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Need help understanding gears and tires

Old 06-11-22, 08:57 AM
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Marc_Diebold
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Need help understanding gears and tires

I could really use some help with this. I'm looking at replacing my 2015 Trek 7.4 FX with a 2022 Trek FX Sport 6, but I'm confused about two of the features, specifically the gearing and tires compared to what I'm used to. The crank on the Sport 6 is fixed at 40 T where the 7.4 FX has a larger ring of 48 T. Since the small ring on the cassette of the Sport 6 is the same size (11) as the 7.4 FX, I assume top speed is lower given the same watt effort. Also, the tires on the Sport 6 appear to be gravel tires, and they're larger - 700x40 vs. 700x32 with the 7.4 FX. I assume that also equates to a slower top speed. Overall the Sport 6 is advertised as the 'fastest' bike in the FX lineup, with "...every performance feature of a high-end road bike, with the added benefit of a flat handlebar for additional comfort and control." It does have a very important advantage of having a full carbon frame and wheels, which is very appealing to me, but overall I'm worried I might be disappointed that it won't be as fast as my current 7.4 FX. Are these concerns valid?
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Old 06-11-22, 09:49 AM
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Originally Posted by Marc_Diebold View Post
I could really use some help with this. I'm looking at replacing my 2015 Trek 7.4 FX with a 2022 Trek FX Sport 6, but I'm confused about two of the features, specifically the gearing and tires compared to what I'm used to. The crank on the Sport 6 is fixed at 40 T where the 7.4 FX has a larger ring of 48 T. Since the small ring on the cassette of the Sport 6 is the same size (11) as the 7.4 FX, I assume top speed is lower given the same watt effort. Also, the tires on the Sport 6 appear to be gravel tires, and they're larger - 700x40 vs. 700x32 with the 7.4 FX. I assume that also equates to a slower top speed. Overall the Sport 6 is advertised as the 'fastest' bike in the FX lineup, with "...every performance feature of a high-end road bike, with the added benefit of a flat handlebar for additional comfort and control." It does have a very important advantage of having a full carbon frame and wheels, which is very appealing to me, but overall I'm worried I might be disappointed that it won't be as fast as my current 7.4 FX. Are these concerns valid?
Hiya Marc,

Welcome to BikeForums. There are a lot of very helpful people here who can give you a detailed answer to your question, but the short answer is yes, the Sport 6 won't be as fast as the FX because the Sport 6 has a lower high gear. The high gear on the Sport 6 is 42x11 (chainring by highest cog) for 104 gear-inches with a 700c wheel, and the high gear on the FX is 48x11 for 119 gear-inches. The small difference in tire widths is not significant.

My question for you is, do you often, or rarely, use the 48x11 on the FX? That's a really high gear. If you seldom use it on the FX, you won't miss it on the Sport 6.

The FX has a 3x9 drivetrain (3 chainrings and 9 cogs) and the Sport 6 has a 1x12 drivetrain. Here's a link to a gear calculator that you can use to map out the two drive trains and see how they compare. Good luck.
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Old 06-11-22, 10:10 AM
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I would not be worried about fast and as expansion to BC's post, the Sport 6 has a 1X gear system, single front chainring on the crank, 11 speeds in back. 11 total gears. The 7.4 has 3 rings in front and 9 gears in back, 27 total. The "range" of gearing on the Sport 6 may offer a near similar high and low gear compared to the 7.4, but you have many fewer in between gears. Those missing gears can be useful when riding a gravel or paved rail trail when you just want to gear down (or up) in more incremental steps. The 1x11 system will have much bigger jumps between the gearing. I personally think that 1X system sucks for riding flat rail trail type rides. I would be looking at bikes with 2X systems - I.E. a 2 chainring crank in front. That plus an 11 speed cassette in back gets you 22 gears. Note that there are repetitive gears, so you don't get 22 "different" gears. A gear chart will show you. Note also that if your rides are in constant hills, up and down all day, a 1X system works OK as you are constantly shifting up and down the cassette to low and high gears. If your rides tend to be flat, then I would not get a 1X bike.

Last edited by Steve B.; 06-11-22 at 01:01 PM.
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Old 06-11-22, 10:11 AM
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Originally Posted by Marc_Diebold View Post
I could really use some help with this. I'm looking at replacing my 2015 Trek 7.4 FX with a 2022 Trek FX Sport 6, but I'm confused about two of the features, specifically the gearing and tires compared to what I'm used to. The crank on the Sport 6 is fixed at 40 T where the 7.4 FX has a larger ring of 48 T. Since the small ring on the cassette of the Sport 6 is the same size (11) as the 7.4 FX, I assume top speed is lower given the same watt effort. Also, the tires on the Sport 6 appear to be gravel tires, and they're larger - 700x40 vs. 700x32 with the 7.4 FX. I assume that also equates to a slower top speed. Overall the Sport 6 is advertised as the 'fastest' bike in the FX lineup, with "...every performance feature of a high-end road bike, with the added benefit of a flat handlebar for additional comfort and control." It does have a very important advantage of having a full carbon frame and wheels, which is very appealing to me, but overall I'm worried I might be disappointed that it won't be as fast as my current 7.4 FX. Are these concerns valid?
Generally speaking: yes. Not so much because of the tires, but the gearing - the top gear of the new Trek is significantly lower than your Trek. You can look at the gear calculator mentioned above and determine which gearing combination in your current Trek is equal (or close) to the top gear in the new Trek, ride your current bike around limiting yourself to that gear, and see if that lower top gear will work for you.

Tires are a different and more complicated story - a fatter tire could very well have lower rolling resistance than a skinnier tire, but the fatter tire will have more air resistance, but air resistance is less of a factor at slow speeds and more of a factor at high speeds.
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Old 06-11-22, 10:15 AM
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The only difference you might notice is spinning out on downhills at a slightly slower speed, maybe something like 40 mph versus 45 mph.

Otto
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Old 06-11-22, 10:19 AM
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Thanks so much for the insight.
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Old 06-11-22, 10:19 AM
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If you're like me, you will appreciate the lighter weight and feel of the bike while constantly wondering how to get those taller gears back. I have a road bike with 52/11 high gear and I use that combination a lot. On my old MTB I had 42/12 high gearing and ended up changing the front ring to a 48T to get more gear-inches because I like to go fast-whether coming down a hill or on a highway shoulder-I like speed. When I look at buying more bikes, the first question I ask is what are the teeth numbers. It's surprising how many people don't even know the gearing on bikes they claim to have ridden for years and are trying to sell. Good luck with your choice, whichever it might be.
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Old 06-11-22, 10:31 AM
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Originally Posted by ofajen View Post
The only difference you might notice is spinning out on downhills at a slightly slower speed, maybe something like 40 mph versus 45 mph.

Otto
We don't really know what the OP is comfortable spinning, but 48/11 vs 40/11 is a little bigger difference than that. At 110rpm cadence, its roughly 38 vs 32mph. I think at speeds in this range, I would definitely missing having the higher range.

Since the cassette goes though to 42 teeth, It might be worthwhile to see if a 44 chainring could be swapped in. You'd still have a pretty good low gear (equiv to a 34/32 roadbike combo).
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Old 06-11-22, 10:31 AM
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Bicycles are only as fast as the motor, which is you.

High ratio gears, more teeth on the front an fewer teeth on the rear the More muscle your legs will need.

Low ratio gears. Less teeth up front and/or more on the rear will be easier pedalling requiring less leg muscle.

For a given pedalling cadence (RPM) the higher ratio gears will move you faster. Depending on you leg muscle it might wear you out very quick.

Lower ratios let you climb hills with ease and accelerate quickly. So if you will be riding hills make sure you have the low ratio gears to get you up then without struggling.

If you ride often, say three times a week, your legs will get stronger quickly. So don't necessarily look for super low ratios you might only use a few months and seldom after that.

A good LBS person can steer you in the right direction with gearing if you converse with them about it seriously and not just as a off the cuff remark
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Old 06-11-22, 10:47 AM
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Originally Posted by Marc_Diebold View Post
Also, the tires on the Sport 6 appear to be gravel tires, and they're larger - 700x40 vs. 700x32 with the 7.4 FX. I assume that also equates to a slower top speed. Overall the Sport 6 is advertised as the 'fastest' bike in the FX lineup, with "...every performance feature of a high-end road bike, with the added benefit of a flat handlebar for additional comfort and control." It does have a very important advantage of having a full carbon frame and wheels, which is very appealing to me, but overall I'm worried I might be disappointed that it won't be as fast as my current 7.4 FX. Are these concerns valid?
In addition to recommendation to check into swapping in a different chain ring on the crank (44t), I'd agree on the tire choice. If you're looking for a fastish flatbar bike for road riding, I don't really get the 40mm tire spec. I read this blurb and got a bit of a chortle: "You want the fastest fitness bike you can get—one that can hold its own with any road bike out there. You want to keep up with faster group rides, put on more miles, set new Strava PRs, and leave a pack of roadies in your dust as you sprint to the town line." So why did they put on a gravel-specific textured tire on this model?

No reason you can't swap in your current 32mm tires on the new bike if you get it. It will reduce the bike's trail a bit as well to make a bit more nimble feeling but still out of the realm of feeling twitchy.

Last edited by Sy Reene; 06-11-22 at 10:54 AM.
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Old 06-11-22, 10:56 AM
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Originally Posted by Marc_Diebold View Post
Thanks so much for the insight.
Lotta numbers and strong opinions about drivetrain and gearing here at BF. Take your time, you can learn a lot. Here's a grade-school explanation of gears and gearing from Sheldon Brown, a respected bike mechanic and gifted teacher/writer. Have fun!
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Old 06-11-22, 11:30 AM
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Originally Posted by Marc_Diebold View Post
... Also, the tires on the Sport 6 appear to be gravel tires, and they're larger - 700x40 vs. 700x32 with the 7.4 FX. I assume that also equates to a slower top speed.
The 700x40 tires will be heavier and slower than the 700x32 tires.

The 40's might be ideal if you will ride on rough surfaces - but the 32's (or similar) will be faster on roads, most paved trails, -
and similar.

As mentioned in a prev post - you can swap to 32's. And 35's might be a good compromise size - or 38's.

I've spent a fair amount of time on 32, 35, and larger sizes on a similar bike. Found the 32's to be a tad small for some of our riding - so switched to 35's. ( Panaracer Gravelking SS 35 actually measured a bit over 36mm mounted - so the switch was ideal ),

In addition to reducing tire weight by switching from the 40mm to 32 or 35 - you can also use smaller tubes for additional weight savings. ( The common tube size step up is @ 38mm ; you can use the smaller / lighter tubes up to 35mm tire size before the larger size tubes are recommended for tire sizes 38mm and above ).
.
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Old 06-11-22, 11:35 AM
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Also, the tires on the Sport 6 appear to be gravel tires, and they're larger - 700x40 vs. 700x32 with the 7.4 FX. I assume that also equates to a slower top speed.
Maybe they are envisioning it being ridden in looser gravel. However you can replace tires easily with the width you prefer.

And take width arguments with a skeptical look. Some people seem to think that if a slightly wider tire is better then a really wide tire is best.

IMHO, that will probably be those that put comfort as the only criteria. A person really needs to try out different widths and compare themselves what works best for them in their riding surfaces and conditions.
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Old 06-11-22, 11:45 AM
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for reference - pic of a Cannondale hybrid fitted with 35mm Gravelking SS

( gearing is Ultegra 6800 50/34 crank driven through 11-30 Dura Ace R9100 cassette )
.
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Old 06-11-22, 12:12 PM
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I think Trek is saying the Sport 6 is the lightest FX in the 2022 lineup, so it's the fastest. They don't care about 2015 models. They probably don't want us to point out the ******** assumptions and - dare I say it? - lies in their marketing 'collateral'.
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Old 06-11-22, 02:06 PM
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Rolling resistance test of the same tire offered in different widths:https://www.bicyclerollingresistance...00-comparison\

Driving a bike @ 110rpm resulting in 38mph over the road speed? Turn pro, or you're going downhill.

"On downhills steeper than 6.5%, coasting in the aero tuck is faster than pedaling with 400 watts." - Jan Heine
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Old 06-11-22, 02:30 PM
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Originally Posted by SpedFast View Post
I have a road bike with 52/11 high gear and I use that combination a lot.
100 rpm (which most experienced riders would NOT call "spun out") is nearly 37 mph in that gear. If you are hitting that speed on a downhill, you will be faster in a tight tuck than pedaling. Otherwise I have a hard time understanding why you would be riding in a 52/11 "a lot."
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Old 06-11-22, 03:15 PM
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Originally Posted by KerryIrons View Post
100 rpm (which most experienced riders would NOT call "spun out") is nearly 37 mph in that gear. If you are hitting that speed on a downhill, you will be faster in a tight tuck than pedaling. Otherwise I have a hard time understanding why you would be riding in a 52/11 "a lot."
On the coast here it seems like I either have a tailwind heading out, or heading back. When I have that tailwind, I'm in high gear and cruising. I ride 6 times/week and sometimes 7 if I can get away with it. When there is no wind I cruise around 30MPH in 52/11. I treat every ride like a race, that's just me. So naturally I've built up the right muscles. I also love climbing hills. I pull around 8MPH on a 12% grade using 36/14 gearing. I have no idea what my cadence is, haven't bothered counting in a long while. I do know that it's a lot faster than when I just rode MTBs.
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Old 06-11-22, 03:33 PM
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Originally Posted by SpedFast View Post
On the coast here it seems like I either have a tailwind heading out, or heading back. When I have that tailwind, I'm in high gear and cruising. I ride 6 times/week and sometimes 7 if I can get away with it. When there is no wind I cruise around 30MPH in 52/11. I treat every ride like a race, that's just me. So naturally I've built up the right muscles. I also love climbing hills. I pull around 8MPH on a 12% grade using 36/14 gearing. I have no idea what my cadence is, haven't bothered counting in a long while. I do know that it's a lot faster than when I just rode MTBs.
If you want to treat every ride like a race, then you should work on your spin. Watch any race and check out the cadence of the racers. 30 mph in a 52/11 is 82 rpm. You can grind away all you like, but all of the research shows that you are riding at sub-optimal cadence.
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Old 06-11-22, 08:44 PM
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Here’s what the gearing looks like. The numbers on top are the speeds at 90 rpm. You can see that you are going to be losing at both ends with the newer bike. The 1x system has a higher low and a lower high which means that you will struggle more going up and coast more going down. You can still spin comfortably at over 30 mph on the triple (the 7.4 FX) while you are going to spin out on the 1x at below that speed. The FX 6 Sport is going to be a little lighter (3 lbs) which will make a smaller difference on uphills that having that low gear will.
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Old 06-12-22, 11:08 AM
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Originally Posted by KerryIrons View Post
If you want to treat every ride like a race, then you should work on your spin. Watch any race and check out the cadence of the racers. 30 mph in a 52/11 is 82 rpm. You can grind away all you like, but all of the research shows that you are riding at sub-optimal cadence.
When I first started riding road my cadence was sub 60. I was a terminal grinder. For me to be up to 80 and holding I feel like I have improved substantially. I do spin up higher on occasion, but I find it tires me out really fast, unless I'm coming down a grade. I have a gps mounted with spd and averages and I'm always trying to best myself. I'm in it for the excersize and I simply like riding. I pass younger riders all the time, sometimes even ebikes. I'm not trying to prove anything, I just don't like going slow and being stuck behind others. I average 150 miles/week, rain or shine. I'm sure the locals around here make comments about the old coot on his bike because they see me almost daily riding by.

Edit: I meant to thank you for doing the math on the cadence and speed for me. I find that helpful.
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