Speedo question

[puddlesurfer]

I've searched but not really found an answer!

IF I was to fit 33" Tyres to my truck at some point would it be possible to change the speedo reading so it was correct again?

If my speedo was reading 30mph when I was driving at 35mph , Would it read 40 if I was doing 45 or 50 when doing 55 etc?

If so, would the simplest solution be to get a new speedo face printed up with all the mph/kph numbers turned clockwise a few degrees? or is there a better way?

[dannyboy77]

you will need to change the diff ratios to get your speedo reading the right speed again. i think the following is correct

31" tyres = diff ratio = 4.3

33" tyres = diff ratio = 4.56

35" tyres = diff ratio = 4.88

if not someone will correct me

[puddlesurfer]

you will need to change the diff ratios to get your speedo reading the right speed again. i think the following is correct

31" tyres = diff ratio = 4.3

33" tyres = diff ratio = 4.56

35" tyres = diff ratio = 4.88

if not someone will correct me

That sounds expensive! I was wondering if there is a cheap option!

[puddlesurfer]

I just looked at my axle code and it's:

G145 Which means:

G = 8" gear
14 = 4.875 gear ratio
5 = 4 Pinion, Limited Slip

If that's right, then if I fit 35" tyres to my truck, the speedo will be more accurate than it is now with 265/70/15's (approx 29.5") - that would be a result! Saying that, I believe that when my speedo say's I'm doing 60mph, I'm Actually doing closer to 55.

[dieselboy]

My speedo was pretty much spot on with 30.5" tyres. Now I have 33's I will need to do a test, if it's off it is not far.
I suppose I could work it out with math.
30.5" tyre = 95.81857" Circumference
32.5" tyre = 102.10176" Circumference.

So for every revolution of a 33" tyre, you travel 7" further.

Not really sure where I was going with that.

[puddlesurfer]

So for every revolution of a 33" tyre, you travel 7" further.

Not really sure where I was going with that.

[puddlesurfer]

There are 63360 Inches in a mile if you want to work it out

[BUSHWHACKER]

Use a sat-nav to check your speed.
33" tyres usually make the speedo read correctly.

[caney]

im on 33s speedo correct, spot on vince,

[stormforce]

with the 275's on the 3rd gen my speedo is reading about 2-5mph over campared to the satnav

[puddlesurfer]

I'll have to borrow a satnav and some 33's to test, anybody want to lend me some?

I'll give them back - honest!!

[noobysurfer]

Get a mate to clock you on a motorway late evening when its quiet

[Twisted Instigator]

I'd never even thought about that! So, with mine having smaller front tyres does that mean I'm doing just under what the speedo reckons then?

[BUSHWHACKER]

I'd never even thought about that! So, with mine having smaller front tyres does that mean I'm doing just under what the speedo reckons then?

Smaller front tyres??? I hope all the tyres are the same diameter or your transfer box will complain..........a lot!!

Anyhoo yes, on standard tyres the speedo under reads.

[JUDWAK]

if you wonna were speedos you do it mate