[skitzlux]

my speedo is way out and i wanna know what you guys have done to fix it i dont want to get a gps and go off that
thanks

[303zuke]

To start with we need to know where you've gone wrong.

What t/case gears? Diff ratios? Tyres?

[alien]

i took mine to a calibration place - in the end the solution was to add more to the spring in the speedo cluster... now at 60km/hr im doing 58.5 (well, that was on my cooper tyres, now with simex im doing 61).

[SuperRoo]

303zuke wrote:

To start with we need to know where you've gone wrong.

What t/case gears? Diff ratios? Tyres?

We dont need to know any of these things.

If you do 2000rpm @ 60kph on the speedometer with 26" tyres, then you will still do 2000rpm @ 60kph on the speedometer with 40" tyres.

The only thing that changes is the actual speed that you are doing.

Recalibrating the speedometer is the only thing that will get the actual speed to equal the speedometer reading.

I havent been to bothered with the 16% difference in reading but I did use my gps to take readings and mark my dash with little tics with a white out pen where 60, 70, 80kph... is so I know when I dont have the GPS in the car. I also made a mental note of the other speeds, so I can remind the missus everytime she drives my car.

[Rusho]

Pretty sure tyres make a difference. I noticed the difference in my speedo going from stock to just 30inch tyres. Could be wrong though

[S13RR4]

Rusho81 wrote:

Pretty sure tyres make a difference. I noticed the difference in my speedo going from stock to just 30inch tyres. Could be wrong though

no your right rusho,

old mate was just saying that the speedo is still reading the correct speed acoording the the TC,

but due to the larger circumference of bigger tyres, the distance travelled by the tyres from one complete revolution of the TC is further, hence your actual speed is greater then your speedo speed.



as far as fixing it, Ive heard you can get kits or places to recalibrate your speedo according to your new tyre size. don't know much about them but you might just have to ring around.

[Ben_Sierra]

Um, diff gears will make a difference as well... as it changes the rate at which the tyres spin in comparison with that of the TC output...

[S13RR4]

Ben_Sierra wrote:

Um, diff gears will make a difference as well... as it changes the rate at which the tyres spin in comparison with that of the TC output...

goop point

[303zuke]

Well, actually all three of the items that I mentioned will change the accuracy of the speedo. SuperRoo is correct that the speedo will still display the same speed to engine revs, but knowing what has changed in the system will allow fitting of either a different drive and driven gear in the t/case (which will give a limited amout of correction), or fitting a calibration gearbox on the cable, which are available in a huge amount of ratios. They are basically a small overdrive or underdrive gear box that changes cable speed by a fixed ratio.

Any Instrument Shop worth their salt will be able to calculate the correct ratio required and may even have the right one in stock. They are commonly used with race/rally cars that have diff and tyre combinations modified, but still require accurate speedos and odometers. Takes about 2 minutes to fit!

Irrespective of the changes to your driveline and tyres, correction can be made to the cable speed to make the speedo accurate to within 5%.

[Ben_Sierra]

Transfer gears will also change the engine-revs to speedo relationship...

The other option is to modify the dash cluster so the needle points to the right speed... I saw some cut-out and stick on speedo dials for a samurai for different tyres and gears somewhere once...

[303zuke]

Ben_Sierra wrote:

Transfer gears will also change the engine-revs to speedo relationship...

Wish I'd said that!

The problem with modifying the actual speedo is that when you next replace gears, tyres or even break the speedo, you have to go through the whole modification again.

The correction box is a quick changeover, and as mentioned above, if bought through a decent Instrument Shop, such as General Auto in Sydney, then any future changeovers will only cost the price of another set of gears (or even swapped for nix, as they have a large supply of exchange stock for rally vehicles). The initial purchase cost will be equivalent (or less then) the labour charge to have your speedo removed and recalibrated, and the correction box can be removed when you sell the vehicle.

[Ben_Sierra]

303zuke wrote:

Well, actually all three of the items that I mentioned will change the accuracy of the speedo. SuperRoo is correct that the speedo will still display the same speed to engine revs.

According to that quote directly from you, changing any of the three things you mentioned (t/case gears, diff gears and tyres), will affect the accuracy of the speedo but not the revs-to-speedo reading...