Can bigger tires on your car mess up your speedometer?

Question

If you put bigger tires on your car/truck than what they came with originally will/can that cause your speedometer to show incorrectly? I am arguing with my husband about this :-)

Answer 1

Simple answer is yes. Putting tires on that are bigger will throw off the reading of your speedometer (and the odometer for that matter).

But you can get it fixed to get it back accurate again fairly easily, it just means changing out a plastic gear for the cable driven ones and a computer adjustment for those with the speed sensors.

Answer 2

I know you have alot of answers, but I'll give mine as well.

Basically its like this, the vehicle speed sensor does not measure actual ground speed, only the RPM's of the drive force output. The computer is told that so many turn of the transmission mean so many turn of the wheels, and it also knows how far you will go for each turn of the wheel, thus it can determine how fast you are traveling. Bigger tires will not change how many times your wheels turn, but, with the larger circumference, they will travel a further distance on each turn as they have more area around the edge. Thus you will actually travel further then the computer thinks you are, and that means you are going faster.

Try this:

Take a Quarter and a Nickel, put a small mark on each near the edge.

Place the nickel on a piece of paper, mark where the mark is on the paper, roll it 1 full turn and mark where the mark is now an measure the distance between them.

Do the exact same for the Quarter, the distance you measure will be further.

Now imagine the stock tires are the nickel, and then you put a Quarter on there, now, for each turn of the wheel, you travel further, thus meaning you are traveling faster then the computer thinks you are.

Answer 3

Yes, but, most times they not interfere with the ABS.
We are talking Bigger Rounder??? I know how you women are. LOL!!!
Take a Baseball and a Basketball mark them with a black dot on one side. Then roll them across the floor counting every time the dot come up. Now, think of the speedometer being calibrated for the Baseball and what it would/should read for the Basketball. Best I know for an example.

Answer 4

yes! the output of the transmission is what controls the spedo. the spedo thinks the tires spin 1 time for every 2 rotations of the drive shaft (these are made up numbers but the concept still applies) now if the drive shaft still spins 2 times, but the tires only go .8 rotation, now you have a discrepancy in your reading. fortunately newer cars can be re programed for the difference. and older cars can have a spedo adapter custom made for the difference.

Answer 5

well you will win this argument they will throw it off,i caused my wife to get her first ever ticket in her life by putting bigger tires on her cavalier than it should have had.i got the ticket took care of once i explained this to them but she always drives right on the speed limit,this time she was over by 8 miles per hour,it does throw the speedometer off on some really bad,good luck with it,you basically won this round.

Answer 6

The answer is yes. But, generally the difference is small on the order of half a MPH unless you go extremely out of size from the manufactures original equipment. tirerack.com has a calculator that will tell you what different sizes will do.

Answer 7

Taller tires will indeed make your speedo inaccurate. It will show a slower speed than you are actually traveling.

Answer 8

Mess up your speedometer..like break it??....No....it will give you a false reading though!!

Answer 9

yes and no for if your vehicle has 235/75r15 and you put on 245/65r15 it won't change your speedo if there is a big difference in tire size it will defenitly affect your speedo.

Answer 10

Yes it will give you a false reading.