Is Bosch off on its speed calculations?

MisterBritcom

Active Member
Almost every car and motorcycle speedometer is optimistic by a couple of percentage points. Anyone who reads Road & Track or Cycle World tests has probably noticed this. I figure the manufacturers are choosing off the shelf parts to get as accurate a reading as possible, and choose to err on the side of caution. Better to display a little higher than a little lower, for purposes of safety and radar detection.
Why would a bike be any different?
I agree that those two mph are more important to me on a speed pedelec, so I'd look into the tire size adjustment.
 
Well the 3 comparisons were side by side as in immediate and visual and included a pace vehicle and all confirmed the same thing - that the Bosch Intuvia was reading 2 to 2.4 miles per hour faster, this meant the motor was cutting out at 26 mph vice 28 :confused: @Carterk, since we have another stock bike showing similar optimistic Intuvia data I am doubly suspicious that something is amiss. Hey folks, more data please. I am suspicious as my scientific nature demands it. Doubt data, redo and or repeat the tests, see if the same results are achieved. Scientific process of sorts. The best method of testing this would be for lots of peoples who own the Bosch Cat 3 Pedelec motors testing their Bosch Intuvia readouts and sharing them.
I agree with Rich C regarding non-military grade GPS. As for Bosch 'cheating us' on speed ( I own two Bosch Powered eBikes ) No Way : ) The
Bosch ebike motor portion of Bosch International is very tiny in their product line up, not even a blimp, so I don't see them 'wasting time etc'
fudging speed numbers....Lets say your computer is shutting down at 26 instead of 28. There's an up side to that, you'll experience longer ride
time because of slightly power drain from your battery at 26 mph

Lastly I also agree again with Rich C..." demand such extreme precision with a bicycle? After all it is supposed to be for pleasure." Great point,
getting out and riding an eBike is all about the fun, joy and freedom that eBiking offers. It's not a science project...Have fun :)
 

AlanDB

Well-Known Member
I agree with John from c too ... the speed discrepancy is not a big deal and has no impact on my riding pleasure. I don't think the speedometer innacuracy is any kind of conspiracy. What real difference does it make if it shows 12.5 MPH when you are really going 11. 2 MPH? From my tests, I personally trust the GPS speed more than I do the Bosch speedometer, but it is just a curiosity for me and has no effect on the pleasure of my ride. The Bosch drive system is wonderful, and I love it, and I love my Gazelle bike.
 
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AlanDB

Well-Known Member
Where you sitting on the bike at the time? An underinflated 2.4 in tyre could account for almost 2% speed " error" ?
Well, that is an interesting point and I don't dispute it. But another poster in the thread I posted (see the link in my earlier post) does. Does tire "squish" from weight change the actual rolling distance for one revolution altering the effective circumference? My initial thought was that it does, but that idea was challenged by another poster in the above reference. I don't really know the correct answer.
 

PDoz

Well-Known Member
Well, that is an interesting point and I don't dispute it. But another poster in the thread I posted (see the link in my earlier post) does. Does tire "squish" from weight change the actual rolling distance for one revolution altering the effective circumference? My initial thought was that it does, but that idea was challenged by another poster in the above reference. I don't really know the correct answer.
Interesting point he makes, although I think he's calculating based on the premise we're riding on a point at the tip of the tyre rather than an oval of tyre contact patch.

Try this experiment - put both f/r valves at the bottom of your tyre , completely deflate the rear tyre and roll the bike forward 5 turns - with my wifes 2.3 inch tyres that equated to a 1/4 turn difference !!!
 

rudym

Member
Please remember the initial question my post is asking - is there an error in the Bosch speed calculation methodology?
My happiness is not at stake; I love riding bicycles of all types all the time.
My question is very specific to the indicated speed on a product advertised to go up to a specific speed / level of assist before the motor cuts out.
This morning I had my police officer biking buddy who was on duty clock me on seven different runs with his freshly calibrated radar unit (we would all love to argue those calibrations in court).
Our method was for me to go as fast as I could and he would clock me at a specific point and place in time. It was a slight downhill run. I would also visually annotate my speed indicated on the intuvia, record it, and go again. On all seven runs my speed was at or above 27 mph at the point it was logged. Tires were fully inflated per Schwalbe super moto X recommendation.
My bike has the latest firmware updates from two weeks ago.
In all seven runs the radar speed read out was 1.8 to 2.2 mph less than my intuvia indicated at the same point in time.
This further supports my assumption that something is throwing something off by an average of approximately 2 mph, which means the Bosch HS motor would be dropping assist at approximately 26 mph rather than 28 mph.

So the real question is - WHY?
Yes I will explore the issue more with the LBS.
Meanwhile I hope curious others will try a similar experiment(s) with the help of a friendly law enforcement officer or two..the more data the better.
 

AlanDB

Well-Known Member
Your test adds additional credibility to the argument that the Bosch system inflates the speed shown on the speedometer. I don't know why Bosch does it, but when I raised a similar issue with my car dealer about my new car's speedometer, he explained that almost all car speedometers will show your speed a couple of MPH faster than you are really going at highway speeds. I have confirmed this with my GPS on the various cars I have owned. His theory is that it helps prevent speeding tickets. That sounded corny to me, but I suppose it is as plausible as any other explanation.
 

Mr. Coffee

Well-Known Member
@rudym

Perhaps I was not being clear.

One way to troubleshoot and better characterize the problem you appear to have is by testing the odometer. Since speed is the simple division of distance by time, I would suspect that any error in calculating the speed will show up as a similar error in the odometer -- both timekeeping and division are so simple it is hard to see how Bosch could mess those up.

Now if you find that your odometer is perfectly accurate but the indicated speeds are still incorrect you have found something genuinely interesting.

Like I said before, I bet if you can accurately characterize an odometer error you can probably figure out what was entered incorrectly in the setup for your bike.
 

rudym

Member
Your test adds additional credibility to the argument that the Bosch system inflates the speed shown on the speedometer. I don't know why Bosch does it, but when I raised a similar issue with my car dealer about my new car's speedometer, he explained that almost all car speedometers will show your speed a couple of MPH faster than you are really going at highway speeds. I have confirmed this with my GPS on the various cars I have owned. His theory is that it helps prevent speeding tickets. That sounded corny to me, but I suppose it is as plausible as any other explanation.
@AlanDB - I think consumers would always be wise to wave the bull poop flag in the face of nonsense - such as the bucket load your car dealer gave you. The consumer has a right to get what they pay for (accuracy being one thing) OR a manufacturer needs to be forth coming and honest about the short falls of a product aka known defects/discrepancies. Again I am more intrigued by the question being posed. An algorithm is only as good as the accuracy of the data it is being feed?
@Mr. Coffee What if the algorithm and the speed indication is more of a "works somewhat ok with tire sizes between A through B? So they can eliminate people fiddling with the data/code? I am trying to wrap my head around which odometer to test because I have four indicators that show the Bosch Intuvia read out is incorrect. What method would be easily validated by both TREK and BOSCH and create accountability, and action for change, assuming they care?
 
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PDoz

Well-Known Member
Here is an article that explains why car speedometers read higher than actual speed: https://www.thrillist.com/cars/your-speedometer-is-wrong-speed-calibration-inaccuracy-in-german-american-and-japanese-cars.

It doesn't really help us with our Bosch speedometer/odometer question, but still, I found it an interesting read.
I think you'll find the answer in that article - the euro regulations ( https://www.unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/r039r1e.pdf ) prohibit any speedo measuring low, but allow up to 10% high readings ( measured with a 75 kg passenger and an extra 0.2 bar tyre pressure ) - including " l" vehicles ( which includes bikes)

So if it's REALY important for someone to get the extra 10% speed, the options are presumably

Change tyres to higher profile
Pump up the tyres enough to maintain their profile ( and lose traction / comfort)
Reprogram the computer ( and risk warranty / law enforcement / public humiliation for cheating / the wrath of the speed gods et al)
Lose some weight so the tyres don't compress as much? Or perhaps that's why the pedal pumpers wear lycra...minimising weight so they can trust their speedos?

Or you could just be glad you're not stuck with a 25 km/ hr speed restriction like we are in Australia?
 

Bruce Arnold

Well-Known Member
Automobile speedometers have an expected variance. SAE standards allow up to 4% at 55 mph. That's 4% of the total mph on the speedo, not of 55 mph, so a speedometer with a top limit of 95 would have a lower absolute variance tan one with a top limit of 180. The main reason in modern cars is tire inflation and tread wear.

Can't for the life of me see why bike speedos would be so much more highly accurate. I can imagine how many hundreds of dollars per unit it would cost to get a significantly more accurate instrument.

I enjoy playing around with all kind of data from my bike, so I get the appeal of figuring this stuff out.
 

tompat

Active Member
Short answer: Yes, the Bosch speedo is showing faster than actual speed.

There is a long thread over at the German pedelec forum of this same subject.
Many are disappointed that their speed pedelecs that are supposed to assist up to 45 kmph cuts out already at 43 kmph while the display is showing 45 kmph. This is consistent with my experience of my Bosch Speed motor.
Real speed measurement can be done by any GPS device.

Funny thing is that the European type approval certificate (Certificate of Conformity) clearly states that the motor assists up to 43 kmph.

The odometer and average speed seems to be accurate by all measurements I've made.

So the Bosch system clearly measures speed accurately but is programmed to show it incorrectly on the display.

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rudym

Member
Here is an article that explains why car speedometers read higher than actual speed: https://www.thrillist.com/cars/your-speedometer-is-wrong-speed-calibration-inaccuracy-in-german-american-and-japanese-cars.

It doesn't really help us with our Bosch speedometer/odometer question, but still, I found it an interesting read.
@AlanDB - what an awesome link - I believe informationally - this is the end of the road in a manner of speaking. Adding one more sublink to it: https://caselaw.findlaw.com/ca-court-of-appeal/1587343.html
For me I would like to know about accuracy but as far as holding anyone accountable, it would seem like we can forget it.
 

rudym

Member
I think you'll find the answer in that article - the euro regulations ( https://www.unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/r039r1e.pdf ) prohibit any speedo measuring low, but allow up to 10% high readings ( measured with a 75 kg passenger and an extra 0.2 bar tyre pressure ) - including " l" vehicles ( which includes bikes)

So if it's REALY important for someone to get the extra 10% speed, the options are presumably

Change tyres to higher profile
Pump up the tyres enough to maintain their profile ( and lose traction / comfort)
Reprogram the computer ( and risk warranty / law enforcement / public humiliation for cheating / the wrath of the speed gods et al)
Lose some weight so the tyres don't compress as much? Or perhaps that's why the pedal pumpers wear lycra...minimising weight so they can trust their speedos?

Or you could just be glad you're not stuck with a 25 km/ hr speed restriction like we are in Australia?
@PDoz - great post. Thanks.
 

rudym

Member
Short answer: Yes, the Bosch speedo is showing faster than actual speed.

There is a long thread over at the German pedelec forum of this same subject.
Many are disappointed that their speed pedelecs that are supposed to assist up to 45 kmph cuts out already at 43 kmph while the display is showing 45 kmph. This is consistent with my experience of my Bosch Speed motor.
Real speed measurement can be done by any GPS device.

Funny thing is that the European type approval certificate (Certificate of Conformity) clearly states that the motor assists up to 43 kmph.

The odometer and average speed seems to be accurate by all measurements I've made.

So the Bosch system clearly measures speed accurately but is programmed to show it incorrectly on the display.

View attachment 23769
@tompat - you folks are AMAZING at your ability to dig up the good stuff. This post in and of itself, says it all. Does anyone think this creates false advertising? What is the financial benefit or legal benefits to fudging the numbers?
 
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tompat

Active Member
What is the financial benefit or legal benefits to fudging the numbers?
Guess that Bosch is doing this to keep things on the safe side of the limit. Let's say the bike was on or slightly above the 45 kmph limit they'd have a hard time in court if a bike was in an accident and the reason had anything to do with speeding.

A small number of users are disappointed with this.

Personally, I don't care, 43 or 45 kmph is almost the same. Pushing near the top speed requires a lot of effort anyways so I'm very seldom at those speeds. Normal cruising speed for me on flat terrain with no wind is about 35-40 kmph (on Bosch speedo.. ;) )

My average speed over an hour is 32 kmph which is satisfactory for me and in line with what I expected. I make my 32 km commute in less than one hour which was my objective when I bought the bike.

Enjoy your bike and don't worry too much.
 

rudym

Member
Guess that Bosch is doing this to keep things on the safe side of the limit. Let's say the bike was on or slightly above the 45 kmph limit they'd have a hard time in court if a bike was in an accident and the reason had anything to do with speeding.

A small number of users are disappointed with this.

Personally, I don't care, 43 or 45 kmph is almost the same. Pushing near the top speed requires a lot of effort anyways so I'm very seldom at those speeds. Normal cruising speed for me on flat terrain with no wind is about 35-40 kmph (on Bosch speedo.. ;) )

My average speed over an hour is 32 kmph which is satisfactory for me and in line with what I expected. I make my 32 km commute in less than one hour which was my objective when I bought the bike.

Enjoy your bike and don't worry too much.
No worries on my end, I don't worry or fret over much of anything - I just find it disturbing that "big business" in general, doesn't feel we the consumer, is worthy of the TRUTH. I really appreciate the good info!
 

JayVee

Well-Known Member
My EU COC says “ Max. Speed of motor assistance: 45 km/h” for a Yamaha powered Sduro with a PW-45.

According to the display it cuts off around 43km/h as well...
 
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