Alright my last thread on Prem. vs. Unleaded got alot of attention, I need help with this one. I have a 2007 MC, (used) with only 8,000 plus miles. I drive this route in the mountains of Colorado almost everyday. I pass one of those speed trap things that tells you how fast your going. Well I notice that it says I'm going 4 miles an hour slower than my speedometer says I'm going. I looked at my tire sizes this morning and noticed that I have 175/65/15 are these to small for the car? Or are they the right size. And how does this effect milage? I am easily avg. over 450 miles on a tank. Now I have passed this speed machine everyday for the last week, and I have checked it everyday for the last 3, and there is definately a difference, a little help here please.

 

Many posts and threads have indicated that the MINI speedometer is off, usually showing the speed a few miles per hour faster than actual speed. Your tires are the right size for the standard 15" tires / rims. I wouldn't assume that the speed indicator you're checking is accurate, but a reading a few MPH slower than indicated is consistent with other posts. If you know someone with a GPS, you can borrow it and use it to get a very accurate MPH reading.

 

Thanks for the reply, I'm used do dealing with alot bigger tire sizes on my Fj and Jeep. Even my wifes mini van has bigger tires.

 

Your speedo reads fast, your odometer is correct. Next time you are on a nice highway reset your trip odometer at a mile marker, and you'll find your odometer will tick off perfectly with the mile markers.

In Europe the regulation on speedometers are VERY strict. So most European manufacturers will have their odometers read high. According to European standards 10MPH high is fine, but 1MPH low results in a hefty fine.

 

175/65-16 tires are usually 24" O.D. That is about 0.5" smaller than the typical 198/55-16 that comes with factory 16" wheels, or 205/45-17 that come with factory 17" wheels. They are usually around 24.5".

However, your onboard computer may have be set for 24" because the speedometer on most 2nd Gen MINIs are optimistic by 4-6 mph at 60 mph. A 10% error is not unusual.

Your tire size would only give you a 1% to 3% difference from the typical OEM 16" tire.

 

I'm going to be getting snow tires here in a few months (cringe) should I stick with the same size or go taller? Is it possible to reset the onboard computer?

 

If you want your odometer to be accurate, get the same size.

 

By going slightly larger your odometer will be off slightly.

If you have access to a GPS or ODBII reader you will find that if the radar trap states you are doing 60 then the GPS will read 60 and the ODBII will read 60. The large Speedometer will show a few miles per hour faster.

There is no way to change the accuracy of the computer.

There are probably 30 threads on this subject and all have come to the same conclusion. Stick with a tire at least close to the OEM size for any of the 15', 16", 17" or 18" rims that MINI would provide and you will find that the Odometer will be very close to accurate and the the speedometer will always read a few miles high.

BTW from band new to fully used is about a 1.2% to 1.5% change in the accuracy of both the odometer and the speedometer.

 

When I am reading the miles per hour I am reading it off the center, from the digital output. I know this is covered in a thread somewhere, but when I go a wider tire is that the 1st, 2nd or 3rd number? I'm thinking next summer, and how does that effect the speedometer, with a wider tire. Does a wider tire give you better ride. Although the ride now is great. Compared to my other cars, and hell of lot more fun!!

 

sounds like whoever owned the car previously tried to save money and put the wrong size tire on it. i would go back to the factory default size on a 16" rim.

i use a passport 9500ix (with GPS) on my MCS, when my 9500 says i am doing 62, my digital speedo (on the tach) says 65 and the wall clock reads about 66. when the 9500 says i am doing 80, digital speedo says 83-84 and the wall clock a little faster. others have reported the same issue. (i have 17" rims on my car, so can't recommend tire sizes to you, but Mini's don't seem to have the most accurate speed with factory sizes.)

you can google "Tire Size Calculator" and use the one on miata.net to figure out what size would be best. according to it, if you should have 195/65-16 tires, and are using 175/65-16 tires, then the speedo will say 60 when you actually doing 57.6 (which i believe roughly matches what you said in your original post).

 

Width of a tire does nothing to the the speed or odometer read outs.

 

Some of the MINI's came standard with 15" rims and tires. So these may be original as teh car only has 8000 miles on it according to the OP

 

175/65/15

175 - Width of tread in MM

65 - Percent of tread width as side wall height

15 - Rim diameter that the tire fits on

more info here on tire markings

http://www.tirerack.com/tires/tirete....jsp?techid=46

 

If you get tires that are not specified for the MINI, you run the risk of them rubbing other parts inside the wheel well. Make sure you know what you're doing before you spend your money.

P.S. Definitely avoid the square ones...they're a very rough ride!

 

Here it is:

http://www.miata.net/garage/tirecalc.html


This thing is awesome - plug in your standard tire size, then your "new" tire size. It tells you all kinds of comparison info, then at the bottom it will tell you your speedometer error with the new tire.

Play with different sizes and see what effects they have. Then when you need to order tires, you'll know which sizes work best.


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Now thats pretty cool. I love technology, I am looking at Nokian hakk 5 for the winter, it will be interesting to see how this effects the speedometer and the milage.

 

The tires size you have is standard for MINI 15" wheels. This is probably the most economical choice.

MINI 16x6.5" wheels usually come with 195/55-16 tires. That's a little over 3/4" wider than your tires. A wider tread will generally give you better handling, better stopping, and worse fuel economy. I bought 16x7" wheels and run 205/55-16 tires. They are about 0.4" larger than the stock 17" tires that came with my MCS. My speedo is more accurate, but still optimistic. Haven't tested it, but my odometer is probably about 2% off. I haven't had any problems with rubbing. Some people use 205/50-16 tires which would be a little undersize.

MINI 17x7" wheels come with 205/45-17" tires. Some people put wider 215 or even 225 tires on them. I have a set of 17x7" wheels, but I prefer the ride of the 16x7 set. If you keep the tire O.D. about the same--as is done on the MINI--the larger the wheel, the less sidewall there is to absorb bumps.

You may want to put snow tires on your 15" wheels (narrow tires do better in deep snow), and get a set of 16x7 wheels with wider tires for summer. Depends whether you want improved cornering and stopping, or economy.

 

Nice, but tires may vary a bit. I plugged in 205/45-17 and got a tire O.D. of 24.3" and revolutions per mile of 811.

The tires that came with my MCS were Dunlop SP Sport 01 DSST 205/45-17. The specs for them at TireRack.com say they are 24.5" O.D. and turn 853 revs per mile. That is a 5% error in revs. The revs seem to change with tire makes and models. So, you might want to check the specific tires at TireRack.

 

Great Info, Robin, I was thinking just that putting winter set on my 15s and then buying new wheels and tires in the spring which in the mountains means May. Thanks for the great info. Marc

 

+1 on all of what Robin said.