Which rear wheel is stronger?

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fastpedaller
Posts: 1905
Joined: 10 Jul 2014, 1:12pm
Location: Norfolk

Which rear wheel is stronger?

Postby fastpedaller » 5 Feb 2019, 9:03pm

Something I was mulling over ........ With same spokes and rim, and a shimano rear hub, which would be stronger either:-
a) 36 hole dished for 8 speed or
b) 32 hole dished for 7 speed??

Brucey
Posts: 33874
Joined: 4 Jan 2012, 6:25pm

Re: Which rear wheel is stronger?

Postby Brucey » 5 Feb 2019, 9:04pm

which OLN(s)?

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

fastpedaller
Posts: 1905
Joined: 10 Jul 2014, 1:12pm
Location: Norfolk

Re: Which rear wheel is stronger?

Postby fastpedaller » 5 Feb 2019, 9:17pm

Brucey wrote:which OLN(s)?

cheers

Oops yes I forgot that detail...... 132.5mm

Brucey
Posts: 33874
Joined: 4 Jan 2012, 6:25pm

Re: Which rear wheel is stronger?

Postby Brucey » 5 Feb 2019, 9:43pm

the tension ratios L to R are about 55% and 60% respectively, but for the rim to be as well supported by the spokes arguably the tension in the 32 spoke wheel ought to be ~12.5% higher. Lets say that the wheel tension is limited by the DS spokes (which is quite normal) at 130kgf. You could build the wheels


8s/132.5mm hub 130/71.5kg average tension 100.75kgf
7s/132.5mm hub 130/78kg average tension 104kgf

However 7s hub designs don't usually make best use of the available wheel dish; the LH lip on the freehub body is thicker than is necessary. Also there is a little space between the chain and the dropout in top gear. This means you can usually improve the dish on a 7s wheel by another 3mm or so, which can get you to ~75% tension balance [you can improve 8s too, but not by as much].

Optimised 7s/132.5mm 130/97.5kg average tension 113.75kgf

You can see that the average tension in the optimised 7s wheel is ~+13% vs the 8s wheel. This is getting on for the amount that could make up for the shortfall in spokes. Note that the fatigue loadings increase whenever you have fewer spokes though.


Probably you are better off building a 7s wheel with 36 spokes and making those spokes thin and stretchy.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

mig
Posts: 1972
Joined: 19 Oct 2011, 9:39pm

Re: Which rear wheel is stronger?

Postby mig » 5 Feb 2019, 11:00pm

the one better built :wink:

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foxyrider
Posts: 4440
Joined: 29 Aug 2011, 10:25am
Location: Sheffield, South Yorkshire

Re: Which rear wheel is stronger?

Postby foxyrider » 5 Feb 2019, 11:11pm

But what wheel size? That has to make a difference too. Will it have rim or disc brakes?

And of course 'strong' might be good on one level but 'springy' can be better in other uses.
Convention? what's that then?
Airnimal Chameleon touring, Orbit Pro hack, Orbit Photon audax, Focus Mares AX tour, Peugeot Carbon sportive, Owen Blower vintage race - all running Tulio's finest!

mig
Posts: 1972
Joined: 19 Oct 2011, 9:39pm

Re: Which rear wheel is stronger?

Postby mig » 6 Feb 2019, 11:38am

foxyrider wrote:But what wheel size? That has to make a difference too. Will it have rim or disc brakes?

And of course 'strong' might be good on one level but 'springy' can be better in other uses.


how is that road surface on the woodhead doing?

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foxyrider
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Joined: 29 Aug 2011, 10:25am
Location: Sheffield, South Yorkshire

Re: Which rear wheel is stronger?

Postby foxyrider » 6 Feb 2019, 12:58pm

mig wrote:
foxyrider wrote:But what wheel size? That has to make a difference too. Will it have rim or disc brakes?

And of course 'strong' might be good on one level but 'springy' can be better in other uses.


how is that road surface on the woodhead doing?


Not been over since last autumn
Convention? what's that then?
Airnimal Chameleon touring, Orbit Pro hack, Orbit Photon audax, Focus Mares AX tour, Peugeot Carbon sportive, Owen Blower vintage race - all running Tulio's finest!