I have a '92 Bonneville. I'm considering putting some bigger wheels on it with some lower profile tires. Is my speedometer going to be messed up when I do this? If it will, how can I fix it?If I change the size of my cars tires, will the speedometer read incorrectly?anytime you put different size tires and wheels on your vehicle the speedometer is going to be off, the only way around it is to measure the height of your wheel tire combination that is on your vehicle now and go ahead and get your bigger wheel you want and then get a tire that has a lower profile to it and make sure the total height of your new combination is the same height as your old set-up.If I change the size of my cars tires, will the speedometer read incorrectly?You won't be able to %26quot;fix it%26quot; because it's done by a gear in the transmission. The only sized gears you can get are ones made for standard sizes of tires the car was offered in.
That being said, a GPS will tell you your actual speed and it's not uncommon for cars to be 5mph high or low due to tolerances, size of tires, or how the gauges are setup. I wouldn't worry about changing the tires since your speedo will only be X percent off. If your new rims + tires are +10% over the old size, simply add 10% to whatever speed you're going.If I change the size of my cars tires, will the speedometer read incorrectly?Yes it will, if you only go one or two rim sizes up, it wont make that big of a difference. If your car has a digitally controled speedo, they can just reprogram the computer to have the new rim size. If it is mechanical, I think you have to get a new speedometer cable.If I change the size of my cars tires, will the speedometer read incorrectly?Speedometers whether they are mechanically driven or work electronically (digitally) are governed by the transmission of your car.
Therefore the diameter of your tyre, whether it's a normal tyre but over or under inflated, or a low profile tyre on a bigger wheel will have a direct correlation on your speedometer reading.
Even on normal tyres correctly inflated there's about 10% variation in the speedo reading which is why most speed cameras allow that amount of variation.
I know of no way to adjust your speedometer to allow for this, your best bet would be to get a GPS.If I change the size of my cars tires, will the speedometer read incorrectly?you put lower profile tires on bigger wheels so the rolling radius is the same, there are charts for this all over the internet you don't mess with the speedo or %26quot;make 10% allowances%26quot; when you drive, a good wheel shop will advise you of the correct size tire for your bigger wheels
