Tire Size

DanThePodGuy · 02-26-2005, 02:16 AM

Just before the Mercedes died and we put in our name for a Prius, we put new Michelin tires on. Sicne the car is shot and the tires new I want to transfer thm to the 2005 Prius. The only difference in tire size is 195 vs. the 185 on the Prius.

I called the dealer and was told that changing the tire size would screw up all of the systems on the Prisu including the regenerative braking. Sicne the dealer said there was no way to turn off the beeping when in reverse, I am highly suspicious of anything they tell me.

Any issues with 195 tires over 185.

Thanks

ammiels · 02-26-2005, 09:58 AM

I should defer to the Mavens like Jorgenson, but.
The difference lies in the width of the tread. If the ratio is the same ie 65 then the height of the sidewall is different and therefore the rolling radius of the tire and therefore the circumference. If all 4 tires are replaced the only problem will be that any calculation that counts tire revolutions will be *somewhat* off. You will appear to be driving slower and less distance than actually. There are no safety issues involved. Your dealer lacks understanding. Peace, Ammiel
If you wish to inform yourself on this subject click on the TireRack ad and go to upsizing

ggood · 02-26-2005, 10:01 AM

I assume you're saying the Michelins are 195/65/15, in which case this tire size calculator says the speedometer would show 2.1% too slow: Miata Tire Size Calculator

Navigation system has a tire calibration setting to adjust for new size tires, which solves the problem for the navigation. I assume this also causes the speedometer to show the correct speed. I'm not sure if the non-navigation cars have this setting.

Because the tire is heavier and wider, you would see a minor reduction in fuel economy, but slightly more stability.

Based soley on reading sites like this one for the last year and a half, I'd say the other dealer arguments are bogus.

DanMan32 · 02-28-2005, 03:25 PM

No, that wouldn't solve the speedometer, or the MFD, or the odometer. The combination guage sends pulses which translates to wheel revolutions to the NAV and the MFD. The NAV compensates for the differential of distance based on revolution pulses based on GPS readings.

02-26-2005, 02:16 AM	#1
DanThePodGuy Join Date: Feb 2005 Posts: 9 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	Tire Size Just before the Mercedes died and we put in our name for a Prius, we put new Michelin tires on. Sicne the car is shot and the tires new I want to transfer thm to the 2005 Prius. The only difference in tire size is 195 vs. the 185 on the Prius. I called the dealer and was told that changing the tire size would screw up all of the systems on the Prisu including the regenerative braking. Sicne the dealer said there was no way to turn off the beeping when in reverse, I am highly suspicious of anything they tell me. Any issues with 195 tires over 185. Thanks

02-26-2005, 09:58 AM	#2
ammiels Join Date: Jan 2004 Location: brewster, ny Posts: 121 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	Re: Tire Size I should defer to the Mavens like Jorgenson, but. The difference lies in the width of the tread. If the ratio is the same ie 65 then the height of the sidewall is different and therefore the rolling radius of the tire and therefore the circumference. If all 4 tires are replaced the only problem will be that any calculation that counts tire revolutions will be somewhat off. You will appear to be driving slower and less distance than actually. There are no safety issues involved. Your dealer lacks understanding. Peace, Ammiel If you wish to inform yourself on this subject click on the TireRack ad and go to upsizing __________________ Peace, Ammiel

02-26-2005, 10:01 AM	#3
ggood ggood Join Date: Jan 2004 Location: Houston, Texas Posts: 1,290 My Car: 2010 Prius Model: V Package: Adv. Technology Thanks: 69 Thanked 163 Times in 112 Posts Friends: 6	Re: Tire Size I assume you're saying the Michelins are 195/65/15, in which case this tire size calculator says the speedometer would show 2.1% too slow: Miata Tire Size Calculator Navigation system has a tire calibration setting to adjust for new size tires, which solves the problem for the navigation. I assume this also causes the speedometer to show the correct speed. I'm not sure if the non-navigation cars have this setting. Because the tire is heavier and wider, you would see a minor reduction in fuel economy, but slightly more stability. Based soley on reading sites like this one for the last year and a half, I'd say the other dealer arguments are bogus.

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02-28-2005, 03:25 PM	#4
DanMan32 Join Date: Aug 2004 Location: Tampa Bay, FL Posts: 3,775 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	No, that wouldn't solve the speedometer, or the MFD, or the odometer. The combination guage sends pulses which translates to wheel revolutions to the NAV and the MFD. The NAV compensates for the differential of distance based on revolution pulses based on GPS readings.