September 17, 20196 yr Hi guys. I've given up on my kit conversion and bought a Cube hybrid cross 500 all road. Very happy with the bike. However I've noticed that my garmin gps is at least 1mph slower than the speed recorded on the purion display. The actual speed doesn't bother me but the idea that the sensor is shutting off assist before reaching the legal limit annoys me. I did change the tyres from the smart sams (42c) to marathon plus (35c). Unfortunately I didn't attach the gps before changing them. The bosch active line plus sensor uses a magnet which probably does depend on wheel diameter. Would a smaller tyre make such a difference? What do you think?
September 17, 20196 yr Author Thanks. I'm reluctant at such an early stage (less than a weeks ownership) to tune it. If there's nothing else I can do I'll think about.
September 17, 20196 yr you can take it to the dealer and they can play about with the wheel size and try to get the extra 1mph but with a dongle it will double the top speed but you also might want a bigger front sprocket. a dongle wont effect the warranty if you dont tell them as other dealers will fit dongles and honer the warranty.
September 17, 20196 yr Author Interesting thanks:). Defo something to keep in mind. Just came across this discussion https://electricbikereview.com/forum/threads/changing-tires-wheels-on-bosch-ebike.22377/ As I have a purion display it looks like I have to get the dealer to plug into it to change the tyre circumference.
September 17, 20196 yr yes only the dealer can change that with the purion display but you can try moving the wheel magnet first and see if that can get you the extra 1mph.
September 17, 20196 yr Author Yeah that's what I was thinking. I'll move it back a bit and give it a go.
September 17, 20196 yr Hi guys. I've given up on my kit conversion and bought a Cube hybrid cross 500 all road. Very happy with the bike. However I've noticed that my garmin gps is at least 1mph slower than the speed recorded on the purion display. The actual speed doesn't bother me but the idea that the sensor is shutting off assist before reaching the legal limit annoys me. I did change the tyres from the smart sams (42c) to marathon plus (35c). Unfortunately I didn't attach the gps before changing them. The bosch active line plus sensor uses a magnet which probably does depend on wheel diameter. Would a smaller tyre make such a difference? What do you think? Easily. Can you measure the exact circumference of both of them still, I bet the difference will show that 1 MPH difference easily. Best of luck Andy
September 17, 20196 yr Author Hmmm moving magnet back or forward didnt have any noticeable effect. Hi Andy. I measured out both the 42c and 35c tyres on the ground and there was little or no difference! The 42c wasnt as well pumped as the 35c tyre (stand pump broke). In theory there should be 5cm in the difference (217cm v 220cm). 5cm every revolution - would that make that much difference? I imagine it would certainly make a difference but 1 mph seems high. John
September 17, 20196 yr Hmmm moving magnet back or forward didnt have any noticeable effect. Hi Andy. I measured out both the 42c and 35c tyres on the ground and there was little or no difference! The 42c wasnt as well pumped as the 35c tyre (stand pump broke). In theory there should be 5cm in the difference (217cm v 220cm). 5cm every revolution - would that make that much difference? I imagine it would certainly make a difference but 1 mph seems high. John One of the measurements is wrong if there is a 5 cm difference. Also, the air pressure plays a role with the radius from hub to the ground... But I have to agree that a little over 2.3% difference does seem too little to make 1 mph difference i speed, it should only make about 0.35 MPH difference, assuming the speed is set for 15 MPH (and if I got my sums right!) Maybe you can program a smaller wheel size, that should increase your speed! 24" is a popular size! I am at a loss to explain it completely, except that GPS is remarkably accurate, but speedo's were never so good. For instance on cars I believe it is allowed to show up to 5% more, but never less than the actual speed, and you are well within that tolerance. Approximately half! regards Andy
September 17, 20196 yr Author One of the measurements is wrong if there is a 5 cm difference. Also, the air pressure plays a role with the radius from hub to the ground... But I have to agree that a little over 2.3% difference does seem too little to make 1 mph difference i speed, it should only make about 0.35 MPH difference, assuming the speed is set for 15 MPH (and if I got my sums right!) Maybe you can program a smaller wheel size, that should increase your speed! 24" is a popular size! I am at a loss to explain it completely, except that GPS is remarkably accurate, but speedo's were never so good. For instance on cars I believe it is allowed to show up to 5% more, but never less than the actual speed, and you are well within that tolerance. Approximately half! regards Andy You're right Andy:) The 42c should read 222cm. I got the measurements from a cateye pdf about setting up one of their speedos. Unfortunately only a dealer can change the circumference on the purion display. I'll have a chat with them. I think they can only go up or down by 5%. If I had the intuvia display I could change it myself. Cheers John
September 17, 20196 yr You're right Andy:) The 42c should read 222cm. I got the measurements from a cateye pdf about setting up one of their speedos. Unfortunately only a dealer can change the circumference on the purion display. I'll have a chat with them. I think they can only go up or down by 5%. If I had the intuvia display I could change it myself. Cheers John Have you looked around on the web for more infos for your unit? Are any of these YouTube videos and other weblinks pertinent? https://www.google.com/search?client=firefox-b-d&q=e-bike+wheel+circumference+on+the+purion+display%3F Regards Andy
September 18, 20196 yr Hmmm moving magnet back or forward didnt have any noticeable effect. Hi Andy. I measured out both the 42c and 35c tyres on the ground and there was little or no difference! The 42c wasnt as well pumped as the 35c tyre (stand pump broke). In theory there should be 5cm in the difference (217cm v 220cm). 5cm every revolution - would that make that much difference? I imagine it would certainly make a difference but 1 mph seems high. John Moving the magnet will have zero effect. RPMs are the same. The tire size is the determining factor. Changing to a smaller tire should have you go slightly faster than the display.
September 18, 20196 yr Author Moving the magnet will have zero effect. RPMs are the same. The tire size is the determining factor. Changing to a smaller tire should have you go slightly faster than the display. Cheers Marcus. Its due a free service in 6 weeks so I'll ask them to input a smaller circumference at that stage. I'm loving the bike as it is. Getting a little more out of it would be a bonus.
September 19, 20196 yr The only way to get a true circumference is to put a mark on the tyre and floor and wheel the bike across the ground to measure the linear circumference. You must be sat on the bike to do this as the tyre compresses. Or, work out the percentage error between the devices and tell the bike shop to adjust by this percentage. I used to do this with the recorded mileage and the OS Map mileage. The figures in the tables were never correct.
September 19, 20196 yr Author The only way to get a true circumference is to put a mark on the tyre and floor and wheel the bike across the ground to measure the linear circumference. You must be sat on the bike to do this as the tyre compresses. Or, work out the percentage error between the devices and tell the bike shop to adjust by this percentage. I used to do this with the recorded mileage and the OS Map mileage. The figures in the tables were never correct. Hi Baz. I wasn't sitting on the bike when I compared the 42c with the 35c tyres. There was only a couple of mil of a difference! Maybe sitting on the bike would help to show a greater difference. In the meantime I've taken the gps off the bike so it won't wreck by head:).
September 19, 20196 yr get a dongle and be done with it will be like a hole new bike 15mph is way to slow. he had a 60s head start, and still owes me 10 quid
September 19, 20196 yr Author get a dongle and be done with it will be like a hole new bike 15mph is way to slow. he had a 60s head start, and still owes me 10 quid I've had 2 bike conversions over the years both of which were unrestricted. They were quick but this time I wanted a legal bike for fitness and one that is covered by warranty. I might think about it when the warranty is up.
September 19, 20196 yr ebike shop sells and fits dongles and honors the warranty so if the place you got it from is saying different then thats there choice alone. dongle motors have been sent to bosch and a full report shows no error on the report so as above bosch dont care. just dont tell the dealer you got it from and there is no way they could ever prove it.
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