Daninplymouth 61 Report post Posted April 7, 2019 Hi I have just fitted new wheels and tyres. 225/40 18, I think these should under read by about 2% so can I just confirm where I normally set my cruise control at 75 I will now be going a little slower and not the other way. i will double check my Speedo against a sat nav but I won’t have that for a few days so just wanted make sure I had it the right way around as it’s full of speed cameras here on my little commute Share this post Link to post Share on other sites
vanko25 70 Report post Posted April 7, 2019 With that tyre setup the speedo will be reading higher than reality i.e. at 60 mph real speed will be 58.88 mph Share this post Link to post Share on other sites
Daninplymouth 61 Report post Posted April 7, 2019 47 minutes ago, vanko25 said: With that tyre setup the speedo will be reading higher than reality i.e. at 60 mph real speed will be 58.88 mph Thank you thought that was the right way. Another benefit of the wheels then it should be harder to get a speeding ticket 😁 Share this post Link to post Share on other sites
Guest 86guns Report post Posted April 8, 2019 Mine has factory 18” wheels. Do you think Toyota will have reprogrammed the speedo? 😂 Share this post Link to post Share on other sites
Daninplymouth 61 Report post Posted April 8, 2019 On 4/7/2019 at 6:56 PM, vanko25 said: With that tyre setup the speedo will be reading higher than reality i.e. at 60 mph real speed will be 58.88 mph Ah think I have this wrong and the Speedo under reads so if my Speedo says 70 I would now be doing 72 Share this post Link to post Share on other sites
Lauren 2259 Report post Posted April 8, 2019 1 hour ago, 86guns said: Mine has factory 18” wheels. Do you think Toyota will have reprogrammed the speedo? 😂 No! 😂 The speedo over reads anyway. Only way to work out your true speed is via GPS. I have a GPS speed read out from my TEIN EDFC, so have used that to get used to what speed I'm actually doing compared to the speedo reading. Share this post Link to post Share on other sites
Tarnish3 0 Report post Posted April 9, 2019 When I compare my dash readout to GPS and OBD app, it seems to read high by about 4%. That's my excuse to drive at indicated 73 anyway! From this tyre size comparison site, it suggests when changing from 17" to 18" wheels the circumferance is 3% more - which should almost negate the over reading. Although maybe everyones car is different. Share this post Link to post Share on other sites
Lauren 2259 Report post Posted April 9, 2019 38 minutes ago, Tarnish3 said: From this tyre size comparison site, it suggests when changing from 17" to 18" wheels the circumferance is 3% more - which should almost negate the over reading. Although maybe everyones car is different. I expect they're all the same. Share this post Link to post Share on other sites
Daninplymouth 61 Report post Posted April 9, 2019 Just done a little test an it over reads 1-2mph at 30,40&50 was about 2mph out at 70 so think these tyres have just reduced the over zealous stock readings Share this post Link to post Share on other sites