My speedo won't stop bein' a dyke!
#1
Drift Nut
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My speedo won't stop bein' a dyke!
My spedometer is reading faster than it should be...but it's not consistently faster...it gets worse and worse the faster I go. I can be doing 45 on my speedo, but I'm really only doing 40...but on the other hand, my speedo is saying 110 when I'm at like 97.
How do I fix this?
Thank you very much in advance,
Collin
How do I fix this?
Thank you very much in advance,
Collin
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I should have stated before...the reason it's doing this is because I'm running 205/40-16s as opposed to the stock 185/70-15s. BIG difference.
Now I guess my real question is...how do I fix this without changing my tire size.
Thanks,
Collin
P.S.: wotnartd...that's not fixing it...
Now I guess my real question is...how do I fix this without changing my tire size.
Thanks,
Collin
P.S.: wotnartd...that's not fixing it...
#5
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I should have stated before...the reason it's doing this is because I'm running 205/40-16s as opposed to the stock 185/70-15s. BIG difference.
Now I guess my real question is...how do I fix this without changing my tire size.
Thanks,
Collin
P.S.: wotnartd...that's not fixing it...
Now I guess my real question is...how do I fix this without changing my tire size.
Thanks,
Collin
P.S.: wotnartd...that's not fixing it...
Stock size was 205/60/15...? (834 Revolutions per mile)
The tires you're running now go 927 revolutions per mile
Last edited by RoughRex; 06-05-07 at 03:22 PM.
#6
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uh, ya, tire size doesnt matter. im running 225/45, a little change doesnt matter, i would say tire size if you were running 35" mudders, THAT would mess things up. it sounds like your speedo cable is off my a tooth. try this, get under your car, and make sure the speedo cable is attached correctly to the tranny, grab the plastic collar and give it a soft twist, if nothing happened, thats not the problem. after that, get behind your guage panel and check the cable into the cluster. if its not off, then i have no idea!
peace
peace
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#8
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uh, ya, tire size doesnt matter. im running 225/45, a little change doesnt matter, i would say tire size if you were running 35" mudders, THAT would mess things up. it sounds like your speedo cable is off my a tooth. try this, get under your car, and make sure the speedo cable is attached correctly to the tranny, grab the plastic collar and give it a soft twist, if nothing happened, thats not the problem. after that, get behind your guage panel and check the cable into the cluster. if its not off, then i have no idea!
peace
peace
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do the math, if you are running 205/55/15, the sidewall would be 3.72 inch, for a grand total of ~19 inches. ok, now, if i am running 225/45/17 then my total tire size would be ~20-21 inches. if you think about it logically, at ~90 rpm, that would only be "off" by less than 2%. like i said, if you are running 35" mudders, THAT would throw it off by a little more than 11%. a toyota 4x4, running 16" wheels with 35" tires, it results by the speedo being 5 mph off, im telling you from first hand experience.
peace
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uh, if you think about it, it would only be .01mph off, being 1% change, so no, it doesnt matter.
do the math, if you are running 205/55/15, the sidewall would be 3.72 inch, for a grand total of ~19 inches. ok, now, if i am running 225/45/17 then my total tire size would be ~20-21 inches. if you think about it logically, at ~90 rpm, that would only be "off" by less than 2%. like i said, if you are running 35" mudders, THAT would throw it off by a little more than 11%. a toyota 4x4, running 16" wheels with 35" tires, it results by the speedo being 5 mph off, im telling you from first hand experience.
peace
do the math, if you are running 205/55/15, the sidewall would be 3.72 inch, for a grand total of ~19 inches. ok, now, if i am running 225/45/17 then my total tire size would be ~20-21 inches. if you think about it logically, at ~90 rpm, that would only be "off" by less than 2%. like i said, if you are running 35" mudders, THAT would throw it off by a little more than 11%. a toyota 4x4, running 16" wheels with 35" tires, it results by the speedo being 5 mph off, im telling you from first hand experience.
peace
i know it will make a difference, thats pretty much like running a stock honda civic tire on your 7
oh yea BTW i have a 86 toyota truck with stock gearing sitting on 36" super swamper tsl radials, and its off my about 15MPH... so 45 = 60.... just a lil FYI do your math!
Last edited by mort2002; 06-05-07 at 04:56 PM.
#15
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uh, if you think about it, it would only be .01mph off, being 1% change, so no, it doesnt matter.
do the math, if you are running 205/55/15, the sidewall would be 3.72 inch, for a grand total of ~19 inches. ok, now, if i am running 225/45/17 then my total tire size would be ~20-21 inches. if you think about it logically, at ~90 rpm, that would only be "off" by less than 2%. like i said, if you are running 35" mudders, THAT would throw it off by a little more than 11%. a toyota 4x4, running 16" wheels with 35" tires, it results by the speedo being 5 mph off, im telling you from first hand experience.
peace
do the math, if you are running 205/55/15, the sidewall would be 3.72 inch, for a grand total of ~19 inches. ok, now, if i am running 225/45/17 then my total tire size would be ~20-21 inches. if you think about it logically, at ~90 rpm, that would only be "off" by less than 2%. like i said, if you are running 35" mudders, THAT would throw it off by a little more than 11%. a toyota 4x4, running 16" wheels with 35" tires, it results by the speedo being 5 mph off, im telling you from first hand experience.
peace
BFGoodrich G-Force Sport
205/60/15----24.7" dia----843 rpmi (stock size)
205/55/16----24.9" dia----836 rpmi (stock size)
*note less than 1% difference in dia and rpmi
225/45/17----24.3" dia----856 rpmi (your tire) ~1.5-2.5% discrepancy in dia and rpmi meh.... I could probably live with that for the extra width. but the correct size for you is ---> 215/45/17----24.6" dia----844 rpmi
205/40/16----22.4" dia----927 rpmi (OP's tire) ~10% discrepancy in dia and rpmi
#16
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There's the problem...
FYI Rex, I'm running 205/40ZR16 Khumo SPTs
Thanks for the insight. Can toss that math up there. I got different numbers when I did it...probably something I left out?
FYI Rex, I'm running 205/40ZR16 Khumo SPTs
Thanks for the insight. Can toss that math up there. I got different numbers when I did it...probably something I left out?
#21
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The FC speed "sensor" is built into the transmission and is mechanical and isn't the same as a miata.
I guess if it's off you have to "deal with it." Here's a tip though: if you can find a friend or anyone with a new Civic, just look at them while they're driving next to you and figure out what RPM corresponds to their GIGANTIC speedometer built into their dash. That thing is visible from miles away. I mean it's HUGE.
I guess if it's off you have to "deal with it." Here's a tip though: if you can find a friend or anyone with a new Civic, just look at them while they're driving next to you and figure out what RPM corresponds to their GIGANTIC speedometer built into their dash. That thing is visible from miles away. I mean it's HUGE.
Last edited by MidnightOwl; 06-05-07 at 07:09 PM. Reason: I can't spell.
#22
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You can calculate a rim/tire's rolling circumference from the tire size: (2*(section width*(profile/100))+(rim diameter*25.4))*pi - will give the circumference in mm (hence the rim size *25.4 to convent the only imperial measure into metric)
For example, my stock tires: 205/60-15 - (2*(205*.60)+(15*25.4))*pi=1970mm
my current street tires: 225/50-16 (2*(225*.60)+(16*25.4)*pi=1984mm, not even 1% larger than stock, so the speedometer would read 1% slower - insignficant. Tire pressures and tread wear likely contribute more to any speedometer error in this case.
with the OP's tire sizes - original 185/70/15 (I thought the 15's always came with 205/60s, but anyway) (2*(185*.70)+(15*25.4)*pi=2011mm
and the current tires: (2(205*.40)+(16*25.4))*pi=1792mm, which is 12% smaller than stock circumference, and hence speedo error will be about 12% fast - almost exactly the percentage difference reported at speeds.
You can get this fixed by having your speedometer re-geared, but that's probably not cost effective, or you can learn to mentally adjust the indicated speed down by a bit more than 10%. Or you could put properly sized tires on it, which is probably the best idea, since this is a relatively huge difference - your engine, gearbox, diff, and wheel bearings are all turning 12% more for every mile you cover, which will translate to increased wear and fuel consumption (remember if you calculate you mileage to reduce the odometer reading by 12% to get actual miles driven).
For example, my stock tires: 205/60-15 - (2*(205*.60)+(15*25.4))*pi=1970mm
my current street tires: 225/50-16 (2*(225*.60)+(16*25.4)*pi=1984mm, not even 1% larger than stock, so the speedometer would read 1% slower - insignficant. Tire pressures and tread wear likely contribute more to any speedometer error in this case.
with the OP's tire sizes - original 185/70/15 (I thought the 15's always came with 205/60s, but anyway) (2*(185*.70)+(15*25.4)*pi=2011mm
and the current tires: (2(205*.40)+(16*25.4))*pi=1792mm, which is 12% smaller than stock circumference, and hence speedo error will be about 12% fast - almost exactly the percentage difference reported at speeds.
You can get this fixed by having your speedometer re-geared, but that's probably not cost effective, or you can learn to mentally adjust the indicated speed down by a bit more than 10%. Or you could put properly sized tires on it, which is probably the best idea, since this is a relatively huge difference - your engine, gearbox, diff, and wheel bearings are all turning 12% more for every mile you cover, which will translate to increased wear and fuel consumption (remember if you calculate you mileage to reduce the odometer reading by 12% to get actual miles driven).
#24
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Look around for a speedo repair/ calibration service...here in Denver, the same shop that calibrates the units for the State Patrol will do it for you too.
They build a little gearbox that goes between the speedo and cable to correct for wheel/tire or transmission swaps.
As an added bonus you get a certificate of calibration so the next time a cop asks "Do you know how fast you were traveling, sir?" you can say "As a matter of fact I do, dickweed".
You and all your new cellmate friends will laugh and laugh.
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