speedo / odo

940 Views 7 Replies 3 Participants Last post by Pete, Apr 10, 2001

schwett

Discussion Starter · Apr 9, 2001

while on i-5 this weekend, i did a couple checks of the accuracy of my speedometer and odometer... interestingly, they were off by different amounts. the speedo is 5% fast, but the odometer is only 3% "fast." i checked several times, with the same results each time. how can they be different? in other words, if you had the speedo at exactly 60, then drove for 10 minutes, the odometer would read slightly less than 10 miles... anyone else noticed this?

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schwett

Discussion Starter · #2 · Apr 10, 2001

anyone else checked their speedo?

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Pete

· #3 · Apr 10, 2001

I've got the same problem. Ran a test with my wife in the car next to me. We got on the cell phones and matched up. When I showed 70, she showed 64. I showed 55 she showed 50, etc. I don't know about the odometer.

I still want to check it with a GPS, just haven't gotten around to it. Her car could be off in the other direction. I'm planning on going with 205/55/R16 tires when I change. I think that should give me a partial correction.

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SlntSam

· #4 · Apr 10, 2001

yeah thats what I was gunna say..maybe it's the tires or tire pressure?

When I had my ugly winter tires on my car (195/65/15) my speedo and odo were off by about 7km/h or so

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schwett

Discussion Starter · #5 · Apr 10, 2001

according to bridgestone, my current tires (215-40R17) are 879RPM whereas the stockers were 864RPM... which accounts for less than 1/2 of the error. (speedo should be off by <2%, but it's off by 5%)

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Pete

· #6 · Apr 10, 2001

<font face="Verdana, Arial" size="2">Originally posted by schwett:
according to bridgestone, my current tires (215-40R17) are 879RPM whereas the stockers were 864RPM... which accounts for less than 1/2 of the error. (speedo should be off by <2%, but it's off by 5%)</font>

What formula are you using? (just curious) I've been taking the diameter or circumference (same ratio) and comparing them to figure a percentage difference. If I switch to 205/55, I won't get much of an increase in size, a little over 3%, but every little bit helps.

The way I figure it, the diameter of the stock rims and tires is 611.4 mm. 205/40/17 would get you 595.8 mm. This is 3.55% smaller. Combine that with the 5% to 7% I think mine is off, and you're close to the 10% range.

I just wonder if Honda did this to us on purpose. 205/50 is not a very common size. 205/55 is VERY common. What size does the Accord V6 use? Maybe our speedo/odo is designed for the Accord?

Maybe they put the lower profile tires on to make the Lude SEEM faster in the tests and reviews.

Maybe they put the lower profile tires on to make the Lude handle better?

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schwett

Discussion Starter · #7 · Apr 10, 2001

no formula - i took the values directly from bridgestone's web site. i don't know how they figure it, but if you take (rim size + 2*(profile*tire width)) you'll get a slightly different number of revolutions per mile. they probably measure a properly inflated tire or something.

<font face="Verdana, Arial" size="2">Originally posted by Pete:
What formula are you using? (just curious) I've been taking the diameter or circumference (same ratio) and comparing them to figure a percentage difference. If I switch to 205/55, I won't get much of an increase in size, a little over 3%, but every little bit helps.

The way I figure it, the diameter of the stock rims and tires is 611.4 mm. 205/40/17 would get you 595.8 mm. This is 3.55% smaller. Combine that with the 5% to 7% I think mine is off, and you're close to the 10% range.

I just wonder if Honda did this to us on purpose. 205/50 is not a very common size. 205/55 is VERY common. What size does the Accord V6 use? Maybe our speedo/odo is designed for the Accord?

Maybe they put the lower profile tires on to make the Lude SEEM faster in the tests and reviews.

Maybe they put the lower profile tires on to make the Lude handle better?

</font>

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Pete

· #8 · Apr 10, 2001

OK, that's the same formula I'm using, but I didn't carry it all the way to revolutions per mile. We'd end up with the same numbers.

So to fix the error, we need to go at least 5% larger than stock. I wonder if we can do that without rubbing...

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