Topic: Battery mounted low in frame?

[johnyvilla]

Anyone have any pics of their battery mounted aft engine in frame? I'm thinking of improving my 750s low center of gravity.

Thanks

[voxonda]

Hey Johnyvilla,

Some do it like this:



Good luck.

[johnyvilla]

That's rad.

[markjenn]

Keep in mind that a lower center of gravity may feel better when rocking the bike at a standstill, but actually hurt handling.  When cornering bikes don't rotate around their tire contact patches, then rotate around their center of mass (COM) and this is a couple feet off the ground.  The tires actually drive out from under the COM.  Much of the work in the last few years with sportbikes has been to centralize the mass of the bike higher off the pavement and nearer the COM.  Your current battery position may be much nearer the COM than having it down near the ground.

- Mark

[davesprinkle]

Keep in mind that a lower center of gravity may feel better when rocking the bike at a standstill, but actually hurt handling.  When cornering bikes don't rotate around their tire contact patches, then rotate around their center of mass (COM) and this is a couple feet off the ground.  The tires actually drive out from under the COM.  Much of the work in the last few years with sportbikes has been to centralize the mass of the bike higher off the pavement and nearer the COM.  Your current battery position may be much nearer the COM than having it down near the ground.

- Mark

And another point of technical trivia is that with a higher center of gravity, a bike will be forced to lean less for a given corner radius and speed.  This is a result of the non-zero width of the tires -- as the bike leans into the corner, the contact patch of the tire moves to the inside of the corner.  This effect becomes more pronounced with wider tires.  Keep in mind that I'm talking about APPARENT lean angle here -- the EFFECTIVE lean angle (angle of the line passing through CG and contact patch) is the same no matter CG height or tire width.  However, apparent lean angle is important because a lower apparent angle will likely yield higher cornering clearance.  (Probably not a concern for our vintage bikes -- if your speed is limited because you're dropping hard parts into the pavement, I applaud your heroism and urge you to trade up your 70's iron for a modern sportbike...)

-dave

[johnyvilla]

That's interesting, and it makes sense. In lowering the juicebox, I was trying to offset the 750s inherent top heavyness. I would like to see her a bit more flickable.

[davesprinkle]

That's interesting, and it makes sense. In lowering the juicebox, I was trying to offset the 750s inherent top heavyness. I would like to see her a bit more flickable.

We should pin down the terms a bit.  By "flickable", you probably mean "low steering torque required to achieve lean angle".  Lots of things affect this, everything from vehicle mass to tire profile to center of mass height.  In very general terms, steering geometry is one of the most dominant contributors, certainly more significant than COM height.  You want to lower steering torque?  Steepen the head-angle, or reduce trail, or do both.  To reduce trail, install triple clamps with more offset.  To steepen head-angle, raise the fork tubes in the clamps and/or install longer rear shocks.

[coyotecowboy]

Just do it like Rob showed ya, he's got more 750 race stuff than anyone should be allowed to have

[ieism]

Try raising the forktubes trough the clamps. This lowers the front and changes the angle of the fork. A good starting point is between 10 and 15mm on our bikes.

[markjenn]

You're not going to make your bike more "flickable" by putting the battery lower.  It's probably optimal where it is.  Good suggestions have been made for other things to try.

- Mark