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I used to run 16" wheels stock with 225/40/16 tires

I switched to 17" wheels running 225/40/17 tires

Now I'm running 19" wheels on 235/35/19

How much of a difference will this make on my speedometer?
 

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i'm sure theres a simple (or not so simple) way to figure it out mathmatically, but the speed is clocked at the differential so there is deffinately some change in accuracy
 

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im gonna say >2 but <5 mph.
 

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what do you mean "difference on my speedometer" like you can go faster now?
 

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Originally posted by donutchow@Jun 8 2003, 10:57 AM
what do you mean "difference on my speedometer" like you can go faster now?
he means the accuracy. like if it reads 75mph he may be going around 80 becuase of his bigger wheels
 

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Originally posted by MrM3+Jun 8 2003, 07:34 PM--></span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (MrM3 @ Jun 8 2003, 07:34 PM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin--donutchow@Jun 8 2003, 10:57 AM
what do you mean "difference on my speedometer" like you can go faster now?
he means the accuracy. like if it reads 75mph he may be going around 80 becuase of his bigger wheels [/b][/quote]
yep thats right....

sorry i was in a rush and didnt have time to type....

i went from a 13" to a 17" wheel on my previous car..... although there was a 4" difference in wheel size there wasnt much difference in the profile....

if i remember i will look it up for you, if not heres how you work out the height of the wheel and tyre.... (its been a while since i have done this with out my referance chart)

so a 235/35x19.....

ok ...

235 is the width of the tyres tread in milimeters...

35 is 35% of the tyres width (= 35% of 235mm) which is the side wall height!

you then convert that figure (35% of 235mm) into inches... and then X2.

you then add that to the wheel size ? +19"

which gives you the overall height of the wheel and tyre.....

SH*T i carnt remember how you then work out the overall diameter!...... i tell you what i will get my book tommorow.... from memory its about 10%= speedo says 50mph you are actually doing 55mph.....
 
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the "35" is the percent of the width (235) that would equal the height of the sidwall...so take 19", convert it to mm, take 235*.35 add it to the 19" converted to mm, and thats the overall hiehgt, do it for the orignal set
 

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Originally posted by SpeedsterBMW@Jun 8 2003, 09:07 PM
the "35" is the percent of the width (235) that would equal the height of the sidwall...so take 19", convert it to mm, take 235*.35 add it to the 19" converted to mm, and thats the overall hiehgt, do it for the orignal set
or you could do it that way.......
:lol: :lol: :lol:
 

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BMW already has a huge problem with speedo accuracy. i think the margin is like 8% . I think that changing wheel size will be ok as long as the overall size of the rim and tire are the same as the stock ones. but if they are too big , the speedo will show you going slower than you are actually going.
 

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the way you guys are finding it is wrong... you are taking the tire width or the wheel size (19" 17" etc) but you have to find the circumference to get the rolling distance.

Step 1: finding total diameter - 19" x 1.35 (35%) = 25.65"
Step 2: finding circumfrence - 25.65 x 3.14 = 80.541" in 1 wheel rotation


so you do that for the old wheel and the new wheel. that gives you the difference. then do ratios of inches to a mile.
 
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Originally posted by Fox@Jun 14 2003, 12:08 AM
the way you guys are finding it is wrong... you are taking the tire width or the wheel size (19" 17" etc) but you have to find the circumference to get the rolling distance.

Step 1: finding total diameter - 19" x 1.35 (35%) = 25.65"
Step 2: finding circumfrence - 25.65 x 3.14 = 80.541" in 1 wheel rotation


so you do that for the old wheel and the new wheel. that gives you the difference. then do ratios of inches to a mile.
35% is .35 btw....and that 35 sidewall is the percent in height of the width of the tire, in his case 235....so in his case his sidewall is 82.25mm......id convert that into inches, and add that onto the height of the wheel....
 

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35% is .35 btw....and that 35 sidewall is the percent in height of the width of the tire, in his case 235....so in his case his sidewall is 82.25mm......id convert that into inches, and add that onto the height of the wheel....
yea but you do 1.35 to already include the 19 inches of wheel thats 135%. and its not the percent of the width its the percent of the actual wheel diameter. and even if you were right, which you are not. adding it to the hieght of the wheel will only find total diamter. You still need to find the circumfrence to get the rolling distance of 1 rotation. Stop trying to correct me when you yourself are wrong.
 
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Originally posted by Fox@Jun 14 2003, 09:00 PM
35% is .35 btw....and that 35 sidewall is the percent in height of the width of the tire, in his case 235....so in his case his sidewall is 82.25mm......id convert that into inches, and add that onto the height of the wheel....
yea but you do 1.35 to already include the 19 inches of wheel thats 135%. and its not the percent of the width its the percent of the actual wheel diameter. and even if you were right, which you are not. adding it to the hieght of the wheel will only find total diamter. You still need to find the circumfrence to get the rolling distance of 1 rotation. Stop trying to correct me when you yourself are wrong.
i hade to correct you 3 times already today...and to further support my theory that a 235/35/19 tire, has a sidewall height of 35% of 235:

4 paragraph down:

http://www.tirerack.com/tires/tiretech/gen...eneral/size.htm

now whos right, son?
 

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Discussion Starter #19
Originally posted by AZ325Ci@Jun 14 2003, 07:17 PM
Fox, you better check your sources before you post and make a fool out of yourself ;)

speedster is right on this
:werd:
 
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