Bob70

When I ride the hills in Missouri near my sister's house, some are steep enough and long enough that a descent can result in significant speeds. I don't have a speedometer on my Specialized Fat Boy bike that I ride there, but I am sure that some of the time I am exceeding 40 mph. The tires on this bike are the 26 X 4.6 Specialized "Ground Control" that came with the bike. I typically run 15 psi in them, with the tire sidewalls marked as having 5 to 20 psi pressure range. The tires are tubed, with Air Lock in them.

My question is, what speeds will this tire safely handle? Has anybody had a fat tire problem that occurred because they were going too fast?

I suspect road type and condition affect the answer to the safe speed limit question. Some of the Missouri hills are gravel (rocks with dimensions averaging perhaps one inch or so.) I don't let my speed build up as much on graveled roads. But what is too much speed? How does the answer to this question depend on the tire pressure?

Thanks for any help.

PS I purchased this Fat Boy bike about two months ago because I thought it would provide better traction and better stability on the gravel hill roads. I am very pleased with the performance of this bike, and the greater feeling of safety (control) that it gives. There have been times when riding fast down these hills on my Cannondale MTB that I thought I was about to loose control. I have never experienced this with the Fat Boy, despite going faster on it than on the MTB.

Bob70

FrozenK

Fifteen psi is really high for a fat tire. I don't ever go over 10psi. Then again, I don't ride my fat bike on the road that much. I still think 15psi would beat the crap out of me on a gravel road.

In any case, you won't go fast enough for speed to damage the tires.

PS: set those tires tubeless. It shouldn't be too difficult with the Specialized tires and rims, and the bike will ride much better.

grubetown

I'm confused by the question. Are you worried about something structural with the tire happening at a certain speed or are you concerned about loosing control at a certain speed?

prj71

I have the same bike and tires. I have done 35 mph numerous times with the tires at 20 psi.

You have nothing to worry about.

prj71

15-20 psi is great for gravel road riding. I did a 95 mile gravel race on my fat bike with the tires at 20psi.

Up to 10 psi for summer trail riding and 5 psi for winter riding are the other pressures I use.

Leebo

No speed limits on tires. Within reason. Psi would be more of a concern. Enough to hold air, not too much to bounce around, not too low to roll in the corners. 230 lb rider here, Hodag up front spec fast track on the rear. Tubeless on jackalope rims. 15-20 psi is what works for me.

Hypno Toad

I have a Pugsley with Fat B Nimble tires, I race this bike on gravel grinders like the Almanzo 100. I get over 35 mph often and have no worries about top speed. I'm typically gearing limited, so I end up tucking and coasting.

Depending on the race conditions, I run 12.5 to 15 psi and it should be noted, I'm a light-weight (165 lbs)

You'll likely be limited by rolling and wind resistance before you get to an 'unsafe' speed.

I also upgraded to fat tires for stability at speed on gravel. I raced the 2015 Almanzo 100 on 28mm tires - used them on other gravel grinders without issue, but the gravel on the Almanzo is soft and deep. So as I was swearing loudly on the long steep descents, I hatched the plan to put drop-bars on my Pug and race it. It was a great choice of me, and I'm excited to get down to Spring Valley on Saturday morning for another fatbike Almanzo 100!

14523168_10154452523694404_534427873910667128_n.jpg

(I hope it's obvious, I'm on the fatbike on the left of this pic)

Hypno Toad

Afterthought, I feel like a fatbike tire would have less issues with high speeds. I would think that a thinner racing tire would be at greater risk of failure, and we know that the pro riders hit speeds over 50 mph.

C Law

I think at a certain speed there would so much bromentum from the fadbike wheels that they would be impossible to stop.

Hypno Toad

Nope, not really. With 4" of tire, the contact patch is much larger, helping stop quicker. Plus our Pugs have huge front rotors (I'm sure most fatbikes have huge rotors).

My daughter was trying her mom's Pug and damn near went over the bars. I was right behind her, watching the rear wheel lift off the ground. She had no idea how quickly that beast could stop.

I'm not sure this picture does justice, but my Pug is next to a standard MTB with standard rotor:
IMG_20150501_153259_096.jpg

Leebo

Tis true, my awesomeness spills over to all around me, Winning. I find the fat bike great for dirt, sand and snow. What kind do you have?

Hypno Toad

Totally missed your condescending tone for poor typing/proofreading.

No bro on this fatbike.

Fat is not a fad in my town, but I live in a place were biking year-round requires a winter bike. You don't need a fatbike to ride in the winter, but it sure a lot more fun. Some people are buying fat as fad, just like some people buy full-suspension MTB as fad, or CF road bikes as fad, or disc brakes as fad... but some people buy all of these options for good reasons too. Don't be a fatbiker hater.

C Law

^jeez. So touchy. My comment was very tongue in cheek.

Pedaling anything on 2 wheels is cool with me.

Hypno Toad

LOL. Shame on the Toad. I know better than to read/post on BF before my second cup of coffee (or third on a Monday).

HerrKaLeun

This thread is totally moot without you actually measuring speed. How do you know you didn't go 100mph or 20 mph? What gearing do you have? I almost spin ut at 40km/h and only make that downhill. tire resistance and drag keep speed down unless you are really strong.

Assuming you don't go that fast for many hours, I doubt tire over-heating is an issue.

Jseis 

In my STP lashup with 3” tires @ 25 psi. . . 30 mph was about a downhill average limit.

OneIsAllYouNeed

I clocked 38mph (per GPS) on the fatty. At no time was I worried about my tires structural integrity. I think traction for turns (it was on snow) was really the only concern.

Banzai

If you exceed 40mph on a fatbike tire, it activates the flux capacitor.

HerrKaLeun

unless you get a motorized bike or better human riders, I doubt tire technology is what is holding you back. Unless we talk about really crappy quality, it is long term heat that kills the tire. Car tires, even cheap ones, are rated for 100mph or above. Even spare tires for 81 mph, off-road tires for 75 mph. And the ratings are for hours of hot weather Interstate driving.

I know there is no official bicycle tire speed rating, but unless you get a home-made fake tire from Alieexpress, I don't see humans exceeding tire limits.

HerrKaLeun

I would be more worried about the derailleur because half of the bikes in the picture are laying on the drive side

Jseis 

Well, my bad, 2nd day and 150 miles in..spinning those tires took its toll. I was pretty happy on top of the St John’s bridge.