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Rim strike... or not?

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Steven11

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Discussion starter · #1 · (Edited)
Hi, Canyon Lux here mounting a pair of Onza Porcupine 29" x 2.4, 60 TPI over Reynolds 309/289 XC carbon wheels.

I have been running lower and lower pressures over time. I ended up being comfortable at what seems to me to be crazily low pressures for my weight. I am 192 lbs, and am inflating 17 F / 22 R.

They just seem too hard if I go more than that. Riding feel is awesome, but... I wonder if it is possible to get rim strikes and just not notice it?:rolleyes:

With my previous bikes I would definitely notice. This is my first full sus bike w carbon rims though, so I maybe it's just possible to not notice, not even on the rear wheel? I tried doing some slow motion shooting while going over pointy obstacles and still it doesn't seem to me that the tires are squeezing out against the rim. On the contrary there seems to be room to let even some more air out.

They are fairly thick and solid tires in their construction, but those pressures just don't seem normal to me. I mean normally it's people weighing 60-70 lbs less than me that run those kind of PSIs.

I have checked rims for dents and the like, and could find nothing.

Any thought is appreciated!
 
#2 ·
Carbon rim strikes aren't as pronounced as aluminum right up until you taco the rim.. I'm 165 fully geared and run 23/26 absolute minimum and still strike on heavy hits or misjudged rock lines.
 
Discussion starter · #5 ·
asrautox said:
I've run everything. Currently on Magic Mary Trail Ultrasoft F, Tacky Chan Soft R. Before that it was Conti KRF DH SS F, KRF EN S R. Before that Assegai Exo+ MG F, DHR Exo+ R.
Click to expand...
Seems something is off with my setup then. Yet, when I use different tires, I surely do run much more than that, up to 30 PSI in the rear wheel. I don't know, unless the Onza are magic...
 
#8 · (Edited)
I also experimented with low pressure like you, looking to achieve optimal riding experience, and also encountered the issue of rim damage AND tire failures.

My bank account can't afford to replace nice tires and carbon rims (broke Stan's Bravo carbon rim despite running CushCore, and Easton Haven Carbon before that), so I pump my tires up to 19psi front and 29psi rear (27.5"), letting it deflate over time to about 25 psi rear before reinflating. Yes, the bike rattles more at these pressure, especially since I weigh 60 lbs less than you, but I'm able to bash into square edges without hitting the brakes, like going up staircases, without fear.

I'm also able to run my favorite tires, Maxxis DHR II, which I had to stop in the past since they were getting pinch damage to the point that they weren't tubeless-viable (tubeless is a must for me).

I believe the benefits of higher tire pressure outweigh the negatives of the rattly ride quality. I went from overcompensating with a 700g WTB HTZ rim (ebike, wanted bombproof since I said "never again" to the walk of shame back), back to a sub-500g RaceFace carbon rim. The ride quality from running carbon rims, running tires that fit my style better, and being more open to "worse" line choice, is noticeably more "fun-inducing" than the ride quality from running ridiculously low pressures.

Recently, I've been able to see the fruits of my decisions--I've been able to witness my tires actually wear down to their fullest, without needing to rely on heavy braking and bike park use, getting over a year/3000+ miles on even on flimsy stock tires. I never expected bald Maxxis tires to still grip so well, but I dared to keep riding them until they became real crash hazards:

Image
Image


^ left Schwalbe Fat Albert with 6000+ miles. Assegai DH 2500+ miles on the rear! (I overcompensated after the last premature failure, but it was good enough for me to not consider changing it out, since it rolled much better after breaking in). I rode 3.5 more months on it!

Image


Image


^ pretty sure this is over 3000 miles.

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^ can't seal this hole. Not tubeless viable any more.

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^ this flimsy tire failed on the first ride. It needed a plug, and I didn't know about the permanent plugs then, so I replaced the tire.

Image
 
#9 ·
If you are making non-destructive strikes with your rim, you should see some cosmetic marks on the rim. If the wheel looks pristine, you should be ok so far. Those low pressures would kill my rear wheel, but the rocks are different everywhere.
 
#10 ·
Tires are suspension. Check your sag to know if you're running the correct pressure. This is easier to do with another person helping. Measure compressed height of the rim to the ground with and without load (you). ~15% sag is a good starting point. Given your weight, I'd expect good F / R pressure ~ 25 / 28 PSI.
 
#12 ·
I've been riding 12F/17R on my hardtail for the past few years.

Mostly with a WTB Vigilante 2.6 F and a Specialized Purgatory 2.6 R. I do use a Huck Norris insert in the rear. I do occasionally get rim strikes in the rear, but they are sufficiently damped by the insert that I don't have any rim damage from them. DT Swiss XM 481 alu rims, btw. I have more rim nicks on the upper surface from loose rocks banging on them.

And I'm in the 200lb range suited up.

I do bump my pressures up a bit when I'm riding fast hardpack trails to make sure the sidewalls don't fold over in hard cornering.

I think part of that is the gauge I'm using. I use one of those Meiser 30psi gauges. When I use the Topeak pump at work, pressures register close to 20F and around 25R. The floor pumps I have at home all have road pressure gauges and the pressures I use on my mtb are hard to read.
 
#13 ·
Steven11 said:
Hi, Canyon Lux here mounting a pair of Onza Porcupine 29" x 2.4, 60 TPI over Reynolds 309/289 carbon wheels.

I have been running lower and lower pressures over time. I ended up being comfortable at what seem to me to be crazily low pressures for my weight. I am 192 lbs, and am inflating 17 F / 22 R.

They just seem too hard if I go more than that. Riding feel is awesome, but... I wonder if it is possible to get rim strikes and just not notice it?:rolleyes:

With my previous bikes I would definitely notice. This is my first full sus bike w carbon rims though, so I maybe it's just possible to not notice, esp on the rear wheel? I tried doing some slow motion shooting while going over pointy obstacles and still it doesn't seem to me that the tires are squeezing out against the rim. On the contrary there seems to be room to let even some more air out.

They are fairly bulky tires in their construction, but those pressures just don't seem normal to me. I mean normally it's people weighing 60-70 lbs less than me that run those kind of PSIs.

I have checked rims for dents and the like, and could find nothing.

Any thought is appreciated!
Click to expand...
If you rode in the Southwest where I do your low pressure riding days would be short lived in favor of finishing the ride and getting home. My last ride one of the guys was from out of town. I looked at his tires before we left and asked him if he was sure he wanted to ride with pressures that low. Well, he did and got a pinch flat about 12 miles in which destroyed his rear tire. I had to ride all the way back, get my truck while we walked out to a location I could pick him up.

I love low tire pressures because it makes for a much smoother ride but you have to be really careful what type of terrain you ride on. I choose 23 PSI front and 26-28 PSI back. It sucks but I never have tire issues.
 
#14 ·
Steven11 said:
Hi, Canyon Lux here mounting a pair of Onza Porcupine 29" x 2.4, 60 TPI over Reynolds 309/289 carbon wheels.

I have been running lower and lower pressures over time. I ended up being comfortable at what seem to me to be crazily low pressures for my weight. I am 192 lbs, and am inflating 17 F / 22 R.

They just seem too hard if I go more than that. Riding feel is awesome, but... I wonder if it is possible to get rim strikes and just not notice it?:rolleyes:

With my previous bikes I would definitely notice. This is my first full sus bike w carbon rims though, so I maybe it's just possible to not notice, esp on the rear wheel? I tried doing some slow motion shooting while going over pointy obstacles and still it doesn't seem to me that the tires are squeezing out against the rim. On the contrary there seems to be room to let even some more air out.

They are fairly bulky tires in their construction, but those pressures just don't seem normal to me. I mean normally it's people weighing 60-70 lbs less than me that run those kind of PSIs.

I have checked rims for dents and the like, and could find nothing.

Any thought is appreciated!
Click to expand...
My go to is 19 F and 21R for my loam and roots. I'm using 2.5 exo+ minion and assegay on enve foundations at 77kg/ 170lb naked.

The pressure you need depends entirely on the pointyness/slipperness of your enviroment and the speed you are going.

The faster and pointier you go the more pressure you need. The thicker wall and bigger volume you go the less pressure you need. The slipperier and slower you go the less pressure you need.

My swing of pressures is 12psi for mid winter slippery moss covered rooty slow steep tech to through to 26psi for high speed pointy rock smashing mayhem.

Test and trial. You will know when you bash a carbon rim... and you die a little inside when you do because carbon does not yeild. If a strong rim it will take more abuse before it fails. But when it fails you smash them to oblivion. There is not bending back a dent in a carbon rim....

So... politely test and find that magical spot that is low as you can go without rim tagging on your hardest reasonable hit or getting tire squirm. That is the point of greatest traction. Anymore pressure is just leading you to harshness and less traction.
 
#15 ·
Harold said:
I've been riding 12F/17R on my hardtail for the past few years.

Mostly with a WTB Vigilante 2.6 F and a Specialized Purgatory 2.6 R. I do use a Huck Norris insert in the rear. I do occasionally get rim strikes in the rear, but they are sufficiently damped by the insert that I don't have any rim damage from them. DT Swiss XM 481 alu rims, btw. I have more rim nicks on the upper surface from loose rocks banging on them.

And I'm in the 200lb range suited up.

I do bump my pressures up a bit when I'm riding fast hardpack trails to make sure the sidewalls don't fold over in hard cornering.
Click to expand...
I was gonna ask about folding the tires over at those pressures.
I'd be rolling them and getting rim strikes constantly running that low, at about the same rider weight.
 
#17 ·
slapheadmofo said:
I was gonna ask about folding the tires over at those pressures.
I'd be rolling them and getting rim strikes constantly running that low, at about the same rider weight.
Click to expand...
Usually don't have issues with them folding over. I get moving at a pretty good clip but my usual trails are rough enough that I don't get the kinds of lateral forces that would make them fold over like that. The only time that's ever happened was when I was on some pretty smooth machine-built flow trails pushing some g-forces in a fast bermed corner. And I just don't ride that stuff very much.

Some of the issue may have been the knobs themselves folding over, but it was such a sudden loss of control on the back tire that I think the casing actually folded.
 
#18 ·
Harold said:
Usually don't have issues with them folding over. I get moving at a pretty good clip but my usual trails are rough enough that I don't get the kinds of lateral forces that would make them fold over like that. The only time that's ever happened was when I was on some pretty smooth machine-built flow trails pushing some g-forces in a fast bermed corner. And I just don't ride that stuff very much.

Some of the issue may have been the knobs themselves folding over, but it was such a sudden loss of control on the back tire that I think the casing actually folded.
Click to expand...
Dig it.

The trails around here tend to have a good amount of tight'n'twisty mixed in with plenty of chunky and I have a habit of pumping corners (or trying anyway), so I'd kill myself running anywhere near that low lol.
 
#19 ·
Steven11 said:
Hi, Canyon Lux here mounting a pair of Onza Porcupine 29" x 2.4, 60 TPI over Reynolds 309/289 carbon wheels.

I have been running lower and lower pressures over time. I ended up being comfortable at what seem to me to be crazily low pressures for my weight. I am 192 lbs, and am inflating 17 F / 22 R.

They just seem too hard if I go more than that. Riding feel is awesome, but... I wonder if it is possible to get rim strikes and just not notice it?:rolleyes:

With my previous bikes I would definitely notice. This is my first full sus bike w carbon rims though, so I maybe it's just possible to not notice, esp on the rear wheel? I tried doing some slow motion shooting while going over pointy obstacles and still it doesn't seem to me that the tires are squeezing out against the rim. On the contrary there seems to be room to let even some more air out.

They are fairly bulky tires in their construction, but those pressures just don't seem normal to me. I mean normally it's people weighing 60-70 lbs less than me that run those kind of PSIs.

I have checked rims for dents and the like, and could find nothing.

Any thought is appreciated!
Click to expand...
At 220 lbs., I've been running 18 psi front, 20 psi rear on 29" Maxxis Minion DHR II 2.4" tires. Ibis Ripley, so 140F/130R travel. These pressures are normal. I'm using a 60psi Accu-Gauge that I've calibrated to confirm accuracy. I can run lower to 16/18 if I keep a close eye on them. Depends on conditions and riding aggressiveness though. But I'm perfectly happy riding Sierra granite at these pressures. Been riding this bike three years and have yet to experience a rim strike, any rim damage or pinch flat/sidewall damage. So it's not like I'm operating on a razor's edge or anything.
 
#20 ·
slapheadmofo said:
Dig it.

The trails around here tend to have a good amount of tight'n'twisty mixed in with plenty of chunky and I have a habit of pumping corners (or trying anyway), so I'd kill myself running anywhere near that low lol.
Click to expand...
I like trying to pump corners, but the trails I usually ride aren't that twisty. Instead, they're pretty wide open and most turns tend to be fairly small adjustments to direction. OR they're super tight switchbacks you have to slow down a lot for, so you're still not generating that much lateral force.
 
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