Gearing up final drive / 5th gear, any advice?

Since i've put 165/45's on my 15's my final drive is very low and my speedo is about 15% out, reading 70 mph but actually doing 59-60mph via gps and an engine speed of 3200rpm, which is a bit high for me. I'd like to drop a good 500rpm off 5th gear or even more for cruising, if I want a bit of go i'll use 4th or 3rd., any ideas?

Btw my car is an 89 cabby 1.8EX with an 020 5sp box, any gearbox's I can do a complete swap for with lower ratio's?

you should look for either a 4T code box which came in cars with a 4+E box, or a CTN code box out of a Mk3 golf tdi.  They're the longest 020 boxes VW made as far as I can tell..

 If you really wanted to you could use these two websites in combination with each other to help choose what tyre size, gear ratio and F.D. suit your needs

http://www.differentials.com/technical-help/differential-gear-ratio-calculator

and

rabbitgtipage.com

Thanks for the links, will look in to it. Also are all input shafts on 020 box's the same? and can cable clutch be fitted to all? or on another note can hydraulic clutch setup be retro-fitted with relative ease?

I understand that the input shaft is different between 8valve and 16valve, the cable can be fitted to any/all, and its a bit of a pain to retro fit hydro - a guy on the scirocco forum I used put a prototype together but he had lots of teething problems getting it to work, so its doable but not easy.

CTN is an 02A box and would require quite a bit of work and bits to fit (clutch/flywheel/hydraulic clutch or cable adaptor/ gear cables/possibly 100mm driveshafts if you dont have them).

You can just cange the 5th gear cogs from another box, might even be possible without removing the box by just lowering the engine down off the mounts and removing the end casing, not sure though as i've never tried it in situ.

The input shaft is different between the 8 and 16v boxes, the 8v boxes have 24 teeth and the 16v have 28 I think (long time since i messed about with 020 boxes).  Simple way round this is to fit a 16v clutch.

Loads of info on this site mate.  http://www.brokevw.com/5thswap.html
That link is for the 5th gear swap, but if you go to the home page theres absolutely everything you could wish to know about 020 box's.