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Tire Pressure Question

Old 09-26-18, 11:50 AM
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Abe_Froman
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Tire Pressure Question

So, I've done a handful of races, and am still trying to figure out tire pressure. Running tubes currently. My question is this...SHOULD the tire be folding over/deforming in a corner, or is this something to avoid? My back tire has been deforming on harder corners. I've got it at 30psi right now. I'm thinkiing ~35psi or so might be more effective...but eh. Figured I'd have the community weight in.
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Old 09-26-18, 12:12 PM
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I'm no expert, but I would suggest it should not be folding. Deforming is normal. 35psi seems low unless they are quite wide (how wide?).
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Old 09-26-18, 12:42 PM
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Deforming - sure, but I'm not sure to what extent you think it is bad. When cornering hard at low pressure, you should feel the tire grabbing turf or even slipping out slightly, and you will feel the rim moving around a bit - all normal. But if it feels like a flat rear would feel on gentle cornering, where the rim is obviously moving a lot relative to the tire, then you probably don't have a high quality rim-tire combo if indeed you have 30psi in a 33c wide tire. When running tubeless I am at 24/26 front/rear and I weigh 155. 30-35 would feel rock hard and would be slower on bumpy ground. Pros running tubeless clinchers are in my ballpark, definitely lower if they are smaller than me. But they have high quality tubeless setups (where the bead pops on with a loud snap as you inflate them). Occasionally I've had to stick a tube into my tubleless setup, I keep it at 26 and don't worry about pinch flats - its just a race.
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Old 09-26-18, 12:58 PM
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Originally Posted by Abe_Froman View Post
So, I've done a handful of races, and am still trying to figure out tire pressure. Running tubes currently. My question is this...SHOULD the tire be folding over/deforming in a corner, or is this something to avoid? My back tire has been deforming on harder corners. I've got it at 30psi right now. I'm thinkiing ~35psi or so might be more effective...but eh. Figured I'd have the community weight in.
Depends on the pressure rating, surface, type of tire, and weight of the rider (all of which you excluded). In all cases there is a range of acceptability according to the rider's preference.
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Old 09-26-18, 01:12 PM
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Originally Posted by KraneXL View Post
Depends on the pressure rating, surface, type of tire, and weight of the rider (all of which you excluded). In all cases there is a range of acceptability according to the rider's preference.
Sorry. I'm 190lbs, on 35mm all purpose cross tires. No idea what the rating is...but I really doubt that makes any difference.

Thinking of getting a set of Compass Steilacoom tires and running them tubeless....but just worrying about tubed setup right now.
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Old 09-26-18, 01:49 PM
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Originally Posted by Abe_Froman View Post
Sorry. I'm 190lbs, on 35mm all purpose cross tires.
Similar weight and tire set up, I have my pressure around 35#'s. The front is usually 1-2#'s lower than the rear.

I like to feel it out in the yard a day or two before racing (so there's no surprises), and add/subtract pressure so there's not too much rim hitting the ground.
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Old 09-26-18, 02:36 PM
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Originally Posted by justin1138 View Post
Similar weight and tire set up, I have my pressure around 35#'s. The front is usually 1-2#'s lower than the rear.

I like to feel it out in the yard a day or two before racing (so there's no surprises), and add/subtract pressure so there's not too much rim hitting the ground.
Ok good to know. Yea the first race of the season I had the back at 35psi...and only noticed what I think was a foldover once, and it was on a very slight off camber that I took pretty hard. Then the next race I had it at 30...and it seemed I had that sensation on pretty much every corner I took hard.
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Old 09-27-18, 06:27 AM
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Originally Posted by Abe_Froman View Post
Sorry. I'm 190lbs, on 35mm all purpose cross tires. No idea what the rating is...but I really doubt that makes any difference.

Thinking of getting a set of Compass Steilacoom tires and running them tubeless....but just worrying about tubed setup right now.
Check out some Donnelly BOS or PDX if you want a good chunky CX tire for tubeless. https://www.probikekit.com/bicycle-t.../11651868.html

I also run 25ish on tubeless (125lb)
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Old 09-27-18, 10:54 AM
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I generally check my pressures during the course previews by lowering it until they bottom out on the roughest sections and then adding back a few psi. Since you are running tubed that may not be an option. A good amount of squirm is normal though and you just get used to it if you are coming from a mostly road background
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Old 09-27-18, 11:05 AM
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Originally Posted by redlude97 View Post
I generally check my pressures during the course previews by lowering it until they bottom out on the roughest sections and then adding back a few psi. Since you are running tubed that may not be an option. A good amount of squirm is normal though and you just get used to it if you are coming from a mostly road background
Well the squirm didnt phase me at all. But the tire folding completely over, the rim sliding sideways across it and onto the ground was a bit disconcerting lol.
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Old 10-04-18, 10:45 AM
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Originally Posted by Abe_Froman View Post
Well the squirm didnt phase me at all. But the tire folding completely over, the rim sliding sideways across it and onto the ground was a bit disconcerting lol.
More then. If it's affecting your line choice, adjustment is needed.
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Old 10-05-18, 08:15 AM
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Originally Posted by 50voltphantom View Post
More then. If it's affecting your line choice, adjustment is needed.
Yea. I've tried it at 34/36...feels much better.
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Old 06-25-19, 12:57 PM
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It doesn't sound like you have a very wide rim. Narrow rims with 35mm tires will fold over more easily. I had a stock rim I raced a few times as backup and it was really flexy and bouncy. I ran 35c tires at or around 32psi with tubes...would pinch flat going lower. For safety purposes I would personally shy away from completely folding the tire over like you're describing. This seems like an accident waiting to happen.

My philosophy is to run higher PSI than you think because if you flat you're essentially out of contention unless the pit is like right there.

So:
If running tubes, add PSI to avoid pinch flat
If running tubeless, consider adding to avoid burp if the course has a lot of off camber
If you run tubulars then go ahead and drop it lower. You can hit rim and get away with it.

I ran under 27psi or so all season on tubulars and those things hooked up so well. I can't imagine running under 20psi though like the pros in some of these muddy races.

Pre-ride and adjust accordingly but over here its very difficult to pre-ride at race speed so this strategy is hard to employ.

Also, keep a log of the course, conditions and PSI for future.
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Old 06-25-19, 03:38 PM
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Trial and error, varies by course and condition. You can run a lot lower pressure in the mud than on rocks and roots. Start at 35 and work your way down til you find the right feel for you.
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Old 06-26-19, 07:58 AM
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Originally Posted by bbbean View Post
Trial and error, varies by course and condition. You can run a lot lower pressure in the mud than on rocks and roots. Start at 35 and work your way down til you find the right feel for you.
Exactly. When it's really sloppy with minimal rocks/roots you can really get into silly territory with pressures. I was running <~20psi in the front and <30psi rear with tubes at the really wet races last year and I weigh about 195. As long as you're not experiencing understeer and can stay light on the bike you'll probably be ok. Yes I bottomed out my front tire a lot. My baseline is 22F/32R.
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Old 08-06-19, 01:54 PM
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Just chiming in here. Every tire is different, but I run 33mm Challenge Baby Limus tubulars on a 23mm rim (Major Tom) typically around 25-28psi and feel some slight folding over on the rear when accelerating out of tight corners, but nothing as extreme as you're describing where the rim is actually hitting the ground.

I'm about 165lbs.
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Old 08-09-19, 12:59 PM
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^ Not in the rear, but my front. Like I said, this was in extremely wet conditions.
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Old 08-09-19, 05:23 PM
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I usually lower the pressure until I hit the rim 1-2x during the preride, then add back a few psi. I assume at race pace I might be going a bit faster and bottom out the rims occasionally. 1-2 times is normal for tubulars, I try not to with tubeless in case I get a catastrophic burp
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Old 09-09-19, 06:23 AM
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Instead of starting a new topic, I'll add my intro to racing.

I think for both CX and gravel I'm way way off base for pressures. I ran 40psi on Sunday's race and felt like I was bouncing all over the place. I weigh 155 lbs. It's a normal narrower width wheelset with tubes.

I also think I was running way way too little tire tread. I bought a tire set a while back when I bought the bike used to serve me as a gravel tire. I have to ride greenway to/from the gravel, so hence the choice.

It's a Tracer in a 33mm. Looking around, I was certainly in the lesser tread on the tire camp. And since I'm new to this, probably not a good thing. I probably need more tire size and more tread.

I'm also guessing that 40psi was super bouncy and slow for my weight.

I have a meter on my roadie, maybe I'll do a little testing to get some numbers for my tire pressures on "easy ride" days. Ride a section in the same gear same cadence/speed and lower the tire pressure each time around.
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Old 09-09-19, 08:55 AM
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Originally Posted by burnthesheep View Post
Instead of starting a new topic, I'll add my intro to racing.

I think for both CX and gravel I'm way way off base for pressures. I ran 40psi on Sunday's race and felt like I was bouncing all over the place. I weigh 155 lbs. It's a normal narrower width wheelset with tubes.

I also think I was running way way too little tire tread. I bought a tire set a while back when I bought the bike used to serve me as a gravel tire. I have to ride greenway to/from the gravel, so hence the choice.

It's a Tracer in a 33mm. Looking around, I was certainly in the lesser tread on the tire camp. And since I'm new to this, probably not a good thing. I probably need more tire size and more tread.

I'm also guessing that 40psi was super bouncy and slow for my weight.

I have a meter on my roadie, maybe I'll do a little testing to get some numbers for my tire pressures on "easy ride" days. Ride a section in the same gear same cadence/speed and lower the tire pressure each time around.
For CX, straight line rolling resistance doesnt matter that much, doubly so if youre new. You'll loose more time each corner from too high of pressure compared to the losses due to RR. A crash or even a bobble will erase any time gained from higher pressure. If tubeless you should noy be any higher than 30psi. Even with tubes you should start at that pressure and see if you get lunch flats, preferablu during practices. Im running sub 28psi at all times in all conditions at 180lbs on tubeless and tubular.
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Old 09-09-19, 09:01 AM
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Originally Posted by redlude97 View Post
For CX, straight line rolling resistance doesnt matter that much, doubly so if youre new. You'll loose more time each corner from too high of pressure compared to the losses due to RR. A crash or even a bobble will erase any time gained from higher pressure. If tubeless you should noy be any higher than 30psi. Even with tubes you should start at that pressure and see if you get lunch flats, preferablu during practices. Im running sub 28psi at all times in all conditions at 180lbs on tubeless and tubular.
Thanks.

The RR thing makes sense versus cornering grip.

Definitely sounds too high though right now on pressure. And maybe too "fast" of a tire for not enough grip for a newer rider. I can ride the park above my house and give it a try. I know one thing, if I was bouncing during the race.....it had to have been 'wrong'.

I know tubeless is the future, but is there any merit on lower pressure and pinch flats and running latex? If I'm into this, I'll probably go tubeless or tubulars. I know how to glue from my TT tire stuff. A latex tube is cheaper/faster to try than selling and buying wheels to go tubeless or tubular.
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Old 09-09-19, 09:05 AM
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Originally Posted by burnthesheep View Post
Thanks.

The RR thing makes sense versus cornering grip.

Definitely sounds too high though right now on pressure. And maybe too "fast" of a tire for not enough grip for a newer rider. I can ride the park above my house and give it a try. I know one thing, if I was bouncing during the race.....it had to have been 'wrong'.

I know tubeless is the future, but is there any merit on lower pressure and pinch flats and running latex? If I'm into this, I'll probably go tubeless or tubulars. I know how to glue from my TT tire stuff. A latex tube is cheaper/faster to try than selling and buying wheels to go tubeless or tubular.
I ran latex tubes my first season during races and never pinch flatted or punctured whereas I snakebited quite a few regular tubes in practices. Conditions were different but I do think latex does offer some additional protection and suppleness
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Old 09-09-19, 10:03 AM
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Originally Posted by burnthesheep View Post
Instead of starting a new topic, I'll add my intro to racing.

I think for both CX and gravel I'm way way off base for pressures. I ran 40psi on Sunday's race and felt like I was bouncing all over the place. I weigh 155 lbs. It's a normal narrower width wheelset with tubes.

I also think I was running way way too little tire tread. I bought a tire set a while back when I bought the bike used to serve me as a gravel tire. I have to ride greenway to/from the gravel, so hence the choice.

It's a Tracer in a 33mm. Looking around, I was certainly in the lesser tread on the tire camp. And since I'm new to this, probably not a good thing. I probably need more tire size and more tread.

I'm also guessing that 40psi was super bouncy and slow for my weight.

I have a meter on my roadie, maybe I'll do a little testing to get some numbers for my tire pressures on "easy ride" days. Ride a section in the same gear same cadence/speed and lower the tire pressure each time around.
My wife runs the Specialized Tracer and its great in dry conditions. When there is wet conditions it will not do well. If you're just starting out I wouldn't necessarily trust what everyone in your category is using (assuming you're racing in the beginner category). Better to look at what the elites are running in their race.

Also, can't stress enough that going out to a park or going to the race venue the day after and doing some hot laps is definitely worth your time when you're just starting out. I've been racing a few years but I still do this...yesterday started at 30 and reduced down until I started hitting rim. At that point there is a finesse needed for your riding, to avoid those rocks and roots that will clank your rim. I run HED Belgium+ and try and not clank the rim because it will dent and then you're hosed. I already have one dent but luckily not affecting the tire/wheel interface. I ended up being able to run 22psi in front and 25psi rear and not lose the tire. The course had a lot of off camber. I weigh 165.

Don't get greedy though. Tire pressure is specific to the course, rider, wheel/tire combo, not necessarily in that order. I'd much rather finish a race because I had a few extra PSI than have to pit for more PSI or a bike change.
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Old 09-09-19, 11:52 AM
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I've been doing 30ish/f 35ish/r with tubes, mostly ok (had a couple of flats last year but otherwise have hit some rocks/roots without repercussions) but I'm starting to feel like it's costing me some time. Wonder if I can get away with like 25-30/f and 30r at 160lbs. It really is a compromise between high pressure/not flatting and lower and risk having a good race ruined. Would love to try tubulars this season, might have to see if someone will lend me some
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Old 09-09-19, 12:42 PM
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Originally Posted by hubcyclist View Post
Wonder if I can get away with like 25-30/f and 30r at 160lbs.
I would say yes. Roots and rocks will affect what you ultimately run on a given day but I'd say those pressures are more than do-able at your weight.
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