Speedometer accuracy and adjustment
#16
Thanks lobux for the info. I don't think VDIM will care too much about the reduction in tire diameter, since the rear diameter will be the same as the fronts, and I'm pretty sure lots of other people have done that. I will probably wait to see how much of a change the tires make on the speedo before actually trying anything.
FWIW, there are 5 distinct speed signals on the CAN bus.
FWIW, there are 5 distinct speed signals on the CAN bus.
#18
But when i made a trip, the odometer was correct, it was just the speedometor. It is known that Audi and many other car companies do this for safety purposes.
#19
But when i made a trip, the odometer was correct, it was just the speedometor. It is known that Audi and many other car companies do this for safety purposes.
#20
I would agree. We had this whole big discussion over at the Audi forum. My old 2003 A4 was totally off. I think it ended up 10-15km's over, which amounts to about 6-10mph at high speeds.
But when i made a trip, the odometer was correct, it was just the speedometor. It is known that Audi and many other car companies do this for safety purposes.
But when i made a trip, the odometer was correct, it was just the speedometor. It is known that Audi and many other car companies do this for safety purposes.
#22
I would agree. We had this whole big discussion over at the Audi forum. My old 2003 A4 was totally off. I think it ended up 10-15km's over, which amounts to about 6-10mph at high speeds.
But when i made a trip, the odometer was correct, it was just the speedometor. It is known that Audi and many other car companies do this for safety purposes.
But when i made a trip, the odometer was correct, it was just the speedometor. It is known that Audi and many other car companies do this for safety purposes.
I believe GPS readings would be the most accurate, thought lobuxracer's method is also accurate because he's doing over a long period and taking an average.
I know there's a yellow box like device for the S2000 (Gernby, you probably know what I'm talking about), but I haven't seen something like that for too many cars.
#23
From hanging out on the VW forums, Audi/VW are about 8% too fast on the readings.
I believe GPS readings would be the most accurate, thought lobuxracer's method is also accurate because he's doing over a long period and taking an average.
I know there's a yellow box like device for the S2000 (Gernby, you probably know what I'm talking about), but I haven't seen something like that for too many cars.
I believe GPS readings would be the most accurate, thought lobuxracer's method is also accurate because he's doing over a long period and taking an average.
I know there's a yellow box like device for the S2000 (Gernby, you probably know what I'm talking about), but I haven't seen something like that for too many cars.
#24
yes your right. It was the first time i had experience a "wrong reading" of my speedometer but i had to make sure that it was just reading that way for a purpose. So as i measured the odemeter and it was correct, i came to the conclusion that the speedometer was wrong on purpose.
#26
Super Moderator
I checked my '00 Audi S4 against the measured mile markers on the Garden State Parkway, and it was pretty close to spot on. The speedo was a little high, but nowhere near 8%, nor even the 5% I'm seeing on my IS.
#27
Tech Info Resource
iTrader: (2)
US law requires the speedo to be within 5%. Anybody remember the 85 mph speedos from the late 70's and early 80's? Those were mandated to be 1% accurate. The loosened the standard when they allowed them to indicate more than 85 mph.
#28
I had my new rear tires installed today. For reference, the OEM rear tire is 26.1" tall, and my new 255/35-18s are 25.1" tall. The OEM fronts, which I'm currently using, are 25.1" tall also. I never liked how much difference there was in the sidewall height between the front and rears, and I like the 3.8% lower gearing (numerically higher gearing). That's about like 10 extra HP to the ground.
So far, I haven't had any issues with VDIM or rubbing. I was more worried about rubbing due to my rear offsets. They also look a LOT better than the OEM "balloon" tires since my fender gaps are now equal.
I'll see if I can borrow another GPS unit to check the effect it had on my speedo.
So far, I haven't had any issues with VDIM or rubbing. I was more worried about rubbing due to my rear offsets. They also look a LOT better than the OEM "balloon" tires since my fender gaps are now equal.
I'll see if I can borrow another GPS unit to check the effect it had on my speedo.
#29
So now you have a smaller ratio tire, which means you will have a little better acceleration, but also put more miles on your odometer. I personal don't think looks are a better option than higher miles on your car.
#30
Tech Info Resource
iTrader: (2)
You've also added caster, changed weight distribution and center of gravity, etc., etc., mostly for the worse because it's only one end of the car moving.