70/75 mph all day long

[Barry]

Is there any chance that the final drive inscription says one thing but the the "guts" are different? Is it usual for a rev counter to give wrong information?

I would think it more likely that the rev counter is reading high.

The speedos also have ratios to match to the final drive which would be 1.267 for a 31/9 final drive and W1267 should be printed on the bottom of the speedo face under the MPH mark

[Adamastor]

If my rev counter is reading high that could be quite bad -> means my idle is too slow = poor lubrication at idle :|

[Rob Valdez 79 R65]

If you have a nice, smooth idle that is not too fast, that is all you need.

It is possible to have a different gear set installed in your final drive housing, but I'd say pretty unlikely.
If you are really worried about it, you could disconnect the u-joint from the transmission, and count the number of times the universal coupler turns in one revolution of the rear wheel.
This will tell you give you the ratio of the gears.

[Lucky_Lou]

The R45/65 Riders Handbook gives graphs of speed/rpm in kmph in all gears at 5000rpm it should be doing 120 kmph in 5th.There given  towards the end of the document.
Lou

[Adamastor]

The R45/65 Riders Handbook gives graphs of speed/rpm in kmph in all gears at 5000rpm it should be doing 120 kmph in 5th.There given  towards the end of the document.
Lou

Hmmm.. Although I still can't test it, I am pretty sure at 5.000 (on my counter) she aint doing 120 km/h (on my speedometer). I will test the speedometer with a GPS tommorow. Hopefully it shows less than it's true (although that would be odd).

If not I will try to check the final drive both the incriptions and count the rotation of one wheel turn.

Thanks for the tips, I will keep you posted..

[Bob_Roller]

I checked my speedometer to tachometer readings on the way to work this morning .

70 mph indicated (68 mph actual) tachometer 5200 rpm .

[Barry]

Here is a table of calculated revs vs mph for the 3.44 final drive and assuming a 4.00 x 18 rear tire (Metric tires will have a different  diameter).  These figures correlate almost exactly with the 120KPH =  5000 rpm in Lou's BMW handbook. Another accuracy check is that speeds in the intermediate gears at 7500 rpm are also given in the handbook and they check out with this table.
If anyone wants to substitute different final drive ratios I can e-mail you the spreadsheet.
Just remembered I can't post an Excel file but I can if it's zipped

[Bob_Roller]

I've got the 3.56 final drive .

[Barry]

Bob

Here's the table for the 3.56 final drive.

Note a 32/9 is really 3.556  and the calculations use this precise figure even though it displays the rounded up figure of 3.56 at the top

[Lucky_Lou]

Purely in the intrests of science and our members i did a test today...
5000rpm = 75mph
6000rpm = 90mph
7000rpm = yeh baby its a 3.44
Lou

[GrimReaper]

 Any info about 3.36 or 37/11 that I have on my '87

[Barry]

Purely in the intrests of science and our members i did a test today...

Lou

I can hear it now "sorry officer I was only doing 90 mph as an experiment to check some figures for my mates in the R65 forum would you mind confirming the speed for me from your calibrated police speedo"

Yours sounds spot on.

[Barry]

Any info about 3.36 or 37/11 that I have on my '87  

You should be able to substitute your ratio in the spreadsheet If you have access to Microsoft Excel or Open office would also work.

Let me know if you can't open the file and I'll post an image of your figures.

[GrimReaper]

Thanks Barry I am working right now and I am using my phone to access the site.Don't have ME or Office on it

[Barry]

Ok here's the 3.36 calcs