# Tire pressure - CX newbie



## AJ88V (Nov 14, 2012)

My new-to-me Motobecane Fantom Cross PRO CX bike has 700X30C Michelin MUD2 clincher tires on it. The Michelin website says 36-73 PSI. I bought this bike mostly for fire roads and such. (Already have a decent MTB for the rough stuff.)

I weigh about 175. Any advice where to start for tire pressure?


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## pretender (Sep 18, 2007)

Start with 50psi and go up or down from there.


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## 4Crawler (Jul 13, 2011)

Yes, 50 might be a good starting pressure, maybe a bit higher. I weigh about the same and on a set of 700x35 Conti. Cyclocross Speed tires (56-85 psi) I run them at 50psi on 19mm rims w/ latex tubes. Below that pressure, I find I bottom out on golf ball sized gravel.

What I did on my first set of tires *700x40 Schwalbe Marathon Mondial) was to start at 50-55psi and then I basically let the tires leak down over a few weeks and multiple rides. I would check the pressure and then see how the tires worked. Finally ended up around 35-40 psi on those tires until I switched to tubeless then I dropped that to 30psi. 

I like to run my tires as soft as possible yet firm enough to keep from bottoming out the rims going over rocky terrain at speed. So when I start feeling that hard thud over rocks, that tells me I am a bit too low and I need to up the pressures. I usually run the front tire the same or a few psi lower than the rear.


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## aureliajulia (May 25, 2009)

Cool thread. Was trying to figure this out yesterday. My bike came with Sammy Slicks. I think the tire pressure is supposed to be between 50 and 85. (Hard to read the numbers are so small, plus, the recommended numbers are in parenthesis. Let's just make it harder to see!). 

I'm 5'7'', 150 lbs, very strong in the muscle department. Plus heavy boned. Translation, I hammer pretty hard, sometimes. Very new to cross as I just got my bike 2 days ago. But not new to road riding. I set the pressure at about 65 for the front, and a little lower for the rear. Does that sound right? 

Thanks.


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## tednugent (Apr 26, 2010)

AJ88V said:


> My new-to-me Motobecane Fantom Cross PRO CX bike has 700X30C Michelin MUD2 clincher tires on it. The Michelin website says 36-73 PSI. I bought this bike mostly for fire roads and such. (Already have a decent MTB for the rough stuff.)
> 
> I weigh about 175. Any advice where to start for tire pressure?





pretender said:


> Start with 50psi and go up or down from there.


That's a good starting point. You really don't need to go less than 40 and enter the pinch flat risk territory, since it's just primarily fireroads. For rougher stuff and off-camber stuff, lower is better to conform to the ground better (until you hit the pinch flat threshold).

Riding cross in the rougher stuff makes things interesting also, and provides new challenges to the trails you already know from the MTB... though I wouldn't take it on extremely technical trails, imo.



aureliajulia said:


> Cool thread. Was trying to figure this out yesterday. My bike came with Sammy Slicks. I think the tire pressure is supposed to be between 50 and 85. (Hard to read the numbers are so small, plus, the recommended numbers are in parenthesis. Let's just make it harder to see!).
> 
> I'm 5'7'', 150 lbs, very strong in the muscle department. Plus heavy boned. Translation, I hammer pretty hard, sometimes. Very new to cross as I just got my bike 2 days ago. But not new to road riding. I set the pressure at about 65 for the front, and a little lower for the rear. Does that sound right?
> 
> Thanks.


Usually, you would like to get less pressure up front than the rear, since more of your weight is distributed to the rear wheel.


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## aureliajulia (May 25, 2009)

tednugent said:


> That's a good starting point. You really don't need to go less than 40 and enter the pinch flat risk territory, since it's just primarily fireroads. For rougher stuff and off-camber stuff, lower is better to conform to the ground better (until you hit the pinch flat threshold).
> 
> Riding cross in the rougher stuff makes things interesting also, and provides new challenges to the trails you already know from the MTB... though I wouldn't take it on extremely technical trails, imo.
> 
> ...


On my road bike, the tire pressure always decreases faster on the front wheel. But that does make sense.


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## AJ88V (Nov 14, 2012)

I used 60 psi for my first "off road" experience with this bike. Road experience was great, but off-road was not so great. It tended to skitter through the corners unpleasantly, at least compared to my MTB where I run fat knobby tires at 30-40 psi depending on condition.

Also, researching this topic before posting, I did find reference to running the rear tire with lower pressure than the front, like aureliajulia (hi sheila!) mentioned. Seems contrary to road bike practice and could be an interesting discussion in itself. - AJ


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## ts8169 (Feb 23, 2009)

AJ88V said:


> I used 60 psi for my first "off road" experience with this bike. Road experience was great, but off-road was not so great. It tended to skitter through the corners unpleasantly, at least compared to my MTB where I run fat knobby tires at 30-40 psi depending on condition.
> - AJ


Sounds very high but I'm a light-weight, 135. For my mountain bike I run 29er tires tubeless at 20-24psi. I used to run 30-40 psi with tubes to prevent pinch flats and thought it made me faster. All it did was destroy my body. Now at 22 with tubeless it's like night & day. Amazing & fast. For cross I'll run 35-ish if I'm racing. Training and all-around cross rides will be higher, 50+/- just to prevent pinch flats. Plus I'll be on the road somewhat. Slicks = 100 psi, it's all my compressor will handle.


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## AJ88V (Nov 14, 2012)

ts8169 said:


> Sounds very high but I'm a light-weight, 135. For my mountain bike I run 29er tires tubeless at 20-24psi. I used to run 30-40 psi with tubes to prevent pinch flats and thought it made me faster. All it did was destroy my body. Now at 22 with tubeless it's like night & day. Amazing & fast. For cross I'll run 35-ish if I'm racing. Training and all-around cross rides will be higher, 50+/- just to prevent pinch flats. Plus I'll be on the road somewhat. Slicks = 100 psi, it's all my compressor will handle.


The 60 psi sucked in the dirt, which is why I did a little reading and then opened this thread. Next time I'll drop to 50 and play from there.

Your comments on the MTB are also interesting. I used to run 25 and still do in steep/rooty terrain (lots of that out here). I bumped to 40 for most else, thinking it would make me faster, and maybe it does, but it also is a lot more harsh.


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## 4Crawler (Jul 13, 2011)

AJ88V said:


> The 60 psi sucked in the dirt, which is why I did a little reading and then opened this thread. Next time I'll drop to 50 and play from there.
> 
> Your comments on the MTB are also interesting. I used to run 25 and still do in steep/rooty terrain (lots of that out here). I bumped to 40 for most else, thinking it would make me faster, and maybe it does, but it also is a lot more harsh.


Yes, just slowly lower the pressure before each ride and note how they do over rough stuff. I have a good test ride about 5 miles from my house, right at the end of a paved bike path. It is a levee access road covered in golf ball to baseball sized rocks. If I can hammer through that without feeling the rims bottoming out, I have a good pressure. I find where I start feeling the rocks on the rim then up the pressure about 10% from there. So on my tubeless 40s, 27psi was about the where I started bottoming out, so I run those tires at 30psi or a bit more. On the tubed 35s, 45psi was the bottom end pressure and I bumped those to 50psi.


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## pretender (Sep 18, 2007)

AJ88V said:


> I used to run 25 and still do in steep/rooty terrain (lots of that out here). I bumped to 40 for most else, thinking it would make me faster, and maybe it does, but it also is a lot more harsh.


Higher pressure is only faster on smooth pavement, and with knobby tires I'm not even sure about that. On bumpy surfaces, lower tire pressure allows the bike to bounce around less, which equates to lower rolling resistance.

That's why the best CX racers run very low tire pressures, and which is also why tubulars are so heavily favored by serious racers.


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## tednugent (Apr 26, 2010)

pretender said:


> Higher pressure is only faster on smooth pavement, and with knobby tires I'm not even sure about that. On bumpy surfaces, lower tire pressure allows the bike to bounce around less, which equates to lower rolling resistance.


HIgh pressure is faster on smooth pavements with knobbies.



> That's why the best CX racers run very low tire pressures, and which is also why tubulars are so heavily favored by serious racers.


With the varied ground surfaces of cross racing, like MTB, lower pressure means the tire gets to conform to the ground shapes better.

Even tubeless is starting get a traction on cross races.

At approx 185 lbs myself... with tubeless, I run about 28 psi in the rear and 25 up front.


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## JohnStonebarger (Jan 22, 2004)

tednugent said:


> At approx 185 lbs myself... with tubeless, I run about 28 psi in the rear and 25 up front.


That's about what I cx at on clichers (22-26 front, 24-28 rear) and I'm 175 lbs. With latex tubes pinch flats haven't been an issue.

For gravel races I'll use 35-45 psi, depending. The risk for pinch flats is greater, of course, but high pressures over anything that chunky are slow and painful.


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## tednugent (Apr 26, 2010)

JohnStonebarger said:


> That's about what I cx at on clichers (22-26 front, 24-28 rear) and I'm 175 lbs. With latex tubes pinch flats haven't been an issue.
> 
> For gravel races I'll use 35-45 psi, depending. The risk for pinch flats is greater, of course, but high pressures over anything that chunky are slow and painful.


I have pinched my front tire at 35 psi (butyl rubber tube) resulting in a DNF on my 1st race.


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## JohnStonebarger (Jan 22, 2004)

Ouch! Butyl is nasty stuff. I carry it for road repairs (since I'm lazy and use co2), but won't use it otherwise. Latex is smoother, faster, and unlikely to flat. Even bottoming out onto the rim generally is no problem. In all fairness I do run 23mm rims, too, so I'm sure that helps run lower pressure, but even on 19mm rims I was able to go below 30psi with latex.


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