Revs at a given speed...

Post by **grahamt7** » Sun Jan 21, 2007 10:33 am

Anyone know what the expected revolutions are for given speeds...

30, 40, 50, 60, 70 mph?

Cheers!

Post by **Dominic** » Sun Jan 21, 2007 11:09 am

If I remember rightly, I think that at 1000 rpm in top gear, a standard 1098 will give a speed of 16.5 mph. You can work out the maths!

Post by **Onne** » Sun Jan 21, 2007 12:17 pm

do you know that figure for the other diffs as well?

Post by **Willie** » Sun Jan 21, 2007 12:29 pm

The figure for the 948cc is: Road speed in top gear@1000rpm=15.18mph
The 1098cc is actually 16.2mph per 1000 rpm in top( assuming that you have original wheels and tyres)!

Post by **Onne** » Sun Jan 21, 2007 1:00 pm

ok and for the series II met stupid axle? Just wondering what my supposed top speed is in the 54
Seems to be about 60 mph

Post by **Onne** » Sun Jan 21, 2007 2:39 pm

so graham if my calculations are right:
4.22:1 axle
10 mph 617rpm
20 mph 1234 rpm
30 mph 1851 rpm
40 mph 2469 rpm
50 mph 3048 rpm
60 mph 3703 rpm
70 mph 4320 rpm
80 mph 4938 rpm

4.55:1 diff
10 mph 658 rpm
20 mph 1318 rpm
30 mph 1976 rpm
40 mph 2635 rpm
50 mph 3294 rpm
60 mph 3953 rpm
70 mph 4611 rpm
80 mph 5270 rpm ( more than I though... my poor car

)

Post by **bmcecosse** » Sun Jan 21, 2007 4:05 pm

That's for the old crossply tires - I think the rolling radius of radials is slightly less. ie more revs for same speed.

Post by **Onne** » Sun Jan 21, 2007 4:17 pm

My very limited calculating skills have calculated for the series II axle
13.02 mph at 1000 rpm
10 mph 768 rpm
20 mph 1536 rpm
30 mph 2304 rpm
40 mph 3072 rpm
50 mph 3840 rpm
60 mph 4608 rpm
70 mph 5376 rpm
80 mph A big bang (6144 rpm)

While I am at it
3.9 diff at 1000 rpm is 17.64 mph
(50 mph = 2834 rpm, 70 mph = 3968 rpm)
3.7 diff at 1000 rpm is 18.6 mph
(50 mph = 2688 rpm, 70 mph= 3763 rpm)

My brain hurts now

Post by **Onne** » Sun Jan 21, 2007 4:25 pm

My calculation (the bottom ones) are calculated using my own size tyres.
145/80x14 which equals to 23.12 "

Post by **Onne** » Sun Jan 21, 2007 4:36 pm

just calculated some more:
taking my size tyres:
3.7:1 diff = 18.6 mph at 1000 rpm
3.9:1 diff = 17.64 mph at 1000 rpm
4.22:1 diff = 16.31 mph at 1000 rpm
4.55:1 diff = 15.12 mph at 1000 rpm
5.286:1 diff = 13.02 mph at 1000 rpm
5.375:1 diff =12.8 mph at 1000 rpm

Post by **Tris** » Sun Jan 21, 2007 10:43 pm

you had some free time on your hands... so how did you do it? admitedly i only spent 5 min on it when you asked erlier

Post by **grahamt7** » Sun Jan 21, 2007 10:48 pm

My head hurts with the figures too. I think I only just understand what a differential is, no idea what things like 4.22:1 mean...how do I (easily) tell what diff I have fitted?

Wondering whether it was better to remain ignorant.

Post by **Tris** » Sun Jan 21, 2007 10:51 pm

surely that depends on your model, isnt your car a standard 1098? or do some 1098's have different diffs?

Post by **chrisd87** » Sun Jan 21, 2007 10:52 pm

Hmm right so that means that you shouldn't exceed about 97mph with a 1098 engine and diff (6000rpm). Sounds like a target

Post by **Tris** » Sun Jan 21, 2007 10:54 pm

well im sure graham said his record was 92 a while back...

Post by **jonathon** » Sun Jan 21, 2007 10:54 pm

Mind, you will only achieve these theoretical figures on a rolling road, once the other factors such as drag are taken into account they would look a whole lot different in the higher speed ranges. Look good on paper though!!

Post by **chrisd87** » Sun Jan 21, 2007 10:55 pm

Mine's 90!

Post by **Onne** » Sun Jan 21, 2007 10:55 pm

All Series III (1956-1963) were fitted with 948 and 4.55:1 Diff
All Series V (1963-end of production) were fitted with 1098 and 4.22:1 diff

There is an exception to the rule:
All LCVs (1956-end of production) were fitted with 4.55:1 diff, no matter what engine.

The simplest explanation for the diff ratio is that the propshaft turns 4.22 times for one turn of the wheel.

Post by **Tris** » Sun Jan 21, 2007 10:56 pm

aaaw mines only 86...

Post by **Onne** » Sun Jan 21, 2007 11:00 pm

Yes, just calculations