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39T rear sprocket

24K views 65 replies 27 participants last post by  aj7840 
#1 ·
Like others in forum want to gear down bike. Was told by Triumph shouldn't put a larger sprocket on rear wheel as it will throw off the traction control and ABS. Does anyone know if this is true.? Are the sensors on the rear wheel or front? Will the Daytona or old 900 carrier work on the rear wheel?
 
#2 ·
Sounds illogical. Putting a larger wheel on the back might cause issues, but I don't see how the sprocket would make any difference. Perhaps they misunderstood your question?

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#3 ·
I agree. Half the time the dealership people don't know much more than anyone else. They speak the language of "don't change the bike" unless you want to purchase chrome accessories. ;)

People have been changing gearing for years. There are no sensors on the sprocket. Sounds like the bike pulls its speed from the ABS ring. Swap away.
 
#5 ·
Just confirming what everyone said above. TC on these bikes kicks in when the back wheel spins at a different speed (faster) than the front wheel, for example hitting a patch of gravel makes the rear wheel spin and kick out so the TC jumps in and pulls back on the throttle. It also gets in the way of fun stuff like burnouts and wheelies so gotta turn it off when you feel like being a hooligan.

Changing the sprocket size affects gearing, but your wheels still turn at the same speed when riding along normally so no issues with TC and ABS.
 
#6 ·
Just got off the phone with Supersproxusa. Look like the Daytona 675 used a six bolt sprocket. Same as the T120. They can custom mill them in one day and offer free shipping but. . . . . . . they are $114.95. ouch! Here is the link below if anyone wants to risk. I am ordering mine today. . . and will let y'all know.

https://www.supersproxusa.com/products.php?cat=1115500

You have to scroll down to the CMC on demand section and choose 39T and the color you want.
 
#7 ·
It should fit. I machined my own 39T sprocket (on the right) and took detailed measurements of the stock sprocket.




I looked on JT Sprockets website and the measurements they list for the 675 Daytona match what I measured.



This is good news. I wish the guy I had spoken with at SuperSprox and spent just a bit more time looking and not told me "no we can't make that".

Next time around I'll order one of theirs if nobody else is making one. I need to contact JT sprockets again and point out the fit is the same as the Daytona. At the moment they only list 47 & 50T sizes.

The SuperSprox sprockets are nice quality, I have one on my Ducati.
 
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#9 ·
I've been working with Raisa at SuperSprox. She's very helpful. I ordered the Black and Gold just for fun. They machined it today and sent it out. ?

She did say if there was a fitment issue I could call and mail it back in 5 days. That was all I needed. $114.95 is a hefty sum for a rear sprocket.

She also said she'd update the website if I had a good fit and correct the mistaken part on their currently for a T-120 since it's actually for a T-100
 
#19 ·
I'm about to pull the trigger on the 16 tooth sprocket also. Was there enough rear fork for the chain to extend that few mm in the adj, or did you have to drop a link out. I did this on my tuono, from 16 to a 15 ..transforms the city riding experience and makes it a bit zippier off the mark.
 
#15 ·
So good match then. Great!

I am in touch with the same person you talked to. Let's see what quote (s)he(?) gives for delivery to Vietnam.

I am after the same as you are: low speed traffic here, and occasionally the steep incline onto a bridge ramp, which could be treacherous if riding 2-up.

A 39T or even 40T would be very welcome.

Thanks for the feedback

NN
 
#16 ·
Received mine from Raisa at SuperSprox. I have to say I am pretty impressed at the quality of the object: a stainless-steel-riveted assembly of aluminium alloy and steel takes precision and proper design to make right, and it certainly looks the part, in person.

I'll fit it and report, hoping it makes the slow Vietnamese traffic and occasional steep incline to a bridge easier to negotiate at walking speed.

Thanks for the directions, it worked.

Just as an aside: the Vietnamese customs are usually pretty sharp shooters of anything that looks like luxury, and they sure did not miss me on this: $50 import tax (plus pretty expensive shipment...) I sure hope it helps the riding.
 
#23 ·
I now have in my possession a 39T rear from PBI in alloy and a 16T genuine Triumph front.

I've only hit 200 miles on the bike so far and plan to wait until after the first 500 mile service. Then I will fit the rear and see how that feels. Sometime during the summer I will add the 16T front and if that's too much it will go back to 17T.
 
#25 ·
Report on the 39T rear sprocket: I love it.

So, that's it, I got around to fitting the 39T, lowering the gearing by just about 5%, which I reckoned would help with the riding conditions in here, in Vietnam.

And I went for a spin, and I just love it the way it is. I totally agree with Danketchpel and MotoMax: it feels perfect to me too.

It makes the bike noticeably nimbler, makes it quite comfortable riding between 40 and 50kph, lazily in 3rd gear but without the need to downshift all the time, and I tried it in the steep incline path I was dreading, it is noticeably easier to get right.

Now I know I am still new to the T120, at about 3000km, and that it has just been broken in, but I waited until now to make the change in order to take this into account, and it is certainly the way I want to keep it now.

In a word: great change, I love it.
 
#26 ·
Posting to revive this thread. I am waiting to purchase a 39 tooth rear sprocket for my T 120 Bonneville. Does anyone have an update as to what is available?
Thanks...
 
#31 · (Edited)
@NN65 @muttskie

Supersprox is/are a bunch of morons... I have been TRYING to simply GIVE them money for a Stealth Sprocket since back in late 2016... They are made in Czechoslovakia. So they have a Europe web-page (and the Buy Products section is, and has been Under construction for almost a year), and a US web-page. Literally just yesterday, they finally moved the US warehouse from So-Cal, to MN... The earliest they can place an order is April 17th. When I called, the phone got passed around literally three times, before I finally spoke with someone that had to call me back, because he had no idea what I was talking about. (They were, however, very friendly though.)

(Side note. Triumph actually originally contracted them for their Black Stealth Sprockets for all three WC bikes. A2018942 for the Thruxtons. I ordered and paid for mine in March... The one from over a year ago. Not the one that just passed. Supersprox were so lazy/late in fulfilling this order, that Triumph actually dropped the contract, and the dealer I originally bought this from, called me and informed me of this to refund my money.) #Lazy as Fuuck

The Supersprox part number for our bikes is:... RST-2012-##-color ...(The ## part is whatever number of teeth you want, ie 37, 42, etc... And the "color" section is where you state the color you want... Most likely Black... As it seems the whole world would like to give them money for a bock one... And not a glow-in-the-dark Blue one.) So, for example, for my Thruxton I would want part # RST-2012-42-Black. Make sense?

I have all but given up on them. As it just baffles my mind how comically careless & lackadaisical all these aftermarket companies are, in regards to getting their items produced and ready for the initial (and likely only) rush and demand there would be for these very niche items. I would get sacked from my janitorial job I have at Wal-Mart if i was even HALF that bad at it.
#The more you make, the less you do
 
#32 · (Edited)
I don't recall a part number. some forum members pointed their way and Raisa at Supersprox, who was useful, came around and actually listed the part for the T120.

Mine is a high-end "Stealth" sprocket. I admit I could not find it online any more this morning (nor any actual parts listing), their website is a bit of a mess now. I see on their website: "We are re-organising our European e-shop stock system and software, because we don't feel that our service has been acceptable last year. ", which bodes well. It is, indeed, a mess.

Following SirCuffsalot's directions, I see heir European operation is in the Czech Republic (maybe their head office?), which bodes well too: I have in time worked with Czech mechanical companies and found they were typically solid and competent. Indeed if the Prague Spring had not happened in '68, they would probably have gone on making good bikes.

Remains to be seen how easy it will be to export to the US now.
 
#55 ·
I've been on a decent two up ride and it's more lively as you would expect. Riding solo it spools up so quick in first that I keep hitting the rev limiter on fast starts from a standstill.

I plan to keep the lube on the rear sprocket well topped up. I will report back if I see it wearing out too quickly.
 
#34 · (Edited)
A2018942 - Thruxton & R - 42t
A2018941 - Street Twin - 41t
A2018919 - T120 & T120 Black - 37t
... All of these are "Stealth Sprockets" They were even called Stealth Sprockets in the Triumph printed accessory booklet. And if you google the part # and then click images, you can see one and even see the Supersprox, StealthSprocket, and Triumph logos all etched in them.
... None of which ever made it to production since the parent company in Europe dropped the ball.

Hence why now the only way to possibly get one, is to buy the same exact RST-2012 Stealth-Sprocket part # from Supersprox (just doesn't have the Triumph logo etched into it), that still doesn't even seem to be available yet... Anyways, that's the best I can do to explain/help with information. Cheers.
 
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#50 ·
The mounting bolt pattern for the 1200 and old 900 are different. The 1200 uses the same mounting bolt pattern as the 675/800 bikes.

Here's the drawing I did from when I made my sprocket.


Here's PBI's drawing for the 675
 
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#39 · (Edited)
"I don't want an alloy sprocket on my T120. Are there part numbers on the PBI website for the 525 chain T120 sprockets? I mean those with the proper 6 bolt mounting pattern."

Why not alloy? KTM and Ducati use alloy as stock on some models. Anyhow for the price of the Supersprox Stealth you can buy two PBI alloy sprockets. I was also against alloy sprockets, no good reason, just sorta didn't feel right. Checked what other people's experience has been and there really doesn't seem to be any issue.
The W/C twins use an identical carrier to the Daytona so rear sprockets are interchangeable.
PBI list these as their 9087 series. You select whether you need a 520 chain sprocket (for a W/C 900) or 525 for any of the 1200's. You also select the number of teeth you want which they list as available in one tooth increments from 35t to 61t !!
Go to gearingcommander.com and see how the changes affect your ride and usefully also how they are likely to affect chain and sprocket longevity. The W/C twins details are loaded so it's a snap.
In my opinion the selection of a 17t front with 39t or 41t rear would be the way to go, I found the 37t a little tall doing top gear roll-ons.
I'm sure we'd all like to know what you do and how it works for you.
 
#54 ·
The W/C twins use an identical carrier to the Daytona so rear sprockets are interchangeable.
PBI list these as their 9087 series. You select whether you need a 520 chain sprocket (for a W/C 900) or 525 for any of the 1200's. You also select the number of teeth you want which they list as available in one tooth increments from 35t to 61t !!
Thanks Caromba. This was the missing link (! pun intended). I had looked at PBI earlier, but the T 120 was not listed. The interchangeability with the Daytona 675 was the key bit of information.
 
#40 ·
Maybe alloy sprockets are much different now compared to many years ago.

Back in the mid 70's, my old Kaw Z1 ate two alloy sprockets up in less then 7000 miles so I've always regarded them as junk.
I've never used one on my 77' KZ1000 after close to 50,000 miles.

Note: I can't remember if I replaced the chains on these bikes every time, which I have always done in the last 25 years.
Hmmm... the more I think about it, probably not every time back then as money was always tight...LOL.

I did try one on an old RD400 Daytona around 1982-83 though but could see it wearing faster then the factory steel with less miles on it, l so I took it off after a couple thousand miles anyhow.
That is my grand total experience with them, and again, depending on what bike, at least 34-42 years ago.
 
#41 ·
I can understand how you feel about using alloy sprockets because your experince is similar to mine, except I had a Montessa 250 back then that just ate chains and sprockets, of course I know now that the tiny 11t cs sprocket was the problem. Like I've said before I did check up on a bunch of posts in various forums for user experiences. The results were fairly evenly divided between guys who are using alloy and are happy and guys ( not necessarily using alloy) like you (apologies) who becaus of long past experience wouldn't even think about it. But clever metallurgists spend a lot of time and money developing new alloys so I for one would be prepared to give it a shot. Of course we can also just wait for our friend Nickolarge to report back in a year or so.?
 
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