An interesting read on suspension, vehicle weight, ride quality, and handling.

ssun30

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This article does a decent job of summarizing how suspension design and vehicle weight affect ride quality and handling characteristics. While not an academic paper or a textbook, it does correctly explain those details that are otherwise 500 pages long.

https://www.rqriley.com/suspensn.htm

Here is an interesting perspective from this article: that weight reduction has significant implications on the ride quality and handling of a vehicle. Now, one of the common complaints about new Lexus vehicles (and TNGA vehicles in general) is their excessive weight compared to the size. What's more, Toyota/Lexus engineers intentionally design their new vehicles to be heavy: they are not incompetent at weight reduction, the Prius Prime (and to some extent the Camry Hybrid) is the best example.

From the article, vehicle weight affects ride quality and handling in following ways:

>>A heavier vehicle has a lower payload-to-vehicle weight ratio. This means the addition of extra occupants has lower impact on the ride frequency and damping coefficient. A lighter car, on the other hand, has a narrower "sweet spot"; more occupants will cause the ride to be too soft while too few will make it too hard.

>>A lighter car is more vulnerable to longitudinal disturbances, which humans are most sensitive too. As a result acceleration and deceleration can cause a 'jerkier' ride. This is exacerbated when there's luggage in the trunk causing the vehicle to pitch up.

>>Going back to payload-to-vehicle mass ratio. Payload will cause a vehicle to sit lower because it compresses the springs; this will cause the center of gravity to shift downwards. A heavier vehicle lowers less than a lighter one. Therefore the heavier vehicle can be engineered to have a lower center of gravity. This is exactly what TNGA aims for.

The Toyota 86, a super light sports car, has a very low center of gravity. But this is at the cost of having very stiff suspension. The natural ride frequency of the 86 is over 2 Hz (like a race car), and prolonged driving will cause pain and even injuries. The similarly light Miata opted for softer suspensions (causing a significant roll) to make the car more practical to drive.

>>As modern cars keep getting bigger tyres and wheels, more powerful brakes, and fancier suspension items, unsprung weight also keeps growing. A lower sprung-to-unsprung weight ratio makes the ride harsher when there are bumps and potholes. Adding weight to the body (more sprung weight) keeps the tires more firmly attached to the road since the springs have more compressive force. In this case the car not only has a smoother ride, but also has more grip.

Lighter cars will always perform better on well-paved tracks, but on actual roads (especially pothole-ridden roads in USA) they may have worse mechanical grip and arguably harsher ride.

I think this is a well-thought argument for Lexus/Toyota's intentional engineering choice when it comes to vehicle weight, not to mention the body rigidity and safety bonuses. Do I think it's the right way to go? Not necessarily, because as electrification kicks in, weight reduction will again be very important since batteries and hydrogen tanks are heavy. But it's a good argument regardless, backed by real world experiences.

I think forum member @spwolf mentioned multiple times that the C-HR, a 1,500 kg subcompact SUV (which is 100-150 kg overweight compared to competion), has the best in-class ride quality and handling and by a wide margin. Recent Lexus sports vehicles also behave very well on tracks and roads alike, despite their weight disadvantage. A more extreme example would be the R35 GT-R, which made competitors wonder for a decade how such a heavy beast just kept beating their stripped-out feather-weight track machines.
 
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spwolf

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@ssun30 - also important is where the weight is spent, and how it is positioned... TMC engineers have been telling us that TNGA will let them lower the center of gravity and we can see that it works... and they use complicated suspension setups that are heavier but also bring better handling, feedback and comfort. This can be easily seen when comparing C-HR to competition for instance. Interesting is that next gen Auris will only have multi-link suspension, vs Europeans recently often doing torsion beam that is lighter (less co2) but also worse for handling and comfort. Will the tables turn next (Japanese better handlers than competition)?

Another example is Jaguar - XE was expected to be the lightest in the class due to the use of aluminium but it did not happen - it was heavier than 3 series... Why? Because of complicated competition setup and indeed it handles really well.
 

mmcartalk

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A generally good article. The only thing I noticed that they forgot is to mention that lower-profile tires, all else equal, not only improve handling but worsen ride quality as well. They mention the effect of wider tires on ride/handling, but not from the lower-profiles.
 
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ssun30

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A generally good article. The only thing I noticed that they forgot is to mention that lower-profile tires, all else equal, not only improve handling but worsen ride quality as well. They mention the effect of wider tires on ride.handling, but not from the lower-profiles.
The article is based on pretty old-school information from textbooks before modern low-profile tires became so wide-spread. But yeah, low-profile tires are full of BS but consumers made their own choice.
 

Levi

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The article is based on pretty old-school information from textbooks before modern low-profile tires became so wide-spread. But yeah, low-profile tires are full of BS but consumers made their own choice.
High profile rim design are usually less good looking also, but aftermarket has solutions. However the main problem with low profile tires, from a design stand point, is that now cars are design around them, so fitting high profile tires does not look good at all. Inversely, cars that are designed with high profile tires, also look good with low profile tires. Best example: BMW 5 Series E39. Another example: Lexus LX with low (bling bling) and high (off-road) profile tires: both look very good. But have you seen how ridiculous German SUVs (bar the G Wagon) look with off-road tires?
 
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