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Half radial lacing on front wheel for road disc?

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Half radial lacing on front wheel for road disc?

Old 11-24-16, 12:04 AM
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tayguer
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Half radial lacing on front wheel for road disc?

Has anyone tried this? Based off a quick search, I've found that this is not generally recommended for mountain bike configurations, but what about road use?

Without thinking too much about it and on an impulse, I went ahead and went for it with my wheel build, and now I'm wondering if it might have been a mistake.

A little bit more info if it helps:
-Rims/hubs are 28h
-Spokes are laced 2x disc side and radial drive side.
-I weigh around 125lb and regularly ride 20/24h road rims without issue (with rim brakes).
-I'll be using a hayes mechanical disc brake with 160mm rotor.
-I don't plan on doing any sort of "MTB" type riding on this bike.

I've attached some pics to show how they turned out.
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Old 11-24-16, 12:24 AM
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I absolutely wouldn't do any radial with a disc brake.
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Old 11-24-16, 12:58 AM
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I've seen an identical wheel . . . on an ego vehicle.
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Old 11-24-16, 06:41 AM
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I don't know but I'm thinking that you can generate more torque with brakes than you can under power.
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Old 11-24-16, 08:29 AM
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What possible benefit does half-radial lacing give for a front wheel?

And radial lacing in general seems a poor idea if using disk brakes.
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Old 11-24-16, 08:40 AM
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Originally Posted by JohnDThompson View Post
What possible benefit does half-radial lacing give for a front wheel?

And radial lacing in general seems a poor idea if using disk brakes.
+1

I would not ask myself 'why not?' before answering 'why?'
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Old 11-24-16, 09:17 AM
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Google "disk brake radial spoke bike wheel" or so, you'll get some good explainin'. Your disk brake has to transfer torque from the hub to the tire to work, and radial spokes can't do this. The instructions with the Shimano disk brakes say not to use radial spokes, and show the spoke pattern to use. Look for "shimano disk brake radial pdf".
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Old 11-24-16, 10:15 AM
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Well...
Full radials are generally frowned upon for any torque carrying hub.
But there's any number of half radial rears.
Which seems to be doing well enough not to cause any undue excitement.


Since you pedal more often than you brake, (and the bigger tension imbalance) fatigue is more likly to strike a rear than a front.


OTOH, braking hard enough to cause rear wheel lift is fairly easy to do.
While popping a wheelie accidentally while being in a regular riding position is quite rare.


So it seems reasonable that hard braking would create more torque than hard pedalling.


OTOH, a sudden "clean" overload while JRA is a very rare cause-of-death for a wheel.
Immediate write-offs are just about always caused by something more unusual. Potholes, crashes, something caught in the spokes, wheel ending up sideways....
So 'd expect you have some strength margin anyhow.
The non-disc side runs, what - 65% or so of the disc side spoke tension. So I wouldn't worry that much immediately about the life of the flange.
I'd expect it to survive with not much of either benefit or drawback. Maybe a little more hub wind-up on hard braking.
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Old 11-24-16, 10:16 AM
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Originally Posted by JohnDThompson View Post
What possible benefit does half-radial lacing give for a front wheel?

And radial lacing in general seems a poor idea if using disk brakes.
The same as on a drive wheel. In this case, the disc will apply torque to the spokes. If the dish is severe, then the less-tensioned outer spokes might get to the point where the tension goes so low as to being nearly completely slack, contributing to eventual failure. Maybe. Half-radial eliminates this scenario.
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Old 11-24-16, 10:34 AM
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Thanks for the responses so far.

Originally Posted by Retro Grouch View Post
I don't know but I'm thinking that you can generate more torque with brakes than you can under power.
That's something I've been pondering since I've had no issue running 2x / half radial on a drive wheel (albeit with rim brakes). Unfortunately, I'm also unsure how torsional loads under hub braking compares with drive torque.


Originally Posted by dabac View Post
Well...

Since you pedal more often than you brake, (and the bigger tension imbalance) fatigue is more likly to strike a rear than a front.


OTOH, braking hard enough to cause rear wheel lift is fairly easy to do.
While popping a wheelie accidentally while being in a regular riding position is quite rare.


So it seems reasonable that hard braking would create more torque than hard pedalling.
Thanks - that's a really great example and explains how hub breaking might cause more torsional load compared with drive.

I've been searching for more answers online but unfortunately haven't been able to find much info, aside from Specialized currently making their Roval wheelsets (for road and cx) with this same configuration.

https://www.specialized.com/us/en/co...c-front/118083
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Old 11-24-16, 10:49 AM
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I know why radial spoke patterns are so liked but I never had that itch. I suspect the proposed wheel would be just fine (I'd use the crossed spokes on the disk side). But again I just don't see the "gain" with radial spokes to begin with. Same with low count spoke wheels in general. Andy.
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Old 11-24-16, 11:17 AM
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Nope, I have no desire to do that ..

1) Road Bike has Rim brakes , (my 28 hole radial spoked wheels are on the Brompton)

2)Wheel for My Disk Brake bikes are 32 hole 3 cross [ 406 & 559 ]

but follow your fashion desires ... [You can report back in a year of Riding on them ]




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Old 11-24-16, 09:17 PM
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You'll be fine as long as the hub has enough material above the spoke holes to keep the radial spokes from pulling out of the hub. I am constantly amazed that people think Radial lacing is bad yet every high end manufacturer uses it. These are companies with really good engineers not forum know it all's. As long as you have one side crossed the drive and brake forces are controlled. Radial lacing also adds lateral stiffness which helps against spoke de-tensioning during lateral forces. Racing Quattro Carbon DB - Road Bike Wheels
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Old 11-24-16, 09:45 PM
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Originally Posted by OnTheRivet View Post
You'll be fine as long as the hub has enough material above the spoke holes to keep the radial spokes from pulling out of the hub. I am constantly amazed that people think Radial lacing is bad yet every high end manufacturer uses it. These are companies with really good engineers not forum know it all's. As long as you have one side crossed the drive and brake forces are controlled. Radial lacing also adds lateral stiffness which helps against spoke de-tensioning during lateral forces. Racing Quattro Carbon DB - Road Bike Wheels

I never said radial lacing was bad. I said that I see no advantage and that I do understand why some might be attracted to it. I also said I have no attraction to it (for my own bikes or the ones I work on). I ended with a comment about low spoke counts also being off my preference list.


I could have instead listed why radial lacing is not as robust or "is bad". But it really doesn't matter as I don't use it.


As to your statement about high end manufacturers using radial lacing- They sell the hope and dreams of performance, this has been shown to be better for their bottom line then the tiny and barely measureable differences between radial and more tangential lacing, or having 4 to 8 less spokes, are FOR THEIR CUSTOMERS.


When one talks about what companies do the business aspects need to be part of the discussions. Andy.
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Old 11-24-16, 09:48 PM
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Simple test anyone can do - do a 18 mph to 0 stop using only the front wheel. Measure the distance. Now, get on your bike with a holder (like a velodrome start) and accelerate from a standstill over that same distance. Note your speed as you go by the other end of your stop. Your max braking vs your max pedaling force for the rear wheel will be the ratio of 18 mph to your speed from a standstill.

For example, say it takes you 15 feet to stop. And on your hardest start you are going 6 mph at that 15' point. Your deceleration stopping force will be 18/6 = 3 times your starting acceleration force.

So, are you comfortable with an animal of a rider fully 3 times as strong as you stomping on your rear wheel built just like your proposed front wheel? Would you trust your body and bike to a front wheel stomped like that? If yes, go for it. (I wouldn't.)

Ben
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Old 11-25-16, 11:38 AM
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Originally Posted by 79pmooney View Post
Simple test anyone can do - do a 18 mph to 0 stop using only the front wheel. Measure the distance. Now, get on your bike with a holder (like a velodrome start) and accelerate from a standstill over that same distance. Note your speed as you go by the other end of your stop. Your max braking vs your max pedaling force for the rear wheel will be the ratio of 18 mph to your speed from a standstill.

For example, say it takes you 15 feet to stop. And on your hardest start you are going 6 mph at that 15' point. Your deceleration stopping force will be 18/6 = 3 times your starting acceleration force.

So, are you comfortable with an animal of a rider fully 3 times as strong as you stomping on your rear wheel built just like your proposed front wheel? Would you trust your body and bike to a front wheel stomped like that? If yes, go for it. (I wouldn't.)

Ben
But bike wheels are generally considerably overbuilt for JRA. (Although if overbuilt enough for this I can't tell).
All my wheel failures have either been through "dynamic" events - i.e. crashes or similar - or fatigue.
If a half-radial felt OK during hard-but-planned braking, I'd be happy to ride one.
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Old 11-25-16, 11:53 AM
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It's built and the time to worry about whether it's a smart decision is past. Ride it, and if you did a decent job, it should hold up OK. Next time, think BEFORE you act.


BTW - while I expect it to be OK, there is legitimate concern about flange failure, especially is you used 14g plain gauge spokes and/or high tensions. That concern is the ONLY reason I'd take it apart, though me being me, I'd probably just rride it.
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Old 11-25-16, 12:12 PM
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The only real advantage of radial spoking is style.
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Old 11-25-16, 12:48 PM
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I had a longer response typed out but it was too wordy. The problem boils down to this, there are now seven trailing spokes getting their tension reduced when it was previously fourteen. A quarter of the time, one of those is also getting reduced by being the lowest spoke when most of your weight is on the front due to braking weight transfer. Will it go loose, get fatigued? Maybe not, the brake side tension is higher due to the dish. But they're definitely going to get worked harder. So, too, the hub flange on the left is getting all the torque and being worked harder.

There's a concern you see about radial lacing putting more load on the hub flange but it seems like it should be less of a problem in dished wheels if you put the radial lacing on the lower tension side.
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