UKC

Sup yall, since I changed the wheelset on my Trek pilot 2.1 when I brake the front forks judder/vibrate a fair bit and I can see the ends of the forks vibrating.

The forks are Bontrager satellite carbon that came with the bike. I dont remember there being a problem with the original wheels but the rims were very worn by the end so braking probably wasnt that good.

Everything else is tight, headset bearings replaced recently, tried a few different types of brake compound, rims are true and clean.

Main thing im wondering really is it safe to have this motion in the forks or is is a risk of fracture?
Im not particularly heavy (72kg) but still not keen on a face plant at 30mph.

In reply to ow arm:

There are many, many possible reasons for this. Google 'fork judder' for solutions.

In reply to ow arm:

Hi, I have experienced this before with carbon bikes, the new wheels are not the problem, I suspect it is the headset that needs looking at.

it may need just a tighten to take up any settling or wear but it might need replacing. Head sets are critical to the handling of any bike.

I would be taking it easy till I have it sorted.

Stephen.

In reply to MaranaF:

dude as I said ive already replaced the headset bearings and its all tight

In reply to ow arm:

Is this on the same front caliper? When you look down on the caliper from above, is there any bend in the caliper arms such that one pad one side could be further forward than the other?

In reply to woolsack:

I was wondering that Ive taken my front mudguard off as I couldnt see - it also mounts to the caliper bolt so could be interfering somehow?
Ill check it tomorrow when I go out for a ride next.

In reply to ow arm:

You might have replaced it but that does not mean it right. I have been there with a brand new bike, same problem.

In reply to ow arm:

Anyway went out for a ride without the mudguard on and couldnt see much other than the fork ends vibrating when braking.
I checked the headset again and its solid.
I stripped the front brake and cleaned it then replaced it - so far there doesnt seem to be as much judder so perhaps this was the cause but I suspect it will return.
The brake is a shimano BR-R650 if its of any interest to anyone.

In reply to ow arm:

Are the wheels true? and dinks in the rims? (I know you said they were new but...)

In reply to balmybaldwin:

nop really nice smooth rims and clean too for a change

In reply to ow arm:

If you drop the front wheel out, and grab the lower part of the fork with one hand, and the bars with the other (standing the bike on its rear wheel)can you recreate the movement you are getting by manually flexing the fork? If you can, then observe the fork/headset interface very closely to see if you can find the movement? could be the ball race on the forks has become unseated/or moves under stress...possible, even with a brand new headset.

Do you have your old wheels still? If so stick them in and go for a ride to confirm it isn't coincidental to the installation of new wheels (are the wheel hubs nice and tight?)

In reply to balmybaldwin:

ive already tried the headset without wheel and its solid.

Ill go out for another ride later and if its still there then Ill try my old wheel

In reply to ow arm:

another thing to double check is the stem if you have a spare - had a very odd thing happen on my friends mtb where the stem changed shape as you tightened the clamp which lead to play... but you could feel this just by rocking the bike on the front brake

Sorry, I know you've probably looked at these things, but you never know.

Do you have a go pro or similar? might be worth sticking it on the bars pointing down when you test ride as it may pick up a bit better where the movement is coming from than you can whilst avoiding hedges and parked cars! (Plus we can get a better idea of exactly what you mean by juddering/flexing and the sound could help too)

In reply to ow arm:

Ive checked a few things on the last few rides, I tried an older wheel Ive got, the rim is pretty worn so doesnt brake quite as well but no juddering.

So it seems its something to do with this wheel - the rim is perfectly true vertically and horizontally, its completely smooth and clean, Ive tried koolstop salmon and the standard dura ace black pads but both are the same.

Confused I am.

In reply to ow arm:

Is this under gentle braking or hard braking or both?

Can you try the wheel on a differnet bike (i.e. a mates?) to see if the problem travels with the wheel (which would eliminate the possiblity that it is a bike/wheel combo and confirm its an issue with the wheel)

What wheel is this new one? could it be that it's flexing rotationally?

In reply to ow arm:
flexing rotationally? I cant even picture that happening, what is it?

Its under moderate or firm braking, I havent got any mates I see often that have a road bike so no cant try that wheel.

Its a custom wheel with a Kinlin XR300 rim if thats of any use, ive emailed the wheelbuilder to ask their opinion as im stumped.

In reply to ow arm:

What I mean by flexing rotationally (turns out thi is knwown as tangential stiffness - see link) is the hub moving slightly independently of the rim... (although thinking about it, my immediate thought was hub twisting within the wheel - which shouldn't happen without disc brakes, but its still relevant in a differnet way.

So as a big force is applied top (brakes) and bottom (road) your momentum causes the hub to move forward on the wheel relative to the rim if the spoke tensions aren't high enough or there is too much flex in the system this could then release resulting in the oscilation you are feeling.

Have a look here:
http://www.noxcomposites.com/wheel_building

Acording to this site, the XR 300 is a rim for rear use not front: http://wheelworks.co.nz/tech-info-on-the-kinlin-range-of-rims/

It also says further down under pros/cons brake pulse is not uncommon

and this little exchange in the comments is interesting:

[quote]Andreas says:
November 19, 2009 at 12:05 am
Hi Tristan

Some KinLin rims cause a strong wobble when braking due to an error occurred during machining the sidewalls.
I had this problem and some other bikers complained about that, too.
Is there a way to tell which rims are affected?

Thanks in advance
Andreas

Tristan says:
November 19, 2009 at 12:13 am
Hi Andreas

This is a problem with the Kinlin rims but it seems to only be with 1-2% of the rims. The XR-270 seems to be the least likely to have this problem, the XR-300 and XR-200 have had a few more problems in my experience. I have not found a way of telling which rims are affected without building them into wheels – it’s a real pain in the arse but in most cases I notice the problem before the wheel leaves the workshop so it can be replaced.

I’ve tried a few ways of measuring the rims before building them to check if there will be any problems but because the rims sidewalls are not perpendicular to each other (all rims have a slight angle to assist the brake pads) I’ve found it impossible to check.[/quote]

In reply to ow arm:
fantastic response and confirmed my thoughts - hence contacting the wheelsmith

oh well its a great wheel otherwise, ill just carry on and brake a bit less on the front

In reply to ow arm:

problem with the frame build?

In reply to ow arm:

You need to toe the brake blocks in. Set them against the rim with a folded lid off a cereal packet clamped under the "trailing" edge of the block. Your problem is that the brakes are grabbing the rim, being pulled forwards, distorting, letting go slightly then springing back to start again. When you toe them in, braking forces will pull the blocks parallel with the rims, their best position.

In reply to ow arm:

thanks i do know how to toe in but this mystery has already been solved as noted in a previous post, its a problem with the rim manufacturing process - google kinlin brake pulse

thanks to everyone that took the time to reply

In reply to ow arm:

+ 1 for rigid raider.

If u have fitted new brake blocks and not toed them in then you should do

In reply to ow arm:

ok its sorted now thanks no more replies without at least reading the previous posts!!!!!