front wheel flexes whilst climbing? cause

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pwa
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Re: front wheel flexes whilst climbing? cause

Postby pwa » 6 Oct 2017, 10:29am

Assuming there is no play in the wheel bearings, isn't the most likely explanation here that the spokes are a little too slack? If it were my wheel and I had put it together I would probably risk going round the wheel adding maybe half a turn to each spoke to see if it improves things. But as a bought wheel I would ask the wheel builder to have a look at it.

martinn
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Re: front wheel flexes whilst climbing? cause

Postby martinn » 4 Nov 2017, 5:05pm

Ok, I changed the quick release, and although there is still a little flex in the wheel, it is dramatically reduced, and the other wheel which I put the other quick release into , now flexes....

Brucey
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Re: front wheel flexes whilst climbing? cause

Postby Brucey » 4 Nov 2017, 5:54pm

presumably this QR does not develop such high tension as others, even when it 'feels tight'?

If you want to get a handle on this, try tightening a perfectly adjusted cup and cone hub (in which there is a little free play that just disappears when the QR is done up tight) and compare the relative effort required to eliminate the free play in the hub with different QRs.

Mad thought; occasionally a QR won't tighten the wheel properly because it bottoms out on the springs or something, and it is really tight on one side only. It is dangerous to ride a bike in this condition. Often simply removing the QR springs will render the arrangement more workable.

cheers
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martinn
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Re: front wheel flexes whilst climbing? cause

Postby martinn » 23 Jan 2018, 7:14am

Update,
I had the spokes tightened when I had the bike serviced. ( Campag and I don't have the tools).
Went for a wet 100, the flex has returned. Could it be that the spokes are too tight.
Do others get flex like this with dynamo hubs?
Should I buy son in future or one of the Shimano range??

Thanks
Martin

Brucey
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Re: front wheel flexes whilst climbing? cause

Postby Brucey » 23 Jan 2018, 7:44am

did you work out why the flex appeared to vary with the QR type before?

cheers
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foxyrider
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Re: front wheel flexes whilst climbing? cause

Postby foxyrider » 23 Jan 2018, 9:07am

You certain it's the wheel not the forks?
Convention? what's that then?
Airnimal Chameleon touring, Orbit Pro hack, Orbit Photon audax, Focus Mares AX tour, Peugeot Carbon sportive, Owen Blower vintage race - all running Tulio's finest!

ANTONISH
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Re: front wheel flexes whilst climbing? cause

Postby ANTONISH » 23 Jan 2018, 10:10am

For what it's worth I've recently built a wheel with SP dyno hub on Open Pro rim - Sapim race spokes 32 mm. Tyre is 28mm "Gatorskin"
I haven't really noticed anything untoward - although I get the impression that the wheel is a bit more flexible - not enough to get rubbing on the brake blocks.
Previously I had a Miche race hubbed on open pro with a 25mm Marathon Plus mounted on the front - that was temporary as I was going out in near zero temperatures and apart from the horrible ride the Marathon plus seems to have better road holding.
I put the difference in feel down to the difference in the tyres.
The forks are Kinesis aluminium.

Samuel D
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Re: front wheel flexes whilst climbing? cause

Postby Samuel D » 23 Jan 2018, 1:27pm

In addition to Brucey’s question, the answer to which is essential to understanding what’s happening, I’d like to know what spoke gauge the wheel uses.

Natural Ankling’s question here also went unanswered. He makes an important distinction.

I don’t think I’d build a 32-hole, narrow-flange wheel for an 80 kg rider who climbs out of the saddle, but I suppose professional wheelbuilders have to build what customers want.

bretonbikes
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Re: front wheel flexes whilst climbing? cause

Postby bretonbikes » 23 Jan 2018, 1:38pm

A slight thread drift but as people have mentioned the extra strain on the 'pulling' spokes of a wheel it's worth remembering that the braking force for most riders if greater than the pedalling force.

martinn
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Re: front wheel flexes whilst climbing? cause

Postby martinn » 23 Jan 2018, 5:42pm

Sorry I don't know what type of spokes they are. The wheel was off an internet supplier, which has a good reputation for hand built wheels. I looked at the website but could not see the specifications.

The wheel definitely touches the brake blocks not the tyre.

I tried another front wheel, which I have only recently received. It's a Revo dynamo, essentially the same as a SP dynamo. Believe.
This maybe moves a mm.
I looked at the wheel off the bike, there seems to be play at the hub. I am therefore thinking that the bearings might have gone. I am a little disappointed as this hub is only a little over a year old and has done around 5000km.
I think you can send them off to be reconditioned.

Does this sound the most likely scenario?
( I can't open the hub to look at the state of the bearings)

Martin

Brucey
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Re: front wheel flexes whilst climbing? cause

Postby Brucey » 23 Jan 2018, 6:47pm

martinn wrote: ... there seems to be play at the hub. I am therefore thinking that the bearings might have gone. I am a little disappointed as this hub is only a little over a year old and has done around 5000km.
I think you can send them off to be reconditioned.....


you can send SP hubs off to have new bearings fitted and it costs about £25 or so. Obviously the wheel has to come apart. Not sure how long the warranty is on them.

Variations in QR pressure can cause the apparent slack in the bearing to vary, BTW, even with cartridge bearing hubs.

cheers
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martinn
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Re: front wheel flexes whilst climbing? cause

Postby martinn » 24 Jan 2018, 5:56pm

Emailed the original wheel builder, they phoned me back and have offered to replace the hub as it's within warranty, they will rebuild the wheel as well.
I think that's pretty good really.
Just got to find a wheel box

Martin

martinn
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Re: front wheel flexes whilst climbing? cause

Postby martinn » 28 Jan 2018, 12:25pm

Ok, swapped over the wheel to the Revo dynamo, which is as I understand it a rebadged sp hub.
This has a dt Swiss r440 rim.
There is physically much less play when I try to move the wheel over with my hand, so thought great this is the problem.
Went on a 200 yesterday, and nope, there is still a large amount of flex, so had to back the brake blocks off, and ended up with large gaps reducing my braking ability.
Interesting this hub has been ok on my fixed which is an old Dawes galaxy 531 frame and forks. The other fork is carbon.

So given that there was a definite problem with the original hub, and this was also apparent on the steel fork, is this also a fork issue?

Previously the changing the QR helped, and admittedly I didn't use that QR yesterday, so that is still a potential variable.
So as I am thinking of getting a new bike, which has disc brakes and a thru axel, and a carbon fork.
I am assuming that the disc for will be stiffer to deal with the forces produced by disc brakes, and that a thru axel will also increase the stiffness, if I get a hub dynamo for this bike, any problems will be due to the flex between the flange and the hub?

So for original wheel if the fork is part of the problem would changing the type of hub have an effect?
For the potential new wheel what hub would the forum recommend? Bearing in mind I am between 76 and 80kg, I climb both in and out of the saddle, and the problem manifests when I am out of the saddle. I also climb quite aggressively, if that makes a difference ( I am usually in the top 10% on Strava as a yard stick)

Many thanks

Martin

bretonbikes
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Re: front wheel flexes whilst climbing? cause

Postby bretonbikes » 28 Jan 2018, 12:39pm

Hi Martin,

It seems you have several problems all combining;-) but the fact that your 'good' hub still rubs does point to the forks being at least partly to blame.

Carbon is of course theoreticall incredibly stiff weight for weight, but that doesn't mean that you can't produce a heavy, wobbly crap fork with it;-) The 531 fork you mention has a near round profile and so resistant (but normally nicely springy) in all directions. Take a carbon 'blade' shaped fork and it can be very stiff fore-and-aft (which isn't necessarily good as it's uncomfortable) and yet very flexible side to side. To negate this needs someone who knows what they are doing to design the fork with special lay-up and different thicknesses/fibres to make up for the thinness. One would hope that somone producing a commercial carbon fork would be just such a person - in your case it would appear not?

Brucey
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Re: front wheel flexes whilst climbing? cause

Postby Brucey » 28 Jan 2018, 3:09pm

bretonbikes wrote:....It seems you have several problems all combining;-) but the fact that your 'good' hub still rubs does point to the forks being at least partly to blame....


I agree. Believe it or not if the wheel itself is flexible (e.g. because of the narrow spaced flanges), a less stiff rim may result in less rim deflection between the brakes. This seems quite counterintuitive, but tests have borne this out.

I would suggest that you think about getting a replacement fork. One of the possible reasons for excessive flex in a fork is that it is falling apart.

cheers
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