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From: badgolferman on 5 Nov 2009 21:02 Tegger, 11/5/2009,4:03:51 PM, wrote: > "badgolferman" <REMOVETHISbadgolferman(a)gmail.com> wrote in > news:xn0ghaisbeui4k004(a)reader.albasani.net: > > > Jeff Strickland wrote: > > > > > The OP wants a larger sidewall for some reason, not a smaller > > > one. (I don't get the logic he's using, but it's not my decision.) > > > > I don't want anything changed on my car. I was just wondering if > > there is a difference between tires with thin sidewalls and those > > with very wide sidewalls when it comes to odometer/speedometer > > readings. And I'm not talking about one inch differences, more > > like 45s vs. 85s. > > > > After you guys work out all this technical minutia let me know what > > the consensus is. > > > > > > > > > You'll never get "consensus". > > The fact is: > Given a specific sidewall height and overall tire diameter, if you > change ONLY the sidewall height (bigger wheel), you WILL change the > rolling circumference. > > If you go from a 60 to a 50, you probably won't notice the > difference. If you go from an 80 to a 45, there would be a big > difference. So will the wheel with the 80 tire rotate more or less than the wheel with the 45? Which one will show more than the correct speed and which one will show less? -- "If you don't read the newspapers you are uninformed; if you do read the newspapers you are misinformed." ~ Mark Twain
From: Jeff Strickland on 5 Nov 2009 22:11 "badgolferman" <REMOVETHISbadgolferman(a)gmail.com> wrote in message news:xn0ghaisbeui4k004(a)reader.albasani.net... > Jeff Strickland wrote: > >>The OP wants a larger sidewall for some reason, not a smaller one. (I >>don't get the logic he's using, but it's not my decision.) > > I don't want anything changed on _my_ car. I was just wondering if > there is a difference between tires with thin sidewalls and those with > very wide sidewalls when it comes to odometer/speedometer readings. > And I'm not talking about one inch differences, more like 45s vs. 85s. > > After you guys work out all this technical minutia let me know what the > consensus is. > > The short answer is, no, there is no difference. The long asnwer is that the overall diameter has to be the same for the short answer to be true. For example, my truck has a 265/75x16. I could go to a 265/35x20 and the tire should be the same overall diameter, therefore no affect on the speedo.
From: Tegger on 5 Nov 2009 22:14 "badgolferman" <REMOVETHISbadgolferman(a)gmail.com> wrote in news:xn0ghau681ojn70000(a)news.albasani.net: > Tegger, 11/5/2009,4:03:51 PM, wrote: > >> "badgolferman" <REMOVETHISbadgolferman(a)gmail.com> wrote in >> news:xn0ghaisbeui4k004(a)reader.albasani.net: >> >> > Jeff Strickland wrote: >> > >> > > The OP wants a larger sidewall for some reason, not a smaller >> > > one. (I don't get the logic he's using, but it's not my >> > > decision.) >> > >> > I don't want anything changed on my car. I was just wondering if >> > there is a difference between tires with thin sidewalls and those >> > with very wide sidewalls when it comes to odometer/speedometer >> > readings. And I'm not talking about one inch differences, more >> > like 45s vs. 85s. >> > >> > After you guys work out all this technical minutia let me know what >> > the consensus is. >> > >> > >> > >> >> >> You'll never get "consensus". >> >> The fact is: >> Given a specific sidewall height and overall tire diameter, if you >> change ONLY the sidewall height (bigger wheel), you WILL change the >> rolling circumference. >> >> If you go from a 60 to a 50, you probably won't notice the >> difference. If you go from an 80 to a 45, there would be a big >> difference. > > So will the wheel with the 80 tire rotate more or less than the wheel > with the 45? Which one will show more than the correct speed and > which one will show less? > The OEM wheel, tire size, and speed rating will be closest to the manufacturer's intended speedometer calibration. When it comes to aftermarket, I wish I could pin that question down for you, but I can't. The answer depends on the actual rolling circumference that each tire describes when loaded the way your car will load it. One maker's 225/45-16 won't necessarily measure the same actual unloaded diameter as another maker's 225/45-16. And those tire-shop tire-size equivalency charts are fraught with uncertainty on account of that. But: Given two differently-seriesed tires with identical unloaded circumferences, the one with the shorter sidewall will have the larger rolling circumference and the lower speedometer reading. The upshot is that the difference will likely not be enough for anybody to notice unless he's very specifically looking for that difference. Even the cops recognize that, which is partly why they give you 5mph grace (or more depending on the jurisdiction) before whacking you. -- Tegger
From: Tegger on 5 Nov 2009 22:22 "Jeff Strickland" <crwlrjeff(a)yahoo.com> wrote in news:hd044q$sph$1(a)news.eternal-september.org: > > "badgolferman" <REMOVETHISbadgolferman(a)gmail.com> wrote in message > news:xn0ghaisbeui4k004(a)reader.albasani.net... >> Jeff Strickland wrote: >> >>>The OP wants a larger sidewall for some reason, not a smaller one. (I >>>don't get the logic he's using, but it's not my decision.) >> >> I don't want anything changed on _my_ car. I was just wondering if >> there is a difference between tires with thin sidewalls and those >> with very wide sidewalls when it comes to odometer/speedometer >> readings. And I'm not talking about one inch differences, more like >> 45s vs. 85s. >> >> After you guys work out all this technical minutia let me know what >> the consensus is. >> >> > > > The short answer is, no, there is no difference. > > The long asnwer is that the overall diameter has to be the same for > the short answer to be true. For example, my truck has a 265/75x16. I > could go to a 265/35x20 and the tire should be the same overall > diameter, therefore no affect on the speedo. > > Supposing the two sizes have identical unloaded diameters, the 35 will have the larger rolling circumference and the slower speedometer reading. -- Tegger
From: Jeff Strickland on 5 Nov 2009 22:35
"Tegger" <invalid(a)invalid.inv> wrote in message news:Xns9CBAE381511EEtegger(a)208.90.168.18... > "Jeff Strickland" <crwlrjeff(a)yahoo.com> wrote in > news:hd044q$sph$1(a)news.eternal-september.org: > >> >> "badgolferman" <REMOVETHISbadgolferman(a)gmail.com> wrote in message >> news:xn0ghaisbeui4k004(a)reader.albasani.net... >>> Jeff Strickland wrote: >>> >>>>The OP wants a larger sidewall for some reason, not a smaller one. (I >>>>don't get the logic he's using, but it's not my decision.) >>> >>> I don't want anything changed on _my_ car. I was just wondering if >>> there is a difference between tires with thin sidewalls and those >>> with very wide sidewalls when it comes to odometer/speedometer >>> readings. And I'm not talking about one inch differences, more like >>> 45s vs. 85s. >>> >>> After you guys work out all this technical minutia let me know what >>> the consensus is. >>> >>> >> >> >> The short answer is, no, there is no difference. >> >> The long asnwer is that the overall diameter has to be the same for >> the short answer to be true. For example, my truck has a 265/75x16. I >> could go to a 265/35x20 and the tire should be the same overall >> diameter, therefore no affect on the speedo. >> >> > > > Supposing the two sizes have identical unloaded diameters, the 35 will > have > the larger rolling circumference and the slower speedometer reading. > NOT true. Well, not entirely true. For every inch increase in the rim, the aspect ratio is decreased 5%. The result is a overall diameter, or radius, or circumference (depending on the specy you prefer) will be virtually identical. The difference -- if done on all four corners -- is insignificant. There will be a small change to the speedometer -- a change measured in single digit percentages. The speedometer would be more sensitive to the circumference, but since circumference is calculated by diameter X pi, or radius X 2 X pi, then all are the same. I assume proper inflation, and ignore any argument that assumes improper inflation. Improper inflation causes a variance, and the variance is measured by the speed sensors, not the speedometer. |