11 replies to this topic

[fjbm]

Hi there

I'm restoring a MK2 Cooper S with its 10'' wheels and I decided to fit a 3.1 final ratio, instead of the original 3.44.
The speedo is calibrated to work with a 3.44 final ration, so how can I make it to read the right speed?

Cheers

[miniboo]

you need to get the right type of speedo drive cogs for the gear box.

Guessworks has a calculator on his clubs website that should help i think. 2 secs wil find it

found it

http://www.rcmoc.org...uff/Ratios.html

Edited by miniboo, 20 November 2006 - 07:19 PM.

[dklawson]

Contact a speedometer repair firm and ask about a ratio-adapter-gearbox.

These are mechanical, inline gearboxes that mount IN the speedometer cable. You'll have to supply the speedometer shop with at least one new cable, and careful measurements of your speedometer error (preferably based on odometer readings). Drive a known, exact, measured distance and report that along with your coresponding odometer reading to the speedometer shop. They'll use that to build a gearbox to match the speedo to your existing drivegears. They aren't cheap but they do work and have been used for years when people have transplanted drivetrains from one car to another.

Picture:
http://www.a1electri...mages/ratio.jpg

[Danny Mini 30]

[quote name='dklawson' date='Nov 20 2006, 08:42 PM' post='387193']

Drive a known, exact, measured distance and report that along with your coresponding odometer reading to the speedometer shop.

Think you may also need the time taken lol

[fikus01]

LMAO!! give speedy cables a call!! either do a google search or 1 on here!! they can recalibrate the speedo to your new requirments!! its not an overnight procedure tho and u have to do a certain amount of groundwork!!!!

[dklawson]

Actually... I meant exactly what I said.

You do not need the time taken, you need the distance you actually drove and the distance as displayed on your odometer. The odometer is hard geared to the drive cable. The needle is subject to calibration errors and it's not what you provide the shop. Providing the speedo shop the two distance measurements allows them to accurately make a gearbox that exactly matches the gearing on your car (both in the transmission and in the gauge). Any subsequent error in the speedometer needle needs to be addressed by gauge re-calibration.

Don't believe me? Call a speedo shop and ask them. As for recalibrating your speedo (Speedy cables or other), you can make an analog needle go anywhere you want. There are only a handful of worm and pinion gears that fit the speedometer odometers. You may not find the combination you're looking for and if you do, it will be very costly. By comparison, the ratio box is an external component that can be changed every time you change your drive combinations without taking the speedo apart.

[miniboo]

just change the cogs after you have figured out what you need.

cheapest option i reckon

[Guess-Works.com]

I'm with miniboo....

A std mini on 10's with a centre speedo and a 3.44 FD has a worm/pinion ratio of 6/17. if you change the FD to 3.1, then you need to change the worm/pinion ratio to 7/18, or if you go for a 3.2, you'll need a 6/16

[taffy1967]

These will sort you out:-

Speedycables Link!

[dklawson]

Regarding the Speedy Cables link above, see:
http://www.speedycables.com/faq8.htm

You'll note that the measurements they ask you to make involve measuring the tyre size and the number of revolutions of the tyres and speedo cable when you go a known distance... not speed.

[sqweaka]

dont bother with any of that just get smeone to drive another car at 10,20,30,40,50,60,70,etc andmark the speedo.
thats what i did when i change the gearbox/wheel sizes on my mini

[Danny Mini 30]

Actually... I meant exactly what I said.

You do not need the time taken, you need the distance you actually drove and the distance as displayed on your odometer. The odometer is hard geared to the drive cable. The needle is subject to calibration errors and it's not what you provide the shop. Providing the speedo shop the two distance measurements allows them to accurately make a gearbox that exactly matches the gearing on your car (both in the transmission and in the gauge). Any subsequent error in the speedometer needle needs to be addressed by gauge re-calibration.

Don't believe me? Call a speedo shop and ask them. As for recalibrating your speedo (Speedy cables or other), you can make an analog needle go anywhere you want. There are only a handful of worm and pinion gears that fit the speedometer odometers. You may not find the combination you're looking for and if you do, it will be very costly. By comparison, the ratio box is an external component that can be changed every time you change your drive combinations without taking the speedo apart.

) get ya get distance per gauge not constant speed lol