)
My diff is out of the casing so i thought i would work out the ratio. How do you work the ratio out? (In numpty language please...none of this pinion
gear, lay gear stuff as i don't understand!! )
here is a diff; 
you can see the big round thing in the centre (the crown wheel), count the wobbly bits around the edge (teeth).
on the right you see a knob shaped thing (pinion) whose wobbly bits engage with wobbly bits in the big round thing - count the wobbly bits on that
(pinion teeth)
diff ratio = teeth on crown wheel divided by teeth on pinion.
[Edited on 15/8/07 by 02GF74]
Couldn't have put it better myself 
I really hope your knob doesn't look like that!...
Brilliant!! Fully understood, thanks very much.
Ok, big wheel (crown) = 35 teeth
Pinion (knob) = 9 teeth
=3:88
I have a 1600 xflow and type 9 box so question is:
Is this diff good for acceloration or motorway cruising?
Depends on your wheel size! I have also have a 1600 xflow, type 9 box, 3.89:1 diff, with 185/70 x 13" tyres, which means I'm just over 3000rpm at 70mph - very relaxed.
sounds good to me.
I'll be using 13" wheels with 185:70:13's
[Edited on 15/8/07 by donut]
quote:
Originally posted by donut
Ok, big wheel (crown) = 35 teeth
Pinion (knob) = 9 teeth
=3:88
Ahh ok, thanks.
Told you i was a numpty with these things!!
The quick escorts - rallying etc use 4.44:1 or even lower for good acceleration.
3.88 will be a good compromise.
Cheers
Mark
i know it has been posted before but if you know your gearbox ratios this is handy;
http://www.westfield-world.com/gtc.html
Just taking this further - is it easy to work out if the diff is still in the casing and the ID tag is missing?
i seem to recall you can turn the prop then count revs of wheel but only if both wheels move same amount - i tried this when building car and seem to
recall getting both wheels to turn same amount wasnt easy in practice.
And is this right - if you have a 3.62 and change to higher number (eg 3.88) do you get better acceleration, and if you change to lower number better
top end?
Is the higher the number the higher the gearing or the other way round?
The higher the number, the quicker the acceleration. I've never been 100% about the higher/lower gearing term myself, as I can't remember which way round it goes!
quote:
Originally posted by DarrenW
Just taking this further - is it easy to work out if the diff is still in the casing and the ID tag is missing?
i seem to recall you can turn the prop then count revs of wheel but only if both wheels move same amount - i tried this when building car and seem to recall getting both wheels to turn same amount wasnt easy in practice.
And is this right - if you have a 3.62 and change to higher number (eg 3.88) do you get better acceleration, and if you change to lower number better top end?
Is the higher the number the higher the gearing or the other way round?
quote:
Originally posted by DIY Si
The higher the number, the quicker the acceleration. I've never been 100% about the higher/lower gearing term myself, as I can't remember which way round it goes!
quote:
Originally posted by DarrenW
, and if you change to lower number better top end?
quote:
Originally posted by mookaloid
quote:
Originally posted by DIY Si
The higher the number, the quicker the acceleration. I've never been 100% about the higher/lower gearing term myself, as I can't remember which way round it goes!
IMHO the higher the number the lower the gearing. so 4.44:1 is low geared 3.38:1 is high geared.
Cheers
Mark
Hi. And boy oh boy do they sound nice at those revs.
cheers matt
quote:
i seem to recall you can turn the prop then count revs of wheel but only if both wheels move same amount - i tried this when building car and seem to recall getting both wheels to turn same amount wasnt easy in practice.
Then add in the gearbox ratios and you open another can of worms.
I make some assumptions here so please bear with me, i have been working on the ideal gear ratios for my LSIS for some time and with the available
gearboxes it's always a compramise. The type 9 has 2 different 1st gear ratios, 3.6 and 3.3 (V6 box) this means that to get a usefull first gear
you need a long diff 3.6 or above however 4th gear top revs has problems with achieving peak power.
Wheel rolling radius can also alter the speed in gears.
The basics of high diff ratio more acceleration low diff ratio more top end do apply but with caveats.
There are some good excel spreadsheets available that let you put in wheel diameter, tyre size and profile, diff ratios, gearbox ratios and peak
revs.
Off the shelf, best ratios in a gearbox i could find before going Quafe or BGH is the T5 cossie, with these ratios its then upto tyre wheel size and
power. 130 to 150 bhp then 3.9 diff is good over that then you can push through a 3.6 this is with CEC engines, V8's like 3.38 diffs.
Bike engines need the longer diffs because of the drop down ratios built in to the gearbox effectively multiplying torque and the fact they run bigger
wheels.
My solution so far is a V6 Type 9 and 2 diffs, 3.9 & 3.6
In general, my gearbox and diff ratios suit me perfectly (3.89:1 diff, Type 9 box, 185/70 x 13" tyres). Once I'm on the move everything
works very well for the sort of driving I do - fast & twisty country lanes, generally not exceeding the speed limit, but not slowing down much
either! 
The only fly in my ointment is the Type 9's 1st gear, which is far too low - when I'm in a hurry I have to change into 2nd at around 25 - 28
mph, and I get to that point all too quickly! My planned solution is to get another box and replace the 1st gear-set, plus an overhaul, ready for a
changeover at a later date.
Otherwise I'm very happy with my set-up - as Donut will be happy with his, once he's up and running again.
DJ