Dynojet speedo accuracy

[OB_Animal]

I was wondering if anyone in general or TLR99 in particular would care to comment on the accuracy of the speed indicated on a Dynojet?

Having just ordered my YellowBox I was planning ahead for a reliable source to check actual versus indicated speed at and I then thought of the fact that the speedo being driven from the rear on the 'Busa means you could use the Dynojet for this?

I also remember that during all those runs I've done with my other bike (about 50 on one and the same Dynojet and about 5 or 6 sets of runs on other Dynojets in my country) the max speed in top gear was always absolutely the same.

This suggests to me that if you held your 'Busa at say a constant 150 mph on the Dynojet speedo while taking an indicated reading on the Busa's display, you could get a very good if not perfect base for adjusting the YellowBox?

Anyone got any useful info on this topic they wanna share?

Animal (a.k.a. BiggerOne).

 

[OB_jeffw]

One word for dyno runs: tire slip.

Oops, that's two words.

 

[Guest]

Good question, Does anyone know my Busa indicated 202mph on the dyno. Is that near accurate?

 

[OB_Animal]

JeffW,
You're right (of course) but that's why I mentioned keeping it at a constant 150 mph for a while, that should normally take care of the slip IMHO.

 

[Guest]

This is one subject that is still a "grey area". I have tried for months to find someone who can report the accuracy of the Dynjet 150 speed reading. No one can/will.

JeffW is right, tyre slip is ONE problem, and yes, you can fix it by holding revs constant.

BUT, I can't vouch for the accuracy of the Dyno reading.

Suggestion: get a bicycle "computer", about $20, measure the cicumference of the Dyno roller, punch this measurement into the little gizmo and it should read true speed of the Dyno roller itself. They are fun gadgets.

Yes, you could do that on the bike, but you still have tyre growth and safety factors. Safer and more accurate on the Dyno. Sorry I can't really answer your question, Animal!

 

[OB_Brock Davidson]

We occasionally bring our dyno(dynojet 150) to my home track (1/4 mile) to track test the "improvements" that are noticed on the dyno.(We do not try to simulate ram-air on the dyno)

I have hit the bikes high limit on the dyno with an indicated max wheel speed of 126mph, then made a pass at 128mph on the track, hitting the limit slightly beyond the beams.

I have noticed similar results at speeds approaching 175mph on some of my faster bikes.

As far as I can tell, the drum speed and trap speeds are within 2-5 mph,with the bike always going faster on the track than the dyno indicates.

Hope this helps
Brock

 

[OB_Dr Busa]

The dyno only slips under hard acceleration. Once you've reached the revlimiter there is no acceleration. The dyno is very accurate since it doesn't get affected by the change of tireradius at high speeds. At that brit video they got 200.2 mph at the limiter.

 

[OB_mjtobler]

One thing to keep in mind: is the dyno you have access to measuring BHP???

"true" horsepower is revealed with a dyno that measures BHP. from the tech-specs i've read about dyno-jets is that they DONT.

 

[sherm]

99TLR, is there any direct relationship between odometer accuaracy and speedometer accuracy on the Hayabusa? If there is could a known odo error be used to calculate the yellow box ratio?

 

[Guest]

Back to the original topic, the Dynojet 150 should read accurate speed if the bike is "coasting" or at least, not under full power.

The question is, how is the DJ150 calibrated for roller speed accuracy, and how many dyno operators really take the time/efoort to make sure their machine is accurate??

I have not been able to get one dyno operator to swear that his machine has an ACCURATE roller speed indicated. Just "whatever it always reads" type comments. Come on guys, it is supposed to be an accurate, calibrated piece of measuring equipment... Isn't it?

 

[sherm]

99TLR, going back to one of my original questions, if you determined the odo error by riding an accurately measured distance, then could you use the odo error to come up with the correction factor (ratio) you enter in the yellow box?

 

[OB_Animal]

As far as relation between odo- and speedometer is concerned, I've found on many bikes that the odometer is exceptionably accurate even when the speedometer indicates plus 5-10 percent (everything still stock of course).
Apparently the speedo optimism is designed in for legal reasons as was suggested before.
But of course this would only help as long as you have everything stock that could influence the reading (like final gearing and on the 'Busa rear tire size as the pickup is from the front sprocket and not the front wheel).

 

[Guest]

Whoa! Better clear this one up pretty quick!

Animal, you are very right and very wrong! On cable driven mechanical speedos you are right on. The odometer/trips is driven by cogs from the cable, and should be very accurate depending on front tyre diameter of course. The mechanical speedos are dodgy things, like a fluid clutch/torque converter, where the indicated speed depends on the slip
in the fluid and the spring tension on the indicator needle. Not much hope for good accuracy or linearity there.

Now, with electronic speedos, the odometer and speedo both measure the number of electrical pulses from the sensor. On the Suzukis, there are exactly 4 pulses from the sensor for every FRONT sprocket rotation.

We attached a stock speedo instrument to our test bench, injected a measured speed of electrical pulses, and checked its performance. The speedo dial is VERY linear, and a high quality unit. The trips/odometer are directly linked to the speed indicator by measuring the same input pulses, and will display exact miles in reference to the speed displayed.

What I am trying to say, is, yes we measured the Suzuki speedo accurately, yes it works well, and yes the odometer will add miles with the same precision as the speedo.

The error can be measured by zeroing the tripmeter, riding the bike over a 10 miles measured distance (freeway markers) and seeing how many miles were clocked on the tripmeter. So with electronic speedos, tripmeters and speed shown are the same.

Hope all of that makes sense!

 

[OB_Animal]

99TLR, thanks for setting this right.

I was indeed referring to mechanical odo- and speedometer experiences as the 'Busa is my first bike with electronic pick-up for this.

On the other hand, the fact that you had already told us how linear the Busa setup was, and that the speedo optimism of 5-10% was obviously designed in somewhere, had me thinking for a moment that trip- and odometer might be dead-accurate and only the speedo being off.

But ... it's a good thing that they are all 100% consistent with eachother on the 'Busa as this will ensure all of them to be accurate once the YellowBox is calibrated correctly!

 

[Guest]

Sherm, yes, that is how I measure and calibrate the speedo on my bike. I only have a 5km marker on my local freeway, but 10km or 10 miles is better still.

This is the best way we have found for calibrating our product with little fuss and no equipment. With one test on the freeway you should be able to get your stock 'Busa error from about 5% down to less than 0.5%.

Just remember to check it every now and then, a new tyre (different brand) might be up to 2% out (rolling diameter) and of course tyre wear makes a significant difference.

Many people can live with a 5% stock error, it is not so bad. But most of the people who buy our product have also changed sprockets, some have errors of 12% or more.

Note, having your stock bike read 5% fast on the speedo is one thing, just remember that it is clocking up 5% too many miles on it too. At least with the old mechanical speedos you didn't devaluate your bike 5% too much. Nobody said Japanese manufacturers were dumb...