Bike Computer Wheel Diameter
#1
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Bike Computer Wheel Diameter
I have a bike computer and I'm having trouble setting up the correct wheel diameter for an accurate mph speed. My wheel is 700C with a 38mm tire. On the bike computer there is no 700C setting, only 6-34.
I'm trying to decide if a 700C wheel is closer in size to a 27 or 28. I'm thinking 27 but I have read that a 700C 32mm or wider is bigger than 27 and so has to be 28.
What do you think?
I'm trying to decide if a 700C wheel is closer in size to a 27 or 28. I'm thinking 27 but I have read that a 700C 32mm or wider is bigger than 27 and so has to be 28.
What do you think?
#2
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Might be helpful if you identify the brand and model of the computer.
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If it shows a list of wheel sizes, it’s making unknown assumptions about the tire size.
This is kind of a dumb way to set this up.
Cycle computers usually let you specify the radius, diameter, or circumference (basically interchangeable) of the whee/tire combination.
This lets you do a “roll out” that will take into account the wheel and tire size, what ever pressure you use, and the load (the total weight).
What you could do is compare the speed reading from the computer against a phone and pick the next higher or lower setting. (Be careful doing that.)
Last edited by njkayaker; 04-29-24 at 02:28 PM.
#5
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That's actually a great idea, I also have a Garmin Edge Explore 2 GPS, I can just compare the two and increase or decrease the input number.
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If the setting is by the circumference, then you can estimate it by adding twice the tire width to the BSD of the wheel and multiplying by 3.14. Tire height on the rim is roughly equal to it's width. A 700C wheel will always have a BSD of 622mm.
So that'd give you a circumference of 2191.72. So use 2192. If you find that is doesn't come up true when you ride a measured distance, you can adjust that number to match by just using simple math to figure out the difference.
Since you are using a really wide tire on that 700C rim, you might find your answer in the tables for a 29er or 29" tire which also will always have the same 622mm BSD. Up until recently, 700C tires where typically less than 30 mm. So a lot of tables for wheel size on bike computers never went larger.
You can also measure it by doing a roll out. Put a piece of tape on the ground and then put the valve stem of the wheel over it. With your weight on the bike, roll the tire one revolution and then measure the distance between in millimeters. Or roll several times keeping track of the number of turns and then measure and divide.
So that'd give you a circumference of 2191.72. So use 2192. If you find that is doesn't come up true when you ride a measured distance, you can adjust that number to match by just using simple math to figure out the difference.
Since you are using a really wide tire on that 700C rim, you might find your answer in the tables for a 29er or 29" tire which also will always have the same 622mm BSD. Up until recently, 700C tires where typically less than 30 mm. So a lot of tables for wheel size on bike computers never went larger.
You can also measure it by doing a roll out. Put a piece of tape on the ground and then put the valve stem of the wheel over it. With your weight on the bike, roll the tire one revolution and then measure the distance between in millimeters. Or roll several times keeping track of the number of turns and then measure and divide.
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You might ask to get this moved to the E-bike subsection there are people with some Bafang knowledge.
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What the OP said and doing a search indicates it’s a list of wheel sizes. I mentioned circumference (why it was better)and the OP didn’t come back that circumference was an option. Seems safe to conclude it doesn’t use circumference.
(It should use circumference, since that allows for a more accurate number.)
(It should use circumference, since that allows for a more accurate number.)
Last edited by njkayaker; 04-30-24 at 06:32 AM.
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The OP mentions that a Garmin Edge Explore is used too. If that's going to be a permanent fixture on the bike to get distance from both. Then that might for various activities be like the proverbial man with two watches.
But it will let the OP find a value that close enough.
But it will let the OP find a value that close enough.
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The OP mentions that a Garmin Edge Explore is used too. If that's going to be a permanent fixture on the bike to get distance from both. Then that might for various activities be like the proverbial man with two watches.
But it will let the OP find a value that close enough.
But it will let the OP find a value that close enough.
The bike is still going to report the speed, etc. What it reports should be as accurate as possible.
Last edited by njkayaker; 04-30-24 at 02:54 PM.
#11
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Guys, I got an email back from the seller and get this, he says to input "29" into the computer.
But I'm pretty sure that my 700c 38mm tire equals to a 28" 1.5 inch tire. At any rate I set it to 28 right now and will compare it to the Garmin GPS.
But I'm pretty sure that my 700c 38mm tire equals to a 28" 1.5 inch tire. At any rate I set it to 28 right now and will compare it to the Garmin GPS.
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Well if you set it to 29 you will see the maximum speed it could possibly be so it you can feel really good about your purchase.
Really it's right in between 27 and 28. You might be as much as 1.8% off!!!
Really it's right in between 27 and 28. You might be as much as 1.8% off!!!
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So does it ask for anything else? Or does it seem that you only enter the approximate overall diameter and it figures it out from there.
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https://support.biktrix.com/kb/guide...1035267,943481
Wheel Diameter
The speed display will show Wd. You will not need to change this setting unless you are putting different diameter wheels on your bike than what came with it. Press the UP and DOWN buttons to change between 16/18/20/22/24/26/700C/28/29 inch wheel diameters.
The speed display will show Wd. You will not need to change this setting unless you are putting different diameter wheels on your bike than what came with it. Press the UP and DOWN buttons to change between 16/18/20/22/24/26/700C/28/29 inch wheel diameters.
Last edited by njkayaker; 04-30-24 at 02:55 PM.
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Looking up the manual for the display shows that it provides a choice of "16/18/20/22/24/26/700C/28/29 inch wheel diameters". This doesn't match what the OP said exactly (which is why I didn't provide the link earlier). But, yes, all evidence points to only being able to enter the "approximate overall diameter". (I'm not sure why you keep insisting following a path that there is no evidence of existing. I'm also not sure why I'm the only person who appeared to do any research.)
https://support.biktrix.com/kb/guide...1035267,943481
https://support.biktrix.com/kb/guide...1035267,943481
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Research was not needed because OP is not confused at all about the way his computer works. He just wanted opinions whether to pick 27 or 28.
27 is clearly the only possible correct answer. <- this is an opinion
27 is clearly the only possible correct answer. <- this is an opinion
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"Bafang 800S" was enough to get hits. Maybe, you used too many search terms?
It wasn't quite clear what was going on. So I did a search. It was easy to provide those results.
Last edited by njkayaker; 04-30-24 at 05:08 PM.
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Just think of me as ADHD without the H and oncoming dementia from old age. <grin>
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Yes, obviously. Things should generally make sense. Having people wonder if a post of yours is one of the ones that "doesn't make sense" seems like an unreasonable ask.
Continuing to talk about the circumference is communicating that it might matter to the OP. When, as far as other indications show, it isn't relevant at all. That is, it looks like you are trying to provide an answer but you aren't really.
Continuing to talk about the circumference is communicating that it might matter to the OP. When, as far as other indications show, it isn't relevant at all. That is, it looks like you are trying to provide an answer but you aren't really.
Last edited by njkayaker; 05-01-24 at 09:32 AM.
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So does it ask for anything else? Or does it seem that you only enter the approximate overall diameter and it figures it out from there.
Maybe I'm not the only one with some type of dementia! <grin>
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This quote is suggesting the OP missed something. And that suggests that the answer still could be the circumference nonsense (it keeps this open as a possible solution).
No, it looks like you aren't paying attention. Since the answer was basically provided earlier.
And kind of lazy. But was fine with a longish (and irrelevant) post about how to do a roll-out. (You said you tried to search earlier. Here, you suggest you didn't do a search at all.)
No. Though, if you actually have dementia, it would certainly explain your posts here.
Last edited by njkayaker; 05-01-24 at 09:54 AM.
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It's the other stuff about the irrelevant circumference that looked like you were providing an answer.
This quote is suggesting the OP missed something.
No, it looks like you aren't paying attention. Since the answer was basically provided earlier.
And kind of lazy. But was fine with a longish (and irrelevant) post about how to do a roll-out. (You said you tried to search earlier. Here, you suggest you didn't do a search at all.)
If you read the posts carefully, the answer was there. Yet you kept asking pointless questions (questions the OP isn't likely to want to answer).
No. If you actually have dementia, it would certainly explain things here/
This quote is suggesting the OP missed something.
No, it looks like you aren't paying attention. Since the answer was basically provided earlier.
And kind of lazy. But was fine with a longish (and irrelevant) post about how to do a roll-out. (You said you tried to search earlier. Here, you suggest you didn't do a search at all.)
If you read the posts carefully, the answer was there. Yet you kept asking pointless questions (questions the OP isn't likely to want to answer).
No. If you actually have dementia, it would certainly explain things here/
I don't see any issues with my question. My prior statements before that don't matter anymore for that question as the OP's comment about entering a simple number that I wasn't sure was a wheel diameter or wheel size name. And I was curious if it'd also ask for something else such as width of the wheel which would have put the accuracy to which the calculation for distance and speed to maybe 2% instead of what might just be 5% or more based on what I currently understand.
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It doesn't seem like you read the OP (very carefully).
You should have read more of the comments in this thread instead of spending the time posting the long (and irrelevant) roll-out post (which indicated you didn't understand what this thread was about).
The question the OP asked was an indication that this wasn't an option.
Not surprising.
You should have read more of the comments in this thread instead of spending the time posting the long (and irrelevant) roll-out post (which indicated you didn't understand what this thread was about).
Not surprising.
Last edited by njkayaker; 05-01-24 at 10:16 AM.