highway riding

[shuckclams]

whats going on guys? im working on my first build and learning very slowly as i go. id like to get some better proformance and thought about changing up the gear ratio. id say im mostly riding on the highway but i jam around town a lot as well. any recomendations on a good sproket combo?

 

[burns]

as I am sure you know, sprocket selection balances torque multiplication (accelleration) against cruising comfort. Bigger front/smaller rear favors cruising while the other way around favors accelleration. The best solution is unfortuantely the most expensive: taller 5th gear. Mikes sells the parts.

 

[5twins]

Yes, gear these things "to the moon" like some seem to like doing and although you will get 3K cruising RPMs, the bike will be a real slug off the line and around town. Might as well buy a scooter or 350 Honda, lol.

 

[gggGary]

I have put an hour or two at a time at 70-75MPH on the stock gearing, even on a special it's fine. Note the gearing change is often done the same time as new tires are installed. Fresh tires may make as much difference as gearing in reducing vibration at highway speed. 1000 mile road trips or a bar hopper then a gearing change might be a good idea.

 

[5twins]

I do think these bikes benefit from a gearing change but just a small one - one tooth less on an 18" wheel, 2 teeth on the 16". You wouldn't think such a small change makes much difference but it really does. You get a 3 or 400 RPM drop at cruising speeds without losing the lower gear "grunt" or the pulling power in 5th. Perfect gearing for this motor in my opinion.

 

[burns]

I've been told that there is not much difference in the circumferance of the tires that fit the 16" and the 18" rims. If that is correct the rear sprocket changes would be the same.

Perfect gearing will vary by how much weight you are hauling around of course.

My seat of the pants experiece is that getting the carbs on the button (throttle synch and mixture screw settings) makes a huge difference.

 

[retiredgentleman]

Yes, just changing the rear sprocket makes a big difference on how the bike feels. The 78 Special, in Canada, came with a 36 tooth sprocket on the rear. Yamaha must have thought we pulled logs with our bikes, or else we were big into drag racing.

I used the 36 for one season, and it was just a riot as to its snappy acceleration around town................just perfect to race from one red light to the next red light............not saying I would ever break a speed limit

Put a 33 on the rear, as I like to go on long trips, and the 33 is a good compromise at dropping the rpm.

Now that I think about it, I really miss that 36. If I didn't go out on the highways, I'd still have that 36 on the bike.................high fun factor

 

[jamesgs4]

Yes, gear these things "to the moon" like some seem to like doing and although you will get 3K cruising RPMs, the bike will be a real slug off the line and around town. Might as well buy a scooter or 350 Honda, lol.

I run a 18/30 combo and my bike is not a slug at all, maybe those with slugs need to tune their bike.

 

[Grinder]

Same here, 18/30 and runs great. You will really like it at 60mph. If I rode strickly in town I might change it, but for my riding it's perfect.

 

[shuckclams]

I guess I used the wrong terminology. I'm looking for the the quick easy way to change it up. Not engin gearing but sprocket combination. I'm used to BMX type terminology haha. I'm running a 16' rear and soon to be 21' front. New tires sitting at the house as well.

 

[shuckclams]

So the 18/30 is good all around then is what I'm getting out of this??? Haha

 

[pamcopete]

Here is a Excel spreadsheet that will give you RPM vs MPH for all combinations of sprockets, gears and tires. This chart uses rolling distance, the distance your bike rolls with one revolution of the rear tire. The yellow cells are pull downs for the wanted values.

Revs vs MPH

The chart shows that a 17/33 combo for an 18" wheel is the same as a 17/32 for a 16" wheel, or about 4,000 RPM at 60 MPH in 5th gear.