Lexus Is250 Speedometer Innacuracy

[Stephen Foenander]

I just returned from interstate after driving my is250 over 1200 kms and worked out from using my navman that my speedometer is out by 10km per hour. At 60km/h the car is doing 50 at 110 km/h it is doing 100 km/h etc. Took it in to the Lexus dealer and they said there is nothing they can do. I am of the opinion that for such a great car with excellent build quality this is just not good enough. Does anybody know if there is a fix for this problem that has been documented by others before me. I shouldn't have to drive at 70 to be doing a real 60. This is also adding extra mileage to my vehicle over long periods. The dealer said they could check the car to determine how innacurate the speedo is but not fix it. UNACCEPTABLE.....

[kogarah]

I just returned from interstate after driving my is250 over 1200 kms and worked out from using my navman that my speedometer is out by 10km per hour. At 60km/h the car is doing 50 at 110 km/h it is doing 100 km/h etc. Took it in to the Lexus dealer and they said there is nothing they can do. I am of the opinion that for such a great car with excellent build quality this is just not good enough. Does anybody know if there is a fix for this problem that has been documented by others before me. I shouldn't have to drive at 70 to be doing a real 60. This is also adding extra mileage to my vehicle over long periods. The dealer said they could check the car to determine how innacurate the speedo is but not fix it. UNACCEPTABLE.....

Hi, mate I think you are with 16' wheel, right? It's just normal if so.

for the OEM wheels speedometer will be 100% correct if you are on the 18'.

[illusivedreams]

It would generally be my assumption that the car is calliberated for the rims it runs. On the jeep we just sold when changing wheel size you simply pop j to the dealer who caliberated the gear box. One I changed the shift points two it shift the speedo. That would explain why mine feels like the gears are so short.

[Bluey]

for the OEM wheels speedometer will be 100% correct if you are on the 18'.

So does that mean my 17" rims will be 5km/h out, since 16's are 10 and 18's are OK. That doesn't sound right.

I always thought the rolling circumference was the same for all rims they offer, they just use lower profile tyres for the larger rims, and conversley higher profile for smaller rims.

From this website http://www.trafficlaw.com.au/speedos.html

The current Rules disallow under-reading, and permit over-reading by up to 4kmh + 10%. So at 60 on the dial it could be travelling at (60-4-5.6(10%)) 50.4km/h and still be legal. at 100 it gets worse, you might actually be travelling at (100-4-9.6)= 86.4km/h and still be legal.

Go figure

[Rap03]

I have standard Lexus 18" wheels on my sports and have found that the speedo reads about 5% over.

I know this and aware, so not an issue. I can go faster, by the speedo.

My only issue, that this means it will read 105,000Kms when I have really only done 100,000Kms.

10% sounds a lot.

As Bluey said, the speed will be a factor of a combination of the size of the wheel and the profile of the tyre. All this gives you is the circumference of the tyre.

If you tyres are not inflated enough or worn, then the circumference will be less, but 10% is a lot.

[illusivedreams]

10% is too much,

My ford is 1 km out at 100 my jeep was spot on.

And like every one sad the circumfrence is important.

Although

16" rims have 55 profile tyre what do 18" rims have . They have a radius of 1" more than 16" that means the profile would need to be give or take 25mm smaller . That is 30 profile and Im sure they are not 225/30-18 245/30-18.

So there has to be a caliberation diffence to counter weigh the size of rim..as the profile in Lexus's case is not enough to keep circumfrence the same.

[Rap03]

The 18" are a 40 profile.

[DANSLEX]

I have exactly the same problem on my 16s. Might speak to my dealer about it next time and see what they say. Dealers tend to differ in their responses I've noticed.

[Poisson]

Same thing on my RX. (Running standard 18s). I read somewhere that this is a deliberate policy by Lexus to keep us safe.

No doubt implemented by the same genius who gave us "I agree" and disabled most of the nav and audio controls when the car's moving.

[FrankyX]

This is a normal thing on all cars. Each car should be calibrated for it's particular size wheels, but the speedo will always show a few km's over.

How did you work out that your car was doing 10km's over on your trip?

[Stephen Foenander]

This is a normal thing on all cars. Each car should be calibrated for it's particular size wheels, but the speedo will always show a few km's over.

How did you work out that your car was doing 10km's over on your trip?

I used a GPS which consistently reads 10kmh less than the speedo. I did this because numerous cars were overtaking me.

[Stephen Foenander]

I just returned from interstate after driving my is250 over 1200 kms and worked out from using my navman that my speedometer is out by 10km per hour. At 60km/h the car is doing 50 at 110 km/h it is doing 100 km/h etc. Took it in to the Lexus dealer and they said there is nothing they can do. I am of the opinion that for such a great car with excellent build quality this is just not good enough. Does anybody know if there is a fix for this problem that has been documented by others before me. I shouldn't have to drive at 70 to be doing a real 60. This is also adding extra mileage to my vehicle over long periods. The dealer said they could check the car to determine how innacurate the speedo is but not fix it. UNACCEPTABLE.....

I had an interesting call from Lexus Sydney management on Friday stating that Customer care were going to look into my complaint regarding the speedo also that the brakes squeal everytime I reverse the car. They will phone me on Monday or Tuesday with some resolution. I will update this forum on their reply.

[Sapphire Cam]

Stephen - I also drive a 2006 model - and had a similiar issue. It's amazing the difference in service from dealer to dealer. I mentioned this to my service manager, and right away he ordered a new speedometer cluster! Two weeks later it was installed in just 20 minutes and voila - the new speedo was right on! According to the service technician, the issue is apparently related to a little bit of friction in the plastic cog wheels behind the dials, that is resulting in the lower speed being displayed.

The issue related to the squeak on the brakes when in reverse I also have - its a sliding caliper pin. It's not a safety or performance issue, just an quality (read 'annoyance') issue. This will be rectified by your dealer - don't worry about that.

Don't want to "dob them in", but my dealer is Melb City Lexus - and their service has been 'second to none'. Pity your dealer isn't the same.

[DANSLEX]

Strange, I had my speedometer cluster replaced due to the weird noise it was making, with a new one, yet there's still a difference in speed readout...

[last1]

18s on mine, speedo seems dead accurate. Tested using sat nav.

BTW My 18s are 225/40 and 255/40. The fronts (225) have a lower profile than the rears. The "40" (or whatever other number your tyre is) is relative to the tyre width, not the rim size.

[OzBoy]

I too can recommend Lexus City Melbourne for their service area. Took my car there (bought from another dealer in Melb, but had issue's with their service area) and they are brilliant.

[Rap03]

18s on mine, speedo seems dead accurate. Tested using sat nav.

BTW My 18s are 225/40 and 255/40. The fronts (225) have a lower profile than the rears. The "40" (or whatever other number your tyre is) is relative to the tyre width, not the rim size.

I don't think so! The "40" is the profile of your tyre. The wide is the "225/255".

[Bluey]

18s on mine, speedo seems dead accurate. Tested using sat nav.

BTW My 18s are 225/40 and 255/40. The fronts (225) have a lower profile than the rears. The "40" (or whatever other number your tyre is) is relative to the tyre width, not the rim size.

I don't think so! The "40" is the profile of your tyre. The wide is the "225/255".

Both right.

The 40 relates to the height of the sidewall, but is relative to the width of the tyre and is called the aspect ratio or profile. the 40 is a percentage of the tyre width. so the wider the tread the higher the sidewall for the same aspect ratio.

Thats why the sidewall on your front 225/40 is lower than the sidewall on your 255/40 rears. 225 will have 90mm sidewall and 255 will have 102mm sidewall.

[Atlantis]

Tested out my new '09 IS250 tonight... GPS was reading 105km/h while my speedo was reading 110km/h, so I get around 5% difference on the "safe" side. I'm running factory 17" wheels and tyres. Just adding some info to the thread.

[LEX51S]

guys

i picked up my 05 is250 last saturday, traded in an is200 and ever since ive noticed alot of impatient ppll up my arse and hearing about this innacuracy is starting to make me think my speedo is out.

i have 16in prestige rims. im gonna have to check this out. but to all those ppl using gps to test your speed. how do you know that the gps is not innacurate. the car is measuring the speed next to itself. the gps is reading the speed millions of kms away.???

[Atlantis]

GPS units are generally accurate to around 10m. So at 100km/h, this is around 1% error rate. People are experiencing up to 10% error with factory speedometers in this thread.

You could always test with multiple GPS units in the same vehicle and get an average, although I think all GPS units would be reading the same speed give or take 1km/h.

[DANSLEX]

Also, most portable GPS units have an accuracy gauge, which shows how accurate the GPS signal is (there could be trees, or other obstructions causing the signal to be less accurate. Just get out onto an open road with minimal obstructions, and make sure the accruacy gauge shows max accuracy or something, and that will be your speed.

Oh, and also, set your cruse control on an even speed, say 60, 70 or 100 or whatever, and travel like that for a few seconds so your GPS catches up. Once you're cruisng at a steady speed, only then take a look at the GPS. I know I'm stating the obvious, but I've come across some people who sped up to a speed, glanced at the GPS straight away and conclude it's not accruate. The GPS receives a signal once every a second or someting, and it calculates speed based on time traveled between the first readng and the next one.

Chances are, you have the same problem as we do :)

[LEX51S]

i took my car out this afternoon after work and had a 10 % error gps says im doing 10% less. (speedo 50 gps 45. speedo 100 gps 90) etc etc.

my car is just under 4 years old. should they be able to sell the car with this error and its out of factory warranty. what are my chances of getting it fixed.

persuit of perfection not so perfect!!!!

being a perfectionist this really really annoys me.

Has ANYONE had succes with lexus?

[IronFist]

Also, most portable GPS units have an accuracy gauge, which shows how accurate the GPS signal is (there could be trees, or other obstructions causing the signal to be less accurate. Just get out onto an open road with minimal obstructions, and make sure the accruacy gauge shows max accuracy or something, and that will be your speed.

Oh, and also, set your cruse control on an even speed, say 60, 70 or 100 or whatever, and travel like that for a few seconds so your GPS catches up. Once you're cruisng at a steady speed, only then take a look at the GPS. I know I'm stating the obvious, but I've come across some people who sped up to a speed, glanced at the GPS straight away and conclude it's not accruate. The GPS receives a signal once every a second or someting, and it calculates speed based on time traveled between the first readng and the next one.

Chances are, you have the same problem as we do :)

Which of the portable GPS has this "accuracy gauge"? I've got one of the latest TomTom units and I didn't see any gauge of this type?

[DANSLEX]

Also, most portable GPS units have an accuracy gauge, which shows how accurate the GPS signal is (there could be trees, or other obstructions causing the signal to be less accurate. Just get out onto an open road with minimal obstructions, and make sure the accruacy gauge shows max accuracy or something, and that will be your speed.

Oh, and also, set your cruse control on an even speed, say 60, 70 or 100 or whatever, and travel like that for a few seconds so your GPS catches up. Once you're cruisng at a steady speed, only then take a look at the GPS. I know I'm stating the obvious, but I've come across some people who sped up to a speed, glanced at the GPS straight away and conclude it's not accruate. The GPS receives a signal once every a second or someting, and it calculates speed based on time traveled between the first readng and the next one.

Chances are, you have the same problem as we do :)

Which of the portable GPS has this "accuracy gauge"? I've got one of the latest TomTom units and I didn't see any gauge of this type?

I've never used tomtom so I don't know where to click it. But in the ones I have used in the past, there was always an indicator when you entered the GPS status window. It ranged from 1.0 (best) to higher, the higher the number the worse accuracy. I used Mio, and when you tap on the little satellite window and it shows the latitute longitute,speed, individual satellite signal strength and so on, it had the accuracy window there as well. If you can't find the accuracy gauge thingy, just make sure the area you're driving in is completely clear. :)