Wheel size, flex and material

PB Forum :: 29ers
Wheel size, flex and material
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Posted: Jan 10, 2019 at 8:14 Quote
Hi,
Just sat daydreaming at work and started browsing wheelset options for yet another unnecessary upgrade! Without starting the whole carbon vs aluminium debate, is there any argument for 29ers benefiting more from carbon construction that their 27.5 counterparts? There's a lot of talk about lateral stiffness with carbon and I just wondered if the accepted wisdom was that 29ers suffered more flex for a given rim/build.

Forgive my ignorance if this is schoolboy stuff!!

Cheers,
J

Posted: Jan 15, 2019 at 23:48 Quote
I can’t offer a direct comparison between a carbon rim and its alloy counterpart but when moving from a HT to fullnsuss 29er I had real issues with keeping the rear wheel true. My hardtail was running standard spesh carve hoops on a 142 hub. For the Mach 429 I I fitted stans arch hoops on 142 hope hubs. (Were bought as a hope hoop factory build.
The full susser opened up faster and rowdier riding and it soon took its toll on the rear hoop. Within a couple of months I was having to true it most rides. This compares to the same rim and hub combo I had on an aggro hardtail in 26 flavour that hardly ever needed truing.

After finding the limits of the 429 and its rear wheel I upgraded to a pivot switchblade with Reynolds enduro carbon hoops on a 157 hub. Revelation. That bike had some stick on DH tracks and naturally rocky terrain and after 18 months I can comfortably say they are the best wheels I have ever ridden on. Apart from some surface scratches from rocks they took some punishment from drainage ditches that caused a few pinch punctures but stayed as true as the day they were new. They were running 28 spokes and I never noticed the harshness that people mention with carbon rims. In fact the back end of that bike felt plusher and offered better small bump compliance than the custom tuned and wheel equipped 170mm mojo Geometron I built for big days.

So I guess you pays your money and takes your chance but I would happily have another Reynolds carbon wheelset.
I have a wheel building bench and spoke tension gauge so keep and eye on my wheels.
There are a lot of variables to consider in the above info but having had numerous bikes and wheel and hub combos I personally haven’t been swayed away from carbon

Posted: Jan 21, 2019 at 7:55 Quote
Thanks for the input Pigglet13! That's all very useful and might just help sway my decision one way over another. I see you're local to me (I'm an ex-Ayton lad) so you automatically qualify as knowing what you're talking about!
Don't know how the Reynolds price up but I'm currently looking at Blue Flow and Sixth Element as wheels at a low-ish price point that will allow me to be disappointed but not devastated if I'm underwhelmed by the whole carbon thing.

Thanks again.

Posted: Feb 11, 2019 at 20:17 Quote
Im having problem keeping my rear wheel true also, I might upgrade to carbon rim eventually.

Posted: Feb 14, 2019 at 0:20 Quote
Josslad wrote:
Hi,
Just sat daydreaming at work and started browsing wheelset options for yet another unnecessary upgrade! Without starting the whole carbon vs aluminium debate, is there any argument for 29ers benefiting more from carbon construction that their 27.5 counterparts? There's a lot of talk about lateral stiffness with carbon and I just wondered if the accepted wisdom was that 29ers suffered more flex for a given rim/build.

Forgive my ignorance if this is schoolboy stuff!!

Cheers,
J

You're right that, all else being equal, larger wheels will flex more and will be less strong. Carbon rims will help, but they a terrible value.

There are various ways to address stiffness and strength:

Spokes: Thicker spokes and/or more of them, especially on the rear wheel. Keep in mind hubs have asymmetrical flange offsets, so the bracing angles of the spokes are different. You can compensate for this by using thicker spokes on the side with the less favourable bracing angle (typically the disc side on the front and cassette side on the rear). Counterintuitively, thick spokes are much more susceptible to fatigue failure (and place more stress on nipples and rims), but they do increase stiffness and strength while they last.

Rims: Wider, stronger, and with offset spoke holes to equalize the bracing angle. If you choose to go carbon, Asian carbon rims have become very good - most carbon rims are just relabeled Light Bicycle or Yishun rims. WeAreOne makes their rims in Canada and they're probably the best in the world - for a lot less than Reynolds or Enve. Highly recommended!

Hubs: Choose hubs with greater flange offset, especially on the side with less offset. The difference can be up to 20%.

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