Front wheel "bends" left when braking

bountainmiker

This is annoying me, when I'm using the front brake the wheel kind of tilts to the left, I put on a thicker tyre the other day and it almost touches the left fork leg.

I'm not liking this at all, the QR is tight, the axle is fine, the hub cones are tight, I have no idea where this flex is coming from, could it be from the spokes? they aren't loose.

it's a very cheap hub and a very cheap rim, but the fork is an RS reba, I don't want to somehow damage the fork that is brand new.(at first I thought the flex was due to the cheap suntour fork)

Any advice? new hub?

Hawmaw

It is the spokes. They may not feel loose but whole lot probably need tensioning. I had the same problam with a rear wheel on a Mongoose which flexed alarmingly.

bountainmiker

I hope so, taking it to the bikeshop then, as I can't true wheels, but I can lace them... need more practise I guess.

Sgray

Have you checked the rubber washer type thing :?: on the QR, on my bike it had started to perish and everytime I pulled the front brake the wheel would lean over.

The Rookie

It's not the spokes...not sure where that came from!

The brake disc moves 'up' through the caliper, as you brake the reaction force is thus to push the left side of the axle down, which moves the top of the wheel/tyre to the left, it is an issue with the mounting of the axle in the dropout, or very possibly he fork.

jairaj

How would a fault on the fork cause this? faulty dropouts or something?

Chunkers1980

It's just flex.

New Rebas 2012 onwards are using the old SID platform so are just more flexy. His wider tyre is just showing what has always happened, more pronouned as it will be more noticable.

bountainmiker

How do I get rid of it? it can't be normal to have this much flex.

mcnultycop

Don't brake.

bountainmiker

Anyone have any useful answers?

Thanks.

Ouija

Just sounds like fork flex as The Rookie said. All my wheels twist slightly to the left under braking as the right leg is thrown forwards against the braking occuring on the left leg. It can become more pronounced if you haven't got the QR skewers done up ultra tight and if there is any play in the bearings. It's one of the reasons that suspension fork stanchions have gotten fatter and fatter over the last decade. The old, skinny 25mm and 27mm forks tended to twist a lot more under braking.

Make sure to clean out any grit or dirt that may be sitting between the fork dropout and the axle end.

bountainmiker

I put the wheel in and hardly tightened the QR, I can definitely see the left side of the QR moving up and down when braking.

The fork isn't flexing, the QR is just not tightening all that well for some reason.

It would be a serious design flaw for a fork like that to flex under my 70Kg

Chunkers1980

Why did you do that?

Your weight has little to do with it, it is the braking forces

Ouija

bountainmiker wrote:

I put the wheel in and hardly tightened the QR, I can definitely see the left side of the QR moving up and down when braking.

The fork isn't flexing, the QR is just not tightening all that well for some reason.

It would be a serious design flaw for a fork like that to flex under my 70Kg

Do you have enough outer axle actually going into the right leg of the fork. Sometimes, especially after doing any bearing maintenance on cup and cone bearings, you can leave too short an amount of axle on one side of the wheel and too much on the other. Your then essentially either resting on the QR skewer or on a tiny stub of axle that 'pops' out of the fork leg under braking.

bountainmiker

To see if that was indeed where the "play" was coming from.

Are some skewers better than others at tightening? maybe I can just get a better one and be done with it.

I don't want to ride like this.

And surely the heavier I am the more force it takes to stop me, creating stronger braking forces?

@Ouija, didn't think of that, will check.

Also, can I completely ditch QR and get a 10mm bolt though axle?

bails87

What QR have you got? Try a cheap shimano one.

bountainmiker

The axle is centred so the problem isn't the stub of axle.

The hub and axle aren't even branded, have to try another skewer.

Thinking of ditching the QR completely though, 10mm is slightly stiffer anyway.

Chunkers1980

10mm is not screw through bolt up so wont make much difference.

It happens on my 20mm bolt thru Reba, you're just noticing it more as the tyre is wider and you can see it getting very close to the bridge.

Oh and it is Mass x Velocity squared, hence wny I said your weight has little to do with it.

cooldad

AS someone said, a cheap Shimano one - absolute best and if that doesn't solve your problem it's not the QR.

supersonic

All forks flex. But a good QR is essential, the cheap ones have poor clamping force and often poor spindles.

Try a Shimano Deore.

It is not spoke tension unless they are completely loose, and you'd have a host of other problems too.

bountainmiker

And how tight is too tight? can I put some muscle into it and not worry about breaking anything?

All this flex in new to me, I notice nothing at all on my 888, but I guess a XC fork is a bit different than a double crown DH fork...

Probikeshop has XT hubs for 35€, but I don't think they come with skewers, will have a look around locally first.

supersonic

A new hub will mean a new wheel build, derore skewers can be had for a fiver.

Too tight can damage the mechanism. Tighten the nut and close the lever - repeat until you feel it start to get hard to close at about 80 degrees, then snap shut.

YeehaaMcgee

I'd put money on the QR not being tight enough.

The Rookie

+1.....

riche0

I had a similar thing on one of my bikes and it was the QR that was crap and seating of the wheel. Strength of the brake pulled the wheel over.

Maybe worth borrowing one from a mates bike for 5 mins and testing to see if it makes a difference. Then at least it's one thing you can rule out.

Giraffoto

I had exactly the same issue, which was cured by replacing the expensive Hope Q/R skewers with cheap Shimano ones. Forks don't flex that much, nor do wheels!

The Rookie

Shimano QR's are 'simply the best' Deore work perfectly well, XT save about 5g an end for about 2 times the price, XTR save another 5g at each end for about 5 times the price!

I had Deore but now have XT as they came with other bits and pieces I was getting.

Hawmaw

Those of you discounting my suggestion of the wheel flexing have obviously never encountered it. I had a new Mongoose full sus with generic hubs and Alex rims. Straight out the box the rear end wandered on trail centre red/black runs. I was convinced the linkage was at fault and stripped the back end and rebuilt it a couple of times.
It was only when I sold the bike that the guy who bought it noticed that the rear rim flexed going around corners. I could actualy see it moving as he rode it around the street.
None of the spokes were noticably slack , they were all of similar tension however the wheel obviously hadnt been built properly. In retrospect I was lucky I didnt have a catastrophic failure of the wheel.

YeehaaMcgee

With all due respect, I've been riding bikes with disc brakes since the mid nineties, and every single time I've seen this issue, it's been because the QR wasn't done up tight enough.
I'm not saying it's impossible for anything else to cause it, far from it. Just that in my experience, I've never come across anything else, hence why I'm jumping immediately to that conclusion.
What's more it's simple, and free to check, before then moving on to other things.

The Rookie

Hawmaw wrote:

Those of you discounting my suggestion of the wheel flexing have obviously never encountered it .

I have, but the symptoms do not stack up with a flexi wheel, it wouldn't always go one way for example....

Giraffoto

Hawmaw wrote:

Those of you discounting my suggestion of the wheel flexing have obviously never encountered it. I had a new Mongoose full sus with generic hubs and Alex rims. Straight out the box the rear end wandered on trail centre red/black runs. I was convinced the linkage was at fault and stripped the back end and rebuilt it a couple of times.
It was only when I sold the bike that the guy who bought it noticed that the rear rim flexed going around corners. I could actualy see it moving as he rode it around the street.
None of the spokes were noticably slack , they were all of similar tension however the wheel obviously hadnt been built properly. In retrospect I was lucky I didnt have a catastrophic failure of the wheel.

It may just be the way you're describing it, but what you experienced could still have been a Q/R that wasn't tight enough