Wheel size affecting speedo

[mikeukrainetz]

This is the first car Ive put oversize wheels on and from what I understood it would throw out my speedo quite a bit. I dont know if its because the speed sensors, ecu, etc are all digital information and they dont know the difference like the old gear driven speedo's but my car is at most +/- 3km/h with 20's.

I drove through a construction zone yesterday with the radar telling you how fast your going and I was doing 39-40km/h and the radar said 41km/h.

Anyone with plus size wheels and tires notice a speedo difference over stock?

My stock wheels were 14" w/ 185/65r14

My new wheels 20" w/ 225/35r20

I think theyre almost 4" dia different.

[YarisPR]

They told me the same. My girlfriends X5 rides on 20's and I was talking to a BMW salesman about how it got really quickly to 130mph and he told me that the speedo sometimes when you change wheel size has to be recalibrated. So he told me recalibrate it and see how fast I can really go. And after that he would tell he how the new 2007 X5 rides.... I believe he wants me to crash so I can buy another one from him :biggrin:

[kimona]

Wow! Your 20's are 11.7% taller (26.2")`than the stock 14's (23.5").

When your speedo shows 60MPH, you are actually doing 67MPH.

1. I'm curious, is there any rubbing with your wheel/tire setup?

2. I don't suppose you've lowered the car, have you?

Well, anyway you've taken care of that wheel gap issue to be sure!

[FlyingDevil]

i usually go to this site:
http://www.1010tires.com/TireSizeCalculator.asp

they have great tools in the tech section to calculate offset speedo. diff. and other stuff, check it out...
when i put ur tire info in the calc. it says that. when ur on ur 20's and ur speedo's showing 60mph, ur actually going 53.7mph. which is not very good... because there is 10.46% diameter diff. btwn ur stock and 20s. i think they recommend u to stay under 3%

[mikeukrainetz]

maybe its because I was only doing 40km that I didnt see that much of a difference? The yaris comes with 15in and 17in wheel options (at least here) so I didnt think the 20's were that much larger overall than the largest wheel / tire combo available. Although from what everyone says my car is calibrated for the 14's. So when Im doing 110km/h on the highway (giving me almost 20km over the speed limit) Im actually closer to 'excessive speeding ticket' territory...

Theres rubbing, mostly at full lock, minor rubbing in the fender wells in the front only on hard cornering with bumps. If I hit a bump midway around a corner it rubs. Nothing bad enough to warrant any major change. At some point I would like to put coilovers on it to keep the spring rate stiffer at the onset rather than progressively.
and no its not lowered, dont think thats possible.

Im still trying to price out the engine swap which might have to wait till next spring, too much on the go right now.

[FlyingDevil]

i read somewhere that the reason they dont let u exceed the 3% in diameter size is because anything over/under that might cause a brake failure