do i have to adjust my speedo if i put bigger rims and tyres on my car?

Question

im leaving the 355 diff and the three speed manual just changing wheel size

Answer 1

Its a possibilty that you will have an effect on your speedo. It may or may not be noticiable though.Tire sizes do affect the gear ratio. In your case you will lower the ratio meaning that your speedo may read slower than what you are actually travelling. This is better for highway travel and economy too.
good luck

Answer 2

As long as the height of the wheel/tire combination is not different from the previous set, then no adjustment is necessary.

The overall height (diameter) is the what determines the amount of ground covered for each rotation of the tire (circumfrence). If you tire is taller than the circumfrence is longer and therefore you will cover more ground per tire rotation. If you tire is smaller than the circumfrence is shorter and therefore you will cover less ground per tire rotation.

Here's how to deteremine if you need a speedo adjustment. Go to your local freeway or some location where you are able to know the specific distance in miles (or KM). Get up to speed and when you pass the marker for the beginning, look at your odometer. When you pass the second marker, check your odometer again.

I have 3/4 FWD that I put 36" tires on. When I do this test, after going 10 miles, my speedo says only went 8 miles. This means that for every 10 miles I travel, I actually went 12. Thus for each 10mph increment of speed I must add 2 miles. Therefore if the speedo says I am going 60mph, my actual speed is 72. The math is as follows, current speed + (( Current speed / speedo check distance) * difference is speedo during check) or 60 + ((60 / 10) *2).

As you can see the best distance to check is 10 miles. This also insures a more accurate reading.

Good luck and I hope this helps.

Answer 3

Car Speedo

Answer 4

Yup.

Bigger tires will travel farther with every turn than will the stock tires. But the speedometer still thinks it's connected to stock sized tires, and doesn't know you went that extra distance. So it computes the speed based on how far it thinks you went, not how far you really went, so the speedometer will read slower than what you actually did. You'll either need to be able to figure your real speed in your head, or adjust the speedometer, or risk more speeding tickets.

Answer 5

Your speedo will read slower than you're actually going and it will seam a little doggier because you killed the gear ratio. Your computer, abs, and other controls will just think you are hauling a bunch of fatsos like myself because of the increased load. Now if you are going from stock 15's to some kind of 22 inch blings, and tire diameter is staying the same, crappy ride will result only.

Answer 6

Yes the changing of the rim and tire size will effect your speedometer. It will also subject you to some local and state codes that you might not be aware of. Some states are going after people that change the tire size. Pa for example you can only change up or down one size. A lot of people do it but you run the risk of being fined.

Answer 7

Ask your wheel/tyre supplier to fit tyres which accommodate the increase in rim size so that your overall rolling diameter stays the same.That way your speedometer will still read correctly.

Answer 8

It will not read accurately or as defined by OEM setup. A few MPH at most is all the difference, that depends on how much of a diff the tyres are.

Answer 9

If you change your rim size, there may be an option to change the tire size too. Bigger rim, say two inches larger, take two inches off the tire size. This way you aren't changing the over-all size, know what I mean?

Answer 10

If the overall diameter of the tire is larger, your vehicle will travel further for every revolution, thus you will be travelling faster then indicated. You should have your speedo calibrated. Please note that if you have traction control, stability control, ABS, or other electronic "helpers" that these devices may not operate properly, or safely, after the switch. Best to ask a mechanic knowledgeable in your vehicle.