Side flex on wheels

figbat

How much side-to-side flex should there be on a wheel? I ask because this week I was riding my alloy Synapse home from work in the wet for the first time. When I got out of the seat I noticed a rubbing sound from the rear wheel, in time with the swaying motion of the bike. With the rims being wet and a bit gritty, the noise was noticeable. Once home I checked the wheels and there is a noticeable flex side-to-side when I manipulate them.

The wheels are Mavic Ksyrium Elites, the hubs are in apparently good order and the bearings are tightened up and run freely. Both wheels do it, with the rear a little more than the front.

Am I running the brakes too close to the rims? They run cleanly when on the stand and riding in the saddle.
Is it spoke tension? They 'feel' tense but I have no idea as to what tension they are or should be.
Is it the frame flexing? I can't see any signs of damage, but this frame does use markedly 'bent' seat stays as a form of suspension.

diamonddog

Probably brake pads too close to rims which will rub as the wheels flex IME.

ugo.santalucia

most people run the pads too close to the rims... less than 3 mm distance is a bit too close

diamonddog

ugo.santalucia wrote:

most people run the pads too close to the rims... less than 3 mm distance is a bit too close

^^This

figbat

OK, I'll look at it (although I do like the response I get from running the pads close).

Should the rims flex much then? Is there a spec or expected limit to this? Does spoke tension come into it? If yes, how does one go about analysing and changing this? Or does one take the wheels to one's LBS/wheel builder?

ugo.santalucia

figbat wrote:

OK, I'll look at it (although I do like the response I get from running the pads close).

Should the rims flex much then? Is there a spec or expected limit to this? Does spoke tension come into it? If yes, how does one go about analysing and changing this? Or does one take the wheels to one's LBS/wheel builder?

Spokes only matter if they get slack while you ride. Sit on the bike and ask someone to check the bottom spokes on the non drive side. If they are not slack, it's not the tension.
A couple of mm of lateral flex is very normal... bear in mind the rim is 630 mm in diameter, so if it flexes by 2 mm, that's 0.3%

diamonddog

I have Ksirium SLS wheels on one of my bikes and if the pads are set too close they rub when putting in a bit of power up hills in and out of the saddle. I only weigh in at 51kg so super light really.

ayjaycee

diamonddog wrote:

I only weigh in at 51kg so super light really.

Are you an elf?

diamonddog

ayjaycee wrote:

diamonddog wrote:

I only weigh in at 51kg so super light really.

Are you an elf?

Yes, a lighter one than Quintana, he's considered chubby in elf land.

ayjaycee

Nice one!

pilot_pete

You could fit disc braked wheels to overcome the problem...(takes cover! )

PP

cycleclinic

Had the same converstaion with someone today.
Him: my wheels rub
Me: how close are your brakes
Him: dont know.
Me: Anything less than 2mm is too close.

Pads 3mm from the rim is good. Best however to use a single pivot brake on the rear. I do and that works great on my race bikes.

The brake should be at full lock when the lever is at about 4/5th's of its full travel.