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  1. #1
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    80mm vs 100mm rim decision

    First some background. I am an endurance racer (Arrowhead 135/Tuscobia 150) hoping that I will get bumped off the wait list and in to the Iditarod. Past years 80mm rims have suited me well, very rarely have I wished for more. With ITI in the hopeful future I am considering 100mm rims. I plan to make these wheels tubeless no matter. My tire of choice right now are Escalators. I have run larrys and bfls before (no longer own).

    Can anyone who has run both tell me am I losing anything/much by going to 100's? I am not as much worried about weight, as I am just the rolling effect/resistance/overall speed. Ultimately, I don't want to sacrifice my riding the entire winter so that an attack on Iditarod can be done on 100's. I am riding in MN, primarily on decently packed snowmobile trails.

    Until my winning lottery ticket gets purchased I don't have the cash to spend on multiple wheels and tires. Thanks.
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  2. #2
    Laramie, Wyoming
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    You've already heard from me but I didn't get beat at any race I did last year by anyone on 100's. But, there were a whole bunch of guys who beat me on 80's and smaller. And they weren't bumpkin races. The winner of last year's ITI was in one of the races and didn't win. Another race featured Mr. retired Specialized who smoked everyone on a not yet released Specialized fat bike.

  3. #3
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    It's all condition dependent. I've been riding 70's for the past three winters, except the ITI last winter. In a fluke of a nice year, the 100's probably weren't needed, but I don't think they necessarily hurt either. It would be nice to own both, but not always possible/practical. Good luck.

  4. #4
    Anchorage, AK
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    You could try an 80 up front and a 100 in the rear.
    --Peace

  5. #5
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    Quote Originally Posted by Lars_D View Post
    You could try an 80 up front and a 100 in the rear.
    Now that's interesting... little rounder profile, little better steering up front... little squarer profile and enhanced floatation rear... that sounds kinda cool!

  6. #6
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    Quote Originally Posted by ward View Post
    Now that's interesting... little rounder profile, little better steering up front... little squarer profile and enhanced floatation rear... that sounds kinda cool!
    I have thought of this before. I have never seen anyone run this combo. I figured there was a reason.

    Still most of the potential negatives exist when running the big on the rear.
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  7. #7
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    I think it might be cool in sand, especially if you were running a susp. fork.... like a sand rail.

  8. #8
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    Quote Originally Posted by ward View Post
    I think it might be cool in sand, especially if you were running a susp. fork.... like a sand rail.
    I ride my Schwinn Stingray Chopper when cruising the beach, but thanks for trying to help.
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  9. #9
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    Almost everyone in the ITI last year had 100mm rims with 4" tires... Lots of Dillingers and lots of Escalators. I think as variable as the conditions are in ITI, the 100's allow a bit more of riding when it gets soft, I don't think in that particular race, you'll notice any speed loss or resistance compared to the 80's.

    You could do what I did and split the difference and go with the Uma 90's.

  10. #10
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    Quote Originally Posted by AKCheesehead View Post
    You could do what I did and split the difference and go with the Uma 90's.
    They would be your best bet for tubeless, also.

  11. #11
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    Have you studied the Surly tire geometry chart on their site? I found it rather surprising... the 'lack' of width increase when going from 80's to 100's.

  12. #12
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    Quote Originally Posted by Lars_D View Post
    You could try an 80 up front and a 100 in the rear.
    Funny, I was going to suggest the opposite. I'm sure you have your reasons (which I'd be curious to hear).

    I've found the vast majority of control improvements come from being fat in front. The rear just kind of trails along in the fronts track. Skinnier front leads to more wallowing, more fighting for control, etc. When I say skinny, I'm speaking "normal" skinny, not fat anything.

    So, extrapolating, the fatter the front can go, the better the floatation and control.

    Skinnier/less weight in the rear simply means less energy going into making and keeping that wheel moving.

    I don't race, don't live in AK (perhaps there's elements within that I don't get), don't do endurance anything, but I do ride, conditions regardless, all year long, several days a week.
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  13. #13
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    First off, the big reason why I would not check out the UMA's is because I work at a shop and can get the Surly rims at cost, UMA's not so much.

    Second, the width chart is great and all, but in rear world practice when rubber hits the snow and the tire spreads out it does make a difference.

    Third, I have wondered about skinny back fat front before as well. Came to my own conclusion that float is most advantageous in the back, something with some float but "rudder" control on the front works best.
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  14. #14
    Anchorage, AK
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    Re: 80mm vs 100mm rim decision

    Quote Originally Posted by Logantri View Post
    I have thought of this before. I have never seen anyone run this combo. I figured there was a reason.

    Still most of the potential negatives exist when running the big on the rear.
    It worked well for me last winter. I didn't notice any negatives only positives of good float in the rear where I used to break through more often.



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  15. #15
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    I have a clown shoe with lou on the rear and a RD with a bud on the front. When you run low pressure with that large of tire you get a lot of rolling around to the point it is tough keep it on the trail. At higher pressure it works fine. But I would not recommend it. I only run it that way because I have been to cheap to buy another clown shoe, but I will before the snow gets deep

  16. #16
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    I have run 70mm and 90mm rims, and there is definitely a bit more rolling resistance for the 90 vs the 70s, especially when it gets really cold. Or at least it seemed that way to me. Having said that, rolling resistance doesn't matter if you aren't riding your bike, and the 90mm rims provide noticeably more float than the 70mms.

    Alas, the Arrowhead and the ITI are way different races - my impression is the Arrowhead has fairly consistently nice trail conditions, while the ITI is a crap shoot.

    I have also run a 70mm front, and 100mm rear setup, and it worked great. Most of the weight (and need for float) is on the back anyway. I would still be running something like that if my frame fit bfls or lues/buds on 100s in the rear.

    Personally, I am going to run the biggest tire + rim combo I can stuff into my frame for the ITI, but then I am a 210lbs+ lard butt who doen't pack all that light, so YMMV.

    Best of luck with the ITI!

  17. #17
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    charly - if going to ITI, i highly recommend 100's with 4.0 tire choice. i do not recommend moving to 4.8 tires, that is where you will start to feel sluggish...give'em a try regardless if you get in or not.

  18. #18
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    Cool, thanks for the replies everyone. I think I may run 80's and then seeing if I can "borrow" some hundred's for ITI. Jay P, interesting with the 4.8" tire comment. I had wondered that myself and thought of trying the big fat larry's at 4.6" but much lower knob height. See you at Arrowhead.
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  19. #19
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    Quote Originally Posted by Jay P View Post
    charly - if going to ITI, i highly recommend 100's with 4.0 tire choice. i do not recommend moving to 4.8 tires, that is where you will start to feel sluggish...give'em a try regardless if you get in or not.
    Excuse me for butting in, as I'm just new at the fat bike scene. I was under the impression that 4" (3.8) tires wouldn't fit/work well on 100mm rims. But I see that there might be an application for them. If so, what advantage might this set up have over running 4" on an 80mm rim?
    - Mark Ehlers
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  20. #20
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    Quote Originally Posted by marathon marke View Post
    Excuse me for butting in, as I'm just new at the fat bike scene. I was under the impression that 4" (3.8) tires wouldn't fit/work well on 100mm rims. But I see that there might be an application for them. If so, what advantage might this set up have over running 4" on an 80mm rim?
    3.8"-4" tires have been used for a long time on 100's, much before the 4.6"+ tires cam out. It seems though a lot of people who run 100's are interested in going as big as possible, so they get the biggest tires they can. It is simply my opinion that a large percentage of these people do it for the gee whiz factor (I have seen it many times) rather than practical use. A wider rim gives a much wider base for the tire, so when you drop the pressures the tire will have a wider contact patch and be able to stand really low pressure without wallowing.
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  21. #21
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    I don't think the 4.8" tire on the front slows one down nearly as much as the 4.8" rear tire. The 4.8" rear tire is impressive at low pressures in softer snow but it is noticeably slower.

  22. #22
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    Thanks, guys. I understand how the wider tire on the narrower rim allows for a wider footprint. I'm sure there must be some limits to how narrow you can go on these rims though. I was wondering what (if any) disadvantage there would be to using a 3.8" on a 100mm rim. And aside from the "wow" factor, is there any practical reason to run a 4.7+ tire on a 100mm rim?
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  23. #23
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    My LBS said that smaller tires like 4.0 won't work with 100mm rims. I assume he meant it won't work well. He also seemed to think that 4.8 tires won't work on 80mm rims. Same assumption. They are very knowledgable and the guy who said this rides exclusively fat bikes. From what I read elsewhere it appears that 80 or 100mm rims would allow for either 4 or 5 inch tires, thus the confusion. I ordered a 907 190mm frame and my intention is to go as big as I can for winter riding on single track and commuting and then hopefully, put smaller tires on in the summer without having to buy a new wheelset. So, what rim will be the most versatile, and allow for the biggest tires? Maybe the 90mm as suggested? I don't want to sacrifice much on the 'big' end though as it does snow lots where I live.

  24. #24
    Location: SouthPole of MN
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    Quote Originally Posted by manorden View Post
    My LBS said that smaller tires like 4.0 won't work with 100mm rims. I assume he meant it won't work well. He also seemed to think that 4.8 tires won't work on 80mm rims. Same assumption.
    Not true at all if you look around these here forum parts

    4.0 tire is fine on 100 and many have ridden Nate's just fine. LOTS of people run 4.8's on 80 (and smaller). But really the point with the 4.8's is to be on 100's and get max float. Whether you need that or not is a totally different issue.

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