General Car Conversation
Lexus Fanatic
Joined: Oct 2003
Posts: 94,328
Likes: 236
From: Virginia/D.C. suburbs
^^^^ Severely worn tire-tread could also account for a small bit of speedometer error (maybe 1 MPH or less) by making the tire-diameter slightly smaller and increasing the number of RPMs the wheel makes relative to true road speed. It is the same effect (but to a lesser extent) as a lower-than-stock profile on the tire/wheel assembly.
Thread Starter
Lexus Fanatic
Joined: May 2012
Posts: 68,466
Likes: 3,990
From: Maryland
^^^^ Severely worn tire-tread could also account for a small bit of speedometer error (maybe 1 MPH or less) by making the tire-diameter slightly smaller and increasing the number of RPMs the wheel makes relative to true road speed. It is the same effect (but to a lesser extent) as a lower-than-stock profile on the tire/wheel assembly.
Lexus Champion
Joined: Jan 2012
Posts: 17,019
Likes: 496
From: Knoxville, TN
I’m not making it up. I’ve read all about it over the years in MT, C&D,
forums, etc. Give people the benefit of the doubt more often. These ones I’m talking about are before digital.
To be fair, it’s high speeds 100+ when they start to read noticeably faster. It’s honestly probably not a bad thing.
forums, etc. Give people the benefit of the doubt more often. These ones I’m talking about are before digital.
To be fair, it’s high speeds 100+ when they start to read noticeably faster. It’s honestly probably not a bad thing.
Lexus Fanatic
Joined: Oct 2003
Posts: 94,328
Likes: 236
From: Virginia/D.C. suburbs
It would, but only by a small amount.....probably less than 1 MPH. Also, the smaller the tire, the more that worn tread would affect it. It would affect it more on an older 15 or 16" tire than on a larger 20 or 22" one.
In fact, that is why Subaru, almost all of whose American-market vehicles are full-time AWD, used to tell owners to replace their tires in sets of 4 at once, not piecemeal or one or two at a time....to keep all four tires the same diameter and rotation-speed, which lessens heat and wear on the center-differentials. I know...I owned an Outback for six years.
Lexus Champion
Joined: Jan 2012
Posts: 17,019
Likes: 496
From: Knoxville, TN
I don’t personally believe apps on phones are as accurate as their stuff, those were mentioned. I’ve used them before; they’re okay.
Thread Starter
Lexus Fanatic
Joined: May 2012
Posts: 68,466
Likes: 3,990
From: Maryland
All due respect to people here but do they have the (I’m sure insanely expensive) equipment like the big car mags do? I’m surprised nobody else has heard of this, regardless if they believe it or not.
I don’t personally believe apps on phones are as accurate as their stuff, those were mentioned. I’ve used them before; they’re okay.
I don’t personally believe apps on phones are as accurate as their stuff, those were mentioned. I’ve used them before; they’re okay.
Bear in mind too that speedometers are off by a %, the faster you go the more MPH they will be off. So if someone is seeing a 3MPH gap at highway speeds, at 100+ it would be more.
ClubLexus Stories
Celebrating Lexus & Toyota from Around the Globe
8 Tips for Improving Your Hybrid or Plug-in Hybrid's Efficiency!
Michael S. Palmer
10 Best Lexus Models No One Remembers
Joe Kucinski
TRD Off-Road Premium: Best 2026 4Runner, Except This One Thing
Michael S. Palmer
Top 10 Lexus & Toyotas to Drive Before You Die!
Joe Kucinski
Top 10 Lexus/Toyotas With The LEAST 5-Year Depreciation
Joe Kucinski
Lexus LC500 Convertible Auction: A Preview of Rising Values?
Brett Foote
GX 550 vs TX 550: Best 3-Row Luxury Lexus Family Hauler
Michael S. Palmer
9 Best Lexus Models You Can Buy for Half Price (And 1 You Shouldn't!)
Joe Kucinski
2026 Lexus NX Buyer's Guide: Models, Features, Prices & More!
Brett Foote
Lexus Champion
Joined: Jan 2012
Posts: 17,019
Likes: 496
From: Knoxville, TN
Somehow I was able to tell that my Lexuses were all about 2 MPH slow. You pass radar things on the road, look at Waze, etc. GPS for speed is actually extremely accurate.
Bear in mind too that speedometers are off by a %, the faster you go the more MPH they will be off. So if someone is seeing a 3MPH gap at highway speeds, at 100+ it would be more.
Bear in mind too that speedometers are off by a %, the faster you go the more MPH they will be off. So if someone is seeing a 3MPH gap at highway speeds, at 100+ it would be more.
Lexus Champion
Joined: Oct 2019
Posts: 18,096
Likes: 1,740
From: Ohio
Lead Lap
Joined: Jan 2003
Posts: 4,991
Likes: 519
From: Maryland
Moderator
Joined: Nov 2016
Posts: 9,597
Likes: 4,787
From: GA
Thread Starter
Lexus Fanatic
Joined: May 2012
Posts: 68,466
Likes: 3,990
From: Maryland
Lexus Champion
Joined: Apr 2019
Posts: 11,196
Likes: 1,582
From: FL
Well I might as well tell the whole story just for fun. lol
My dad is in his 70's and likes to wear baggy cargo shorts with big low pockets.
He puts his I-Phone in the big pocket so he can reach it easy but the pocket has no flap.
I warned him about going to the store like that and reached down and pulled his phone to show him how easy it is to get your phone stolen.
Well...
Last year he calls me and says someone stole his I-Phone out of his pocket while he was standing in line to get checked out at Walmart.
Surprised anyone??? haha
He said he called the police and they tracked the phone until it lost signal and was turned off somewhere in a bad neighbourhood across town.
So, since he had insurance he called and made a claim and the wait was 2 days to get one shipped expedited.
Very next day he calls me and says he needs a ride to a police station about 100 miles north.
Turns out whoever stole it- their father turned it in to a church and the church turned it into the police dept.
On the way back of approx 100 mile trip, I started my stopwatch on my Timex watch(don't laugh) and counted the mile markers back with cruise set to exactly 60 mph.
Did some math and came up with 2 MPH "over error" for the trip.
Timex watch with Indiglo technology.
Plz try to contain your excitement! haha
Spoiler
Last edited by Margate330; Jan 22, 2023 at 09:45 AM.