Tire revs/mile and odometer calibration

[justme1969]

HMM? question everything that you know to be fact! LOL
Well Ive done similar and had a similar result and also gained slightly more at higher speeds. So I determined distance with combination measurements from yahoo maps and google. I dont know if they factor in cornering etc. but they did fall closer to the distance traveled by Mile marker count on a trip instate.
Afterwards I found things get real messy trying to figure multiple states but I firmly base my weekly mileage against yahoo maps rite or wrong I cant say.

[aardvarcus]

One thing that I am sure most of you are aware of, but it is worth pointing out, is that tires change diameter as they wear. On a 25” OD tire, if you wear it half way (suppose 6/32 tread wear) the radius would change (6/32”)/(12.5”)=1.5%. Thus even if you were able get the absolutely perfect speedometer adjustment done initially, as your tires wear you will start to drift away.

[PaleMelanesian]

Originally Posted by Old Mechanic

Basically an optomistic speedometer protects the manufacturer from a class action suit where many drivers would argue that an underregistering speedometer was the cause of a traffic citation.

An over registering odometer means fewer miles before the manufacturer can deny a warranty claim.

Which can also be the source of a class action suit. It happened with a number of 02-04 Hondas, including my Odyssey. My warranty ran out of years first, so it wasn't relevant to me.

[hawk2100n]

I did some digging and I was successful in finding the OE tires and size.

This doesn't apply to me but pretty much all other 6th gen Civic owners.

1996 Honda Civic EX - Technical Specs - Long-Term Wrapup- Motor Trend

Tires Firestone FR680, 185/65SR14

More digging...

Tire Sizes and Specifications Firestone FR680FR680 02



So we are looking at 886 revs per mile for the OE tires for 1996 Civics if you are on 185 65 R 14s. I am on 175 70 R 13 originally and now 175 65 R 14" so 906 revs per mile is probably closer. I would assume that all 6th gen Civics use the same tires although this may not be the case. This compares nicely to the reported revs per mile on my new Michelin Defenders at 905 revs per mile. Still doesnt change much as far as odometer accuracy but now we know.

[California98Civic]

Nice job with the OEM tire identification. The EX might have had a sportier tire, than the DX or the HX. But thanks for the citation.

Doing more calibration tests. today so far, using a good android app "GPS Odometer" I have measured a 4.14% stock odometer undercount on the stock odometer. yesterday, I measured a 4.88 undercount. The app claims to be accurate to within a % and these numbers compare well the 5.5% average undercount I got using ridewithgps.com and a handheld Garvin gps unit. I'll keep testing. But when I change over to the175/70-R13 tires that just arrived for my VX wheels, it will be fun to see of the calibration changes, because if 906 RPM was the stock rate, then these tires should change my calibration from correcting an undercount to correcting an over count on the stock odo.

EDIT: 35.93 / 34.31 = a 4.72% under count on the odo, as measured by GPS Odometer (Android tablet app).

[California98Civic]

Originally Posted by Fat Charlie

It makes sense: the more you deviate, the more slop there is to correct for. Do the best math that you can going forward, and next time you have a long trip, stop at a mile marker, zero out an odometer, fire up the GPS and go as far as you can to get the longest sample you can.

Then stay with that math until you change hardware again.

Having change the wheel tire combination from 185/65-R14 to 175/70-R13, I neededto re-calculate my odometer calibration. With GPS, on a 112 mile ride today, I calculated a 2.9% undercount on the OEM odometer. 112.54 miles (GPS) ÷ 109.3 (OEM odometer) = 1.02964. I'm gonna be slihtly conservative again and go with 2.9%.

I do not understand why this undercount persists. I expected these tires/wheels to yield an even count or and overcount. But there it is... that's what the instruments show.

[gone-ot]

...a useful equation to know: http://ecomodder.com/forum/showthrea...tml#post270069

[California98Civic]

Originally Posted by Old Tele man

...a useful equation to know: http://ecomodder.com/forum/showthrea...tml#post270069

Yes, quite cool. I also foundthis post by you a couple items downin the same thread. It's also very interesting:

Originally Posted by Old Tele man

...a tires' revolutions-per-mile (rpm) number are measured at 45 mph test speed and its rated load capacity, but that number varies with changes in speed and/or load. ...for example, below are the speedometer-vs.-actual results for my '70 AAR 'Cuda (S=speedometer; A = actual):

S = 100.0 mph, A = 102.0 mph, or 2.00% high.
S = _90.0 mph, A = _91.5 mph, or 1.67% high.
S = _80.0 mph, A = _81.2 mph, or 1.50% high.
S = _70.0 mph, A = _71.0 mph, or 1.43% high.
S = _60.0 mph, A = _60.5 mph, or 0.83% high.
S = _50.0 mph, A = _50.0 mph, or 0.00% no error.
S = _40.0 mph, A = _40.0 mph, or 0.00% no error.
S = _30.0 mph, A = _29.0 mph, or -3.33% low.
...thus, tire "error" is not static, it gets bigger above & below 45 mph!

The GPS reported my average speed about 51 mph across the 112 mile trip today. But I wonder if this table applies to steel belted tires.

james

[gone-ot]

Those were Goodyear Polyglass tires on my AAR 'Cuda, not steelbelted radials.

[California98Civic]

Ran another check of the odometer calibration using a work-related road trip today: odometer read 121.1 miles when the android GPS app showed 124.43, which is about a 2.9% undercount on the stock odometer (again).