The folks at the Dells rally got to hear Dave Schembri discuss smart USA's take on aftermarket wheels. From their perspective, the OEM wheels are integral to the smart's crash structure and are designed to work with other parts of the car to mitigate forces from a crash. Changing the wheels to something not tested by smart may have unintended consequences in the event of a crash. Which is why smart USA doesn't offer aftermarket wheels.
..not yet...as Mr Presidente led us to believe when it was said that "they were missing the boat" on the after market wheels...then the subject changed to the Brabus wheel size and the whole park got real quiet...Hummmm...wonder why
You seem to know an awful lot about the design decisions that went into the car. I envy you the clarity of your insight.
And the uninformed don't know "reasonable" so you can't suggest that a reasonable person will always make an informed choice.
I don't know "an awful lot", just what was available in the information researched (assuming sources were accurate), and background knowledge as well as my own experience. The fitting of staggered wheel and tire sizes are usually done as a result of stability testing, and that certainly was a factor with the smart. This sort of testing is also common in circuit racing. Staggering can even be done side to side as well as front to back.
Yes, you are right, the uninformed do not know reasonable. That's why I said to act with knowledge meaning that one should become informed before acting. People such as the OP are beginning to do just that after having the benefit of the experience from those who have already made these particular changes.
It's not clear what your stance is on this issue or what your related experiences are.
The folks at the Dells rally got to hear Dave Schembri discuss smart USA's take on aftermarket wheels. From their perspective, the OEM wheels are integral to the smart's crash structure and are designed to work with other parts of the car to mitigate forces from a crash. Changing the wheels to something not tested by smart may have unintended consequences in the event of a crash. Which is why smart USA doesn't offer aftermarket wheels.
Perhaps you may be misunderstanding the reason for the comment regarding the wheels being integral to crash protection. It has nothing to do with staggering, or with the particular OEM wheels being used. It has everything to do with the positioning of the wheels and a rationale behind the safety design of the smart. Exactly the same protection would be offered with any after-market wheel or any tire size installed on those wheels. In fact, the larger the wheel and tire the better the side protection.
Was Mr Schembri directly confronted with the question regarding the crash protection vis-a-vis different sized wheels and tires?
Last edited by fortow; 07-05-2009 at 10:38 PM.
Reason: typo
Was Mr Schembri directly confronted with the question regarding the crash protection vis-a-vis different sized wheels and tires?
No; what he said was if it hasn't been crash tested with the entire car it won't be approved for/by smart. So, do whatever you want, including bigger is better. Could be that the smart OEM wheels are designed to fail by absorbing a certain amount of impact force; fitting bigger, sturdier wheels may instead transfer those forces to the suspension and on to other parts of the car not designed to absorb them. Merely conjecture on my part, as is the idea that the larger the wheels the better protection offered.
My personal stance is that I choose not to change my tires.
The opinions which affect my choice that were shared - while certainly not verified fact - suggest that the smaller front wheels may help keep the car righted during extreme maneuvers by slipping the car rather than having it roll and that changing the wheel characteristics can affect performance particularly in oversteer near the stops, getting the car into a situation where the wheel will whip out rather than returning to center (this may only result for markedly different outside tire diameters, however). Deeper penetration into the snow with the narrower width could provide some benefit for steering in severe winter driving by using the factory sized tires.
When looking at the horsepower required for rolling resistance in performance vehicles ("performance" due to limited data available) I formed my own opinion that the smaller footprint front wheels could noticeably affect mileage. You have noticed no change and the basis for my opinion could be flawed.
What I'd hate is to see people fleeing to larger tires to get the better ride but suffer when in an accident or while trying to avoid one.
Could be that the smart OEM wheels are designed to fail by absorbing a certain amount of impact force; fitting bigger, sturdier wheels may instead transfer those forces to the suspension and on to other parts of the car not designed to absorb them.
I agree with this observation whole-heartedly. Seeing the damage done to Smarts involved in some of the nastier incidents shows where the wheels have been severely altered by the forces involved. I thought I read in the literature where the wheels were designed to fail in a specific manner during collisions. It seems to be much more than just having a pneumatic tube that's at the edge of the impact.
John H, you may not understand the concept of under and over-steer. It does not refer to the position of the steering wheel. What it means is that the car will either tend to push straight ahead (understeer) or the rear end will tend to slide out (oversteer) regardless of the steering wheel position when cornering. For instance, if you are cornering in a reducing radius curve and moving at a velocity that is beyond the traction capabilities of the tires and if the car tends to understeer, it will make no difference whether you turn the steering more, the car will only plow straight ahead when the front wheels lose traction, and they will if the speed is too great, the brakes are used, or from the wrong steering inputs. If the car tends to over steer and given the same situation, then it will be the back end that will want to break loose and the rear end will want to spin out unless counter steer is applied to the steering. Inexperienced drivers are usually unable to understand or react properly to oversteer and will spin out. It is safer for them to simply plow straight ahead and lose speed - unless they go over a cliff, hit a wall, or plow into oncoming traffic, that is.
An aspect of having the same traction with the front wheels as the rear wheels in combination with a rear wheel drive and rear engined light front end car could result in a rollover in emergency manoeuvers that employ turning the wheel one way then to opposite lock. That is what prompted the manufacturer to reduce traction on the front end and design electronic measures that help control the vehicle.
These electronic systems are the electronic stability program as well as cornering brake and acceleration skid controls. Because of these it is virtually impossible to spin the smart regardless of tire size unless on very slippery pavement (ice) and then it would make no difference what size tires are on the front or rear of the car, or what electronic contols are active.
With wider tires and the same size all around, the tendency to understeer is reduced giving more control back to the driver.
Your fears regarding oversteer as well as performance in snow are not entirely realistic. Yes, when buying snow tires it is best if they are narrower than summer tires to enable them to penetrate the snow cover and get better traction. That is only a factor in deep, unplowed snow and not applicable for most winter driving. What is more critical is that true winter snow tires be installed. The rubber compounds don't harden as much in cold weather giving more traction and the tread designs are more applicable to wet and snow conditions. Although the OEM tires are OK for most driving on plowed and salted roads in winter, they are no more suitable than any other "mud and snow" or all weather tires regardless of width. For people driving in snow belt regions of the continent, they should be changing wheels and tires for the winter.
As far as the effect on fuel mileage is concerned, I have noticed no difference, and that has been the case with others as well. Tire pressures, are a greater influence on that than tire width - tire design can also have an effect, although not as much as pressure. There are also many other factors that involve driver behaviour and skill, mechanical maintenance, fuel used, altitude, weather, wind, and road conditions all of which have a bearing on fuel mileage.
People do have a choice here. My point of view has been outlined in other posts. I appreciate your opinion which is of course the safe and approved thing to do. However, it does not take all factors into consideration. Have you heard from anyone who has made the change to wider tires and/or the same sizes all around who has indicated that they made a mistake? I haven't -and I also have the experience of driving with the OEM wheels and tires and aftermarket wheels, wider tires, and the same size on all four wheels during winter (I drive in a snow belt region) and summer months.
No; what he said was if it hasn't been crash tested with the entire car it won't be approved for/by smart. ...
Yes, certainly - that is obvious and perhaps reasonable.
It doesn't imply, or one shouldn't assume that it does, that the OEM wheels and tires offer greater crash protection than alternatives, however. In all liklihood, the official stance would be to bring owners to the conclusion that it is safer to only use the OEM wheels and tires.
It seems that few people are considering the possibility that there are alterior motives for making these inferences.
Do any other manufacturers also not approve of using anything but OEM wheels and tires? I haven't heard of any - and if they did it would surely be ridiculed. Why is it that so many smart owners are intimidated by these types of inferences? Owners of other brands are not so reluctant to make simple changes like tire and wheel sizes (both in diameter and width as well as brands).
A safety advertisement by the manufacturer states the following for passive safety measures;
Crash Protection Systems (Passive Safety) > tridion safety cell – a steel safety cage reinforced with high-strength steel > Two driver and passenger front airbags > Two side airbags for head and neck protection > A collapsible steering column to provide additional space and energy absorption in a front-end collision > Safety seats and belts, including belt tensioners that reduce the slack in a matter of milliseconds and belt-force limiters that carefully release the necessary length of belt to avoid exerting too much pressure on the chest
As to official publications which make mention of wheels and crash protections - here is the official word:
Wheel buffer. The compact design and ultra-short wheelbase of your smart fortwo actually enhance its overall safety. The front wheels are mounted on solid lateral supports that help to absorb the force of a front impact, allowing the passenger compartment to avoid damage and the doors to still open easily. In a side impact, the other vehicle will often hit a wheel, allowing the suspension components to absorb some of the force of the impact.
There have been too many assumptions made regarding wheels.
As is evident from that official wording, it is not the wheels themselves that are at issue but the fact that they act as a bumper of sorts and convey the forces to other structural components.
Smart cars have been delivered with steel wheels, alloy wheels, with different sized wheels and tires. There's no reason to make the assumption that the car can only have what is installed on it at the time of delivery.
This is the moose test aka Elk that the prototype smart laid over on.
No new sedans sold in the US will fall over as a result of steering input. There are lots of other vehicles that will and people are driving them without killing themselves. Using the Ford Explorer debacle as an example of why the manufactures and there various agents are so circumspect on the topic.
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