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Wheels size questions about rotating mass vs acceleration ?

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Wheels size questions about rotating mass vs acceleration ?

Old 07-12-15, 03:07 AM
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damo010
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Wheels size questions about rotating mass vs acceleration ?

Hi,

I,ve used both 26 & 700 and have seen / felt the advantages of both sizes and have long since been a fan boy of the 650B size as the best all round compromise between the two but I am wondering if any one can explain the science of rotating mass and acceleration for the two sizes at different speeds?

I find that the 700's work great on the more flat routes when i can get the bike above 15MPH but it always feels more sluggish bellow this speed and the smaller wheels feel better at a more modest touring speed <15MPH.

I know that the smaller wheel will accelerate better with less rotating mass but do they have disadvantages as higher speeds?

The 700 also feel terrible on long & slow climbs and i always feel that the 26's would be a better bet for more hilly riding.

Do the different sizes have a sweet spot for different speeds? just thinking out loud here!

cheers damo
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Old 07-12-15, 04:58 AM
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But, if you slash a tire & stop at a nearby mom&pop shop, what are the chances they'll have a tire?
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Old 07-12-15, 05:40 AM
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I've seen the math done on this issue and on the road it makes absolutely no practical difference. What you are feeling is likely placebo
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Old 07-12-15, 06:19 AM
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Originally Posted by damo010 View Post
...
Do the different sizes have a sweet spot for different speeds? just thinking out loud here!
...
Quite frankly I think that you are overthinking this.

Here is how I look at these options:

- 700c is hard to find in sizes wider than about 35 or 37mm. Yes the newer mountain bikes that are called 29ers use wider tires that makes availability of 700c better, but those tires might not fit in most 700c touring bike frames. I tried a 42mm tire on my 700c touring bike and the tires rubbed on the fender stays, am using 37mm wide tires.

- 26 inch tires are most commonly found in sizes of 1.75 or more, but are also easily available in 1.5 width by mail order. But good quality narrower tires are very hard to find and your choices are quite limited. The 1.5 width tires I have bought for 26 inch wheels are 40mm wide according to the size molded into the sidewall. Most 26 inch touring bike frames will easily take a 2.0 inch wide tire with fenders, some frames will take wider than 2.0.

I have toured on 37mm wide and 40mm wide tires, I consider them to be about the same. Of the above options, if you want a tire that is 40mm or wider, you are probably better off with a 26 inch bike. But if you want a tire that is 37mm wide or narrower, you want the 700c. And if you want a 37/40mm tire width, decide which wheel size you want based on other factors.

Other possible issue is that if you are not very tall, you might prefer the smaller tire to reduce toe overlap issues.

Try to find a 650b tire in a hardware store in a small rural town and you might decide that is not the best option.

Thus instead of looking at the math, I am looking at the pragmatic aspects of being able to buy what I want when I want it.

Last edited by Tourist in MSN; 07-12-15 at 06:23 AM.
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Old 07-12-15, 09:01 AM
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I,ve toured on both sizes and am well versed with the pro & cons of both wheels sizes and the limited options with 650B currently.

FYI I'm in Thailand at present and 650B is very popular here and old wisdom of 26" being available anywhere in the world is not as solid as it may of been in the past, when touring in Laos I checked all the bike shops / hardware stores on the way through and its mostly 24" and not a single 26" to be found to my surprise so I always carry a spare tire now so I'm not too bothered what size now as you either have a spare or not tbh!

What I do find is that the big wheels are very good on long road section but are a total pain in the ass when moving the bike on and off transport / in and out of hostels and up and down stairways. Plus they can be very sluggish to get going after you stop and at slow speeds when climbing.


Sure i'm probably over thinking it but hell we all have lots of time on the bike thinking about the dream set up and improving offences so we have carry an extra luxury item with a gain made somewhere else!

But i have often found a sweet spot on some wheels where they over come drag or have a certain amount of momentum at a given speed when a given amount of power seems to give more rewards than at a slower speed. but when fully loaded i seem to be too slow to get in to this efficient speed of the bigger wheels so would di be better on the smaller wheels if my average is 13MPH?

thanks all :-)
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Old 07-12-15, 01:47 PM
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Originally Posted by damo010 View Post
...
FYI I'm in Thailand at present and 650B is very popular here ...
I have heard that 650b is very common in regions that were French colonies decades ago. So you might be in an unusual situation.
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Old 07-12-15, 02:17 PM
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Know nothing about the arcane mathmatics that could scientifically analysis the question. Do know that the lighter the wheel/tire, the more nimble the ride. I tour on 700x28's. A carbon fiber wheel($$'s)and a 28 mm tire would be awesome. Forget disc brakes. Too heavy.

Every pedal stroke is accelerating the bicycle. The less mass to accelerate, the more effective the stroke. If a 26" wheel/combo is lighter than a 700 wheel/combo, than the 26" wheel wins, assuming all else is equal.

Or something like that.
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Old 07-12-15, 10:38 PM
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For some strange reason I ended up with a physics degree from a USA state Univ. If I was a tri-person going for kona or a regional masters calaber mtb / rodie I might actually worry about this kind of question.

This is the touring forum. Fit, parts replacement, durability, ease of adjustment and portability are a wee bit more important. Unless I have a good tail wind averaging 15 mph over a full day with four bags is not happening.

In terms of bike handling, if you are 5 foot nothing on a good hair day take a long look smaller wheels. Conversely a traditional double diamond frame running 26in wheels will look very odd when scaled to someone 6 foot three.
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Old 07-13-15, 12:01 AM
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Originally Posted by damo010 View Post
Hi,

I,ve used both 26 & 700 and have seen / felt the advantages of both sizes and have long since been a fan boy of the 650B size as the best all round compromise between the two but I am wondering if any one can explain the science of rotating mass and acceleration for the two sizes at different speeds?

I find that the 700's work great on the more flat routes when i can get the bike above 15MPH but it always feels more sluggish bellow this speed and the smaller wheels feel better at a more modest touring speed <15MPH.

I know that the smaller wheel will accelerate better with less rotating mass but do they have disadvantages as higher speeds?

The 700 also feel terrible on long & slow climbs and i always feel that the 26's would be a better bet for more hilly riding.

Do the different sizes have a sweet spot for different speeds? just thinking out loud here!

cheers damo
Many bikers claim that 622 mm (700C) wheels feel faster than 559 (26") or at least ride smoother over bumps. Riding both 622 & 559-wheel touring bikes I don't see a drastic difference. Wheels are certainly always a target to save weight due to importance of cutting rotating mass. Using lightest possible rims/tires will outweigh minor 622 vs 559 differences. Touring experts often recommend heavy-duty stuff but lighter riders can gain efficiency by experimenting with lighter wheels/tires.

Checked out carbon 559 rims, they're pretty expensive & not that much lighter than light alu rims?





I'm riding a 559-wheel Surly Disc Trucker & the ride feel in re wheels seems fairly close to previous Novara Randonneur w/622 wheels. I think to gain speed or efficiency one should switch to lighter rims & tires; wheel size itself a secondary choice. I'm a lighter rider & have never had much problem with rim damage even with lightweight rims. Touring experts often recommend heavy rims, 40-spoke etc. Practical advice yes, OTOH when folks often built their own wheels they had the option to try light rims; now wheels are usually bought as a package so experimenting is more difficult. Look at pro racers, they stick w/622 for ages while material & construction changes.

Last night I checked out carbon (559) rims for touring & there's limited availability + high cost.
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Old 07-13-15, 06:32 AM
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Originally Posted by elcruxio View Post
I've seen the math done on this issue and on the road it makes absolutely no practical difference. What you are feeling is likely placebo
+1. 26", 27", 28" wheels are close enough in diameter to make no practical difference. This subject comes up all the time in the folding bikes forum, where we regularly ride 16" and 20" wheels, and even there the difference in diameter makes hardly any difference.

You may feel a significant difference between your bikes for any number of reasons, including the quality of tires, gearing setup, etc; and let's not forget the weather.
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Old 07-13-15, 09:17 AM
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We're talking about touring...what ever feels better is better. The most important thing is to choose your talismans and believe in them, for the reasons you want to believe in them. When your talisman stops working get a new one
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Old 07-13-15, 01:16 PM
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I ride both 26 and 700 regularly, and frankly, I think there are too many variables to come up for a real answer. My bikes probably have wheels that are similar in weight, the 700 tires (28 slicks) are certainly lighter than the 26in 1.5in Marathons, but the 26 rims might be lighter. I dunno, the bikes feel so diff due to frame geometry etc and drop bar vs riser straight bars that are higher than the drops. The 26in bike steers much quicker than the 700 bike, at slow speeds and fast, so that changes how they feel too.

as someone else said, we are talking riding with carrying panniers and stuff, so in the end, the differences are surely pretty darn small, if there are any, and you wouldnt feel it any way plugging along with loads of stuff on the bike.
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Old 07-13-15, 04:25 PM
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All the bikes I ever had came with 700c wheels. That's road bikes, hybrid, cyclo-cross and a 29er. I should be done this week with my touring bike build.

It's a 90's TREK MTB. Got NOS Bontrager 26x1.75" tires wrapped on brand new Sun Ringle Rhyno Lite wheels. I'm not expecting a huge difference.

Should be a lot of fun rocking 26 inch wheels on a touring bike (conversion).
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Old 07-13-15, 04:57 PM
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don't know those tires, but putting lighter tires and lighter tubes generally is clearly noticeable with a given wheelset, or thats been my experience, but again, put a bunch of crap on a bike and its all kind a moot point in the end.
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Old 07-13-15, 05:14 PM
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The differences you think you're feeling between 700c, 650B, and 26" wheels are far more likely to be a consequence of the different bike geometries. Long-wheelbase bikes handle and feel better at low speeds, short-wheelbase bikes handle and feel better at high speeds.

The other big factor, as mentioned in at least one post above, is handlebar positioning relative to the saddle and pedals.

Compared to those two factors, assuming similar tire dimensions, the effect of wheel diameter is negligible.
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Old 07-14-15, 12:17 PM
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Originally Posted by mijome07 View Post
Got NOS Bontrager 26x1.75" tires...
I meant to say 1.6 inch.
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Old 07-14-15, 12:24 PM
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406-47 on my bike friday works well .. its rotational mass reduction is significant* Vs 29>26>650b is all bigger, maybe less significant.

* even with marathon plus tires and TR tubes..

Last edited by fietsbob; 07-14-15 at 12:28 PM.
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Old 07-18-15, 11:10 AM
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Thanks for the replies so far :-)

lets not dismiss the aggregate of minimal gains over a long distance! If we are talking minor differences (and i'm sure we are) these do add up and can make a difference to life on the bike after 100's of hrs!

I guess what I'm asking is about momentum really. Bigger wheels take a bit more effort to get them going but once the momentum is achieved they pay this back by maintaining this speed with less effort, this seams to be the case for 26 vs 29 in the MTB world but if we are already carrying a lot of weight then surly it better to have a wheels set that lends it self to easier starting acceleration and then relay on the load out weight for the on going momentum?

My back ground is XC / endure MTB and i can say for sure that smaller wheels feel better in slow speed situations and the bigger wheels plough on better once they have got going on the smoother or flatter ground.

I know that I stop a lot when touring to check maps, take in the view and so on and every time i need to give a big push to get the bike going again and more so with the bigger wheels and certainly on hill starts!

so in summery i do suspect that 26 or 650 is easier to live with on a tour with smaller size when moving the bike around and easier starting momentum, but this is purely subjective / instinctive so i was looking for some sort of proof either way to close off the line of thinking / guide my future planning.
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Old 07-18-15, 01:01 PM
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Isn't the whole 29 vs 26 thing emphasising the 29 wheels roll over stuff easier, obstacles etc?
Not being much of a mtn bike rider, I can't relate to the 26 vs 39er stuff.,but can certainly relate to less load accelerating easier, but of course that has nothing to do with rotational weight.
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Old 07-18-15, 02:28 PM
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I honestly can't feel any difference between how each of my derailleur touring bikes (a 26 inch and a 700c bike) accelerates when I have them loaded up with camping gear. I also can't feel any difference in how fast the 26 inch bike is when I use 40 mm wide tires or 50 mm wide tires, but my computer says that the 40 mm wide tires are faster.

When I want to see if all my wires are connected right on my dynohub powered light, I lift the front wheel off the ground and give it a spin with my hand to see if the light comes on. It takes virtually no effort to spin the wheel to see if the light is working and spinning the wheel like that is probably at about half of touring speed. Spinning two wheels up to touring speed should not take too much more effort than that.

I prefer my 26 inch touring bikes to my 700c bike for one simple reason, the 700c bike has a soft frame that develops a shimmy, which has absolutely nothing to do with your question.
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Old 07-18-15, 02:33 PM
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Originally Posted by damo010 View Post
I guess what I'm asking is about momentum really. Bigger wheels take a bit more effort to get them going but once the momentum is achieved they pay this back by maintaining this speed with less effort, this seams to be the case for 26 vs 29 in the MTB world but if we are already carrying a lot of weight then surly it better to have a wheels set that lends it self to easier starting acceleration and then relay on the load out weight for the on going momentum?
This is the theory, and it might actually work that way. An object in motion tends to stay in motion, so if you've got a higher mass spinning, it could theoretically spin longer. But also remember that nothing comes for free when it comes to energy. Smaller wheels usually mean smaller mass, and the less mass you have to push forward, the less energy you have to spend to do it. So basically, you spend more energy spinning up your bigger wheel because it's heavier, and you may "bank" some of that energy because you have now expended more energy, but in the long run, you will expend more energy to push more weight down the road, no matter the wheel size.

So ultimately, to my mind, momentum and rotational mass are non-starters. There is no question that a heavier wheel requires more energy to move it, and if a bigger wheel is a heavier wheel, the question is, "What do I get in exchange for my bigger wheel?" Momentum is nice, but it's still a net loss, energy-wise. What you get is smoother rolling. The angle between the tire and the road/surface is smaller with a larger wheel. It makes any irregularities less jarring. Currently my bikes are either 700 wheels or 20" wheels. My speed varies very little between the two sizes. The amount of cussing I do when I hit a pothole varies, though.

I think that's why mountain bikes and all terrain bikes are moving away from 26 inch tires. Partly I suspect it's marketing, but theoretically a larger wheel will handle rough surfaces better. But the sacrifice, as you point out, is that a larger wheel doesn't accelerate as well, which is a bigger problem when the terrain forces you to have uneven speed. I think that's why 29" has not taken over off-road bikes, and the newer trend seems to go towards the 650b, which is only slighter bigger than 26".
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Old 07-18-15, 09:09 PM
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Originally Posted by Rob_E View Post
I think that's why mountain bikes and all terrain bikes are moving away from 26 inch tires. Partly I suspect it's marketing, but theoretically a larger wheel will handle rough surfaces better. But the sacrifice, as you point out, is that a larger wheel doesn't accelerate as well, which is a bigger problem when the terrain forces you to have uneven speed. I think that's why 29" has not taken over off-road bikes, and the newer trend seems to go towards the 650b, which is only slighter bigger than 26".
I agree, MTBs have been around a long time, a bit weird that they only discovered the '29 rolls easier over bumps' thing. Most high-end MTBs have suspension anyway, no? For touring I'd like to see some builders experiment with elastomer damping. This would allow stiffer frames w/better handling & lighter high-pressure tires. Tour de France broadcast featured one company that built special elastomer-equipped bikes for the cobbles.
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Old 07-19-15, 08:20 AM
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If you are curious about effort to spin a wheel up to speed, put the bike on a trainer and keep the resistance set at zero (roller off the tire). See how many seconds it takes to spin up to touring speed. Multiply by two since on a trainer you only spun one of two wheels up to speed, that tells you have many seconds of effort it took to accelerate the wheels up to speed.

Then try the same on a bike with the other size wheels and tires.

Compare the difference between the two wheel sizes.

Then decide if those extra few seconds are important to you.
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Old 07-19-15, 10:59 AM
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It's all about accelerating mass. Every pedal stroke is accelerating the bicycle. With long distance touring, every ounce does count. The cumulative is very significant. And yeah, the more mass, the longer the coast. We've probably all noticed how a heavier riding buddy can coast down a long hill faster. Is it my bearings? Nah.
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Old 07-20-15, 10:12 AM
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Originally Posted by Tourist in MSN View Post
If you are curious about effort to spin a wheel up to speed, put the bike on a trainer and keep the resistance set at zero (roller off the tire). See how many seconds it takes to spin up to touring speed. Multiply by two since on a trainer you only spun one of two wheels up to speed, that tells you have many seconds of effort it took to accelerate the wheels up to speed.

Then try the same on a bike with the other size wheels and tires.

Compare the difference between the two wheel sizes.

Then decide if those extra few seconds are important to you.
Accelerating a bicycle with a hundred-something or two hundred-something pound human being on it up to speed bears pretty much no resemblance to spinning up a pair of unloaded wheels.
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