In its official press release, Lexus claimed the IS sedan’s “body rigidity was enhanced” starting from the 2021 model year. For the record, “body rigidity” is a very ambiguous term. It may have different meanings, for example there are torsional rigidity and also bending rigidity. At the same time, different sections of the vehicle has its local rigidity values, and the whole car body also has global rigidity numbers as well. Besides that, there are also rigidity factors related to crash test (to show how rigid of the passenger cabin to withstand impact forces). All of these have dramatic different meanings, and they may be even calculated by different unit of measurement. Unfortunately Lexus does not specify what the “body rigidity” it is referring to.
From my own experience behind the steering wheel of the vehicle, the only conclusion I can make is, the latest (3rd) generation Lexus IS has higher torsional rigidity than the 2nd generation. However, I do not know the exact number or range because Toyota/Lexus never published it, and even for those rare occasions that Toyota sent engineers to give presentation in professional conferences, they all tried to avoid talking about detail numbers for specific car models. In order to not being subjective, the following analysis is based on testing data obtained from 3rd party entities, or document/illustration published by Toyota.
One of the unusual fact I discovered for the Lexus IS is, the structural change in the 2021 model year facelift is actually a downgrade for some aspects. It did upgrade some components to use high strength steel (HSS), but at the same time it downgraded some other components to mild steel, which previously was made of HSS.
Please see the below two illustrations (first one is the pre-2021 model, the second one is the 2021+ model). We can see the differences.
The good:
- The 2021+ models use hot stamped HSS for the whole B pillar while the 2014-2020 models only uses it for the upper part of the B pillar.
- The 2021+ models finally use HSS for the transmission/central tunnel, while the old models still uses mild steel. These are all good stuffs.
The bad:
- The engine compartment front rails are downgraded to mild steel;
- The longitude ribs (parallel to the transmission tunnel) in the passenger cabin flooring are also downgraded to mild steel only.
Since the above materials are all from Toyota’s official publication, I am assuming the information is correct and there is no mistake in the drawing. While we can not absolutely equate mild steel = weaker rigidity, however given the same thickness and stamping, mild steel does have weaker rigidity than HSS. With that being said, if Lexus wants to maintain the same rigidity, it will need to increase the thickness of the mild steel for those components that were using HSS previously. However, thicker metal sheets are heavier and cost more, so no one with logical thinking would ever do this: why should I make a change which increases the weight but has no real cost benefit? Therefore I highly suspect the actual rigidity for those components that changed back to mild steel.
Also one more thing worth noting: there is no cross strut tower reinforcement on the IS. This may not cause issue on “normal” trims such as the IS300, IS350; but as discussed in the IS500 bumper sagging article, it did caused problems on the IS500.
From steel material illustration we cannot tell how rigid or how good the structure can adsorb impact stress. We can quantitatively evaluate this by comparing the IIHS crash test data. I typically look at 3 indexes: moderate overlap frontal crash test, side impact test, roof strength test.
The reason why moderate overlap test is a good indicator is, it systematically involves the rigidity of both of the front rails and the whole passenger cabin (safety cage). Performing well in this test means the car body can effectively handle stress in the longitudinal direction well without deforming the safety cage too much. Usually this also means good selection of steel materials, and also state-of-the-art body joint technologies.
To investigate a car’s capability of handling load stress, cross-comparing the moderate overlap frontal test results is meaningful, due to the fact that a car’s load stress is proportional to its weight. Now let’s take a look at some IIHS data. In the following, the larger the number means the more the deformation is. So larger number is worse, smaller (or negative) is better.
First is the 2022 Lexus IS v.s 2002 Toyota Camry (moderate overlap frontal crash test – to view the data, in each of the testing section, use the left button of your mouse to click “Technical measurements for this test” and the data will be shown in the drop down list):
I know, for some Lexus owners, especially those who owns an IS500, will feel this to be absurd and think I am making false claims. Please look at the numbers – numbers don’t lie and they are from IIHS. The moderate overlap crash test standard are the same across the years as well. The 2002 Camry may perform worse in other crash test categories, but in terms of moderate overlap crash, it is definitely holding up better than the 2022 IS.
Next is the 2022 Lexus IS compared to the 2006 IS, still moderate overlap frontal test. We can see some numbers are better but some are worse; so not a substantial improvement in this area. But for side impact test (see “Side: original test” ), the 3rd generation IS is much better than the previous generation.
The last one is the 2022 Lexus IS v.s 2008 Mercedes C Class, moderate overlap test. See the huge difference? (for side impact, roof strength, the C class is also way better than the IS)
You can also check out the 2007 Toyota Camry data, you will see the Camry surpasses the latest IS in almost all aspects (frontal, side, roof strength).
For the current IS, there is an interesting common issue on the IS500, and I have written a dedicated article to discuss it, lots of structural info there.
Summary: compared to the previous generation, while the current 3rd-gen IS provides a better driving dynamics due to some enhancements/improvements in the car body, its structure design in fact is quite lousy, and way behind its competitors. Data won’t lie, not even be able to match (let alone beat) the 15 or 20-year old Camry’s crash rigidity results, is absolutely ridiculous and unacceptable from my point of view.
There is no regulations or laws in any countries in the world, that requires newer models need to perform better than the older models during crash tests. Toyota is a for-profit company, its job is to sell as many as possible vehicles, grab as much as possible profit from the market, within the legal boundary of each market. As long as people still keep buying, there is nothing wrong for the factory to save cost, or let newer product performs worse than the older model in some specific tests. This is exactly how a successful business works.
