I have a K75 rear diff on my sidecar. This makes it very "revvy" at highway speeds but is good for starting off etc. I'm considering changing to the standard 2.9 K100 diff (have one in the shed) for general road use. I do get a small overall reduction (2-3%) from the 15" wheel. Any comments?. What ratio are people using on these?

I'm just using the stock RT final drive set-up. I considered using a K75 one but basically I find the standard gearing more than adequate for my own needs. I like that I am still doing the factory ratios and speeds...4grand at 100kph etc. I find the motor produces enough torque to give me enough power all the way through the rev range, which of course is one the K's best characteristics even in solo trim. My outfit is quite light weight, though I haven't ever actually weighed it, I imagine it's lighter than most fibreglass set ups...DJP, HRD etc. In the end I suppose it comes down to horsepower.....and you can basically never really have enough ponies with a sidecar. I recommend the stock RT final drive.

Hi Rockman,
I use the RS gearing with a full profile 145x15 tyre; I don't want to use a low profile as that will lower my gearing. Never had any problems even towing an overweight trailer loaded with my ¼ scale traction engine.

I just love the torque of these engines.

As you have a spare bevel box, go for it, you probably won't notice any reduction in 'get away' speed, you'll just be changing gear a bit later.

Cheers,
Paul.

I am pulling a very heavy EML sidecar and I am using the original RT final drive.
I get a lot of torque and the bike is pulling fast up to 120kms. Sometimes, I would prefer an RS final drive to get a lower engine RPM.
With the 15" wheels, the engine revs at 4 to 4500 rpm at 100km/h.
My problem is that the bike is a pig on gas when riding on the highway. At 100-110, the 7 liters fuel level light comes on at 165km.

CF

I'm still running the lower K75 gearing. I had a good look at the spare final drive I had and the splines are close on stuffed so I wont be using that. At 100 kmh I'm running at around 5000 rpm and get 12-14 km/litre so its not too bad. If I spot a good K100 drive at  the right price It'll go on but I'm not in a hurry. Cheers Phil

I've run RT gearing on most of my previous outfits, it seemed to be the best choice overall. My current outfit is running RS gearing with a 165/80-15 rear.  It works OK, but I'd like to either fit an RT rear or drop the tyre to a 155/80.

Flat running its fine, but it's not that good in hilly country. 

Al