I got a killer deal on a SE 6 speed gear set, Paid my indy to install (no Garage or special tools) Shifts great and the overdrive is nice to have to have but with the extra power I have with the 103" I could have just changed the pulleys and got the same top drive gear ratio. I have never gotten a good explanation on which is better the DD or OD, the final drive ratio is the same for the most part, the DD changes the output gear and the OD is a true OD but the RPMs at MPH are the same if I'm not mistaken, so which has the better mechanical advantage?

 

Interesting question. Stock Harleys since the 5-speed days have had a high top gear, which while direct drive, has the effect of providing an overdrive style ratio. From an efficiency point of view, a direct drive gives best numbers, in other words lowest power consumption. The clutch (input to the trans) and output shaft (to the front pulley) are essentially locked together, so the only power consumed is as windage (turning all the gears and oil over, even though they are non of them driving anything).

Getting around to answering your question, a DD trans would be best, as long as top gear is usable most of the time. If the performance of the engine is such that it is necessary to keep changing down to a lower gear, then mpg is likely to go up, because of power losses inside the trans.

On the other hand if top gear is only used on the open highway and fifth is more useful at other times, then an OD would be the better choice, because fifth, on most Harley 6-speeds that are OD, is direct.

Hope that all makes sense!

 

Get that thing in!!!!
Your gonna love it, I have about 1000 miles on mine and its WAAAAAAAAAAYY better than the stock 6 sp.

No 1st gear clunk and better gear ratios, click click click shifts!!

 

All I can say is wow, wow, wow and grin from ear to ear. Festus your post is exactly correct. This transmission is simply awesome! Click click click into all gears and neutral is found so smoothly. Neutral was next to impossible to find with my old six speed. I also love the closer gear ratios. My bike feels like I just gained horsepower and torque. I also love the lower first gear. First gear is now like it should have came from the factory. I had a harley mechanic friend install the transmission as the special tools required were going to cost me over $600.00. We documented the install with pics which I will be posting in a few days. The install was pretty simple. Took longer to remove the exhaust, starter and primary stuff than it did to remove and install the transmission.