Thread: Speedo Out

Originally Posted by Fluids

Hi Dave.

Quick dirty correction .... add 10% to what the speedo shows to get you to actual road speed.

From D2 std tyres 235/70*16 to 265/75*16 is a 9.39% increase in diameter.
Not all manufacturers 265/75*16 are the same diameter. They vary.

So 90 = 99 (100!)

See *Alloy Wheel & Tyre Size Calculator

Cheers

% will also vary slightly from new to worn tyres , Its a can of worms

Originally Posted by Redback

You guys need to get a speedo correction unit

Baz.

I reckon you're right Baz. She is often in the car with me.

This being out by 10% or so, would it effect the TC lock up in 4th?

Having read this and recemtly discovered that my speedo is out I'm surprised I have my license still.. :-/

Originally Posted by plaven

This being out by 10% or so, would it effect the TC lock up in 4th?

Having read this and recemtly discovered that my speedo is out I'm surprised I have my license still.. :-/

I'm only on 245/75-16 and it's a bugger. I need to be over not on 80km/h to get lockup. I find it takes over 85km/h exactly (not 84) which is a worry when most of the in town speed limits on arterial roads around Darwin are 80km/h. Not only am I speeding but just about every other car slows me down and then I'm out of lock up.

A question though. Will the speedo corrector effect the lockup speed or only the speed shown on the speedo. IE will the speedo show just show the correct speed and lock up still not happen until 85km/h or will the speedo show 80km/h and lockup happen then as well?

Happy Days

Originally Posted by joel0407

I'm only on 245/75-16 and it's a bugger. I need to be over not on 80km/h to get lockup. I find it takes over 85km/h exactly (not 84) which is a worry when most of the in town speed limits on arterial roads around Darwin are 80km/h. Not only am I speeding but just about every other car slows me down and then I'm out of lock up.

A question though. Will the speedo corrector effect the lockup speed or only the speed shown on the speedo. IE will the speedo show just show the correct speed and lock up still not happen until 85km/h or will the speedo show 80km/h and lockup happen then as well?

Happy Days

A very good point Joel, and something I had not thought of. I will have to check this on mine.

I'm on 255/70*16 - about 4% oversize. TC lockup in 4th still happens at about 80-82 but if I push it to 78-80 then ease my right foot off the loud pedal a bit it drops into TC lockup .... and if I'm not too aggressive with the loud pedal I can hold lockup down to about 72 or so ..... but that's about 1600-1700 rpm and there's absolutley nothing in the engine at those rpm's.

The reluctance of the TC to lockup may be due to the amount of torque being developed to hold the road speed due to the larger diameter wheels ?? Feathering the throttle seems to work for me .... same too for 3rd TC lockup.

I can usually hold 4th lockup under 80 on the speedo (76 or so on the speedo gets me 80 on the road) ..... and as I approach a 60 zone I usually downshift to 3rd with enough time (above 70) to get the TC to lock in 3rd and ease off to 60 so I can hold 3rd lockup in the 60 zones .... until it unlocks at about 48-52 on the speedo.

Kev..

My 245/75/16 BFG AT read spot on by 2 independent GPS sources. Stock tyres I think over read by a little, as do most cars.

Originally Posted by eckolsim

My 245/75/16 BFG AT read spot on by 2 independent GPS sources. Stock tyres I think over read by a little, as do most cars.

My D1 reads about 6 kays fast at 100 Kays with stock tyres

My D2 with stock tyres was pretty much spot on and SWMBO's last car an NL Fairlane was within 1 kph at 110 on the overhead speed check gantries we have in Vic.