'Nother Chain/Sprocket/Speedo question

[coaz4x4]

2002 Honda cb900f '919'

I have stock sprockets. My speedometer reads +12ish% conformed by both my GPS and trailing someone with cruise control on.

What would cause that inaccuracy?

Also, based on the photos attached I'm assuming I need a new chain and sprockets?







Thanks! I know it's sort of a n00b question... but I'm sort of a n00b...
-Peter

[Ezzzzy1]

I have heard that bikes from the factory are off by 5%. I know all the street bikes that I have owned have been off by that much if not more.

Tire and wheel size will change the speed reading as well. Are you running the manufacture spec tires? Stock wheels?

Its not just your speedo thats off its probably your millage as well

[Spiderman]

Most speedometers read a bit high for the stock setup.

I've tried using the GPS on my phone to see if my speedo was off, but the app was bouncing between 2 and 5 mph slower than my speedo was reading (while I was holding a steady speed) - I need to use a real GPS for this test to be reliable.

You could run your numbers through this calculator just to see how they compare: http://www.cosportbikeclub.org/misc/SpeedCalc.html - it matches my speedometer at 5000 rpm in 6th gear.

And based on your pictures, it's hard to tell if you need a new chain & sprockets. If that's rust on the current chain, then yes; if it's just grime, then probably not. How many miles do you have on the ones on there now? I get almost 20,000 miles out of a chain & sprockets, and I'm not known for taking good care of them!

[TinkerinWstuff]

You moved up from the VF500 eh?

[coaz4x4]

I did move up from the mini-ceptor... Quite a difference!

Tires are stock size.

Chain has 15,400 on it. I assume it's stock, may have rust if it sat outside before I owned it. I was hoping the shots of how far back the adjusters are for the rear wheel would show more of an indication of chain life remaining.

[CYCLE_MONKEY]

That looks like nothing but normal wear to me, and you have more life left in them. A little light surface rust isn't a big deal, but it looks like they should be lubed more as that'll keep down any rust. You can't spray the chain with too much lube, just make sure you wipe off the excess.

[coaz4x4]

I did make a trip to the coin-op to de-bug today... Photos taken before chain was re-lubed.

[crypto0793]

My R1 was +8MPH because the Sprockets were changed to -1 in the front and +2 in the rear for better acceleration and I just replaced them with new OE gearing chain and sprockets and its spot on now oh and my chain was very warn

[Zach929rr]

Yours looks fine.

[TFOGGuys]

Yours looks fine.

There's still life left in that one...

[Zach929rr]

I take no credit for that sprocket. However, that is what happens when you see a sprocket is cracked and go, "Meh" and go race on it.

I'll adjust mine as far back as I can until I can start seeing some teeth when I try to pull the chain off the sprocket.

[coaz4x4]

At this point I'm more interested by the inaccuracy than chain life... I figured since it was adjusted so far out/back that it was near the end.

[TFOGGuys]

Most stock speedos are off by 6-9%, but you'll usually find that the odometer is accurate. There are many theories why the factories do this, including inflated performance figures, drive by sound testing, etcetera. Stock gearing should be 16/43 (2.69:1 ratio). Going to a 17 tooth front would alter your gearing by about 6%, but I would recommend changing both sprockets and chain at the same time to ensure the longest life for the new components. If you went to a 17/42 combo, your gearing change would be 8%, and the chain length (and wheelbase) would remain stock.

[fiveninerzero]

I've heard that most non-ABS Japanese sportbike speed-o-meters estimate speed based on some sort of calculation of what gear you are in relation to how many RPMs you are doing. I've also heard that some have a sensor at the front sprocket that measures its revolutions. Anybody have the real deal scoop?

Sportbike speedos are horrible stock, and it gets worse when you alter your final drive ratio, i.e. get a bigger or smaller sprocket as many of us wannabe racers do.

IIRC, DOT certification allows about 10% too fast for a speedo reading.

Older bikes and ABS equipped bikes tend to have an actual wheel speed sensor.

I'm no 919 expert, but you should look into a Speed-o-healer if you really want this as accurate as possible. Either that or procure an ABS bike with a sensor at the wheel, or do what most guys do and simply roll with it.

[coaz4x4]

I'm thinking healer... But wondering if what TFOG says is true, will using the healer throw the Odometer off? I haven't checked that yet against a known distance.

[vort3xr6]

Yours looks fine.

LOL. I take credit for that.

[CYCLE_MONKEY]

Yours looks fine.

Looks like you simply geared down a couple teeth in back......

[CYCLE_MONKEY]

2002 Honda cb900f '919'

I have stock sprockets. My speedometer reads +12ish% conformed by both my GPS and trailing someone with cruise control on.

What would cause that inaccuracy?

Also, based on the photos attached I'm assuming I need a new chain and sprockets?







Thanks! I know it's sort of a n00b question... but I'm sort of a n00b...
-Peter

Oops, sorry, didn't notice this before. This isn't good, you're at the end of your adjustment. either it's been regeared and they didn't shorten the chain, or it's worn out. Either way, replace it all as a set, there's another thread or 2 on that here.

[crypto0793]

I just did mine its not to hard just make sure you have all the tools before you start

[coaz4x4]

Most stock speedos are off by 6-9%, but you'll usually find that the odometer is accurate. There are many theories why the factories do this, including inflated performance figures, drive by sound testing, etcetera. Stock gearing should be 16/43 (2.69:1 ratio). Going to a 17 tooth front would alter your gearing by about 6%, but I would recommend changing both sprockets and chain at the same time to ensure the longest life for the new components. If you went to a 17/42 combo, your gearing change would be 8%, and the chain length (and wheelbase) would remain stock.

Got in 33 mi on the odometer tonight... before the skies opened up. Checked google maps... 32.3

Ok, so if I put in a speedo healer, or change the gearing to correct the speedometer will that throw off the odometer?

[cbrjohnny]

Yours looks fine.

lmao! was your bike like this the last time we ran down deckers together? hehe

[Zach929rr]

Nah that was off vortexs bike after the sumo double header at hpr.

[TFOGGuys]

Got in 33 mi on the odometer tonight... before the skies opened up. Checked google maps... 32.3

Ok, so if I put in a speedo healer, or change the gearing to correct the speedometer will that throw off the odometer?

Sounds like your odo reads just a touch (4-5%) fast, so a slight gearing change might get both the speedo and the odo in the ball park. (or a speedo healer)

[rfranks303]

I just did mine its not to hard just make sure you have all the tools before you start

What you don't like riding in my dirty ass truck lookin for a 36 mm socket now I'm offended.

In your service manual you will find a service limit for your chain mine is 12.73 inches across 20 links. Its not hard to swap a chain and sprokets just make sure you follow your tourque specs.