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Auto tuner needed with 240tire?

4119 Views 26 Replies 13 Participants Last post by  bandit85
Added a 240 metzler tire and lowered my bike last week but noticed lower mpg. Do I need to use a auto tuner to get my gas milage back? Has anyone had this problem?
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Toby said:
Straightjacket said:
Hey Toby, the speedos off anyway so your just fixing their screw-up by puttin on a bigger tire to correct! ;)
Ya I suppose so but I think it's not so much a screw up as it is intentional knowing you are gonna want to get and have to spend money to put a nice tire on there to fit that nice big fender.lol.
I highly doubt that.

You would think that with today's technology they could've put an accurate spedometer on the bike. Just my .02
Ok, all humor aside, I did read an an article on this subject, that stated that manufacturers of motorized vehicles including motorcycles, produce and sell vehicles with speedometers that vary in accuracy +/- 2% and often are set to read higher then the speed you are actually traveling. One article on the subject put forth that this was to prevent the manufacturer retaining any liability if there was an accident resulting from speeding etc.
this article in Car & Driver has a pretty good explanation =)


I stand corrected. Just seems that it should be dead on accurate.
MY said:
Ok. Let me get this straight. If the auto makers set the speedo off, then does that mean that the makers of GPS's set them off as well. My GPS reads the same as my speedo on my car? What do you think? I think it's all one big conspiracy, between a alien world and our Goverment. ;D
GPS is accurate as it calculates from satellite signals...time traveled between point A and point B. That's how I realized how inaccurate my stryker speedo was.....several mph under.

I beat a speeding ticket in court(me vs. a city attorney), and we got into this debate. The judge seemed to think I was right lol. Thank God I saved that gas receipt. It ended up being all the evidence I needed to prove my case. The only speeding ticket I ever got in my life.
WildFan said:
Here's my experience with gps and speedos - I've driven in my truck and car with the gps, and they both seem to match the speed shown on the gps. I've also rode my previous bike ('05 ninja with a digital speedometer readout) and my Stryker with the gps. Here's what I noticed with both of the bikes - at slower speeds the speedo read a couple mph over the gps reading. As I went faster, the gap between the speedo reading and the gps reading got larger. For both bikes, when the gps read 75mph on the freeway, my speedos on the bikes read 83mph. Again, no answers, just my experience.
Well, not to sound like an ass but that's pretty obvious. The calculation is a ratio and therefore is more distorted at a higher speed (higher number).
Eventually I see GPS technology being used for speedos. That way, your speedo would always be accurate no matter what tire size, or other modification done to the vehicle.
Gotcha.....just didn't wanna seem like an ass :p
tremorous said:
So bigger tires equals more accurate speedo? How big a tire would through the speedo to show less then what you are traveling?
It's really simple if you think about it. The speedo counts revolutions of the wheel to calculate speed. When you put a bigger tire(diameter not width), it takes longer for the wheel to make one revolution. So the speedo thinks you're going slower even though you have covered the same distance.

This is very common with trucks. I run a bigger tire than the oem, so the speedo reads a few miles slower than I'm actually going.
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