Road Speed Per 1000 Rpm

[acetip]

if this question has come up before then ill say sorry in advance.

ive been for sometime trying to find out the road speed in each gear of my auris 1.6 vvti duel per 1000 rpm.

its a 2007 (reg 08). and has a 5 speed g/box.

anyway ive now found it on a road test on a simuler model on a website

first gear 4.6 mph per 1000 rpm

second gear 8.6 mph per 1000 rpm

third gear 12.5 mph per 1000 rpm

fourth gear 16.9 mph per 1000 rpm

fifth gear 20.0 mph per 1000 rpm.

in my car it should be showing 40 mph at 2000 rpm on the speedo, but its showing 42 mph and 63 at 3000 rpm in top

gear.

as in all cars the speedo is optomistic so when trying to check fuel consuptiom .

and we are not going to get it accurate.

evan if the speedo was spot on and we new the exact amount of fuel we put in how do we allow for the distance

a tyre covers per revolution, when that changes with tyre wear.

electronic read outs vary from car to car ,

the two mondeos i had varied the ghia read 8 mph over what i made to use and the ST showed 0.1 less than i worked it out.

anyway i hope these figures may be of interest to someone.

[MarqsM]

The whole idea of a car's speedometer is interesting because AFAIK all speedos do show LOWER speed than the actual one. Of course I mean the original specs cars, without any wheels changes etc. Isn't that all car producers are obliged to do it that way? So when the speed limit is 40 and you're doing 40kph, you are really driving at 36kph?

[acetip]

The whole idea of a car's speedometer is interesting because AFAIK all speedos do show LOWER speed than the actual one. Of course I mean the original specs cars, without any wheels changes etc. Isn't that all car producers are obliged to do it that way? So when the speed limit is 40 and you're doing 40kph, you are really driving at 36kph?

hi MarqsM

yes you are correct, but a few hundred yards from my home is one of those flashing signs that comes up when you

exeed the 30 mph limet, its just around a bend so catches a lot of drivers out, including a police car i saw once trigger it. the wife swears that it once started flashing when she was pushing one of grandchilds pushchair,

there was no car in sight or anybody else arond.

if you approach it at the slightest bit above the and i mean just a little bit just above exactly on the 30 mark

its triggered.

i have had three different cars since i maved here and its the same with all of them.

as you say most speedos are optomistic but with that speed warning sign if its accurate (as they should be)

so it seems the speedos are accurate at 30 mph.

we have not got 40 or 50 flashing warning signs near me to test a those speeds.

so if anyone has got one of those maybe they could check it out and post their results.

cheers for the reply.

[Aurissimo]

OEM have to ensure the speedos do not under-read (show a lower value than ACTUAL speed) and are allowed to over-read ( show larger value than ACTUAL speed)

This is allowed to cover for may errors for different tyres and the fact that tyres are not accurate in diameter (Search "ETRTO" for more information) , so to account for this error and other effects this error margin is allowed. If I remember correectly ... it is 10%+10mph. Normally they try and get 30 spot on , but then as you increase speed, the 10% allows for a greater error margin, which manufacturers can use for 2 purposes.

1. Help Drivers not get caught out by speeding. (If it indicates 75 mph but actually doing 68 mph ) you will not get "flashed" by the police...

2. Help themselves in terms of showing better fuel consumption figures (If you think you are running at 70 but actually running at 65mph, your fuel consumption figures will be better...than actually running at 70mph), so manufacturers can adjust gear rations to "suit" this allowed error margin...

My experience the Toyota Speedo is pretty accurate compared to my previous cars... and i think as GPD units become more and more popular, the manufacturers will have less and less chance of using the allowed error margins as Customers will expect "GPS" accuracy.

If you fancy doing a better study of your vehicle performance I suggest you use this free software package.

Though you'll need to find out the gear ratios for your car and work out some of the other variables...(see owners manual+ metric tape might come in handy... )

http://www.vehicle-analyser.com/features.html

[Badgers]

If you've GPS, the speed shown in that is pretty accurate if you are travelling at a constant speed. On the T180 I find 75mph indicated = 70mph on GPS.

[MarqsM]

Thanks aurissimo for your thourough post.

In my auris the deviation between the car's speedo and the GPS is approx. 8-10 kph (speedo always showing more).

[Fivish]

All speedos have a 3 mph offset. They read 3 mph high. 70 on speedo = 67 in reality etc. 

[FROSTYBALLS]

Speedometer over-read isn't set at 3mph. Speedometers are set to over-read as it is illegal to show a speed less than the true soeed.

The original topic is almost 9 years old.

[eygo]

to get a speeding ticket you have to be doing more than 10% of the speed limit + 2mph

so in a 30mph you would be ok up to 35mph.

once i knocked on the door of a speed detector van parked across the road from me and asked

him if it where 10% + 2mph he said he couldn't tell me but told me he will set the camera at 35mph.

 

[furtula]

That's nice, in Europe they generally allow +2kmh more over the speed limit, but i know of a lot of speed cameras that are set to 60 or 70 kmh instead of 50kmh.

There was a recent case near where i live, with a camera set on entrance to a smaller city. It was set to 70kkmh by the locals, after 2 years police came and moved it to 50kmh.

In a day it generated like 400 tickets, so the mayor complained to the police to put it back, as it's too much work for them to send out so many tickets.