Topic: 836 drag gears Q?

[Don R]

 1/4 mile, street bike  mildly built 836, ported, cam, 4-1 early carbs. 17/48 gears OK to start with?  I've been a car racer for years, I know in our car, anything I can gain in 60' will be double at the other end.
  Gotta start somewhere.

[754]

I liked 17/54 but ran mostly 1/8 mile.. And street.. Probably. Be ok for 1/4
Then to run on highway for long rides I would switch to 19 on the front.

[scottly]

With a 48 tooth rear and a 17 front, which is close to Frank's 19/54 combo, my bike runs about 110 MPH @ 8850 RPM in 4th gear, according to the dyno. The smallest front sprocket you should run is a 16, which I have run on the road with a 48 rear, but it was a bit too buzzy for long trips, and the small sprocket size is harder on the chain. An 18/54 is the same as a 16/48, but since rear sprockets are more expensive than front sprockets, the 16 is a good choice for drag racing. If you feel the need for lower gearing than 3:1, you will need to go to a larger rear sprocket.

[madmtnmotors]

My current 17/48 setup with C.I. 836 pistons puts me right at redline in 4th gear at the finish line. Getting ready to bolt on a larger rear sprocket, and if that ain't enough, I'll bolt on a 16T front.

[Bill/BentON Racing]

We ran 16/52 on the auto and 16/50 on my CG. Now running 17/52, but have a 54 and a 50. I have to use 5th or I hit the rev limiter in 4th, ask me how know, lol, Bill

[SBR-CB400F]

I am running with 16/52 on the monster for the 1/4 that puts me on the limiter in 5th going over the line. I drop it down to a 15 on the front for 1/8 mile racing.

[madmtnmotors]

I am running with 16/52 on the monster for the 1/4 that puts me on the limiter in 5th going over the line. I drop it down to a 15 on the front for 1/8 mile racing.

Yep, I'll be changing to 17/52 and I'm pretty sure test-n-tune will reveal 16/52 to be the sweet spot. 

Switching from 17 to 16 will lengthen the wheelbase too! 

[dragracer]

I'm using a 17 tooth Cycle Ex offset front sprocket and a 51 tooth rear. I'm using 5 th gear in the 1/4 but not on the light until well after the trap. I need to re-gear at some point to lower my,60' and ET.

[scottly]

16/48=3:1
17/51=3:1
18/54=3:1

[dragracer]

Yeap, simple division gets it down to true ratios.

[Bill/BentON Racing]

Yep,  mines a 17 off set also. 17/52....,but you don't need to go any quicker, lol.

[scottly]

Yep, I'll be changing to 17/52 and I'm pretty sure test-n-tune will reveal 16/52 to be the sweet spot. 

Switching from 17 to 16 will lengthen the wheelbase too! 

If you are changing rear sprockets, consider a 54; this will give you a range of 3:1, 3.176:1, or 3.375:1, depending on if you use an 18, 17, or 16 front.

[dragracer]

Kinda locked in on the cycle ex offsets to 17 tooth the last time I bought one. Hope they're producing a 16 tooth by now. I prefer changing the front versus the back. Chain length becomes an issue otherwise which does affect wheelbase like Wilbur mentioned. Drag racers want to be longer, not shorter. Lol.

[Bill/BentON Racing]

They ain't making any 16's offsets yet! As of a couple months ago.

[dragracer]

They ain't making any 16's offsets yet! As of a couple months ago.
[/quote

They ain't making any 16's offsets yet! As of a couple months ago.

Ahhh , dang it!!! Might need to buy a new chain cause I'm not shortening up!!!!

[Old Scrambler]

Good discussion

For other readers, consideration for the tire diameter, and the load placed on the out-put shaft (bearing) should also be considered. The later model K and F motors have a much beefier out-put shaft and bearing to help to take the flex-load of the off-set sprocket and wider tire. For extreme motor-builders, further consideration has to be given to the internal harmonics of the power-strokes to the complete drive-train.............or teeth will be broken

[Don R]

 The bike had 17/48 with the 1124cc motor when I got it but that could have been changed because it sat in the bike shop for years and got parted out a little. It had an early 18" rolled rim, that's why I bought it. That rim came off the sandcast bike in the same shop and I'd already bought it. .
 The wheelie bars were gone and it had gummed up stock round tops on it. The fiberglass tank was also gone but I found one unused since the 80's.
  I know he had pegs on the swingarm, after launch he laid as flat as he could and shifted with his left  hand, he was locally famous for that. I think he told me he didn't get into 4th gear.  He also used cb400f handlebars, ard mag and a drag specialties small tach.

[scottly]

Using Bill's last dyno test as an example, he should chose a gear ratio that allows the RPM at the end of the strip to be about 8900 RPM, the peak HP point, but his motor makes nearly the same HP from about 8500 to 9300. His shift points should be evenly split on either side of the peak; say, for instance, pulling numbers out of a hat, there is a 1000 RPM drop when shifting from forth to fifth gear, you would shift at 9400.

[Bill/BentON Racing]

Right now, I shift 9500-10,000 rpm's. Going set shift light to 9500 rpm's. Our easy up died a horrible death at the high winds we experienced Saturday!  Lol.

[scottly]

Sorry about the EZ-up; glad it wasn't You!!
So if you shift at 10k, what is the RPM drop? I hate pulling numbers out of my a.. um, hat.
Your motor does have 105 HP or more from about 7500-9800...

[Bill/BentON Racing]

Roughly 500 rpms.

[Don R]

 Here is a combo of my 836 bike and the drag bike parts.