How do I prevent speedometer inaccuracy when fitting larger wheels?

Question

My car currently has 13" stock steel rims. If I put on 15" alloys, the speedo will be inaccurate. Is there a way to recalibrate the speedometer in accordance to the size of the new wheels?

Answer 1

It all depends on the type of car. The older ones you would have to change the plastic gear in the trans. On the newer ones you can set that with the computer.

Answer 2

If it's an electronic speedo than you can get a scaler from Jaycar electronics that will adjust the reading. If it's mechanical you need a replacement speedo head. However if you also fit low profile tyres you may be ok. The important measurement is the height from the ground to the centre of the wheel, ie the rolling radius. Most speedos read a bit fast, so a small change would be within the margin.

Answer 3

As long as the outside diameter of the tyre remains the same (In other work fitting larger rims with low profile tyres) there should be not difference in the accuracy of the speedo.
On older cars there is a small plastic gear between the gear box and the speedo cable, this can be change for a larger of smaller gear.
On modern cars with electronic speedo's its possible to re-program the speedo.
Ja.

Answer 4

Should be able to do it with the tyre selection. Below is the figures you need to know.

Wheel size 13" = 330.2mm
Tyre size eg. 165/70r13 = 115.5mm side wall *2 = 331mm
(165/100*70= one side wall height x 2 = answer)
Total wheel and tyre size 661.2mm

Wheel size 15" = 381mm
Tyre size = width by height% multiplied by two
total wheel and tyre package must be as close as possible to 13" set up.

eg. 165/70r13 tyre numbers mean
165 is 165mm wide
70 is 70% of the width
R is radial compound
13 is the wheel size in inches, convert the inches into mm by multiplying by 25.4.

Please note that you lose 13mm tread throughout the life of a tyre so the closer to the original total figure the more acurate the speedometer reading.

Good luck and merry Christmas.

Answer 5

for each inch in diametor, top of tire, the fee would be off by aprox. 5 M.P.H. Speedometer reads 30 your doing 35 with a million" taller tires. Take vehicle to broking and characteristic them marvelous speedometer. Take your restore value ticket to trafic court docket and tell the decide you acquire the vehicle with greater tires and did no longer understand speedometer had no longer been corrected. maximum circumstances the value ticket would be brushed off in case you instruct prof of restore. this might keep you 10% on your coverage per 12 months for 3 to 5 years looking on state. .

Answer 6

you don't have to necessary correct for speedo inaccuracy when just changing the wheels as long as the circumference of the outside of the tire stays the same but if your changing the circumference then a power programmer is your best bet however brakes are a different matter bigger wheels results in a bigger rolling mass and henceforth longer stopping distances.

Answer 7

the rim size shouldn't matter too much when fitting the new wheels, what would be a factor would be the circumference of the new tires.

You can use the calculator listed below to figure out which tires would be closest to what you need.

Answer 8

you can buy a recalibrator. Ask ur local parts counter. (Source: Husband, Mechanic over 16+ yrs.)

Answer 9

if your tyres have the same circumference, no reclaibration will be needed. you will need lower profile tyres on 15" than on 13".

Answer 10

The error will not be enough to be concerned about and it's not worth bothering about.