Author Topic: TIRES - 700c vs 26 inch for long tours AND S&S Couplers  (Read 14455 times)

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Offline sanuk

Re: TIRES - 700c vs 26 inch for long tours AND S&S Couplers
« Reply #30 on: June 23, 2010, 12:16:11 am »
Fitting my bike into a suitcase sounds very appealing compared to the cardboard bike box I've got it in right now ready to fly out in a couple of weeks.  But 23 kg would still be 23 kg whichever way you pack it.
On the tyre size issue, isn't what you call a 700c wheel the same as a 28 inch?  What does 700c refer to?  After reading 'The Man who Cycled the World' I can see some of the advantages and disadvantages.  He rode on one of the best bikes around - Koga Miyata - and still his double-rimmed back wheel  - a 28 inch - broke spokes and had to be re-built at least twice during his trip.  Maybe gave him a few more miles per pedal, but evidently a weaker wheel when loaded it seems.

Offline whittierider

Re: TIRES - 700c vs 26 inch for long tours AND S&S Couplers
« Reply #31 on: June 23, 2010, 02:22:39 am »

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On the tyre size issue, isn't what you call a 700c wheel the same as a 28 inch?  What does 700c refer to?

Yes, 28" is the same size as 700c, and the MTB world calls them 29".  There used to be a 700A, 700B, and 700D too, but the common one left now is 700C.  They all had the same outer diameter of the tire (close to 700mm), but to get there, the smaller cross section tires took a larger-diameter rim.  700A had the biggest diameter of rim, with a bead seat diameter (BSD) of 642mm.  700B had a BSD of 635mm, and 700D had a BSD of 587.  Today we use the same C rim size with a 622mm BSD for all of them, so you can use a range of tire widths on the same wheel.

Offline Galloper

Re: TIRES - 700c vs 26 inch for long tours AND S&S Couplers
« Reply #32 on: June 23, 2010, 08:12:10 am »
  After reading 'The Man who Cycled the World' I can see some of the advantages and disadvantages.  He rode on one of the best bikes around - Koga Miyata - and still his double-rimmed back wheel  - a 28 inch - broke spokes and had to be re-built at least twice during his trip.  Maybe gave him a few more miles per pedal, but evidently a weaker wheel when loaded it seems.

He blamed the wheel breakages on a combination of rim brakes and over tensioning of spokes.   He also said that if he was doing something like this again, he'd use disc brakes.

Offline briwasson

Re: TIRES - 700c vs 26 inch for long tours AND S&S Couplers
« Reply #33 on: July 05, 2010, 11:29:22 am »
Since the discussion includes S&S couplers, I should also note that 26" wheels are way easier to pack in a standard S&S 26x26x10 case. 700c fits, but you have to deflate the tires usually and the wheels take up more room in general.

Offline TwoWheeledExplorer

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Re: TIRES - 700c vs 26 inch for long tours AND S&S Couplers
« Reply #34 on: July 10, 2010, 01:14:10 pm »
Just came back from a ride on my 26" Safari; The 700 Volpe is in the shop getting ready for next week...I think. Reports (from friends in the area) are, due to flooding last month, that the county road on the L&C 7 miles south or Marty is still out, meaning we may have to divert on dirt roads around or carry the bikes over. (We have a SAG van, so we are not riding fully loaded. The van will have to divert around.) Given that change, should I stick with the Volpe, or take the safari instead?
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Offline digimarket

Re: TIRES - 700c vs 26 inch for long tours AND S&S Couplers
« Reply #35 on: July 26, 2010, 08:21:12 pm »
  After reading 'The Man who Cycled the World' I can see some of the advantages and disadvantages.  He rode on one of the best bikes around - Koga Miyata - and still his double-rimmed back wheel  - a 28 inch - broke spokes and had to be re-built at least twice during his trip.  Maybe gave him a few more miles per pedal, but evidently a weaker wheel when loaded it seems.

He blamed the wheel breakages on a combination of rim brakes and over tensioning of spokes.   He also said that if he was doing something like this again, he'd use disc brakes.

Unlikely.  If the stresses from rim brakes were the cause of broken spokes - the front ones would break also (most of the braking in extreme stops is on the front) - it is always the back ones.  The combination of driving forces, too much weight, uneven tension from wheel dishing, and not enough spokes is why tourists have broken spokes on the back.  Spoke quality and hub design make a difference also.  The best modern wide based cassette hubs (135mm) with properly rounded holes and slight inward angles on the flanges combined with 36 quality spokes and an expert hand-build will stand up well to touring loads up to about 150 pounds on the rear wheel.  Above that, expect broken spokes or go to a 40 spoke tandem wheel.

There may be some slight truth to the theory that mountain bike rims (26) are "better braced" than 700's - but that also means that the spokes are leaving the hub flanges at a more acute angle - which contributes to breakage.  Mountain bike hubs at 135mm spacing have a slight advantage in dishing over 130 road hubs.  It's easy to spread the rear forks on a steel frame to 135.

As has been mentioned by other posters - if the rim construction and tire construction is the same between 26" wheels and 700C wheels - the circumference will be less and the spokes shorter for a slight overall weight advantage for the smaller wheel.  The inertial weight advantage will be very slight as the smaller diameter wheel also has accelerate faster to reach the same road speed.  The very low hub rolling resistance will be slightly higher for the smaller wheel at any given speed and the smooth surface rolling resistance of the tires (assuming identical construction) should be identical.  On rougher surfaces the larger diameter tire should have a slight rolling resistance advantage.  All taken together - the overall difference is so small that it hardly matters on a touring bike.

What makes the difference is that the tire construction is almost never the same.  It is very difficult to find really lightweight thin tread 26" tires in a 1 1/4 (32mm) or 1 3/8 inch (35mm) size.  For that matter it is fairly difficult to find tires of that description in a 700c.  So what happens is that the 700c tourist ends up buying a narrower tire that needs to be pumped up harder and the 26" tourist gives up and buys a wider tire that has much thicker than optimal tread thickness and doesn't roll as well at the appropriate pressures.

My opinion is that the ideal touring tire for lighter tourists and loads is 32mm (save the 28's for credit card touring only) as the rider and load gets heavier 35mm tires are ideal.  38mm is only for the heaviest loads or if you expect to be on dirt a lot.  The really wide knobby mountain bike or cyclecross tires are for dirt only - way too slow to make mileage on a tour and all wrong on pavement.

I was talking with two young men from England yesterday on the American River Bike trail in Sacramento, California.  They were on their second to last day of a cross-America tour.  With over 3,000 miles on their clocks they had each broken one spoke (32 spoke wheels) and worn out their rear 32mm tires (and replaced them with 28's).  All their camping gear was on the back wheel and they were lightweight riders.  If they had used front lowriders, and rotated their tires halfway through, they might have done the entire tour trouble free.
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Offline whittierider

Re: TIRES - 700c vs 26 inch for long tours AND S&S Couplers
« Reply #36 on: July 27, 2010, 12:57:49 am »
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He blamed the wheel breakages on a combination of rim brakes and over tensioning of spokes.   He also said that if he was doing something like this again, he'd use disc brakes.
Unlikely.  If the stresses from rim brakes were the cause of broken spokes - the front ones would break also (most of the braking in extreme stops is on the front)
+1.  Disc brakes put a lot more stress on spokes.

About the spoke-bracing angle though-- that makes the wheel a lot stronger, and is why tandem wheels are so much stronger, and famous wheel builder Peter White insists that 36 spokes are virtually always enough for a tandem when the wheel is built right.  I found out about him on the tandem forum where everyone raved about his trouble-free 36-spoke tandem wheels, including for loaded touring.  To get that wider spoke bracing angle though, tandem wheels use 145mm or 160mm dropout spacing, not 130 like road bikes'; so you can't just put a tandem rear wheel in a single road bike or even a touring bike.  Decades ago when tandems' rear dropout spacing was 135 or less, they had a lot more wheel trouble even with 40 or 48 spokes.  To further press the point about bracing angle:  For the last 9 years, Santana has been selling 16-spoke tandem wheels which have proven to be very reliable.  The dropout spacing is 160mm, and the spokes from the right flange go to the left side of the rim, and vice-versa, to improve the spoke bracing angle.



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The inertial weight advantage [of the smaller 26" wheel] will be very slight as the smaller diameter wheel also has accelerate faster to reach the same road speed.
No, it's the same number of feet per second.  RPM itself is not the issue.  The myth of rotational weight is exploded in this wheel-science web page though.  You can see for example in the middle of the first table that the wattage savings in the uphill portion of a training ride if you cut the front wheel's rotational inertia in half (an absolutely huge reduction!) is only 0.004%.  IOW, it doesn't matter.

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The very low hub rolling resistance will be slightly higher for the smaller wheel at any given speed
very low, yes-- totally negligible.

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and the smooth surface rolling resistance of the tires (assuming identical construction) should be identical.
It's a hair higher with the smaller tire, due to more energy being wasted by the slightly sharper bend at edges of the contact patch; but yes, the difference is too small to matter.

Offline playpiano1980

Re: TIRES - 700c vs 26 inch for long tours AND S&S Couplers
« Reply #37 on: July 27, 2010, 09:24:28 pm »
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He blamed the wheel breakages on a combination of rim brakes and over tensioning of spokes.   He also said that if he was doing something like this again, he'd use disc brakes.
Unlikely.  If the stresses from rim brakes were the cause of broken spokes - the front ones would break also (most of the braking in extreme stops is on the front)
+1.  Disc brakes put a lot more stress on spokes.

About the spoke-bracing angle though-- that makes the wheel a lot stronger, and is why tandem wheels are so much stronger, and famous wheel builder Peter White insists that 36 spokes are virtually always enough for a tandem when the wheel is built right.  I found out about him on the tandem forum where everyone raved about his trouble-free 36-spoke tandem wheels, including for loaded touring.  To get that wider spoke bracing angle though, tandem wheels use 145mm or 160mm dropout spacing, not 130 like road bikes'; so you can't just put a tandem rear wheel in a single road bike or even a touring bike.  Decades ago when tandems' rear dropout spacing was 135 or less, they had a lot more wheel trouble even with 40 or 48 spokes.  To further press the point about bracing angle:  For the last 9 years, Santana has been selling 16-spoke tandem wheels which have proven to be very reliable.  The dropout spacing is 160mm, and the spokes from the right flange go to the left side of the rim, and vice-versa, to improve the spoke bracing angle.



Quote
The inertial weight advantage [of the smaller 26" wheel] will be very slight as the smaller diameter wheel also has accelerate faster to reach the same road speed.
No, it's the same number of feet per second.  RPM itself is not the issue.  The myth of rotational weight is exploded in this wheel-science web page though.  You can see for example in the middle of the first table that the wattage savings in the uphill portion of a training ride if you cut the front wheel's rotational inertia in half (an absolutely huge reduction!) is only 0.004%.  IOW, it doesn't matter.

Quote
The very low hub rolling resistance will be slightly higher for the smaller wheel at any given speed
very low, yes-- totally negligible.

Quote
and the smooth surface rolling resistance of the tires (assuming identical construction) should be identical.
It's a hair higher with the smaller tire, due to more energy being wasted by the slightly sharper bend at edges of the contact patch; but yes, the difference is too small to matter.

Great informative post, what is your thoughts on mags compared to spokes regarding momentum?
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