All about the speedo

[alien]

Hi all

Ok, so i went to have my speedo calibrated professionally today since i now have 31" tyres and a 5.14 tcase... so i help the guy strip out the instrument cluster and attach his own measuring box, we drive a kilometre (marked on the road) and get back to the shop... a few calculations are done and in the 637 turns of the cable to get 1km, mine did 637.5... it was DEAD ACCURATE!

I was sure the speedo ran purely on the wheel speed, and the tcase was after the speedo, but now we werent so sure.. We were both a little confused, so he hooked the guage up to a box that spins the cable at exactly 60km/hr (using an osciliscope to confirm voltage to rpm) and the guage read spot on, he then went to 120km/hr and it was spot on - he even remarked it was the most accurate he'd ever seen from a mechanical guage.

so now begs the question:

26" tyre to 31" tyre = 19.2% increase
calmini 5.14 tcase gears = 18.3% reduction

was my speedo 1% out of whack before i did the lift? or is there something im missing here??

[want33s]

?????
Have you measured your tyres? Are they a genuine 31"?

[GRPABT1]

?????
Have you measured your tyres? Are they a genuine 31"?

What he said ^^^

[dank]

yeah probably your tyre size....haha...

I found out the other day that my trail tough 4.9:1 tranfers gears and yukon 4.57 diff gears with 33.8 inch tyres brings the speedo back to spot on measured with a GPS....

[hyzook]

I thought transfer gears would have no effect on the speedo as the speedo drive is on the output shaft which is why when in Lo range your speedo still reads right? diff ratios will effect it though.

[bulldogy]

Zook gears affect both hi and low range.

I would say as above it is the tyre size that makes it wrong look how many tyres vary from brand to brand.

[PJ.zook]

I agree with hyzook, crawler gears wont do squat to youre roadspeed and youre speedo reading. Think about it, if youre doing 60km/h with standard gearing, the transfer output speed to the diff is going to be exactly the same with crawlers doing 60km/h.

[alien]

the tyres do measure just under 31"... theyre like 30.5" or something.

It still doesnt explain why the guy checking my speedo swears its accurate... perhaps a dyno test is in order?

[GRPABT1]

I agree with hyzook, crawler gears wont do squat to youre roadspeed and youre speedo reading. Think about it, if youre doing 60km/h with standard gearing, the transfer output speed to the diff is going to be exactly the same with crawlers doing 60km/h.

Why would transfer gears be advertised to correct speedo for certain sized tyres then?

[dank]

trail tough 4.9s are 16% reduction in high range plus a 23% reduction going from 3.7 to 4.57 diff gears....

on 31s with the 4.9s only the speedo was showing slower than actual speed...33.8 inch tyres and overall 39% reduction in high range gave me spot on speedo or close enough!...wasn't expecting it ....don't ask me to explain how it works though

[alien]

im going to get a few people in different cars to do 60 infront of me and ill match speed to check if im accurate or not =) i think its the safest practical way to test without involving calculations! hahaha

[built4thrashing]

get hold of a gps unit and check it that way. alot safer than tailgating one of ya mates with you constantly looking at ya speedo.

[Highway-Star]

get hold of a gps unit and check it that way. alot safer than tailgating one of ya mates with you constantly looking at ya speedo.

X2, GPS is the best way to check it out. Mine with 31" tyres is 10% out, which I like because 10% is the easiest on earth to compensate for. I put my TT 4.9 gears in a guess what, NO DIFFERENCE! Gears do not fix your speedo! Unless there is some new set recently out that comes with a new speedo drive...

Another way to check is use your tacho if your car has one. People do not be affriad of simple primary school mathematics; its all you need to figure this stuff. If you know your tyre size you can figure your tyre circumference (pi*D), and if you know your gearing in each gear (very well documented if you do a search), you know what revs your engine must be doing in each gear at any speed. Example: a stocker should be doing roughly 3500rpm in 5th at 100km/h.

trail tough 4.9s are 16% reduction in high range plus a 23% reduction going from 3.7 to 4.57 diff gears....

on 31s with the 4.9s only the speedo was showing slower than actual speed...33.8 inch tyres and overall 39% reduction in high range gave me spot on speedo or close enough!...wasn't expecting it ....don't ask me to explain how it works though

Explaination: 33.8" tyre is 30% bigger than standard 26". 4.57 diff is 24% lower than standard 3.7. Not a perfect compensation, but cable speedos are rarely spot on to start with (My fathers zook is freakishly accurate standard). Your transfer gears have no effect on speedo, only on driveability; I would imagine your car would be slightly over geared for on road use in this arrangement.

[Gwagensteve]

TRANSFER GEARS DO NOT CORRECT THE SPEEDO

The speedo drive is AFTER the gears. Trust me, they have no effect. I cannot comment on your setup alien, bit the transfer gears aren't correcting your speedo.

spinning the cable though won't prove anything as all suzuki's run 637 turns/km, even 1.0's and 660 sierras.

Sorry I don't have an answer, but those are the facts.

Steve.[/code]

[GRPABT1]

Then how do you explain peoples speedo working after getting the right tyre/gear combo?

[alien]

my head hurts... lol - im certainly going to test this on the weekend - dont know anyone with a GPS so im gonna do the tailgate thing (carefully).

[zookimal]

I'm with Steve.

Gears do nothing re the speedo. They will fix your driveability by correcting the gearing back to a suitable rpm range but not the speedo. I'm down by 15-20% on the speedo from memory, ie. 80=95-100kmh.
I use the tacho and know my 10kmh intervals for most gears/rpm.

No idea Alien, don't know what's happening with yours.

[Dee]

i too dont think the gears affect the speedo whatsoever.

I've got 6.5:1's with 33's and stock diff gears and my speedo is waaaaaaay out of whack. (like 60kms/hour = 43km/hour reading on the speedo!)

[GRPABT1]

i too dont think the gears affect the speedo whatsoever.

I've got 6.5:1's with 33's and stock diff gears and my speedo is waaaaaaay out of whack. (like 60kms/hour = 43km/hour reading on the speedo!)

Bugger, cause that's the combo I'm gonna run. Oh well, it's not like my speedo works anyway lol.

[alien]

righto - tested today and the results are in.... while the cable is infact doing 637 turns to the km, the speedo is MILES out... ie: 51 on the speedo is 60.. and 42 is 50...

So back to the calibration place i go for an explanation =)

[alien]

*phew* what a morning... ok - so the speedo guys have NO IDEA why its doing the correct rotations on the cable but reading 20% out of whack... so, tested it again and its doing the right rotations (628rpkm, last time was 637).. so out comes his GPS unit - which confirms speedo is out...

solution? lengthen the speedo spring and adjust the half/half ratio on the dial (that little arm thingo) - using one full wind more of spring soldered on the speedo is now nearly spot on. (guage reads 60, actual is 58.5).

between the two guys there though, with years and years of experience, they have no idea why its out in the car but correct on the bench - much like all of us here.. haha

[Gwagensteve]

They're missing the point Alien, that's why they're confused.

you've put a 19% bigger tyre on the car, so for each turn of the speedo shaft the car is moving 19% further down the road. (so the speedo will be 19% slow)

Your revs/gearing is now spot on, as you have transfer gears, but the speedo can't see them.

Any checking of the speedo RATIO will show it to be spot on.

If you put stock tyres back on and drove down the road, it would be spot on too, but you will be revving 19% higher than stock for the same road speed.

I have been caught out by this too.

Another trick to to use a Baleno instrument face - It will correct the speedo about 20% as it reads to 200 kph and has a slightly different sweep. (see photo - compare the 100kph position with about 80 on a sierra dash)



The best solution though is to use a GPS as a speedo. Due to some jiggerypokery with faces, speedo units etc, my speedo isn't currently that far out (about 8%) but I always drive against the GPS, not the speedo. (I don't have a tach either, so I can't drive on revs)

[v6hilux]

They're missing the point Alien, that's why they're confused.

you've put a 19% bigger tyre on the car, so for each turn of the speedo shaft the car is moving 19% further down the road. (so the speedo will be 19% slow)

That is spot on!

[alien]

thats what i kept saying - and hence why i insisted they just "make it read right" and not rely on their ratio box for a measurement =) (so used GPS to calibrate the spring and modify the tension).

pretty simple job to calibrate if you have a hair spring and know how to solder too.

[jono_785]

Hey guys does anyone know what year the Baleno instrument cluster is out off?

[Gwagensteve]

The one the pic is a year 2000 model G16 engined sedan. I am unsure if there were any significant changes between years.

Steve.

[nicbeer]

The one the pic is a year 2000 model G16 engined sedan. I am unsure if there were any significant changes between years.

Steve.

That one a copy of the actual face?

As would be great if someone can do a image/pdf of original face.

[Gwagensteve]

No, that's the actual face - we had a front cut so we used the tach and speedo face.

Ironically, the original sierra face would have been more accurate in this partiucular car - it runs 35.5" tyre and 3.9 diffs.

Steve.