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Discussion Starter · #1 ·
Would an 80 mm rim do a 5.05" tire justice? Would a 90/95mm rim be a good compromise for a 5.05" and still allow for somewhat decent clearance on a typical fatty?

Incidentally, I've asked a bunch of fat biker manufacturers about using100mm rims and all have told me one can only go to a max of 4.8" tires.
 

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Elitest thrill junkie
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90 is a terrific compromise that works great at the D5-sizes, much better than 65-80 IME. Much better side-wall support and profile IME. So it's naturally better for the even-wider tires.

I can fit 2XL or J5 on my CS-197. I was able to on my Mayor V3 as well. All on the 90mm rim.

Do you need that wide to run a true 5"? No, but I highly recommend it for the tire profile, as the bike will handle better.
 

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Discussion Starter · #3 ·
90 is a terrific compromise that works great at the D5-sizes, much better than 65-80 IME. Much better side-wall support and profile IME. So it's naturally better for the even-wider tires.

I can fit 2XL or J5 on my CS-197. I was able to on my Mayor V3 as well. All on the 90mm rim.

Do you need that wide to run a true 5"? No, but I highly recommend it for the tire profile, as the bike will handle better.
Obliged!

How would a 90mm rim be with 26x4.8 aggressively knobby tires then? I, too, am on a 197fatty.
 

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Elitest thrill junkie
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Obliged!

How would a 90mm rim be with 26x4.8 aggressively knobby tires then? I, too, am on a 197fatty.
Great.

What doesn't work great is a 3.8 tire on a 90mm rim. It ends up looking like a low-pro car tire, the rim sticks out WAY too far. So for 4.0 tires, a 90mm rim can be a little on the short side. As long as it's a 4.2-ish tire, it's usually fine. But even a D5 doesn't work great on a 65-75mm rim IME, the sidewall support from the wider rim is better for the wider tire. Even on much skinnier mtb tires, there's a fairly optimum "ratio" that you should shoot for IME. It doesn't mean you can't run outside of that...but you don't get the amount of benefit that you'd get if you were also changing the rim size.

I think the prevalence of 75-80mm rims is due to the majority of fatbikes being sold with 4" tires and not necessarily for snow conditions. 4" is also cheaper and lighter, so that's another thing that probably motivates the OEM spec. For true winter riding, I'd start at an 80mm rim minimum, but I think a 90 is a good compromise all around, some of the benefits of 100, some of the benefits of 80, better optimized for those mid-fat tires, D5-size, etc. I don't like 4" tires much, I just find them too skinny and not as much fun, if only because you can't lower the pressure as much.

If you are doing competitive winter racing on a fat-bike, then I might steer someone more towards 80mm, it's rare that you need super-wide and really, you don't want to be the guy up front breaking trail, you want to be the guy riding in their tracks, saving all your energy, to out-sprint them at the end...
 

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Discussion Starter · #5 ·
Great.

What doesn't work great is a 3.8 tire on a 90mm rim. It ends up looking like a low-pro car tire, the rim sticks out WAY too far. So for 4.0 tires, a 90mm rim can be a little on the short side. As long as it's a 4.2-ish tire, it's usually fine. But even a D5 doesn't work great on a 65-75mm rim IME, the sidewall support from the wider rim is better for the wider tire. Even on much skinnier mtb tires, there's a fairly optimum "ratio" that you should shoot for IME. It doesn't mean you can't run outside of that...but you don't get the amount of benefit that you'd get if you were also changing the rim size.

I think the prevalence of 75-80mm rims is due to the majority of fatbikes being sold with 4" tires and not necessarily for snow conditions. 4" is also cheaper and lighter, so that's another thing that probably motivates the OEM spec. For true winter riding, I'd start at an 80mm rim minimum, but I think a 90 is a good compromise all around, some of the benefits of 100, some of the benefits of 80, better optimized for those mid-fat tires, D5-size, etc. I don't like 4" tires much, I just find them too skinny and not as much fun, if only because you can't lower the pressure as much.

If you are doing competitive winter racing on a fat-bike, then I might steer someone more towards 80mm, it's rare that you need super-wide and really, you don't want to be the guy up front breaking trail, you want to be the guy riding in their tracks, saving all your energy, to out-sprint them at the end...
Thank you! You've really helped me with your insight. I'm in conversation with Mike C. of lacemine29.com as I write.
 
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