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We are planning on doing some mountain biking in a few weeks time and we'd like to get some wider tyres for my wife's hybrid. I know there are similar questions and answers out there on this topic, but I need some specific help to make sure I buy the right tyres.

The bike is a Ladies Scott Sportster 50 2015, the best website I could find with a fairly accurate spec is here

Scott Sportster 50

It's currently got Kenda K-180 700 x 38c / 30TPI tyres on it, which are fairly good all rounders and capable of running on clean forest paths but I don't think they would handle anything heavier.

It's got disk brakes so there isn't a clearance issue there, but I have noticed the frame is generally narrower than true MTBs, here are some photos i took of it.

enter image description here

Has anyone put larger, knobblier tyres on this kind of hybrid? whats the largest I can get away with? - I'm also slightly confused by all the tyre sizing, I'm sure someone told me this is a 27.5" tyre, but 700 seems to mean 29" on a lot of websites.

Any advice is very much appreciated, Thanks.

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    A 700c is a 700c, except that it's also an ISO 622. It's the ISO size (in small print on the side of the tire) that matters. Your wife's tires are ISO 38-622. Bike manufacturers like to use inch sizing for what were traditionally called 700c tires because "700c" is the "French" designation and sounds too prissy for a real (Chinese) American off-road bike. Thus you get several 29" and 28.whatever" sizes. Ignore the carp and look at the ISO sizing. You must match the larger number but can "play" with the smaller number to a degree. (But note that a 38mm wide tire is already pretty wide.) – Daniel R Hicks Mar 23 '16 at 12:21
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    How much room is there between the tyre and the frame (or mudguard)? The chainstays and seatstays are most likely to be the limit. In general the clearances are likely to be enough to go up one size at least, but adding tread complicates things. – Chris H Mar 23 '16 at 12:26
  • ChrisH - I need to check the clearance when I get home, I might update the question with some actual photos. @DanielRHicks - Thanks for the explanation, So in MTB terms this hybrid would be a 29er - but tyres advertised as 29" are aimed at MTBs with more clearance? – Wez Mar 23 '16 at 12:53
  • 700c and 29er both share the same ISO (622) so either will fit on the rim. The difference you will find is that the 38 in your other measurement (700 x 38) is equal to about 1.5" (1.49...) you will be hard pressed to find a "29er" that is smaller than 29 x 1.90, but there are a ton of 700c x__ that are smaller than 1.9 but larger than 38(mm). Confused yet? : P – Nate W Mar 23 '16 at 17:31
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    Sheldon Brown attempts to make sense of the nonsense, but it takes a little effort on your part to translate things into common terms. (To show you how crazy it is, a 29" tire fits a smaller rim than a 27" tire -- the inch designations are meaningless.) – Daniel R Hicks Mar 23 '16 at 17:40
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For a 700c tyre you would be replacing it with a 29" MTB tyre. The best way for you to determine what size tyre you can get to fit is to simply measure the gap between chain and seat stays as these are the most likely areas to cause problems with clearance.

Providing you don't want to ride anything too gnarly (i should hope not on a hybrid), a 700x35C cyclocross tyre could give you a much more grippy/knobby option without needing more clearance. Something like this maybe?

  • Sounds like a good option, so this would technically be a thinner tyre than what she already has, but just more knobbly? – Wez Mar 23 '16 at 12:45
  • Yes, the carcass of the tyre itself will technically be narrower, although you may find due to the shoulder knobs the actual footprint and clearance required in the frame are similar – Andy P Mar 23 '16 at 12:59
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    I would think you could go with a 700x40 as well if you wanted a little more girth, i imagine there would be enough room but i would visually check your clearances in the frame before going larger. – Nate W Mar 23 '16 at 17:27
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    As an added issue of concern, I have had tires that clear the frame fine but the front derailleur would hit the tire while on the smallest chainring – mikes Mar 23 '16 at 20:04

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