Odd asymmetrical tire incident

[DriveHard]

Tire: General G-Max AS-05
https://www.tirerack.com/tires/tires.jsp?tireMake=General&tireModel=G-MAX+AS-05

Car: Fiat 500 Abarth
Size: 205/40-17

I just replaced all four tires on my new to me Fiat 500 Abarth. Car has roughly 40,000 miles with receipts in the glove box for all maintenance that goes above and beyond the manual including two different alignments. Car tracks perfectly straight, and is simply beautiful to drive on the highway. The new tires were amazing, and some of the best I have ever had on a car...quiet, VERY grippy, track VERY straight. They track so well, even in a cross wind I can take my hand off the wheel for a considerable amount of time before having to make a correction.

Now for the odd...
I got a large screw in the sidewall of my front right. As the tires have less than 3000 miles, I simply ordered a new one, with no concern of replacing a pair, instead of just this single tire (usually if my tires are less than 50%, I will replace a pair instead of just one). Got the tire in, pulled the rim off the car, and dropped them at a local shop on my way to work. Picked them up on the way home, all was good. I mounted the tire with the intention to drive the car to work in the morning.

In the morning, I set off from my gravel road onto the highway and immediately notice the car pulling hard to the right under acceleration. It also won't track straight, with a slight pull to the right under cruise that increases with the addition of torque. Being totally frustrated by the time I get to work, I figure it must either be a difference in the new diameter to such a small car, or a pressure imbalance causing it.

I get back home that night and check the tire pressures...it was about 5 psi lower than the others. As I was fixing it to match, I notice the shop had mounted the tire literally "inside out" with the "inside" label on the outside. I drove the car the next day again with no time to take it back to the shop, and even with the air pressure adjustment, it was still pulling pretty hard (no change). Not thinking that the inside/outside thing would cause the pull was convinced the small change in diameter due to wear was causing the issue.

I take the tire to the shop yesterday to have it flipped. Slapped it back on the car last night, and balanced the pressure once again. This morning on my way to work...car tracks PERFECTLY!!! Once again, she is a beautiful highway cruiser!

I was totally blown away that the asymmetrical tread pattern would have that much influence on the straight line tracking for my car...just crazy!!! Be sure to check your mounting if you get asymmetrical tires!

 

[Kira]

Many thanks for that report.

Do you think feeling such an effect would be something auto tech students would benefit from? I do.

 

[MParr]

I just had a set of tires put on. Before I left the dealership, I made sure the tires were mounted correctly. Folks make mistakes. It's also a good idea to check the torque of your lug nuts after any tire mounting or rotation.

 

[CT8]

I have always wondered! Thanks !!

 

[oil_film_movies]

Originally Posted by DriveHard
Tire: General G-Max AS-05 Car: Fiat 500 Abarth I was totally blown away that the asymmetrical tread pattern would have that much influence on the straight line tracking for my car
Suprising it would afffect it that much. The only explanation I can think of is that the Abarth might be set up with Positive Scrub Radius, which means additional drag on the bad tire's side would steer it in that direction (or less drag on the bad tire & negative scrub radius). Usually cars have negative scrub radius to counter-steer a blown front tire. .......... Somebody on an Abarth/500 owner's forum would probably know what the suspension geometry was. I can see how an unusual positive scrub radius would make a hard, braking, turn more stable, less tail skidding.

That Abarth must be fun to drive. I put those same General's on a control blade suspension (C-Max, the Focus's suspension) and they do seem like good tires. Tire Rack likes them in their tests anyway.

 

[oil_film_movies]

Originally Posted by DriveHard
I have widened, lowered, and added a stiffer rear anti-roll bar on mine..
"Widened" meaning, wheel spacers or aftermarket wheels with different offset? That would turn the stock negative scrub radius into neutral or positive scrub. That might explain it.

 

[CapriRacer]

Originally Posted by DriveHard
...…. I was totally blown away that the asymmetrical tread pattern would have that much influence on the straight line tracking for my car...just crazy!!! Be sure to check your mounting if you get asymmetrical tires!


Sorry, but it wasn't the tread pattern that caused this. it was a tire property called Conicity - root word "cone". Conicity is a force pushing sideways. It can be pushing in or pushing out or not pushing at all!.


It was just coincidence that the one tire you got had a large enough conicity value to cause a pull.

 

[RayCJ]

I made this mistake many years ago on my son's car that had directional tires. I did a standard front wheel drive wheel rotation and when the criss-cross on the front takes place, the tires are rotating opposite to their markings. The car will wander and pull all over the place depending on what side of the crown of the road you encounter. Jacked-up the front end, flipped the front tires... Problem solved! With directional tires, you can only rotate front-to-back and must keep them on the same side.

Learned that lesson about 15 years ago and I no longer buy directional tires because I prefer to do rotations with the criss-cross pattern.


Ray

 

[FordBroncoVWJeta]

.

 

[Cressida]

Originally Posted by CapriRacer

Sorry, but it wasn't the tread pattern that caused this. it was a tire property called Conicity - root word "cone". Conicity is a force pushing sideways. It can be pushing in or pushing out or not pushing at all!.

It was just coincidence that the one tire you got had a large enough conicity value to cause a pull.


Very interesting. Are you telling us that if a tire has what is often referred to as "radial pull" (Conicity), it might be eliminated by remounting the tire as in this example. In the past I've had an alignment shop diagnose a tire with radial pull by swapping the tire from side to side. First I've heard that the condition might could be eliminated by flipping the tire on the wheel; if that's what you are saying?

 

[CapriRacer]

Originally Posted by Cressida
Originally Posted by CapriRacer

Sorry, but it wasn't the tread pattern that caused this. it was a tire property called Conicity - root word "cone". Conicity is a force pushing sideways. It can be pushing in or pushing out or not pushing at all!.

It was just coincidence that the one tire you got had a large enough conicity value to cause a pull.


Very interesting. Are you telling us that if a tire has what is often referred to as "radial pull" (Conicity), it might be eliminated by remounting the tire as in this example. In the past I've had an alignment shop diagnose a tire with radial pull by swapping the tire from side to side. First I've heard that the condition might could be eliminated by flipping the tire on the wheel; if that's what you are saying?


It isn't that reversing the tire eliminates the force, it reverses the force's direction. Plus, it's the combination of BOTH front tires. Let me give you an example.

2 front tires are both pushing outwards - one at +7 pounds, one at +5#. The vector sum is +2#, in the direction of the +7# tire. However, if I reverse the direction of the +7# tire, it becomes a -7#, and the vector sum is now 12# (or -12#, depending on which way the net force is pointing).
That's a change from 2# to 12# - and that's the difference between having a pull and not.

To complicate things even further, the vehicle alignment plays a role here. So let me add to the example that the vehicle's alignment results in a 3# pull - and depending on the combination I could get a value as low as 1# or as high as 15#. That's why swapping the tires side to side helps determine where the problem lies.

What is interesting is that it's only the front end that seems to be affected by this - BUT - it is possible to wear conicity into a tire while it is on the rear. Back to our example: If the 5# tire is worn into a 7# tire, I could be looking at a value as high as 17# or as low as 3# - and you would only discover this when the tires are rotated.

So it isn't that there is one bad tire, or that the forces are eliminated. It's that adding all these forces up can result in high values for some combinations and low values for others.

 

[RayCJ]

This link make the problem easy to understand. Keep in-mind that some asymmetrical tires have basically the same properties outlined in this link. Have a look here: https://freeasestudyguides.com/directional-tires-explained.html or here: https://www.tirebuyer.com/education/directional-tires

If a tire has "outside" stamped on it or if it has arrows that show direction of rotation, it's a directional tire and it cannot be mounted wrong or spun in the opposite direction. Tires like these can only be rotated front-to-back on the same side.


Also, here's a good diagram that shows correct standard rotation patterns for tires. https://www.tirebuyer.com/education/tire-rotation-patterns
Ray

 

[CapriRacer]

Originally Posted by RayCJ
…….If a tire has "outside" stamped on it or if it has arrows that show direction of rotation, it's a directional tire and it cannot be mounted wrong or spun in the opposite direction. Tires like these can only be rotated front-to-back on the same side. ……..


Ah …… Mmmmm ….. Not exactly.

If a tire is marked "Outside", it's an asymmetrical tire - the kind this thread is about..

If the tire has an arrow, it is a directional tire - NOT the kind this thread is about

I discuss this in more detail here: Barry's Tire Tech - Directional and Asymmetrical Tires

 

[krzyss]

Yes: asymmetric and directional are two separate attributes.
There used to be tires that were asymmetric and directional: that make tires to be like shoes: left and right.

Asymmetric tires can be rotated on your car to your hearts desire.

Krzys

 

[DriveHard]

Originally Posted by CapriRacer
Originally Posted by DriveHard
...…. I was totally blown away that the asymmetrical tread pattern would have that much influence on the straight line tracking for my car...just crazy!!! Be sure to check your mounting if you get asymmetrical tires!


Sorry, but it wasn't the tread pattern that caused this. it was a tire property called Conicity - root word "cone". Conicity is a force pushing sideways. It can be pushing in or pushing out or not pushing at all!.


It was just coincidence that the one tire you got had a large enough conicity value to cause a pull.



Capri-
If the tires are asymmetrical, is it possible the conicity is designed in? Meaning, the tire OEM designed the force to be in a certain direction, and since the tires are asymmetrical, when mounted correctly, they would offset? Would the OEM mean to design in conicity to achieve a certain performance attribute - meaning, can conicity when used correctly, be a positive in performance or handling?

 

[DriveHard]

Originally Posted by oil_film_movies
Originally Posted by DriveHard
I have widened, lowered, and added a stiffer rear anti-roll bar on mine..
"Widened" meaning, wheel spacers or aftermarket wheels with different offset? That would turn the stock negative scrub radius into neutral or positive scrub. That might explain it.


Both...although it is less than 10mm difference in the front, much more in the back.

 

[oil_film_movies]

https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=12 for a great discussion about conicity & geometry. Conicity was induced by asymettry here it appears.
Suspension geometry on a modified (spacer or aftermarket wheels) chassis should be examined by an alignment shop and calculations of wheel shift done by https://www.wheel-size.com/calc/
Spacers over about 5 or 6 mm can be real trouble, breaking studs due to extra bending torque at the stud root.
Changing an Abarth's geometry is going against those crafty Italian engineers who have already tuned their 500 Abarth like Mama Cucina's spaghetti sauce is perfecto. (Mama C says it can't be improved, BTW.)

 

[CapriRacer]

Originally Posted by DriveHard
Capri-
If the tires are asymmetrical, is it possible the conicity is designed in? Meaning, the tire OEM designed the force to be in a certain direction, and since the tires are asymmetrical, when mounted correctly, they would offset? Would the OEM mean to design in conicity to achieve a certain performance attribute - meaning, can conicity when used correctly, be a positive in performance or handling?


Yes, one could design a tire to have conicity all one direction, but that doesn't solve the problem - because the problem is the variation.

However, there are some creative solutions to handle the variation problem.

1) Make both sides of the tire exactly the same, and then mark which side you want out so that EVERY tire is the same direction, but the variation is cut in half. Mercedes does things this way and they use the Radial high point mark to indicate the side out - and then line that mark up with the mark on the wheel.

2) Separate the production so that all tires within a group are within a small range. This is the approach Ford takes - but it means that every shipment has to be a multiple of either 4 or 5 depending on how many tires there are on a vehicle - and then if something happens to make things uneven, the factory folks have to adjust the production line so that every vehicle only sees tires from one shipment.

And neither of those solutions work well for the aftermarket where white sidewalls are pretty common.

 

[DriveHard]

Originally Posted by oil_film_movies
https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=12 for a great discussion about conicity & geometry. Conicity was induced by asymettry here it appears.
Suspension geometry on a modified (spacer or aftermarket wheels) chassis should be examined by an alignment shop and calculations of wheel shift done by https://www.wheel-size.com/calc/
Spacers over about 5 or 6 mm can be real trouble, breaking studs due to extra bending torque at the stud root.
Changing an Abarth's geometry is going against those crafty Italian engineers who have already tuned their 500 Abarth like Mama Cucina's spaghetti sauce is perfecto. (Mama C says it can't be improved, BTW.)



Measured during lunch...front spacer is 4mm - so thin it almost looks like a glorified washer.