Source
r/MTB•
MTBSPEC

Rim strikes and tire pressure

Question

When you “ring” your rim because you take a really hard hit on your rear wheel, does that mean you are rim striking?

I recently upgraded to my first 29er hardtail and have been playing with tire pressure trying to get it right. I weigh 170 lbs and I am running an I9 trail 270 wheelset (27mm) with maxxis 2.4 WT Dissector front and Rekon back. I had roughly the same set up with 27.5 and I ran 21 front and 26 rear. I have been running 20/24 but at 24 in the rear I had some hard hits that kind of rattled the rim/spokes. It feels really good on the trail and when I went to 25/26 it felt too hard in the rear end. Do you guys think I am risking my rim too much at 24 PSI?

Posted May 19, 2022, 1:33 AM UTC

323
nobamboozlinmeUnited States of America•

Yeah I run higher psi or I ring the shit out of rims just like this. I have a new dt swiss wheelset and I’d rather run higher pressure and adjust over the day once I feel it out.

3
cloudofevilTennessee•

When you “ring” your rim because you take a really hard hit on your rear wheel, does that mean you are rim striking?...I had some hard hits that kind of rattled the rim/spokes

I'm not sure what you mean by rattle the rim and spokes. A rim strike is usually pretty obvious. You'll literally feel the tire bottom out on the rim and maybe hear the rim ping of the rock. If you're not sure you're getting rim strikes, not getting pinch flats or dinged rims then I don't think you need to increase your tire pressure.

3
RawmanceMTB•

When you “ring” your rim because you take a really hard hit on your rear wheel, does that mean you are rim striking?

Yeah.

I ran 21 front and 26 rear. I have been running 20/24 but at 24 in the rear I had some hard hits that kind of rattled the rim/spokes.

Yeah no wonder with that kinda pressure. There is no optimal solution. You run what you run and the tires eat up the small stuff perfectly, but everything strikes the rim at higher speeds and your tyres will come off in aggressive turns. With higher pressure it's just a rough ride. I'm about 1,8bar. It's still not quite enough for the most aggressive turns the wheels will come off, but you won't run into those kinds of turns outside of bike parks.

Even with inserts you can lower pressure but because of the reduced volume it ramps up way faster so that is not a solution either.

There isn't an optimal solution to the problem.

2
gonzo_redditor•

Look into tire inserts like cush core. Adds weight but protects your rims and lets you really play with low pressures.

2
bkturr•

Came to say this

1
HalloweenBlkCat•

I would say air up a little if you’re hitting the rim like that. I used to ride at 25psi up until a week ago when I hit a rock a little weird and, for the first time ever, had to experience the gut-wrenching agony of regret as I looked at a dented rim as it sprayed out the last bit of sealant (also put a small hole in the tire). That. Sucked. Used a tube to get home and was able to get it bent back into shape just enough to reseal as tubeless, but it really didn’t want to. A guy at my LBS told me that bending rims back is sketchy and if you put too much pressure on the apex of the dent, the rim will often crack and then you’re hosed. I was super careful and got lucky, but that period of wondering if I could afford a new wheel anytime soon and how long it would take to get one got me to err on the side of caution. Moral of the story, if you don’t have cash to burn on a new rims, a minor downgrade in trail feel is probably worth it. If traction/bounce is your concern you may be able to solve that with a different tire choice(?).

1
wD4D247•

If your terrain is really rocky and you don’t wanna increase pressure I’d go with one of the various tire inserts. Another option is getting downhill casing for the rear but you won’t find rekons with dh casing. I really like the dissector front and rear and it is available in dh casing.

1
gzSimulator•

I got doubledown tires and I run them 2-3 less psi than my exo tires and they do an amazing job at not rim striking (and not squashing around in heavy corners even at lower psi, which was the main reason I got them)

Theyre heavy as hell and roll like wet garbage, but once you’re pointed downhill at a rocky cheesegrater of a mountainside, it’s all worth it

1
choadspankerride fast eat ass•

24 in the rear is def low at your weight. I'm 175-180 lbs and I run 24 in the rear with a tire insert, 27 before I got inserts

1
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-2
Heinzelboss•

Objectively, OPs tire pressure isn’t too low but yours is too high. At least when we talk about Enduro/dh

7
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-5
Heinzelboss•

your a joke

good reply. Average Reddit.

And let me tell you something: You have no fucking clue what you are talking about. But gladly your reply already shouts that you won’t change your mind no matter what. So I’m not gonna waste my time

4
doginahat•

Dude...

Richie Rude weighs almost twice what you do (93kg), and I bet he hits things a little harder than you do - and he runs 26/27 psi.

https://bikerumor.com/pro-bike-check-richie-rudes-yeti-sb150-with-rad-prototype-fox-38-at-tweed-valley-ews/

With all due respect - I don't think you have any idea what you're talking about.

1
Viffer98Colorado - 2022 GG Trail "Pistola" / 2016 Stumjumper 650b•

WTF... I run 24 front/26 rear and weigh 275. I almost never ding a rim on rocky front range terrain.

6
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-1
gonzo_redditor•

The higher pressure could actually slow you down. Most studies show lower pressure rolls faster over uneven or bumpy surfaces.

5
MTBSPECOPKona Explosif SS•

Well if you look at the SRAM calculator it puts it at 22 psi rear if I click XC riding. I don’t find it that low.

It’s a hardtail and that’s the balance between comfort/speed. If I go higher I feel like the tires bounce around too much on the roots and I actually feel slower.

I am also running tubeless

5
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MTBSPECOPKona Explosif SS•

Yeah I ride my bike a lot bro. I’ve ridden those pressures for years more or less. I stepped up to a bigger wheel size and have a pricey wheelset that I don’t want to ruin. I was wondering if anyone else rings their wheel like that.

I was using that as an example of my psi not being way too low.

3
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-1
ace_deuceeeMI - 2019 GG Smash/TrailPistol - 2018 Transition Vanquish•

30/32 psi is significantly sacrificing rolling speed, though I could see needing that pressure for DH racing to prevent rim strikes. There's an ideal pressure for every setup to minimize rolling resistance, and 30 psi (especially at 50kg) with MTB tires on MTB terrain ain't it. Low 20's is perfectly reasonable for tubeless trail riding.

5
ian2121•

If you corner very hard low 20 will feel like a wet noodle

2
Psychological-Put844•

I would say get some foam tire inserts like Cushcore and depending on the riding you do, I would go higher psi. I ride downhill mostly so I run higher psi but I weigh 150 lbs (about 175 with gear) and I run 40-45 psi. I used to run 30 psi and I went through rims faster that the paychecks came in. I bought new heavy duty DH rims, cushcore inserts and started running higher psi. And so far I haven’t gotten any dents, but I might have gone a little over the top.

-2
CaCoD•

???

40-45psi at 175 is pretty crazy. Were you on xc casings and wheels with zero spoke tension? I cannot think of a single rider on the world cup dh circuit let alone an average rider that runs anywhere near those pressures. High 20s front low 30s rear is usually the max the wc guys will go.

And you run inserts? That's a pretty... intense set up.

Also just curious what are you riding with that adds 25lbs of gear?

1
Psychological-Put844•

oh my bad I switched up my numbers, I meant to say that I run 30-35 now and used to run 20 (I was half asleep when I commented this) yes I know that that is high but have had zero problems and have been running this setup for 2 seasons now

Yes I run inserts and as I said I might have gone a little over the top

I carry water and I wear a lot of pads

1