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MTB Rim Damage


rudi-h
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In the last year I managed to crack one rim to the point that I had to throw it away (Mavic 317 Disc). My new rim (DT Swiss) is supposed to be of better quality, but that also has two seriaas dents presumably after the rocky riding in either Lionman or Clarense MTB race.

 

I'm no Greg Minnaar, but I weight 90kg's and ride way faster than average midfielder on the downhills.

1) Is it common to dent / break rims, or is there something wrong here?

2) The rims don't show any scratch marks. Wouldn't a rock normally take off the paint?

 

Oh yes, I normally inflate my tyres to 2.2 Bar.

 

Any feedback would be appreciated.

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At that weight and riding heavy will cause dents for sure.

So what to do choose better lines and try to ride lighter.

Oh yes most dents in the rim can be sorted out with a bit of soft ands and a shifting spanner.

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I'm 97Kg and Ride ZTR Arch rims. Never had a problem. Are you breaking spokes or hitting rocks ? or both.

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rudi-h....hardtail or dual sus??? suspect that will also make a HUGE difference....I assume it's your rear wheel...me, 90kg,,ride XT rims..dual sus...no problem....touch wood... :lol: :D :D :D

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Aluminium rims don't break from hitting obstacles. There is one exception and that's if you hit the obstacle square-on at the weld. Then sometimes the rim breaks the weld.

 

Rims break from fatigue.

 

If you are denting your rims, you are hitting rocks harder than your tyre pressure can handle. Either hit the rocks softly or inflate your tyres more.

 

If you are bending rims, that is another issue again. It could be wheelbuilding or just klutzy riding.

 

What is the real problem?

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I weigh 100kg and ride dual suspension.

I dinged my Mavic 819 rear rim (and punctured the tyre) because I hit a dry rocky riverbed at speed on my rear wheel. Silly riding and low tyre pressure were the reasons.

The rim remained true, but now has a flat spot and a repaired/straightened sidewall at the impact area.

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I am heavy guy, weigh around 105kg and use the standard rims that cam on my GT, have had no trouble and I ride in Magalies, BUT I do ride on quite hard tyre pressures (around 2.8-3 bar) so maybe that helps? I ride with Larsens 2.0 tyre up front and a Crossmark 2.1 on the rear. Both are tubed.

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Thanks for all the feedback guys.

 

There's been quite a few questions, so I'll try to answer them:

 

1) It was the rear rim in all cases

2) I ride a full sus XC bike

3) I did break spokes on my previous rim (Mavic 317), but I was told that that was as a result of the cracked rim

4) I never bent a rim, its just dents. The first rim was dinged on the weld, thus it cracked

 

I thought the whole purpose of tubeless is so that you can run your tyres at lower pressure for better ride handling on rocks, so I would not like to inflate more? Also, if I inflate tubeless tyres to 2.8 - 3 Bar as suggested by Mojoman, then the Stans fluid would not seal any punctures. What pressure is ideal then?

 

It seems however that it is likely to be my riding style, but it still sucks to replace the rim every year (pricey!!!). Maybe I'll try stronger rims next time I replace.

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Cracked rims and denting wheels cannot cause spokes to break. But that's not central to your problem.

 

Back to you bottoming out and damaging your rim.

 

This is common sense and you're not going to find some Zen, supernatural solution to your question. If your tyres bottom out, our tyre pressure is too low. This assumes you're not riding very narrow tyres, since going wider gives you a bit more volume and you'll thus not bottom out as much. However, width is limited. Forget about numbers, pump the tyres until you don't bottom out or, ride only on tennis courts.

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Thanks, I'll run my tyres a bit harder.

 

I would still like some advice on tyre pressure though, as it's quite expensive to find a "trial and error" solution @ R1000+ for each "error".

 

If I do get new rims, what rims can I look at that are strong? I mostly ride XC and marathons, so I don't want an extra heavy downhill rim.

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I have/had a similar problem. I ride technical/rocky/downhill sections as hard and fast as possible because I love the rush.

 

I don't want to ride higher pressures because of the loss of traction. I don't want to ride slower because it's not as much fun. I'm already picking lines as best I can, and riding as light as I know how and my friends say I'm a smooth rider.

 

Thus I've made peace with the fact that dinged rims, occasional buckles and the odd cut tyre are par for the course when you ride aggresively.

 

I wore out my previous rim, a Mavic 717 laced with Revolution spokes and mostly run with Hutchinson Python 2.0, in 6 months. That combo was simply too light. Switched to a DT EX 5.1D with Competition spokes and higher volume tyres and it's still running after more than 3 years. Lots of scratches and a few serious dings, but no major problems.

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I wore out my previous rim, a Mavic 717 laced with Revolution spokes and mostly run with Hutchinson Python 2.0, in 6 months. That combo was simply too light. Switched to a DT EX 5.1D with Competition spokes and higher volume tyres and it's still running after more than 3 years. Lots of scratches and a few serious dings, but no major problems.

 

Minty, my reply may appear pedantic but I want to point out that the Revolution spokes had nothing to do with the problems you experienced. As far as the rocks and rims are concerned, they cannot "see" the spokes and the effect on the rim hitting the same rock at the same speed will be the same regardless of the type of spokes on the wheel.

 

In that application Revolution spokes are perfectly fine. If it was a heavy dowhnill rim, the Revo's may have been too light to bring the wheel up to proper tension. But that has nothing to do with denting.

 

Further, the only thing that will prevent the sidewalls from denting is more metal - much more metal and that is not possible. The difference in amount of metal in the crucial area (the sidewall/bead area) between a very light rim and very heavy rim is probably in the order of 0.1 or 0.2mm and that is just not enough to prevent dents. They will still happen but be 5% or 10% smaller.

 

In my opinion, the only effective way of doing this is to increase tyre pressure, tyre thickness and tyre volume.

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Sorry, I didn't mean to imply that the spokes were a cause of the dings in the rim. Specifically, the problems I had were 1) Dings in the rim and 2) after a few months the wheels would go out of true after every single ride.

 

At the time I was advised that overall the wheel was too weak for heavy riding with the suspected causes being too light a rim for no.1 and a combination of too light a rim and spokes being the cause of no.2

 

Agreed on the larger volume tyres being the only real solution. Never thought about it, but have seen dings on DH rims as well so it makes sense.

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Thanks, I'll run my tyres a bit harder.

 

I would still like some advice on tyre pressure though, as it's quite expensive to find a "trial and error" solution @ R1000+ for each "error".

 

If I do get new rims, what rims can I look at that are strong? I mostly ride XC and marathons, so I don't want an extra heavy downhill rim.

 

Rudi-H,

 

I put a flat spot in my previous Mavic 819 rear rim and had to straighten the rim bead by hand (padded spanner). All due to very low pressure after a tyre cut (that Stans sealed)

I now have a Stans Flow which is a wide, strong rim.

In my opinion you should ride with the biggest volume, widest tyres that fit your frame. Do not trust the manufacturer's specs. One company's 2.0 is another's 2.2!

I do not know what tyres you are using now, but would suggest a minimum of 2.25's. That way you don't need to run such high pressures too.

You really don't need downhill tyres though, as they weigh substantially more due to a re-inforced casing.

So I would suggest rims with an INNER diameter of at least 21mm. Preferably tubeless or Stans "bead socket" rims.

The wider inner rim diameter will make your tyres run "wider" too.

Tyre pressure: the lowest pressure that you can ride without your tyres "bottoming out" onto the rim on rocky sections...

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