155mph speed limiter question

Pondrew · Post by **Pondrew** » Tue May 25, 2021 9:08 pm

Mr Tidy wrote: ↑Tue May 25, 2021 8:24 pm Apologies to Pondrew, but at least pubs are now open again!

Yes Mr T. I know. Doesn't mean I want to go in one anytime soon.

Maybe bragging rights with a loud hailer outside is the order of the day?

Mr Tidy · Post by **Mr Tidy** » Tue May 25, 2021 9:16 pm

Pondrew wrote: ↑Tue May 25, 2021 9:08 pm Yes Mr T. I know. Doesn't mean I want to go in one anytime soon.
Maybe bragging rights with a loud hailer outside is the order of the day?

Just go with a smoker - they'd be quite happy outside!

Nictrix · Post by **Nictrix** » Tue May 25, 2021 9:20 pm

A lot of bikes with digital speedos stop at 186mph even though it will still pull past this.
Im sure 186mph is 299kph

Colin_E · Post by **Colin_E** » Tue May 25, 2021 9:53 pm

Nah, keep the limiter & invent your own hypothetical top speed. Who's gonna prove you wrong down the pub anyway? My remapped N20 is good for n+5mph (where n is the professed top speed of my mates car

)

Pbondar · Post by **Pbondar** » Tue May 25, 2021 10:22 pm

The limiters function on road speed as perceived by the DSC unit..

On most cars max speed is hit in one or two lower gears than top which is a fuel efficient overdrive..

On a 20i auto top speed in 6th is 160mph..in 7th it’s 191mph

So deristricted and re-mapped top speed will be fall between the two gears…probably..

Mr Tidy · Post by **Mr Tidy** » Tue May 25, 2021 11:17 pm

Nictrix wrote: ↑Tue May 25, 2021 9:20 pm A lot of bikes with digital speedos stop at 186mph even though it will still pull past this.
Im sure 186mph is 299kph

Many years ago I bought a Yamaha XJ550 that was an import from the US - the speedo stopped at 80 mph!

But shortly afterwards I managed to buy a UK model with a knackered engine so got a speedo with 3 figure numbers on it, and might have needed them (on a private road obviously).

My MC seems to be geared for at least 170mph in 5th - maybe one day I'll find out!

Pondrew · Post by **Pondrew** » Tue May 25, 2021 11:42 pm

Mr Tidy wrote: ↑Tue May 25, 2021 11:17 pm My MC seems to be geared for at least 170mph in 5th - maybe one day I'll find out!

There are very complicated physics that come into play. Aerodynamics become the predominant player over about 130mph IIRC. Over a certain speed the drag is exponentially superior to the power. Not that any of this matters, as I am far too old to travel above 60mph anyway

Pondrew · Post by **Pondrew** » Tue May 25, 2021 11:44 pm

Colin_E wrote: ↑Tue May 25, 2021 9:53 pm Nah, keep the limiter & invent your own hypothetical top speed. Who's gonna prove you wrong down the pub anyway? My remapped N20 is good for n+5mph (where n is the professed top speed of my mates car

Yeah like the thinking. Out of interest; why n? Why not X?

As a sideline; I have a (V8 AA) Ford which is limited to 155mph aswell. I thought it was just zee Germans; the septics are at it too.

buzyg · Post by **buzyg** » Wed May 26, 2021 1:41 am

Mr Tidy wrote: ↑Tue May 25, 2021 11:17 pm
Nictrix wrote: ↑Tue May 25, 2021 9:20 pm A lot of bikes with digital speedos stop at 186mph even though it will still pull past this.
Im sure 186mph is 299kph
Many years ago I bought a Yamaha XJ550 that was an import from the US - the speedo stopped at 80 mph!

But shortly afterwards I managed to buy a UK model with a knackered engine so got a speedo with 3 figure numbers on it, and might have needed them (on a private road obviously).

My MC seems to be geared for at least 170mph in 5th - maybe one day I'll find out!

Indeed the ///MR will do approx 171 mph and there is no limiter on 5th, that I know of. Not bad for a aging hair salon. Been talked to death over the years on here.

ph001 · Post by **ph001** » Wed May 26, 2021 9:13 am

Pondrew wrote: ↑Tue May 25, 2021 11:42 pm There are very complicated physics that come into play. Aerodynamics become the predominant player over about 130mph IIRC. Over a certain speed the drag is exponentially superior to the power.

Aerodynamic drag is the dominant factor at much lower speeds then 130mph. In simple terms, drag is proportional to the square of the speed (Drag ∝ v2). So basically if you want to go twice as fast you have to work four times harder. e.g. if it takes 10bhp to go 30mph, it takes 40bhp to go 60mph and 160bhp to get to 120mph. This does ignore the drag coefficient of the tyres and the running gear.

buzyg · Post by **buzyg** » Wed May 26, 2021 1:57 pm

A good thread here..

viewtopic.php?f=2&t=6572&hilit=top+speed

Looking forward to reading the first proper report on what top speed a modified M40i has. Surely faster than the older models, but not seen any facts to support that assumption yet. Could also be that it is not stable enough to go much faster. As is certainly the case in the ///MR, where the front end starts to go light above 160mph.

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