Easy way to figure out differential gear ratio?

[Wally]

Hi guys,

I'm not entirely certain what differential gear ratio I am running in my JDM 86 has a TRD 2way in it, though not sure what diff gear ratio thats in there.

Does anyone know a way to work it out?

On the highway it touches 4000rpm at 117km/h :soldier: which is pretty high, I don't remember my ADM being like that.

Any help would be great
Cheers,
Chris.

[xero]

its a 4.3 wally. at about 3500-3700rpm, should be about 100km/h, and 4300-4500rpm should be about 120km/h.

the kid had a similar thing as well, was unsure what his ratio was.

[Wally]

Thanks mate.

Yer 4000rpm and its dead smack on 117 (digital dash).

Hoping the new TRD tranny gear set doesn't much around with it too much in top gear.

[slydar]

4000x60 = rev/h 240000
240000/.861 (t50 5th gear ratio) =278745.6
278745.6 = revs at diff' drive flange per hour

roll out on 185 60 14 = 1.8146m
1000m/1.8146 = 551.1 revs per klm.
so 64478.7 revs per 117k

278745.6/64478.7= x

= 4.3xxx

its nice to brush up on some infrequently used maths skills every now and them :)

[Adsie]

Wouldn't your speedo be out once you change your diff ratio?

[Jonny Rochester]

That is right. But the tacho is still true. So you can calculate your real speed knowing your revs, gearbox ratio, diff ratio, and tyre circumferance.

[driftke70]

dodge way is to mark your tail shaft and tyre, turn your tail shaft one full rev and see how many the outside of your tyre does.

[xero]

Thanks mate.

Yer 4000rpm and its dead smack on 117 (digital dash).

Hoping the new TRD tranny gear set doesn't much around with it too much in top gear.

from what i know, the TRD 3 set and TRD 5 set dont really change the final drive ratio in the gear box.
i know for sure that the TRD 3 set doesnt touch the final gear.

[Wally]

Yer i think the 5th gear in TRD set is virtually if not the same.


That is right. But the tacho is still true. So you can calculate your real speed knowing your revs, gearbox ratio, diff ratio, and tyre circumferance.

mmm so would that mean it's displaying slower or faster?


4000x60 = rev/h 240000
240000/.861 (t50 5th gear ratio) =278745.6
278745.6 = revs at diff' drive flange per hour

roll out on 185 60 14 = 1.8146m
1000m/1.8146 = 551.1 revs per klm.
so 64478.7 revs per 117k

278745.6/64478.7= x

= 4.3xxx

its nice to brush up on some infrequently used maths skills every now and them :)

oh awesome.

go a spreadsheet?

[slydar]

i can do simple maths, but not spread sheets :)

anyway, your cars jdm? and the box is too? your speedo will be correct then, j' cars come with a 4.3.

[Wally]

Yer JDM Trueno.
Box will be aftermarket though. T50 with TRD gearset, though like Adam said the TRD gearsets probably have similar final gears.

[racsov]

jack your car up, rotate your rear wheels 1 exact rotation and count how many times your tailshaft rotates. really needs to be out of the car with markings and a protractor setup to get an accurate measurement but yeah you get the idea

[matt99]

its nice to brush up on some infrequently used maths skills every now and them :)

English too, haha.