Questions???

[sunir]

1) would larger rims (i.e 18 or 19") effect speedometer calibration readings such that the speedometer reads less than the actual speed of the car?

(2) Lets say I had different wheels/tires on the car.... then for example if my speedo says 60 mph, but my car is traveling at an actual 70 mph lets say on a highway that has a speed limit of 70 mph. If so then when I went to 70 mph according to my speedo...my car would actually be traveling at 80 mph and I could get stopped for speeding.....Is it correct to assume the error relationship of the difference between speedo and actual remains the same, in this hypothetical case and error of 10 mph, with increasing speed....can someone confirm this???

Sunir
'95 M3 LTW

[NoSoup4U]

1) Yes, but, you must also consider tire size as well, e.g. diameter. This affects your speedometer reading. I had a link that calculated how far off you would be.

2) It is linear in relationship, the faster you go, the bigger the discrepancy would be.

3) BMW has calibrated the speedometers with a pretty large margin of error though. Thus, in BMW's, when the speedometer says 100 mph, most likely you are NOT going 100 mph but something below that, maybe around 90 mph in actuality for instance.

If I understand the reason for your question, this argument has no merit. You will not only fail in court; but, you will piss off the judge.

[96technoM3]

Yes that will happen, but I dont know how large the change in wheel diameter would have to be in order to throw off your speedo by that much. If you are looking for a loop hole in court (assuming from your other post) then this is actually valid in VA. I got a speeding ticket in VA in my 4runner, it was considered reckless driving and I had to show up in court. When my case was heard I didnt really have a defence but pleaded not guilty anyway, it didnt work but the judge did say that if my truck had larger tires/wheels on it and I could prove that they threw off my speedo then he would lower the fine. I never had my speedo calibrated so I couldnt prove anything (the speedo is accurate anyway) so I just paid the fine and was done with it. The points didnt transfer but a reckless driving charge did show up on my driving record. Hope this helps Sunir, by the way we have meet a couple times, starbucks, auto x's, and the drive down to PTG. I hope all works out for you
Christian

[NoSoup4U]

Bad Advice IMO -

Reckless = 20 mph+ over, 98-55 = 43 mph. I doubt the above-referenced situation the person was going THAT fast. No matter what, he would STILL be considered SPEEDING. NO size tire would get him to a speed of 75 mph or lower.

Plus, the officer that paced him will be asked, when was the last time you calibrated your speedometer, he'll say like last month, or last week....

Very bad advice whomever suggested this one to you Sunir.

[96technoM3]

You are right NoSoup4U, I forgot that he was paced by an officer, my ticket was from radar. I was just letting Sunir know my similar experience. Anyway the judge did say if I could prove my speedo was off he would lower the fine to whatever it came out to be but I dont think this will work when an officer pased you.
Sorry for the confusion
Christian

[sardil]

Its very much so upto the judges discretion. More than likely though, the judge probably has heard this excuse a million times. If you were given a ticket for only a few miles over, maybe you'ld have a better shot, but at 43 miles over man, don't bother. The charges you're dealing with are pretty serious. Def. get yourself a lawyer. Yes, it'll cost some money, but they have good experience with these things, and work a significant deal out.

[Andy]

I think Sunir is asking this question because he is thinking about getting dem 19" Hammans.:dunno
I say go for the 20". You ain't bling unless yous gots dubs........YO!

[ajm]

http://www.smokemup.com/auto_math/tire_diameter.php

may help