On woods web page some of his cams have comments like this cam likes 3.37 gear ratio or this cam needs gearing. What does he mean? On the Big Boyz web site using his calculators for my year bike (2007 big twin) and drive train it tells me that with engine sprocket and clutch basket sprocket 52x69 (open belt drive) is a primary drive ratio of 1.327 and my transmission sprocket 24 and rear wheel sprocket 51 (chain drive conversion) is a secondary gear ratio of 2.125. Do you add the two ratio's together to come up with over all gear ratio? It says on Big Boyz site that 1st gear is 3.37 ratio. Is this what woods is referring too. Please someone explain what these ratio's mean?

 

The top gear ratio is the one that's usually considered when choosing a cam. Your '07's is 2.79.

 

How did you come up with that figure RK4ME? Are you talking stock (07) 6th gear being 2.79? If thats the case then the gearing calculator is saying when I put in my gearing numbers it comes up 2.82 for 6th gear. Please explain if you don't mind. Thanks.

 

Yeah, top gear is what they are talking about....'99-'01 FI Twin Cams cam with 3:37 gearing. All other 88" 5 speed bikes were 3:15. I don't know the final gearing of an '07 but 2.79 sounds right for a 6 speed.

 

Gear ratios and sprocket specs are typically in Specification sections in the Owner's Manual.

 

Just a guess - it may mean that the cam produces tq in a higher rom range than others and is better suited for lower geared bikes. Otherwise you may have to downshift more, more prone to pinging... Its smart that they take gearing into account when choosing a cam.

 

Before the advent of the six speed transmission and since 2002, all Harley's run 3.15 final drive ratio; 25/36 primary ratio of 1.44 and secondary ratio of 2.1875. Mulitply the pirmary times the secondary for the final drive ration; 1.44 x 2.1875 = 3.15. When the TC engine was introduced in 1999, the carbed touring bikes were fitted with 3.15 final drives and the EFI touring bikes were fitted with 3.37 final drives. The 3.37 final drive was achieved by changing the primary sprockets from 25/36 to 24/37. In 2002, all touring bikes were fitted with 3.15 final drives. The 24/37 primary hardware is still available and some of us five speed guys that don't believe these bikes need six speeds will convert the 26/36 primary to a 24/37 primary. This change will do more for a stock TC88 than a 95" upgrade or addding cams. Highway cruise rpms increase about 200rpms but the low end torque improvement is significant. Combine the lower primary with more cubic inches, cams and headwork and the lead sled doesn't become a Hyabusa but rear tire longevity is reduce significantly.

When Woods, or any other cam vendor, says a particular cam likes 3.37 gearing, they are simply saying that the cam may be a little soft on the bottom end and likes the higher rpm ranges.

 

That is a good explanation thankyou. Does this mean that lowering your primary drive ratio will give you better bottom end or torque off the line? While overall drive ratio or final drive ratio affects top end or cruising?

 

So it sounds like the gearing change should be my next performance mod.

 

Not really. The final drive is a function of the primary and secondary drive and will determine both low end acceleration and highway cruise rpms. A lower final drive ratio will accelerate faster through the gears but will require more rpm to achieve the same highway cruise speed as a higher final drive ratio. 3.37 is higher numerically than 3.15 but lower in terms of gear ratio.