Correct. Also, IIRC, you have a Verde transaxle in your GTV6, right? Which speedo amplifier are you using? Which speedo? The Verde transaxle will introduce some error if you're using the stock GTV6 amplifier and speedometer (but it should make the car go faster than you actually think it's going).
bs ________________________________ From: George Graves <[email protected]> To: Will Owen <[email protected]> Cc: "<[email protected]>" <[email protected]> Sent: Wed, November 11, 2009 2:52:23 AM Subject: Re: [alfa] Re: Speedo check Can't speak to your situation, Will, but in my case I think that the lower profile than stock tire (for any given wheel size, the lower the profile, the smaller the diameter of the tire) is making my car go slower per wheel revolution than would a larger diameter tire. Therefore when the high-gear revs of the rear tires are of some certain number, the speedometer "thinks" that the car is traveling a certain speed. Each revolution equals a certain number of linear feet traveled which equals the tire's circumference. A smaller tire has a smaller circumference, therefore fewer feet are traveled with each revolution. This will mean that it will take more revs per mile to cover the same distance as a larger profile tire, this equates to a lower speed than that indicated. Increasing the tire profile from a 50 to a 55 or a 60 ( Pirelli P6 15 X 60s are apparently what the car came with) should raise the actual speed so with the proper (that is to say stock) diameter tire, an indicated 80 mph should equal 80 mph (or at least be closer to 80). Of course, the car will suffer a bit on acceleration because the ratio between tire and road will be greater. George Graves '86 GTV-6 3.0 'S' On Nov 10, 2009, at 9:44 PM, Will Owen wrote: > George Graves wrote: >> The GPS SHOULD be much more accurate than any other kind of speedometer. >> After all, if it can pinpoint where you are within a few yards, it should be >> able to figure out how fast you're going within a very small margin of error. >> >> George Graves >> '86 GTV-6 3.0 'S' > You'd think. My point was that my GPS is telling me that my MPH/thousand is > basically what your factory figures were telling you, as opposed to what your > GPS is telling you. So: is you GPS out of whack? Or is *MY* GPS out of whack? > Or has your car somehow been endowed with some kind of mud-wrestling final > drive? > > FWIW, I've been driving the 164S over the last few days and its gearing seems > to be about the same. Have not hooked the GPS into it because its cig lighter > socket spits the GPS plug out every few miles, which is a major recurring > pain in the ass. > > Will -- to be removed from alfa, see http://www.digest.net/bin/digest-subs.cgi or email "unsubscribe alfa" to [email protected] -- to be removed from alfa, see http://www.digest.net/bin/digest-subs.cgi or email "unsubscribe alfa" to [email protected]
