speedo clibration

[ozyprd]

hi guys just wondering does any one no i i fit 19s wat is the go with the speedo as the car has 15s on it now and i have heard that the speedo will under (egthe speedo says 60 and its more like 70) any ideas and wat does it cost to fix it?

[JA2Z]

Hi,


If your speedo is correct now (with 15"s) just make sure that the "external" diameter of the 19" tyres you will put on have the same "external" diameter of you current tyres:

for e.g.:

stockies generally are: 195x65x15 -- meaning:

195 mm wide x 65% of width height in the walls of the tyre x 15inch rim.

So total external diameter = 15inch (367.5mm) + (65% of width(195mm) x two walls each side of the rim)

= 367.5mm + (126.75mm x 2 walls each side of the rim)

= 621mm


-----

So just make sure that the tyres you fit onto 19" rims are something like 225x35x19 tyres. Because;



= 465.5mm(19" rim) + 35% of width of tyre (225mm)

= 465.5mm(rim) + (78.75mm x 2 walls each side of the rim)

= 465.5mm(rim) + 157.5mm(total of both tyre walls)

= 623mm "external" diameter,

This means the tyre is 2mm larger, which is fine because it will make your speedo out by just under 0.001%/per kilometer (nothing)


You can use the same formula for working out any wheel/tyre combo. or just refer to the table i made up below for you.

Rim Width Ratio External Diameter
(inches) (mm) (%) (mm)

18 185 50 626
18 190 50 631
18 195 45 617
18 200 45 621
18 205 45 626
18 210 45 630
18 215 40 613
18 220 40 617
18 225 40 621
18 230 40 625
18 235 40 629
18 240 40 633
18 245 35 613
18 250 35 616
18 255 35 620
18 260 35 623
18 265 35 627

Rim Width Ratio External Diameter
19 185 40 614
19 190 40 618
19 195 40 622
19 200 40 626
19 205 40 630
19 210 35 613
19 215 35 616
19 220 35 620
19 225 35 623
19 230 35 627
19 235 35 630
19 240 30 610
19 245 30 613
19 250 30 616
19 255 30 619
19 260 30 622
19 265 30 625

Rim Width Ratio External Diameter
20 185 35 620
20 190 35 623
20 195 35 627
20 200 35 630
20 205 30 613
20 210 30 616
20 215 30 619
20 220 30 622
20 225 30 625
20 230 30 628
20 235 30 631
20 240 30 634
20 245 25 613
20 250 25 615
20 255 25 618
20 260 25 620
20 265 25 623


so that your speedo doesn't get effected, you will want to choose a wheel/tyre combo that keeps the 'external' diameter similar to your current tyres.

hope that helps

Cheers

JA2Z

[maldotcom2]

As JA2Z said, as long as your rolling diameter is the same it won't affect your speedo. In otherwords, bigger rims run lower profile tyres to achieve this.

If you do find your speedo is out, a Jaycar speedo corrector can be installed to fix it.

[ozyprd]

hey guys thanks for the info well just waiting for them to turn up a mate has them and im like a kid waiting for christmass lol

[kill_switch]

As JA2Z said, as long as your rolling diameter is the same it won't affect your speedo. In otherwords, bigger rims run lower profile tyres to achieve this.

If you do find your speedo is out, a Jaycar speedo corrector can be installed to fix it.

Hey mate one quick question,
Do you have any idea on how much one of them is going to set me back? as it might be a cheaper solution to my problem.
Thanks

[delcowizzid]

Speedo Corrector MkII Kit - Jaycar Electronics

[NORTI]

Pity you dont have a Calais..... You can calibrate the digital dash to correct it.