How do I know if my wheel is flexing?

Discuss light weight issues concerning road bikes & parts.
thisisnotaspoon
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Joined: Thu Aug 30, 2012 8:42 pm

by thisisnotaspoon

This is bugging me.

Stan's alphas are known for being a bit on the flexy side, but I built them 28 spokes and 2x on the rear and 24 radial on the front, so should be stiff. Spoke tension is at the max without a tyre fitted (and almost completelyeven with a tension meter). Spokes are DT Revs, Tyres are schwalbe ultremo ZX's and michelin ultralight butyl tubes.

Is the flex all in my head? Not sure If I've convinced myself that they're flexing and therefore feel it, or if they're actualy really bad?

Any sure way to tell? Otherwise I'm going out to find a steep hill and disconnect my rear brake and see if it feels any faster.

Before anyone asks, I'm not a modern day Eddy Merckx, but I'm not him from his glory days either, I'm 200lb give or take a rost dinner and not very fit!

Greg66
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by Greg66

I may be completely wrong about this, but I've always thought the easiest way was when the rims are wet, and you're out of the saddle pedalling, the amount of rubbing you can hear on the brake blocks indicates how flexy the wheel is (wet rims are noisier when they squeak).

Happy to be corrected...

aerozy
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by aerozy

Well best thing would be to try out a stiff wheelset of a buddy of yours and you'll have something to gauge your opinion with.

When a wheel is stiff it feels rock solid when out of the saddle sprinting. My Edge 165's for example give an outrageously spongy feeling when sprinting while my shimano C50's on the hand give super solid feedback .

Off the bike try moving the rim sideways towards the brake pads with your fingers. You can see how much it flexs. If the wheel easily touches the brake pads then its too soft.
Sunny cycling holidays in Portugal @ Cherry Cottage Vintage B&B

thisisatest
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by thisisatest

With thin spokes, a stiff rim will rub brake pads more. It's been proven. Also, spoke tension has almost zero effect on wheel stiffness (high tension makes the wheel very slightly LESS stiff), up until the spokes go slack. Rouesartisanales.com is a good source for this info.
So, are you interested in knowing if your wheel is stiff, or are you most concerned with whether or not your rim is rubbing the brake pads under high effort?

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PSM
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by PSM

Interesting question. I just got my Alpha340,24/28/Tune Mig70/Mag170, Alu nipples, Sapim CX-wheels. The weigh (decal stripped) 1265 gr. I've ridden the C24 C 7900 this season. (1430 gr) My body weight avg. 74 kg.

Expecting my new Pro4 to arrive tires any day now, but we will probably have snow now so it won't be possible to make a test ride either... :(
Last edited by PSM on Wed Nov 28, 2012 3:32 pm, edited 1 time in total.

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CharlesM
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by CharlesM

Rim rubbing the brake block is not a good indication of a flexy rim.


In similar spoke and hub build:

-A flexy rim will generally deflect at the road surface from a combo of side load and the spokes being compressed.

-A stiff rim will generally deflect less at the road and instead press the rim at the top of the wheel toward the brake block opposite the road loaded side.


It's the deflection at the road, and the hysteresis / friction that happens constantly (and gets way worse under big load) with very flexy rims that's a lot worse than the brake track rubbing some people notie when they make huge sloppy efforts.


There's a ton of misconception about rim versus wheel stiffness...
Last edited by CharlesM on Wed Nov 28, 2012 3:43 pm, edited 2 times in total.

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PSM
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by PSM

CharlesM wrote:.,..........



??

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WMW
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by WMW

CharlesM wrote:There's a ton of misconception about rim versus wheel stiffness...


Yep. Say you have a flexy rim... the rim flexes to the right at the road... it will also flex to the right at the brake blocks. This will be opposite the direction the frame and axle flexes, so may very well *keep* the brake from rubbing rather than cause it.
formerly rruff...

spud
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by spud

I don't know that I agree with Charles' assertion that flex below the axle is much worse than rubbing brake blocks when it comes to energy efficiency. That's a comparison between a dubious amount of hysteresis vs. a very definite drag on the rim at the brake block, which will definitely be dissipated as heat and wear on components. I do imagine a stiffer rim will yield better handling, but I don't think I've ever ridden really flexible/light weight wheels, nor have I done back to back testing.

I raced Zipp 404s and had to open the quick release skewers to keep from getting big brake rub when going hard out of the saddle.

Valbrona
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by Valbrona

So, you build with flexy DB spokes. You only use 28 at the back. You only use 24 at the front. Why would such wheels not be flexy?

What else do you want to ask on this forum? Like, is the Pope Catholic?

Mr.Gib
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by Mr.Gib

Yeah, that's a flimsy build for someone your size. I would never ride that build and I am a svelte 190lbs. You don't say what the hub is not that it will make much difference.
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.

bm0p700f
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by bm0p700f

That the sort of build (OP) that I can ust about get way with at 170lbs. You need a 32H rear wheel with comps.race spokes DS at least. Ot a stiffer rim like the Velocity A23 or DT Swiss RR465 e.t.c then you can run revs/lasers on both sides.

Still thicker spokes DS is not a bad idea on any wheelset unless weight reduction is you primary goal.

artray
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by artray

I have some stans 18/24 .1182grms , im 84kilo [no fat] and they ride sweet no brake rub . They don't feel any more flexy than my old r sys or Topolinios . I did try a friends heavier set of clinchers [FF] and did not notice to much difference apart from the extra weight made them slower , they just did not react as good. Can it be that the way the wheel is built can make a huge difference? Jon who built my wheels has vast experience . Im in the process of building some new wheels Kinlin xr200 Dati superlight hubs, should come in around 1200 grms 24/28 .Im expecting great performance from these.

drchull
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by drchull

I also have been wondering how much difference the skewers make. My very stiff 32h HED Belgiums seem to rub like crazy with crappy Reynolds skewers but with much more solid Easton Skewers they are rock solid. It took really tightening KCNC skewers to get them to work at all without the wheel just pulling out. Now I am a big rider and so some of these lightweight ww stuff just isn't compatible. Thinking of moving to RWS skewers as they are supposed to provide more clamping force but man they are expensive.

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WMW
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by WMW

drchull wrote:I also have been wondering how much difference the skewers make.


If you don't tighten them enough, it can make a lot of difference. KCNC Ti have pretty good clamping force. Ti itself is ~60% of steel's stiffness, but what you need is enough tension in the skewer to keep the dropouts and hub pressed together.
formerly rruff...

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