Speedo Error

[greeneyes]

Most people don't know their speedo error, and generally it is about 10% fast (optimistic)on standard tyres!! So the Cop isn't being nice and knocking a few K off the speed you were doing, he is probably writing down the real speed!

You will need a stop watch, or a watch with seconds showing and a passenger. You will also need some of Transit NZ's marker posts, either the proper 5km speedo test beside the motorway or similar, or the white posts with a single green strip and a km number. I use the green striped posts when travelling down country.

You will have to drive very exactly at 100kph on your speedo for at least one km, but preferably more, with the time being taken. A kilometre at 100kph takes exactly 36seconds, and at 120kph it takes 30seconds. If it takes you 40seconds, you are averaging 90kph for that kilometre. Divide 3600 by any speed and the answer is the number of seconds to do one Km.

I replaced the 175/70x13" tyres on the front of my Sentra with 185/65x14" rims & tyres. this reduced the speedo error to almost zero, geared the car up, gave much better front wheel grip and reduced the understeer in cornering noticeably.

So, you are probably not going as fast as you think, and unfortunately your car is using more petrol than it it telling you!

keith

[frylai]

Most people don't know their speedo error, and generally it is about 10% fast (optimistic)on standard tyres!! So the Cop isn't being nice and knocking a few K off the speed you were doing, he is probably writing down the real speed!

You will need a stop watch, or a watch with seconds showing and a passenger. You will also need some of Transit NZ's marker posts, either the proper 5km speedo test beside the motorway or similar, or the white posts with a single green strip and a km number. I use the green striped posts when travelling down country.

You will have to drive very exactly at 100kph on your speedo for at least one km, but preferably more, with the time being taken. A kilometre at 100kph takes exactly 36seconds, and at 120kph it takes 30seconds. If it takes you 40seconds, you are averaging 90kph for that kilometre. Divide 3600 by any speed and the answer is the number of seconds to do one Km.

I replaced the 175/70x13" tyres on the front of my Sentra with 185/65x14" rims & tyres. this reduced the speedo error to almost zero, geared the car up, gave much better front wheel grip and reduced the understeer in cornering noticeably.

So, you are probably not going as fast as you think, and unfortunately your car is using more petrol than it it telling you!

keith

Hey Keith:

Yeah I found out that the petro reader is also not what it is, I don't know if its only happens on IS200 / 300 or also Altezza, Altezza have a 60 litre petro tank, and IS have 70 litre...so that because we got the same gauge, the meter think the tank only have 60L, but it really has 70L, so that when you fill up a whole tank, in the beggining, it loks like it uses hardly any petro, and when you get to the bottom 1/4 it goes down like a mother fu*ker...just to let you guys know..:D

Matt

[4ROLLN]

I think i have discovered this too. I have a Apexi RSM and noticed that it was reading a lesser speed than the speedo at different speeds, I found it to be unaccurate at speeds over 100 km/hr, I have tuned it to read more like the speedo which is therefore probably incorrect but figured I 'd rather be going slower than i thought, than faster than I thought. Does any one know the top speed when it cuts out. I have reached a top speed of 192 km/h way of the clock, but because of my tuning of the RSM it may in fact be over 200 km/hr which I suspected it was as it seems to go way off the clock and keep accerating........

Can these cars have their speedo's recaliborated, any one know about price etc?

cheers.

Hayden

[SSML]

Hi Guys:

I dont know how accurate the speedo is in our cars, but one thing I have noticed since I got my car is that the trip metre of my car (215/45/17) seems to clock more KMs than other cars!?

E.g . For the same distance( point A to Point B) My IS 200= 72.3KM, my 94 ES300=69.9KM (205/65/15) and my frined's 318= 70.3KM.

I also find that IS200 with 205/55/16 tyres shows less KMs on the trip metre than 215/45/17 IS200.

I asked service department to check when I had 10,000KM service done and computer reading was normal. and all within the limit.

I suspect it's got somethng to do with the overall diameter of the 215/45 17 tyres.(slightly smaller than 205/55/16)

I was thinking to get 225/45 17 tyres so that my trip metre will clock less. :P

What do ya guys think?

SSML

[4ROLLN]

I've got 17 inch wheels 215/45/17, may test out this theory and see if my lexus equals that of our other cars too. Will be interested in seeing the results!!!

[frylai]

I've got 17 inch wheels 215/45/17, may test out this theory and see if my lexus equals that of our other cars too. Will be interested in seeing the results!!!

LOL, like you new qoute hayden.....

Matt

[greeneyes]

Dead right SSML, changing the tyre size will change the km the speedo records. Replacing the 13" rims with 14" ones on my Sentra made the speedo accurate as well as giving me a better range of tyres.

I stuck with 215/45x17 on Greeneyes so I can swap front to rear for handling. I've seen 235/40s on the rear of Altezzas and 215/45s on the front.

Somewhere on a tyre webpage I saw a list of circumference for each tyre size. Problem with the web, I can never find the same page twice... :(

[frylai]

Dead right SSML, changing the tyre size will change the km the speedo records. Replacing the 13" rims with 14" ones on my Sentra made the speedo accurate as well as giving me a better range of tyres.

I stuck with 215/45x17 on Greeneyes so I can swap front to rear for handling. I've seen 235/40s on the rear of Altezzas and 215/45s on the front.

Somewhere on a tyre webpage I saw a list of circumference for each tyre size. Problem with the web, I can never find the same page twice... :(

Hey Keith:

Hows the nre tyres going? good? I send 25 cards down to Palmy North Yestreday, anyone In Hamilton Wellington or Christchurch PM me and I will give you 25, well maybe more for welly and CC, thanks...

Matt

[SSML]

I will get all 4 tyres replaced with 225/45/17 tyres when the stock tyres worn out.

I know 225/45/17 is still smaller loverall diametre than 225/40/18(very popular size for IS), but I have no intention of going up to 18" now.

one interesting fact I found is that the new Audi A4 has a wide range of tyre sizes with a big difference in overall diametres: 195/65/15; 205/55/16(same as standard IS200); 235/45/17 (big OD). Other cars like IS, Mazda 6, Accord Euro have 205/55/16 and 215/45/17, whereas BMW 3 series have 195/65/15; 205/55/16; 225/50/16 and 225/45/17. I am not sure whether the speedos have been calibrated for each of the specific tyre set up. Otherwise there will be a pretty large discrepency.

I m going to Brisbane Forrest Park for mountain Rd drive, I think there are 60+ KM of mt roads.

It's a fun road to drive. Also the speed limit is quite high too. at least 80km/h , even for some hairpin corners,(with advisory 20km/h sign). I have been there for a few times, but not recently.

That's also a very popular road for motorcycle riders.

SSML