Forum bmwbike.com

I'm looking for a complete final drive 7 x 25 for sidecar use. Offer welcome.

I have not heard of a 7/25 final drive ratio. It might be very rare and hard to find. The proper sidecar ratio for an R69S is 6/26.

It may be easier for you to find a used complete final drive of any ratio, then buy the 6/26 gearset from Huggett or elsewhere, and have the final drive rebuilt with the new gearset.

Thanks for your replay.
7/25 final drive ratio seems to have been mounted on R 50 S. From owner's advice, it seems to be better for sidecar use than 6/26. The reason is that 6/26 is really very short.
Nevertheless, I agree with your solution due to the difficulties to find a complete one.

Here's all the various ratios and uses:
26/6 4.333 (R69S sidecar)
27/7 3.857 (R60 sidecar)
25/7 3.571 (R50S)
27/8 3.375 (US Forks)
25/8 3.125 (Earles Forks)

The 25/7 would be better for the R69S than the 25/8, if the sidecar was small and light. However, if the sidecar was large and heavy, the 27/7 would be better. And if the sidecar was large, heavy, loaded with passenger, equipped with a windshield, and used in hilly country, the 26/6 would be necessary. BMW specifies the 26/6 for R69S with any sidecar.

I had an R69S with heavy Ural sidecar for five years and used the 26/6. The R69S does not have much torque at low to middle rpms.

I now have an R60/2 with a light LS200 sidecar. The R60/2 has so much torque at low to middle rpms that it could pull the sidecar pretty well with solo 25/8 drive. However, I also own an R69US and I moved its 27/8 drive to the R60/2, and this is perfect for the light sidecar.

There is a big difference in way that the R60/2 and R69S engines feel, especially when pulling a sidecar. The R69S does not have good torque and needs a high drive ratio like 26/6 to avoid "bogging down". And although the 26/6 ratio seems so "short" that it might rev-limit the top speed, the extra 1200 rpm of the R69S engine compensates.

If a complete 25/7 final drive from the R50S is available at a cheap price, and you have a small light sidecar, you might be satisfied. But I would not put much money into buying or building a 25/7 drive for an R69S sidecar outfit.

Thanks for advices.
My side is from french make "précision", very similar in weight with the Steib LS 200.
My final drive is 25:8. My bike was built (probably!) in july 67 just before BMW changed the final drive for R69S to 27:8
Another fact is that the rubber is 110/90 x 18 that give also longer ratio.... As it is rather difficult to find correct size for tires, I prefer change the final drive.
27:7 choice has been given to me by a friend who rides his 69S with side since 25 years ! He says that 26:6 is really to short, and as he also own an R 50 S, lucky guy ! he can tell about this.
I believe in any way, that due to difficulties to find those parts, I must be prepared to compromise.
In that way, 27:7 or 27:8 would be correct to fit the bike. If you hear of some.....
Regards
Jacques