Folding Bikes - Disadvantages of small wheels over std bikes

I have just recently cycled two 100Km rides on my Birdy fitted with a Rolhoff hub. comfort wise no problems, but despite being reasonably fit, I couldn't keep up especially on the hills with normal road/touring bikes. Is this an inherent problem with 18" wheels and would I be better off on Audax rides using a 'normal' bike.

Andrew

There are races where people on 16" compete with full size bikes, in particular when climbing (downhills its more difficult). See, for example, Rob English from Bike Friday, http://bicycle-musings.blogspot.com/2008/06/csc-manayunk-hill-climb-time-trial.html
"Rob English, riding a titanium Bike Friday finished in first among the folders with a time of 1:35:22 (my time was 5:35:99) which was only about 9 seconds behind the race winner on a regular bike. Pretty impressive."

If your bike is geared properly to compensate for the small wheel circumference then you can hang with the big wheeled boys but accomplishing that seems difficult and often problematic with most folders.

But wait, you have a Rolhoff! That thing has wicked gear ratio/range! You shouldn't have had a problem on those hills. Hmmm... Odd. How many teeth does your chainring have?

...but despite being reasonably fit, I couldn't keep up especially on the hills with normal road/touring bikes. Is this an inherent problem with 18" wheels and would I be better off on Audax rides using a 'normal' bike.

Andrew


Uphill or downhill?

I find I am a bit slower in the flats and downhill but faster up hills on my small wheel folders.

You have really asked two not-quite-related questions.

Your relative slowness is probably not inherent to your 18" wheels. But it may be inherent to other aspects of your bike.

Note that the Moulton still has a world speed record, and riders using BF pocket rocket pros or Air Glides are able to achieve results that are very very close to those reached by riders using nonfolding road/racing bikes. This wouldn't be possible if there were something inherently slow about the wheels.

However, the bikes mentioned above are both very lightweight, have an aerodynamic cockpit with drop bars, etc., and have gears appropriate for racing.

Rohloff equipped Birdies weigh 28 lbs, IME have a fairly upright riding position, and don't have racing-appropriate gears.

So you may want to consider using a road bike the next time, but the reason to do so would be for the other advantages inherent in the design, not just because they have 700c wheels.

Although what you should *really* do is spend $4,000+ on a dura-ace equipped PR Pro, or maybe more on a Moulton, and ride that.

(It is also possible that you are slower than the other riders for reasons unrelated to your bike :@).

Uphill or downhill?

I find I am a bit slower in the flats and downhill but faster up hills on my small wheel folders.

Interesting.... Where I ride the terrain is full of short sharp hills with practically no flat bits between the ups or downs and I find when riding large wheel bikes that, compared to small wheel bikes, they carry more momentum from the downhill helping you up the first bit of the uphill, but are slower to accelerate down the first bit of the downhill.

Over all it seems to even out but I remember when asking around, before I bought the Pacific, someone was saying they found their Birdy hard up hills due to excessive up and down movement of the front when pushing hard and I had similar issues with my old Moulton APB. The Pacific simply does not seem to do this though what the difference is I am not sure, maybe the suspension design?

If you click on these 2 links (to the Strida website) you will find the speed difference between 16 and 18 inch wheels.

http://www.strida.nl/english/products.php?subpage=50

http://www.strida.nl/english/products.php?subpage=sx

I have a Dahon D3 Curve and a Specialized Crossroads comfort bike (about 9 years old). The SC is easier to pedal and travels faster than the DDC in my opinion.

If you click on these 2 links (to the Strida website) you will find the speed difference between 16 and 18 inch wheels.

http://www.strida.nl/english/products.php?subpage=50

http://www.strida.nl/english/products.php?subpage=sx



That's really nothing to do with comparing inherent speed differences between 16" (305mm) and the 18" (355mm) wheel sizes.. the difference in this particular instance is that the 16" single speed Strida is running a smaller diameter wheel, hence lower gearing.. so the overall speed will be lower for the same cadence..

Note to EvilV... I installed the 355/Kojak combination on the fake.. wow!! practically pedals itself now compared to the old 305/Maxxis combo I was running ... even though I'm going faster for the same cadence it feels like I'm in a lower gear and not putting out near the effort .. those slick Kojaks are fast..I'm actually finding myself using the brakes ..:lol:

Note to O/P .. if you're not running Kojaks on your Birdy.. try a pair .. who loves you baby!

If you click on these 2 links (to the Strida website) you will find the speed difference between 16 and 18 inch wheels.

http://www.strida.nl/english/products.php?subpage=50

http://www.strida.nl/english/products.php?subpage=sx

I have a Dahon D3 Curve and a Specialized Crossroads comfort bike (about 9 years old). The SC is easier to pedal and travels faster than the DDC in my opinion.

Have a look on here then see what you think: http://www.moultonbicycles.co.uk/heritage.html#recordsracing

Note to O/P .. if you're not running Kojaks on your Birdy.. try a pair

Bruce beat me to it. I was going to ask what tires you have on the Birdy. I swapped the stock tires for Schwalbe Stelvios, and there is a very noticeable speed difference. No problems doing long weekend rides with friends on full size bikes. I have a Capreo Birdy though, no internal gears. I don't know if it makes a huge difference - I use to ride my Sturmey-Archer 8-speed equipped Xootr Swift on long (60-70 mile) road bike rides and have no problems hanging with the pack either.

niggle - thanks for the link, I enjoyed reading it again. I wasn't making a point about Strida, just that I noticed it the other day and thought it was worth adding to this discussion.

For the type of cycling I do (minimum effort) I find that larger wheel bikes require less effort to go at the same or slightly faster speed than when I'm on my Curve. This may be because of gearing, I'm not sure? The larger wheel bikes have been more comfortable in basic spec than the Dahon with upgrades. This may be because of different geogmentry or because the larger wheels cushion the ride better? Again not sure but the differences between the larger and smaller wheeled bikes do add up and I feel in my opinion that to travel the same terrain and distance the large bike* is easier and more comfortable.

While I have owned many large wheeled bikes, I've own only one folder so my compasion may not stand true, particuly when compared to a Moulton.

joose, the Curve D3 has a very noticeable drag that requires more effort from the rider. I recently got a Xootr Swift and I immediately noticed the difference. I will be upgrading the crankset and bottom bracket soon to see if it improves a little bit.

Joako - I wasn't aware of the drag problem before. Are you saying it is caused by the crankset and bottom bracket? My understanding is that the Xootr Swift has 20" wheels compared to 16" on the Dahon. Does this factor at all in the improvement? Ps, I ride the Dahon at max pressure.

Joako - I wasn't aware of the drag problem before. Are you saying it is caused by the crankset and bottom bracket? My understanding is that the Xootr Swift has 20" wheels compared to 16" on the Dahon. Does this factor at all in the improvement? Ps, I ride the Dahon at max pressure.

No, it has more to do with the integrated gear hub. I flipped both bikes and the Xootr wheel spinned for longer than the D3 wheel.

niggle - thanks for the link, I enjoyed reading it again. I wasn't making a point about Strida, just that I noticed it the other day and thought it was worth adding to this discussion.

For the type of cycling I do (minimum effort) I find that larger wheel bikes require less effort to go at the same or slightly faster speed than when I'm on my Curve. This may be because of gearing, I'm not sure? The larger wheel bikes have been more comfortable in basic spec than the Dahon with upgrades. This may be because of different geogmentry or because the larger wheels cushion the ride better? Again not sure but the differences between the larger and smaller wheeled bikes do add up and I feel in my opinion that to travel the same terrain and distance the large bike* is easier and more comfortable.

While I have owned many large wheeled bikes, I've own only one folder so my compasion may not stand true, particuly when compared to a Moulton.

I agree with what you say re. the ride of small wheels and the effect this has on rolling resistance, however factor in suspension (tuned for road use) and things are rather different. With such bikes as the Reach, the Birdys or the Moultons you can run just as high pressures as the big wheelers and get an even better ride into the bargain. Also acceleration is improved by small, light wheels though this does mean they have a reduced flywheel effect.

I have a distinct impression my Birdy (Kojak front, Marathon Plus rear) is a bit slower than my faster bikes (Swift, Moulton APB), but it is very hard to know if this is perception only or real. I have com pared the Birdy against my Swift while commuting, and the difference seemed close to indistinguishable. But I can't shake that feeling that it is a smidge slower. For example just yesterday I rode the Moulton and today the Birdy, and it just seems the Moulton pedals a little easier.

Very hard to make an objective call in the absence of a rigorous Stig test.

The Pacific simply does not seem to do this though what the difference is I am not sure, maybe the suspension design?

Yes. The Birdy has two critical design points.
1) the rear pivot is not placed such that the chain force is directed onto it (which does eliminate pedal impact on the suspension). You can setup a front chainring to fit this, but mostly it does not (probably with Rohloff it is possible?).

2) the front suspension has the pivot behind the wheel axle. Modern designs are the other way round, e.g., German-A force kilo (Dahon Jestream XP) or Pacific Reach. And dampening is simple elastomere. Overall this design results in some 'dive in' on changes in weight distribution which does consume some energy. Best way to compensate is to remain in the saddle an keep a steady cadence with a round spin.

Also, as the front comes closer on hills, a long bar reach does help. You could try fitting a drop bar or a bullhorn, these bars help.

Going downhills at >60 km/h is not very stable on most folders. You need a stiff front, at least. Folders that feature that are Bike Friday, Swift, or Airnimal. Birdy's front construction is a bit twitchy and folding/telescoping handlepost isn't stiff enough. You can however replace it by some single piece fork plus ahead stem which will make it much lighter and stiffer (but affects folding of course). See Birdy thread.

Furthermore I think the Rohloff isn't very efficient uphills. It cost you ~3% efficiency plus ~1kg extra weight.

No, it has more to do with the integrated gear hub. I flipped both bikes and the Xootr wheel spinned for longer than the D3 wheel.

The Xootr's wheel can hold a much larger degree of rotational momentum than the D3 wheel. How did you know you put the same amount of energy into each?

If you had two bikes that were exactly the same (geometry, gear inches, weight, tire pressure, etc) in every way except for wheel diameter the difference in speed on smooth pavement would be almost nothing.

It is nearly impossible to have those two bikes.

I have a distinct impression my Birdy (Kojak front, Marathon Plus rear) is a bit slower than my faster bikes (Swift, Moulton APB), but it is very hard to know if this is perception only or real. I have com pared the Birdy against my Swift while commuting, and the difference seemed close to indistinguishable. But I can't shake that feeling that it is a smidge slower. For example just yesterday I rode the Moulton and today the Birdy, and it just seems the Moulton pedals a little easier.

Very hard to make an objective call in the absence of a rigorous Stig test.

Jur,

If you like...I'll be the Stig and test all your bikes....just send'em up here....you know where I live ;)

When I was on my Mu P8 w/more upright positioning, and 8spds, I was able to keep up w/full sized road cyclist, but w/effort. When I switched to my Xootr Swift, I immediately noticed the bike, and set up allowed me to again keep up w/full sized bikes, but now with MUCH less effort.

IMHO, I'd say the difference between my Mu & Swift, that made the Swift more effecient was:
- Less rolling resistince w/Durano's, compared to the wider Marathon's on the Mu.
- More gearing on the Swift to find that perfect gear/cadence. (20spd vs's 8spd)
- More foward/less drag riding position on the Swift, compared to the upright, 'draggy' Mu.
- Just my opinion, but I also felt it much easier to get a more powerful pedal-stroke on the Swift.

I don't own a full size road bike, but last week I borrowed a friends full size bike w/the same exact gearing as my Swift, both front & rear. Only differences were the wheel size. (okay...so the wheel size will change the gearing...but both bikes have 53/39 front & 12-25 rear)

We did the same lunch-course that I ride w/my Swift. Granted the 700cc wheels did up the gearing on the full size bike, I didn't feel much 'faster' on it, nor did it make it easier to keep up w/my friend on his full sized bike.

There's alot more to getting an effecient ride that just wheel size.
just my 2yens worth..

just my 2yens worth..

Which is worth more than 2 US ¢ (shock horror). :)

If you had two bikes that were exactly the same (geometry, gear inches, weight, tire pressure, etc) in every way except for wheel diameter the difference in speed on smooth pavement would be almost nothing.

It is nearly impossible to have those two bikes.

and totally impossible to find smooth tarmac where I live (hence my obsession with suspension).

Jur,

If you like...I'll be the Stig and test all your bikes....just send'em up here....you know where I live ;)Just send me a pic of you in white leather suit with FF helmet under your arm and I'll shoot them over. :thumb:

I have a distinct impression my Birdy (Kojak front, Marathon Plus rear) is a bit slower than my faster bikes (Swift, Moulton APB), but it is very hard to know if this is perception only or real.


The Marathon Plus is as slow as a wet week, particularly in small wheel sizes.

Just send me a pic of you in white leather suit with FF helmet under your arm and I'll shoot them over. :thumb:

Would a black leather jacket, jeans and Doc Martins do?

BTW, my Kawasaki ZR7 is quickly than any of your folders :p

BTW, my Kawasaki ZR7 is quickly than any of your folders :p

and the Kawasaki has only got 17" wheels, so I rest the small wheel case ;)

and the Kawasaki has only got 17" wheels, so I rest the small wheel case ;)


:thumb:

- Less rolling resistince w/Durano's, compared to the wider Marathon's on the Mu.
- More gearing on the Swift to find that perfect gear/cadence. (20spd vs's 8spd)
- More foward/less drag riding position on the Swift, compared to the upright, 'draggy' Mu.

I don't think these are the reasons. In fact the Marathon Racers are among fastest tires - you can pump them pretty hard. Also more gears have almost no impact, see single speed racers. You can ride the Mu P8 in quite streamlined position. Its a bit Graham O'Brien like ;-)



- Just my opinion, but I also felt it much easier to get a more powerful pedal-stroke on the Swift.

yes, the single piece main tube design of the swift might be stiffer. And if you have a very strong stroke, the flex of the Mu frame can absorb some energy. But this won't be much.
BTW, the last Smithfield Nocturne has been won by a Dahon MU SL rider. Second Airnimal. Then Swift. These bikes are all three fast. The Mu SL is a tiny bit faster than my MTB with slicks (don't have a full size racing bike to compare). But I feel quite a difference in speed between my Mu SL and my Mu XL Sport. I attribute it mostly to the gear hub and the wheelset, plus the stiffer handlepost on the Mu Sl (non telescoping). Also the pedals are important. Lastly the Pantour hub allows for better front traction and thus slightly faster cornering.

I don't think these are the reasons. In fact the Marathon Racers are among fastest tires - you can pump them pretty hard. Also more gears have almost no impact, see single speed racers. You can ride the Mu P8 in quite streamlined position. Its a bit Graham O'Brien like ;-)


yes, the single piece main tube design of the swift might be stiffer. And if you have a very strong stroke, the flex of the Mu frame can absorb some energy. But this won't be much.
BTW, the last Smithfield Nocturne has been won by a Dahon MU SL rider. Second Airnimal. Then Swift. These bikes are all three fast. The Mu SL is a tiny bit faster than my MTB with slicks (don't have a full size racing bike to compare). But I feel quite a difference in speed between my Mu SL and my Mu XL Sport. I attribute it mostly to the gear hub and the wheelset, plus the stiffer handlepost on the Mu Sl (non telescoping). Also the pedals are important. Lastly the Pantour hub allows for better front traction and thus slightly faster cornering.

Think you meant Graham Obree Peter :) Good points though...

- More gearing on the Swift to find that perfect gear/cadence. (20spd vs's 8spd)

How'd you get 20 speeds on a Swift? I've got 24 with a Sram Dual Drive, but I can't figure out a 20-speed.

yes, the single piece main tube design of the swift might be stiffer. And if you have a very strong stroke, the flex of the Mu frame can absorb some energy. But this won't be much.

As Sheldon Brown pointed out, the issue of frame flex 'absorbing' energy is a red herring: the energy does not get absorbed, it is fed back into the drive system as the flexed bit straightens out again (mechanical memory and all that, otherwise the frame part concerned would become permanently bent).

How'd you get 20 speeds on a Swift? I've got 24 with a Sram Dual Drive, but I can't figure out a 20-speed.

10 speed block with two chain rings? Or Schlumpf drive? My Pacific Reach has gone from stock 8 speed to 16 speed by adding a second chain ring etc.

How'd you get 20 speeds on a Swift? I've got 24 with a Sram Dual Drive, but I can't figure out a 20-speed.

53/39 rings on the front & 12-25 10spd cassette on the rear. Works great!
I was really wanting a dual drive for the simplicity, but the double ringed front was the easier, lighter route. Gear inch range isn't "huge", but the gearing/cadence for riding the in the sweet-spot is great!
Tuned the front derailer once, and no chain jump issues since. :thumb:

Aha--I forgot they can have derailleurs in the front now.

Aha--I forgot they can have derailleurs in the front now.

Yup, as an option. :)
The FD mount even has a pulley/wire to change the cable-pull from top, to bottom, since the cable can't be run from underneath the BB on the Swift.

Its interesting that you mention a Moulton, most of these rides are with a friend who has just recently purchased a moulton, he is certainly quicker uphill and also has the edge downhill, I think the slightly larger wheels and better suspension my help but on the flat we are evenly matched, Fitness is a contributory factor also keep swapping from a recumbent may not help.

Bruce beat me to it. I was going to ask what tires you have on the Birdy. I swapped the stock tires for Schwalbe Stelvios, and there is a very noticeable speed difference. No problems doing long weekend rides with friends on full size bikes. I have a Capreo Birdy though, no internal gears. I don't know if it makes a huge difference - I use to ride my Sturmey-Archer 8-speed equipped Xootr Swift on long (60-70 mile) road bike rides and have no problems hanging with the pack either.

I have replaced the stock tyres with Marathon Plus, I think that there is a slight trade off on speed, but so far no puntures

If your bike is geared properly to compensate for the small wheel circumference then you can hang with the big wheeled boys but accomplishing that seems difficult and often problematic with most folders.

But wait, you have a Rolhoff! That thing has wicked gear ratio/range! You shouldn't have had a problem on those hills. Hmmm... Odd. How many teeth does your chainring have?

I will need to check the chainring, it was the standard that come with the bike, I am still undecided whether the Rolhoff is as good as people make it out to be, yes there is a very good range of gears, but I cannot help but feel that there is greater resistance in the 1-7 gears, maybe after a few more miles on it, it will loosen up

Still waiting on the answer from the OP on whether he has problems going uphill or downhill...:rolleyes:

Unless conditions are exactly the same on exactly the same route, surely this 'faster' business is all a bit of an illusion?

Yesterday I cycled to work 30 seconds faster than today. Same bike though... 'Feels faster' is probably as accurate as it gets.

IMO the biggest disadvantage of small wheels is clearance when riding off-road.

Unless conditions are exactly the same on exactly the same route, surely this 'faster' business is all a bit of an illusion?

Yesterday I cycled to work 30 seconds faster than today. Same bike though... 'Feels faster' is probably as accurate as it gets.

"Faster" can be objectively measured but you're right that if you are comparing average speeds, you have to run the same route under the same conditions, only varying one factor at a time. The varying factor might be the bike, the rider, the time of day ... whatever you want to compare. You probably have to run each test several times to account for variables you couldn't control. Like, why were you 30 seconds faster? Maybe on the slower run, you had to slow for a pedestrian who wasn't there the second time. Or maybe you were tired. Or maybe 30 seconds is such a short time that it is just random. That's why statisticians have methodologies for figuring out if a difference of 30 seconds is significant.

yes, the single piece main tube design of the swift might be stiffer. And if you have a very strong stroke, the flex of the Mu frame can absorb some energy. But this won't be much.

People talk about frame flex absorbing energy on folders, but I wonder, does the handlebar or seatube really intercept any useful forces? You don't pedal with your butt or very efficiently with your arms, so why would anything need to be stiff except the bottom bracket? And wouldn't the bottom bracket be stiffer on a folder due to the lower top tube?

Just a thought.


As Sheldon Brown pointed out, the issue of frame flex 'absorbing' energy is a red herring: the energy does not get absorbed, it is fed back into the drive system as the flexed bit straightens out again (mechanical memory and all that, otherwise the frame part concerned would become permanently bent).

Bull****. Suppose you want to put a heavy package up on a shelf, except you have to keep lifting because the shelf keeps sagging because it's too flexible. Is the energy fed back into the "drive system"? Nope.

Another word for "memory" is hysteresis and the reason it's associated with losses is because unless your power source is in perfect sync with the memory delay your own force comes back to fight you, which increases the losses inside the source as it has to work harder to achieve the same output.

Think about it. It's like rowing a boat with a friend, except he's pushing when you're pulling. It's not a red herring, Sheldon Brown just prematurely declared aok after he missed the "leak".

People talk about frame flex absorbing energy on folders, but I wonder, does the handlebar or seatube really intercept any useful forces? You don't pedal with your butt or very efficiently with your arms, so why would anything need to be stiff except the bottom bracket? And wouldn't the bottom bracket be stiffer on a folder due to the lower top tube?

When climbing or accelerating I go out-of-saddle. The handlepost/bar flex becomes an issue.

Furthermore my Dahon has the central hinge. Don't know how well it transmits torsional forces, but a slight loss might be attributed to it (but I would not expect this to be more than 1%).

When climbing or accelerating I go out-of-saddle. The handlepost/bar flex becomes an issue.

Furthermore my Dahon has the central hinge. Don't know how well it transmits torsional forces, but a slight loss might be attributed to it (but I would not expect this to be more than 1%).

Yeah, but even out-of-saddle what percentage of total force is really coming from your arms? Or, to put it in another way, in the worst case scenario it can't be worse than riding in saddle, which some claim is more efficient anyway.

Moreover, I would not expect loses due to flexure of the central hinge to be more than 0.01% because I just can't see that part bearing/transmitting more than 1% of the useful forces. There's a video online somewhere of man riding a bicycle whose front and back halves are connected by springs instead of tubes and, except for the difficultly of controlling a bike with a changing wheelbase, he seems to move along just fine.

Of course, it also depends on technique. For example, if you ride pushing down on both pedals simultaneously you'll be lacking efficiency on any bike without rotor cranks.

Yeah, but even out-of-saddle what percentage of total force is really coming from your arms? Or, to put it in another way, in the worst case scenario it can't be worse than riding in saddle, which some claim is more efficient anyway.

I am testing my bike for a single speed conversion. And then you get into situations where arms contribute significantly. Periodically going out-of-saddle - that's what single speed efficiency is about. Stiff handlepost is a requirement.

Bull****. Suppose you want to put a heavy package up on a shelf, except you have to keep lifting because the shelf keeps sagging because it's too flexible. Is the energy fed back into the "drive system"? Nope.

I don't get how this analogy helps your argument at all: the shelf sags under the package's weight, then what? You have to keep lifting it? For what reason? Because you want the shelf to stay level? If you are lifting it the shelf becomes irrelevant as what we have is you holding up a heavy package, but the shelf returns to its original shape due to mechanical memory (unless it is permanently deformed) and as it does so it moves upwards, in the same direction as you originally applied the lifting force....


Another word for "memory" is hysteresis and the reason it's associated with losses is because unless your power source is in perfect sync with the memory delay your own force comes back to fight you, which increases the losses inside the source as it has to work harder to achieve the same output.

Think about it. It's like rowing a boat with a friend, except he's pushing when you're pulling. It's not a red herring, Sheldon Brown just prematurely declared aok after he missed the "leak".

Thinking about it :rolleyes: and I do not see that the energy changes direction as you describe: if you push hard on the pedal frame flex may allow the rear wheel to move closer to the bottom bracket, slightly. Then the mechanical memory of the frame straightens out again, pushing the rear wheel back, which pushes the bike forwards. Ok not fed back through the drive system exactly (my bu115hit not Sheldon's), but definitely not pushing against the direction of travel, so no, I do not agree with you and Sheldon remains a god :p