Wrong Speedo Meter And 16" Rims Mod

[qha_vn]

Hello all,

the ex-owner of my 1990 LS400 has changed its original rims from 15"to 16" everthing seems okay except that the speedo meter indicates wrong speed. GPS shows my car running at 100km/h but the speedo meter tells only 80km/h

i guess this is because the rims have been changed to a bigger one with bigger dia. which cause wrong speed calculation

my question is: can i replace the current speed sensor with the one for LS400 93-94 models which use 16" rims?

i dont want to go back to 15" rims that means i need to pay for 4 new rims and tires. also, the new rims make the car look nice actually

thanks

[lee_iceman]

Usually the bigger the rim, the lower profile tyre you use to compensate for the bigger diameter.

[GoldfingerLS]

iceman is right. As long as the rolling radius (diameter of the rim including tyre) is kept the same the speedo should be ok.

[Alex JB]

what tyre size do you have?

originals were 205 x 65 = 266.5, x 15" = 607mm rolling dia

I have 235 x 40 = 188, x 18" = 645mm rolling dia

But, my speedo is still reading onder what my GPS says so the tyres you have on your 16" wheels must be far to large in width and profile to put your speedo that far out.

[GoldfingerLS]

Hi Alex,

If your originals were 205 x 65 x 15" and your new ones are 235 x 40 x 18" then your rolling radius is the same.

(205 x 0.65 x 2) = 266.5 then 266.5 + (15 x 25.4) = 266.5 + 381 = 647.5mm is the old rolling radius.

(235 x 0.40 x 2) = 188, then 188 + (18 x 25.4) = 188 + 457.2 = 645.2mm is the new rolling radus

So your only 2.3 mm out :) hence your speedo should remain unchanged.

[genius149]

This Tyre calc linky should give you the differences and how much your speedo should be out by.

[ontheroad1]

nothing unusual about that I have 16" wheels on mine which was an upgrade in 1993 including breaks, mines a november 1991 series 1 with all the mods a 1993 has, large discs/twin piston calipers/16" wheels and standard according to the book