Speedometer Errors
 

Hey guys,

Purchased an 02' SH yesterday and as soon as I got on the highway the speedo seemed off...Traffic was keeping up and passing me, and I felt as though I was doing 60-70 mph, while the speed was showing 80-85 mph. Not knowing if it was really off, or just different perception switching from my Magna, I decided to just keep up with the flow of traffic, and slow down if I saw cops.

Well, i finally found one of those "posted speed" radar areas that was in a 30 mph zone. I was going 31 according to radar, while indicated 39, so an 8 mph error at 30 essentially 30 mph or nearly 26% :confused:.

This would show that my 80 mph figure to be about 60 mph, and 90 mph indicated is closer to 67 mph...Seems a bit excessive to be "built in error", so I'm wondering what you guys think it could be?

It seems like our bikes use a speed sensor, which I assume is attached to the transmission, so changing gearing, or tire sizes will make the difference...or potentially a failing speed sensor. The tire sizes are stock front and back, so that leaves the gearing, having never changed gears I can't notice anything that doesn't look "Stockish". The sprocket set is pretty plain, old, and dirty. Is there typically a stamp on the sprocket to tell us the tooth count?

Also, are speed sensors known to fail on this bike?

Thanks all!

Check the sprockets for changes in gearing i.e -1 +1 compared to standard. Sometimes stamped on the sprockets but easy to count. You mentioned the chain was 'rusty so a good time to service the bike , change fluids and treat it to new chain and sprockets (530 Heavy Duty X-ring recommended) - searchable Honda service manual PDF > VTR1000F Honda Service Manual OCR.pdf as if the chain snaps it can be painful and potentially smash crankcases/lock up rear end at speed.

Yes the speed sensors can fail - they begin reading erratically, if at all.

Well, if the sensor fails, the speedo shows nothing... It's plain and simple not possible to fail in the way that it shows the wrong speed that way consistently... They either fail outright, or they start to "flicker", as in the speedo does all sort of wierd stuff, which makes it pretty obvious something is off...

On most sprockets there is a mark... But it's not really easily readable as new, and is your unlucky, it's hidden behind the cushdrive, so it's a whole lot easier to just start counting... 16 in front, 41 rear... It's a very, very common mod to swap in a 15 in front and a 43 in the rear... Or other combo's, that easily puts you 10-15-20% off... Add around the generally accepted 3-4% speedo error, and you're there...

Altough, keep in mind, 30 mph isn't really the speed where the gauges are calibrated at, and +/-1 mph at that speed makes a large difference in %, so it's not really a valid indicator for how much your gauges are off by...

Alright, so all this being said I'll likely rule out the speed sensor...which leads me to the sprockets...I'll go counting. So stock is a 16/41 F/R setup? I had looked in the manual, but wasn't 100% sure with the numbers I had found. I'd assume this is the final reduction number, but i'd have to recheck the manual to be sure.

Now begins the fun of improving all the niggling problems.

To fix your speedometer, get a SpeedoHealer and it will solve your problems. I went up one tooth on the rear with a Supersprox and was easily able to calibrate that error.

Agreed on broken chains...they can wreak havoc on an engine case. I'll take a better look at the chain while it's on the stand. I didn't find any binding links during the pre-buy inspection, but we'll find out. It definitely isn't a "pretty chain". It was the sprocket that looks considerably old, and oily from cheap lube or poor wax.

Given that you're in Florida I'd be willing to bet the C/S Sprocket is a 15 and the rear is more than 41 though less likely. It seems the wheelie crowd prefers the 15 and that equals 3t in the rear and could cetainly contribute to your speedo error.

Who's in Florida? I'm from MissourA

Crap I don't know why I thought that, must be the wine!

I wish there was a Like button...:)

To all, I went out and counted the rear sprocket (looked like the slave cylinder gets pulled to get at the front sprocket, correct?)

43 teeth on the back. So I'm thinking someone stepped it up...changes my RPM's, and gives me my stupid high error rate. Teeth are wearing down a bit on the back, so I think I'll be swapping them out within the year or so, probably at the end of the riding season...unless something makes me do it sooner...at that time, I'll decide on going back towards stock, or living with the difference. I'll plan to count the front on another day. Thanks guys!

Leave the slave attached to the chaincover, the bolt at the slave doesn't go down into the block, also pull the handle in and tie it to the handle... Failing to do that, you get the fun work of bleeding the clutch... Do it this way, you can skip that...

:) Thanks! I knew there'd be a trick to it to keep me from having hydraulic fluid all over the garage. Greatly appreciated. I'll count the front after work, bet it's dropped down a tooth also.

So I pulled the front sprocket cover just now and it's a 16T front sprocket. So it looks like the previous owner only upped the rear sprocket in his modifications.

What i'm finding so odd though, is that the speedometer error also means an odometer error, guessing in the 20% range still. If that's the case, my first two calculated fuel readings of 31 and 29 mpg might be considerably worse! My first time out I refueled with the odometer showed 98 miles and the light was flashing, second time I refueled at 52 miles but was only at a half tank. If a 20% error occurred, my actual first odometer reading might have been as low as 79 miles, and my second at 41 miles, changing my fuel economy figure to 25 mpg, and my second to 22 mpg!!!

That's a bit extreme ever for my liking. I know my 210 lbs isn't helping matters, but my hopes are for a clogged/dirty air filter, or carbs that are setup WAAAAAY rich. I'm not getting a gas smell from the rear of the bike that I've noticed, but there is a noticeable "pop" when switching from gas to engine braking. Wonder if the previous owner rejetted the carbs in a bit of excess when he installed the new slip-ons?

The 16/43 setup is quite common and basically just gets 6th gear to be less of an overdrive. It shouldn't be more than @3% effect on the speedo. I would also say that Honda speedos are notoriously optimistic.

Well, not at all odd... Odo and speedo are calculated of the same signal, so why wouldn't they be off by the same amount from sprocket changes? They are however different by the factory speedo error that's commonly around 10%...

And since 16/43 is actually exactly 4.65% off vs the OEM 16/41, the odo should be of by that, plus possibly a few % for tire wear, say round it off to 5% or so... And add the normal factory error of most Honda speedo's and your speedo should by then be 10 to 15% optimistic... So at an indicated 90, you are doing around 77 to 81... And at an indicated 30, you are doing probably 25 to 27...

But no, looking at the radar at 31, and the radar at showing 39, does NOT translate the other way... It's actually calibrated at reading above actual value at all times, but not above 55 at 50 true speed, as per the US standards... Basically what that means in actual practice is that a speedo calibrated that way reads usually around 54 at 50, with the difference increasing at both higher and lower speeds... So not uncommon to see 10 to 15% error at 30, even with stock sprockets...

(BTW EU standards are a bit more stringent...)

Thanks! Good to hear that my fuel economy figures (however bad) are at least not worse. These were a combo city/highway driving though, i'd hope for 30 mpg in town, and a bit more on the interstate.

What type of difference do you typically see with RPM with the 16/43 setup vs a 16/41 stock setup?

I'll plan to take the tank off in the near future and get a look at the filter...given my fuel economy, shouldn't take long to empty it out. lol.

Why do you even know this stuff? I wouldn't even think of looking up published standards to it?

NavyJ, there is also a chance that carb/airbox mods are contributing to poor fuel economy. Most mods done are for performance and not for economy with this bike, so if it was tinkered at all from factory, it is likely not running at optimum mpg's. Couldn't hurt to have new oil and control that ever so influential right wrist if you're really worried ;)

I understand...I've had a few bikes over the years and none have been quite this thirsty, that's what had me thinking about it. I also wonder if the performance mods are really increasing performance...some do, some are done poorly (IMHO).

I know with my Magna, a lot of folks would change the exhaust or rejet the carbs, and typically the bikes dyno'd worse than they did stock....they did sound better though.