UKC

uneven tyre clearance/disc brakes

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 malk 12 Apr 2017
wide tyres are almost rubbing on my chainstay on disc side of rear wheel. looks like it needs about 2mm adjustment.
what's the best way to shift the rim? do mechanical disc brakes have this much adjustment? would redishing with a quarter turn do the job in the simplest way? (no need for brake adjustment)
thanks
 Dark-Cloud 12 Apr 2017
In reply to malk:
Not quite sure why you think that's a disc brake issue, the disc will stay where it is even if the wheel is redished ?

Is it a new wheel ? Is it in the drop out properly ? What bike is it ?
Post edited at 12:48
 gethin_allen 12 Apr 2017
In reply to malk:

First question, is the wheel equally dished in the first place?
OP malk 12 Apr 2017
In reply to Dark-Cloud:

it's a new wheel on new GT bike fitted with 35mm tyres. dropout fitting seems ok- no adjustment there.
axle threads look even- i would usually do a cone adjustment to shift the rims, but as a disc newbie was wondering of the disc body can be adjusted by this amount (~1.5-2mm)
the brakes work fine so would rather not meddle with atm..
 MonkeyPuzzle 12 Apr 2017
In reply to malk:

Hold a small length of card from the chainstay so that it's just touching the rim and rotate the wheel. If there's a noticeable movement away from or towards the card at the point where your tyre rubs you'll know it's the rim and you can do a quarter turn each side to re-true the wheel. If 35mm tyres are the absolute maximum your frame can take, there's no guarantee that the tyre carcass is 100% evenly manufactured, in which case you can either accept the tight clearances or replace the tyres.
OP malk 12 Apr 2017
In reply to gethin_allen:

i have to assume yes
 Dark-Cloud 12 Apr 2017
In reply to malk:

In theory if you were to adjust the cones then yes the disc caliper would move that far, they are usually slotted, however by adjusting cones you will shift the cassette further over which will give you issues on the other side.

The wheel sounds wrong or the tyres too big for your frame, also some rear ends are asymmetrical.
OP malk 12 Apr 2017
In reply to MonkeyPuzzle:

rim is true to <1mm. tyre-chainstay varies ~1mm when rotating. if a quarter turn on each side would shift it 1.5mm i would be happy if a spoke were to brake (hold on....
 LastBoyScout 12 Apr 2017
In reply to malk:
Spin wheel as it is and note the distance from disc-side chainstay to rim and chainstay to tyre at several points around the rim. Assuming that's even, then the wheel is at least straight.

Now, take wheel out of bike, turn it over and drop it back in the frame* - check the clearances again**.

If it is a bigger gap on the rim, then the wheel is incorrectly dished. It's also possible the tyre is incorrectly seated.

* you'll obviously need to make sure the chain and mech are out of the way and that the cassette doesn't catch the brake caliper - best to take both off, if you have the tools.
** Wheel QR/whatever needs to be tight on both measurements, or it'll skew the results.

Even easier, pop it down to your LBS - they'll drop it in their jig and tell you immediately if it's dished right.
Post edited at 13:36
 LastBoyScout 12 Apr 2017
In reply to malk:

I can't see that adjusting the cones will shift the rim either way - it's the spokes you need to adjust to do that.
 Dark-Cloud 12 Apr 2017
In reply to LastBoyScout:

Assuming its a cup and cone wheel and it can be adjusted it will shift the whole hub over and hence the rim but its not the right solution and will cause more issues than it will fix
OP malk 12 Apr 2017
In reply to LastBoyScout:
thanks for the wheel reverse tip- the clearance is spot on when reversed (could possibly fit 38mm). that means the wheel could be incorrectly dished (as mentioned above an asymmetric rear end would be another cause?)

have just tried a non disc wheel on the bike and the clearance is even
Post edited at 14:27
 due 12 Apr 2017
In reply to malk:

Redishing a finished (tight) wheel can be tricky as the spokes will start to wind, where the spokes will twist first before any actual adjustment begins. It can take a bit of skill and experience to account for this otherwise they will ping back once you start riding.
OP malk 12 Apr 2017
In reply to due:

how much would a slight adjustment (quarter turn) each side move it and would that compromise spoke integrity?
 LastBoyScout 12 Apr 2017
In reply to Dark-Cloud:

> Assuming its a cup and cone wheel and it can be adjusted it will shift the whole hub over and hence the rim but its not the right solution and will cause more issues than it will fix

No, it won't. Adjusting the cones will shift the hub in relation to the spindle, but not in relation to the rim, as the cups are part of the hub and therefore can't move.
 LastBoyScout 12 Apr 2017
In reply to malk:

> thanks for the wheel reverse tip- the clearance is spot on when reversed (could possibly fit 38mm). that means the wheel could be incorrectly dished (as mentioned above an asymmetric rear end would be another cause?)have just tried a non disc wheel on the bike and the clearance is even

That's why I said to only measure it from the disk side chain stay, to account for the possibility of assymetric stays. The rim should be the same distance from that stay, regardless of which way round it is.

Using the disk side avoids working around the chain.
Rigid Raider 12 Apr 2017
In reply to malk:

You can make a simple dishing gauge out of a wood batten the same length as the rim diameter with long screws through each end and short through the middle. Set the middle screw in the end of the axle then turn the end screws until they just contact the rim. Then try it at the other end of the axle. The rim should be dead centre on the axle.

You can loosen one side and tighten the other side spokes but this is complicated on a rear wheel by the fact that the drive side spokes are flatter so have a higher tension. Whatever you do, don't allow that spinning tyre to touch the inside of the chainstay; a wet mucky tyre will wear through alloy, steel or carbon in a few minutes. If your gauge shows the rim to be off centre and you don't trust yourself with the spoke key, take the wheel back to the retailer for a re-true.
OP malk 12 Apr 2017
In reply to LastBoyScout:
yes, was thinking inserting a spacer on disc-side axle
think i'll just replace with the 28s that came with bike for now and take to LBS when have time.
Post edited at 15:21
 Si_G 12 Apr 2017
In reply to malk:

I'd say your disk brake will be fine.
Without knowing the frame or brake fitting : once your wheel is centred you just slack the bolts holding the brake caliper, fully engage the brake, then re-tighten the bolts.
 LastBoyScout 12 Apr 2017
In reply to Rigid Raider:

> Whatever you do, don't allow that spinning tyre to touch the inside of the chainstay; a wet mucky tyre will wear through alloy, steel or carbon in a few minutes.

I use helicopter tape on the inside of my chain stays for exactly that reason - prompted after hitting a pothole on my road bike. No damage to wheel on initial inspection, but by the time I got home, a tiny crack had spread around a spoke hole, slowly causing a wobble that meant the tyre could just touch the inner chainstay. Fortunately, I was on the way home and it wasn't far - it took the paint off, but stopped just short of major damage.

One of my mountain bikes has a line of zip ties to prevent chain suck damage on the carbon stays - they also protect it from the tyre.
 Dark-Cloud 12 Apr 2017
In reply to LastBoyScout:

Yes you are right of course, was thinking about spacing rather than moving.
OP malk 13 Apr 2017
In reply to LastBoyScout:
yes, glad i replaced with 28s for now- even though the clearance was maybe 2mm, i could see it was starting to rub the chainstay when riding..

the observations that reversing the wheel and trying another wheel (8sp vs 9sp, same axle length) both give even clearance suggests dishing issue rather than frame?

thanks everyone
Post edited at 11:21
 Dark-Cloud 13 Apr 2017
In reply to malk:

What bike is it ?

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