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Old 04-17-12, 09:13 PM   #1
krobinson103
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Difference in top speed speed between 44t and 48t at the front

My old bike has a 48t large cog at the front. My new mtb has a 44t. I've been running the new one as my exercise bike as the old is worn out enough that I know it can't stand up to the stress of 250km a week.

I noticed though, that while the new bike being newer has better brakes, smoother suspension, etc the top speed down my favorite hill at maximum safe output for the road is only 47.5km/h compared to the 52 km/h I got on the old bike.

I suspect this is because the gear ratio is slightly lower making it better for climbing/slower speeds but not so good if you want to travel faster. I went to the LBS and they say it would be possible, but expensive to put a 48t in place of the 44.

So... is the net gain in speed actually worth spending $200-$300 on? I'm tempted just to do an n+1 and add a roadbike to my stable for the days I want speed...
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Old 04-17-12, 09:24 PM   #2
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Not worth it. Learn to spin. A 48t is only 9% bigger than a 44t, so you need to cycle 9% faster to get the same speed. The power output will be the same, just a different energy source fueling the bike (aerobic v. anaerobic). With time you will as fast as you were with a 48t, but now with higher rpms should be able to hold that speed longer.

What is your smallest rear cog? Unless you can hold 90rpm with your highest gear combo then it is w/o question not worth it.

I thought the same thing some time back. I had a hybrid with the highest gear combo of 48x12. I switched out the 12 for an 11 to be 'faster'. Many miles later I am riding a fixed gear at 48x16 and am much faster than I was on my hybrid because I spin at 90rpm at top speed instead of 60rpm on my top hybrid gear.

A good test? Ride with your 44txsmallest cog for 10 miles and time yourself. The next day ride with your 44txsecond to smallest cog for 10 miles and time yourself. You might surprise yourself.
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Old 04-17-12, 09:53 PM   #3
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Use Sheldon's Gear Calculator. My biggest chain ring is 42t and I have as yet to attain the highest possible speed on the flats- I just don't want to spin that much.
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Old 04-17-12, 09:54 PM   #4
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What is your smallest rear cog? Unless you can hold 90rpm with your highest gear combo then it is w/o question not worth it.
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Old 04-17-12, 10:04 PM   #5
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Its either 12 or 14.. kind of hard to get an exact count. I've been working on spinning faster in the highest gear by gradually pushing my target speed up a notch every week. Started struggling at 18kph on the flat. Got it to 26-27kph with a little effort. I can push 30-32kph for about 2km before pain sets in. Working on pushing the pain threshold back and gradually making progress. I'm pretty sure that running off road tyres its going to take a massive effort to maintain 40kph plus for any length of time, thus I think I'm aiming to be able to comfortably cruise at about 35 and maintain that for the length of the ride. Think its going to take a few more months of torturing those muscles yet.

Down hill I can get to about 50, but then rather than my energy its my self preservation that kicks in. I'm not wearing any of the padding that I wear on the motorcycle and I know from experience that a fall at 25kph hurts. 50 has to REALLY hurt - especially wearing cycle shorts and a Jersey.
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Old 04-17-12, 10:18 PM   #6
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Can't you just replace the 44 gear to 48?
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Old 04-17-12, 10:20 PM   #7
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Mtb cogs have 4 bolts. The 'standard' cogs have 5 bolts. They tell me its hard to get a 48t mtb cog.
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Old 04-17-12, 10:35 PM   #8
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I used to have a 46T which is still 4 bolt shimano compatible. It was a hair faster but it takes more torque and more shifting in response to hills depending on the percent of load that it puts you at. Part of why most non-road bikes went 44 or 42 was because the extra percent of speed was deemed irrelevant under most conditions. A larger difference would be noted by going from 12 or 14(as stated) to 11 on the rear. With a 44t you should be able to get a respectable cruising speed. Personally 80-100 pedaling rpm(cadence) is my fast cruise which gets close to 20 mph. 48T would likely be too high percent of load to sustain in most conditions other than downhill combined with a 11T rear. The descent speed would be handy but how much of your routine would you be able to use it?
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Old 04-18-12, 02:15 AM   #9
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http://www.gear-calculator.com superior gear calculator. Unless you spend a significant portion of your ride at maximum speed, it doesn't seem like it's worth $200. With a larger ring, the gear spacing is going to be further apart.

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Old 04-18-12, 02:27 AM   #10
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Can't you just replace the 44 gear to 48?
Not necessarily. I was looking into this exact thing a year or so back, wanting to upgrade my 44t ring on the MTB to a 48t. The FD had limitations on the maximum difference between the large and small rings, and a minimum difference between the large and middle rings.

So changing 44-32-22 to 48-36-26 would have worked, but I didn't want to give up the 22t granny ring. Changing 44-32-22 to 48-32-22 would have worked in theory (just buy the 48t ring and swap them over) but the FD may have struggled to shift, or simply not shifted at all, with such a combo.

My LBS said much the same as people have already said here, although also mentioned that if I wanted a bike for speed on the road then starting from a MTB probably wasn't the best way of doing it. As it happened I had three more gears above the one I regularly used (I'd previously thought I only had two) and then I realised that if I had three more gears I didn't use because I wasn't fast enough to use them I figured there was no point trying to gear the bike to be faster until I routinely ran out of options in the highest gear.
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Old 04-18-12, 10:54 AM   #11
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I went the opposite direction with my Giant Cypress DX. I just bought a new crankset w/crank arms appropriate for my bottom bracket replacing the stock Suntour 28/38/48 with a Shimano M191 24/34/42. Cost $28 and I installed it myself. I don't know why it would cost $200 to make that change.
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Old 04-18-12, 02:32 PM   #12
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i searched for 48t mtb chain rings and got many results/.

now of course i do not know if they will work or not, but they are 4 bolt.
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Old 04-18-12, 03:17 PM   #13
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Not necessarily. I was looking into this exact thing a year or so back, wanting to upgrade my 44t ring on the MTB to a 48t. The FD had limitations on the maximum difference between the large and small rings, and a minimum difference between the large and middle rings.

So changing 44-32-22 to 48-36-26 would have worked, but I didn't want to give up the 22t granny ring. Changing 44-32-22 to 48-32-22 would have worked in theory (just buy the 48t ring and swap them over) but the FD may have struggled to shift, or simply not shifted at all, with such a combo.

My LBS said much the same as people have already said here, although also mentioned that if I wanted a bike for speed on the road then starting from a MTB probably wasn't the best way of doing it. As it happened I had three more gears above the one I regularly used (I'd previously thought I only had two) and then I realised that if I had three more gears I didn't use because I wasn't fast enough to use them I figured there was no point trying to gear the bike to be faster until I routinely ran out of options in the highest gear.
Thanx for the explanation and makes sense. I have thought about doing this before, but wasn't on the top of my upgrade list.
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Old 04-18-12, 06:15 PM   #14
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I suspect it would mean I would need to change out the front derailer as well. I don't think its up to the task of shifting a larger chain ring. One of the drawbacks of cutting costs a little and going entry level. I have the Sun race m50 24 speed drive train and it works great. On the road its smooth and fast enough, I can clog it with mud and it still shifts. But I think the answer to this one may be to train my legs to the maximum limits of the bike and then look at a different bike if I want more speed.

I tried shifting down a cog and spinning faster. You can indeed maintain the same speed with a different sort of effort. Been running 2km intervals at higher rpms for the last week or so to try and get the cadence up. I think its working. Today I managed to stay anerobic for the whole interval and the recovery time was minimal.
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Old 04-19-12, 03:41 AM   #15
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I suspect it would mean I would need to change out the front derailer as well. I don't think its up to the task of shifting a larger chain ring. One of the drawbacks of cutting costs a little and going entry level. I have the Sun race m50 24 speed drive train and it works great. On the road its smooth and fast enough, I can clog it with mud and it still shifts. But I think the answer to this one may be to train my legs to the maximum limits of the bike and then look at a different bike if I want more speed.

I tried shifting down a cog and spinning faster. You can indeed maintain the same speed with a different sort of effort. Been running 2km intervals at higher rpms for the last week or so to try and get the cadence up. I think its working. Today I managed to stay anerobic for the whole interval and the recovery time was minimal.
You're probably right about training being the best approach. Unless you're routinely using your highest gears and still needing more power there's not much to be gained by increasing the gearing.

If you do decide to look into it further check out the specs of your FD. Mine can cope with the standard 44-32-22 or a larger 48-36-26. Much larger than 48t at the front and I'd have to consider the clearance between the chainring and the chainstays as well as whether the FD could handle a chainring that size. It doesn't work too well if the teeth on the chainring act as a circular saw blade against the chainstays.
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Old 04-19-12, 03:54 AM   #16
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Is it a need for more power or simply the desire to go faster because I can? I think the later. Why else would we strive to ride faster averages? I looked at switching to semi slick tyres, they would be faster, but then I lose the ability to go offroad whenever I feel like it. I feel its time to put some cash away for the n+1 road bike. I'm sure my wife will love that one.
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Old 04-19-12, 04:38 AM   #17
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Is it a need for more power or simply the desire to go faster because I can? I think the later. Why else would we strive to ride faster averages? I looked at switching to semi slick tyres, they would be faster, but then I lose the ability to go offroad whenever I feel like it. I feel its time to put some cash away for the n+1 road bike. I'm sure my wife will love that one.
Increasing your gearing won't make you go faster in isolation. You need to be strong enough to turn the pedals in those higher gears. That was what put me off the idea of changing the rings on my bike - I was using my high gears but not the very highest gears. The reason I wasn't using those highest gears was because I wasn't strong enough to keep the pedals turning at a decent speed in those gears. I can ride in the very highest gear I've got but not at a sensible cadence, and if I am using the very highest gears I'm not strong enough to lay down a burst of power if I need it.

If I was routinely using the highest gears and constantly spinning furiously wanting more, then I'd have either regeared it or changed bikes.

If you want tyres that are fairly fast on road and will also cope with off road take a look at the Schwalbe Marathon Extreme. It won't cope with full-on mud baths as well as the full-on MTB tyres will but will certainly cope with gravel paths and a fair amount of mud, and rolls easily on the road. I did 110 miles on my MTB with a Marathon Plus on the front and a Marathon Extreme on the back.
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Old 04-19-12, 04:56 AM   #18
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I prefer to run the highest gear and just push through the pain. I'm slowly increasing the cadence I can maintain that way. I tried spinning faster a few gears down, but its just not my thing. Great for getting up the hills, but on the flat I'd rather be powering through. I'm sure its not the way to win races, but I don't intend to race anything but yesterdays time. I've also noticed running intervals in top gear is really helping build my leg muscles. To the extent that some of my work pants are getting pretty close to not fitting over my thighs.

I can run at about 70rpm continuous and push that to around 80 if I must for several kilometers. Any higher than that and its SERIOUS pain territory. Working on shifting those numbers to 80/90 with lots of training. I noticed that the uphill sections I used to shift down on are now pretty much optional. I can shift down for a bit more speed, or I can just power on up with no problems.

I saw some nice "small 8" patterened tyres in the LBS today. I think when I wear out my current set they will be my replacements. Enough grip to deal with gravel and some mud, but less friction on the road.
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Old 04-19-12, 05:06 AM   #19
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Regarding your rear cluster, you said it was hard to count the teeth on it. My cassette is made of helpful cogs that say things like "12T" on them. So it's easy to tell that it's a 9-speed 11-32t.

I'd hazard a guess if your small cog at the back is a 14t you'll gain a lot more by changing your cassette to include smaller cogs than changing your chainrings, and assuming your RD can cope with it it should be a whole lot cheaper too.

Changing from 44 to 48 at the front results in 48/44 = 9.1% increase in speed, all else being equal. Changing from 14 to 11 at the back results in 14/11 = 27.3% increase.
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Old 04-19-12, 07:05 AM   #20
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Thus a decent improvement... if the engine can run it without stalling. I don't think my legs are up to 48/11 just yet. I'll work on getting the cadence up some more and then consider the options. I did notice that the 2 smallest gears on the rear cluster actually come apart from the rest. It seems to me thats because they wear the most, but it also suggest they would be easy to change.
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