Chainset change

[notmyrealnamebutclose]

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

No you assume wrong! Also I'm well aware that air- wind resistance is going to have more of an impact with flat bars but it isn't that critical that it's stopping me riding just 5mph faster. We're talking about the difference
here which is between roughly 20 to 25mph not 30 40 50mph.
It's the gearing that's the main problem and I'm not that convinced there is going to be a significant difference in distance between the outer ring and smaller ring on the new 2x chainring (same brand shimano) If I'm wrong I'll own it

 

[Jameshow]

You could fit a ht2 BB and chainset which tend to be cheaper than a quality sq taper chainset. Probably get one for £25 tiagra?!

 

[notmyrealnamebutclose]

You could fit a ht2 BB and chainset which tend to be cheaper than a quality sq taper chainset. Probably get one for £25 tiagra?!

Thanks but not going to spend a lot on new chainset, found a shimano fc-ty501 with chain guard for £25 + postage
at Bikester shall ring them in morning to see what bb they recommend could combine postage then.

Edit: INB4 it's only a 46T

​

 

[C R]

No you assume wrong! Also I'm well aware that air- wind resistance is going to have more of an impact with flat bars but it isn't that critical that it's stopping me riding just 5mph faster. We're talking about the difference
here which is between roughly 20 to 25mph not 30 40 50mph.
It's the gearing that's the main problem and I'm not that convinced there is going to be a significant difference in distance between the outer ring and smaller ring on the new 2x chainring (same brand shimano) If I'm wrong I'll own it

I've used a double with a triple flat bar shimano indexed shifter and it worked fine.

 

[davidphilips]

Agree %100 with sharky, changing from a 42 front to a 48 chain ring would increase your top speed from about 25mph to 28mph at a cadence of 90 but really not very many could maintain 25mph never mind 28mph.
If you really want to try and up the gearing why not just fit a new cassette when you old one is due replacement with an 11 to 28.
My advice would be spin more and keep your gearing as is, for more speed better lower rolling tyres and more aero on your bike is the way to go faster.

 

[notmyrealnamebutclose]

I've used a double with a triple flat bar shimano indexed shifter and it worked fine.

Nice, so it's not that uncommon to do that then. I wonder what doubting tomo would say

 

[notmyrealnamebutclose]

Agree %100 with sharky, changing from a 42 front to a 48 chain ring would increase your top speed from about 25mph to 28mph at a cadence of 90 but really not very many could maintain 25mph never mind 28mph.

That's quite disappointing only a 3mph increase, are you sure? Hardly seems worth it if true!

If you really want to try and up the gearing why not just fit a new cassette when you old one is due replacement with an 11 to 28.

How much more top end would I potentially get going down to an 11t ?

 

[Sharky]

How much more top end would I potentially get going down to an 11t ?

Become familiar with gear tables, then you can calculate exactly what the ratios are.

As a guideline, a 4 tooth difference on the front chain wheel is about the same as 1 tooth difference on the cassette. So an 11t at the rear will give you what you are thinking of.

 

[notmyrealnamebutclose]

As a guideline, a 4 tooth difference on the front chain wheel is about the same as 1 tooth difference on the cassette. So an 11t at the rear will give you what you are thinking of.

Okay thanks. Thing is, there is slight play in the bb so thought would be a good time to replace the chain set that
I'm not that happy with atst. So we can establish that an extra 4t would potentially give us only a 3mph increase that
means I need a 48t which should unlock around 5mph.

As it was when I went from a 14t down to a 12t I unlocked just 3mph!

 

[Ajax Bay]

Great post and thanks for taking the time to post it.

Well go back to my post (#12) and actually comprehend it. It provides the answers to the questions you then pose (below) so I am tempted to assume you didn't understand the post or couldn't cope with the maths, or both.

[changing from a 42 front to a 48 chain ring - from about 25mph to 28mph] That's quite disappointing only a 3mph increase, are you sure? Hardly seems worth it if true!
How much more top end would I potentially get going down to an 11t ?

Are you sure? If true? Do you think 'we' just post this stuff for fun?
From 15mph you'd only get 2mph faster! Am I sure?
For the 12t >11t see post #12.

Become familiar with gear tables, then you can calculate exactly what the ratios are.

@notmyrealnamebutclose Go and access my post #12 (page 1) and open the gear calculator: have a play.
Then post your flat 25mph rides on Strava for us (just a few minutes would be fine).

 

[davidphilips]

That's quite disappointing only a 3mph increase, are you sure? Hardly seems worth it if true!

How much more top end would I potentially get going down to an 11t ?

If you changed from a 12 smallest on your cassette to an 11 then at 90 cadence you would be going at 27.2mph instead of 25, check the gearing out on speed at all cadences this is the the link, https://www.google.com/search?q=inch+gearing+and+cadence+speed+calculator
What sharky said stands true if you just up your gearing all you would end up doing is same speed but with a lower cadence and this would tire you out quicker and in the end you would end up cycling slower and taking more time to recover.

 

[notmyrealnamebutclose]

Go and access my post #12 (page 1) and open the gear calculator: have a play.

Well just having had a look at the GC link you kindly provided I don't see my shimano tourney tx derailleur on
the tab. What do you suggest I do I'm not familiar with using that graph. No harm in asking for peoples
opinions and knowledge (even if they do often conflate) I can see how people can get a bit frustrated when
relative noobs ask possibly mundane questions but plse bear in mind not every cyclist has the time patience or
even interest to analyse confusing graphs.

Then post your flat 25mph rides on Strava for us (just a few minutes would be fine).

?

 

[Ajax Bay]

Well just having had a look at the GC link you kindly provided I don't see my shimano tourney tx derailleur on
the tab. What do you suggest I do I'm not familiar with using that graph. No harm in asking for peoples
opinions and knowledge (even if they do often conflate) I can see how people can get a bit frustrated when
relative noobs ask possibly mundane questions but plse bear in mind not every cyclist has the time patience or
even interest to analyse confusing graphs.

The gear calculator link doesn't have derailleurs (RD) on it (so not surprised you couldn't find). No graphs there either.
RD have no bearing on top gear. Mundane questions - great. Answered. Answers doubted. Mundane Q asked again: not so great.
Conflation is good; congruence (see posts above) is better.
Context: 42 large ring on a 12-28 7sp cassette and are spinning out.
1) Swapping to an 11-28t cassette will give an extra 9% 'speed' (for the same cadence).
2) Swapping to a 48-38-28 chainset will offer a 16% increase in 'speed'.
'New' set up': https://www.gear-calculator.com/?GR...20,23,28&UF=2170&TF=90&SL=2.6&UN=KMH&DV=teeth
Current set up: https://www.gear-calculator.com/?GR...21,24,28&UF=2170&TF=90&SL=2.6&UN=KMH&DV=teeth
Have a play: you can move the 48t 'cog' icon to 46t and see what difference it make to 'top speed'. You can change the cadence to 100 (vice 90) likewise.

So we can establish that an extra 4t would potentially give us only a 3mph increase that
means I need a 48t which should unlock around 5mph.

No, your maths is failing here (not helped by some rounding/integer issues) - 'we' can establish that your statement is not the case. You need to work in ratios, not 'an extra x mph'.
12>11 = 1.091
42>46 = 1.095
42>48 = 1.14
Multiply your current spin-out speed (say 20mph) to get the 'new' spin out speed.
Cycling at 25mph rather than 20mph will require about 95% more power.
Best of (self-made) luck.

 

[notmyrealnamebutclose]

If you changed from a 12 smallest on your cassette to an 11 then at 90 cadence you would be going at 27.2mph instead of 25

Is that calculation relative to a 42t or 48t ch/ring?

Just to be clear I am stickiing with my 12-28t

 

[Sharky]

To give you a little more insight to speeds...

In the world of time trialling a 20 mph ride, either 10 miles or 25 miles, will be achieved by probably 99% of riders by the end of their first season.

But those achieving a 25mph ride in their first season is a very very low %. In my case, in over 500 timetrials, spanning over 50 years have only ever beaten 25 mph once. But at the tender age of 72, can still do a 10 mile TT at 20mph.

So you can see aspirations to increase speed from 20 to 25mph, will require gigantic effort.