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I have an hybrid bike with 28 in wheels and 40 mm wide tires. The problem is that the recommended pressure is 70 psi. They are quite thin compared to mountain bike tires and that pressure makes me feel every stone on the way. They have terrible grip making the bike slip and the wheels to deviate on any stone bigger that a pingpong ball.

In resume I feel really uncomfortable in that terrain. This problems can be solved if I go with some speed; I can just jump over the obstacles. But this is impossible in group rides as they will be going far slower (also that speed breaks don't work well: my bike just slips on stones). Some of my mates insist that I could mount wider tires without any problem. But I didn't find any wider ones on the internet. Do they even exist ? Also I really doubt that my wheels can handle wider tires as far I am aware they are made for a small variation in wide.

EDIT (looks like there is more that enought room):

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Edit2: I got 1.95 tires but the back one is hitting the frame partially it is because it is to big and partially it is because I have to true the wheel but even true they would be millimetres to frame. I cant understand why it is so much bigger!it should be only 10mm wider.

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    We have no idea what size tires you have, or what size wheels. 28' means "twenty-eight feet", and I've never seen a tire that large, even on a pennyfarthing. Is 40 the metric width or something else? And what sort of tread is on the tires? And how wide are the rims? When you say "thin" do you mean "narrow", or do you mean they have very little tread? – Daniel R Hicks Nov 25 '16 at 12:32
  • In parts of Europe 622 rims are often called 28 inch. I think they are sometimes called 29ers in the states. I suppose there is simply a prime missing, hence what Daniel interprets as feet are indeed inch. – gschenk Nov 25 '16 at 13:39
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    I assume he means 28" in the 700c/622m sense, and 40mm. – armb Nov 25 '16 at 13:46
  • Related - bicycles.stackexchange.com/questions/15172/… – armb Nov 25 '16 at 13:58
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    If the current tires are really 700c you can certainly go significantly wider. From the pictures your rims are not excessively narrow, so I'd guess you could go to 50mm or so. And the frame can handle that width and maybe a hair more (though note that a knobbier tread will cost you frame clearance). Your mistake is in looking for "28 inch" tires instead of 700c or ISO 622. – Daniel R Hicks Nov 27 '16 at 1:20
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Ok so I presume your tyres are 700x40C. First of all, that pressure sounds high - is it recommended or max pressure? I am sure you could decrease it a fair bit, although if you decrease it excessively you run the risk of pinch puntures.

If you do want to change your tyres, 700c road rims and 29" MTB rims are the same diameter, so you can use, for example, a 29x2.0" tyre - if your rim is a suitable width - see the table at the bottom of this page for recommended rim/tyre width combinations

EDIT: As armb has quite rightly pointed out, you will also need to check for sufficient frame clearance if fitting wider tyres - and remember you'll need to allow some space for mud accumulation if riding off-road

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    +1 for high pressure. I suspect a typical hybrid won't have the frame clearance to go all the way from 40mm to 50mm (1.5" to 2.0") though. – armb Nov 25 '16 at 14:08
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There are three questions: can your existing wheels take larger tyres, for which you should look at the "Width Considerations" section of Tire Sizing, can your existing frame take larger tyres without them hitting the fork, chainstays, or seatstays, (edit: now that photos have been added I don't think you will be able to go much larger), and are suitable tyres available.

However, making some assumptions about your tyre sizes, the thing you are probably missing is that tyre sizes in inches are based on an outside diameter (but often a nominal size, not the actual outside diameter of the tyre). Again, Tire Sizing will help you. Your 28" tyre is probably on a 622mm rim; mountain bike tyres for the same rim diameter are usually labelled as 29".

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