Tires


#1

I was looking at the Chevy Traverse and wanted to know if there are any advantages or disadvantages to the 20 inch wheels


#2

Advantages: fashionable, possibly sharper handling
Disadvantages: harsher ride, expensive tires, expensive to replace if something happens to them, typically wear out faster than smaller, more common tire sizes (20 inchers are usually performance tires).

Personally, I could quite happily live without them if I were interested in the vehicle, especially when it came time to replace the tires.


#3

Mark9207 has made some good points. Let me add that potholes, curbs and under inflation all become huge concerns along with those good looks. I’m also of the opinion that a large SUV like a Traverse with factory rims and payload capacity has that capacity compromised by these rims. Even though the payload may be un affected technically if the tires are wider than OEM, there are just too many added precausions you’d have to take to make the vehicle practical for what it’s intended use is.


#4

Get the tire sizes on the 20" rims and compare prices to the replace the 20" tires compared to the standard size tires. Likely, the 20" tires are very pricey and might not last as long. 20" tires are very harsh in general going over bumps in the road and are more easily damaged by potholes.


#5

I can’t think of any advantages, but there are lots of disadvantages. I wouldn’t buy a vehicle with 20 inch wheels.


#6

The one advantage of buying a used vehicle that road on 20 inch rims would be that it may not have been used to tote heavy loads or go off road.


#7

Agree; stick with the standard size for this vehicle. Tom & Ray had a column in the morning paper on that very subject, and they stated all the disavantages cited.

You don’t buy a Chevy Traverse for its Rally-like handling in the first place!


#8

Since it comes stock with 17s, with 18s and 19s available, no way I’d go with 20s. The 18s or 19s (both with 55 series tires) might be an option, if you really want the ‘bigger wheel’ look, but skip the 20s.


#9

If you like the looks, then that would be the only advantage. Everything else is compromised, including handling.

The handling could be salvaged with different spring and shock rates, but now you are getting into money. You would need to buy a complete system where the springs, shocks, wheels, tires and alignment specs have been properly engineered to work together.


#10

A mojor part of any vehicle’s suspension is the flex of the tire’s sidewall 'tween rim and road.
Low profile 20s don’t have that sidewall flex.

If you’ve never driven these kind of tires you’ll be greatly disappointed at their ride.
Then add the fact that you must also change your driving style to meet the need of those tires or you’ll end up buying a new rim or two every year that you bend by driving your old way.


#11

It will ride like a fork-lift and the first pot-hole you hit, kaa-Ching, $700 please…

It’s strictly a visual impact thing…Did they offer to put multi-color LED lights in them??


#12

I did shimmy stability analysis for airplane landing gears for a couple of decades. When I started to see low-profile tire discussions at this site, I wondered whether or not those tires contributed to shimmy problems in cars; it would make sense that they do. I tried the Google search “low profile tires shimmy” and saw that there were several hits.

The tire parameter most implicated in shimmy for landing gears is tire coefficient of yaw, a measure of the degree to which tire side force contributes to tire twist. I guessed that the stiffer, low-profile tire, would be stiffer in coupling these freedoms too. (I don’t have have actual data on low-profile tire parameters.)

Torsional free-play in landing gears is also an important contributor to shimmy instability, and should be an important factor for cars. If low-profile tires deliver greater shock to suspension components, free-play is sure to develop.


#13

I’m not sure a direct connection can be made due to the alignment capabilities on automobiles, including toe in and caster angles, and the relative lack of stability in the alignment parameters in airplanes. .

Other factors in comparing automobile low aspect ratio tire/wheel combinations with regular (65 and above) aspect ration combinations would be the weight of the tire, the center of the mass’ distance from the axis or rotation, and the ability of the tread to move laterally relative to the bead. In a wheel/tire combo with a very low profile tire, the Cg is far from the axis and the tread has little freedome to move laterally due to the lesser sidewall. I uderstand that you’re postulating that the lesser sidewall would cause transmission of more of the force to the wheel, but would not less mass moving less create less force?

Airplane wheels roll freely, as you pointed out, and through largely varying caster angles. Automobile wheels do not.

I like the discussion. Post back.


#14

FORGET the 767, lets stick with the Chevy…


#15

MB: I didn’t mean to overdo the comparison. I thought the tires might cause shimmy and found some evidence online that they do. I thought I’d be adding to everyone else’s cautions to the OP.

I’m not aware of having pointed out that “airplane wheels roll freely, and through largely varying caster angles.” It is true that geometric and mechanical trail vary from one landing gear design to another but not during taxi for a single design. I’m wondering if that’s what you think I meant by “torsional free-play”, which I’m certain must also play a role in car shimmy. I’m talking about slop between suspension components, created by wear, damage, or design tolerance, allowing a range of free rotation about a wheel diameter – rotation through a slop interval, unrestrained by the suspension.

“… would not less mass moving create less force?” I’m guessing that the loss in tire mass is made up for by increase in wheel mass. It sounds as though you’re thinking of shimmy as a squirming or wiggling of the tire between the wheel and tire footprint. Once the instability is initiated the whole tire, wheel, and flexing suspension go along for the ride. (Sorry if I’m misinterpreting your comment.)

Caddyman: I’m not aware of a shimmy problem on any 767 (plenty of other vibration problems, but not shimmy), so I’m all for forgetting about it. Shimmy is a much bigger deal on airplanes than cars. The results are often catastrophic for airplanes. You’re right to insist on sticking to Chevies, but I get the idea from looking online that these tires do contribute to shimmy problems for cars. I came at the issue the only way I know how.


#16

You have to be careful doing internet searches on tires - particularly regarding vibrations and shimmy. there are many causes of these conditions and the average guy doesn’t know enough to be able to determine the root cause of the problem and my incorrectly assume that his shimmy was cause by the low aspect ratio when his problem may simply be the tires (or wheels0 were out of round.

To my knowledge, low profile tires are not - in and of themselves - the cause of shimmy. Usually it is out round tires, or out of round wheels, or non-concentric mouting of the wheel to the hub.


#17

Acually, I liked your input. I didn’t think it was overdone. I made me think in an unconventional way about wheel shimmy.

I was interpreting “torsioal free play” as meaning the freedom of the wheel to move back and forth around the axis of it’s wheel trunnion, the trunnion being the mounting axle that allows the wheel to turn freely. Precessional forces can cause shimmy in the wheel, as in evidence in shopping carts. Typically in a car this is controlled by the combination of caster and toe in specs in combination with physical controls (tie rods etc.). With heavy off-road wheels it can become a problem, as the forces become considerable, and needs additional steering stabilizers.

While taxiing isn’t a problem with aircraft, the critical points of touchdown, deceleration, acceleration and liftoff introduce in most aircraft substantially varying caster angles. It is evidenced in large aircraft not only at liftoff and touchdown when the angle of attack is greatest, but also during deceleration when the fromt trunnion depresses. Some large aircraft, those with “roller skate” setups such as the B-52 and C5, aren’t as susceptable, but most civillian aircraft including General Aviation craft are.

I’ve never been able to verify my theory about larger diameter alloy wheels with low profile tires being lighter than a combination of a smaller wheel with larger profile tire when the same overall diameter and width is resultant. I keep hoping that someone out there will be in a position to weigh them and validate or invalidate the theory. I suspect it’s true, but I don’t honestly know.


#18

CapriRacer: I take your point. Looking more carefully at what I found online, I see more shimmy conjecture than hard evidence. I’ll only point out that the culprits you point to – wheels or tires out-of-round, etc. – can be depended on to cause vibration whenever wheel rotation speed produces resonance. Some of the complaints, however, talk about the problem being intermittently excited with speed. That sounds more like shimmy. In the same way as for windshield-wiper shudder – a self-excited vibration like shimmy – sometimes you get it, sometimes you don’t.

To say it again, I should have been more careful.

MB: I now see what you’re saying about changing caster at touchdown and during braking. Airplane shimmy is typically confined to high-speed and (otherwise) steady-state taxi. Braking, in particular, seems to be a stabilizing influence, although it is not a cure once shimmy is underway.

If large diameter wheels combined with low profile tires are lighter than the other way around, the yaw coefficient effect might be mitigated, as you say.


#19

Back when folks were replacing narrow high-profile tires with much wider low profile tires, writers often commented on the steering being less stable, which is understandable given the greater leverage the wide tire would have. But now the change is often just to the tire profile, keeping the width constant.


#20

Folks who put oversize tires on 4x4 vehicles often experience the direct relationship between the added rotating mass (with added rolling resistance and greater leverage) and shimmy. Their next addition is generally steering stabilizers.