quick question, for sportbikes like ours, which gear is preferred for a full dyno run? 5th or 6th?

i know harleys are dynoed in 4th normally if they have 5 speed gear boxes. im not sure with the 6 speeds though.

 

I had my bike dynoed just for the fun of it a few years ago. The dyno guy ran it in 4th gear. Also, every bike we saw up there was done in 4th.

I know cars, 5 speeds or 6 speeds tend to run 4th as well. Im not sure why, although I think it probably has to do with 4th gear being the 1:1 ratio for most applications. In a 5 speed, the 5th gear is overdrive. In a 6 speed, the 5th and 6th are overdrive. I would assume it also applies to bikes, that they would run in the 1:1 ratio gear. Just a guess though. I couldn't say for certain.

 

Depends on the type of dyno.

The reason for the 1:1 gear ratio is due to the Dynojet. Dynojet mathematically creates a horsepower number based on mass (which is the known weight of the rollers) and accleration (how fast the car is accelerating the known weight).

F=ma

From force (F), you can calculate horsepower.

Dyno the bike in 2nd gear, and acceleration (a) goes way up, causing force (F) to go way up.

So by dynoing in the gear closest to the 1:1 gear ratio, you eliminate any acceleration advantage or disadvantage caused by the transmission.

As for other dynos out there (i.e. Mustang and Dyno Dynamics) - they use a load cell to measure roll force (the amount of force the tire is placing on the roller). Based on roll force and the radius arm going to the load cell, you get roll torque. Based on roll torque and roll speed, you get vehicle horsepower. Vehicle horsepower and vehicle RPM gives vehicle torque. It doesn't matter what gear you run in on load cell style dynos as they are measuring force, not acceleration. Force does not change from gear to gear.

 

hm ok. mine was run on a dynojet i believe and ran in 5th. ill have to double check. how would the gears effect hp/tq? higher gear = higher hp and lower tq?