Tracer trike Conversion from fixed to 6 gear.

[stearman65]

I've begun a thread on this in the motability forum, but thought this was a more appropriate place for an answer. The rear fixed sprocket is 105mm dia' over the teeth (not sure how many teeth) it will/ could take 140mm dia'. The front chain wheel with the pedals is 80mm dia' & could take 130mm dia'. Currently, the fixed gearing is too low. I don't want to alter the front c/wheel if possible, I want to fit a 6 speed cassette with free wheel. Is there a formula for working out how many teeth to wheel diameter. From my old cycling days I remember the larger the front chain wheel, the higher the gear & visa versa for the rear rear sprockets. What size cassette would you suggest to match the front chain wheel, with the middle cog around the same or slightly higher than current. Hope this make sense.
https://www.flickr.com/photos/eric_shepherd/albums/72157671957784806

 

[Tim Hall]

Teeth are spaced half an inch apart (12.7mm). Your rear sprocket has a circumference of 105 x 3.142. Number of teeth is circumference divided by spacing, so 105 x 3.142/12.7= 26 teeth. Your chain wheel has 80 x 3.142/12.7 = 20 teeth. The proposed 130mm chainring will have 32 teeth, which is still quite low. You may ve a bit limited on the choice of 6 speed freewheels, as they're quite old tech.

 

[stearman65]

Thanks Tim. Halfords have the 6 speed freewheels on their web site, but I didn't want to change the existing 80mm chain ring as it's a bit of a pig. Now you've given me the formula I can hopefully work something out. Thank you.

 

[Ajax Bay]

Your current gear ratio is 80/105 = 0.76. If the wheels are 700c, then this is a 21" gear length. To get the same ratio (as at present) in the middle of a 6sp freewheel (it's not a cassette) you'd need a chainwheel of about 12 teeth (ie much smaller than at present) - assumes a 14,15,16,17,18, 20 freewheel.
I find the OP a bit confused but I don't think you can do this, because you may find a corncob freewheel (I have one) but don't think you'll find a 12t chainwheel. On the other hand if you want to have your current ratio as your lowest gear, then the freewheel I've mentioned above will deliver, with your current chainwheel.

 

[stearman65]

Hi Alex, thanks for the info, the current set up is too low for flat roads, which is why I wanted to emulate that around the middle of the set up. I won't be doing any racing or speed trials just the odd cycle path with gradual gradients. Forgive my ignorance, from what you are saying, is there no freewheel (where I can stop peddling) on a cassette? BTW The driven wheel is 24inch. From the pictures of my bike, the one showing the wheel hub, how would you suggest fixing the gear cogs to the wheel.
Regards.

 

[Tim Hall]

The freewheel and cassette stuff is just terminology. You can have a screw on freewheel, where the gubbins (technical term) that allows you to not pedal is all part of the six or seven sprockets that you screw on to the hub. Or you can have a bolt on freehub (which contains the gubbins) onto which you slide a 7, 8, 9, 10 or 11 speed cassette. Your wheel will be built for either a freewheel or a freehub & cassette.

With a 24 inch wheel, that sounds like very low gearing. (Goes off to look at your photos)

 

[Ajax Bay]

I can't see how a freewheel would fit onto that axle. And furthermore I can't see how you'd mount the derailleur to change sprockets, or that there is space for one. Sorry not to be more help. To help frame the problem though, it seems to me that your current gear length - which is 18" - is the lowest you want, not the ratio in the middle of the sprocket cluster but the ratio when the lasrgest sprocket (of 6) is engaged.

 

[Tim Hall]

Ok, having had a look at your photos and the Theraplay (tracer manufacturer's) website, this does look more than a bit tricky. It seems that your rear sprocket is bolted directly onto the axle shaft, so fitting a freewheel won't ve easy. The manufacturer's say a Shimano 5 speed can be fitted to the Tracker (is that what you have, although you say Tracer?) but importantly it can't be retrofitted and must be specified at time of order.

 

[stearman65]

I can't see how a freewheel would fit onto that axle. And furthermore I can't see how you'd mount the derailleur to change sprockets, or that there is space for one. Sorry not to be more help. To help frame the problem though, it seems to me that your current gear length - which is 18" - is the lowest you want, not the ratio in the middle of the sprocket cluster but the ratio when the lasrgest sprocket (of 6) is engaged.

Hi AJ
The reason why I think the present set up should be my middle ratio, I'm 76, had heart surgery last year, due for knee surgery this year & around 3 stone overweight, the current set up on the flat I can manage easily, a little higher would be fine.
Regards
PS. If you check out the picture links there are examples on there, the yellow Aussie trike being the simplest method to mount the derailleur.
https://www.flickr.com/photos/eric_shepherd/albums/72157671226656711

 

[stearman65]

Ok, having had a look at your photos and the Theraplay (tracer manufacturer's) website, this does look more than a bit tricky. It seems that your rear sprocket is bolted directly onto the axle shaft, so fitting a freewheel won't ve easy. The manufacturer's say a Shimano 5 speed can be fitted to the Tracker (is that what you have, although you say Tracer?) but importantly it can't be retrofitted and must be specified at time of order.

Hi Tim
It's the Tracer, which is pretty unique, I can't find any info on it at all. maybe it was a prototype that was discontinued. I'm expecting to have to do some welding to the rear tubes to mount the derailleur similar to that shown on the yellow Australian trike in the pics. Then maybe bolt the cassette to the existing gear wheel? or extend the axle & use the same method as the existing. I haven't dismantled anything yet, so I'm not sure if there are any bearings in the axle tubes.
Regards Stearman65
PS The US end is named Triaid & the UK end Theraplay. I found lots of Chinese variants with gearing, even wondered about getting the gear train insert from the yellow Aussie trike & fitting that. Another idea would be replacing the existing driven hub with a Sturmey Archer hub, but the chance of getting the gearing correct would be small.

 

[TheDoctor]

Personally, I'd sell the trike you have and buy one with gears. I can't see an easy way to get multiple sprockets onto your trike, or a rear mech. Used trikes on eBay go for about £200.

 

[mickle]

What the doctor said.

Like I said in the other thread, fitting a multi-geared set up to one of these is far from straightforward. We sell trikes of all kinds including, occasionally, used versions of this machine. It would be 'possible' to fit gears to it, presuming that you have some engineering skills - but it's not something that we would ever consider - it just wouldn't be cost effective. I'll have a look at one when I'm back in on Monday and see if an easy fix comes to mind, such as raiding the rear end off a geared one. But I don't hold out much hope.

 

[stearman65]

Hi The Doctor
I did a lot of research before I bought the Tracer, & I got it used from Ebay at a very good price, a fifth of retail. I toyed between this & a recumbent folding trike, but they are way out of my price range, also we live in a 1 bedroomed retirement flat, so my car is my shed / garage. What I bought had to be easily dismantled. We live in a flat coastal town so it is no hardship using the trike with the gearing it has, but I would like to take it elsewhere where gears could be needed. I've been an engineer all my working life, so this is a challenge to see if I, with some help can overcome the problem. Finally I had heart surgery last year & have a scheduled knee replacement later this year. I've just emailed Trike Bike Australia, who have a similar trike with gearing to see if they would sell me the rear assembly of their trike or alternatively put me in touch with the manufacturer.

 

[stearman65]

What the doctor said.

Like I said in the other thread, fitting a multi-geared set up to one of these is far from straightforward. We sell trikes of all kinds including, occasionally, used versions of this machine. It would be 'possible' to fit gears to it, presuming that you have some engineering skills - but it's not something that we would ever consider - it just wouldn't be cost effective. I'll have a look at one when I'm back in on Monday and see if an easy fix comes to mind, such as raiding the rear end off a geared one. But I don't hold out much hope.

Hi Mickle
I've just replied to a post from the Doctor, the Australian trike has a separate rear assembly with the derailleur attached. I was an engineer all my working life, so although not an easy fix, can be done. I've emailed the Australian company to ask if they would sell me the rear assemble or put me in touch with the manufacturer, thanks for your interest. If you have something similar, I have a local bike mechanic who may be able to attach it.

regards Stearman65.

 

[TheDoctor]

If you're a skilled engineer then good luck with it. I was aiming my reply at someone who didn't seem to be able to count the teeth on a sprocket. If changing the chainset is a bit of a pig, then fabricating and welding a rear mech bracket, and fitting a freewheel, would seem to be a step too far. Like I said, I wouldn't do it. If Mickle wouldn't either, then that's it settled. I've built many bikes, and got no end of notionally incompatible things working, and Mickle is a far better bike mechanic than I'll ever be. I'd replace the trike.