Tyre pressures for Autobahn

Vatreni · March 6

Well my 300H has landed fresh off the boat, all good so far, but lots of options and config still needed.

Just something caught my eye in the manual that may not come up very often - tyre pressures

I do drive in the EU quite regularly, including the Autobahn. How would you interpret this table? Germany is a 50/50 mixture of driving around or above 160kph and around 100kph or less. 46psi sounds extraordinarily high.

Another associated query - I've seen a published top speed somewhere of 180kph. This seems low for the engine size, anyone know the real top speed (I will drive at 200kph for times on the Autobahn)?

ta

peniole · March 6

It's been a few years, drove ours on the autobahn. Does not crack 200kph. Can't remember exact top speed. It's electronically limited.

Jon Dee · March 7

Seems legit... here is the tyre pressure info for the 2008 ISF (FWIW) 😀

Cheers...

e-yes · March 7

9 hours ago, peniole said:

It's been a few years, drove ours on the autobahn. Does not crack 200kph. Can't remember exact top speed. It's electronically limited.

Limited to 112mph or about 180kph.

Vatreni · March 7

3 hours ago, e-yes said:

Limited to 112mph or about 180kph.

I read the user guide cover to cover and couldn't find that. That really isn't that fast for the Autobahn - is this a Lexus "safety" feature?

Mincey · March 7

It's for emissions isn't it?

NemesisUK · March 7

I thought it was because of the rpm limit on MG1

DBIZO · March 7

15 hours ago, Vatreni said:

Well my 300H has landed fresh off the boat, all good so far, but lots of options and config still needed.

Just something caught my eye in the manual that may not come up very often - tyre pressures

I do drive in the EU quite regularly, including the Autobahn. How would you interpret this table? Germany is a 50/50 mixture of driving around or above 160kph and around 100kph or less. 46psi sounds extraordinarily high.

Another associated query - I've seen a published top speed somewhere of 180kph. This seems low for the engine size, anyone know the real top speed (I will drive at 200kph for times on the Autobahn)?

ta

I'm surprised by the low-speed pressure, never seen such values for a road car. What I understand of the theory, is that at high speeds you can start with somewhat lower because of the heat-up in friction, but you want to maintain maximum contact for grip. Maybe these values are for the OEM tyre only that behaves differently? Also, at 46 psi the ride quality must be much harsher too. That's a long way of just tend to go for 36-38ish, particularly in winter, when heat is not an issue.

These cars are limited not by power but gearing and rotation of some components, specifically one of the electric motors is protected from too high 'g' loads, so your car will just take the throttle off once you hit the electronic limiter. Yes, the engine would keep pulling, but the car controls won't let. The 'faster' transaxle Toyota/Lexus has is bigger, heavier, more expensive, and no one really needs to go that fast in a cruising saloon. The G-platforms transaxle is probably not even in production anymore, I don't know. The ES300h or IS300h are not gran turismos.

I drive on the Autobahn myself too, maxed out at 125 mph sometimes, but only for fun, and to keep up with my brother-in-law in a 911. I find 100-110 mph on the speedo is plenty even if the traffic is light and allows it. Above that, the cabin noise gets much higher, and fuel economy drops off by quite a lot, and the engine audibly is not enjoying itself that much. It likes a 3.5-4.5k rpm pull, it sound pleasant, above that it's comes across a bit of a struggle for the relatively low torque and the cont. variable gearing not giving the 'lock-in' of gearing but sliding back first before increasing gearing again. Just my experience of an IS300h. I know the feeling of wanting to go faster, but there is a difference between want and need.

Vatreni · March 7

Interesting post - yes does sound more like it's the car protecting some of the components from rotating too quickly. Maybe it would setup a flux capacitor effect in the stator and I'd end up in 1988.

I certainly don't cruise at much more than 160kph but like to see how a car performs and feels at the top end. Will report back assuming the massive lengths of roadworks in DE last time I drove through allow a decent run...

Rabbers · March 7

Before setting out on long drives that include stretches of autobahn I add 0.2BAR to the recommended pressures. This follows the advice I got several decades ago from a trusted BMW mechanic, and it became a habit with every car I have had ever since. Supposedly one gets better high-speed fuel consumption (something to do with reduced surface attrition?), but if so, I must admit I have never been able to quantify it.

On the subject of autobahn speeds, it should be borne in mind that speedometers overstate actual speeds by a significant amount. In my present RC300h I have calculated the overstatement to be as much as 10-11% with an average of 9% in my normal everyday driving mix. The car’s electronic limitation is 190kmh, although on occasional drives on the autobahn I have seen the speedometer touch 215kmh on fairly gentle downhill stretches and maintain readings of 205-210kmh for long stretches on the flat.

NemesisUK · March 7

Higher tyre pressures are required for prolonged (>1hour) high speeds because of the degree of tyre deflection as it rotates and this causes heat and tyre instability.

If one measures the wheel/tyre radius on the loaded side (between the axle and the road) and the unloaded side (between the axle and the top of the tyre) there is a significant difference. As the tyre rotates it has to deform/deflect numerous times per mile. This deflection has to be controlled and this is done by increasing the internal pressure to help equalise these to measurements.

e-yes · March 7

10 hours ago, Vatreni said:

I read the user guide cover to cover and couldn't find that. That really isn't that fast for the Autobahn - is this a Lexus "safety" feature?

IIRC both 0-62mph and top speed are to conform to some emissions standards.

However, the ES hybrid has been known to have been under advertised. Some reviewers on YouTube have measured 0-60mph times of close to 7.5s

The boot space has been measured to be well over 500 litres.

No one I remember has claimed to have tested the top speed (I think Autogefuehl channel on YouTube tried an autobahn sprint)

Personally I know it goes from 70mph to a “certain” speed like no one expects this car to go. But being in U.K. I didn’t attempt to stick to that speed for too long… simply wanted to loose a Range Rover whose driver couldn’t relate to the fact that a car other than his was making rapid progress in the fast lane and decided to tail gate as that was the best thing he could react with.

Hopefully you may be able to report the correct top sustained speed which the ES can carry.

—E

Vatreni · March 7

1 minute ago, e-yes said:

IIRC both 0-62mph and top speed are to conform to some emissions standards.

However, the ES hybrid has been known to have been under advertised. Some reviewers on YouTube have measured 0-60mph times of close to 7.5s

The boot space has been measured to be well over 500 litres.

No one I remember has claimed to have tested the top speed (I think Autogefuehl channel on YouTube tried an autobahn sprint)

Personally I know it goes from 70mph to a “certain” speed like no one expects this car to go. But being in U.K. I didn’t attempt to stick to that speed for too long… simply wanted to loose a Range Rover whose driver couldn’t relate to the fact that a car other than his was making rapid progress in the fast lane and decided to tail gate as that was the best thing he could react with.

Hopefully you may be able to report the correct top sustained speed which the ES can carry.

—E

Interesting about the boot space, as I've just come from a somewhat churlish review on Honest John where it states the 454 litre boot is small compared to its rivals (boot looks massive to me especially compared to my previous AR Giulia). The review also specifies the 24 Premium edition ES comes with an 8" screen controlled with a touchpad. Not sure when it changed (2022?) but mine is the larger touchscreen, thankfully. So Honest John hasn't really reviewed a 2024 model.

Jon Dee · March 7

16 hours ago, e-yes said:

Limited to 112mph or about 180kph.

This is the most plausible explanation for the 180kph limit...

Japanese cars are not specifically limited to 112MPH/180KMH by law. However, many Japanese car manufacturers voluntarily limit the top speed of their vehicles to 112MPH/180KMH as a safety measure. This is done to comply with industry standards and to prioritize safety and fuel efficiency over higher top speeds. It's worth noting that speed limits and regulations vary by country, and vehicles sold in different regions may have different speed limitations.

J Henderson · March 8

Limiting the top speed to protect the MGU seems plausible, but Lexus doesn't appear to do this with "bigger" cars like the GS450h or LC500h. They'll do 155mph if required.

On a related subject, I caught the tail end of an old Top Gear episode the other day, where Clarkson was driving the then-new Nissan GT-R, in Japan.

That car was also limited to 180km/h like everything else, but interestingly, the limit was removed when the car knew (via it's navigation system) that it was on the Fuji Speedway racetrack.