Who do I believe....Bosch Purion or Garmin?

[billwarwick]

New bike day yesterday. Cube (29)with Bosch 625 and Purion. Been riding Haibike (27.5)with Yamaha 400 for over 3 years. On the road, I was surprised how quickly I was hitting the assistance cutout. Noticed that the Purion was consistently showing speed at 1.25 mph higher than the Garmin. Which is likely to be more accurate? I squeezed 50 miles out because I wanted to see what the range was. Garmin said 50 exactly, Purion said 52. If Garmin is accurate, then I am losing assistance at 14mph.

 

[Voluptua]

Assuming the Garmin is using GPS as its data source, it's likely to be more accurate than the Purion, which is counting how many times the wheel goes round.

I believe with the Kiox you can tweak the settings to get get a closer result (tyres will vary slightly in circumference), but I don't think the Purion has this feature.

 

[Mteam]

sounds like the bosch software isnt correctly configured for your wheelsize.

With the kiox display you can specify the circumference of the wheel exactly so you can get accurate speed/distance/assist cutout, but this is not possible with purion.

Time to go back to the dealer and ask them to set the wheel circumference correctly I reckon.

 

[stiv674]

I find the GPS distance of my rides can vary, I think the bike distance is more accurate if the wheel circumference is correct.

Do the Garmin devices record distance in 3D?

 

[Konanige]

Put it this way, your car speedo isn't GPS its mechanical so provided your circumference isn't too far out (check it with some chalk on the floor) then the Purion will be more accurate than Garmin.

 

[Mikerb]

gps is more accurate??!! So on your Garmin what GPS chip is used? How many TP per second? No GPS unless V expensive is accurate. Say for example the TP rate is 1 per second...it effectively straight lines between each of those TPs. If you are travelling at 15mph you cover 22 feet in that second........perfectly straight??Thought not!
How many satellites does it track and what signal strength of each does it accept or reject? The more it tracks the less chance of a glitch in triangulation when it loses one.

 

[urastus]

gps is more accurate??!! So on your Garmin what GPS chip is used? How many TP per second? No GPS unless V expensive is accurate. Say for example the TP rate is 1 per second...it effectively straight lines between each of those TPs. If you are travelling at 15mph you cover 22 feet in that second........perfectly straight??Thought not!
How many satellites does it track and what signal strength of each does it accept or reject? The more it tracks the less chance of a glitch in triangulation when it loses one.

Yes, and I'm not sure that gps takes into account climbing or descending when measuring distance. I think it just measures everything as though you are riding on the flat. Riding in flat country gps would be accurate; in hilly or mountainous country not so accurate.

 

[billwarwick]

Thanks for the replies, but I’m still confused. The Purion is a basic controller and I have no way of changing settings. From what you guys are saying, the dealer will enter data when setting up the bike. But how much scope do they have to alter the wheel size? Would they be able to tweak it to increase or decrease the cutoff speed, or would the system not allow that? Also, it sounds like the Kiox allows you to alter settings , but to what extent? Surely Bosch would not allow too much leeway. I know that these sound like basic questions, but me and electronics are total strangers?‍.

 

[urastus]

Thanks for the replies, but I’m still confused. The Purion is a basic controller and I have no way of changing settings. From what you guys are saying, the dealer will enter data when setting up the bike. But how much scope do they have to alter the wheel size? Would they be able to tweak it to increase or decrease the cutoff speed, or would the system not allow that? Also, it sounds like the Kiox allows you to alter settings , but to what extent? Surely Bosch would not allow too much leeway. I know that these sound like basic questions, but me and electronics are total strangers?‍.

The bike probably measures speed and distance based on the circumference of your rear wheel - so many rotations to each km etc. Well, it's actually the outside circumference of whatever tyre you have fitted to the rear. Different tyres have different circumference. Even tyres with the same stated size will have different circumference. For example maxxis dhrII and dhf are fairly high volume tyres; I'm guessing a 2.6 in either of those will be a longer circumference than that size in a different brand. The easy way to measure is put a mark on a flat surface, manouvre the valve of your rear wheel directly over that mark. Move the bike forward for one full rotation of the rear tyre, until the valve is directly above the ground again - mark that off. Measure between the two marks to get the circumference. I usually subtract a cm or so because the tyre is usually a bit compressed when we're riding (our weight) - that's just my guesstimate but with me on a bike the circumference will be less to some degree. Take that measurement into the lbs - it will save him doing it. It's a pity that you can't change this yourself. And of course a new tyre will have a bigger circumference than a worn tyre - it should all be fairly close though.

 

[Mteam]

Thanks for the replies, but I’m still confused. The Purion is a basic controller and I have no way of changing settings. From what you guys are saying, the dealer will enter data when setting up the bike. But how much scope do they have to alter the wheel size? Would they be able to tweak it to increase or decrease the cutoff speed, or would the system not allow that? Also, it sounds like the Kiox allows you to alter settings , but to what extent? Surely Bosch would not allow too much leeway. I know that these sound like basic questions, but me and electronics are total strangers?‍.

On the KIOX you can alter the circumference value by plus or minus 5 percent from its factory setting. I presume a dealer is not limited by this and can set it to whatever they need to. Changing this value will and does change the cutoff speed ,on the kiox you can gain about 0.5mph at most - depending on actual wheel circumference, but its hardly noticable.

 

[GrahamPaul]

I find that the Purion consistently reads high when compared against both GPS and other riders with Yamaha and Shimano motors when we ride side by sie. Both bikes, my wife's and mine, read identical speeds when travelling along together. The difference to Garmin is around 5%.

Which is correct? None of them...

Total motor drop off doesn't happen until around 27km/hr, so I guess Bosch are doing a little "marketing" by showing a higher speed than is actually there just to make the rider feel good.

 

[Darren66]

Put it this way, your car speedo isn't GPS its mechanical so provided your circumference isn't too far out (check it with some chalk on the floor) then the Purion will be more accurate than Garmin.

You think a car speedo is accurate ?

 

[Mikerb]

Most modern car speedos are electronic. Police cars have their speedos calibrated regularly and are these days rarely inaccurate. A multi function gps device is only as accurate as the gps chip it uses and a fast multi satellite version costs more on it's own than most Garmin etc. GPS logging also needs to be fed through additional software to remove spikes and anomalies. Strava on a phone recently recorded my mates max speed as 35mph on a forest trail ride where our max speed would more likely have been about 15mph!!

 

[Mikerb]

.....and as for calculations of calories watts etc.....you should take all of that with a pinch of salt.

 

[Konanige]

You think a car speedo is accurate ?

More accurate than GPS, and if that doesnt satisfy you, how about the tachograph in my horsebox, still mechanical and accurate enough to be used as evidence in court. If you think GPS is that accurate go ride round your local quarry in the dark with no lights!??

 

[stiv674]

I had two devices recording my ride yesterday, smart watch recorded 52.34 miles, 3850ft climbing, Komoot on cheap smartphone 52.7 miles, 3250ft climbing and bike computer said 54.3 miles...

The differences between each are consistent over most rides.

My mates Garmin went mad a few weeks ago and by the time we'd finished he'd done nearly 100 miles (was actually 36) at an average of 24mph

 

[billwarwick]

I find that the Purion consistently reads high when compared against both GPS and other riders with Yamaha and Shimano motors when we ride side by sie. Both bikes, my wife's and mine, read identical speeds when travelling along together. The difference to Garmin is around 5%.

Which is correct? None of them...

Total motor drop off doesn't happen until around 27km/hr, so I guess Bosch are doing a little "marketing" by showing a higher speed than is actually there just to make the rider feel good.

Could be ‘marketing’ or covering their arse somehow. Went out again yesterday to make sure it wasn’t a one-off. There’s definitely a noticeable difference between the Bosch and the Yamaha I’ve been riding for 3+years on tarmac. Off road, can’t really notice it. Thought maybe cos I’ve gone from 27.5 to 29, I’ve got to cutoff quicker, but can’t see that. Will just have to get used to doing more pedalling .

 

[sunstoner]

New bike day yesterday. Cube (29)with Bosch 625 and Purion. Been riding Haibike (27.5)with Yamaha 400 for over 3 years. On the road, I was surprised how quickly I was hitting the assistance cutout. Noticed that the Purion was consistently showing speed at 1.25 mph higher than the Garmin. Which is likely to be more accurate? I squeezed 50 miles out because I wanted to see what the range was. Garmin said 50 exactly, Purion said 52. If Garmin is accurate, then I am losing assistance at 14mph.

Ive been meaning to ask this question too. The assistance cutout on my Haibike according to the Purion display is 16.7mph. I just put this down to the inaccuracies of the system and assumed its around the 15.5mph mark.

Maybe I should gps it to check.

 

[PanchoBuc]

It's really hard to tell, all of them will have an error. Even with the correct tire size, it will change due to temperature, pressure, elevation, and so on. Just pick one and stick with it. I always used garmin, and that's good enough for me. Also remember most garmin devices can be set up on how to sample data, and according to that, you can get also different final stats.