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      05-03-2014, 01:36 PM   #1
Igor@ONEighty
 
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Limited at 155MPH? Not with 6MT...

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I know the word on the street is that stock F10 M5s are limited at 155, but no say about 6MT.

Aside from BMS Stage 1 tune (which doesn't de-limit our cars), resonator delete and charcoal filter delete... the car is completely stock. Didn't get a chance to go into 6th gear either, that was at top of 5th (as you can tell the car is telling me to go into 6th).

Have a video if interested....
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      05-03-2014, 01:55 PM   #2
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Your speedo is high. Meaning if a cop were to radar you, your top speed would still be 155mph even though your speedometer says 169mph. Same with GPS. GPS will give true speed.
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      05-03-2014, 01:56 PM   #3
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Can you post the video?
I know DCT can reach 160 but 170 is interesting
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      05-03-2014, 02:33 PM   #4
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Most report an indicated 167-172MPH on the speedo, also on the DCT cars. Speedo is reading high and true speed is around 155MPH.

If we saw 180+MPH on your 6 MT car, then that would have been higher than the DCT cars do...
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      05-03-2014, 02:36 PM   #5
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Still limited like the rest of us
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      05-03-2014, 02:59 PM   #6
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what do you mean speedo reads high? you mean the actual speed is like 90 mph when speedo is reading 100 or something like this?? why???
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      05-03-2014, 03:47 PM   #7
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Quote:
Originally Posted by M6-Coupe View Post
what do you mean speedo reads high? you mean the actual speed is like 90 mph when speedo is reading 100 or something like this?? why???
Yes, every speedo reads high, for a couple of reasons

Difference in rolling circumference of tires (standard and optional tires might have a +/-5% difference in rolling circumference). When going from summer to winter tires, or from 19" to 20" tires (both available on the M5) you still want the speedo to show a higher speed than you are actually travelling in...)

A speedo is by law required to show a "fairly accurate speed reading, but not less than actual speed". This is to avoid a driver going faster than the speed limit, even though his speedo said he was going at the speed limit.

So, in order to allow for tolerances on rolling circumference (a similar size tire but from two different brands might also have a slight difference) it's important that the manufacturer calibrates the speedo to show more than real speed in any scenario while allowing for all optional tire sizes specified by the manufacturer.

And, perhaps most importantly for the driver, make sure that the speedo doesn't show less than real speed at any time. It would be unfortunate if the speedo shows 55MPH but true speed was 60MPH...

The ususal tolerance is 5-10% over true speed. Meaning that most speedos will show 94,5-99MPH when travelling at a true speed of 90MPH
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      05-03-2014, 04:15 PM   #8
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Pretty sure the BMW tolerance is 10% + 2.2mph.
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      05-03-2014, 04:24 PM   #9
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That proves nothing. Show us 180 or 190mph on the speedo then we will believe you.
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      05-03-2014, 05:09 PM   #10
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Quote:
Originally Posted by Boss330 View Post
Yes, every speedo reads high, for a couple of reasons

Difference in rolling circumference of tires (standard and optional tires might have a +/-5% difference in rolling circumference). When going from summer to winter tires, or from 19" to 20" tires (both available on the M5) you still want the speedo to show a higher speed than you are actually travelling in...)

A speedo is by law required to show a "fairly accurate speed reading, but not less than actual speed". This is to avoid a driver going faster than the speed limit, even though his speedo said he was going at the speed limit.

So, in order to allow for tolerances on rolling circumference (a similar size tire but from two different brands might also have a slight difference) it's important that the manufacturer calibrates the speedo to show more than real speed in any scenario while allowing for all optional tire sizes specified by the manufacturer.

And, perhaps most importantly for the driver, make sure that the speedo doesn't show less than real speed at any time. It would be unfortunate if the speedo shows 55MPH but true speed was 60MPH...

The ususal tolerance is 5-10% over true speed. Meaning that most speedos will show 94,5-99MPH when travelling at a true speed of 90MPH
Thanks for great explanation.
Now, I agree with the fact that speedo may read a bit high but not that much!and I am not talking about people who change the rims and tires by their own with no attention to ratios and so. I'm talking about BMW wheels installed or offered by factory. Now let's do the some calculations.
You referred to circumference. M5/M6 have standard and optional wheels.
The standard one is 19" and tires are 265/40/19 for front and 295/35/19 for rear. The diameters are 694.5mm front and 689 mm for rear
The optional wheels (343M) are coming with 265/35/20 for front and 295/30/20 for rear. now the diameters are 693mm for front and 685mm for rear. as you can see the difference in circumference between these two sets is 0.5% and not 5%!
You mentioned the calibration for manufacturer of tires and I think Michelin, Good year, Dunlop or Bridgestone, that mostly provide BMW tires are high rated in quality and accuracy.
You also explained about law which makes sense to me but how much? 5%?
this does not make sense to me. overall having a number like 1-2% may be real but 5-10% is too much! OP captured 169 mph over 155 speed limiter. what I am trying to say is that definitely the actual speed limit is not what is claimed by factory and can be something about 160-165 mph.
Anyways I'm engineer and good in math and not lawyer to know the law
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      05-03-2014, 05:36 PM   #11
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Quote:
Originally Posted by M6-Coupe View Post
Thanks for great explanation.
Now, I agree with the fact that speedo may read a bit high but not that much!and I am not talking about people who change the rims and tires by their own with no attention to ratios and so. I'm talking about BMW wheels installed or offered by factory. Now let's do the some calculations.
You referred to circumference. M5/M6 have standard and optional wheels.
The standard one is 19" and tires are 265/40/19 for front and 295/35/19 for rear. The diameters are 694.5mm front and 689 mm for rear
The optional wheels (343M) are coming with 265/35/20 for front and 295/30/20 for rear. now the diameters are 693mm for front and 685mm for rear. as you can see the difference in circumference between these two sets is 0.5% and not 5%!
You mentioned the calibration for manufacturer of tires and I think Michelin, Good year, Dunlop or Bridgestone, that mostly provide BMW tires are high rated in quality and accuracy.
You also explained about law which makes sense to me but how much? 5%?
this does not make sense to me. overall having a number like 1-2% may be real but 5-10% is too much! OP captured 169 mph over 155 speed limiter. what I am trying to say is that definitely the actual speed limit is not what is claimed by factory and can be something about 160-165 mph.
Anyways I'm engineer and good in math and not lawyer to know the law
I was also thinking of the factory set of wheels available. But since the law in EU allows tires to be changed as long as they are within +/-5% of standard rolling circumference, any manufacturer has to make allowances for aftermarket tires being as much as +5% over standard rolling circumference (not diameter BTW, diameter and circumference are two different things you know ).

Every manufacturer does this and depending on the tires that are on the car, and speed range (some have a higher tolerance at higher speeds), the "error" might range from 1% to 10%.

The M5 also has winter tires that are 255/40R19. The 265/40R19 summer tires are 1,17% larger and makes a difference of 1km/h in speedo reading.

The 167-172MPH runs done by M5 owners, have in reality been 155MPH when they have verified true speed on a GPS during their runs AFAIK. I'm pretty sure you can find several posts confirming this

Last edited by Boss330; 05-03-2014 at 05:43 PM.
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      05-03-2014, 05:43 PM   #12
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All you have to do is run a GPS app to see that the BMW speedo reads high. I've never seen an instance where the difference isn't around 5-10%.

I drive a large variety of rental cars during travel, and many of those cars' speedos are spot on. Not sure why BMW would choose to be different in this aspect. I always thought it had something to do with my 20' rims versus the base '19s.
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      05-03-2014, 05:46 PM   #13
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Quote:
Originally Posted by ShainoF10M5 View Post
All you have to do is run a GPS app to see that the BMW speedo reads high. I've never seen an instance where the difference isn't around 5-10%.

I drive a large variety of rental cars during travel, and many of those cars' speedos are spot on. Not sure why BMW would choose to be different in this aspect. I always thought it had something to do with my 20' rims versus the base '19s.
One explanation is that BMW's generally come with a variety of optional tire combinations. Making it necessary to allow for more variation in speedo readings...
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      05-03-2014, 06:07 PM   #14
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167 indicated for me. Really 155.
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      05-03-2014, 06:33 PM   #15
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Quote:
Originally Posted by Boss330 View Post
I was also thinking of the factory set of wheels available. But since the law in EU allows tires to be changed as long as they are within +/-5% of standard rolling circumference, any manufacturer has to make allowances for aftermarket tires being as much as +5% over standard rolling circumference (not diameter BTW, diameter and circumference are two different things you know ).

Every manufacturer does this and depending on the tires that are on the car, and speed range (some have a higher tolerance at higher speeds), the "error" might range from 1% to 10%.

The M5 also has winter tires that are 255/40R19. The 265/40R19 summer tires are 1,17% larger and makes a difference of 1km/h in speedo reading.

The 167-172MPH runs done by M5 owners, have in reality been 155MPH when they have verified true speed on a GPS during their runs AFAIK. I'm pretty sure you can find several posts confirming this
Thanks again... BTW 5% difference in diameter is equal to 5% difference in circumference and cause 5% difference in speed calculation since it's based on the circumference and number of rotations
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      05-04-2014, 02:38 AM   #16
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My car with stock everything also hit the speed limiter at 270 kph = 172 mph.
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      05-04-2014, 03:20 AM   #17
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An indicated 328 km/h in my car was on gps 316 km/h, which is less than 4%.
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      05-04-2014, 03:21 AM   #18
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Quote:
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Quote:
Originally Posted by Boss330 View Post
I was also thinking of the factory set of wheels available. But since the law in EU allows tires to be changed as long as they are within +/-5% of standard rolling circumference, any manufacturer has to make allowances for aftermarket tires being as much as +5% over standard rolling circumference (not diameter BTW, diameter and circumference are two different things you know ).

Every manufacturer does this and depending on the tires that are on the car, and speed range (some have a higher tolerance at higher speeds), the "error" might range from 1% to 10%.

The M5 also has winter tires that are 255/40R19. The 265/40R19 summer tires are 1,17% larger and makes a difference of 1km/h in speedo reading.

The 167-172MPH runs done by M5 owners, have in reality been 155MPH when they have verified true speed on a GPS during their runs AFAIK. I'm pretty sure you can find several posts confirming this
Thanks again... BTW 5% difference in diameter is equal to 5% difference in circumference and cause 5% difference in speed calculation since it's based on the circumference and number of rotations
That's true.

But ideally you don't want to use diameter X 3,14 when calculating the rolling circumference of a tire

A tires rolling circumference is influenced by the contact patch to the road. This creates a "flat spot" on the tire, meaning it's not a true circular shape anymore... AFAIK this means that tires of different dimensions use different "pi" to calculate rolling circumference. At least that's what ETRO (European Tire and Rim Organization) does, and they are "the law" used by the manufacturers and authorities here

The above means that just calculating tolerance based on diameter X 3,14 won't give you the correct % deviation in some cases.
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      05-04-2014, 03:23 AM   #19
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Quote:
Originally Posted by M-bitious
An indicated 328 km/h in my car was on gps 316 km/h, which is less than 4%.
Which tires and tire dimension did you have on that run?

I thought you had 21" wheels, correct?
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      05-04-2014, 06:57 AM   #20
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I got my M5 on X-Mas Eve. I had it back at the dealer before New Years complaining about the my speedometer accuracy, as I noticed it right away with no GPS or anything. I'd be rolling down the road @ say 60, and the speedo would be saying I was going faster. I had my wife roll next to me in her vehicle which confirmed my suspicions. I could just tell that this was not the case. The dealer immediately produced a piece of paper detailing BMW's range of tolerance... and that was that... I still don't like it.

Interestingly, when I was in college I ordered a new Mustang GT. I ordered it with a 3.08 rear end vs the standard 2.78 that I think 99% of the GTs on the road had. 5 minutes after I drove it off of the lot I could tell the speedo was running fast. About a week later, I took it back to the dealer and told them what was happening, that the nylon speedo drive gear was wrong, that it was the one for the 2.78 (long before electronic drives). They were, as dealers are still today, perturbed with me for "telling them what the fix was". They tried to figure out what was wrong for a day before finally realizing I was right...which made them even madder...
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      05-04-2014, 11:34 AM   #21
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Quote:
Originally Posted by Boss330 View Post
That's true.

But ideally you don't want to use diameter X 3,14 when calculating the rolling circumference of a tire

A tires rolling circumference is influenced by the contact patch to the road. This creates a "flat spot" on the tire, meaning it's not a true circular shape anymore... AFAIK this means that tires of different dimensions use different "pi" to calculate rolling circumference. At least that's what ETRO (European Tire and Rim Organization) does, and they are "the law" used by the manufacturers and authorities here

The above means that just calculating tolerance based on diameter X 3,14 won't give you the correct % deviation in some cases.
well yes and no
"pi" is always "pi" but what you are referring to is the actual diameter which is changed based on those flat spot you explained and cause different circumferences. My point is the percentage! those "flat spot" are not more than 2-3 mm and this amount for a over 600mm diameter is far less than 5% you mentioned. we are not talking about worn tires or low pressure tires which have a lot diameter and circumference deviation and we are not talking about rainy day and uneven roads which affect the calculation and you know those effects
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      05-04-2014, 01:41 PM   #22
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Quote:
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well yes and no
"pi" is always "pi" but what you are referring to is the actual diameter which is changed based on those flat spot you explained and cause different circumferences. My point is the percentage! those "flat spot" are not more than 2-3 mm and this amount for a over 600mm diameter is far less than 5% you mentioned. we are not talking about worn tires or low pressure tires which have a lot diameter and circumference deviation and we are not talking about rainy day and uneven roads which affect the calculation and you know those effects
I think you misunderstood what I was trying to say

Of course a "flat spot" doesn't account for 5% difference. My point was that ETRO use a variable pi factor depending on tire dimensions (as it logically should since the relative size of the "flat spot" will vary between large and small tires etc). This means that you can't just use pi=3,14 or pi=3,05 (as an example) for all tires...

We are still not talking about a difference of 5% in the above calculations, but I have seen examples where a generic online tire calculator says the tire is just over 5% larger than stock tire, but where the ETRO tables list the same tire size as being 4,8% larger than the stock tire. This is due to the fact that ETRO uses a tire specific "pi" factor, whereas most online tire calculators just use the same generic factor for pi (in fact some use 3,14) for ALL tire dimensions.

But these are the exceptions to the norm

The point is that the speedo has a tolerance and that it needs to allow for aftermarket tires with as much as +5% rolling circumference and still not show less than actual speed.
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