rec3036

For the last several weeks we have been enjoying exceptionally mild weather here at the Jersey Shore, so I have been taking advantage of it and going out to one of my local State Parks and doing some trail riding. nothing extreme staying on hard packed fire trails in the Pine Barrens and for some reason was blowing out my rear tire every ride. Well this week I brought the pressure up 20 psi to 60 psi in my rear wheel. While the ride was noticeably harder, I was able to complete our 8 mile ride without having to change or repair a flat. Does anyone have any suggestions as to what to do to smooth out the ride a little bit without getting a flat? I was able to log almost 500 mile on my thinner street tire with no flats last summer and fall, but as soon as I switched over to the wide knobby tires I had been getting flats.

We are only doing about 8-15 miles on hard packed sandy fire trials with intermittent soft sand patches to power through and average about 7-8 mph over semi smooth terrain. no real hill climbing or jumping / dropping.

TREK 4300 Disc using the stock Bontranger 26 x 2.75 directional knobby tires Presta Valve Tubes.

cyccommute 

It sounds to me like you are inactive in the saddle. Mountain biking is far more kinetic than road biking (although road biking should be more kinetic than most people do it). When riding off-road, anticipate wheel impacts and take the weight off the bike by standing up over the bump. I don't mean standing up straight legged either. Flex your legs at the knees and let your thighs act as the giant shock absorbers they are. As you approach a potential impact, lean rearward on the bike to lift the front wheel and then, as soon as the front wheel has cleared the obstacle, move forward to take the weight off the rear wheel. Done properly, you should be moving constantly on a mountain bike with flexed arms and legs. This is especially important with a hardtail.

I've run 2.1" tires at 45psi for as long as I can remember on mountain bikes and I've never had a pinch flat. I bomb down trails that are littered with babyheads and roots, too. But I ride very light in the saddle.

rec3036

Thank you I have been getting up out of the saddle like you said but, even on a flat section of hard pack dirt I getting a lot of vibration, it almost seems like the pebbles are boulders... in any event I will definitely get out of the saddle more if I air down a little more.

nymtber

Pinch flats or debris.... A few things to check out are as follows (coming from someone that might have ran 35psi in 2.1" panaracer Fire XC):

-Tube size. Correct tube for tire? Better err on the smaller (width) size. Tubes stretch better than they fold over themselves in a tire!
-Rim tape. If you have a rubber rim strip, toss it and install some Velox rim tape. Best stuff out there.
-Sharp nipple holes/nipples poking through - de-burr before installing rim tape where necessary.
-Something is in your tire. Check the inside of the tire, make sure nothing sharp (rocks, glass, thorns, etc) is poking through, remove anything that is. Running a cotton ball along the inside of the tube is much safer than your finger. Anything sharp enough to damage a tube will grab some cotton and you will see it
-baby powder the inside of tires lightly so the tubes don't stick. This just makes life easy.
-inflate tires partway after installing (10-15psi should be enough), check around rim for tube sticking out between tire and rim, and if its ok, inflate fully to your desired PSI.
-MOST IMPORTANT: make sure tubes are not being pinched AS you install them, between rim and tire. I sometimes have to use a tire lever to get a tire on, I am super careful if I have to. Try to only use tire lever to remove tires..

I don't even pump my tires much past 50 to ride on smooth fine gravel paths. 35psi offroad is about what I would use. 60 is WAY too high for offroad use (this is MY opinion anyway...)

If you still have problems, take the wheels to a bike shop and see if someone can help you out, or find a fellow mountain biker to maybe look things over?

That is all I have for now. Been a while since I have been real mountain biking, but I was pretty thorough with my tire/tube installation whenever tires/tubes were removed. Never had a flat, either. I almost think I am still riding on 8-10 year old tubes...

Leebo

Recheck that tire size, 2.75 is downhill sized. My mt bike tires vary in pressure in between 28 to 35 psi for 26 x 2.3 to 2.5 inches. For my 29er, I run a 29 x 2.4 at 28 to 32 psi, tubeless so get no flats