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Small 65mm rim vs Medium 80mm rim vs 100mm rim and tire sizes/profiles.

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#61 · (Edited)
Welnic said:
The main advantage of wider rims with any bike tire and rim combination isn't that the contact patch gets bigger with the wider rim at the same pressure, it is that you can run a lower pressure with the wider rim and it will work. ...
Click to expand...
Welnic speaks the truth!
Weight / psi = size of contact patch
If you have a 170 lb rider on a 30 lb bike, that equals 200 lbs. So if the tires are inflated to 10psi...
200 lb / 10psi = 20 sq in of rubber touching the ground. Drop the pressure to 5psi and you end up with a 40 sq in contact patch. Makes no difference if the tire is a 29 x 3 or a 26 x 5, as long as there is enough pressure to keep the rim airborne, the contact patch is the same size.
A larger tire will have a wider contact patch with less lengthwise flattening of the tread when compared to a smaller tire.

Likewise, the air pressure on the inside surface of the rim is what supports the bike, so the amount of sidewall deformation is a direct product of rim size both in circumference and width. A tire mounted on a 50mm wide rim will have twice the sidewall deformation as that same tire mounted on a 100mm rim at the same pressure. That means that that a BFL can run at half the pressure on a 100mm rim without burping or bottoming out than what would be possible on a 50mm.
Same thing with rim diameter, a 26 rim needs 11% more pressure to keep the rim airborne as opposed to a 29+ of the same width. So the sidewall deformation of a 29+ running at 10psi is the equivalent of as a 26 running at 11psi but because the 29+ is at a lower pressure, it will have more rubber on the ground.
Bottom line, if you are running on soft surfaces, a larger rim will allow you to have a larger contact patch without bottoming out but the trade off is that it comes at the expense of additional rotating mass.
 
#62 ·
I built up a Borealis Echo with DTswiss BR710 rims, 80mm, running tubeless Bud and Lou 4.8". I'm around 190lbs and ride mostly undulated terrain and the beach along with some snow trails. Reason for this is broad application, i can run the tires well inflated for quicker runs in the summer and on harder surfaces with still a nice grip once its gets slippery and enough flotation for the occasional sand patches that i encounter at the east end of Long Island. When i want to take the rig on the beach i just deflate severely and im good to go. The other day i did a ride when i expected and harder packed surface, but 2 min in i noticed it's all loose sand, so deflation and i was ready to go (for the most part). I ended up on a harder packed beach with some soft patches and all was good. Sometimes i wish for a 29" setup for summer harder and quicker trail runs, but they are only a few, i'm happy with my setup. Maybe Jumbo Jim is my future...
 
#63 ·
I currently own a Salsa Blackborow with 100mm Clown shoes, while its great in the snow it is slow as molasses compared to my Jones in the summer. Thinking if I find a set of Marge Lites or even 80mm wheels I'll be much happier in the dry months. Oh and I only weight 145# so I really don't need the wide wheels I don't think.
 
#64 ·
edved37 said:
I currently own a Salsa Blackborow with 100mm Clown shoes, while its great in the snow it is slow as molasses compared to my Jones in the summer. Thinking if I find a set of Marge Lites or even 80mm wheels I'll be much happier in the dry months. Oh and I only weight 145# so I really don't need the wide wheels I don't think.
Click to expand...
I don't think it would be a huge difference to drop to a 65mm rim if you are still running 4.8" tires. And if you go to smaller tires the bottom bracket will drop. If you are going to get a new wheelset anyway I would try 27.5"x3.8" or 29"x3".
 
#65 ·
Welnic said:
I don't think it would be a huge difference to drop to a 65mm rim if you are still running 4.8" tires. And if you go to smaller tires the bottom bracket will drop. If you are going to get a new wheelset anyway I would try 27.5"x3.8" or 29"x3".
Click to expand...
I would run a 3.8 tire most likely which along with he 65mm rim should drop 3-5 lbs off what I'm running now I would think and the blackborow has a higher bottom bracket so I didn't think the drop would effect it too much, but I could be wrong.
 
#66 ·
edved37 said:
I would run a 3.8 tire most likely which along with he 65mm rim should drop 3-5 lbs off what I'm running now I would think and the blackborow has a higher bottom bracket so I didn't think the drop would effect it too much, but I could be wrong.
Click to expand...
Going to 3.8" with the 65mm rim will be a big difference. You should just put the 3.8" tires you are going to use on your 100mm rims and see what you think. You won't be able to get as rowdy with the 100mm as the rims won't be that well protected, but it should give you a good feel for the bottom bracket height. Rim width doesn't affect tire diameter very much.
 
#67 ·
Love this forum! I had a concern on building up a summer wheelset and low and behold, after a google search I find this thread. So, my question to you all... I'd like to build a 65mm wheelset to use with 4" tires for summer trail riding. Currently have 100mm clownshoes on 4.8 JJ's. Will there be a significant difference in diameter?? Any help would be appreciated.
 
#68 ·
Yeah. They'll be smaller. I can take a picture when I get home. I happen to have one bike with 65mm rims and 4" tires and another with 100mm rims and 4.8" tires.
The little ones look anemic in comparison.
If you want diameter, build a pair of 29+ wheels for summer. Almost exactly the same as 4.8" tires in height. My son doesn't even want his Marge Lites and Huskerdus any more. He likes his 29+ so much he asked for Darryls and 4.8" tires for fat.
 
#69 · (Edited)
Branner said:
...I'd like to build a 65mm wheelset to use with 4" tires ...Will there be a significant difference in diameter?
Click to expand...
If the tires stay the same, there will be no difference in diameter.
All other things being equal, the differences are threefold:
A narrow rim will reduce rolling mass while increasing casing flex which will result in a softer ride at the expense of handling and load capacity. A narrow rim also reduces exposure to rim and casing damage due to terrain hazards.

I wider rim spreads out the casing, reducing flex which increases the load capacity allowing one to gain a larger footprint by running at lower tire pressures. This comes at the expense of added rotating mass but is usually preferable on soft surfaces such as sand and snow.

It has been my experience that 3.5-4.0" tires on 100mm rims exhibit significant self-steer when ridden on hard surfaces. Self-steer is reduced on rims with less than 80mm inner bead-bead width.

NYrr496 said:
...If you want diameter, build a pair of 29+ wheels for summer. Almost exactly the same as 4.8" tires in height...
Click to expand...
Mega dittos! A 29+ wheelset will be lighter while maintaining the same diameter and pedal clearance.
The diameter of a 3.0 x 29 Knard is identical to a 4.8 x 26 Bud but the effect on the bike is akin to turning a Hummer into a Mustang. :)

(see link below)
 
#70 ·
N8R said:
...I measured the imprint width in the sand of 4" tires on 100mm and 80mm rims. At around 5 psi, they were the exact same width. The tread width stays the same...
Click to expand...
True, weight of bike - tire psi = contact patch in sq in. So if you maintain the same tire pressure, the contact patch area will be the same regardless of rims or tires.

A 100mm rim has 20% more load capacity than an 80mm, so the load capacity and rolling resistance of a tire running 5psi on an 80mm rim is equivalent to the same tire at 4psi on a 100mm rim.
If you are riding on firmer surfaces at higher pressures, the narrow rim has the weight advantage.
 
#72 ·
sryanak said:
...It would be helpful to know what the new tire will be.
Click to expand...
Agreed, my point was that tire diameter is determined by tire size and is not affected by rim width. A Vee Apache Fattyslick or a 29+ wheelset would be the answer for someone looking for lighter, faster summer wheels while maintaining the same diameter and ride height.
 
#73 ·
Sry & FBSW: Here's more info.. My bike is a 2016 Salsa Blackborow, size medium. Currently running clownshoes on 4.8" JJ's. I want to run a 65mm with either a 4" or 4.4" JJ for summer riding along with a suspension fork. I tried a 29+ bike and didn't like it. I like the confidence I get from the fat tires and want a fun, sporty ride for the summer. I'm 99% sure that's the direction I'll be heading.
 
#74 ·
Branner said:
Sry & FBSW: Here's more info.. My bike is a 2016 Salsa Blackborow
Click to expand...
Like you, I ride a 2016 Blackborow with Bud, Lou and/or JJ 5's tubeless on Clown Shoes.
In March, at the end of snow season, I installed a set of 3.5 x 26 Vee Speedsters on the Clown Shoes for added speed and to avoid trashing the expensive knobby tires when riding on pavement and dry trails.
With the smaller diameter tires, it soon became evident that the stock 39-11 top ratio was not tall enough for running on pavement.
With the 1" lower ride height, pedal strikes also became an issue when riding off road on rough terrain and climbing stairs.
So, I bit the bullet and laced up a 29+ NoTubes Hugo wheelset that is the same diameter as the 26" fatties which has enabled me to run with the road bikes on the summer rides.
(You can click this link for details and photos)
http://forums.mtbr.com/fat-bikes/notubes-hugo-52mm-rim-921705-4.html#post12682747

Branner said:
I like the confidence I get from the fat tires...
Click to expand...
As I eluded to above, running a lighter, faster wheel that is smaller in diameter seems counter productive to me.
If you want to stick with the 4" tires, I would suggest doing a 27.5 wheelset. That way, you would maintain close to the same ride height and gear inches.

(see link below to compare tires and rims)
 
#75 ·
Bud and Lou tubed / 100mm Clownshoes on a Fatboy Trail Pro with Bluto. About 1/4" clearance front and rear. I weigh 210 lbs.

The whole setup works fine but barely. If I went tubeless or got rowdy in gnarly stuff I'd probably have at least a little tire rub going on.
 
#77 ·
I have some experience on 3 setups from 80-90 mm rims and 3.8 to 4.6 tires, and my riding weight is 210ish. The softer the terrain, the better a wider the rim is. The said, tread design and psi usually makes a bigger difference.

I think you will get the best all around with an 80mm rim and then an appropriate tread for the terrain. Going extreme doesn't yield you that much more riding capability, that is fun anyways. Going 100mm rims with 5.0 tires might get you out another day or two. If all you do is ride sugar sand dunes, then that would be awesome. Like all things, if you have a specific use in mind, the best solution usually means giving up some function elsewhere.

This winter I plan to pick up some Bud and Lou's to put on my 80mm rims...... I will run the Kendas until we have snow. Studded CX bike for when it's icey, which is most of the time :)


Sent from my iPad using Tapatalk
 
#78 ·
Upinflames7 said:
not sure what spoke tension has to do with the chain hitting as it is just gravity working not wheel flex as I can just stand and lean the bike over and the chain touches the tire
Click to expand...
I've had bikes where the tire rubbed the chainstays under power and tightening the spokes helped. So with little clearance, these things become more critical.
 
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#79 ·
I'm really liking my 80mm rims with JJ 4.0/4.8, but I don't have anything to compare them against as far as fatbikes. My experience has been limited to riding my friends fatboy a few times.

I want to build a new set of carbon wheels, basically just to save some weight, but now I'm very torn on what to build. I was planning to get 80mm carbon, but the Nextie 90mm have caught my eye. Love the looks of the snow dragon. Problem is I don't really want to change how the bike rides, just save some weight. I bought the bike originally for snow, but it's too much fun on dirt to be only for snow. Will there be a significant difference going from 80mm to 90mm with 4.0/4.8 tires? I don't want/need the tires any wider.

Now, tHis thread has me thinking about 65mm rims. Would the 65mm perform well with 4.0/4.8 tires? I already have 2 new sets of tires in those sizes, so I don't really want to get more. I have a couple nice bikes for summer riding, but I have a feeling I'll be riding the fatty a lot in the summer now. 155lbs with gear.
 
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