Club 80-90 Forums

Has anyone got the equation for figuring out cruising speeds?

I currently have a 1 y 1.9n/a so the top reving speed will be around 4500 RPM and a DM gearbox with a final drive of 5.43, I have 14/185/70 profile tyres

I imagine the engine will be reving it's little head off to get to 70mph?

Thanks in advance

Don't know what the equation is but I try to stick to 3000 rpm. This gives low 60's.

The question was has anyone got the equation to work out engine speed to road speed

Second download in the list here from Syncronauts website:

http://www.club80-90syncro.co.uk/Syncro ... nloads.htm

or html version: http://www.club80-90syncro.co.uk/Syncro ... %20rpm.htm

Main thing is to get your TRC worked out failry accurately (chalk marks on tyre and ground, shove it along a few revs, measure, calcualte, adjust by suggested slip-factor)

Based on a 205/70R70 turning 836rev/mile, you are turning 4000rpm at 62mph. Not sure what your tires will actually turn, but more then a 205/70 for sure. Mark tire and ground, make one revolution, and measure. 5280 divided by feet you measure and you have it. The more revolutions you roll van the better. Let me know and I can plug it into excel

DM, DS 20.5254 11.1858 6.8418 4.62636 0
RPM 1st 2nd 3rd 4th 5th
1000 3 6 10 16
1500 5 10 16 23
2000 7 13 21 31
2500 9 16 26 39
3000 10 19 31 47
3500 12 22 37 54
4000 14 26 42 62
4500 16 29 47 70
5000 17 32 52 78
5500 19 35 58 85
6000 21 38 63 93

found a figure online for your tire size: 860 revs/mile.

DY, DZ, 6D 22.1508 12.0716 7.3836 4.99272 0
RPM 1st 2nd 3rd 4th 5th
1000 3 6 9 14
1500 5 9 14 21
2000 6 12 19 28
2500 8 14 24 35
3000 9 17 28 42
3500 11 20 33 49
4000 13 23 38 56
4500 14 26 43 63
5000 16 29 47 70
5500 17 32 52 77
6000 19 35 57 84


5000rpm at 70mph

Time for better ratio'd box then I think

thanks very much for you help

with my original transmission and stock size tires i could cruise at 88-90 kph [50 mph ] at 3600 rpms, right where the tach needle stops being in the solid green, That was with the 5.5 rear end. Now with a 4.83 diff i can cruise at 105 [65 mph] and around 107-110 with 215/65/16s . I also have a 1.9 na

So the diff is worth 13% and then the tyres are worth 15% on that to give 30% overall (65/50)

I used this to do the working out
http://www.partsemporium.co.uk/rpm&speedcalculator.htm