I can't say for sure.

Are you sure the road had no crown? I've NEVER seen a road that was actually flat...

 

Ask them how much weight they used. If it was less than 275, then I think you have your answer.

 

I have a Toyota truck that had an alignment issue. Actually drove it around for a long time since it's my beater truck now. Anyways, took it to a very reputable shop to get it fixed. The guy aligned it. Afterwards, he told me the numbers are good. But it will still pull to one side because of the tires. When he swapped the tires, the truck pulled to the other side. I never heard of such thing, but I suppose it makes sense.

It didn't matter too much since I was going to get new tires the following week. With the new tires on, my truck drove perfect.

 

On a crowned road, the slope almost always goes down to the left, so you'd expect the car to drift in that direction rather than up. I've got excellent eyes and a sense for when things are level and on level road or on one that's sloping to the right just a bit, the car will still drift to the left. I haven't contacted BR Racing yet, but I will.

As for the tires, I plan on swapping those around as well. And most certainly, tires can make a difference as well.

And, of course, I'll be asking them if they used any weight in the car and if so, how much.

When I get more info, I'll report back.

 

I would expect a pure race car to be aligned for traveling on a flat surface; however, a street car should be aligned with the expectation that the road would be crowned (i.e. slope to the right). On a truly flat surface a street car should track to the left; however, on a crowned road it should track straight. Sounds like your alignment is off to me.

 

How are the tire pressures? Check them with a good gauge; a couple of PSI low will make the car pull to one side.

 

Great answer, why didn't I think of that first.

 

Do you ever/often have a passenger? Would you take that into account when aligning.

 

Tire pressures are perfectly set. When I picked up the car, they were all set at 35. I confirmed it the next morning. They were right on. (Seems my gauge and their gauge agree.) I then set the fronts to my usual 38 and the rears to my usual 36. (Running Hankook Ventus V12 Evo's, 215/40-18.) I'm pretty religious about tire pressures. Same with my motorcycle and bicycles.

I rarely carry a passenger.

In my commute, which varies a bit every morning depending upon traffic, I managed to find a road or two where the road slopes noticable to the right. Hands off the wheel, steady-state cruising and the car drifts slowly off to the right.

I may be being too picky and sensitive about it all. I'm just really sensitive to subtle changes in a car's handling and performance. There's a guy here at work that is about my size and weight and I may ask him to take a short drive with me in the passenger's seat and I'll see how the car performs then.

In the meantime, thanks all for your feedback.

 

I've actually performed alignments in a shop setting. As little as 150 lbs is enough to change the alignment numbers as much as 0.50 degrees on some cars. Suspension parts move in arcs, mind you.

I've never had a MINI on the rack before, so I can't say how much it's numbers would move.

A 0.50 degree spread in camber or caster is enough to either compensate for road crown, or cause a pull. Camber pulls to the side more positive, and caster pulls to the side more negative. How much each car is affected by these spread varries. Most front wheel drive cars aren't that sensitive to caster changes.

Anyway, the thing to do if your slight slight pull is troubling you is to go back and have them redo it with you sitting in the car. I've had to do it before. Couldn't get the numbers right until someone got in the car, and they were perfect. So I stopped fiddling with the camber adjustments.