speedo

[cadetchris]

ah, i thought the half shafts had to come out as well, but i wasnt sure.

as for the accuracy, i did the counting thing 10 times, 5 with me under the car and 5 with my brother under the car, and each time the prop shaft rotated 25 times whilst the wheel rotated 10 times. not sure how much more accurate i could be, without whipping out the diff

[MikeHA4]

Interesting. From the statement much earlier in this thread:
10 wheel turns (one wheel fixed) gives 25 prop shaft 360°turns.
25/10= 1 wheel turn, 2.5 prop shaft turns.
Divide this result by two to allow for one wheel not turning on the axle and the other effectively describing the circumference of a circle on the ground = 1.25.
so it is 1.25:1 ratio.

If both rear wheels could turn in unison, as in straight-line travel, 10 wheel rotations would equal 12.5 rotations of the prop shaft.

That right?

However, doesn't this require the pinion to be about the same size as the crown wheel? That doesn't seem right.

[MikeHA4]

Ah, it may not be the ratio of TURNS you are looking for - The ratio as quoted for a differential (or gearbox) is the ratio of TEETH on the engaging gearwheels.

"Diff ratio refers to the number of teeth on the crown gear (output or axle wheel) divided by the number of teeth on the pinion gear (input). For instance, a diff might have a crown gear with 40 teeth and a pinion gear with 10 teeth, giving a diff ratio of 40/10 = 4:1.

"Shorter" diff ratios (i.e. larger numbers) offer better accleration, but lower top speed in each gear. "Longer" ratios (i.e. smaller numbers) offer less acceleration, but more top speed in each gear. Thus the reason why installing a shorter diff ratio is a common performance modification to cars fitted with longer ratios for fuel economy."

This could be the explanation and the answer will be found by counting teeth/reading the stamped ratio on the crownwheel.

?