30 Tooth Rear Sprocket Evaluation

bdholsin

bdholsin

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I'm swapping the stock 34 tooth rear sprocket to a 30 tooth sprocket on my '83 Heritage Special. The parts are expected to be here today. UPS hasn't let me down yet so I'm confident I'll be tearing the rear wheel off by this afternoon.

Stock setup:
Cruising at 70 MPH, I'm turning at about 5,000 RPM.
Current mileage is 50 MPG.
Vibrations are "normal" for these twin cylinder bikes.
Goals: Improve mileage, reduce my cruising (engine) speed and reduce vibrations at highway cruising speeds.

Stay tuned for my report back as I continually update this thread.
 
Here is an Excel spreadsheet that shows MPH vs RPM for all combinations of sprockets, wheels, tires and gears. The orange cells are pull downs to select the desired values. Rolling distance is the distance that your bike rolls forward with one revolution of the rear wheel.

RPM's vs MPH

Using the spreadsheet, you will get 4406 RPM @ 70 MPH and 3777 RPM @ 60 MPH with a 16" rear wheel and a 17 tooth front sprocket.
 
i'll be doing mine today too! I got it sometime last week, but had finals all week. boy, do i love summer. got my new rockhard lid coming in today too!
 
I just finished the 34 to 30 tooth sprocket swap. I have my little one with me right now so I can't ride but at the first opportunity after the wife gets home I'll be taking it out. Stay tuned.
 
I swapped the biggest Mikes XS had on the front and the smallest on the rear. Ups? Better mileage, less vibration, and cruising RPM's much lower. Downs? up hill starts are rougher.

I took that trade off easily since most of my riding (commuter bike) is done on state highways at 55-60mph. I do wonder about running at 4k on the interstate to get to my unit 100miles away though. Is that where these bikes like to cruise at? I'm a bit of a newbie at how these bikes like to run so...

By the way I found the front easier to replace than the back.
 
bd,
Yeah, post your results on that 30T. I was thinking 32 or 33 but maybe I'll go 30. Although I don't want rough uphill starts so maybe 32T is the way to go. My goal is to have a decent highway crusing RPM. I wish there was a way to slide a 6th gear in there!
 
maxwell said:
how long did it take? was it simple?
Click to expand...

20 minutes.
1. Put her up on the center stand.
2. Disconnect the brake rod.
3. Disconnect the tensioner rod.
4. Remove the castle nut cotter pin.
5. Remove the castle nut (1 1/16" wrench by the way).
6. I found that a Craftsman #2 phillips screwdriver works perfect for this part...pull the rear axle out (toward the right) by inserting the screwdriver in the through hole on the right side of the axle. Collect any parts (dust seals) that fall. Your chain tensioner indicators will probably fall as well as the "thread spool".
7. Slide the wheel a bit forward and loop the chain on your left side swing arm to get it out of the way.
8. Roll the wheel back and lay her down (may need to remove the brade drum too).
9. Using a 17mm wrench, remove the six bolts that secure the sprocket. Probably going to need something to flatten out the metal plates that are holding the bolts in place.
10. Put on the alternate sprocket and reverse the above steps for assembly.
11. DON'T FORGET TO TIGHTEN THE TENSIONER ROD NUT!!!!!!!!!!! Here is why.

That should pretty much take care of it. Did I leave anything out?
 
gdcpony said:
I took that trade off easily since most of my riding (commuter bike) is done on state highways at 55-60mph. I do wonder about running at 4k on the interstate to get to my unit 100miles away though. Is that where these bikes like to cruise at? I'm a bit of a newbie at how these bikes like to run so...
Click to expand...

I just don't have too many hills around here to deal with. The few that I'll encounter will just cause a little more of dragging the clutch to get going. I'll be alright.

gdcpony said:
By the way I found the front easier to replace than the back.
Click to expand...

True dat!! <---I can't believe I actually wrote that.
 
Hey.


I run a 17/29 setup with a 18" rear wheel. Find it to be much more useful then 17/34. The engine has the torque to manage that setup.......well, I have 750 pistons installed but with the 17/34 the 3-4 gear are about the same, I think.
/BigBoreSwede
 
Took a quick 2 mile test run tonight. I like the lower engine speed. It is just a tad bit doggy coming off a full stop but nothing that I wasn't expecting. This bike isn't a race bike. I'm using it for the joy or riding and it gets better mileage than my F-150. I'll have more thoughts after this weekend.
 
I take it the same chain was a good length for both the 30 and 34?
 
xjwmx - I'm right at the end of my adjustment. It probably wouldn't be the end of the world if I removed a link to account for chain stretch. For now (since I don't have a chain break tool) I'll be good. I'm hoping to replace my current chain in the not too distant future. I have no clue as to whether it is stock or how many miles are on it. I'll go with the presumption that it is the original stock chain and order a new 530 chain soon.
 
You don't need a fancy tool to break a chain. A demel or an angle grinder, even a bench grinder. Grind the pins down flush with the side plate, Drive the pins through the side plate. The pins should slide out of the links. Now you have a shorter chain.
Leo
 
BigBoreSwede said:
Hey.


I run a 17/29 setup with a 18" rear wheel. Find it to be much more useful then 17/34. The engine has the torque to manage that setup.......well, I have 750 pistons installed but with the 17/34 the 3-4 gear are about the same, I think.
/BigBoreSwede
Click to expand...


With the change I found 3rd and 4th to be much more functional. I do a lot of gear changing in the hills and hollows and sometimes drop her into 1st if it's a 90 degree turn in a gravely intersection, turning to go uphill.....sometimes.
I keep a constant gear count going in my head...OCD? Probably.
 
Well, i'll come out and say it - bike is a complete different bike. it took me a little longer than i wanted it to, but it's what ever. i'm using the same chain, didn't take any links out, but i too am literally at the end of my adjustment - she just barely made it. i'll probably wind up taking a link out myself if i ever get a day with nothing to do on it. i'm going to tighten up the brakes a bit tomorrow, double triple check all my bolts (i still can't believe the sprocket bolts were only 22 ft lb's - can anyone confirm/deny this?), and take her out on the highway with a smile on my face.
 
hmmm.. well, those lock washers were a pain in the ASS. i think what i'll do is monitor it. if anything starts loosening up i'll re-torque em.
 
The manual calls for 22 and it doesn't look like one of their misprints, so I'd be completely and utterly content. Depending on what your po's did, more could have started things stripping and stretching. And that's a sickening feeling. It ain't goin nowhere with those locking tabs. Go a bit over until you get to a flat for a tab, if you have to.
 

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