The science of why some cars are lemons

four toy cars and a lemon in a row

Nick Platt

Posted March 27, 2020

When life gives you lemons, you have the right to ask for a repair, replacement or refund under Australian Consumer Law.

It might not have a formal definition, but when you’ve bought a lemon, you know it. For most people a ‘lemon’ is a product with a persistent defect that prevents it from living up to expectations. It’s not that the type of product is inherently bad, you’ve just – unluckily – picked a poor example of it. But why are some products lemons and is there anything you can do about it? RACV vehicles engineer Nick Platt explains how lemons are made and what to do if you’ve bought one.

Why some cars are lemons, and what to do about it

Why does a high-tech production line pump out the occasional lemon?

Unfortunately, no matter how good a manufacturer is at making things, the processes they use always produce slight variations from one item to the next. Take something simple like a biro pen, which consists of four main parts. If we take apart the two critical components, the barrel and the refill and measure the area where they fit together, you’d notice that the refill is slightly larger than where it fits into the barrel, which means they require a little bit of force to fit together.

This slight interference is crucial to make sure the two parts stay together. If the refill is too small or the barrel too big then the refill will fall out. On the other hand, if the barrel is too small and the refill too big then you won’t be able to push them together in the first place. In other words, there is a sweet spot of barrel and refill size ranges with which a viable pen can be made. Anything outside this and the resulting pen will not meet the customer’s expectation of a pen, making a lemon if you will. This sweet range is called the ‘specification’.

If you measure a thousand pens, you’ll find a lot of variation. Virtually none of the parts will be the same size but they’ll be close. The range of variations is called the ‘tolerance’.  

So, if the range of tolerance is inside the range of specification you’ll be making good pens. If it’s outside the range of specification, you’ll begin to make lemon pens and the further it is outside the more lemons you’ll make.

Are certain products more susceptible to being lemons?

When products have hundreds of parts, just one of them being out of specification could make the whole thing fail. The task of analysing the tolerances of all the components and how much they could possibly vary is incredibly complex on something like a car and costs a great deal of money and time to get right. The willingness and ability to do this is the main reason why some manufacturers seem to have more faults than others. 

Are lemons the fault of machines or man? 

To further complicate things, many items are assembled by hand which adds a human element to the mix. You know how it goes, give 10 people a task and they’ll do it 10 different ways. 

While diversity is a good in most things, it’s bad when it comes to screwing things together and having them work consistently. Depending on what the product is, something put together incorrectly can be life threatening. Ultimately, this too is a design issue, since a good part or process design will be one that eliminates choice in how it’s assembled.


man standing next to suv on side of road in desert

Knowing the signs of a lemon can be the difference in making a good or a bad investment.

Are some brands better than others at reducing nuances in a product’s design or assembly?

Toyota is particularly good at it. Not only do they have a history of putting incredible effort into designing a product that is easy to assemble (in the early days often at the expense of aesthetics), they also encourage a culture where those assembling the product are engaged in the outcome. This leads to an environment where faults occur relatively infrequently since they’ve been designed out from the start and, when they do happen, the workforce is willing and enabled to fix it quickly. 

Is quality a lemon metric?

Quality is not necessarily a measure of durability or how unlikely a product is to break down. It’s simply how well it does what the customer thinks it should. Usually this is a functional requirement – like a lightbulb lighting or a phone charger charging, but sometimes it’s more subjective. 

What’s the difference between something being a lemon, or just poor quality?

Take, for example, two pairs of shoes; one a pair of fluffy moccasins, the other leather brogues. The fact that either pair ends up falling apart in short order does not mean they are poor quality or a lemon, as long as the initial expectation of looking good on your feet or being warm is filled. How long they should last is a secondary expectation in this case. Something can be perceived as being of poorer quality, but still function perfectly. However, if any of the shoes had a defect that meant they couldn’t be worn properly you’d have a lemon on your hands (or feet), since they cannot live up to the primary customer expectation. 

So what should you do if you’ve bought a lemon? 

The good news is that although Australia doesn’t have lemon laws as such, there are significant consumer protections. Assuming what you bought is faulty and not just that you’ve changed your mind, you have the right to ask for a repair, replacement or refund under the Australian Consumer Law. If the problem with a product or service is minor, you must accept a free repair if the retailer offers you one. 

However, if the problem is major, you can ask for a replacement or refund. The replacement must be of an identical type to that originally supplied and refunds should be the same amount you have paid and in the same form.

Finally, The Australian Competition and Consumer Commission is the consumer watchdog and the place to go if a retailer is not playing ball. Make sure you have all the details to hand such as correspondence, receipts and a log of events before you contact them with a problem.