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dougy

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I have been reading about gearing and decided to check out what my bikes have.

The apollo orion 125cc has 15 front and 43 rear. (14" front, 12" rear)
The TDR 150 (140cc) has 14 front and 41 rear (17" front, 14" rear)

firstly, from what I have read 16 or 17 front and 37 back will be good for the 125 giving it better top end without a great loss down low. So how should I gear the TDR to compensate for the larger back wheel? or will the extra power mean it will still work?

Next problem.... finding rear sprockets to fit my bikes... the ones on ebay all seem to be smaller or larger bolt patterns then both my bikes....

These measurements may not be 100% spot on but should be close enough to identify the sprockets..... both have 4 bolt holes.

the apollo holes are approx 89mm apart from the holes closet and 127mm across to the opposite hole

the TDR holes are approx 50mm apart from the holes closet and 71mm across to the opposite hole

Please help me find where I can find 37t sprockets to suit!
 
i can tell you now you will never be able to find a rear sprocket for your apollo 125...I had the same problem with mine, and i ended having to get a new rear wheel that i knew i could find sprockets for....Sorry dude, they might have them now, but there was another user on here with the same problem not too long ago and he couldnt find any that were the right size :(

The tdr on the other hand, we should be able to get sprockets for. DHZ sell a variety of different sizes,http://www.dhz.com.au/shop/sprocket/37
remember its always a good idea to change your chain whilst doing the sprockets, plus you'll probably have to get a new (shorter) one to accomodate the new sprocket sizes. I would suggest the D.I.D NZ3 chain.http://www.dhz.com.au/buy/did-420nz3-gold-chain-120l/SW-33.GOLD420 .
What pitch is your chain? Pitbike chains are usually #420 or #428.
Also when measuring your rear sprockets, you need the size (mm) of the bore, and diagonals of the bolt holes, and to really do this accurately you should use verniers.
 
dam... should have mentioned they are both running 428. you did well finding those two links..... let me know if you can find any in 428
 
dougy said:
think I Found one for the TDR

http://www.ebay.com.au/itm/161039401180?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

The apollo is not looking so good..... what wheel did you end up buying blender?
Click to expand...

i was lucky enough to have bought a spares bike. the rear wheels was the same as an atomik nitrous rear wheel, and the sprocket size is quite common. i heard somewhere that the hubs are called "sdg" hubs? I dont really know. i cant find a rear wheel from a nitrous, this seller is what i use, he usually has more items at the end of each month. he strips atomiks down and sells the parts, so i've found him pretty helpful, and he also does TDR also :)
http://stores.ebay.com.au/Bikes-n-B...9009018&_sid=1079518518&_trksid=p4634.c0.m322
 
dougy said:
I decided to buy two of these 18t sprockets for a start

http://www.ebay.com.au/itm/260982314711?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

Won't be as tall as 17:37 but will improve the ratio on both bike significantly from where they are now
Click to expand...

dont you have to get your cases filed down abit to fit the 18 tooth sprocket? i was going to buy one aswell, but then i was told it would fit unless i did some case-modifieing. i can see what they mean, i got the 16 tooth instead, and its pretty damn close to the case!
 
my 17T sprocket fits easily on my Lifan, i think you'll have no problems with the 18T

although the 125 will struggle to take off with the 18T, and will definately be a slug out of the corners and accelerating.
 
I don't have any first hand experience yet with changing ratio's. I'm basing this idea on the discussion of gearing on this forum. A lot of people seem to suggest that 17t front, 37t rear is ideal as it gives a moderately higher top speed and the engines seems powerful enough that the apparent low down loss is not hugely noticeable.....

17t / 37t = Target Ratio 2.18

Apollo 125cc
stock: 15t / 43t = Ratio 2.87
Test: 18t / 43t = Ratio 2.39

TDR 140cc
stock: 14t / 41t = Ratio 2.93
Test: 18t / 41t = Ratio 2.28

So from the figures above, the 18t on the front of the 125 isn't really as tall as it sounds because of the large rear. its actually pretty close to running 15/37. once I get around to testing it I'll report back!
 
adding 1 tooth to the front sprocket, is like taking off 3 or 4 teeth from the rear.


with that bigger jump in front sprocket size (4Teeth), you may need to shorten your chain on the TDR 140


a 125 will struggle with that gearing, not enough torque, the 140 might just be ok.
 
Check here.. I have the Orion 14/17tire 125 and this guy has been a great help due to his site having pictures with measurements so you can see what you need. My bike didn't come with any paper work letting me know what specs the bike/parts are so I have had to measure and rig ever since I bought it. It was my first pit bike buy and a lesson learned. Good luck..

http://www.pccmotor.com/rear-sprockets.html
 
dougy said:
I don't have any first hand experience yet with changing ratio's. I'm basing this idea on the discussion of gearing on this forum. A lot of people seem to suggest that 17t front, 37t rear is ideal as it gives a moderately higher top speed and the engines seems powerful enough that the apparent low down loss is not hugely noticeable.....

17t / 37t = Target Ratio 2.18

Apollo 125cc
stock: 15t / 43t = Ratio 2.87
Test: 18t / 43t = Ratio 2.39

TDR 140cc
stock: 14t / 41t = Ratio 2.93
Test: 18t / 41t = Ratio 2.28

So from the figures above, the 18t on the front of the 125 isn't really as tall as it sounds because of the large rear. its actually pretty close to running 15/37. once I get around to testing it I'll report back!
Click to expand...

good on ya mate, you seem to know what ur doing, front sprockets are pretty cheap :) Btw , did u make sure to measure your sprocket shaft width before you bought the front sprocket? pitbike sprocket shafts are usually 17mm or 20mm, they are all different, so it pays to get out and measure it with a set of veniers :)
 
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