Altering the sprockets for relaxed riding

[HoughMade]

I have a '79 XS400 with standard final drive- 16 tooth to 37 tooth. It seems to me that 1st gear revs up fast and is very short and that at 55 mph, the engine is close to 5500 rpm (maybe 5400) which is a little frenetic for my taste (but I can live with it if I have to). I know the engine can take even more revs than that, but I would like a more relaxed cruise.

I would prefer to be at 55 mph at a lower rpm. I was thinking of dropping to a 36 tooth rear sprocket, but I can't find one (yet). I could go to a 17 tooth front, but that will be the equivalent to over a 2 tooth drop at the rear. However, it seems easier to find a variety of front sprockets.

Is the 17-37 too much of a change? (I kind of don't think so because first is so short). Is there a source for a 36 tooth rear sprocket for the XS400? The XS650 sprockets will not work- 6 bolts VS. 4 bolts.

Any thoughts would be appreciated.

 

[Hornix]

In my opinion the XS400 has to be revved to make it perform. But hé, I rebuild it in a caferacer so it has to go fast from cafe to cafe. I changed my final drive from 16/37 to 16/40 and now the 6th gear is used more often. The 400 engine is a relative short stroke type of engine, not and old english longstroke, so make it revv. I runs really smooth at about 7000 rpm
When you go from 16 to 17 in front, it is about the same as going from 37 to 34 in the back. Wouldn't recommend it....
At the JT sprocket site, you can see the alternatives available for our powerhorses
http://www.jtsprockets.com/52.0.html?&L=0&sel_uid=2377&p=

 

[bcware]

I am interested in how this works out. Would changing the number of teeth have any affect? Intuitively I would think you would want to change the size of the sprocket, not necessarily just the number of teeth. I don't, however, have any idea what I am talking about here

 

[bcXS400-81]

^^ Changing the number of teeth IS changing the size of the sprocket. Easiest way to think about it is like a bicycle: in the rear, a larger sprocket makes pedalling easier, but you go slower (on a motorbike, gives you more torque but less top-end speed), and a smaller sprocket makes it harder to pedal but you go faster (less torque, more top-end speed). Up front it's the reverse. It's a pretty common upgrade in the sporbike world to go -1F/+2R with sprockets, makes 3rd gear wheelies too easy

 

[bcware]

I see; changing the number of teeth without increasing the size of the sprocket would change the distance between teeth and the size of the teeth and this make the chain pretty unhappy. Anyone do a wheelie on an xs400?

 

[xschris]

I run a 16/37 on mine and in 6th gear it turns at 4800? Stock is 16/39

 

[HoughMade]

I see; changing the number of teeth without increasing the size of the sprocket would change the distance between teeth and the size of the teeth and this make the chain pretty unhappy. Anyone do a wheelie on an xs400?

Yep, talking tooth count is just shorthand for sprocket size since we need to maintain the same pitch. It's just easier to talk about a tooth up or down.

 

[ahale2772]

[Anyone do a wheelie on an xs400?]

..aww hell I cant make the quote thing work


...I'd also be interested in knowing how well a xs400 should run. I think i have mine tuned like crap so ive got no base line for what power the bike should have.....my bike feels like its trying REAL hard to keep me at 55mph

 

[HoughMade]

Mine runs at 55 to 60 mph real easy...but the engine is running really fast.

 

[drewpy]

[Anyone do a wheelie on an xs400?]

..aww hell I cant make the quote thing work

need to put a / into the front of the last QUOTE

 

[HoughMade]

As it turns out, I have a 16-39 (always count...don't trust the paperwork). I just bought a 37 tooth on eBay for a decent price. I'll give it a shot and see how it works out. I can always change back if I don't like it.

 

[OliverB]

Interested in seeing how you like the change and what it does to cruising RPMs and power curve.

 

[xschris]

When I dropped down to a 37 tooth the rpm's drop was about 400-500(4800rpm 6th gear), and still good power. I also weigh 165lbs

 

[HoughMade]

....I also weigh 165lbs

I don't.

The way I figure it, if 1st gear isn't too high (it seems very low right now), because there are 6 gears with close ratios, it should work fine. It may alter what gear I am in at a given speed, but with plenty of gears, I should be able to keep it in its power band.

 

[drewpy]

the power band is 7k revs

 

[OliverB]

My '80 rear sprocket is 37. Haven't pulled the cover to check front sprocket. So maybe a P.O. already made the change.

Update:
Counted teeth on '79 rear disc brake wheel I bought recently and that sprocket has 39 teeth.

Interesting. I have always thought my '80 gearing was just a touch tall on takeoff, needing clutch to be slipped a little more than normal. Since I have been riding scoots for five years before I got the Yamaha and this was the first cycle I have ridden in 40+ years, I thought maybe the gearing was a little different than my old Honda or I just forgot. Actually, I did ride my son's '81 a month or so before I bought my '80 last June and didn't remember his bike needing the same clutch action.

Well, I can also testify that a 37 tooth rear sprocket is just fine on the XS400 and probably does give just a touch lower RPMs at cruise. I'll have to get back on my son's '81 again to compare the two since now I know how mine feels after putting on 1K miles in the past 10 months.

 

[jayel]

[Anyone do a wheelie on an xs400?]

..aww hell I cant make the quote thing work


...I'd also be interested in knowing how well a xs400 should run. I think i have mine tuned like crap so ive got no base line for what power the bike should have.....my bike feels like its trying REAL hard to keep me at 55mph

needs a back slash / in the second quote as for gearing if you can find the pinion gear and clutch hub gear size for the 400 and the gear ratios check this thread from the 650 site
http://www.xs650.com/forum/showthread.php?t=7334

 

[jigm400]

i have been running a 17 tooth front sprocket on mine for a while now and the bike runs great 85 + mph on the freeway

 

[drewpy]

17's better as it gives a wider circumference for the chain to wrap around so lessens wear.

it = about 3 teeth on the rear

 

[HoughMade]

Installed the 37 tonight. Took longer than I expected, but what doesn't? Hoping to test it tomorrow. I shall report my findings.