Chainset change

[notmyrealnamebutclose]

I want to go faster. I now have a 12-28 7sp cassette new shimano IG51 116 links. Has a triple crank T42-34- ? (never used it no interest) Hybrid I would really like just a 2x chainring set with either a T48 or T46. Can I easily do that? Thing is it's a newish chain so would like to keep it ideally. Willing to sacrifice the big gear and make do with a 6 speed if it means the chain will still fit ? Will likely fit a new sq taper bb also but not much experience in them tbh. Know the bb shell size 66mm x 38mm there were some markings on it, a chinese brand that has long gone I think.google struggled to find anything very useful about it.

Edit. My bike is a hardtail (no idea which model) falcon, possibly 15yrs or more old, 6061 alloy frame with flat bars and already has 700c x 32c road tyres on alloy twin walled 19mm rims. I appreciate it is not a roadbike as such but that's where it works. I'm aware It will never touch 30mph (with me on it!) but I'm hoping to realistically achieve 25mph one fine day on the flats.

PS I am happy with my bike, I don't want a skinny wheeled drop bar roadbike thanks

 

[Sharky]

I want to go faster.

Sorry to tell you, but changing to a slightly higher gear, won't make you faster - you will just pedal slower!
There are other ways to get faster. Slicker tyres, a more aero position no surplus weight, clothing which doesn't drag. Training also helps. To improve overall avg speed, focus on the slower sections of your ride. Trying to be faster on the downhill sections, never compensates for the slower headwind or down hill sections.

Your BB will be a 68mm width.

If you really want to make those changes, best to discuss and get a quote from your LBS. Going the DIY route, you would need to buy the tools as well and the costs will not be dissimilar to the LBS option and latter will fit the correct sizes.

If your current ride is a flat bar hybrid, I would suggest saving your money towards a lighter road bike.

But good luck, it will be a good learning experience, which ever option you take.

 

[Alex321]

Sorry to tell you, but changing to a slightly higher gear, won't make you faster - you will just pedal slower!

That depends. If he is spinning out in the highest gear he currently has, then it will allow him to go faster - and going from a 42T chainring to a 48 isn't really just a "slightly" higher gear.

But I'd be inlcined to agree about going to the LBS if he is needing to ask those questions.

 

[Jameshow]

I'd suggest not changing your gears but your tyres this will make your faster than gear changes.

Put some 700x 32/35 slicks on and you'll notice the difference.

 

[T4tomo]

I want to go faster. I now have a 12-28 7sp cassette new shimano IG51 116 links. Has a triple crank T42-34- ? (never used it no interest) Hybrid I would really like just a 2x chainring set with either a T48 or T46. Can I easily do that? Thing is it's a newish chain so would like to keep it ideally. Willing to sacrifice the big gear and make do with a 6 speed if it means the chain will still fit ? Will likely fit a new sq taper bb also but not much experience in them tbh. Know the bb shell size 66mm x 38mm there were some markings on it, a chinese brand that has long gone I think.google struggled to find anything very useful about it.

just for completeness, how will you change gears with a 3x changer and a 2x chainset?

BTW the highest gear on my gravel bike is 38-11, very similar (a smidge lower) than your 42-12. I can pedal it to 30mph on the flat if I have the lungs / legs (and Ideally a mate in front of me).

Getting fitter and potentially a change of tyres may help your quest for speed.

 

[Sharky]

I've used a triple FD on a double. Was OK.

Another consideration is, what is the combination being used when on the flat, at a comfortable speed? Ideally, this would be the mid sprocket to give a smooth chain line and capacity to drop down a gear, and still keep to the big ring. Using a bigger 48" ring, will make you ride closer to the largest sprocket and you may find your self having to drop to the small ring more frequently to maintain a comfort gear. Could also be a risk of cross chaining.

You can probably deduce, that I've spent far too long studying gear tables for that perfect ratio. The irony is that, my favourite ride is a SS and I ride TT's on a fixed gear!

 

[T4tomo]

I've used a triple FD on a double. Was OK.

I meant with an 3x indexed shifter and 2 rings, I think your referring to the derailleur. That's where friction shifting comes into its own!!!

 

[Ajax Bay]

Simple solution for the OP. They have an 'MTB style' chainset with a 42 large ring on a 12-28 7sp cassette and are spinning out.
Swapping to an 11-28t cassette (see H-f link) will give an extra 9% 'speed' (for the same cadence).
Swapping to a 48-38-28 chainset will likely allow use of the current BB and offer a 16% increase in 'speed'.
See this gear calculator for the 'new' set up': https://www.gear-calculator.com/?GR...20,23,28&UF=2170&TF=90&SL=2.6&UN=KMH&DV=teeth
Old set up is: https://www.gear-calculator.com/?GR...21,24,28&UF=2170&TF=90&SL=2.6&UN=KMH&DV=teeth
For the same assumptions (wheel circumference and cadence (90, but many will boast of their impressive souplesse at 120rpm) spin out speed rises from 25mph to 30mph.
I would source one second hand or from Spa Cycles chainset (£41) who can specify the BB spindle length required: this one needs a 110mm; OP needs to measure theirs, which I suspect is 122.5mm). So likely new BB (inexpensive <£20) and sounds like a 68mm BSA threaded. As an aside, those cranksets offered also allow the OP to choose a crank length: anyone under 5'8" might benefit from a 165mm crank, and shorter, shorter. Easier to get the cadence up.
Front derailleur would need to be shifted up the seat tube (about 12mm).
The increased large/large would mean a new chain unless the current one is a bit long, or an extra two 1" links added in. Just changing the cassette to an 11-2x would not need a new chain, and that'd be an easy change, to see if this 'need for speed' is sustained.

 

[si_c]

@Ajax Bay has pretty much nailed it, the best way to do this is to change the whole chainset and get the front derailleur repositioned and re-indexed. If you're really after an increase in gearing, then a 48t might work, but I'd also suggest looking at a 50t top as well, you might find that shifting the gearing so high does mean you use the lower gear range as well.

In terms of quality and performance, the suggested Spa Cycles chainset looks pretty much spot on, but also consider the Spa Cycles TD2 Stronglight chainset as well, which has a few options for rings and size. You'll need a new BB for either of these too realistically to get the axle length correct.

 

[notmyrealnamebutclose]

Sorry to tell you, but changing to a slightly higher gear, won't make you faster

Thanks for the advice but....6 extra teeth over a T42 to a T48 is roughly an increase of 14% so one revolution at the crank is going to propel the rear wheel 14% further than the T42 which I'm sure you will agree is not to be sniffed at.

If you really want to make those changes, best to discuss and get a quote from your LBS. Going the DIY route, you would need to buy the tools as well and the costs will not be dissimilar to the LBS option and latter will fit the correct sizes.

No LBC anywhere near me, besides in the last 2 yrs I have built up quite a collection of essential bike tools aswell as many car/motorcycle maintenance tools I've bought over the years, as to pretty much be able to dismantle and reasemble any bike ever made! (within reason) lol.
I've already recently had the bb out for cleaning and fresh greasing

 

[notmyrealnamebutclose]

just for completeness, how will you change gears with a 3x changer and a 2x chainset?

If I were going from a 2x to a 3x I'd agree lol but can't see a problem going the other way
with the thumb shifter just using the first and second selectors. Yes the front derailleur will
need raising obvsly and the cable end will probably need some fettling, loosening.

 

[notmyrealnamebutclose]

Simple solution for the OP. They have an 'MTB style' chainset with a 42 large ring on a 12-28 7sp cassette and are spinning out.
Swapping to an 11-28t cassette (see H-f link) will give an extra 9% 'speed' (for the same cadence).
Swapping to a 48-38-28 chainset will likely allow use of the current BB and offer a 16% increase in 'speed'.
See this gear calculator for the 'new' set up': https://www.gear-calculator.com/?GR...20,23,28&UF=2170&TF=90&SL=2.6&UN=KMH&DV=teeth
Old set up is: https://www.gear-calculator.com/?GR...21,24,28&UF=2170&TF=90&SL=2.6&UN=KMH&DV=teeth
For the same assumptions (wheel circumference and cadence (90, but many will boast of their impressive souplesse at 120rpm) spin out speed rises from 25mph to 30mph.
I would source one second hand or from Spa Cycles chainset (£41) who can specify the BB spindle length required: this one needs a 110mm; OP needs to measure theirs, which I suspect is 122.5mm). So likely new BB (inexpensive <£20) and sounds like a 68mm BSA threaded. As an aside, those cranksets offered also allow the OP to choose a crank length: anyone under 5'8" might benefit from a 165mm crank, and shorter, shorter. Easier to get the cadence up.
Front derailleur would need to be shifted up the seat tube (about 12mm).
The increased large/large would mean a new chain unless the current one is a bit long, or an extra two 1" links added in. Just changing the cassette to an 11-2x would not need a new chain, and that'd be an easy change, to see if this 'need for speed' is sustained.

Great post and thanks for taking the time to post it. I need to discuss the bb further but for now let me
just explain that yes you're right, it was a mtb orientated bike. Originally had a T14-28 screw on set up.

This past summer I was left with no choice but to upgrade the rear wheel completely to facilitate a T12-28 free hub
for more top end spd as I was constantly spinning out (very flat where I live) however it made only a small improvement in top spd!
I did consider a 11-28 att but the choice wasn't there with the vendor who I bought from. The deal was a T12-28
cassette with the new 700c wheel and 7/8 sp chain, also has a QR skewer which I wasn't really looking for
tbh. I have plans to change that to a nutted axle eventually.
So with hindsight I should have probably stuck with the original rear wheel and focused on the larger size
chainset and longer chain.

 

[T4tomo]

If I were going from a 2x to a 3x I'd agree lol but can't see a problem going the other way
with the thumb shifter just using the first and second selectors. Yes the front derailleur will
need raising obvsly and the cable end will probably need some fettling, loosening.

I can! lol!

hint - check the spacing on a triple vs a double

Thanks for the advice but....6 extra teeth over a T42 to a T48 is roughly an increase of 14% so one revolution at the crank is going to propel the rear wheel 14% further than the T42 which I'm sure you will agree is not to be sniffed at.

you're assuming that your legs have the power to turn the cranks at the same cadence in the bigger gear and seem to have forgot that the biggest obstacle to going faster is the increased air resistance at greater speeds. Otherwise we'd all have 70T chainrings and cycle at 50mph.

 

[Ajax Bay]

@T4tomo You have to agree that on a hard surface in flat terrain and a hybrid bike (700c rear wheel), a 42/12 top ratio is rather low and a normal set of legs will spin out before they have reached the power they can sustain. Let alone a slight downhill or with any wind behind.

 

[T4tomo]

@T4tomo You have to agree that on a hard surface in flat terrain and a hybrid bike (700c rear wheel), a 42/12 top ratio is rather low and a normal set of legs will spin out before they have reached the power they can sustain. Let alone a slight downhill or with any wind behind.

That is a different point entirely. My point was there is a lot more to increasing top speed than simply increasing the gear size, which i'm sure you'll agree is correct.

Re your point, my gravel / winter bike has a top gear of 38-11 which is pretty similar to 42-12 (a fraction lower in fact 93/94 gear inches). Whilst it is quite spinney at 30mph (approx 110 rpm) it is doable (albeit takes some sustaining if riding alone). A more "normal" 90rpm returns 25 mph.

On my road bike with a 50-11 top gear, theoretically I could get to 40mph @110rpm but I cant, or at least I haven't found the right lead-out man yet! (in fact I now run a 12-29 cassette rather than 11-28 as a lower gears are more useful).

So whilst 42-12 is maybe a smidge low, I don't think its unduly so, particularly as I suspect its a flat bar hybrid, so a less aero riding position.