Wrong millage due to my tire ?

[denvette78]

When i bough my vibe it has 16" 205/55 .The same week i put winter tire with same size and i notice that my millage was always lower than it should be. We did a 500 KM trip and my Brother in law got 60 KM more than what i listed. So after that i started to check with my other cars and i did find out that my millage was always lower with the vibe than the true millage. I thought it was my winter tire but, Yesterday i put my mag wheels with 225/45/17 and those are suppose to be the exacly the same diameter as the stock 16" wheels and today i went for a 200 km drive an i still have less that what i got everyday with my other cars I do that trip everyday with my other cars so i know exacly how much millage it should have. Does anybody notice the same thing?

[joatmon]

Have you noticed if the speedometer is accurate, or is the speedometer off by the same percentage the odometer is? Tire size can affect it, but it sounds like your tires are the size they are supposed to be. Maybe have the dealer check it out.

[denvette78]

I have notice that my speed is not accurate either. As i was following my brother in law i was almost 5 km slower than him. When he was doing 100 KM/h, mine was reading 95 Km/h. I wonder if i go with the spec of the GT for my tire, if it would be better. The GT have specs of 215/50/17 and they are a bit smaller in diameter.

[joatmon]

If you lost 60kms in a 500km trip, that a significant percent difference. You could correct it with a smaler tire, and that would probably give you quicker takeoffs, if that matters to you. Since you have a vette, probably not much that could be done to the Vibe to impress you Probably a safe assumption that you haven't overinflated the tires so much it causes a 10% error in the diameter.what I know of the system is that the vehicle speed sensor in the transmission (or the ABS controller if you have ABS) sends a pulse train signal to the computer and the instrument cluster. The cluster converts the frequency of pulses in this signal to generate the speedometer movement, and counts the pulses to increment the odometer. It could be that that there is a calibration on the instrument cluster that is possible, but it's something the dealer might be able to do, or it might be something the dealer would have to send it off somewhere to have done, or it might not be an option on these clusters. It could be possible that there is something wrong with the vehicle speed sensor, but I would expect it to fail completely instead of slowing down. It is gear driven, so it seems unlikely that it could slip 10%. I suppose it is theoretically possible that an incorrectly geared VSS somehow got put in your tranny, seems highly unlikely though. I assume that the repairs done to your car were all body/frame work things, no tranny work.I don't know. I'd be inclined to take it to the dealer, if you've still got a warranty on it, just to see what they say about it. A new set of tires is an expensive fix.

[1oldbanjo]

I bought a base Vibe and got stock 16" steel wheels with 205/55-16 tires...so I could get my own 17" wheels of my choice. In order to help with my decision if I should get 215/50-17 or 225/45-17 tires I drove my car last week at exactly 60 mph on a highway with mile markers along the side of the road. It took almost exactly 60 seconds to go between mile markers.....which means that my speedometer was pretty accurate with the original tires. The more miles you travel for this test the more accurate it will be.....we watched the second hand at each milemarker and did not reset the stopwatch at each mile. When we started this timing I had set my odomotor to 0.0 as we passed the first milemarker. I noticed that when we passed the first milemarker the odometer took a few feet longer to change to 1 mile - and with each milemarker we passed it was farther past the milemarker before the odometer would switch to the even mile. Somewhere around the ninth mile I was reading 8.9 when we passed the milemarker that should have been 9.0 miles. If you divide 8.9 by 9.0 it shows that the odometer was reading about 98.89% of the actual mileage. Although the error seemed large when I saw the readings going off so quickly - it is really only off by about 1.11%.Based on the fact that the speedometer was pretty accurate I went ahead and got the 225/45-17 Kumho Excsta ASX tires and when I tried the test with the milemarkers again - there was not any noticeble difference. As for going with the GT tire...it is not smaller....it is larger and will turn slower and will make your mileage error even worse. The 205/55-16 tire is listed as having a 24.9 inch radius and turns 837 revolutions per mile - the 215/50-17 has a radius of 25.5 inches and turns 814 revolutions per mile - which is 3% slower turning. You could possibly go with a 215/45-17 or 215/40-17 tires if you want a more accurate reading......but I would be afraid of the harsh ride and potential for rim damage with such short sidewalls.Just out of curiosity I calculated the change in reading for a tire with full tread verses one that is down to the 3/32 inch wear bars. If the tread depth is 10/32 inches and the diameter is 24.9 inches like the original 205/55-16 size - the diameter would be 24.46 inches when it reaches the wear bars - which means the circumference of the tire when worn is 98.23% of the original size - or 1.8% less. It appears that as the tire wears my odometer will me much closer to being accurate - while my speedometer will be reading a bit fast.If the error really bothers you.....you could install a converter like the one at the link listed below. It will allow you to adjust the reading to the correct speedometer and/or odometer reading for any tire size....but not both if they don't match very well. You will have to determine which one is important if they don't match.Here is the link for the converter. http://www.gaugeguys.com/ratioesa.htmDave

[Mavrik]

I run stock 205/55R16 winter tires and while driving on those tires I get the best km per litre. For my summer tires I run 215/45R17 which of course is not exactly perfect match but very close. I get less. And here is the thing to consider. Well this is what I assume anyway. My tires are a little bigger, a little wider and alittle heavier. All that goes towards fuel milage. Driving habits and air pressure in the tires effect it to. How much difference is there in weight of your 17" tires and your 16" tires?