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New rim needed,yet again

Old 09-19-13, 11:29 AM
  #1  
car knocker
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New rim needed,yet again

Since we bought our Periscope 4 years ago we have had 3 cracked rims. First a Sun Rhyno Lite went bad on our cross country trip. Replaced it with a Velocity Cliffhanger,and that was replaced with their Chukker, which just cracked . Its a 40 hole, 26" with disk brakes. We are a 350lb team,and do a loaded tour every year, but no camping gear is carried.
The cracking is in the area of the braking surface,the tires are Schwalbe Marathons,and the pressure is 90psi. I suppose Velocity will replace it under warranty,but after 3 times I wonder if we should try something else.
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Old 09-19-13, 11:49 AM
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How wide are your tires that you run at 90 psi?

Wider tires exert surprisingly more outward pressure on rims than narrow tires at the same pressure.

I had a similar problem with cracks in the middle of the brake track that would track the perimeter of the rim in an arc. Some research reveled a way to calculate the outward force on the rim which pushes the top of the brake track outward cracking the rim in the brake track. If this is your problem careful selection of rims can help but just buying heavier rims is not the best answer.

Last edited by waynesulak; 09-19-13 at 11:53 AM.
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Old 09-19-13, 12:18 PM
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I recently replaced our Velocity Fusion rear rim after about 3 years of service.
It also had a crack in the brake track near the joint.
I assume this is from the brake track wearing down, it did feel somewhat concave.
We have rim brakes only so that would account for the wear, surprised you are having this problem with disc brakes.
Sounds like it could be tire related as Wayne suggested.
In general I find Velocity rims to be pretty durable.
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Old 09-19-13, 02:02 PM
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We are using 1.5 26" tires.
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Old 09-19-13, 03:16 PM
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I have cracked 3 Velocity 26" Aeroheat rims in the last 6 years and over 10,000 miles. Velocity has replaced the rims but it does get old rebuilding wheels. Two of the three problems were on out of town rides and my wife and I had to give up the ride. The tires have been 26 x 1.5. The 700 c Dyads with the same cross section have been great. The last set of Dyads rolled 23,000 miles before I replaced them.
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Old 09-19-13, 03:50 PM
  #6  
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Originally Posted by car knocker View Post
We are using 1.5 26" tires.
That is interesting because we are using 38mm 650B tires which are just about the same width. Using 80 psi we cracked two sets of wheels with Synergy rims built by two different trusted wheel builders and two rims provided under warranty. All told six rims. I refused further replacements as a waste of time. Some were built in Australia before the move to the US and some built in the US.

The Synergys like a lot of modern rims have a deep well to make mounting tires easier. This results in tall brake tracks and much less support to resist outward pressure from the tire. Trying to research the problem I ran across the post below on a Google Forum and downloaded the pdf file and the excel spreadsheet. I just tested the drop box links and they still work.

Using the Excel file I tried to test the of effect shorter unsupported brake tracks and with a little trial an error found that shorting the brake track 1 mm was much more effective than thickening the brake track and had the advantage of not using a rim that was thicker all over and very heavy. Desperate to find a solution I purchased some Velocity A23 rims. They are even lighter than than Synergy rims but because they are "tubeless ready" they have a very shallow well with shorter brake tracks. This does make the rims much more difficult to mount tires but so far I have not had failures and no visible weakening of the brake tracks. Currently my wheels have about 3,000 miles on them with no problems. I think a Synergy rims would crack on average of about every 1,000 miles of use with visible outward movement of the brake track after about 500 miles.

You should have a much wider selection of and "tubeless ready" rims to choose from for 26" wheels but may need to change tire models if your current ones are too difficult to mount. I suggest looking at the specifications of rims to find the shortest unsupported brake track available. Lowering tire pressure as much as you are comfortable with would also help.

Contact me off list if the links do not work. Good Luck,

Wayne
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Re: [650B] Re: Velocity Synergy Rims - UGGG

On Tue, Sep 4, 2012 at 1:39 PM, Brad <riendeau...@gmail.com> wrote:
> There must be a reason for that. If big tires were such
> a big problem than mountain bike rims using narrow road extrusions should be
> bursting all over the place. Are they?


Unrelated to Synergy rims, but as far as wide tires generating too
much leverage on narrow rims, Harald Kliems posted the following to
the Bob list recently. The PDF that he references has some excellent
diagrams that show how a tire that overhands the rim significantly
generates more leverage against the rim wall. I've also posted the
Google Translate output after Harald's message.
There are examples on the net of wide tires at high pressure
causing rim failure, I remember seeing a pretty long thread on it as
back as maybe 2007 where a Mavic CXP33 (not a junk rim!) blew up.

On Sun, Aug 26, 2012 at 3:24 PM, Harald Kliems <kli...@gmail.com> wrote:

> Please note that MTB use, even when racing, is not the hardest use case, as
> tire pressure is usually low. The problematic case is: wide tires, narrow
> rims and high pressures, as it is common amongst touring cyclists or tandem
> riders. If you want to calculate the forces, here's a pdf with the formulae
> and an easy Excel sheet, created by someone on a German touring forum. It's
> all in German but you should be able to figure it out.
>
> https://dl.dropbox.com/u/7489636/Einf...nbelastung.pdf
> https://dl.dropbox.com/u/7489636/Felgenbelastung.xls
>
> Since ibobs mostly seem to follow the Frank Berto/Jan Heine philosophy of
> wide tires--low pressures this shouldn't be much of a problem, especially
> with disc brakes where rim wear doesn't come into play. But it's useful
> knowledge anyway, I believe.



Influence of tire pressure and width on the rim stress
The tour Forum discussion about the effects of different tire widths
and Luftdrücke was on the load on the rim. This particular case was
about whether a MTB rim as the a 50mm tire with max. Designed 4bar, is
a 25mm tire to cope with 8 bar pressure can be bent without them too.
Since I has not left in peace, I once counted something: The bending
stress on the rim sidewalls consist primarily of two components, the
direct internal pressure acting on the flanks, and the horizontal
portion of the circumferential force of the tire. The latter one has
to think about this: The tire section is simplified seen a ring. When
this pressure is evenly under tension. Because of the "ring" but the
lower part is open and there is held together only available via the
rim, the rim must take this tension there. Interesting for the bent-up
in the case only the horizontal component of the voltage at the
junction of tire rim. This is the exit angle of the sidewall of the
rim depends. All horizontal forces are not neglected because they
hardly relevant for the question have. The calculation is based only
on one edge of the rim on the other hand, the burden of course
identical. Exposure to peripheral force: The exit angle α the sidewall
can be calculated geometrically: with b = B = inside rim width tire
width
The tangential force is calculated according to the boiler formula as
follows: p = tire pressure (1 bar corresponds to 0.1 N/mm2) D =
Outside diameter of the rim horizontal component FU_X obtained cos α
available via:
Calculation of the resulting force in the middle of the edge: the area
of ​​the inside of the rim edge A is: h = height inner rim flank This
results in the resultant force Fp_R:
Calculation of the moment on the rim: at the foot of the Cross, the
forces lead to a bending moment to the outside: It all looks a mess
out in a formula, you get this: h = internal height rim flank p = tire
pressure (1 bar corresponds to 0.1 N/mm2) B = Tyre width D = Outside
diameter of the rim b = internal width of the rim means of this
formula, you can now compare what you nicely with the appropriate
tires and air pressure of its rim so exacts. For ease, I've also
created a small Excel document to calculate.

Last edited by waynesulak; 09-19-13 at 03:54 PM.
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Old 09-19-13, 03:53 PM
  #7  
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Originally Posted by waynesulak View Post
How wide are your tires that you run at 90 psi?

Wider tires exert surprisingly more outward pressure on rims than narrow tires at the same pressure.

I had a similar problem with cracks in the middle of the brake track that would track the perimeter of the rim in an arc. Some research reveled a way to calculate the outward force on the rim which pushes the top of the brake track outward cracking the rim in the brake track. If this is your problem careful selection of rims can help but just buying heavier rims is not the best answer.
What's your method of calculation?

I go "max tire pressure*tire width = 3000" though I've run as high as 3200 when touring. Schwalbe calls their 1.5" Marathon a 40. Using 40, the OP is at 3600. Schwalbe shows max sidewall pressure as 85, which would still be 3400, still more than I'd be comfortable with. They might try reducing pressure to 75-80 and see what happens.

We use rim brakes in the PNW and go through about a rim/year from cracking on the worn brake track. Wish we had discs, but we don't. For us, it's just a cost of doing business as a tandem. We run Deep-V rims, which work for tires up to 28c like the new ZX which is rated at 115. 115*28 = 3220.

Ah, I see we posted at the same time.
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Old 09-19-13, 03:57 PM
  #8  
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Originally Posted by Carbonfiberboy View Post
What's your method of calculation?



I go "max tire pressure*tire width = 3000" though I've run as high as 3200 when touring. Schwalbe calls their 1.5" Marathon a 40. Using 40, the OP is at 3600. Schwalbe shows max sidewall pressure as 85, which would still be 3400, still more than I'd be comfortable with. They might try reducing pressure to 75-80 and see what happens.

We use rim brakes in the PNW and go through about a rim/year from cracking on the worn brake track. Wish we had discs, but we don't. For us, it's just a cost of doing business as a tandem. We run Deep-V rims, which work for tires up to 28c like the new ZX which is rated at 115. 115*28 = 3220.


Apparently we were posting at the same time. See above post. 38mm x 80 = 2,850 The pressure rating of the tire we used was 75 psi. The problem is rims strength as these problems were in the summer with no wet riding, none. No brake track wear. The rims just could not handle tires inflated to their normal pressure. The Velocity Rep agreed that the rims should work in our application and was willing to continue to warranty rims. I just got tired of buying spokes and building wheels.
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Old 09-19-13, 05:13 PM
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Hi, We are running DT Swiss EX 500 36h rims with Schwalbe Marathon Supremes 1.6". We are on our second season with no problems so far. We are a 350 lb. team, but no loaded touring on our Co-Motion Mocha. We run 95 psi front / 100 psi rear. The quality of the DT rims seem good, but I am keeping a close eye on them. They are a wider rim, which fit the 1.6" tire well. Good luck, Dale...

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Old 09-20-13, 05:57 AM
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Just posting to illustrate the height of the unsupported segment of rim wall below the bead on some of the velocity rims. Since the velocity pics are not to the same scale some interpolation is needed. Still I believe it illustrates that the difference in support to the bead against outward pressure. The A23 and other tubeless ready rims have just enough space under the hook for the tire bead to fit tightly under the lip. When removing the tire the bead sticks in that groove under the lip after the tube is deflated. The Chukker is a strong heavy rim but it appears much of is mass is attributable to its high profile and the brake track thickness is no greater than other rims.



SynergyA23Chuckker
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Old 09-20-13, 06:33 AM
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SynergyA23Chuckker

It appears that the A23 has the best support with the internal cross member positioned in the center of the brake track.
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Old 09-20-13, 12:04 PM
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Velocity is building a new wheel for us, using the Chukker again. I wanted to try the Atlas but alas, it doesn't come in 40 hole. The rep said hopefully it was a fluke and you won't have a problem again. We shall see. Thanks for all the replies.
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Old 09-24-13, 10:05 AM
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I have also had a crack in the braking track on a Deep-V, but after about 5,000 miles so I didn't bother trying for a warranty replacement, I just replaced it with another Deep-V. This was on my single, but maybe relevant because I weigh about 270 all by myself, which is within shouting distance of some of the lighter teams around here.

I do like Velocity rims because they seem to stay more true than the Mavic rims that I have tried. I put Rhyno Lite on the tandem though, we'll see how that goes...
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Old 09-25-13, 10:34 AM
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Originally Posted by car knocker View Post
Since we bought our Periscope 4 years ago we have had 3 cracked rims. First a Sun Rhyno Lite went bad on our cross country trip. Replaced it with a Velocity Cliffhanger,and that was replaced with their Chukker, which just cracked . Its a 40 hole, 26" with disk brakes. We are a 350lb team,and do a loaded tour every year, but no camping gear is carried.
The cracking is in the area of the braking surface,the tires are Schwalbe Marathons,and the pressure is 90psi. I suppose Velocity will replace it under warranty,but after 3 times I wonder if we should try something else.

Just came across this thread and wanted to say its been an interesting discussion. I C&P'd it in an email to some of the guys here at Velocity HQ.

car knocker - I will say your situation sounds pretty atypical. We do a fair bit of OEM and aftermarket tandem builds and don't see many issues, especially with the Chukker. Hope round two does it for you in this case!
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Old 09-25-13, 11:04 AM
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I suspect that most tandems that get a lot of mileage have tires 30mm wide or less. Most 28mm or less. The few high mileage tandems using 38mm tires also have some captains that build there own wheels. This would leave a small percentage on shop built tandems.

All I know for certain is that I had two wheel builders build up wheels and 6 rims out 6 rims fail. These rims where intentionaly purchased 2 at a time at different times. Some were before the move to the US and some after. That seems like a pretty good test of the design. The change of 3 pairs out of 3 having the same rare manufacturing defect seems small to me. The math clearly indicates that wider tires stress the design more and would reveal weakness of the brake track due to the length of unsupported height below the tire bead.

Likewise 4 out 4 of Velocity's A23 rim with a short rim wall have not failed in the same usage on same bike at same inflation on same roads with the same riders.
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Old 09-25-13, 02:51 PM
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Originally Posted by waynesulak View Post
Likewise 4 out 4 of Velocity's A23 rim with a short rim wall have not failed in the same usage on same bike at same inflation on same roads with the same riders.
I totally agree with your theory on the sidewalls. It makes sense, and you're right, I'm betting most of our tandem customers are on a 32c max, with most being in a 25-28c range I'd say. I recommend the A23 pretty confidently to everyone from XC mountain bikers, to loaded touring cyclists and nearly everyone else. I find them to be a super strong and versatile rim combining the best attributes of the Dyad design with the tubeless-ready bead and a nice wide profile.

If you ever have difficulty mounting tires, give something like our Velotape or Stan's a shot in place of the conventional rim tape or Veloplugs. Two layers and my Panaracer Pasela's almost fall onto the rim.
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Old 07-30-14, 02:55 PM
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I finally stopped cracking cliffhangers (28mm wide) when I switched to a 26x1.35 tire. I run them at 76 psi on the rear and 65 psi on the 20" from tire. Any wider tire and the rims crack around the rim on the brake track. bk
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