Would that mean the tire is ‘growing’?
How fast on an uncorrected speedo?
- Thread starter Blacksmith
- Start date
Would that mean the tire is ‘growing’?
From memory it was something like 8% at 70 and 13% at 150 mph. Both over reporting speed.
It means it didn’t grow radially on the drum. Dyno speed vs engine rpm was a straight line. Speedo vs dyno mph error was not linear.
Thanks for that clarification. I'll just have to keep under 150 ... for now
Mythos
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@HayaWakened I think I heard of a speedo being under at low speed and over at high speed on a Honda. As for the busa, I'm sure it's x% high at all speeds. The Speedohealer corrects by a +/- percentage. My ZX-14 with Speedo healer is correct at all speeds up to 90 mph according to my GPS tests. I was not comfortable testing it higher because it's necessary to hold the speed for about 4 seconds to compensate for satellite transmission lag. If I'm going to risk doing triple digits, I'd rather not do it cruising at one speed. It would be possible though. You cover a lot of ground in 4 seconds at 100 mph.
For me it doesn't really matter,once above the posted speed limit,you have put out the welcome mat for Mr.Policeman and HIS sometimes inaccurate measure of speed.The other thing unimpressive about a Busa speedo is the fact that it uses a little needle on a face plate to give you your speed.Nobody can tell me looking down at a speedo at any speed can say exactly how fast they are going. Gen III Busa...big DIGITAL speedometer using some sort of forward facing radar(no sat trans lag) .
But I admire your pursuit of the exact scientific answer.
Rubb.
But I admire your pursuit of the exact scientific answer.
Rubb.
I learn something new everyday. I was under the impression the Busa read off the counter shaft sprocket.
Rubb.
This speed equation deal for me sort of equates to dyno numbers. 10 different dyno's testing the same bike. You would have 10 different sheets. The speed,torque and HP values would vary dramatically.With the limited science we have today,there is just no way to get an' exact number on these values. So if your using satellite (GPS) tech to give you an' exact number(on rate of speed),your not going to get it. A simple GPS location error of 1-20 feet has been reported by the U.S. military (the list of variables is huge) using their own satellites. (there one would have to believe that it is never more than 20 feet)
So if your looking for an' accurate estimate of speed,the formula uses the simple(in theory) distance traveled from point A to point B then factoring in that variable of 20 feet (using the extreme) ....
Say for instance you ran your speed test over a mile.5,280 feet. Your variable then becomes 264 feet according to the U.S. military.
Meh....IDK.
Rubb.
So if your looking for an' accurate estimate of speed,the formula uses the simple(in theory) distance traveled from point A to point B then factoring in that variable of 20 feet (using the extreme) ....
Say for instance you ran your speed test over a mile.5,280 feet. Your variable then becomes 264 feet according to the U.S. military.
Meh....IDK.
Rubb.
Actually,the 1-20 error,can only be applied once,and its not a percentage. The satellites could still be inaccurate on any distance thou. First pinpointed on one side of the street you could then walk to the other side and GPS could pinpoint you being 1-20 feet from the actual spot. Same margin for error if point A was Los Angeles and point B was New York.
O well. Somebody who is actually smart would have to work out how it works for speed.1320 ft in a 1/4 mile.Satellite could mark you having traveled 1300 or 1340 ft.
Rubb.
Mythos
Registered
Apparently, the speed sensor is bolted to the end of the countershaft sprocket so it would be effected by tire size. Come to think of it, any speed sensor would be effected by tire size/wear No matter what it reads off of.
Ti Sprocket Nut--Possible? | Busa Mods
I had planned to draw up a CAD file of an OEM countershaft sprocket nut and submit it to emachineshop.com. I'd like the nut to be made from Ti steel to drop a little weight. I did some research and found info indicating that Ti is nonmagnetic or "paramagnetic" at best. If so, Ti is not going...
About analog gauges v digital, yes, the needle is not as exact as a digital display. I still prefer analog for a quick glance and that's the kind of glance I normally do when looking at the instruments.
If this 1-20 foot formula is to compensate for variation off of a straight line, I assume a straight road is perfectly straight if they had some civil engineers out there with transits. Asphalt is too expensive to not have a perfectly straight road if a straight road is what they intend to build. Hopefully you don't vary more than 10 feet when you're doing 190 on a straight road!
We're talking about splitting hairs with a few feet variation off of a straight line. They can't tell the exact speed of a fighter jet if they're that particular about it.
To riders and street racers like us...Yer right,who cares. I got chatting with a physics guru buddy of mine,thats why I looked into all aspects of it.Apparently, the speed sensor is bolted to the end of the countershaft sprocket so it would be effected by tire size. Come to think of it, any speed sensor would be effected by tire size/wear No matter what it reads off of. Thats what I said earlier about the countershaft sprocket,U disagreed,I didn't wanna be rude. Weird huh. LOL. Its where u plug in a speedo healer.
Ti Sprocket Nut--Possible? | Busa Mods
I had planned to draw up a CAD file of an OEM countershaft sprocket nut and submit it to emachineshop.com. I'd like the nut to be made from Ti steel to drop a little weight. I did some research and found info indicating that Ti is nonmagnetic or "paramagnetic" at best. If so, Ti is not going...www.hayabusa.org
About analog gauges v digital, yes, the needle is not as exact as a digital display. I still prefer analog for a quick glance and that's the kind of glance I normally do when looking at the instruments.
Totally.
If this 1-20 foot formula is to compensate for variation off of a straight line, I assume a straight road is perfectly straight if they had some civil engineers out there with transits. Asphalt is too expensive to not have a perfectly straight road if a straight road is what they intend to build. Hopefully you don't vary more than 10 feet when you're doing 190 on a straight road!
Nothing to do with a straight line. It's earth physics stuff.
We're talking about splitting hairs with a few feet variation off of a straight line. They can't tell the exact speed of a fighter jet if they're that particular about it.
I don't really feel any more enlightened or enriched thou.
Party on Mythos.
Rubb.
Hayabusa Wannabe
Registered
I just used a speedo app on my 2017, and it is stock. The speedometer is dead on at 30 mph. At 65 mph the bike reports 5-6 mph fast. I hate calibrated instruments that do not work correctly, how counterproductive. Bah.
A buddy just bought a digitally controlled bread toaster.
Rubb.
Mythos
Registered
I don't know what tire size is recommended to replace the stock 180. If it's a 190, that will just about correct your speedo for normal street speed...at least until it wears down a bit.
180 or 190 would be no difference in speed/speedo reading. On reading tire size the 180 or 190 relates to the tire width. No change in speed or speedo reading. The Gen II busa sports(stock) a 190/50R17 . The "50" is the height of the tire. Going from that stock size to a 190/55R17 would affect speed and speedo reading.The difference in tire height(depending on tire brand as well) is about 8MM approx. So if I got out my calculator you get a difference of 2.5% meaning the 55 would be going faster 2.5% faster than indicated by the speedometer. And of course also increasing the Busa top speed,but again not actual speed exhibited.
A whole can of worms could be opened discussing the pro's/con's of changing tire size from stock. A lot of riders change to a bigger tire claiming better traction and/or handling. If you consider the physics and physical characteristics of a tires profile ie width X height X contact patch X useable sidewall etc. you get a great debate.
This new thread would have arguments like which is better in the twisties? Which is actually faster? Bigger contact patch in the 1/4 mile?
For instance for me, when wearing out the stock tire I have gone to the 200 MM for the better looks,caring not about the rollover capabilities in the twisties. Or the gained weight of the tire.
The 180,190,200 50 0r 55 debate means nothing to me anymore as I now sport the Super Squid, Super Bike Night Poser...330MM rear tire.
Rubb.
Mythos
Registered
You got me again, Rubb. Thanks for the correction. Going from a 50 aspect ratio to a 55 should pretty much correct the speedo---the tire is larger in diameter on center. I've never checked my busa but a 55 on my ZX-14 seems to correct that speedo by comparing to speed of other traffic. I think the tire width can also contribute to height. If the rim is meant to have a 180 on it and you put a 190 on it, that's 10 mm of extra width that has to get squashed between the bead surfaces of the rim. If the width gets squashed, it probably causes the height to increase a little.
This is fun.
I'm gonna add you to that following thingy a mijig feature.Squish=height increase...concur.
55 tire=speedo fix...cool.
If my math serves me correct brother Mythos, going from a 50 to a 55 tire solution would/could also be achieved by a +1 tooth increase on the countershaft sprocket if desired. Then a stock tire could be run if desired. Some bonus's to the larger sprocket too. Less chain wear for example. The chain doesn't turn as tight a circle,etc. Downside... Acceleration with a +1 or a taller tire will be less than the stock set-up.I could decipher that number if desired. I would have to think about it,build or find the equation.We have the four values,just need the formula. I'm just about positive the ensuing brain splitting headache would be well worth it.
Rubb.
Hayabusa Wannabe
Registered
@Mythos you are correct before any squishing is concerned. The aspect ratio is a percent of the width to the height. To Mythos' point take a 180/50 vs 190/50 and the 190 is taller as the heights are represented as 50% of 190 > 50% of 180.
So glad this happened as I discovered this as a result:
180/50-R17 vs 190/50-R17 Tire Comparison - Tire Size Calculator | Tacoma World
190/50-R17 tires are 0.39 inches (10 mm) larger in diameter than 180/50-R17 tires and the speedometer difference is 1.6%
www.tacomaworld.com
In Mythos' example, one mph is gained theoretically.
But you have brought in squishfulness to the conversation so it seems that the final product of size changes is unpredictable.
Now with this theoretical calculator, attempting to fix the speed from the stock size Rubb provided:
190/50-R17 vs 200/55-R17 Tire Comparison - Tire Size Calculator | Tacoma World
200/55-R17 tires are 1.18 inches (30 mm) larger in diameter than 190/50-R17 tires and the speedometer difference is 4.6%
www.tacomaworld.com
Theoretically I gain 3 mph, nowhere near the 6 mph current error. But from Mythos' experience the fit may provide the additional height required to further correct the speedometer.
Then there is the fact that tires do not comply exactly with the sizes marked on them, which can render a spec based discussion moot! Molds are expensive and I had read that they are reused. So if the tire compound is changed but the same mold used, the result can vary.
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