Changing Gear system on Folding bike

[Medic101]

Hi Guys,

Just a quick question I've been offered a folding bike from someone I know. It's a Tern bike but noticed it had twist gears rather than shifters, dose anyone know if its possible to replace this system? Sorry I'm sure its a simple answer but I'm not really firing on all cylinders at the moment.

[sreten]

Hi,

Not really worth replacing but it can be done.

rgds, sreten.

[Medic101]

When you say its not really worth doing, what exactly do you mean by this?

[531colin]

Hi Guys,

Just a quick question I've been offered a folding bike from someone I know. It's a Tern bike but noticed it had twist gears rather than shifters, dose anyone know if its possible to replace this system? Sorry I'm sure its a simple answer but I'm not really firing on all cylinders at the moment.

Which one? http://www.ternbicycles.com/bikes A lot of the current ones (on their website) are showing this grip, so they are not twist grips.....http://www.ternbicycles.com/features/biologic-arx-grips-t-tool
For almost any Shimano gears, you can get a shifter that's not a twister, and its just a case of new shifter, new cable, new handgrips. I suppose there might be a gear somewhere that you can't get a shifter for....?

[markfh]

I assume that the bike you are being offered has a rear derailleur. If so it is likely to be either a Shimano or a Neos. As far as I am aware both use the same pull ratio although the Neos is a "rapid rise" design, so it works in the opposite way to most dérailleurs. If the bike currently has a twist shifter is could well be a SRAM one, but don't let this confuse you as SRAM make some shifters (both trigger and twist) that are designed to work with the Shimano pull ratio (2:1) rather than SRAM's normal one (1:1).

I have a Dahon folder which also uses the Neos rear dérailleur and I swapped the originally fitted SRAM twist shifter to a SRAM trigger shifter (one designed for the Shimnao pull ratio) as I personally don't like twist shifters.

The important thing is to match the number of gears. If you change shifter from a twist to a trigger you will also need to change the grip on that side. If the rear derailleur is a Neos then you probably won't be able to find a "matching" trigger shifter so you may find that the gears work in "reverse" - not insurmountable just takes some getting used to.

Also one option is to change the twist shifter and the brake lever on that side for a Shimano integrated one. Assuming that you have either 7 or 8 gears then a compatible Shimano integrated shifter can be got on ebay/amazon for about £10-12.

Just to add to the above, according to the SRAM web site the SRAM Attack and TRX trigger shifters and the SRAM Attack, Centurea and MRX twist shifters use the 2:1 Shimano pull ratio (for rear dérailleurs).

[Medic101]

Thanks for the replies guys much appreciated, markfh that seems a nice informative post I will read it again with my attention tomorrow when I'm more awake but seems like I understand what you are saying. I managed to find the make of the bike and its the Tern Link P24h so will need to see what components its using and cross reference that with your post

[Brucey]

there is a review here;

http://wheelosopher.com/the-bike/tern-link-p24h-the-little-bike-that-could/

If yours is like this then it has a Neos Rear mech, 8s SRAM MRX gripshifter plus a 'Neos' branded sturmey archer 3s hub that is operated by a LH gripshift. This lot gives 24 speeds.

The Neos rear mech is a reverse action rear mech ( aka 'rapid rise' if it were a shimano unit). This will make the shifting 'weird' in any event, gripshift or not, as will the 3s hub gear which will (I think) also work in the reverse from most triple chainset front mechs.

So the usual arrangement for a 3x8 drive (with derailleurs) is that the x3 shift is bottom normal and the x8 shift is top normal. On this bike I think that both will be the other way round.

My suggestion is to just learn to ride the bike as it is if you can and to live with it. You could replace both shifters with trigger units but it will be a lot of faffing about for relatively little gain.

cheers

[al_yrpal]

If you are thinking of keeping the bike long term how about replacing the rear wheel and current gearing with this which includes the shifter and cable.
http://www.amazon.co.uk/gp/product/B00A ... M896J0595Y

Al

[mjr]

Just a quick question I've been offered a folding bike from someone I know. It's a Tern bike but noticed it had twist gears rather than shifters, dose anyone know if its possible to replace this system? Sorry I'm sure its a simple answer but I'm not really firing on all cylinders at the moment.

I've replaced a trigger on my Dawes Jack folder with a friction lever shifter because the adjustment seemed to drift with each fold, the trigger was so big it was very easy to catch in the fold and you can tell the gear on a lever by feel (important at night or on busy roads when I don't want to look down). As long as the pull ratio is close enough, it'll work fine. Just in case, try not to destroy the twist shift and you can always put it back and sell the new shifter as nearly-new.

[markfh]

Just to help you "size up" the job if you are still considering the change when I changed the twist shifter on my Dahon, I managed to keep the original gear cable outer although I did change the inner as the new shifter came complete with an inner and it was easier to change rather than extracting the original inner from the twist shifter and worrying if it would be long enough .

Also assuming that the left hand shifter is a "standard" 3 speed and as SRAM use the same shift ratio for front dérailleurs as Shimano MTB ones then it may also be possible to use a Shimano left hand trigger shifter as well. No only are Shimano individual STI levers available at a reasonable cost but there is currently a 3 x 8 pair on amazon for £20 (Shimano Acera STEF65 EZ Fire 3x8 24 SPEED Sti Gear & Brake Bicycle Lever set), although it would be worth checking that the shift levers will not foul anything when folding or folded. One possible advantage of the Shimano Acera STI shifters is that both left and right appear to have barrel adjusters for the gears so that any small changes due to folding/opening can be dealt with whilst in motion.

[sreten]

When you say its not really worth doing, what exactly do you mean by this?

Hi,

I meant there is nothing inherently worse on a folder about twist shifters than levers.
For both types the overall quality of the system is more important than the execution IMO.

FWIW I recently rode an old 3 speed folder where the whole of the right handgrip
was a twist shifter, annoying or what ? but you would get used to it after a while,
and avoid the the false shifts you get riding around at first, being unused to it.

I just meant if they worked well enough it wouldn't bother me, I'd learn to use them.
I'm aware they are nightmare on proper MTB's, but they are not on road folders.

rgds, sreten.

[Medic101]

thanks everyone for your comments there is a lot to think about and consider certainly interested in what al_yrpal has suggested although I'm not going to lie I'm not entirely sure what benefits that would offer me if any. As I say a lot to think about and a number of obstacles and challenges that need to be looked at. If anyone has experience in upgraded Tens I be really keen to hear about it.

[karlt]

I've replaced grip shifters on kids' bikes because they're often too stiff for little hands, but I think the "ghost shift" problem is overstated and they're essentially cheap and effective.

[Brucey]

if you are not that familiar with bicycle mechanics, it might be just as easy to sell the bike you have and buy a different one as it would be to 'upgrade' -actually modify is a better word- the existing one.

Do bear in mind that not all 'upgrades' are considered such by others; more gears, fewer gears, trigger shift or twistgrip, some prefer one over another. I can think of several reasons why any changes to the spec of your tern might be considered a downgrade in fact.

For example, if your standard condition bike falls over and the rear mech hits the ground, the rapid rise neos rear mech will pull the gear cable tight as it is pushed inwards. With most styles of gripshift this will cause the shifter to move before the mech is damaged. But with typical trigger shifters this won't happen; something will likely break instead.

Also; trigger shifters often stick out from the handlebars more than gripshifts, which can impede the fold.

So whilst I am not a big fan of gripshifters, I don't think they are necessarily a bad choice in this case.

cheers

[Medic101]

It is an interesting point you raise Brucey and one I spent about an hour on the phone to Evans discussing, I certainly have no intentions of getting rid of the bike any time soon, its just there a few things that I would like in an ideal world to change to make it more suitable to me. For instance in an ideal world I'd love to have quick release wheels but due to the internal hub that would not be an option or least everyone I've spoken too has said it would not be. The only thing this bike offers me is that as I have not gone out and spent 100's on buying a bike it gives me a greater opportunity to develop my technical knowledge and maintenance skills, having spoke to my LBS they have said they would show me and coach me how to change the shifters myself for a small fee, so the long term benefits are not just having a bike more to my liking but to enhance my overall knowledge of the other side of cycling that I have not been able to acquire until now.