Do Some Tires Have Better Straight-line Stability?

[RidingOnRailz]

I would like to know if some tires inherently roll "straighter" - requiring fewer corrections at the wheel - than others. I'm not looking for brand recommendations, but would like to know if lower- or higher profiles roll straighter/resist turning forces better. Does speed-rating(T vs H vs V) matter in this respect?

Thanks for your responses in advance.

[MagicRat]

Interesting topic.

Of course a vehicle's suspension geometry (such as the scrub radius) and alignment (caster and toe) all contribute to the predilection for a vehicle to track in a straight line.

In my experience, a narrower tire is more likely to track straight. Wider tires simply hit more bumps and irregularities in the road, and are more likely to be diverted by them.

Also, radial tires seem to track straighter than the old bias ply designs.

Finally, I have experienced a tendancy for some old tires to produce a sense of wandering steering or a pull to one side. Such tendencies disappear when I have installed new tires, so I think the old set had uneven wear issues or a distortion in the shape of the tire carcass itself.

IMO it is best to coordinate proper alignment specs as well as a proper choice of tire to get the handing you want. Stock alignment specs are often a compromise. A good alignment shop can deviate from the stock specs to emphasise a certain desired handling characteristic including a stronger return-to center and enhanced tracking.

[fredjacksonsan]

I think tires can make a difference, even with the same size.

In doing my research to replace the Goodyear Wrangler ST's on my 2004 Grand Cherokee, the reviews in several places indicate that the wandering experienced on the highway went away when switching to Michelins LTX M/S.

I'm sure that a better quality tire can help, and agree with Rat's assessment that wider tires are more subject to the road conditions - after all, wider tires allow a greater moment of torque to be applied by a bump in the road, since it is applied further out from the center of rotation.

[MagicRat]

Originally Posted by fredjacksonsan

I think tires can make a difference, even with the same size.

In doing my research to replace the Goodyear Wrangler ST's on my 2004 Grand Cherokee, the reviews in several places indicate that the wandering experienced on the highway went away when switching to Michelins LTX M/S.

.

Good points. After I wrote my first post, I considered the poor handling I have experienced with some snow tires. Such tires have many small tread blocks and tend to wander more, (at least for me) because the tread blocks are more apt to flex and squirm, imo. Summer tires and high performance tires, with larger tread blocks may well track better.

Tire pressure is a factor, as well, with some cars. My 1977 Lincoln Mk V wanders all over the road like a lost puppy if the front tires are at 35 psi. The tracking is improved when the pressure is dropped to the factory-recommended 30 psi.

[RidingOnRailz]

OK, so we have as possible influences:

- Tire width/aspect ratio
- Types of Tread
- Stock Alignment vs Performance Alignment

As for the first one, I suppose the issues with wandering wider tires can be overcome with more aggressive doses of Caster and/or SAI.

As for the final suggestion, I'd love to know of a shop that is willing to "go out side the lines" as far as achieving a more performance-oriented setup. Most major "chains" will not do it. They are afraid to even go *near* the maximum or minimum recommendation for some parameters. Believe me, I'd go for the max caster allowed if the shop was capable of drilling the slots and making the adjustment.

OTOH, and this deserves a thread unto its own - I have my own idea of how some alignment parameters shold be set - that is, dynamically.

- 100-150lbs in the driver seat(bricks, cases of motor oil, a couple o' tires - on the rims, inflated mind you).

- Adjusting toe such that it will attain the correct toe-in or -out at speed, not on a lift. That is, hypothetically, if a certain Chevrolet requires 5/100" of toe-in, you need to be able to determine how much PLAY is in those front wheels. Knowing that play will enable you to set the correct static toe that will translate into the correct dynamic toe once the vehicle is in motion and the suspension has reached compliance with that motion.

Another case: Suppose a particular Mazda requires between 3 -4 degrees positive caster, with 3.5 being nominal. You many need to dial in 3 3/4 positive to compensate for compliance and reach that nominal setting. Now let's take that Mazda a little further. Suppose the driver wants tighter handling. A-HAH!! He wants that 4 degrees of caster, which means a potential in-shop setting of 4 1/4 to 4 1/2(!!!) to settle into that 4 degrees under way. See what I mean? Now that's thinking outside the box.


For most AF members this is common sense, BUT - Does this common sense exist inside the bays of most alignment shops - particularly large chains??

[Nereth]

Various factors will change how a tyre tracks straight.

For a start the length of the pneumatic trail would be extremely important. Depends a lot on the rubber and surface, since it is based on where on the tread the majority of the cornering force comes from, which in turn is based to a large extent on at what point does the tread come loose and slide, when the tyre is at a slip angle.

Further, the cornering stiffness of the tyre will have an effect - a tyre with very high stiffness will generate a lot of lateral force for only a little slip, that lateral force acts through the pneumatic (and mechanical) trail to center the tyre.

The value of these is dependent on tyre and tread geometery, rubber and road composition and condition, and presumably plenty of other thinsg.

[RidingOnRailz]

Originally Posted by Nereth

Various factors will change how a tyre tracks straight.

For a start the length of the pneumatic trail would be extremely important. Depends a lot on the rubber and surface, since it is based on where on the tread the majority of the cornering force comes from, which in turn is based to a large extent on at what point does the tread come loose and slide, when the tyre is at a slip angle.

Further, the cornering stiffness of the tyre will have an effect - a tyre with very high stiffness will generate a lot of lateral force for only a little slip, that lateral force acts through the pneumatic (and mechanical) trail to center the tyre.

The value of these is dependent on tyre and tread geometery, rubber and road composition and condition, and presumably plenty of other thinsg.

"Nereth"?? Is you from Pandora in the Alpha Centauri system? Listen you blue savage, your people kicked us out the first time and denied us your Unobtanium, but MAKE NO MISTAKE, we WILL be back, and FREEDOM will PERVAIL!

LOL! I couldn't resist. Avatar rocks.

As for the composition of the rubber and sidewall construction, it looks like we may have to go brand specific. Tread pattern of course also counts. As for moi, I have a set of Mastercraft(Cooper) Avenger LSR MS rated all-season t-rated tires http://stopandgotires.com/modelsize....11302&src=frgl on my Optima(mine are 16" the 4-rib on the left). I went with T to replace the old H-rated Kumhos that Kia put on http://www.tirerack.com/tires/tires....del=Solus+KH16 because those things slid standing still(!)

Great road feel the old Kumhos but worthless in anything beyond rain. The T-rated Mastercraft combines the softer S-rated ride with some of the handling of an H-rated tire, but I may decide to go H-rated with my next set of Mastercraft Avengers. Not to mention these things eat snow and ask for seconds. Sadly, I'm really anal about my tire pressures, so my present set won't need replacing for another 4 years - I put 'em on in January of 2009!

[Nereth]

Originally Posted by RidingOnRailz

"Nereth"?? Is you from Pandora in the Alpha Centauri system? Listen you blue savage, your people kicked us out the first time and denied us your Unobtanium, but MAKE NO MISTAKE, we WILL be back, and FREEDOM will PERVAIL!

LOL! I couldn't resist. Avatar rocks.

What?

Check my join date, I've used this name well before that movie came out - and I've only actually watched half of the movie but I was unaware of anyone named nereth in it?

[RidingOnRailz]

Originally Posted by Nereth

What?

Check my join date, I've used this name well before that movie came out - and I've only actually watched half of the movie but I was unaware of anyone named nereth in it?

http://www.imdb.com/character/ch0098391/

With names like that on the planet, your's would blend right in!

[jdmccright]

Tires that are narrower and have a more rounded contact patch will likely be more stable in straight driving, especially when the road itself is not flat.

We have all felt the effects of rutted roads that are caused by heavy vehicles such as semi trucks. In cars that have wider, low-profile tires, the contact patch is wide as well, but is generally centered around the suspension's steering pivot point (an imaginary line going through the a-arm's ball joints or through the macpherson strut, through the tire and to the road surface). But when the road is not level due to ruts, the contact patch moves away from this center and acts on one or the other of the tire's edges instead. To counteract this opposing force, the driver must constantly steer in the opposite direction to keep the car in the lane.

Cars with rounded profile tires are less susceptible because the rutted roads do not cause the contact patch to move as far away from the pivot center.

Hope this helps!

[RidingOnRailz]

Originally Posted by jdmccright

Tires that are narrower and have a more rounded contact patch will likely be more stable in straight driving, especially when the road itself is not flat.

We have all felt the effects of rutted roads. In cars that have wider, low-profile tires, the contact patch is wide as well, but is generally centered around the suspension's steering pivot point (an imaginary line going through the a-arm's ball joints or through the macpherson strut, through the tire and to the road surface). But when the road is not level due to ruts, the contact patch moves away from this center and acts on one or the other of the tire's edges instead. To counteract this opposing force, the driver must constantly steer in the opposite direction to keep the car in the lane.

Cars with rounded profile tires are less susceptible because the rutted roads do not cause the contact patch to move as far away from the pivot center.

Hope this helps!

Interesting! And I instinctively assumed the opposite: wider, low profiles tracked straighter.

So this thread now has a tangent arm: If narrower, taller sidewall tires track straighter, then what is behind the trend toward increasingly lower profile sidewalls and increasingly taller and wider rims - aesthetics? 1940s - 60s: 70-80 profile. 1970s-80s: 70 profile. 1990s-2000s - 50-60 series profile. 2010s - ? 20 series tires? Good Lord!

I do know that by the same token what you described above is also the reason why wider, low profile tires are more responsive to commands at the steering wheel. Higher levels of Caster & SAI would be needed to keep things straight when a turn is not desired.

[jdmccright]

Cars are increasingly engineered to have more performance-oriented characteristics, but not just to give the driver that racetrack feel. The car companies want their vehicles to perform well for safety and avoidance maneuvers since those "star" ratings and consumer magazine reviews can make or break a new model. Ratings that the older, round, tall-profile tires just can't deliver versus the low-profile tires. Thus, more cars are rolling on the lower-profile tires (they aren't necessarily wider).

The low-profile tires don't flex as much during cornering, giving the vehicle quicker response with less driver input than a tall tire that can flex significantly side-to-side. In order to compensate for that wall flexure, the driver has to react and counteract the tire's tendency to flex by adding more wheel input, giving a squirrely, less-than-confident feel.

[RidingOnRailz]

Originally Posted by jdmccright

Thus, more cars are rolling on the lower-profile tires (they aren't necessarily wider).

The low-profile tires don't flex as much during cornering, giving the vehicle quicker response with less driver input than a tall tire that can flex significantly side-to-side. In order to compensate for that wall flexure, the driver has to react and counteract the tire's tendency to flex by adding more wheel input, giving a squirrely, less-than-confident feel.

Well I don't know. My first "real" car, a 1996 Ford Contour, had wider tires than the 1981 Buick Century/Regal? I owned before it. The Buick = 195/75-R14. The Ford had 205/60-R15. About 10mm wider than the buick tires.

Perhaps the trend has gone toward rims of the same width but taller, allowing a lower profile tire of the same width(shoulder>shoulder) as before.

[RidingOnRailz]

I did this diagram to prove that tires are getting lower profiled but also getting wider. From what has been said on hear, taller narrower tires track straighter. If that really is the case then how come the ideal situation - which I rendered at the bottom, - is not happening? It offers the best of both worlds:

Narrower, taller tire/weel combos for straighter tracking with shorter sidewalls for less hysteresis(flexing of sidewall) when turning.

[RidingOnRailz]

I'm reviving this old thread of mine because I think Capri Racer was not around when I brought up the particular issues I did.