how to be sure of a gear ratio

[kpop]

im looking to buy a 2nd hand set of diff gears lsd package. but how can i be sure what im buying is what the seller claims it to be

for example, seller claims its 3.7, but in actual fact it might be a 3.46

how would i go finding out what it reall is

[BlownVR]

If it is just the gears, count the teeth. Divide the number of crownwheel teeth by the number of pinion teeth to get the ratio.
If it is an assembled diff, count how many revolutions of the pinion are required for exactly one revolution of the crownwheel. If it is too hard to resolve the difference between 3.46 revs and 3.7 revs, do it for 10 revs of the crownwheel. Pinion will be 34.6 revs or 37 revs.
Maybe there are other ways to do it but that has worked for me in the past.

[Wonky]

They usually have tags on them, but anyone unscrupulous could change that, so what BlownVR said will work.

I would have thought you'd be better off with a 3.46 anyway as the Alloytech 190s only had 2.87s as standard. If you go to a 3.73 you will be revving 30% higher!! That's a huge jump! Even the few people who go from 3.46 to 4.11 as many guys do are only jumping 19%.

[kpop]

thanks for that guys. in regards to revving higher, 99% of my driving is short distance suburban driving. i rarely go over 80kph. so im looking for shorter gears. in the end it also depends on whats available - if i see a set of 3.4's ill most likely get them. but 3.7's wouldnt be bad either.

the gearing i have now, 1st gear stretches all the way upto 80kph, and there is essentially nothing below 2000rpm

[vyssbeast]

I hear ya mate

I got an alloytech too... let me know how the gears go, may consider them