Topic: Want to change my gearing...

[Venarius]

How many spokes come standard on the front and rear sprockets? 

If I wanted faster acceleration at the loss of topend power (how often to I see 110mph anyway?), would I get more or fewer sprockets on the replacement sprockets.

I need to get both front and rear sprockets anyway (cause mine are worn out), so I thought this would be an easy addition for acceleration...

[TwoTired]

less front teeth or more rear teeth or both= faster acceleration.

I don't know what bike you have for a stock tooth count.

[hcritz]

Smaller front/larger rear will help acceleration....but will add RPM to your cruise.

[cb650]

Too small front could put to much stress on sprocket or chain.




              Terry

[Venarius]

I have a 1981 CB750 C

I'm looking at sprockets from the old bike barn...
Hmm but I just looked again and it appears they don't have any sprockets for my bike specifically...

Any links?

[GroovieGhoulie]

Didn't the early 750s have problems with blowing primary chains from the 16/45 ratio?

How does this ratio compare to the 18/48 ratio performance wise?

[mrbreeze]

DON'T!!!!.....#1 go that small on your front sprocket and #2 buy anything from Old Bike Barn unless you are a glutton for punishment!!!

[DammitDan]

Well, let's give an example...

On my '82 CB650 I wanted lower RPMs at my cruising speed (usually around 60-70mph).  I changed the front sprocket from a 16 tooth to a 17 tooth, and left the rear sprocket alone (38 teeth).  At 65mph, it dropped it from 6300 RPM to 5500 RPM.  I consider that a gigantic difference since I have a 40 minute one way drive to work, and keeping the RPMs down (and in effect keeping the heat down) is nicer to the 24 year old engine.  And for all that I only noticed a very slight loss in low-end acceleration.

I can only assume that making the front sprocket smaller for more powerful acceleration would boost RPMs just as much on the high end.  I wouldn't do it unless you spend most of your time under 40mph.  I can't imagine trying to make my engine run at 7.5k for long periods of time.  Ya gotta admit, these bikes aint what they used to be!

 - Dan-0

[SteveD CB500F]

An '81 will be DOHC - do they have the same characteristics?

[Venarius]

Few things here...

1) Why is OldBIkeBarn so bad?  Why are their products "trouble"?  Has anyone else here had bad experiances with them?

2)What is the difference between a SOHC (Single over head cam) versus a DOCH (is that A Double over head cam?)

3)Good point about the RPM disadvantages of changin my gearing...but as of yet I don't know if I'm worried because I have a 2003 VTX as my main bike...and thats a lot more comfortable for highway cruisin anyway.  With the CB750 cafe I want to build, I'm only looking for a 2nd bike thats fun to throw around in the twisties...so long jaunts on the highway aren't really going to be what it's used for.

[cb(r)]

Few things here...

1) Why is OldBIkeBarn so bad?  Why are their products "trouble"?  Has anyone else here had bad experiances with them?

2)What is the difference between a SOHC (Single over head cam) versus a DOCH (is that A Double over head cam?)

3)Good point about the RPM disadvantages of changin my gearing...but as of yet I don't know if I'm worried because I have a 2003 VTX as my main bike...and thats a lot more comfortable for highway cruisin anyway.  With the CB750 cafe I want to build, I'm only looking for a 2nd bike thats fun to throw around in the twisties...so long jaunts on the highway aren't really going to be what it's used for.

type in "sprocket ratio" in for a search. we had a similar discussion about a week ago. It will help out about understanding part of you sprocket question. 

[eldar]

the problems with bike barn are that they can take forever on shipping and think they are bike gods and look down on anyone who questions them. Their biggest problem is rudeness.

depedning on what you want to do with gearing, changing the rear sprocket affects your ratio less than the front does. 3 teeth on the rear equals 1 tooth on the front. You can fine tune easier by changing the rear.

[SteveD CB500F]

Here's the story on Old Bike Barn:  http://www.sohc4.us/forums/index.php?topic=7235.0

SOHC is what this site is all about. DOHC site is here: www.cb1100f.net

[byidesign]

Do remember, that a change of one tooth smaller on the front,
      is close{ratio wise} to adding three teeth on the rear {to gear for more power,higher rpm}

     Or do the  the reverse to cruise at lower rpm.

             Hope it helps
                       bruce

[cd811]

I started my project with 16/44...at highway speeds the motor would scream...sounded like I needed to shift...so I went to 18/44...more better ...will spin a wheel in 1st and 2nd and still rpm's are nice at hightway speeds...I've got gone results ordering parts from denniskirk.com....lowridersbysummers.com...cr2omline...partsnmore

[neilbron]

Hi guys,

It seems that gearing issues crop up fairly frequently on this and other motorcycle sites, and the math(s) causes some people quite a bit of confusion. On the yahoo cb750 group one of them members wrote a small basic program specifically for nighthawk gearing, but it is in DOS and a bit clunky (no offence meant).

Although I'm not a programmer by any means I have written a simple Microsoft Excel calculator based on Jeff Saunders post of Feb 27th which will allows you to calculate your new speed or new RPM with different sized sprockets.

Is this of interest to the forum, and if so how could I send it?

Cheers,

Neil.

[Bob Wessner]

Is this of interest to the forum, and if so how could I send it?

I can check with Glenn to see if there is some way to host it on site someplace for folks to download it for use. How large is it?

Wouldn't be called Gearcalc would it?

[neilbron]

Hi Bob,

Its only 19 KB, and isn't Gearcalc (just had a look at that - its a bit more sophisticated than most of us would use I think).
As is said earlier - I'm no programmer, but this will give a quick idea of how speed or rpm will change with different sprockets. And it runs in Micrososft Excel, which most people would have. And of course the calculation was originally posted by Jeff Saunders, so I am not the brains behind it.

Here's a cut and paste version (which looks a bit odd due to the format):
                                                    Input your    Results calculated
                                                   data here       here
Current setup     front sprocket             17   
                   rear sprocket                    47   
                   ratio (rear / front)                         2.76
New setup     front sprocket                18   
                   rear sprocket                   48   
                   ratio (rear / front)                         2.67
Speed calc      current speed  @ XXX RPM   65   
                   new speed      @ same RPM          67
RPM calc       current RPM   @ YYY speed   4500   
                   new RPM   @ YYY speed                4340

I can pm you or Steve with the file if you like. If it's not usefull, no probs.

Cheers,

Neil.

[Bob Wessner]

Sure, go ahead and send it, can attach it to an eMail if you like. I'm sure folks would like to have it available. I thought Gearcalc was pretty sophisticated also, seemed more for someone contemplating designing a transmission or modifying one.