Cable speedo correction

[fester2au]

Hey guys I read on here or lcool (having trouble finding correct thread again) that going up tooth/teeth sizes on the speedo drive gear that plugs into the transfer increaqses your speedo reading to suit larger tyres or was it the other way going down. Went to Toyota spare parts and the guy was vague but though it was the other way that you have to go down in number to increase the speedo and mine already has the lowest 31 tooth cog.

My brain is not comprehending the correct set up, gear ratios always stuff me up. Which way do I have to go to speed up the speedo reading.

[vk7ybi]

If the wheel has gotten larger, then the rotations will be lesser for the same given vehicle speed. Therefore driveshaft rotations will be less. To cause proper deflection of speedometer needle at given vehicle speed, speedometer drive cable rotation speed will need to increase relative to drive shaft rotation speed, or be made same as would be if original tyre. Speedometer drive cable speed can be increased by enlarging drive gear, or reduction of driven gear, or combination of both.

[vk7ybi]

Your best bet might be to find someone that has the solution, and get the Toyota part number/s from them.. You cant expect the parts guy to do the thinking for you..

[fester2au]

I don't expect him too and have never found a person of his position whose opinion I could trust hence the ask on here. I went in to ask for what was told to me and he said he thought it was incorrect but he too was quite vague on which way is correct. No one has part numbers that I found and they are easy to find in his fische, there are only 3 options 31, 32 and 33 tooth which I believe to be the driven gear as it is the removeable one from the conection to the box, the drive gear remains inside and can't be changed for another size (save for custom made gears or course)

[80's_delirious]

did you check the price?? if they are only a few bucks, just take a punt.

less teeth will turn the speedo cable faster I think

[vk7ybi]

Use a GPS as a speedo, or get one of them kit type ones that measure tailshaft speed and display vehicel speed digitally..

[+dj_hansen+]

Using GPS is fine aslong as you have a nice sky window... not so practical around town IMHO.

You want a speed increasing combination, the bigger the drive gear gets in relation to the driven, the faster.

Say the driving gear has a circumference of 2, and the driven has a circumference of 1, this is a 1:2 ratio, so for every turn of the driving gear, we get 2 turns of the driven... and so forth.

To answer your question, you need to go up in the number of teeth, and work out the ratio increase from factory tyre size to your 315s (which by my rough calcs of 265/75/15 to a 315/70/17 equates to a ~12% increase, which when worked out on a 31 tooth cog, you will need a 35 tooth cog to even it out)

I think your after this post fester http://www.lcool.org/forum/viewtopic.ph ... r&start=30

[Stackson45]

I just recently got my speedo calibrated after installing 4.56 diff gears and 35's (which should have been pretty close anyway, but the engineer wants it calbrated) they guy uses a ratio box - which plugs in where your speedo cable goes into the transfer, and the cable plugs into the ratio box. He calculates how far out it is, then builds a ratio box with the correct ratio adjustment. Can get a pic if you want

[brendan rooke]

I had a speedo correction box put on my 60 with 37's as requested by the good old engineer.

It cost me $220, i asked about price on other gears for it to run 35's and they said about $70 each and that i could change them myself if i wanted.

[fester2au]

did you check the price?? if they are only a few bucks, just take a punt.

less teeth will turn the speedo cable faster I think

try $70 hence my desire toget it right first time.