Newbie tyre size question

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tomtom090477
Posts: 5
Joined: 25 May 2020, 9:39am

Newbie tyre size question

Postby tomtom090477 » 25 May 2020, 9:51am

Hi Folks,
I'm new on here. Although I have some experience of tinkering with bikes one thing still leaves me constantly confused: wheel/rim/tyre size. I've read that Sheldon Brown thing about it and loads of other pieces but am still so confused!
In this Covid bike rush my GF has asked me to fix up an old bike. The bike in question has rims that have this measurement: 18 x 622 (28 x 1 5/8) 0.9. I have a tyre that is 25-622 (28 x 1.00 - 700 x 25c). Clearly this is totally the wrong fit as it is very loose on the rim. What size tyre do I need (bearing in mind this is for plodding around on).

Would really appreciate your advice!

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531colin
Posts: 12970
Joined: 4 Dec 2009, 6:56pm
Location: North Yorkshire

Re: Newbie tyre size question

Postby 531colin » 25 May 2020, 2:06pm

Should be right
622 is the bead seat diameter
18 is the rim internal width
25 is the tyre width
So it should be an "OK" fit; ideally a wider tyre, because 25 isn't a lot wider than the rim

LittleGreyCat
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Joined: 7 Aug 2013, 8:31pm

Re: Newbie tyre size question

Postby LittleGreyCat » 25 May 2020, 3:22pm

Did you bother to pump up the inner tube, or just notice that the tyre was loose when first fitted uninflated?

Carefully pumping it up should result in a snug fit.

tomtom090477
Posts: 5
Joined: 25 May 2020, 9:39am

Re: Newbie tyre size question

Postby tomtom090477 » 25 May 2020, 6:12pm

Thanks for you replies. I pumped it up and that was when it came off. I pumped it to 100. Would going lower make it sit better in the rim?

tomtom090477
Posts: 5
Joined: 25 May 2020, 9:39am

Re: Newbie tyre size question

Postby tomtom090477 » 25 May 2020, 6:21pm

btw the tyre had 85-115 ppi so I assumed 100 should be fine.

rotavator
Posts: 451
Joined: 6 Jun 2016, 9:50pm
Location: North Wales

Re: Newbie tyre size question

Postby rotavator » 25 May 2020, 6:29pm

tomtom090477 wrote:Thanks for you replies. I pumped it up and that was when it came off. I pumped it to 100. Would going lower make it sit better in the rim?


Were both beads properly seated in the rim before you inflated the tube? Are you using the correct sized inner tube? If you answer yes to both of these questions, then there is something badly wrong and personally I would go and find a different tyre.

Is the tyre old and stiff by any chance?

tomtom090477
Posts: 5
Joined: 25 May 2020, 9:39am

Re: Newbie tyre size question

Postby tomtom090477 » 25 May 2020, 6:58pm

I think its the right size inner tube. 700 x 19 x 25. And I believe the beads were seated properly, but maybe I went wrong somewhere. I'll try it again and see if its any better, but it did seem to just pop out pretty promptly. The tyre I'm using is brand new, so I guess it must be ok. Thanks for your help!

tatanab
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Joined: 8 Feb 2007, 12:37pm

Re: Newbie tyre size question

Postby tatanab » 25 May 2020, 7:14pm

You say "old". Is it possible that you have a non hooked rim? e.g old British "racers" with 27" wheels would not have hooked rims and nothing over 70psi was advisable. What is the rim - model name if visible - material steel or aluminium.

tomtom090477
Posts: 5
Joined: 25 May 2020, 9:39am

Re: Newbie tyre size question

Postby tomtom090477 » 26 May 2020, 12:36am

Ah, Yeah maybe. Its a steel wheel and at guess from the early to mid 80s. Maybe older but not much newer certainly. I'd never heard of this hookless rim business but now that I've googled what that is I'll check it in the morning. I bet you're right! Does that mean I need a different tyre/wheel or will it be ok at 70 and below?

Thanks!

tatanab
Posts: 4083
Joined: 8 Feb 2007, 12:37pm

Re: Newbie tyre size question

Postby tatanab » 26 May 2020, 8:17am

This thread about 27" tyres viewtopic.php?t=21744 suggests it will be perfectly ok provided you run at lower pressures.

Brucey
Posts: 39436
Joined: 4 Jan 2012, 6:25pm

Re: Newbie tyre size question

Postby Brucey » 26 May 2020, 10:04am

tomtom090477 wrote:Ah, Yeah maybe. Its a steel wheel and at guess from the early to mid 80s. Maybe older but not much newer certainly. I'd never heard of this hookless rim business but now that I've googled what that is I'll check it in the morning. I bet you're right! Does that mean I need a different tyre/wheel or will it be ok at 70 and below?


you would be OK at lower pressures with new tyres. It is a very good idea to use a solvent to clean both rim and tyre edge (it will have mould release compound on it, which is slippy and will 'help the tyre off the rim').

However once tyres have blown off the rim, they are sometimes damaged and will be a looser fit on any rim than they should. All you can do is to try and see.

cheers
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