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Tyre Pressures

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scotia
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Tyre Pressures

#347477

Postby scotia » October 13th, 2020, 5:53 pm

My (electrically assisted) folding bike has 20 inch wheels with tyres which should be inflated in the range 40 to 60 psi. Is it OK to operate these at a significantly lower pressure? I know it will increase the rolling resistance, but it will also make the ride a bit more comfortable along our old tarmac-surfaced former railway line, where tree roots have turned it into a corrugated track. Or maybe I need a mountain bike with appropriate suspension :)

staffordian
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Re: Tyre Pressures

#347485

Postby staffordian » October 13th, 2020, 6:07 pm

My preference has always been to inflate the rear tyre harder than the front as that is where there is most weight.

The key problem with underinflation is the greater tendency for snakebite punctures, where the inner tube becomes sandwiched against a rim when the tyre hits a bump, and the inner tube receives two nicks.

A second issue might be a lack of precision in steering and control as the tyres will have a greater tendency to move sideways under lateral pressure such as when cornering.

Others may disagree, but I don't feel there is a major issue as far as additional wear or structural damage to the tyre is concerned, as there definitely would be with a car tyre, so I would suggest the best bet might be to start with the front at just under the 40 mark, the rear a little higher and go from there, reducing them over a period of time if you get no ill effects.
Last edited by staffordian on October 13th, 2020, 6:15 pm, edited 1 time in total.

UncleEbenezer
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Re: Tyre Pressures

#347486

Postby UncleEbenezer » October 13th, 2020, 6:12 pm

scotia wrote:My (electrically assisted) folding bike has 20 inch wheels with tyres which should be inflated in the range 40 to 60 psi. Is it OK to operate these at a significantly lower pressure? I know it will increase the rolling resistance, but it will also make the ride a bit more comfortable along our old tarmac-surfaced former railway line, where tree roots have turned it into a corrugated track. Or maybe I need a mountain bike with appropriate suspension :)


That's already pretty low pressure. Lowering it further will increase the tyre's momentary distortion each time it passes the bottom of the wheel and takes your weight. That in turn can lead to damage including splitting. That applies more to a narrower tyre than a big fat one.

The easiest way to introduce suspension is in the bit that goes between the pedals, saddle and handlebars. Occasionally it might even want to detach from the saddle part of that if the terrain is rough.

scotia
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Re: Tyre Pressures

#347487

Postby scotia » October 13th, 2020, 6:25 pm

UncleEbenezer wrote:
scotia wrote:My (electrically assisted) folding bike has 20 inch wheels with tyres which should be inflated in the range 40 to 60 psi. Is it OK to operate these at a significantly lower pressure? I know it will increase the rolling resistance, but it will also make the ride a bit more comfortable along our old tarmac-surfaced former railway line, where tree roots have turned it into a corrugated track. Or maybe I need a mountain bike with appropriate suspension :)


That's already pretty low pressure. Lowering it further will increase the tyre's momentary distortion each time it passes the bottom of the wheel and takes your weight. That in turn can lead to damage including splitting. That applies more to a narrower tyre than a big fat one.

The easiest way to introduce suspension is in the bit that goes between the pedals, saddle and handlebars. Occasionally it might even want to detach from the saddle part of that if the terrain is rough.

I assure you I had to frequently detach that part from the saddle. :D

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Re: Tyre Pressures

#347534

Postby servodude » October 13th, 2020, 11:02 pm

scotia wrote:My (electrically assisted) folding bike has 20 inch wheels with tyres which should be inflated in the range 40 to 60 psi. Is it OK to operate these at a significantly lower pressure? I know it will increase the rolling resistance, but it will also make the ride a bit more comfortable along our old tarmac-surfaced former railway line, where tree roots have turned it into a corrugated track. Or maybe I need a mountain bike with appropriate suspension :)


as long as you're not bottoming out on bumps you should be OK (have someone watch your wheels as you ride past)
you might consider fatter tyres if they could fit (you don't say what width you have on)

My current daily commuter I got from the Embra Co-op after queuing outside for their new year sale years ago
- rode home in the snow on 2.25" tyres at what must have been 30psi; it was like riding an arm chair (both in sensation and speed!)
- it also had a suspension seat post which could be an option?

- sd

GrahamPlatt
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Re: Tyre Pressures

#347552

Postby GrahamPlatt » October 14th, 2020, 7:33 am

Had the same problem myself. Swapped the seat & all is well now.

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Re: Tyre Pressures

#347585

Postby Gerry557 » October 14th, 2020, 10:19 am

Others have mentioned most of the points.

Personally I would adopt the "honk" position, semi stood up, bent knees and arms, bottom hovering over seat, acting as personal suspension over those type obstacles unless it is the whole route continually.

You can get bouncy seat posts and or front suspension forks or change the bike to full suspension! Each costing increasing amounts.

UncleEbenezer
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Re: Tyre Pressures

#347619

Postby UncleEbenezer » October 14th, 2020, 11:48 am

Gerry557 wrote:Personally I would adopt the "honk" position, semi stood up, bent knees and arms, bottom hovering over seat,

Was that meant to be posted in this thread? :twisted:

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Re: Tyre Pressures

#347665

Postby redsturgeon » October 14th, 2020, 3:57 pm

In addition to the points already raised I would add that for a bumpy track 20 inch wheels will always be sub optimal compared with larger wheels. 26 inch wheels used to be the standard for off road bikes but now it is 27.5 or even 29 inch. The larger wheels taking larger tyres with more air volume to soak up the bumps and being able to ride over the bumps rather than down into each dip makes for a significantly smoother ride. Those who wish to run very low pressures while avoiding snake bites can also go tubeless, so no inner tube to pinch.

John

scotia
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Re: Tyre Pressures

#348111

Postby scotia » October 15th, 2020, 10:05 pm

I should probably have added that the 20 inch wheels are on a folding bike (Carrera Crossscity), which can fit in my car's boot. The tyres are Kenda 20 by 1.75. Although the bike's name suggests I should be on smooth tarmac roads, I have actually used it to penetrate deep into Assynt fishing territory on peat roads - originally designed for pony and cart. And it coped adequately. But its the track much nearer home that is now proving more difficult - and it will only get worse. The disused railway line was given a tarmac cover several years ago - ideal for cycle riding at that time. But there are long sections with trees on either side which have their roots crossing the track- underneath the tarmac. And the roots have grown creating bulging corrugations which will only get worse. I was off on the track again today, and I now realise that the worst effect is the jolting through the arms, since I can stand out of the seat on going over the corrugations. So I haven't proceeded with a seat suspension system. I have tried adjusting the handlebar position to allow some bend in my arms, which should help a little - along with going more slowly on underinflated tyres. The obvious cure is to get the local authority to add a further tarmac coating a few centimetres thick. But I suppose that's unlikely. On the bright side, the canal towpath is still corrugation free.

redsturgeon
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Re: Tyre Pressures

#348565

Postby redsturgeon » October 18th, 2020, 7:14 am

It is simply the wrong bike for the job. You need larger wheels, bigger tyres capable of running lower pressures and also front suspension. With all that your track will be a pleasure to ride. Anything else, while you can minimise the discomfort, will always be suboptimal.

John


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