Let’s Talk About Steering “Pull”
What can cause your vehicle to pull to one side? Let’s assume the obvious reasons have been rectified.
Your vehicle’s alignment has been checked and has either been re-set to the manufacturer’s specs or it is in good shape.
What could cause your vehicle to continue to pull to one side or the other?

Three Reasons Your Vehicle May Pull
There are three main reasons your vehicle may pull to one side.

  • Number One – And most common, you might have improper inflation in one or more of your tires.
  • Number Two – You might have severe, irregular or uneven wear on one or more of your tires, this is often caused by worn suspension parts, a lack of rotation, or an alignment issue.
  • Number Three – You might have a radial pull or “conical” pull caused during the tire’s construction.

Improper Inflation
Improper inflation, particularly on your vehicle’s front tires will certainly cause your vehicle to pull to one side. The wrong inflation on your rear tires, especially if your vehicle has a shorter wheel base, can also cause your vehicle to pull to one side. For instance, if one of your front tires has 35 pounds of air pressure and the other front tire has 28 pounds of pressure, your vehicle will pull toward the side with the smaller amount of air pressure. Not only is the tire with less pressure sitting just a bit lower than the other tire, but there is also more rubber contacting the ground with an under-inflated tire. More rubber contacting the ground causes the tire to grip the road even more causing your vehicle to pull in that direction.

Alignment Issues – Severe, Irregular or Uneven Tire Wear
Severe, irregular or uneven tire wear can cause a vehicle to pull to one side. If you have a newer tire with more tread on one side, particularly on the front of your vehicle, and an older tire with much less tread on the other side, the tire with the newer tread is going to grip the road better. Your vehicle will pull in that direction.

Tire Conicity and Radial Tire Pull
The third reason your vehicle may pull to one side could have been caused when the tire was built. This is called tire “conicity”, or sometimes, “radial tire pull”.
This is what this post is all about, the first two issues are easy to correct, where as tire conicity is much misunderstood.

Release the steering wheel and your vehicle pulls or veers (depending on servility) to one side. A front end problem, right, must be the alignment.
That pull is what most folks think of a wheel alignment problem. Surprisingly a tire can also cause your vehicle to pull. Tire “conicity” is a common phenomenon even in new tires.
Many people also call it a “radial pull” and sometimes a “tire pull.” You’ll see kinds of attempts to fix it, changing the air pressure in one tire only, shops that don’t understand issue trying to “fix it” with an alignment. None of that really works.

So, What Is “Tire Conicity”?
Tire conicity is where a properly inflated tire causes a vehicle to pull to the right or left when driven. Tires do not get conicity. They are manufactured them with the tendency. It is considered a defect and tire manufacturers cover tire conicity under their warranty, if we diagnose it properly and promptly.

Tire conicity or radial pull is usually different from a pull we feel with improper wheel alignment. A caster or camber related pull is normally constant, whatever the vehicle speed. This is because the misalignment does not change as the vehicle increases speed. When radial pull or tire conicity is the problem, the degree of the pull may increase with vehicle speed. It may be hardly noticeable at low speed and quite severe at 60 MPH or more.

Here’s An Example
You have a professional shop install a new set of tires on your vehicle and the wheel alignment is set. It is remarkable how well the vehicle now handles and drives. The driver can release the steering wheel and the vehicle tracks perfectly straight. The vehicle is a joy to drive. You smile, satisfied with your purchase.

Then it happens. After a few thousand miles it is time to rotate the new tires. After the tire rotation the vehicle now has a hard pull to the right. The pulling gets worse as we drive faster. What happened? Did the alignment suddenly go out? We perfectly inflate the tires, but the vehicle veers hard to the right when driving. A likely cause is tire conicity, a defect in a new tire.

A Proper Diagnosis Of Tire Conicity
Example – After a few thousand miles you have the tires rotated.  Now the vehicle has a hard pull to the right that gets worse as you drive faster.
What happened; Did the alignment suddenly go out?  As long as the tires are properly inflated, more likely is tire conicity, a defect in one of the new tires.
Diagnosis is straight forward; temporarily cross the suspected tire to the other side and see if the vehicle pulls the other way, or stops pulling.

  • We need no rocket science, because diagnosis of tire conicity is straight forward.
  • We first drive the vehicle to confirm the problem.
  • After test driving, we temporarily cross the suspected tire to the other side of the vehicle.
  • If the vehicle now pulls in the other direction, or stops pulling, it suggests tire conicity.
  • The tire on the side with the pull, is the normal cause.
  • To confirm the issue we rotate the suspected tire back to the rear.
  • If the vehicle again drives straight, we have found the problem tire.

Tire Conicity Is Different From Thread Separation
Tire conicity should not be confused with a separated, worn or damaged tire.
Though each of these problems can also cause a vehicle to pull, they are each separate issues.
Tire conicity or radial pull exists from the time we install the tire, because they build it into the tire when they manufactured it.

Why Does Conicity Occur?
Tire conicity results when tire belts are not perfectly aligned when the manufacturer builds the tire. Placing the layer of belting to one side creates the problem. Because more belting is on one side than the other, the tire surface inflates improperly. The side with less belting is not as strong as the other. Inflation pushes the tread out, more on the side with less belting. The result is a tire that inflates to a cone-shape, thus the name conicity.

When we roll a cone on a flat surface, it rolls in a circle toward the point of the cone. The same thing happens with a tire. This is why the vehicle pulls when the defective tire is placed on the front. When we place the tire on the rear, the effect is much less, but can also cause a pull if bad enough. We exaggerate the above illustrations for clarity. In reality we cannot see conicity with the eye.

When we install a new tire that has conicity on the front, the effect is obvious. It may go unnoticed when we originally install the tire having conicity on the rear. A driver may only notice the problem several thousand miles later, when they rotate the tire to the front and feel the pull.

Warranties – This Is What They Are For
The vehicle owner needs to notify the tire dealer in a prompt manner. Drivers require prompt action in reporting this condition to the tire company.
Tire manufacturers cover conicity under the new tire warranty, but quick notification is best. If you allow the tires to wear significantly, the wear may be [falsely] blamed for the pull and warranty may be much more difficult. Replacing the tire solves the problem.

Shops should not try to modify the wheel alignment to compensate for tire conicity.
The problem is the tire, not the alignment.
Changing the alignment will only result in the pull returning, when the tires are  rotated once again.

Prevention 
We suggest replacement only with quality name brands, Michelin, B.F. Goodrich, Pirelli, Continental.
These are the brands we use, with Michelin in particular being the brand we most often recommend for durability, handling and warranty.

Final
That’s our goal with each and every client car, fix it right the first time, and prevent problems from happening in the first place.
35 years of service experience have well taught us that “an ounce of prevention is worth a pound of cure.”
Be cured, once and for all, and give us a call, we’re happy to answer any service questions you might have on your Audi, BMW, Mini Cooper Mercedes, Lexus, Volvo or Volkswagen.

Earning your trust, every time you turn the key…that’s what we do…every day…for the last 30 years.
If you have questions, or if we can be of further assistance, just call us at (207) 882-969, we’d love to meet you, and your car!

Warmly,
Bruce and the AMC Service Team