Why don't disc wheels follow Josh's rule of 105 and are mostly still narrow?

Dec 19, 17 18:54

Post #1 of 16 (4451 views)

Was looking at upgrading my disc and I noticed something interesting.

Since Josh at Silca has told us about the rule of 105 (i.e. wheel width must be at least 105% of tyre width to avoid flow seperation), and wheel companies obviously know this since wheels are going wider- then why are many discs still narrow, especially the tubular discs?

For example-
Zipp 900- 21mm (optimal tyre 20mm)
Ffwd disc - 22 mm (optimal tyre 23mm)
Reynolds element - 20.8mm (optimal tyre 20mm)
Renn - 21mm (optimal tyre 20mm)
RON - 19mm (optimal tyre 19mm)
Mavic comete (previously 19mm, now 21.5mm) - optimal tyre 22mm)
Lightweight- 20mm (optimal tyre 19mm )
Pro-lite padova -21mm (optimal tyre 20mm)
Dt swiss -20mm (optimal tyre 19mm)
3t orbis - 21mm (optimal tyre 20mm )
Ursus- 20mm (optimal tyre 19mm)
Citec 8000- 21mm (optimal tyre 20mm)

OTOH, we have wide discs like the zipp super9/sub9, flo disc, hed jet and stinger, the new premier, D2Z, pro, and these guys seem to be the trendsetters for aero.

So if wide = better given the trend toward 23 and 25 tyres, why havent most discs gotten wider as well? Is this a matter of the big aero boys being ahead and the others playing catch up? Or is it a case of width doesnt matter as much for the rear wheel and there are other factors at play?

If I had to hazard a guess, it would be that flow seperation isnt as much of an issue on the rear disc because of the huge surface air has to be controlled all the way to the rear, and other more important factors- like say making sure your disc can fit a majority of bikes- is the goal here.

What are your thoughts guys?

Re: Why don't disc wheels follow Josh's rule of 105 and are mostly still narrow? [davidalone] [ In reply to ]

Dec 19, 17 19:57

Post #2 of 16 (4381 views)

Disc wheels are a low volume seller, so they aren't first inline for upgrades. For example, ENVE still doesn't make a disc and I don't think you can actually buy the Specialized disc yet.

For HED and Flo, they are just gluing a cover on a regular wheel, so their discs are as wide as their regular Areo wheels.

I wouldn't say everybody is going straight to 25s. The Aerocoach disc is recommended for a Corsa Speed 23 as the fastest tire. While too wide a tire doesn't cause the typical flow separation of a front tire, you do have a low pressure area behind the wheel and adding tire width increases the size of this area and can cause more drag.

Re: Why don't disc wheels follow Josh's rule of 105 and are mostly still narrow? [davidalone] [ In reply to ]

Dec 19, 17 22:08

Post #3 of 16 (4280 views)

http://www.tririg.com/...s_Gretchen_25_Review

Cheers, Neal

+1 mph Faster

Re: Why don't disc wheels follow Josh's rule of 105 and are mostly still narrow? [davidalone] [ In reply to ]

Dec 19, 17 23:56

Post #4 of 16 (4220 views)

I believe Renn is now produced in 24mm, at least the clincher one

Re: Why don't disc wheels follow Josh's rule of 105 and are mostly still narrow? [davidalone] [ In reply to ]

Dec 20, 17 0:17

Post #5 of 16 (4206 views)

Moulds for a full carbon wheel are very expensive and sales are low. It's more the type of thing you have in the range to show that you care than to make money from.

Re: Why don't disc wheels follow Josh's rule of 105 and are mostly still narrow? [cyclenutnz] [ In reply to ]

Dec 20, 17 5:34

Post #6 of 16 (4017 views)

The Alto Disc is 25mm wide

Re: Why don't disc wheels follow Josh's rule of 105 and are mostly still narrow? [cyclenutnz] [ In reply to ]

Dec 20, 17 8:58

Post #7 of 16 (3897 views)

cyclenutnz wrote:

Moulds for a full carbon wheel are very expensive and sales are low. It's more the type of thing you have in the range to show that you care than to make money from.

The molds actually arent that much different in cost....but yes the volume is in the low hundreds instead of many thousands, also the scrap rate can be a problem. Outside of a few concepts, you can't "true" the wheel like a traditional wheel to mitigate molding variance.

Lastly, Frame clearance is a big driver in a wide disc wheel. Think more about lens-chainstay clearance than the "wheel well" clearance most people think about.

Re: Why don't disc wheels follow Josh's rule of 105 and are mostly still narrow? [GatorRacer] [ In reply to ]

Dec 20, 17 9:26

Post #8 of 16 (3850 views)

GatorRacer wrote:

Lastly, Frame clearance is a big driver in a wide disc wheel. Think more about lens-chainstay clearance than the "wheel well" clearance most people think about.

^^^

This! There are still many frames in use into which a "wide" disc won't fit, or has a chance of rubbing. Discs are already a small volume item, so if a company is going to make one they want it to work in the majority of the frames out there.

Re: Why don't disc wheels follow Josh's rule of 105 and are mostly still narrow? [nealhe] [ In reply to ]

Dec 20, 17 11:52

Post #9 of 16 (3743 views)

nealhe wrote:

http://www.tririg.com/...s_Gretchen_25_Review

I'm pretty sure my Zipp clincher disc is wider than my Dash clincher disc.

Dimond Bikes Superfan

Re: Why don't disc wheels follow Josh's rule of 105 and are mostly still narrow? [ericlambi] [ In reply to ]

Dec 20, 17 17:43

Post #10 of 16 (3628 views)

Hello ericlambi and All,

I do not see the Dash Gretchen disk on their website at present ... perhaps they do not sell it now.

Cheers, Neal

+1 mph Faster

Re: Why don't disc wheels follow Josh's rule of 105 and are mostly still narrow? [nealhe] [ In reply to ]

Dec 21, 17 6:12

Post #11 of 16 (3491 views)

nealhe wrote:

Hello ericlambi and All,

I do not see the Dash Gretchen disk on their website at present ... perhaps they do not sell it now.

I don't have any information about that, but based on my purchasing experiences for the disc and a recent saddle purchase I would guess that the disc is difficult for them to produce and that they have a backlog for their saddle production, so maybe it's better business-wise to just focus on saddles.

Dimond Bikes Superfan

Re: Why don't disc wheels follow Josh's rule of 105 and are mostly still narrow? [davidalone] [ In reply to ]

Dec 21, 17 7:37

Post #12 of 16 (3453 views)

There is very little dish on the drive side so going wider means bulging out and then coming back in for the cassette.
Make sure you don't hit the chain, chainstays or seatstays while you are at it.
If rear ends were made longer this would be easier as well as bring back proper running drivetrains, but everybody is too scared to make a bike with a 405mm rear end.
It's a bit like how the MTB manufacturers took so long to finally get the balls up to make a frame that riders have been asking for.
TT land is still stuck in the quagmire of too scared to make any changes for fear of being different.

At least road bikes are finally coming of age and allowing up to 28mm tyres and wide rims now.

Re: Why don't disc wheels follow Josh's rule of 105 and are mostly still narrow? [A_Hooligan] [ In reply to ]

Dec 21, 17 19:08

Post #13 of 16 (3311 views)

A_Hooligan wrote:

The Alto Disc is 25mm wide

That's right! At Alto we made sure to create our disc in the same fashion as our standard rims -- 25mm wide and tubeless compatible.

Cheers!

Re: Why don't disc wheels follow Josh's rule of 105 and are mostly still narrow? [lyrrad] [ In reply to ]

Dec 22, 17 5:05

Post #14 of 16 (3202 views)

Quote:

everybody is too scared to make a bike with a 405mm rear end.

NP3 is almost there at 399mm. Given that it's the same rear end throughout the line, that length rides wonderfully on the 45 size.

No coasting in running and no crying in baseball

Re: Why don't disc wheels follow Josh's rule of 105 and are mostly still narrow? [nealhe] [ In reply to ]

Dec 22, 17 7:16

Post #15 of 16 (3139 views)

nealhe wrote:

Hello ericlambi and All,

I do not see the Dash Gretchen disk on their website at present ... perhaps they do not sell it now.

Hopefully they realized that garbage product was just diluting their brand value.

Re: Why don't disc wheels follow Josh's rule of 105 and are mostly still narrow? [kileyay] [ In reply to ]

Dec 22, 17 8:14

Post #16 of 16 (3092 views)

kileyay wrote:

nealhe wrote:

Hello ericlambi and All,

I do not see the Dash Gretchen disk on their website at present ... perhaps they do not sell it now.

Hopefully they realized that garbage product was just diluting their brand value.

I’ve done several races, including IMLP, on the Dash disc and not had any issues with the brake track. You’re concerns are completely invalid in my view.

Dimond Bikes Superfan

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