To try and isolate cause, I installed the old tire/wheels on the front=smooth as glass.  Increased tire pressure to 30 from 28 on the new tires and for giggles, switched sides and no vibration.  Switching sides must have offset the gravitational pull of the moon.??. Glad it somehow worked out because I’m not sure about on-car balancing considering the mini’s gearbox/diff.

You are probably right.  The smaller the diameter of the rotating parts the less critical balance is (in general).  However, the on-car balancing was the thing to have done when I was a kid.  It was considered much better than common bubble balancing.  In the mid- to late-1970s I saw my first computerized balancing machine and suddenly that was the method to use.  Tire shops around here often charged a premium for the computer balancing which is the default today.

About a decade ago we took a family vacation trip through PA and visited the Mack Truck assembly plant.  At the end of the assembly line they tested the trucks on rollers.  The trucks would bounce violently since they did NOT balance the tires.  The tour guide said that these trucks (part of their "Granite" series) were used primarily off road and on construction sites so balancing was considered an unnecessary expense.  It was almost frightening to watch.

I'd be really surprised if all this is necessary...

Minis are not really that sensitive to balance problems.  Did they calibrate the balancer??  A good shop will do this regularly and probably before doing your tyres if you ask nicely.  They do go out of calibration but this easily and quickly treated.

I've only had an oscar balance done once, on the front of my 2002 - which are quite sensitive.

The flat tow question is (IMH not really relevant.  The device only spins up one wheel so the diff is going to be working overtime - in a way that it's not really intended.  

I would try for a check rebalance after they do a calibration run and then check the rotor/drum for runout....and the hub for looseness (steering arms to connection) and anything else...  Wheel balance is not the only cause of vibration.. 

Cheers, Ian

Now if you could pull this off while driving, you would really save some time.

A picture is OK but to fully appreciate this equipment you have to see it and how the operator uses it.  See the YouTube videos linked below.  They shows a MUCH nicer version of what I remember from my youth.

Basically, a road wheel is driven up to speed by a contact roller on the balancing equipment.  The equipment has both a strobe and an accelerometer.  The equipment uses the accelerometer to determine the magnitude and location of highest imbalance and relays that back to the operator in terms of degrees from the reflective mark on the tire/wheel and ounces of balance weights to apply.  A video is worth more than text.




And for more detail on a very modern machine see the video linked below.



The balancers I remember from my youth were a lot more scary looking.

We had an on car balancer in our high school auto shop, used it a bunch of times. Yes mark a stud, wheel bolt hole and the drum/rotor for future reference. Make sure you know if you have a limited slip, positraction, or open gear. The procedure was to place the wheel opposite the one to be balanced on a wheel rim to stop it moving, while one person drove the car to speed, about 35 mph indicated which is 2X at the spinning wheel, while the other person balanced the spinning wheel.

CAUTION if the car had a posi it would spit the rim out with great force so this is important to know. There was also a spinner motor that was pushed into non driving wheels to spin them for balancing. you would look for a reflected light in the paint and adjust until it was still first static, then dynamic. Never had a better balanced car than with this system. This is a much more dangerous method than current systems, so you don't see it much anymore, certainly not in a high school auto shop.

There are a lot of times that seemingly out-of-balance wheels/tires are actually due to bent wheels.

Flat towing mini's are totally acceptable IE = 4 wheels on the ground.
   So this type of balance is A/OK

Please take a picture of this type of 'balance'   Ive never personally see it and am genuinely curious, how or equipment wise how its done.


I would more so wonder if they were quoting you a  "road force" balance.. where a tire machine has a drum that applys road type forces to the tyre while balancing...

I remember dynamic on-car balancing.  I watched a guy do a couple of sets of wheels at a local tire shop when I was a kid.  

As I understand it, the advantage is that the process takes into account ALL the rotating parts including the hub and brake drum/rotor.  I have a question about the process though.  Does the person doing the balancing paint mark a wheel stud and the rim so you can put the wheel back in the "right position" if you have to remove it for some reason?

I don't see why you could not on-car balance the Mini tires as long as the front end is tight as 6464 said.

Make sure all your ball joints are snug. Diagonal tie rod bushes are good and steering rack joints have no play. Then go for it. Sounds like you'll find your inbalance.

While stationed in Germany, I took my GTI (front wheel drive) to a local tire shop for new tires and balancing.  They did the coolest thing.  The wheel/tire assembly would be balanced to the top speed rating for the tire but was balanced dynamically, while installed on the car.  I'm having a little trouble getting the front tires on the mini balanced to the point where there is no vibration, even though the 'computer balancing' read out is fine.  A local tire shop tells me that they have the capability to do the same, i.e. balance the wheel/tire assembly up to freeway speed while mounted on the car.  So my question for all of the transmission /drivetrain experts; is it possible to do that to a mini with the  gearbox in neutral? Any concerns regarding the diff?  Both wheels off the ground at once?  One wheel off the ground?