Matching rear tire size with final drive ratio

[skyler.robbins]

Hello Gang,
I picked up a 1957 R60 last weekend.
It needs new tires.
I’m going with the 3.50x18 for the front, but would like to install a 4.00x18 for the rear like how my 1969 R60US is set up.
Is that possible with this bike, or is it not recommended because this has the Earles forks and my US has the telescopic?
Also..
The final drive is marked 32/11 and speedo is 1.6
How much would a taller rear tire effect this?

Thanks all!

[schrader7032]

Not sure why want to use a taller tire on the rear of the '57. It's going to change the speedometer response, will change the handling geometry of the bike, and may have an impact on the acceleration performance. I'd just keep the 3.50x18 on the rear and enjoy the bike.

[therealkennyboy]

If the final drive is truly 32/11, the speedo should be a 1.12 (mph) or 0.7 (kph) to read correctly with standard (3.50x18) tires.

The 1.6 speedo is for a 25/6 rear end, which is typically used for the R50 and R69 side car drive. The R60 S/C used a 27/7 rear end (and either a 1.44 [mph] or 0.9 [kph] speedo).

It is certainly possible a PO changed the rear end gearing--the only way to figure out what you have is to either count the gear teeth (if you are taking the rear end apart to put new seals in) or spin the engine and figure out the engine revs to rear wheel turns. A quick site search should detail how to perform that procedure.

[Slash2]

Don’t do it. These bikes behave better with 3.50x18 on the front and rear regardless of model or year.

[mcsherry1328]

I agree, that's a good recommendation, stay with the 3.50 x 18 front and rear.

[weh8127]

We've had this conversation before. Duane's article on neutral steering and tire size explains things well. https://w6rec.com/bmw-motorcycle-neutral-steering/

[skyler.robbins]

Thanks everyone!.. just ordered two 3.50x18 tires…