any advantages to low-profile tires/bigger wheels?

[wirelessF]

 Originally Posted By: Buffman

 Originally Posted By: Kestas

 Originally Posted By: HTSS_TR

Advantages of plus sizing: better handling/performance and shorter stopping distance. Disadvantages: firmer/hash ride, lower fuel economy, more expensive tires...

The published reports I've read are that low profile tires have greater stopping distance. It also hurts acceleration. Rubber is lighter than alloy wheel. A low profile setup has more rotational inertia than a stock setup. Also, they are less resistant to pothole damage.

Typically seen on the Impala crowd. They put those 22" rims on their cars, and then they end up needing at least 3.73s if not 4.10s to get the performance they lost from all that added weight. Plus without a proper brake upgrade, stopping distant increases. But man looking like a 4x4 is sure cool :\

Donk cars What is the advantage on light duty trucks though? Low profile tires/bigger wheels are okay on cars, but what is the purpose on trucks?

 

[Buffman]

Make it easier to change the oil?

 

[Dualie]

well originally when doing it on light trucks it was to clear big brake kits. That's the original reason I did a truck I used to own. but now a days its just for looks.

 

[TylerL]

 Originally Posted By: saaber1

 Originally Posted By: wcbcruzer

The "downside" to plus sizing is that most people end up with wheels that stick out 3" from the side of the car.

There are calculators online to determine the offset of the wheels to get the exact look you want and fill out the fenders perfectly. Those goofball tires sticking out are either someone who paid no attention to the wheel offset or they are doing it on purpose (Why do they do this? I don't know, same reason they put big spoilers on cars with 76 horsepower I guess).

Mine stick out a little not because of poor planning but because I was limited by clearance between the strut and the tire. Others have this same issue so the choice is wheel spacers or low to medium offset wheels (depends on wheel width, wider wheels need more offset to still fit) I'm not sure why they would need wheel sticking out 3 inches, may they feel the need to cause more wear and tear on their vehicle.

 

[firemachine69]

 Originally Posted By: IndyIan

The only other thing I can add is that if you put low profile rubber on a car with lots of body roll, you might end up with less cornering grip as the you are only using the outside edge of the tire, the inside and middle of the tire have very little weight on them.

If this is the case, it should be offset with adjustments to the camber.

 

[RacerE7773]

 Originally Posted By: Buffman

 Originally Posted By: Kestas

 Originally Posted By: HTSS_TR

Advantages of plus sizing: better handling/performance and shorter stopping distance. Disadvantages: firmer/hash ride, lower fuel economy, more expensive tires...

The published reports I've read are that low profile tires have greater stopping distance. It also hurts acceleration. Rubber is lighter than alloy wheel. A low profile setup has more rotational inertia than a stock setup. Also, they are less resistant to pothole damage.

Typically seen on the Impala crowd. They put those 22" rims on their cars, and then they end up needing at least 3.73s if not 4.10s to get the performance they lost from all that added weight. Plus without a proper brake upgrade, stopping distant increases. But man looking like a 4x4 is sure cool :\

I agree. Not my impala, though. I just want to be able to find a steel stock wheel so I can get a replacement tire. Rock Auto is where I'll probably order from whenever I get the money.

 

[javacontour]

 Originally Posted By: firemachine69

Circumference should remain the same. A wider tire results in higher traction (more rubber on the pavement), but of course, worse fuel economy (even with lightweight alloys, more traction = higher rolling resistance).

Just a nit-pick. You DON'T get MORE rubber on the road, you have a different shaped contact patch. Given two tires of the SAME construction and same air pressure, you have the same area when it comes to contact patch. So if you have a tire pressure of 30psi and a car with 900# of weight on that tire, you'll have a contact patch of 30 square inches. If you go with a wider tire, you'll have a wider contact patch, but no more rubber on the road. A wider tire will give you better cornering and "MAYBE" better stopping. A narrow tire will typically give you better traction in rain or snow, but cornering will be less than the wider tire. A wide tire will more easily hydroplane when compared to the same tire in a narrower width. So it's a pet peeve of mine to hear folks say a wider tire will put more rubber on the road. That is 100% false. Width merely changes the shape of the contact patch. Physics dictates that for a given air pressure, the contact patch will be a fixed area for a given mass.

 

[javacontour]

FWIW, on my SVT Contour, I went from the factory 16" wheels that weighed about 19-20# per wheel to a 17" O.Z. wheel that was about 12-13# per wheel. So you can go +1 and reduce the mass being rotated.

 

[bluemax1]

 Originally Posted By: javacontour

 Originally Posted By: firemachine69

Circumference should remain the same. A wider tire results in higher traction (more rubber on the pavement), but of course, worse fuel economy (even with lightweight alloys, more traction = higher rolling resistance).

Just a nit-pick. You DON'T get MORE rubber on the road, you have a different shaped contact patch. Given two tires of the SAME construction and same air pressure, you have the same area when it comes to contact patch. So if you have a tire pressure of 30psi and a car with 900# of weight on that tire, you'll have a contact patch of 30 square inches. If you go with a wider tire, you'll have a wider contact patch, but no more rubber on the road. A wider tire will give you better cornering and "MAYBE" better stopping. A narrow tire will typically give you better traction in rain or snow, but cornering will be less than the wider tire. A wide tire will more easily hydroplane when compared to the same tire in a narrower width. So it's a pet peeve of mine to hear folks say a wider tire will put more rubber on the road. That is 100% false. Width merely changes the shape of the contact patch. Physics dictates that for a given air pressure, the contact patch will be a fixed area for a given mass.

Sorry, but this is incorrect. It's what you'd call the pseudo intellectual urban legend. You can actually find tests and SAE papers that show that wider rubber DOES actually increase the contact patch as opposed to the 'high-school physics hypothesizing' that assumes that the contact patch would just change shape and not change in size. That said, aside from aesthetics, there is no mechanical advantage to simply increasing the size of the wheel, i.e. going from a 17" to an 18" wheel. The primary reason racers get bigger wheels is to clear bigger brake kits. Reducing sidewall height is another potential benefit for sharper turn-in, but there are ways to do that. The reason for wider wheels is obviously to allow for wider tires. If you don't need bigger wheels to clear bigger brakes, there are potentially many more downsides to bigger wheels than there are to simply retaining the diameter but increasing width to allow wider rubber. Among the potential disadvantages are redistribution of mass which could increase rotational inertia (primarily hurting acceleration and braking). Larger diameter tires are also significantly more expensive. For example, I upgraded the wheels on the car I take to the track from the stock 17x8.5 with 245/45/18 tires to 18x9.5 with 265/35/18 tires. I needed to get the bigger wheels to clear the Stoptech 355mm brake kit as no 17" wheels can fit over them. 265 wide 17" competition tires are about $70-$100 more per tire than the equivalent width in 18" sizes and there's a much greater range of tires available for 17" wheels. I needed the bigger brakes though so I had to get bigger wheels to clear them. I did get lightweight forged wheels to decrease the weight penalty (and the forged 18x9.5 wheels are actually lighter than the stock 17x8.5 wheels), but 17x9.5 forged wheels would have been even lighter. Here's another interesting thing to note: Folks might assume that while retaining the same rolling circumference, larger diameter tires might end up being a little lighter than smaller diameter tires of the same width since they are the same width but have less sidewall. Interestingly enough as it turns out, there is usually very little difference in measured weight because the lower profile tires have more reinforcement in the sidewall which tends to make up the weight difference. (BTW, my current wheel/tire combo has a smaller rolling circumference than the stock size. 275/35/18 tires would have retained the same rolling circumference. The 265 wide tires are a better compromise fit to the 9.5" wide wheels though and the slightly smaller rolling circumference offers a slight mechanical advantage. Max

 

[javacontour]

It really depends on how much the actual sidewalls of the tire support. I recall a study by Avon where at the typical loads of a tire, the contact patch of wide and narrow tires were compared as well as tire pressures. For those tires, at 550 pounds the wide and narrow tires both had nearly identical contact patch areas. Above and below those figures, the wider tire did have a greater contact patch. So yes, tires are not a simple as my very simple balloon physics. The sidewall does play a role in how much rubber is on the road. However, when they did things like double the load on the tire, the contact patch did NOT double, but only increased about 50%. For the typical consumer, the contact patch will remain the same area, but change shape. Of course, I also said if everything else remains the same. Seldom do folks switch to a wider tire and keep the same model of tire. As you correctly mention, many tires with a wider width also come with a shorter sidewall, and that sidewall changes the contact patch. But the physics is largely correct, that given the SAME tire including aspect ratio, at the same air pressure, changing ONLY the width, the contact patch will remain, MOSTLY the same area, changing only in size. But as you said, most folks change more than just the width, and those changes do drive the area of the contact patch much more than just an area = mass/pressure relationship. And of course, you know that bigger brakes don't necessarily mean a car will stop faster. One is typically limited by traction. What many bigger brakes will do is allow you to stop more often, as they can take more stops or stops from higher speeds before fading. It is certainly un-nerving to step on the pedal on the track (or on the street) and find that either your brakes are doing nothing, or worse, the pedal has dropped to the floor because you've boiled the fluid. But that's another story.

 

[bluemax1]

 Originally Posted By: javacontour

And of course, you know that bigger brakes don't necessarily mean a car will stop faster. One is typically limited by traction. What many bigger brakes will do is allow you to stop more often, as they can take more stops or stops from higher speeds before fading. It is certainly un-nerving to step on the pedal on the track (or on the street) and find that either your brakes are doing nothing, or worse, the pedal has dropped to the floor because you've boiled the fluid. But that's another story.

Yep, most folks don't get this point. Too many people just upgrade to bigger brake kits for the 'bling' and to say "Hey, I've got Brembos/AP Racing/Stoptech/Wilwood... etc.". If they can lock up the wheels with the tires they're running and the brakes don't overheat with the kind of driving they do, then there's no need to waste money to upgrade them. Tires are what stop the car, once you can lock up the wheels/tires, increasing brake torque doesn't do anything other than make it easier to lockup the wheels. If the braking system is incapable of locking up the wheels with the tires that are being used though, the easiest way to increase brake torque is to simply use pads with a higher mu (friction coefficient). In addition, most of them don't even realize that the majority of the time, when they simply upgrade the fronts with a big brake kit, they're actually DECREASING their at-the-limit threshold braking ability. What they don't realize is that they're altering the brake bias. Although the change in brake bias from simply installing bigger brakes tends to err on the safe side by increasing front bias, it also tends to decrease at-the-limit performance although for the most part, the owners will extol the virtues of their new brakes with the, "Man! It stops so well now! The braking is incredible!". they don't realize that what they perceive as a dramatic improvement in braking ability is simply an increase in braking force vs pedal pressure at lower speeds and deceleration rates. At the limit though, because the brakes are now front biased, the rear tires (which do only contribute a smaller amount of tractive force) are being underutilized which reduces absolute braking distances and decelerative G's. To optimize a big brake installation, the owners should use a brake proportioning valve, but most folks wouldn't know what to do with one or how to adjust it and adjusting it poorly could lead to a crash th first time they really get on the brakes hard. Max

 

[IndyIan]

Another point in favour of wider tires is that the contact patch is more consistent under heavier sideloads. My 155 width snowtires have a much grippier compound than my 185 width all seasons and in 60F weather on pavement I'd bet the snowtires would stop the car faster in a straight line. Turning though is another matter as the snowtires roll over and overload the outside edge of the contact patch which gives them less overall grip than my wider all season tires in cornering. I have been tempted to try wide low profile snowtires(ones too worn out for snow duty) for solo 2 as a cheap alternative to R compounds. I know the local circle track guys who run in a street tire class say that the newer ice tires were faster but they have been banned. Ian

 

[Corran]

I wouldnt recommend changing the offset of the wheel very much, if at all. If the wheels you want wont fit unless you install spacers to reconcile clearance issues (ie tire hits the strut): your wheels are too wide, or have the wrong offset. I've seen far too many cars with incorrectly offset wheels with prematurely failing wheel bearings, to think it is a coincidence. Another thing to consider is the types of road you will be driving on mostly. I had 215/40R17 tires on my car. the very first time I drove with the wheels on I hit a mild pothole and it felt like my car fell in a pit, the result was a bent wheel and a bubble in the sidewall. I switched to 225/45R17 and havent had any more bubbles eventough I've since have hit too many potholes to count (I comute to Manhattan everyday, and the roads are terrible). Yes, all four wheels are bent I think the taller sidewall offers more protection against sidewall damage.

 

[Kestas]

 Originally Posted By: Corran

I've seen far too many cars with incorrectly offset wheels with prematurely failing wheel bearings, to think it is a coincidence.

As you say, it's not a coincidence. Simple math and geometry calculations show the bearings are overloaded when offset wheels are used. Original bearing design has no robustness built into it.

 

[HTSS_TR]

 Originally Posted By: Corran

... I had 215/40R17 tires on my car. the very first time I drove with the wheels on I hit a mild pothole and it felt like my car fell in a pit, the result was a bent wheel and a bubble in the sidewall. I switched to 225/45R17 ...

Overall diameter of 225/45R17 is 24.97" and 215/40R17 is 23.77", your new tire is 1.2" or 5% larger. To have similar diameter, the new tire should be 225/45R16 (need 16" wheel).

 

[Corran]

 Originally Posted By: Kestas

 Originally Posted By: Corran

I've seen far too many cars with incorrectly offset wheels with prematurely failing wheel bearings, to think it is a coincidence.

As you say, it's not a coincidence. Simple math and geometry calculations show the bearings are overloaded when offset wheels are used. Original bearing design has no robustness built into it.

Exactly, the original wheel bearings are dealing with a much higher load, from a different angle then designed.

 Originally Posted By: HTSS_TR

 Originally Posted By: Corran

... I had 215/40R17 tires on my car. the very first time I drove with the wheels on I hit a mild pothole and it felt like my car fell in a pit, the result was a bent wheel and a bubble in the sidewall. I switched to 225/45R17 ...

Overall diameter of 225/45R17 is 24.97" and 215/40R17 is 23.77", your new tire is 1.2" or 5% larger. To have similar diameter, the new tire should be 225/45R16 (need 16" wheel).

I'm not much concerned with the outer diameter. I was simply stating that a taller sidewall, regardless of outer diameter of the tire, would offer a better protection against sidewall damage.

 

[Dualie]

I have seen catastrophic wheel barring/spindle failures that ended up killing people from vehicles running huge offset wheels. Its no joke

 

[BuickGN]

As soon as the factory 235/45/17 tires were worn out I went with 255/40/17s all around on the factory 8" rims. I've tracked the car on both the factory tires and the wider tires and there's no comparison in braking and cornering. The car never had much of a traction problem off the line before due to the wonderful lack of low end torque but even the little chirp off the line was gone. Overall diameter is reduced about 1/4", something I wanted to avoid but that wasn't possible. I just wish I could've tried the factory tires in the same size so I would know how much of the difference was from the size and how much of the difference was from the ultra high performance rubber.

 

[BuickGN]

 Originally Posted By: Kestas

 Originally Posted By: Corran

I've seen far too many cars with incorrectly offset wheels with prematurely failing wheel bearings, to think it is a coincidence.

As you say, it's not a coincidence. Simple math and geometry calculations show the bearings are overloaded when offset wheels are used. Original bearing design has no robustness built into it.

Would you say this is more true with newer cars? The reason I ask is I've run rims with twice the offset of the factory rims on the GN for over 10 years with no bearing problems. I'm not doubting what you said, it makes sense, just wondering if they were more overbuilt in the older cars.

 

[Kestas]

Yes, I've seen designs get tighter over the years. One disturbing trend is that the auto manufacturers typically take an existing design and want the bearing manufacturer to somehow make it stronger without making it any bigger. This results in a lot of nonsense at the design end. This is often driven by the fact that the manufacturer wants the same SUV or pickup to handle heavier loads for the next model year, or they start making a vehicle bigger and heavier.