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How to calculate correct tyre pressures?

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This is for my mobility scooter. The importer specifies a ridiculous 35psi front and rear, which makes it a hard, bouncy ride, almost no give in the tyres, despite there being front and rear suspension. Dropping the front to 10psi, more heavily loaded rear, to 20psi makes things much better, but there must be a better way to calculate a correct tyre pressure, based on tyre cross-section, and the applied load.

Has anyone come across such a formula, please?
 
I set all of my tyres to 36 psi.

Yesterday, the shaded side ones were at 37, while the ones in the sun were at 41.

Driving around saw them fluctuating between 38 and 42.

Unless you're filling them with (nitrogen?), I can't see you being able to exert much fine control over them.
 
I don’t know of any such formula Harry, but 36 psi sounds ridiculous and the ride, because of the lack of weight will be most uncomfortable.
However I reckon 10 psi is too low and you run the risk of the tyre coming off the rim.....I guess the tyres are tubeless?
You also risk sidewall splitting if pressures are too low.
Maybe consider 20 psi? At least the tyres will stay on!
John
 
Start at the recommended 35psi and drop them 2psi at a time until you find what is comfortable. 10 is too low but 28 or 30 may be more comfortable.
 
However I reckon 10 psi is too low and you run the risk of the tyre coming off the rim.....I guess the tyres are tubeless?

Yes, tubeless. Even at 10psi, the tyres are barely bulging, with contact with the ground. I have brought them down, in 5psi steps. My little tractor, with tubeless tyres, recommends 10psi in the tyres.
 
According to the Veleco website, the pressure should be 32.5 psi, but that does seem a tad high.
I'm considering a class 3 scooter from Drive as this time of year all the ruddy grockles take up all the Blue Badge parking spaces and the bus is no good either.
 
The link refers to cycle tyres and on.y goes up to 2.80 width but I would suspect the principle is the same.

Google AI gives 25 to 30psi

 
According to the Veleco website, the pressure should be 32.5 psi, but that does seem a tad high.
I'm considering a class 3 scooter from Drive as this time of year all the ruddy grockles take up all the Blue Badge parking spaces and the bus is no good either.

It seems to depend on which spec. you check on which site, for pressures.

This make of scooter, comes in for a lot of criticism, because they have no UK dealer network, and the usual shops will not repair them, because they cannot get repair info on them, plus they massively undercut the dealers profit, selling direct from Poland. Parts seem not to be a problem, they sell on ebay, and they are much better specified than anything sold in the UK. They are perfect, if you can do a bit of servicing, and fixing yourself.

I eventually used my deceased partner's Class 1 Rascal, which she had hardly made use of, then it being stored for several years, unused. I found it a useful, for being easier than struggling to walk the half mile, or take the bus, certainly much quicker than getting the car out. Then a few months ago I started looking for something a bit more up-market, and spotted this Class 3 Gravis, brand new, never used, just stored for two years, but at half the cost of new, so I bought it. The Rascal sold within a week of my advertising it, and the Gravis is absolutely great, better than I expected, quite well-built in fact.

It does all the weekly local shopping, lots of storage under the seat, box on the back of the seat, a bag hook under the steering. I also shifted 3x bags of compost, just laid across the foot-plate. Unlike the Rascal, it doesn't lose speed on the up hills.
 
The link refers to cycle tyres and on.y goes up to 2.80 width but I would suspect the principle is the same.

That will be the weight, on just two tyres, mine has 4, but has a much heavier bodywork, plus my weight - so call it similar. It suggests 1.2bar, so around 17psi -ish..
 
@Harry Bloomfield It was the spares etc and their availability that made my mind up that Drive would be my first consideration. Although some other makes are less expensive, the availability of spares and service agents are essential to me. Lifestyle & Mobility are a main agent for Drive and they have a branch right in the centre of my town. I've yet to place my order, but I'll do so after a hospital appointment next Friday.
 
This " pigheaded Dutch selfdeclared tirepressure specialist " registered to answer here.

Look on tires for next.
1 maximum load or loadindex
2 kind of tire to determine the referencepressure , if you find AT xxx psi or kPa, thats the referencepressure mostly.
3 , speedcode to determine the reference-speed.
For reference-pressure and reference-speed the tiremaker calculated the maxload.

Then a scooter can be weighed per wheel with a persons-weightscale, and some help to hold it with you on it upright, without adding extra weight.


Then you can add 10% to that for reserve, and calculate lineair the needed pressure.
Then with that 10% extra, still comfort and gripp acceptable.

Or you give all the info here, and I calculate with a formula in between official for cartires ( I got hold of end 2007, and went running with) and lineair calc.
Can even make a cold pressure/ tireloadcapacity list for both , most likely different tires.
 
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