Custom gearbox or bigger wheels/tyres?

[grizgut]

Not sure what section to post this in so plumped for mechanical?

I have a 2.5 Subaru quad cam engine mated to a vw1.9 petrol 5 speed box. 1st gear is pointless and the revs are very high when cruising. The PO fitted 16 inch alloys with quite 'thin' tyres, this means that the wheel/tyre combination is just under 3% smaller than the standard wheel/tyres combination fitted when new. I don't think this helps!

Question is would fitting the largest rolling diameter wheel/tyre combination possible help with my gearing problem or should I be looking at a custom gearbox build from someone like Aidan Talbot?

[faggie]

i would fit a custom gearbox from bears transmissions

[Aidan]

what code box ?
4.14 final drive would drop the revs 15% if it's an ABN

[grizgut]

Hello Aidan,

Crawled under the van this morning to look for the code but the box is filthy. Is the code on the o/s or n/s and near the bellhousing/clutch or the mount? I'm assuming it's not on the bellhousing itself or the RJES adaptor would have replaced it?

Thanks, Simon.

[Aidan]

n/s 4-5 inches below the reverse switch housing

[discipleofsketch]

Ok, although i'm convinced that a transmission upgrade is the best option for giving me a better cruising speed now that i've had a 1Y fitted, it's an expensive upgrade that I can't do in the near future. As an interim measure, if I wanted to put bigger than standard diameter tyres on my 14" steelies what size should I go for?

[grizgut]

Aidan,

I will confirm by scraping away some gunk on the box itself but the manufacturing sticker is still in place by the steering column:) It shows DG as the original engine code and 8E as the gearbox code. Can you let me know what my options might be with this box please, many thanks, Simon.

[Aidan]

Aidan,

I will confirm by scraping away some gunk on the box itself but the manufacturing sticker is still in place by the steering column:) It shows DG as the original engine code and 8E as the gearbox code. Can you let me know what my options might be with this box please, many thanks, Simon.

same as for ABN - it's just about the same as the 8E just later
@discipleofsketch
205R14C is the biggest you will be able to fit

[nevill3]

See this website for the results of Aidans advice (you can change any of the variables e.g. tyre size or final drive etc.)

The settings on the left are what you have now (I used Aidans recommended tyre size) and the ones on the right are what you would get with a different Final Drive Ratio.

The graph underneath shows the differences too.......I played with this to try and work out what my tyre size choice had done to my speedo accuracy.

http://www.teammfactory.com/gearcalcula ... on+1+%26+2

[nevill3]

Just to add I got the information for the gear artios from The Brick Yard http://www.brick-yard.co.uk/VehicleSpec ... fo/gbx.htm

[grizgut]

Thanks for that Nevill, does not look like just the final drive on its own makes a huge amount of difference, just a couple of hundred rpm? Is there any other gearbox modification that helps?

[ghost123uk]

@discipleofsketch - 205R14C is the biggest you will be able to fit

Sorry to "hop on" But what is the percentage increase over std 185/14 tyres by going up to those please ?

( I know there is a calculator somewhere but now I cannot find it )

[grizgut]

Using this

http://www.tyresave.co.uk/tyresize.html" onclick="window.open(this.href);return false;

its about 5% over I think, have a look and see.

[ghost123uk]

Using this - http://www.tyresave.co.uk/tyresize.html" onclick="window.open(this.href);return false; - its about 5% over I think, have a look and see.

Thanks, Yep 5%, not much is it.

[grizgut]

Tyres and final drive together looks like 20% drop in revs, but I bet the cost of both is high? If I could get a better percentage drop just via gearbox final drive changes and perhaps custom gear sets it might just be worth it?