Gear teeth query

[Pageant]

Hi all,

As it is only in the last few days that I have got my hub kit up and working properly, I have only just come across this problem.

In order to fit the throttle for my kit it was necessary to remove the twist gear changer for the main chain drive (I had only ever used the largest of the three cogs anyway). I now run on 5 gears rather than the possible 15.

Now the bike is behaving nicely I find that when powered speed is up to 15mph my legs are working almost flat out in keeping up with the motor even though I am permanently on the largest chain wheel and using the smallest (5th) rear sprocket.

The large crank drive wheel has 48 teeth and the rear 5th has 14.

Would it be possible/easy to get a larger front gear than the 48 tooth one?

I reckon if I could use a larger than 48 tooth drive then I could quite easily improve my top speed without too much extra effort on the pedals.

If/When the battery runs down I should hopefully be able to compensate by using a lower rear gear than 5th (which it normally remains in when on electric)

Have you any advice please?
(sorry I dont know the correct terminology for parts I have spoken about but I think you'll get the gist !)

Thanks alot,
Richard

 

[Ian]

The big cogs at the front are called chainrings and are available up 52 teeth or larger, however not all are removable and those that are removable do differ in the fixings. The replaceable type are usually secured to the RH crank "spider" with 4 or 5 bolts. The important things to specify are the number of bolts and the PCD (Pitch circle diameter) of the bolt holes. That is the diameter of an imaginary circle centred on the bottom bracket and passing through all of the bolt centres.
Another way to gain higher gearing would be to change the freewheel for one with a 12 tooth small sprocket, this might involve going to a 6 or 7 speed and may be complicated by chain and shifter compatibility issues.

This site gives excellent advice on many aspects of bicycle gearing

 

[coops]

Hi Richard

I get the gist and its a common issue on electric bikes: I've found the easiest way to sort gearing is find what cadence (i.e. pedalling "rhythm") you're comfortable with, and choose any gear changes accordingly.

Since you've only recently returned to bikes and only just got your kit working well, you might want to try it for a while to see if your riding style "evolves"... its an individual thing, and to me 15mph at 60rpm cadence with your top gear would be comfortable for me on most bikes, and even 17mph at a 72 cadence would be fine (unless you're being economical with stating your top speed...!)

Otherwise, if you're sure you want to change gearing, you can either increase front chainwheel size as you say, which will shift all your gears up proportionally, including your lowest of the 5... or you could possibly change the rear freewheel on the hub motor - have you seen flecc's advice on rear freewheel choice for his Q & T-bikes? - and maybe cheaper too (depends if your rear gear changing derailleur mechanism needs changing too...).

A good range of gears is what's usually needed for ebikes, not the number or individual spacing so much. Just a rear freewheel change, if its replaceable, with smallest sprocket 12 teeth will boost your top speed at your current 15mph cadence by 1/6th i.e. by around 2.5mph to 17.5mph. If thats not enough, you either can change front chainwheel (too) or go for an 11 teeth smallest sprocket - it will wear more quickly though.

What size is your largest sprocket on the freewheel currently (teeth number), and what rear mech does it use, if you know?

Stuart.

 

[Pageant]

What size is your largest sprocket on the freewheel currently (teeth number), and what rear mech does it use, if you know?

Stuart.

Hi Coops and Ian, thanks for both your replies. Unfortunately it seems my chainwheels are riveted and not bolted to the spider, so no joy there then

But in reply to Coops, the largest sprocket on the freewheel has 28 teeth and the gear mech says Shimano SIS. When the kit was first delivered, the wheel had been fitted with a 6 sprocket freewheel rather than the 5 I had asked for. The wheel with 6 sprockets was far too wide to fit between the dropouts and they replaced it with the 5 sprocket one.

It sounds as though I might just have to stick with what I have got, its not a problem at all really, just me thinking I might be able to tweak a bit more speed out of it, some people are never satisfied eh?

Thanks again to you all,
Richard

 

[coops]

You're welcome Richard .

A 5-speed freewheel with 12-28 teeth would help as I said, if its available, EDIT: the 5-speeds seem to be 14T smallest, so 6-speed looks your only option... & it should be quite cheap - have a look at wiggle.co.uk, or a wider range 12-28+ would also work and give you lower bottom gear, but may require either a longer chain or rear mech replacement (also not too expensive or difficult), or both .

You might find in time that your pedalling speed adapts - 60 or 72rpm is not that high, although it depends on how well your hip is . Certainly it shouldn't be too difficult to fit higher gearing to a suitable bike if you find you do want to though .

Stuart.

 

[Pageant]

Thanks for that Coops, I shall take a look.

Richard.

ps. just noticed on bottom of main forum page Largest Number of people viewing was 225 on 29 June at 7.34am -Thats two hours before my first cuppa!

 

[Ian]

Unfortunately it seems my chainwheels are riveted and not bolted to the spider, so no joy there then

That's a shame Richard, it would be still be possible to replace the entire chainset, ie. chainwheels,cranks and possibly the bottom bracket. While that is quite an expensive solution there are often bargains to be had on ebay.

It's probably best to see how you get on with what you've got before making any drastic changes, but it's worth remembering that being able to make a substantial contribution with the pedals at higher speeds is likely to significantly increase the range.

 

[Pageant]

Thanks for that Coops, I shall take a look.

Richard.

:

Oh well, I've just read your edited post (only available in 6 cog).

Never mind, I'm still really pleased with it all as it is.

Regards,
Richard

 

[Pageant]

It's probably best to see how you get on with what you've got before making any drastic changes, but it's worth remembering that being able to make a substantial contribution with the pedals at higher speeds is likely to significantly increase the range.

Thanks Ian, I will stick with it at the moment but will make some enquiries about a poss change of entire chainset.

Meanwhile, A full tight fitting Lycra head to toe suit might just give an extra mile an hour......
Yep, I can see me in it already........ looking like Rodney Trotter in the Batman & Robin sketch

 

[Ian]

The Tour-de-France starts at the weekend, I expect to see a lot of lycra clad cyclists emulating their heros Might even try it myself

 

[Pageant]

The Tour-de-France starts at the weekend, I expect to see a lot of lycra clad cyclists emulating their heros :

I knew I could find a use for all that bubble wrap which came with my kit..... I can shape it to simulate calf and thigh muscles and put it in my lycra suit. Any left over can pad out chest, shoulders and arms.......... I will look like Arnie Shwartzenneger with a bad case of acne

Richard.

 

[coops]

I forgot to say Richard, that the bike speeds for pedal cadences I specified were all based on the assumption your bike has a 26" wheel, which it looks to be, but if that's wrong then you'd have to adjust the speeds proportionally to the size difference .

P.S. go easy on the lycra & bubble-wrap!

Stuart.