Gears

[audi321]

Hi all. My first post so please be gentle!

Due to age and bad knee I've bought myself an electric assisted mountain bike to try and get back into cycling after 20 years! It's got a single front sprocket with 52 teeth and a 6 speed rear cassette (14-28).

Problem is, it doesn't seem to be geared properly enough (i.e. my normal cycling speed is around 18-20 mph and my legs are going too fast). It's nothing to do with the electric part as this cuts out at 16mph.

So my question is, could I get a smaller rear cassette or a larger front sprocket/chainring? If so, what size should I go for?

Thanks all, I appreciate these electric bikes are frowned upon by the masses but it serves a purpose for me.

 

[summerdays]

Welcome, I don't have a problem with electic assist bikes, I think they have a very useful place in cycling and at some point I could see myself using one, though I think some see them as a bike shaped moped instead.

I'm not sure you need an electric assist bike? If that's your normal speed, then you are not using the electic assist, and instead you are cycling a heavier bike? Or is it the assist kicks in on hills when you struggle?

If you have a bad knee then I think you don't want to be pushing too large a gear either.

Hopefully someone more knowledgable on gears will be along to answer that question.

 

[cyberknight]

All the above and a 52 x 14 at 90 rpm which is the recommended rpm is 31mph
Also if its 6 speed its liable to be a screw on freewheel, you can get a 13 but they are harder to come by with the 14-28 being pretty much standard .

 

[audi321]

Thanks chaps, so is dropping down to a 13 at the back going to make any noticeable difference? I can get one of these for £30 but if I'm not going to notice it then I won't bother

 

[audi321]

Also, is it possible to put a 7 speed cassette on? I know the derailer would only reach 6 but I could live without the biggest cog

 

[cyberknight]

Thanks chaps, so is dropping down to a 13 at the back going to make any noticeable difference? I can get one of these for £30 but if I'm not going to notice it then I won't bother

I would learn to spin your legs faster ,if you think you cant go any faster than 20 mph in 52x14 your grinding your gears and it will not do your knees any favours.

Also, is it possible to put a 7 speed cassette on? I know the derailer would only reach 6 but I could live without the biggest cog

If your bike has a 6 speed freewheel then its worth checking the distance size of the gap between the rear drop outs as 6 speed is normally 126 mm and 7 speed + is 130 mm so it would not fit properly and a cassette will not fit on a freewheel hub if thats what you have.
freewheel

Cassette

 

[sreten]

Hi,

Its geared pretty well, I'm 50+ and have 14/28 and 52/42 and 700C wheels.
40 to 100 gear inches. FWIW I've done about 35mph on the flat (strong
wind behind) with 18/52 pedalling at a demonic rate, learn to pedal fast.

FWIW my other bike is a folder, 30 to 60 gear inches, and forces
me to pedal fast to go fast, i don't mind I can't go really fast on it,
it forces me to pedal fast, at a high cadence, good practice.

Which is what you want with a dodgy knee, high cadence, lower torque.

20mph on my road bike I'm nowhere near running out of gears.

For a MTB doing 20mph you want decent road tyres like :
http://www.chainreactioncycles.com/michelin-city-bike-tyre/rp-prod69985

rgds, sreten.

 

[audi321]

Thanks for all your replies guys. So it looks like the rear cassette is a non starter then. How about a bigger chainring? It's 52T at the moment, if I went to 56 or 58 would I notice that much difference at 20 mph? Does anyone know how to calculate these cadence rates?

 

[cyberknight]

Thanks for all your replies guys. So it looks like the rear cassette is a non starter then. How about a bigger chainring? It's 52T at the moment, if I went to 56 or 58 would I notice that much difference at 20 mph? Does anyone know how to calculate these cadence rates?

As i have already said if you have a 52 front and a 14 back you need to learn to spin your legs faster , at average recommended leg rpm with that set up you should be doing 26 mph .

 

[Nigelnaturist]

@cyberknight not many people spin a 97" gear

 

[cyberknight]

@cyberknight not many people spin a 97" gear

But the OP says he is running out of gears at 20 MPH on a 52 x 14 top gear , which i have stated twice that they should be spinning their legs faster to go faster rather than trying to get a bigger gear by changing chain rings or gears, after a quick play with sheldon brwon s gear calculator seems the op is pedalling at about 65 rpm to go that speed .
EDIT so they should be in a lower gear and pedal a bit faster to go the same speed and save their knees .

 

[Tigerbiten]

As it's a MTB, if the tyres are 32-559 then the gearing could be as low as 91" in top.
That ~21 mph @ ~80 rpm, which isn't bad as I tend to only spin at 80-90 rpm.
So without knowing the tyre size, it hard to workout the exact cadence.

Back to the OP.
As 1 tooth at the back equals 4 teeth in front in top it may be easier to find a 56 tooth chainring vs a 13 tooth block. Both give the same top gear.

 

[cyberknight]

Maybe the OP should be looking at his original bike choice .......................

 

[Big_Dave]

Go to http://www.bikecalc.com/speed_at_cadence put your tyre size in, chainring sizes and cassette/freewheel sizes this will tell you how fast you can go at different cadences. Although speed/cadence figures do not show how much power you have to put into turning the pedals. you are probably pedaling at 60rpm - 70rpm to get approx 18mph - 20mph with 52 14 gear(this depends on your tyre size), and your legs are pedaling too fast, if you had a bigger gear up front, you will pedal harder to achieve that same cadence but on a 56/14 gear at 60-70rpm your speed will be approx 19 -21 mph, not a lot of difference speed wise but a lot more effort to get it

 

[sreten]

Hi,

Just ride the bike, there is nothing wrong with the gearing. Just learn to spin.
With wind and inclines in my favour I can pedal 20mph on 20" wheels and 14/48.

rgds, sreten.