13x5 rims for Bounder

[Burgerman]

Some black mobility tyres are also "non marking" and just as useless.

Road tyres last way better. Tyres with substantial AREA of tread/rubber also last much better. So off road style dont live long.

The reason that decent road going tyres leave marks on carpets if they are wet is that they have carbon (carbon black) used in the rubber compound which makes them last and not crumble away as you roll. Thats what actually makes them black.

They remove this in non marking tyres, and in the black ones they add a colour (black dye) instead. But they lose the wear resistance. And instead of wearing normally they are easily cut up by the road surface and they sort of crumble away. The difference isnt small.

[fishinjunky]

Done.

What size tires fit these rims?

[emilevirus]

Done.

What size tires fit these rims?

13x5, 13x6, 14x6, 145/70 They're 4.5" wide.

[Burgerman]

All of them will fit I think but those are not tyre sizes so I cant be sure what you mean.
Its normal to find a tyre thats the overall diameter you want/need. Then choose the width you require. Then see what profiles are available and the best type of construction and tubed or tubeless and then decide if that better suits a 5, 6, or 8 inch diameter rim. And depending on tyre size which would be the best rim width. And if it need be tubeless.

You can fit a fat tyre to a narrow rim, it looks bad, and needs higher pressure. Or you can fit a skinny tyre to a rim thats either too narrow or too wide and that tyre will then sit on the rim differently. Theres no correct. It depends what you are looking for.

"NORMAL" needs would dictate a rim a small amount narrower than the tyre size/ So a 5 inch tyre would go on a 4 inch wide rim. Give or take half an inch.

figurs like 13x6 is not a tyre tize. It means nothing other than a bad description of a complete wheel.
A 15 x 6.00 - 6 is a tyre size. It is an IMPERIAL (UK old style measurement) sizing that means:
15 inch OUTER DIAMETER. 6.00 TYRE SECTION WIDTH. 6 INCH DIAMETER RIM.
(And a 4.5 or 5 inch rim is fine. As this is about an inch narrower than the tyre.)

A 145/70 - 6 is a METRIC sizing system like your car. 145mm tyre SECTION WIDTH. With a 70% tyre sidewall HEIGHT (70% of that 145mm) and so you need to add the numbers up to find the overall diameter. And it fits a 6 inch diameter rim. I will do the maths. 70% of 145mm is 101mm. Theres two sidewalls, one at the top and one at the bottom. So 101 + 101 + that 150mm (6 inch) wheel rim. So its 101 + 101 + 150 = 352mm overall diameter. Thats 14 inches and a bit... But tyre sizes are NOMINAL and most 145/70-6 tyres are about 13.5 inches and a bit small and so grip worse.

In both cases a 4.5 rim is fine.

[emilevirus]

But that's what I struggle to understand. 145/70 is supposed to be smaller but not the ones I bought. They're borderline too big. They're almost 15". Err.. After checking, the site says 145x70 not 145/70. So they're actually 14.5" x 7".

[Burgerman]

Buy glasses!

[emilevirus]

No! See: https://www.micperformance.com/products ... uMwoyvT9Iu
Title says 145/70. Description says 145x70. That explains why they were so easy to install tubeless. If you get a 13x5 there's no way you can mount them yourself. You have to go to a shop.

[Burgerman]

Product title: Pack of 4 tires KENDA 145X70-6 2PR SCORPION K290

Says 145 section width, 70% profile. 6 inch diameter rim. They have used an x instead of the / because they dont know what they are doing.
Either way that fits a 6 inch rim. There are no 145 imperial tyres. That may be a 6 x 4, 6 x 4.5 inch rim etc. Te correct way to write the rim size is rim diameter then rim width. With a J. Which means between rim beads.

So those tyres can ONLY fit a 6x4.5J or a 6x4J rim etc. Its not possible to fit a tyre that wants a 6 diameter rim to a 5 inch wheel!

2PR means equivelent to a 2 ply tyre. So weak. Flexible.
You also cannot fit a 6 inch tyre on a 5 inch rim. Its impossile. And you cant fit a 5 inch rim tyre, to any 6 inch rim diameter either No matter what tyre shop you go to.

[emilevirus]

But here's what I don't understand. Stock tire was 13" and was geared to 11.5mph. I replaced motor gears from 23T to 19T because motor would just stall if going uphills. It'd go around 9mph and gained a lot of torque. After replacing my tires to 14.5", speed is back to around 11.5mph but I don't seem to have lost torque. How?

[Burgerman]

Well unless you break the laws of physics thats impossible.

Gearing is gearing. Doesent matter if it gears, chains, wheel diameter, or whatever. Gear for half the speed and you get double the torque. Gear for double the speed and get half the torque. All else being equal.

So its in your mind. How are you measuring speed? How are you measuring torque? No seat of pants or any other non precise measurement is not accurate!

13 to 14.5 inches diameter is a 11.5% gearing increase. Or speed increase. Or torque reduction... Or battery current increase.
A gearing sprocket change from 19 to 23 is a 20% change. So 20% faster/slower. Your 11.5mph with 11.5% bigger tyres cannot be correct. How exactly are you determining this?

[fishinjunky]

@shirley_hkg what is the price for the rims with knobby 13x5.00-6 tires and shipped to the U.S?

[emilevirus]

@shirley_hkg what is the price for the rims with knobby 13x5.00-6 tires and shipped to the U.S?

He just ships the rims. Tires would cost way too much to ship. Just get them on Amazon.

[emilevirus]

A gearing sprocket change from 19 to 23 is a 20% change. So 20% faster/slower. Your 11.5mph with 11.5% bigger tyres cannot be correct. How exactly are you determining this?

Stock tire was 4" width but I think it had more contact to the ground. New tire may be 6" wide but if only 3" is actually touching the ground that'd make the motor pull less amps no?

[Burgerman]

Stock tire was 4" width but I think it had more contact to the ground. New tire may be 6" wide but if only 3" is actually touching the ground that'd make the motor pull less amps no?

I doubt you could even measure the difference. Rolling resistance will be almost identical.

Even if it DID pull a couple of % more amps, it does so to compensate. So it wouldnt change the speed. Only the range. Again how are you measuring speed?

[shirley_hkg]

£25 with alloy rims, excluding shipping.

[shirley_hkg]

Good brand name £20 with steel rims, excluding shipping.

[emilevirus]

Even if it DID pull a couple of % more amps, it does so to compensate. So it wouldnt change the speed. Only the range. Again how are you measuring speed?

Ehh.. As soon as there is a small incline, I lose 3-4 km/h. If going down an incline I've seen it go up to 22km/h. On a flat road around 17-18km/h. If going uphills around 11km/h. According to phone GPS.

[Burgerman]

Then the motors are weak, because of too high motor impedance, too high battery impedance, and/or load compensation is set too low or both. And so your gearing is much too tall for your current configuration.

If a motor had zero impedance, and the battery had zero impedance, motor compensation would never be required. As load increased on a hill, the correct amount of compensation is automatically added by ohms law. As you microscopically slow on a hill, the motor draws a proportional extra current to match the speed, battery and motor voltage to maintain speed almost exactly. Actual speed slowdown in this case would be insignificant. so your couple of extra amps naturally drawn WOULD naturally work like the compensation we have to set. However...

There are no 0 Ohm motors and 0 Ohm batteries, wiring etc. So instead we need a programmed motor load compensation algorythm to ADD the required torque as needed. By increasing voltage (pulsewidth) sent to motors get that speed back to where it should be.

With a high quality low impedance 30 to 45mOhm motors compensation works great on most chairs. If set too high it can even SPEED UP a motor under load. So it goes faster UPHILL! One way to know its set too high.
But with a higher impedance weaker motor it cannot work properly at all. Because the compensation amount needs to be huge. To try and overcome a huge RPM loss at a small load, it would need to add MUCH more power than your battery voltage allows. This gets worse the faster you travel as you are already using up all the headroom the compensation needs to work.

There should be almost zero significant speed change up or downhill with a low impedance motor and a correctly configured controller. If the motor isnt up to the job then all bets are off. And it will also eat batteries and perform very inefficiently at all speeds, and compensation cant work properly even at low speed.

GPS phone speed is only accurate in straight lines over maybe 400 yards minimum and away from buildings with 14 or more satelites. Even then I have 3 different phone GPS aps and each one reads a different figure. Lots of bad rounding and averaging of data seems to be going on in the sattelite positions/timing with these aps. That doesent matter at car speeds. It does in a low speed chair.

[Burgerman]

Let me put this another way.

If I take 2 hobby drone motors. BOTH are say 100 RPM per volt. So the SAME rpm at 20V. (2000RPM) Both have the same tiny free running unloaded current (less than 0.2A)

We feed each with 20V
Motor A is weedy, and high impedance. and turning at 2000rpm
Motor B is super low impedance heavy windings... Also turning a 2000rpm

If I load motor A it slows down a lot. And draws slightly more current but not much.
If I load motor B the SAME amount, it slows very little, because it naturally pulls much more current due to heavily increased emf.

I Cannot remove the large RPM loss on the motor A as all I have is 24V battery. 4 volts extra isnt enough even if I apply full battery voltage. I may need 30 or 40V
I can remove the small RPM loss on on B because it responds WELL to the extra 4V and draws much more current to overcome the rpm loss.

Thats what compensation tries to do. Your bounder motors are unsuitable for tall gearing. Your motor compensation will run out of steam at about 1/4 of the max speed. And be unable to do much if going any faster.

There comes a point with a low power motor (high impedance) where increasing gearing doesent make it faster at all. It can even make it slower while drawing even more current.
And as strange as it may sound a LOW impedance high current type motor actually pulls LESS battery current at any given load than a higher impedance motor. The opposite to what is intuitive. So gets better range too.

[emilevirus]

So technically if I had 9 cells, leave output voltage to around 24v. It would have a lot more headroom to compensate?

[Burgerman]

I dont know what it would do in that case as your motors seem to be too high for compensation to be effective. And the motor sag under load stays the same. It might be faster generally though. And it might kick out over voltage errors when you hit back stick brake etc.

[emilevirus]

No but right now output voltage is 25v. It only has under 1v to compensate. Even a low impedence motor would slow down. My other chair has a 30mohms motor and still slows down uphills but that's normal as I set output voltage higher. I suppose if I set voltage to 21v, it wouldn't slow down at all but then I lose speed going on flat roads. I'd rather use all speed it can provide. If I really want a constant speed I can just set speed to 75% and it'll compensate as needed.

[Burgerman]

Not quite.

A ZERO impedance motor wouldnt slow at all. If we ignore a few tiny resistance losses in batts/wiring even with no motor compensation at all. As you load it it will just draw more Amps and turn at the same speed. So it wouldnt need the "voltage" ramping up to "compensate" at all.

A low impedance motor can be helped over a large speed range. By a compensation algorythm. But it will not be able to do the FULL speed. Because its already at full speed when it slows, so it cant return the seed by ramping up.

A high impedance motor say 60mOhm or more instead of 30, can only be assisted at half the speed that the 30mOhm one can. So maybe up to 2 or 3 mph. After that speed under load it does little to nothing. But at low MOTOR SPEEDS theres still good compensation possible.

For e.g a high impedance motor maybe cannot pull 120A even is stalled. Or it JUST can. So as it begins to rotage at 1mph it generates voltage. So now it cannot pull 120A ever. No matter what % pulsewidth you apply.

Remember that CURRENT is directly proportional to AMPS. Once this high impedance motor begins spinning, it would need an EXTRA 24V to draw that 120A.

These are all simplicated figures to help you understand.

What I am really saying is that you need either 48V battery or motors with half the impedance for compensation to be effective. Its the same reason that most chairs use 2 pole motors (because cheaper but higher impedance on normal motors) of slow geared chairs because they dont need 120A to make enough torque. (Low gearing does that. Your bounder motors are approx the same impedance 2 pole motors. What is that? 70?

[emilevirus]

What is that? 70?

Double that...

[Burgerman]

Well 6mph gearing is already too much for those motors.

If they were not turning, and stalled against a wall, in order to pull 120A from the battery. If that voltage was 22V (its likely less*) your motors would need to be 183mOhm. And that would need FULL forward stick with working compensation. (ohms law).

At 1/4 full speed where the motor is already generating 1/4 of the free running voltage of 24V nominal you would need to be able to supply 6V (motor generating) + 22V to be able to reach 120A. So no amount of compensation is possible at all. Your batt voltage is too low now...

*because under load we have resistance in controller, battery, cables, etc too. With lead it is much less like 18V.


What are bounder on?
This is a case of the motor manufacturer not understanding the control system required on a chair. The control system manufacturer not knowing or having control over what motors the manufacturer will be using. Non of them understanding batteries. And the chair manufacturer understanding non of it other than how to order parts, and to make/weld up frames.
You end up with design by committee of people that only understand their own bit.