If you like our site, please consider joining our club!
By joining you will help ensure that we can continue to provide this service
JOIN HERE!

Final drive gear ratio

User avatar
wa1nca
Posts: 1213
Joined: Thu Sep 27, 2012 5:15 pm
Location: Ashfield Ma
Has thanked: 6 times
Been thanked: 12 times

Final drive gear ratio

Post by wa1nca »

35/11 final drive gear ratio is 3.18
25/8 final drive gear ratio is 3.12
gear ratio almost the same

What is the difference
Does one have a better top end or low end better than the other
Tommy
Tommy Byrnes
54 R51/3, 55 R50/Velorex 560 sidecar, 64 R27, 68 R69US, 75 R75/6
Ashfield, Ma
USA

Daves79x
Posts: 680
Joined: Sun Aug 09, 2015 8:13 pm
Location: Knox, PA. USA
Been thanked: 2 times

Re: Final drive gear ratio

Post by Daves79x »

The 35/11 is just a little shorter. BMW used both ratios in the '50s, and I think used the same speedometer ratio of 1.2.

Dave
Dave

User avatar
Flx48
Posts: 259
Joined: Sun Oct 25, 2020 3:11 pm
Location: NW CT
Has thanked: 2 times
Been thanked: 5 times

Re: Final drive gear ratio

Post by Flx48 »

Hi guys-
I'd always gone with the ASSumption that the 11/35 gears basically were used in the '50s models, while the 8/25 was with the '60s bikes.
This conclusion only from looking at the instruction and shop manuals of the day, and my cursory observations of different bikes through the years.
I figured it was probably a cost cutting measure, to simply have to cut thirteen less teeth for basically the same ratio.
(no doubt there's someone out there that can sense the difference of a 0.05 ratio in use, but it's not me)
Using the same speedo also makes sense; again would a different speedo ratio be warranted for 0.05?
Seems one could have that much of a difference by virtue of their tire choice.
Best-
George

User avatar
vechorik1373
Posts: 260
Joined: Fri Oct 27, 2006 3:00 am
Been thanked: 15 times

Re: Final drive gear ratio

Post by vechorik1373 »

I have seen R69S's with the 35/11 gears. In my experience, the down side of the 35/11 is the ring gear teeth are not near as robust, and I have seen them break the teeth off the ring gear. Not always, but sometimes. Just for your information...
Vech
Technical Adviser, Former owner, Bench Mark Works
662 312 2838 cell 9 am to 4pm CST PLEASE!

User avatar
wa1nca
Posts: 1213
Joined: Thu Sep 27, 2012 5:15 pm
Location: Ashfield Ma
Has thanked: 6 times
Been thanked: 12 times

Re: Final drive gear ratio

Post by wa1nca »

Thanks
Tommy
Tommy Byrnes
54 R51/3, 55 R50/Velorex 560 sidecar, 64 R27, 68 R69US, 75 R75/6
Ashfield, Ma
USA

sherman980
Posts: 149
Joined: Fri Oct 27, 2006 3:00 am
Has thanked: 1 time
Been thanked: 9 times

Re: Final drive gear ratio

Post by sherman980 »

Been a while since I've looked carefully, but pretty sure the original 35/11 ratio came in the early unvented rear drive case and the 25/8 came in the later vented rear drive case. Don't think I've seen an original of either in reverse. Could be wrong here, but worth a good look if you're trying to get it "right".
Thanks.
Chuck S

Wayne J in MA
Posts: 91
Joined: Fri Nov 02, 2012 8:18 am
Has thanked: 1 time

Re: Final drive gear ratio

Post by Wayne J in MA »

My early ‘62 R69S has an unvented 25/8 final drive.
'62 R69S, '71 R75/5 SWB, '78 R100S Motorsport
Westwood, MA USA

sherman980
Posts: 149
Joined: Fri Oct 27, 2006 3:00 am
Has thanked: 1 time
Been thanked: 9 times

Re: Final drive gear ratio

Post by sherman980 »

Did a bit of looking deeper into this. I have factory parts books from March 1956, August 1961 and March 1966. The non-vented housing is the only one shown in the '56 book along with the 37/11 rear drive for solo R50 and R69 machines. By late '61, the non-vented housing is still the only housing shown, the 37/11 rear drive is still shown for R50, R60 and R69 solo machines, but the 8/25 rear drive is also listed for these and for all /2 solo models except for the R50S. I'd guess that at some point after '56 and before '61, the 8/25 gear set became the standard production set? The '66 parts book no longer lists the unvented housing or the 37/11 rear drive, and the 8/25 gear set is the standard at this point for solo machines. There are also a wide variety of rear drives available for sidecar use with different models through the years, but I did not attempt to track these. There are also a wide variety of speedometer ratios listed in each book to go with the various rear end ratios, but way too much info for this post.

Anecdotally, I went back and looked at pics of bikes I've owned over the years. I owned a 1958 R50 with a non-vented 37/11 rear drive, a VERY original 1961 Dover White R69S that had a vented rear drive housing (I don't have any info on what ratio it had at this point), and a very original 1962 R50S with a vented rear drive housing and 25/7 rear drive.

Does anyone have any parts books dated in between mine? I'd be curious to know when the 25/8 ratio was actually introduced and when the vented housing went into production and became standard.
Thanks.
Chuck S

User avatar
schrader7032
Posts: 9016
Joined: Fri Oct 27, 2006 3:00 am
Location: San Antonio, TX
Has thanked: 2 times
Been thanked: 29 times

Re: Final drive gear ratio

Post by schrader7032 »

The library link in the Knowledge Base shows a 1963 and 1965 parts list for the R60/2.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

sherman980
Posts: 149
Joined: Fri Oct 27, 2006 3:00 am
Has thanked: 1 time
Been thanked: 9 times

Re: Final drive gear ratio

Post by sherman980 »

Took a look at the KnowledgeBase Parts books (thanks for the reminder that they're there!).

The November 1963 Parts book shows both the 37/11 (for the earlier models) and 25/8 (for later models) ratios available. It also shows what I believe is the vented case part number (ending in 306) listed but the exploded parts drawing still shows the unvented case and the actual vent, cap and screw that hold it in place are not shown in the parts list....

Looks like 8/25 was the standard solo ratio by February 1965. The 37/11 ratio is no longer listed here. What I believe is the vented case part number (ending in 306) is listed but the exploded parts drawing still shows the unvented case and the actual vent, cap and screw that hold it in place are not shown in the parts list....

Does anybody care about this stuff or am I just talking to myself... ?
Thanks.
Chuck S

Post Reply