Tweaked carbon wheel truing/rounding

Everything about building wheels, glueing tubs, etc.
Post Reply
Abl3rider
Posts: 30
Joined: Tue Jul 05, 2016 3:34 am

by Abl3rider

As I shared in my post 'tubeless troubles' , I flatted first race on new Giant TCR. The bike comes with Giants' SLR 1 carbon tubeless wheelset. Good news is i havent flatted since... just pumped it back up and it's been fine so the general consensus was that I must have punctured and it resealed but too late as it left me with only about 15 psi to finish the race. I'm going to go with Orange sealant in the future instead of the Stans it comes with.

But this post is about what happened to the front wheel in the same race... as I realized I had a problem with my rear tire pressure I made the mistake of trying to look back to see just how low it was. In doing so I slightly swerved my front spokes into the QR lever of the rear wheel of the bike next to me. TINK TINK TINK! Lucky nobody went down.

So it got tweaked. Out of true but not severely so, still rideable without noticeable brake pulse or rub. So I took it to the Giant dealer. They had to order the proprietary spokes and spoke wrench. Normally I fix and build my own wheels but these are my first low spoke count carbon rimmed wheels (16 h front 21 h rear) and the nipples are hidden. So 3 spokes were bent but not badly.

They replaced two of the three bent spokes (left the least bent on the wheel). The wheel is now true and centered. But not perfectly round. And the spoke tension is uneven. Before the incident all the spokes had identical tension I know because I played them like guitar strings and the pitch was the same. Now they are not.

I'm wondering if the rim got tweaked as an aluminum rim may get, requiring uneven spoke tensions to compensate, or if it is just not a perfect wheel truing job. It's probably round enough not to be a problem, and probably still plenty strong even with the imperfect tension, but I'm tempted to order the wrench and see if I can do better. I realize that with so few spokes it is more difficult to overcome rim imperfection.

Does anyone know how carbon rims tend to react to impacts and/or spoke damage because I find it hard to believe it bends and stays bent like aluminum. Thanks.






Sent from my iPad using Tapatalk

by Weenie


Butcher
Shop Owner
Posts: 821
Joined: Sun Jan 03, 2010 4:58 am

by Butcher

I'm fairly certain carbon will bounce back or break. Those are the only options.

mattr
Posts: 3412
Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

Might be time to actually "unbuild" the wheel and start again, rather than replacing spokes in an already tensioned wheel.

(Unbuild meaning untensioning all the spokes, not dismantling it)

joejack951
Posts: 276
Joined: Fri Feb 18, 2005 6:50 pm
Location: Wilmington, DE

by joejack951

How many spokes are loose? If they are in an isolated area that corresponds with the out-of-round area, the fix seems simple and is worth attempting without completely dismantling the wheel. If the shop did something stupid and messed with a bunch of spokes, then you might be better off just starting over.

Carbon fiber is very unlikely to have yielded like an aluminum rim could, unless the rims have an aluminum core. The only way to find out for sure how true the rim is on its own would be to dismantle the wheel, but that seems totally unnecessary here given the isolate repair.

NovemberDave
Posts: 164
Joined: Sat Oct 09, 2010 11:42 am
Contact:

by NovemberDave

Bad rebuild. Carbon doesn't do that. It may be broken inside and that may manifest in other ways, but that's not how it would manifest. De-tension completely and start over (or have them do it, but that sounds like a dead end).

Abl3rider
Posts: 30
Joined: Tue Jul 05, 2016 3:34 am

by Abl3rider

That's what I thought thanks all who replied!


Sent from my iPhone using Tapatalk

totalcompactroad
Posts: 32
Joined: Tue Jan 31, 2017 11:12 pm

by totalcompactroad

On these wheels, Giant use what they call 'dynamic balanced lacing', the spokes work in sets of three and there are different tension requirements etc. One of our mechanics at work ignored this and tensioned like he would a normal wheel and cracked a rim.

Giant Dealer should know this allready, they can get all the techdocs from Giant if needs be

User avatar
sugarkane
in the industry
Posts: 1798
Joined: Wed Jan 19, 2011 11:14 am
Location: SYD
Contact:

by sugarkane

It's a triplet laced wheel so... it's even more important separate lateral and vertical truing..

So dial out the vertical true using the drive side spokes. Any thing under 0.3-02mm is totally fine. Then get your lateral true using ONLY the non drive side spokes.. high tension =vertical.. lower tension= lateral

Not stuff you learn in your average LBS

mattr
Posts: 3412
Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

sugarkane wrote:Not stuff you learn in your average LBS
But nice to hear that working it out from first principles worked. (Only trued one triplet wheel, not likely to do it again!)

Svetty
Posts: 447
Joined: Thu Mar 26, 2009 11:06 pm
Location: Yorkshire - God's Own Country

by Svetty

sugarkane wrote:It's a triplet laced wheel so... it's even more important separate lateral and vertical truing..

So dial out the vertical true using the drive side spokes. Any thing under 0.3-02mm is totally fine. Then get your lateral true using ONLY the non drive side spokes.. high tension =vertical.. lower tension= lateral

Not stuff you learn in your average LBS


It's his front wheel........

User avatar
sugarkane
in the industry
Posts: 1798
Joined: Wed Jan 19, 2011 11:14 am
Location: SYD
Contact:

by sugarkane

Ohh my bad. The rim would defiantly break before deforming
You could back it off and start again but if it's your first time that might not work any better..


If it's pretty straight then chasing out hop is relatively easy. Just make sure you work in left and right pairs to keep the true in place. Bike in stand. Place a solid object perpendicular to the rim, use this to help see Te vertical change. Find where it appears to move away from you and count the number of spokes in the vertical change.. now back these off an 1/8th of a turn each counting you way back across the spokes. Now move To the section closest to your baseline and count the spokes again. These guys get 1/8th turn more of tension.

Keep working small changes and moving your reference closer to the rim. If it's not working out then take the wheel to a wheel builder and get it retensioned..

Any thing under 0.5mm you won't feel once a tire is on the rim and any thing under 0.2mm is pretty good

by Weenie


Abl3rider
Posts: 30
Joined: Tue Jul 05, 2016 3:34 am

by Abl3rider

Thank you! I ordered more spokes and am waiting to see if I'm gonna need a special spoke wrench (when I see the nipples). At least I'll need an extension


Sent from my iPad using Tapatalk

Post Reply
  • Similar Topics
    Replies
    Views
    Last post