Just got Ecopias installed...

[daring4]

On paper the new tires are just under half an inch taller. Factory was 185/60 new tires are 195/60 15. Scanguage showed 47 mpg on the drive home, hopefully I can keep improving the mileage... still need injector kill switch.

[gone-ot]

...what is "revolutions-per-mile" number for the original tire vs the new Ecopias? That will "...tell the tale..." as to whether you NEED to make a milage correction or not, and if so, by how much.

[daring4]

Originally Posted by Old Tele man

...what is "revolutions-per-mile" number for the original tire vs the new Ecopias? That will "...tell the tale..." as to whether you NEED to make a milage correction or not, and if so, by how much.

I was going to bring my gps to work tomorrow to check speedo error. I guess I could measure the roll out...

[user removed]

Most speedos and odos are optomistic. You may find that the larger tires actually correct that. I like to check mine on the mile markers on an Interstate, for about 50 to 100 miles. I wonder if GPS or mile markers count elevation changes and the added distance.

regards
Mech

[sheepdog 44]

I know my gps will not correct for climbing and descending hills. It'll report a mile or two under in those situations.

[gone-ot]

FWIW, GM electronic speedometers are typically 2 mph higher than reality, but the odometer "seems" to be fairly 'close', but seldom perfectly accurate.

We've had all our recent GM vehicles "calibrated" on a chassis dynometer by the shop that has the contract to calibrate the AZ highway patrol cars, so I feel the above info to be 100% verified & valid.

[NeilBlanchard]

You cannot go by the odometer or the speedometer - you need to calibrate them by driving a known distance; using the mile markers or map software or GPS. The longer the drive the better. If the tires are larger than the previous ones and/or the speedometer/odometer is overestimating your speed then is likely under estimating the distance - and both of these will combine to lower the calculated MPG when you pump the tank full each time you fill up.

The onboard factory MPG meters almost always overestimate the MPG, but with larger tires, then it might not be off by as much?

[Miller88]

Originally Posted by Old Tele man

FWIW, GM electronic speedometers are typically 2 mph higher than reality, but the odometer "seems" to be fairly 'close', but seldom perfectly accurate.

We've had all our recent GM vehicles "calibrated" on a chassis dynometer by the shop that has the contract to calibrate the AZ highway patrol cars, so I feel the above info to be 100% verified & valid.

It seems like most vehicle - I've confirmed this on a bunch of Fords and a few Chryslers.

[daring4]

Originally Posted by NeilBlanchard

You cannot go by the odometer or the speedometer - you need to calibrate them by driving a known distance; using the mile markers or map software or GPS. The longer the drive the better. If the tires are larger than the previous ones and/or the speedometer/odometer is overestimating your speed then is likely under estimating the distance - and both of these will combine to lower the calculated MPG when you pump the tank full each time you fill up.

The onboard factory MPG meters almost always overestimate the MPG, but with larger tires, then it might not be off by as much?

Neil if you dont mind me asking, how are you figuring out your mileage on the Scion? Are you running stock size tires?

[kamesama980]

Originally Posted by Miller88

It seems like most vehicle - I've confirmed this on a bunch of Fords and a few Chryslers.

Because the gov't standards say you can be a few % over but not under. That way people can't claim the speedo said they were going the speed limit when they were speeding.