I Need Help! My Speedo Is 15Kph Slower

[AlexWaltham]

1993 R33 Skyline GTS

I Need Help When Im Doing 100kph my speedo reads 85kph What The F*@k do i do to fix it

Someone Please Help me is there a easy fix ( Car had a Manual convertion ) not done by me Previous owner

PLEASE HELP ME Iv Got no idea what to do

ANY HELP WILL BE APPRICIATED

[S3RK]

A speedo corrector will do the job!

[AlexWaltham]

thank you so much

[niZmO_Man]

Could try running bigger tyres

[AlexWaltham]

im running 225/40r18 and the tyre placard says to run 245/40r18s but the width of the tyre wouldnt make much of a difference

[niZmO_Man]

It does, that's almost 5km/h difference on your speedo. Plus your car was converted from auto (different diff ratio).

Speedo corrector is a better and cheaper way though.

[AlexWaltham]

how much are they and where do i get it from

[Reedo]

mighty car mods online shop. 60 bucks i think. also what n/a r33 runs 18 inch rims stock? mine runs 15s.

[AlexWaltham]

na iv got after market 18's on it i didnt like the stock wheels but thank you for your help ill purchase it now

[niZmO_Man]

Jaycar

[Albus]

Why not get a wheel balance and alignment?

[-S-]

quick one... how did u know u were doing 100 kph?

[MBS206]

im running 225/40r18 and the tyre placard says to run 245/40r18s but the width of the tyre wouldnt make much of a difference

The height of the tyre, is proportional to the width.

That number 40, means 40% of the width.

IE, a 225/40 has a side wall that is 90mm

A 245/40 has a side wall that is 98mm

Once you start to factor everything in, that's a much smaller rolling distance, and it means for your car speedo saying 100KM/H, your car is going quite noticeably slower.

But I would say, you really need to convert the diff from auto to manual so that it'll all read correctly again, this would be the easiest and best way to fix your problem as well as changing tyres to the correct size.

[donut_kng]

The profile is actually a percentage if half the width.

So your 225/40 would be half of 225 and then 40% of 112.5 which is 45mm- 90mm sounded a little high for a 225/40!

[mad082]

The profile is actually a percentage if half the width.

So your 225/40 would be half of 225 and then 40% of 112.5 which is 45mm- 90mm sounded a little high for a 225/40!

Sorry but you are wrong. I can provide links to various tyre manufactures websites to verify that it is the percentage of the full width if the tyre if you like. you have to remember that the sidewall starts at the bead of the tyre. 45mm is small. For me it's the width of 2 thumbs, and given that the rim covers about 1 thumb width, I know that the tyres on my skyline were more than a thumb width from the rim