Mountain Bike Reviews Forum banner
1 - 20 of 22 Posts

·
Registered
Joined
·
59 Posts
Discussion Starter · #1 ·
Ok, I'm getting my Spec Epic Comp 29er soon. Just doing some research on setting it up.

I won't be replacing any parts until they wear out or break. (If it matters, I'm 173cms tall and weight 68kgs, race cross country endurance type stuff, 50 to 100k, not elite but competitive)

1. What tyre pressure should I use? I have ridden 26" bikes at around 40 to 45, but read reports I should have been around 35. I'm from a road background so not familiar with best pressures for off road. Should tyre pressures be different for 29" bikes. For example, the contact patch is already bigger on a 29" so does that negate the need for lower pressure to increase contact??

2. What about pinch flats on 29ers? If you can run higher pressures does that then mean you don't get pinch flats as often so therefore there really isn't a need for tubeless tyres on a 29"

3. There is a lot of info around on 26" tyre pressures and combo's etc but it will take a while for similar database of knowledge to build up with 29". So if anyone can assist me on my path of discovery, point me to some good articles etc I'd appreciate it.

Cheers.
 

·
Ride.Recover.Beer.
Joined
·
255 Posts
I run tubes, @ 40psi, and have had only 2 flats "knock on wood" riding 4-5 times a week hard for the past 6 months. I was planning on going tubeless, not no mo.

I ride with a buddy that runs tubless @ 35psi rear, 30psi front to soak up some of the beating on his rigid SS, and hasn't had a problem eaither.

Don't know if I helped at all. Look forward to pics of the Epic 29er!!
 

·
Registered
Joined
·
249 Posts
@ 170 LBS I run tubeless with 20 front and 22 rear on my 2010 Specialized Stumpjumper 29r. No burps, or other problems so far.
 

·
Administrator
Joined
·
11,694 Posts
The best advice is to experiment with what you get. I have gotten many many miles on a set of tires that a friend slice the side wall of in one ride. I have never sliced a side wall yet my regular riding buddies do it all the time.

Tires and pressures are so subjective that taking advice is just a valid as guessing. Best bet is to buy a pressure gauge and go out and ride. If it feels like it is to hard drop 2-5 psi and keep riding, keep at this until you feel like it is either wiggling under you or you feel rocks hitting your rims regularly on hard impacts. Pump up a few PSI and ride like this for awhile.

Pressures will vary with all tire, rim and tube/less combinations so experiment and carry a spare tube or 2. When you get it all sorted for your weight and riding style then you will probably feel safe jumping to tubeless.

my $0.02
 

·
Registered
Joined
·
59 Posts
Discussion Starter · #5 ·
Does the difference between 26" and 29" have a bearing on tyre pressures?

E.g. should you automatically run higher pressures on a 29er or vice versa for equivalent 26 set up??
 

·
Registered
Joined
·
1,832 Posts
If I was as light as you, running tubeless, in AZ rocks and sand, I'd run 20 psi on my
Flow / Weirwolf combo.
 

·
JustRide44
Joined
·
133 Posts
I'm 170ish & live in Boise (High Desert) where it can be very loose but we also have big granite baby-heads. The G-Spot seems to be 26 & 24 with an ignitor up front & crossmark in the rear. I would run lower (& have without issues) but I worry about burping on baby heads...
 

·
Registered
Joined
·
125 Posts
I'm 85kg and I run tubeless 22 front 25 back on my rigid 29er. No problems at all. I might try lower pressures.
 

·
Registered
Joined
·
1,832 Posts
thaphillips said:
Maybe if your 80lbs
I weigh 190 and run WW 2.55 at 24-26 psi. Have for a very long time. Great traction and handling. I'll run smaller tires at 26-28 psi.
 

·
Always Learning
Joined
·
9,608 Posts
Bushranger said:
Ok, I'm getting my Spec Epic Comp 29er soon. Just doing some research on setting it up.

I won't be replacing any parts until they wear out or break. (If it matters, I'm 173cms tall and weight 68kgs, race cross country endurance type stuff, 50 to 100k, not elite but competitive)

1. What tyre pressure should I use? I have ridden 26" bikes at around 40 to 45, but read reports I should have been around 35. I'm from a road background so not familiar with best pressures for off road. Should tyre pressures be different for 29" bikes. For example, the contact patch is already bigger on a 29" so does that negate the need for lower pressure to increase contact??
Pressures for off road riding are going to be so low compared to your road background, that you will be left scratching your head and saying "that can't be" when you compare the two. Off road on 29"ers pretty much puts you in a 20 - 40 psi range depending on a few things.

It all depends on the width/volume of the tire you are using. As well as the width of the rim. Wider rims allow for lower psi's and narrower rims usually need a bit more air to prevent squirm. The smaller volume 29"er tires (1.8's, 1.9's) tend to require a bit more psi to avoid squirm than the larger volume tires. I'm taller and heavier than you and will usually run the smaller volume race tires in the 24 - 28 psi (tubeless) range. Larger volume tires usually are in the 20 - 26 psi range (tubeless). Again, depending on tire, terrain and conditions. If running tubes, all of those psi's get bumped up just a bit (2 - 7 psi) to avoid the dreaded snake bite. I usually ran everything around 30-32 psi when I used tubes with no problems whatsoever - except for thorns. In addition to the ride being so much better tubeless with traction, cornering, rolling resistance, the fact that I don't have to deal with thorns any more leaves me in a position that I don't even consider tubes (although I've got a box full of them).

Bushranger said:
2. What about pinch flats on 29ers? If you can run higher pressures does that then mean you don't get pinch flats as often so therefore there really isn't a need for tubeless tyres on a 29".
If you're running higher pressures, you're not going to have to really worry about pinch flats. Your new FS bike is going to absorb a lot of the terrain with the suspenion working to keep your wheels glued to the ground, but that doesn't mean the best solution is to run high pressures in the tires. You don't want the tires bouncing along and you fighting for traction with over-inflated tires. Running in the 40's will leave your tires feeling hard/harsh and your traction will suck.

If it were me and that bike, I would go directly to tubeless. Do not pass go. Your Epic comes with a tubeless ready Captain and Fast Trak. Get the rim strips, convert them and you will not go back to tubes.:cool: Supple performance and handling. Traction galore. It's all worth it - trust us.

Bushranger said:
3. There is a lot of info around on 26" tyre pressures and combo's etc but it will take a while for similar database of knowledge to build up with 29". So if anyone can assist me on my path of discovery, point me to some good articles etc I'd appreciate it.
This subject was actually quite a frequent topic back in 2003, 2004 and 2005 as many on this forum were just getting into 29"ers and wondering about tire pressure on the big wheels. I posted several times wondering about tire pressures and pretty much always got the same response. The usual consensus at the time was that you just have to get out on your terrain, with your riding style and an air pump and gauge until you dial in what works on the front for you and what works on the rear for you with each tire you own. There really isn't any other short cut - such as a database. What works for you - may not for another. If you stick with tubes, just experiment as to how low you can go before getting a pinch flat, but still retain good sidewall support and no squirm.

Here's an example of me running a similar bike design to your new one (4" travel full suspension race/endurance bike) with 1.9 Kenda Karma's tubeless. The front tire is 22 psi and the rear is 24 psi. That's about as low as I'll go tubeless with the smaller volume tires at my weight, but they do well in the mid-20's on the wider (28-29mm) rims. Notice that even at that low weight and my 180 lbs. aboard - the sidewalls do not appear to be bulging out like an under-inflated tire. Great traction, cornering, rolling resistance, thorn protection, etc.... .



That'll leave one scratching their head from a background of running psi's over 100+ lbs. on the road. But it is true, I run most everything in the psi of 20's since I run tubeless, wider rims, etc... .

Best of luck experimenting and getting used to it all.

BB
 

·
Vaginatarian
Joined
·
5,685 Posts
Bushranger said:
Does the difference between 26" and 29" have a bearing on tyre pressures?

E.g. should you automatically run higher pressures on a 29er or vice versa for equivalent 26 set up??
no, it doesnt
 

·
Vaginatarian
Joined
·
5,685 Posts
I Drink Blatz said:
I`m 180lb and run 25psi front and back with no problems. If you run high presure you`re kind of missing the point with tubleless imo
exactly right
there have been studies that proved
1) that riding without a tube decreases rolling resistance and
2) riding with lower pressures also decrease rolling resistance on uneven surfaces
this is because instead of bouncing off and up small rocks, roots etc., the lower pressure allows the tire to simply absorb and roll over

My preffered method is start at say 28psi, ride your favorite trails if you feel the rim getting banged add a couple of psi, if not lower a couple , when you start to constantly get rim strikes add a couple and that should be good. You can go too low and not get rim strikes if that happens your tires will squirm around too much and may come off the rim

I weigh 225 and I generally use 27psi tubeless, never over 30 even with tubes, but if you're more of a plodder rather that trying to avoid bad hits you may need a few lbs. more
 

·
Registered
Joined
·
919 Posts
Bushranger said:
For example, the contact patch is already bigger on a 29" so does that negate the need for lower pressure to increase contact??
Not quite right. The theoretical contact patch area for any flexible tire is determined by the load divided by the pressure. At the same load and pressure, the 29er will have a longer, slightly narrower contact patch, with less maximum tire casing deformation. Most people seem to find that they can run slightly lower pressures without pinch flats.
 

·
Registered
Joined
·
59 Posts
Discussion Starter · #18 ·
BruceBrown said:
If it were me and that bike, I would go directly to tubeless. Do not pass go. Your Epic comes with a tubeless ready Captain and Fast Trak. Get the rim strips, convert them and you will not go back to tubes.:cool: Supple performance and handling. Traction galore. It's all worth it - trust us.

BB
Wow, thanks for the in depth replies folks and especially BB.

Just a question on this - what do you mean by my Epic comes tubeless ready and what is Captain and Fast Trak???

What are rim strips and where do I get them (well obviously from a bike shop, but tubeless is not really common here in Aus in my area)

And why aren't thorns an issue with tubeless - the tubeless tyre can still be penetrated can't it? So wouldn't it still have the same puncture issues for everything except pinch flats?

Yes this is all totally new to me. I've always had a MTB for the past 5 years for variety, but all I did was buy it from the shop, put air in tyres and ride like hell through the bush. I've never bothered to look into the technical side of it. Now I'm looking at smashin a few mates in some off road races I will need all the help I can get!
 

·
Always Learning
Joined
·
9,608 Posts
Bushranger said:
Wow, thanks for the in depth replies folks and especially BB.

Just a question on this - what do you mean by my Epic comes tubeless ready and what is Captain and Fast Trak???
I checked the Specialized site to see what the Epic came with stock out of the box.

Here is what it says:

FRONT TIRE
S-Works The Captain, 29x2.0", 120 TPI, tubeless ready aramid bead, dual compound

REAR TIRE
S-Works Fast Trak LK, 29x2.0", 120 TPI, tubeless ready aramid bead, dual compound

When a company says that a tire is "tubeless ready", it means that you can put some sealant inside the tire using some sort of a rimstrip on the rim.

Here is a tutorial on the Bontrager "tubeless ready" system:

http://www.bike-manual.com/brands/bontrager/om/BT/tr_system.htm
http://bontrager.com/technology/tubeless-ready

The rimstrip can be a special rim tape designed to seal all the air and sealant that could come through the spoke holes or it could be a rubber strip designed to fit in the rim to keep air and sealant from escaping through the spoke holes or it could be made out of plastic. I'm not sure what Specialized sells or what works with that custom DT Swiss X450SL, 29" rim that comes on your bike. I know they call their tubeless ready stuff "2Bliss". Regardless, Specialized is saying that if you want to add the special rimstrip - you are set to go with some sealant. The tire bead and the rimstrip form a bond between each other thanks to the sealant that "glues" them together more or less so air stays in the tire. And the sealant fills all the little pinholes in the walls of the tire to keep air inside the tire.

Bushranger said:
What are rim strips and where do I get them (well obviously from a bike shop, but tubeless is not really common here in Aus in my area)
Continuing from above, I'm not sure what is the best strip for that rim. Perhaps somebody that has more experience with the DT Swiss and Specialized goodies could speak about that. I use rimstrips from NoTubes.com such as these. If you go to that NoTubes site and watch their movies, you'll be up to speed on how it all works pronto. It can all be ordered online and shipped throughout the globe.

Bushranger said:
And why aren't thorns an issue with tubeless - the tubeless tyre can still be penetrated can't it? So wouldn't it still have the same puncture issues for everything except pinch flats?
Thorns create small punctures that the sealant automatically seals so that you do not flat and continue riding. Now, yes, some thorns can still be a problem - like big goatheads. I've only had one huge thorn (nearly like a wooden nail) that did not seal and I had to take the tire off at home and put a patch on the inside of the tire (just like you patch a tube) to keep using that tire. It was a humungo thorn. But 99% of the thorns that I face in my local terrain are not as menacing and I was changing and patching flat tires on average 2 - 3 times a week before I switched to tubeless with sealant. It's pretty hard to pinch flat the actual tire when running tubeless unless you were running a really low pressure and flew into something so hard that the rim cut through the tire. It can happen though, although I've never experienced that.

Bushranger said:
Yes this is all totally new to me. I've always had a MTB for the past 5 years for variety, but all I did was buy it from the shop, put air in tyres and ride like hell through the bush. I've never bothered to look into the technical side of it. Now I'm looking at smashin a few mates in some off road races I will need all the help I can get!
Google around and read up on tubeless mountain bike tires and how to convert tires to tubeless.

BB
 
1 - 20 of 22 Posts
Top