Is there a way to adjust the MINI so the speedometer will reflect the correct speed after changing wheel diameters?

Thanks

 

We recomd using a tire and wheel combination within 3% of the OD on your
original setup. Seach function will show many previous posts.

Alex

 

Visual and numeric:

Miata Tire Size Calculator

Sorry, I don't know how to adjust the speedo for different size tires. If I did, I'd run the smallest diameter tires and adjust my speedo.

 

As different Mini's come with 15", 16" and 17" tires I'd bet you can do it through the ECU? A gear swap would require 3 seperate sku's.

I just subtract about 4mph after swapping 17" runflats for 16" with 215/45 Azenis.

Pro's....what's the scoop here?

 

Wheel (rim) size has nothing to do with overall diameter of the tires. Tire size has the #1 say-so in effect of the overall diameter. Go to the miata site and play around with their tire size calc and you can see what I mean. You can get the same overall diameter from a 14" rim as you do with an 18" rim for the MINIs. It's a matter of the size of skins (tires) you put onto those rims. Remember, it's overall diameter that determines roll-out (circumference).

_________________
Happy Motorin'

 

Thank you Alex. I am aware the 3% rule you mentioned. Unfortunately, what I can't find through searching (yes I did search) is anyone who has been able to do more than a "seat of the pants" speedometer adjustment to compensate for a greater than 3% change in wheel diameter. Is it possible to compensate for this through a gearing change on the mechanical speed sensor or through a parameter change in the ECU?

Thank you

 

My '03 MC reads 4 mph faster than I am actually going. However the odometer is dead accurate, and I tested it over 300 miles on the NY State Thruway. Miles were within 2 tenths. I have the 15 inch standard tires. Dealer says there is no way to adjust. I am not sure that rim size will make that much difference. Use a GPS to determine your actual speed, for old tires and new tires, then decide for yourself.

 

I don't know of any way to change the distance impulse multiplier. FWIW, I used a handheld GPS to compare my actual speed to indicated speed when I used 205/45-16 tires:

speedo -vs- gps
enkei's
205/45-16

indicated - gps
40 - 37
60 - 55
70 - 64

 

>>My '03 MC reads 4 mph faster than I am actually going. However the odometer is dead accurate,

My MINI does the same thing. Wierd...

 

From my understanding BMW (possibly others) have a built in "fudge factor" in their speed indicators. This prevents any type of litigation where they would be on the hook because the speedo was reading slower than the actual speed of the car. It was my understanding that this "fudge factor" was progressive, aka the faster you went the farther off it was, so its interesting to hear otherwise. Maybe with the total Drive By Wire solutions, its just a static value.

The diameter of the wheel does have a direct correlation on your speed readings. Not getting into the math, but dropping your diameter by 5% causes a 5% change in speed readings. Its easy to adjust for mentally, but it would be nice to actually correct. This also affects your mileage readings, which can be an even bigger problem. Odometer is reading 100K miles, my readings were 5% off, so I only really drove 95K miles. That’s only 5K miles, but if you are running it close for a warranty issue or such, that could be enough to hurt!

But you say, 5%, that insane! That would be a huge change in tire/wheel combo. Not so. Changing from the 195/55R16 to a 205/45R16 yields a 4.83% change. Doesn't take much.

Thanks

 

Twice I was pulled over...both times the radar gun got the same value as my Speedo. Mine is dead-on accurate. I do, however, have the 17" S-Lites and Goodyear all-season runflats.

 

>>The diameter of the wheel does have a direct correlation on your speed readings. Not getting into the math, but dropping your diameter by 5% causes a 5% change in speed readings.

I wholeheartedly and respectfully disagree. Go to the miata link I gave you in the second posting in this thread. Wheel size determine wheel size. It's the "tallness" of rubber on the wheel that makes for overall diameter.

Go to the calc and leave the default numbers in for one of the tires. This is for a 14" rim. The default size is 185/60r14. Notice the diameter is 22.7 inches. This diameter is what affects your speedo...not the wheel size of 14".

Now change the dropdowns to 155/30r18. Notice this is an 18" wheel with the same diameter of 22.7 inches.

_________________
Happy Motorin'

 

>>I wholeheartedly and respectfully disagree. Go to the miata link I gave you in the second posting in this thread. Wheel size determine wheel size. It's the "tallness" of rubber on the wheel that makes for overall diameter.<<

Right. I'm only speaking from what I've read on this site, but my understanding is that the 15", 16", 17" (and presumable 18&quot wheel/tire combos offered by MINI all give you the same ultimate wheel/tire circumference, and there is no re-programming of the ECU necessary when you switch between these wheel options. Only when you go to aftermarket products might this be a necessity.

_________________
"In all matters of opinion, our adversaries are insane." -Oscar Wilde

 

I think we need to pull the needle off and stick it back on in the right place on the pin. That would put the speedo closer. Or just put stick-on markings to the face of the dial as to the real speed. Ha Ha, anybody got the guts to try?

 

I am sorry if I was unclear, but if you look at my example, the rim size did not change:

"Changing from the 195/55R16 to a 205/45R16 yields a 4.83% change."

I was speaking of the total diameter of the combination for tire and wheel. You can get these changes by changing rim diameter as well as by changing the tire diameter. We are making the same statements, just disagreeing on how we state it. :smile: This is why Alex and other re-sellers advise you to stay within +-3% of the original OEM diameter to keep the speedo from being off too much.

Again, anyone have any solution for when you go outside that 3% comfort zone?