70 MPH sure is SLOW!
in [Toyota]
|
From: C. E. White on 3 Sep 2009 11:05 "Sharx35" <sharx35(a)hotmail.com> wrote in message news:XgLnm.43588$PH1.10766(a)edtnps82... > I'd suggest that GPS would be more accurate than 99% of auto > speedometers. So many things can affect the accuracy of those > speedometers. Tire wear, even. My experience is that the GPS is very accurate for speed and distance (assuming you don't lose your satelite lock). A funny thing about tire wear - it has negligible effect on the speedometer accuracy, at least for modern radial tires. I know this seems counterintuitive, but my experience says it is true. A friend explained the reason years ago, and until I started paying attention to the GPS vs speedometer readings for speed and distance, I thought his explaination was BS. It goes like this - Radial tires are not like solid round wheels. The number of rotations per miles is not directly related to the outside diamter of the tires. The actual rolling diameter is a function of the diameter of the steel belts in the tire. When the tire rotates, it acts more like a tank track than a solid wheel. Think about the way a tank tread moves. Then imagine how a tire moves at the contact point with the road. The steel belt is not going stretch but the rubber can and the treads can flex like the segments of a tank tread. The explanation maybe hard to understand, but my comparions of speedometer to GPS readings over the life of tires says that conclusion is valid, if not the actual details of the theory. Ed
From: Michael on 3 Sep 2009 11:39 On Sep 3, 1:43 am, "Sharx35" <shar...(a)hotmail.com> wrote: > "Michael" <mrdarr...(a)gmail.com> wrote in message > > news:6d61dabc-27c5-4516-9507-f7236817e541(a)v37g2000prg.googlegroups.com... > > > > > On Sep 2, 4:25 pm, Hachiroku ハチロク <Tru...(a)e86.GTS> wrote: > >> On Sun, 30 Aug 2009 21:44:52 -0700, PHATRS wrote: > > >> > I did 298 km/h in my RenaultSport Megane 225 the other day down Toorak > >> > Rd. > > >> Hmmm... > > >> Speedo in my Scion tC said 122 (MPH), but GPS only registered 116. > >> Which do I believe? > > >> Would have tried to go a little more, but was coming up on an 18 wheeler > >> and a blind hill. I-91 in VT, 2 year old pavement. Nice and smooth. > > >> Must be getting cowardly in my 'old age'. I took the Hachi up to 131, > >> then > >> to 125 for ~25 minutes, but only hit 122 for about 2 minutes. > > >> Maybe another run next time...see what top speed is... > > > Be glad you don't live in Canada. 100 km/h max speed (63 mph?) > > > I wonder if the Toyota speedometers are conservative, telling you > > you're going faster than you really are. I've seen a few SPEED LIMIT > > ENFORCED / YOUR SPEED = xx machines, and they seem to tell me I'm > > going slower than I think I'm going... > > > re: cheap computer parts: try Craigslist. I just got a 400 GB IDE > > hard drive for $40. I refuse to go SATA - I'd have to upgrade my > > mainboard for starters... > > > Michael > > In my experience most factory speedometers read too high. BTW, Many 4 lane > rural highways in Alberta have a speed limit of 110 KPH or approx. 68.3 > miles per hour. Nice! We came back from a road trip to Toronto, and 100 km/h is just crawling... going back home, in Utah the limit was 75 mph. I liked the warning signs in Ontario: Go 50 km/h over the speed limit, get a roadside vehicle seizure and loss of license... we need something like that here in the US. Michael
From: Floyd Rogers on 3 Sep 2009 11:41 "C. E. White" <cewhite3(a)removemindspring.com> wrote > "Sharx35" <sharx35(a)hotmail.com> wrote >> I'd suggest that GPS would be more accurate than 99% of auto >> speedometers. So many things can affect the accuracy of those >> speedometers. Tire wear, even. > > My experience is that the GPS is very accurate for speed and distance > (assuming you don't lose your satelite lock). GPS is far more accurate than a speedo, even accounting for hills, etc. The sample rate is such that typical errors are less than 0.5 mph. Garmin has some stuff on their website if you're interested. > A funny thing about tire wear - it has negligible effect on the > speedometer accuracy, at least for modern radial tires. I know this seems > counterintuitive, but my experience says it is true. A friend explained > the reason years ago, and until I started paying attention to the GPS vs > speedometer readings for speed and distance, I thought his explaination > was BS. It goes like this - > > Radial tires are not like solid round wheels. The number of rotations per > miles is not directly related to the outside diamter of the tires. The > actual rolling diameter is a function of the diameter of the steel belts > in the tire. When the tire rotates, it acts more like a tank track than a > solid wheel. Think about the way a tank tread moves. Then imagine how a > tire moves at the contact point with the road. The steel belt is not going > stretch but the rubber can and the treads can flex like the segments of a > tank tread. Ed, this theory is bunk, sorry to say. One of the ways that manufacturers have implemented tire-low-pressure systems is to monitor the rotation of each tire (using the ABS sensors on each wheel.) If the steering wheel is straight ahead (they need a steering-wheel position sensor, handy for DSC), then the rotations should be equal. When they aren't, it determines a low tire. This is because the wheels' angular velocity is determined by the *effective* radius. When the tire is low, the center of the wheel is closer to the road (ie, smaller radius), and the angular velocity is higher for that wheel. None of that would work if your theory were correct. FloydR
From: Jeff Strickland on 3 Sep 2009 11:57 "Hachiroku ????" <Trueno(a)e86.GTS> wrote in message news:pan.2009.09.02.23.25.27.998935(a)e86.GTS... > On Sun, 30 Aug 2009 21:44:52 -0700, PHATRS wrote: > >> >> >> I did 298 km/h in my RenaultSport Megane 225 the other day down Toorak >> Rd. > > > Hmmm... > > Speedo in my Scion tC said 122 (MPH), but GPS only registered 116. > Which do I believe? > The GPS. The speedo will always (unless oversized tires are fitted) read faster than you are going. The idea is that if you get a ticket for doing 50 in a 45, it is not a valid defense to say, but my speedo said I was doing 40. If you are doing 50 in a 45, your speedo will be reading 55-ish at the time. The GPS is far more accurate than your speedo will ever hope to be, since its job is to actually report real information. You might be able to dial in the speedo n the tC by getting the next size WIDER tire. Here's why. The tire size, 215/45 says that the tread is 215mm wide, and the sidewall is 45% of that, or 96.75mm. If you bumped from the 215 to a 225, the tread would be 10mm wider, and the tire circumference would increase from 77.3 inches to 78.4 inches. this inch of added circumference would slow the speedo relative the actual speed of the car. The result is that you should get a speedo reading of 117-ish when the actual speed was 116. The wider tire, by itself would not change the speedo. But the aspect ratio (sidewall height) is a percentage of the width, so the wider tire will give a taller tire if the aspect RATIO remains the same. 45% of 225 is a bigger number than 45% of 215, so the 225 is not only wider, it's taller as well.
From: Jeff Strickland on 3 Sep 2009 12:53
"Scott in Florida" <MoveOn(a)outa.here> wrote in message news:nvev9556la4odrubhus9igcfgvucif0oti(a)4ax.com... > On Thu, 03 Sep 2009 12:13:31 -0400, Hachiroku <Trueno(a)e86.GTS> wrote: > >>On Wed, 02 Sep 2009 23:21:33 -0400, JoeSpareBedroom wrote: >> >>> "Hachiroku ????" <Trueno(a)e86.GTS> wrote in message >>> news:pan.2009.09.02.23.25.27.998935(a)e86.GTS... >>>> On Sun, 30 Aug 2009 21:44:52 -0700, PHATRS wrote: >>>> >>>>> >>>>> >>>>> I did 298 km/h in my RenaultSport Megane 225 the other day down Toorak >>>>> Rd. >>>> >>>> >>>> Hmmm... >>>> >>>> Speedo in my Scion tC said 122 (MPH), but GPS only registered 116. >>>> Which do I believe? >>>> >>>> Would have tried to go a little more, but was coming up on an 18 >>>> wheeler >>>> and a blind hill. I-91 in VT, 2 year old pavement. Nice and smooth. >>>> >>>> Must be getting cowardly in my 'old age'. I took the Hachi up to 131, >>>> then >>>> to 125 for ~25 minutes, but only hit 122 for about 2 minutes. >>>> >>>> Maybe another run next time...see what top speed is... >>> >>> >>> Wait for winter and add 20 mph. Do the world (and your mother) a favor. >> >> >>Insults are all you have? >>It's apparent you have no brain. >> > > Pretty pathetic, ain't he..... > Pathetic? He'd have to improve to be pathetic. Pathetic is on his list of goals on his performance review. If he was pathetic, maybe his wife would still be around and putting up with him. You need to apologize to pathetic people everywhere for putting him in the same class with them. |