Tyre size

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Tyre size

Postby davidpaul » 29 Nov 2021, 18:48

Hello, fitted some turf tyre's to my sons chair which are 16 x 6 x 8, which have turned out too wide for accessing cafe's and toilets when we are out, it's not much maybe 50mm so 25mm each side, so been looking for other tyres about 16" diameter and found 10" scooter tyres with a diameter of 17" (so I was told) which have turned out 18" in diameter.

Is this just going to be too much for the motors ? MM V6 with 120a control module and 200ah lithium battery my son is probably average build and weight for a 21 year old.

With the 16" tyres she will still climb my test curb with me on, I'm 20 stone so a fair test.
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Re: Tyre size

Postby martin007 » 29 Nov 2021, 19:09

Why should they be too big for the motors?
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Re: Tyre size

Postby davidpaul » 29 Nov 2021, 19:39

Because of the rise in circumference, raising the gearing ? The std tyres were 14" - 15"

I should have said would the extra load be too much for the electrical system
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Re: Tyre size

Postby Burgerman » 29 Nov 2021, 22:47

I use 120/70 - 8 tyres. Where width matters. 14.4 inches tall. On 3.5 or 4 wide rims.
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Re: Tyre size

Postby davidpaul » 29 Nov 2021, 23:14

The one's i have are 120 x 80 x 10, in old money they are 18" in diameter which I would expect to reduce a bit when fitted to a rim, do you think they will be too much for the electric side of things ?
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Re: Tyre size

Postby Burgerman » 30 Nov 2021, 00:12

Maybe, less torque, less range, more heat.

These are better strong etc but not off road. https://www.wheelchairdriver.com/board/ ... 00#p122818
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Re: Tyre size

Postby davidpaul » 30 Nov 2021, 11:24

Those wont be suitable for what we use the chair for, how do the likes of Qaudrix use 24" bike wheels on their scooter/powerchairs ?

My sons V6 is modified with a 120a power module and 200ah battery pack
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Re: Tyre size

Postby Burgerman » 30 Nov 2021, 12:03

Lower gearing. If you take a 3mph powerchair motor on 14 inch wheels. And fit 28 inch wheels it then has 6mph speed and the same torque as a normal 6mph chair.
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Re: Tyre size

Postby davidpaul » 30 Nov 2021, 13:42

Then they speed it up with more volts ?
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Re: Tyre size

Postby Burgerman » 30 Nov 2021, 14:11

Motor RPM depends on volts, or equally impedance. Half the resistance in ohms = double the rpm. So does double the volts. Same thing. Ohms law.
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Re: Tyre size

Postby davidpaul » 30 Nov 2021, 19:02

There's been some confusion by the seller of the tyres, the tyre they measured was not the one I asked about, the tyre they measured at 17" was a smooth road tyre.

I'm not going to try them, it's too much work to alter the height of the castors and making an adapter for the wheels only to find out they are too big.

My search continues
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Re: Tyre size

Postby shirley_hkg » 01 Dec 2021, 05:12


I'd certainly go tubeless , if it was already using 10" rim .

It costs just £10…20 , and can last 6 years (on my chair) .
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Re: Tyre size

Postby rover220 » 01 Dec 2021, 07:19

We use 4.00-8, not tubeless though.
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Re: Tyre size

Postby Burgerman » 01 Dec 2021, 13:09

I you want to maintain the same diameter, then you must use lower profile tyres.

The 4.00 x 8 imperial inches tyres for e.g mean 8 inch rim, and a 4 inch sidewal top and bottom. So 4+8+4 means 16 diameter. Stock diameter is a 3.00x8 tyre. Which is 3+8+3 = 14 diameter.

Metric tyres are like this. 120/70-8. As on my salsa. Thats 120mm wide (less than 5 inches) with a sidewall that is 70%. So the sidewall hieght is 70% of that 5 inches width. Or 3.5 inches. 3.5+8+3.5 15 15 total. On a 3.5 to 4 inch rim thats actually 14.75 inches due to metric / inch rounding errors by me. Close enough.

Only a little taller, around 6% less torque and 6% more current and 6% faster!
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