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Quick newbie question,

A friend of mine told me that when you upgrade your tires (i.e. from 15" to 17" lets say) because of the difference in diameter your speedometer has to be altered to compensate to keep it accurate. I told him this wasn't neccessary.


Please do not laugh I just need to know whether he is wrong or not thanks. :D
 

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mint said:
Quick newbie question,

A friend of mine told me that when you upgrade your tires (i.e. from 15" to 17" lets say) because of the difference in diameter your speedometer has to be altered to compensate to keep it accurate. I told him this wasn't neccessary.


Please do not laugh I just need to know whether he is wrong or not thanks. :D
Well it really isn't neccessary if you can remember that when your speedo says your doing 35, your really doing 40. I know that what mine did when I went from 15 to 17.
 

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your really doing 40. I know that what mine did when I went from 15 to 17.
What size did you go to in tire..? I went from 15's to 17's..with a 205/40/17...and my speedo shows to be maybe 1 mph off..(tested by Phoenix Police roadside speed wagons). If you went with a 45 series.then you will be off a lil more
 
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So do people actually go through the hassle of getting their speedometer changed? I just find it wierd that I've never heard of anyone bothering to get it changed when they change tire sizes...

anyone with experience with this have a price quote on how much it costs?
 

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When you go to a bigger rim, you just go to a lower profile tire. Where ever you go to buy your wheels and tires they should be able to tell you what size tire to put on those new rims so that your speedo is correct. The way I look at it, if your having to change your speedo your doing something wrong.
 
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Discussion Starter #6
ok great thanks. Yeah i didn't think it was a common thing to do.



thanks all for the advice.
 

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For a B13 with a GA16DE tire upgrades go like this, 175-70-13 = stock, 185-60-14 = plus one, 195-50-15 = plus two, 205-40-16 = plus three, etc...
 

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Black200SXSER said:


What size did you go to in tire..? I went from 15's to 17's..with a 205/40/17...and my speedo shows to be maybe 1 mph off..(tested by Phoenix Police roadside speed wagons). If you went with a 45 series.then you will be off a lil more
I went with 205/35/zr17. I did a road side by side test with a friend on stock 15's. But I didn't really get the chance like you, but I camn up with around 5 over the limit.
 

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Most people don't have their speedo readjusted because the difference in total wheel/tire diameter and speedometer reading often ends up being pretty negligible. The height of the sidewall is the most important part, you can get very close to stock size depending on what sidewall size you pick. In that case your speedo will be very nearly correct. My speedo is slightly slow and I just take that into account every time I look at it... if it shows 70, I'm actually going about 72. This usually doesn't mean the difference between getting a speeding ticket or not. One thing it also affects though, is your odometer mileage! My car has more miles on it than my odometer shows, and after many miles, I bet those fractions of miles add up. :p

But the way you adjust your speedo is with a simple adjuster pin. It doesn't cost much and I don't believe it's very difficult.
 
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