38 tooth gearing experiment

[Growl]

So far I have run 30, 34 and 38 tooth rear sprockets. All with 17 tooth front. I really liked the 30 tooth for all around use. One thing has become clear. The changes have less impact on low first gear than on 5th. Now that my bike is set up for exploring on back mountain roads (some are gnarly dirt roads) I gave the 38 tooth a try... I'll stick it with maybe until I have the carb tuned right, but probably will try the 36 tooth next.

 

[pamcopete]

Growl,

Here is an Excel spreadsheet that shows RPM vs MPH for all combinaitons of sprockets, gears and wheels. This sheet uses rolling distance for one revolution of the rear wheel as a more accurate measure than tire diameter or circumference. Just pull down the numbers in the yellow cells for the numbers you want.

RPM vs MPH

 

[XS650D]

I run the 17/30 tooth set-up on my 77 standard and really like it.I find thease bikes have lots off pull off the line stock so they can afford some loss there to make hwy cruising a lil more enjoyable.I have very lil vibs on my bike,definately no more than a rubber mounted 08 Sportster 1200 that i had.I have ridden other stock 650,s and my hands would go numb.I also have wider handle bars with bar end weights and thicker rubber grips,the wheels are balanced perfect,chain aligned ,carbs set perfect and all rubber bushings are new.I think if u can address all the little things,together they all add up to a much smoother running bike.

 

[fredintoon]

Hi Growl,
pete's comprehensive spreadsheet gives you the numbers.
All I can offer is a seat of the pants comparo.
Assuming that an XS650 solo on back mountain roads would be happy running the same gearing as my XS650 & sidecar on the street:-
I got a 38T sprocket when I first attached the Velorex and found that it's 17/33 solo gearing took more clutch slip to pull away than I was happy with and running mostly in 4th while using 5th as an overdrive didn't please me neither.
17/38 worked great in city traffic but revved too high for comfort at highway speed.
So I swapped back to the 36T sprocket that the bike came with when I bought it.
Like Goldilocks and baby bear's porridge, 17/36 was just right.

 

[Growl]

Thanks Gents! Pete, I have used your spreadsheet before but I am glad that I looked at it again. I will play with it some more, particularly to see what Heiden's "wide ratio" gears actually do.

Fred, actually not solo. If this bike were primarily for solo use I would try 17/33 gearing. The mission for this bike is to get my wife and I out into the back country exploring.

When you ran a side car did you use an oil cooler?

 

[Growl]

Yo XS650 Addict... I hear you about the little things. I've been fussing with it getting the little things right. That's why I am switching to a single carb that hangs off to the side in plain daylight... so I can fuss away with the jetting. Imagine a jetting change that takes 5 minutes! Hopefully the single carb manifold will provide a reasonably balanced charge to each cyl.

 

[fredintoon]

Thanks Gents! Pete, I have used your spreadsheet before but I am glad that I looked at it again. I will play with it some more, particularly to see what Heiden's "wide ratio" gears actually do.

Fred, actually not solo. If this bike were primarily for solo use I would try 17/33 gearing. The mission for this bike is to get my wife and I out into the back country exploring.

When you ran a side car did you use an oil cooler?

Hi Growl,
Heiden's alternate primary gearset spins the clutch faster than the stock gearset does.
This is claimed to increase the bike's gearing options.
Solo in the sense that the bike only has two wheels, not three.
For two-up solo work on back roads your use of 17/36 or17/38 sounds about right; especially with those big fat saddlebags loaded full.
Use an oil cooler in Saskatchewan?
Except for perhaps two weeks in mid-August it'd be more appropriate to fit an engine blanket, eh?
Mind you, we did a Geezers on Wheezers tour on my XS11 sidecar rig in 105ºF Montana and it survived that OK without having an oil cooler.
My wife and I suffered more than the rig did. Stopping our tour every mid-afternoon and cooling off in a motel pool was about the only thing that kept us from mutual murder.
The tour participants who'd opted to camp out swapped to motels after the first night.