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Converting my fat bike into MTB without replacing Rims

Old 09-09-21, 10:35 AM
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Adil
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Converting my fat bike into MTB without replacing Rims

I want to replace my fat bike tires 20x4 inch size with normal 20x2.5 inch MTB tires but could not afford to replace the wide rims with narrow rims. Few of the spare parts shop onwers told me that you can do it easily and told me that they have replaced several fat bike tires with normal MTB tires without replacing the rims on their customer bikes. Is it possible to install narrow tires on wider rims.
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Old 09-09-21, 11:14 AM
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Short answer. Probably not.

Long answer. Even if the tires would fit, your bike was designed with a bottom bracket (bb) height optimized for 20x4 tires. Assuming that's what came with the bike. When you replace those with 2.5 tires you will drop the bb significantly closer to the ground which will cause pedal strike when you turn corners.
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Old 09-09-21, 11:26 AM
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I wouldn't mess up the bike to convert it to something it wasn't intended to be. Maybe if it was an old POS.

You'd be doing yourself a favor to just get another bike that is already a mountain bike whether new or used. Sell the other if you have no desire for it or just give it away to someone.
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Old 09-09-21, 11:30 AM
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Originally Posted by Adil
the spare parts shop onwers told me that you can do it easily and told me that they have replaced several fat bike tires with normal MTB tires without replacing the rims on their customer bike
If these shops say they can and have done it, then let them do it on yours. If it fails, you can hold them accountable.
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Old 09-09-21, 01:10 PM
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2.5 tires will probably mount up fine. Guys were running them on Surly Pugsleys years ago. If you just want it to be faster rolling, switch just the rear out first. My fatbike has had a 27.5 x 2.5 wheel and tire on the back and 26 x 4 in the front for over a year.
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Old 09-09-21, 01:23 PM
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What is the rim width? Internal width, more specifically?
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Old 09-09-21, 06:33 PM
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Originally Posted by c_m_shooter
2.5 tires will probably mount up fine. Guys were running them on Surly Pugsleys years ago. If you just want it to be faster rolling, switch just the rear out first. My fatbike has had a 27.5 x 2.5 wheel and tire on the back and 26 x 4 in the front for over a year.
This person wants to fit the smaller tire on the same fat rim.

it is very common for fat bike owners to have a second wheel set for summer use, using a 29r rim and mtb tires (26×4+ for snow). Your described mullet set up (27.5/26) follows that thinking. Did these Pugsley owners do that? or mount 2.5 mtb tires on their 26x4" rims.
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Old 09-09-21, 07:26 PM
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2.1" tire on a 45mm rim is my record. It worked out just OK but it looked kinda



That's more of a plus size rim than fat size though.
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Old 09-09-21, 07:38 PM
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Originally Posted by Happy Feet
This person wants to fit the smaller tire on the same fat rim.

it is very common for fat bike owners to have a second wheel set for summer use, using a 29r rim and mtb tires (26×4+ for snow). Your described mullet set up (27.5/26) follows that thinking. Did these Pugsley owners do that? or mount 2.5 mtb tires on their 26x4" rims.

2.5 hookworms work fine on fatbike rims.
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Old 09-10-21, 08:24 AM
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Originally Posted by c_m_shooter
2.5 hookworms work fine on fatbike rims.
Wow! Just googled 2.5 hookworm tires and fat bike rims and came up with a lot of references. I never knew. Thanks for the connection
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Old 09-10-21, 08:47 AM
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Originally Posted by Happy Feet
Wow! Just googled 2.5 hookworm tires and fat bike rims and came up with a lot of references. I never knew. Thanks for the connection
Yeah, the only drawback is Hookworms weigh just as much as fat bike tires

Semislicks probably aren't what the OP is after though.
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Old 09-10-21, 09:04 AM
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Originally Posted by LesterOfPuppets
Yeah, the only drawback is Hookworms weigh just as much as fat bike tires

Semislicks probably aren't what the OP is after though.
I agree I still would be worried about pedal strike. And this appears to be a 20" rim which will show the height difference between a 4" and 2.5" tire that much more.

I think the easiest thing is just for the OP to buy a cheap new or used mtb tire or two and try to mount to see. This isn't a very expensive experiment in the scheme of things. So far they haven't listed their rim size so I'm a little jaded as to their effort level.
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Old 09-10-21, 09:05 AM
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Originally Posted by LesterOfPuppets
Yeah, the only drawback is Hookworms weigh just as much as fat bike tires

Semislicks probably aren't what the OP is after though.
Hookworms are better off road than most give them credit for at first glance. Every week or so at my local trailhead some idiot looks at my bike and says those tires won't work out here. I've been riding these tires for about 10 years, and these trails for about 20, what do I know?
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Old 09-10-21, 10:19 AM
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How wide are the rims? I switched 4" tires to 2.3" with neither it looking untoward or causing handling/mechanical issues, but the rims were only about 3.5" wide AIR.
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Old 09-10-21, 12:12 PM
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Originally Posted by 2old
How wide are the rims? I switched 4" tires to 2.3" with neither it looking untoward or causing handling/mechanical issues, but the rims were only about 3.5" wide AIR.
I am trying to wrap my head around running rim 1.2" wider than the tire.

If you say it works I believe you, but that sure does not sound right.
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Old 09-10-21, 12:20 PM
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We've all seen this...
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