Rear Sprocket

xsleo · Posted: July 1, 2009, 2:22 am Post subject: Re: Rear Sprocket

That's what Ivan's gears do. With the lower ratio the trans input shaft spins faster than stock. Faster input = faster output = faster wheel speed at any given engine speed.

650skull · Support Staff Joined: Jul 19, 2007 Posts: 1186

yamaman wrote:

Standard primary gears are 27 - 72 so ratio is 2.666:1
Ivans primary sets are 20% taller so they should be around 2.133:1

Ok, apparantly Ivans primaries are 32 - 69 gears, giving a 2.156:1 ratio

Skul, could you count your teeth & make sure thats right please?

Yea confirmed 32/69 So your equations are on the money yamaman

highspeedhamish · Full Member Joined: Jun 25, 2009 Posts: 62

Good news all. The XS 650 (1979-81 model year) has been added to the gearing commander website.

Based on the following:

Brand: Yamaha
odel: XS
Version: 650
Year: 1979
>--------------<
axRPM: 7000
TireWidth: 130
TireAspect: 90
TireDiameter: 16
PrimaryDrive: 2.666
FrontSprocket: 17
RearSprocket: 34
Gear 1: 32, 13
Gear 2: 27, 17
Gear 3: 26, 20
Gear 4: 23, 21
Gear 5: 22, 23
Gear 6: 00, 00
ChainPitch: 530
ChainLinks: 108

Enjoy!

wally · Posted: August 2, 2009, 5:31 am Post subject: Re: Rear Sprocket

wally wrote:

I have ridden with the club member & his primary geared bike
It gets along I can tell you, don’t know what sprocket set up he had
he was hard to keep up with thats for shore
He also racers a 650
Not many sets left for sale by the way

www.xs650.org.au/Racers.htm
www.xs650.org.au/The%20Pits.htm

Rode again with Ivan today doing same freeway speed but me at 4000 rpm & him with his primary gearing on 3000 rpm

jmstrand · Full Member Joined: Jan 18, 2007 Posts: 23

Pardon me for being slow. I am switching out my rear tire and rim for a 160/80-18 setup for my track/street bike and would like to know what size rear sprocket would put me at the same gearing as stock. I'm actually gonna prolly go up a tooth or two from stock to get a lil more get up and go out of it. Any thoughts. The motor will pretty much be all stock, except for a port and polish job, track exhaust, and flat slide carbs. So looking for a recomendation as far as gearing with my slightly larger tire. Thanks!

jmstrand · Full Member Joined: Jan 18, 2007 Posts: 23

Sorry typo, the rear i'm running is a 160-60-18.

jayel · Posted: November 3, 2009, 1:22 pm Post subject: Re: Rear Sprocket

jmstrand wrote:

Sorry typo, the rear i'm running is a 160-60-18.

here's a gearing calulator

www.rbracing-rsr.com/gearspeed.html

width of the rear tire doesn't matter but dia. does, also I wouldn't worry about tire "growth" with a street machine

pamcopete · Posted: November 3, 2009, 1:57 pm Post subject: Re: Rear Sprocket

jmstr5and,

Well, if it's not too late, you should figure out your rolling distance before you change out your existing tire. Then, when you install your new size tire, figure out its rolling distance as well.

The reason for this is that it is impossible to calculate or even measure the effective circumference of a motorcycle tire. A motorcycle tire has a circular cross section and, therefore, an infinite number of circumferences. Brand of tire, tread design, inflation pressure, and other factors will influence the effective circumference. The only accurate way to figure out the effective circumference used to calculate RPM vs MPH, is to roll the bike forward for one revolution of the rear tire. That distance is the effective circumference.

This spreadsheet uses roiling distance to yield RPM vs MPH for any combination of gears and sprockets on the XS650.

www.amckayltd.com/xs650revs.xls

The gearingcommander site also allows you to input the rolling distance, which they simply call circumference, to obtain a more accurate calculation.

Here's how to find the rolling distance of your rear tire:

1. Mark the sidewall and the floor.
2. Roll the bike forward until the Mk on the sidewall is once again on the floor. Mark that spot on the floor.
3. Measure the distance between the two marks on the floor. That is your roiling distance.

For greater accuracy, you can roll the bike forward for two revolutions of the rear wheel and then divide the distance by 2.

jmstrand · Full Member Joined: Jan 18, 2007 Posts: 23

Sounds like a lot of work just to get me in the ballpark. LOL. Well I am going to have to get a custom sprocket made for this bike anyways and I'm OK with just getting it close and can always fine tune later. Even if I'm damn close to stock, but maybe a touch lower geared (more RPM for given MPH) I think I can go from there? No? I'm trying to get parts rounded up before winter to get this build rolling, but won't have the tires built for a month or two. Im using a HD aluminum hub laced to a WM9 Sun rim with the 160. I have a 1/4 offset sprocket from Gary Poh and just wanted to get a rear sprocket so I could get some measurements and buy the one I will be using in the end. I'm not even for sure the 1/4 offset front sprocket will clear a 160 (Gary suggested he thinks it will) so Im in the process of trying to round up a rear sprocket to give me something to measure from for an offset spacer I'll need to machine.

yamaman · Posted: November 3, 2009, 3:10 pm Post subject: Re: Rear Sprocket

Why you'd want to gear a XS beyond 17-34 is beyond me, most go the other way............Have you ever ridden it? Ever ridden a trials bike? lol

That tyre is not going to be a hell of a lot different to a stock 18" wheel. So in the main, you'd want a rear sprocket in the low 30's. Of course if you want to run a 45 tooth rear, well thats fine too.........Be sure to keep us posted! Cheers

jmstrand · Full Member Joined: Jan 18, 2007 Posts: 23

Sorry. For some reason I was thinking stock was a 36 tooth. Working on to many bikes!! Lol. I'll look around for a 31 tooth drive sprocket fir HD. I know Sprocket Specialties goes down to like 17 and up to 79. HD and the xs both run 530 chains

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Yamaha xs650