Hacker News Reader

Comment by SketchySeaBeast | Hacker News Reader

Is there any particular reasoning as to that value? If we assume major highway limits of 70 mph and add an excessive 20-30 mph for passing, that's still a ton of extra lethal kinetic energy.

edit: Apparently even the Autobahn has a recommended speed of 80 mph (I'm aware you can go faster, but then why have a limit at all?)

View on HN

As I mentioned in another comment, tires with an "S" speed rating go to 112 MPH, while tires with an "H" rating go to 130 MPH. I'm guessing they either downgraded the factory tires or were concerned about lawsuits from owners who installed aftermarket "S" rated tires.

Yeah, I had the same guess. I'll bet their current higher performance models come with fancy Pirellis or something equivalent, and this is a way to reduce cost.

Lower speed rating also usually means lighter construction and a 'harder' compound, both of which reduce cost and improve fuel milage.

Actually it's the opposite I believe, at least for the same family of tires.

Sure there are high efficiency tires with harder compounds and are more efficient.

But if you get the sporty tire from whatever brand the higher speed ratings generally have the less flexible/harder material. The limiting factor being the heat generated from the flexing builds up. So generally a 150 mph rated tire gets less traction, costs more, and is worse when it's cold than a 112 mph rated tire.

So even on a fairly sporty car and tire you are best off getting the lowest rated tire that will accommodate your max speed.

Conceptually that may be true, but it's next to impossible to get performance tires in speed ratings under W and within any particular model it often varies only by 1, rarely 2, speed ratings.

I've got an old Porsche 996 S4, and I can't say it is a fast car. (fun around the corners, but not fast). I had V rated tires which were rated for 150mph. Not silly expensive either for that matter. I've never driven fast enough to need those tires (or even H rated for that matter) but it would irritate me to no end to know the limiter was there.

It's roughly 180 km/h. Your assumption of a 70mph speed limit is based on the US, and it's incorrect. Portions of highways in the US have 85mph speed limits (i70 on the eastern part of Utah comes to mind).

Even then, the difference between 85 and 112 is a rather large one.

Also, while the speed limit on I-40 through Arkansas is nominally 70 or 75, it's not at all uncommon for traffic to be moving at 85-90 MPH.

In Texas 85 is a thing. At that speed, you really don’t see much speeding. Maybe up to 90. And an occasional need to burst up to 100. Many people start feeling uncomfortable at these speeds even in open road conditions.

I think part of it is they also don’t want people to hit the limit often. It’s for egregious drivers. Driving at that speed and suddenly decelerating to a stop is not the safest thing either.

I've done 120 or 130 on the stretch between Wendover and Salt Lake City. Most people go about 90

Heh, yeah, that area is perfect for high speed driving. Mostly perfectly straight, good quality roads, and excellent visibility. There's an annual race in Nevada not too far from there (highway 318) that's the world's fastest road race. Last year someone average 219mph and was doing 4 wheel drifts at over 200 mph on the sharpest (almost straight at normal speeds).

Not bad for a normal highway.

If we took the top end of your excessive figure (i.e. 100mph), the difference in kinetic energy between 112 and 100 is equivalent to the difference in kinetic energy between 0 and 50. Lethal kinetic energy indeed.

I mean, I get by with an EV limited to 88mph (not sure if that's a in-joke or what). It gets to 88 really fast, but can't go faster. Probably saves me a ton of battery and I still cruise or lead on the left lane.

112 is 25% faster, way more lethal. I'm guessing it's 112mi*1.6km/mi = 180kph.

> an EV limited to 88mph

Which one?

Ford Focus EV. Got a massive deal on it back in 2017. Pretty happy with it.

One of the new Deloreans.

With the 1.21 gigawatts packs.

I suspect they decided that 180 kph is the sweet spot of "still significantly more survivable than higher speeds" and "won't prompt much consumer outrage". Though I'm sure there will still be no lack of people raging about Volvo impeding their freedom.

Why would there be consumer outrage? If you're planning to speed past 180kph don't buy a Volvo.

I doubt the Venn diagram of both groups shows much overlap anyway.

As a german:

- A speed limit of 140km/h would be fine for me, although sometimes disappointing when the road is really empty and there's a lot of distance to cover.

- A speed limit of 160km/h would be totally fine for me. Around that +-10km/h is somewhere around the limit that I find comfortable on the Autobahn.

- A limit of 180km/h probably also satisfies most of the other customers, and might be the sweet spot between still being very fast and not losing a lot of customers that would want to go even faster.

There are markets for cars that have higher speed limits. Or none at all

So why THAT limit?

Tires. Manufacturers rate their tires for certain speeds.

https://www.bfgoodrichtires.com/tires-101/tire-basics/about-...

Many cars use S-rated tires and that's the 112mph limit. It's all about liability.

Sports cars usually use higher speed ratings, whereas a truck or van might be limited ~ 100mph. They typicaly have off-road or tires with higher towing capabilities which have lower speed ratings.

It's reasonable enough to make any higher limit unreasonable, while still being high enough for fast drivers. German cars are usually limited to 250 km/h. With this new, still high limit from Volvo, the German manufacturers now have to justify why their own limit is so high.

"Because the customers want that, and won't buy a car that is limited that low, possibly out of principle."

And good luck getting politicians to push them to do otherwise.

Reply on news.ycombinator.com