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pmk

OSSA MAR Countershaft Sprockets

37 posts in this topic

Curious about opinions regarding front sprockets sizes and how they effect the selection of gears.

Stock, my MAR had a 12 on the front. I have ridden the 12 since I finished getting the bike going.

I see that 10 tooth and 11 tooth are available.

Today I removed the 12 and installed an 11.  After riding around the yard a bit, the 11 certainly is capable of being very controlled at low idling speed in first gear.

So with first being lower so is second, Second currently with the 11 feels about a bit taller than first with the 12.

Does the 10 tooth make second gear about the same as first gear with the original 12 tooth?

Curious what others run and how it compared to the stock 12.

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11 / 46 on my OSSA TR77 Verde, original fitment would I think have been 11 / 42. 

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Yo don't say what you have on the rear.

Original gearing on MK1 was 12 / 46 which became 11 / 42 from MK2 onwards. They're virtually the same ratio, 3.82 and 3.83

I've run 10 / 42 before which gives 4.20 ratio which gave a still useable low first. Using the 10 front puts it lower than you really need I think and the 10 also gives problems with the chain catching on the sprocket nut. There is a nut with a shoulder which faces against the sprocket to space the edge of the nut away from the sprocket to clear the chain and you need this for a 10

The dished sprocket from Spain that is reproduced now is 44 tooth and  I find 11 / 44 low enough in bottom, ratio being 4.00

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Sorry Woody, stock 46t rear, so I had 12/46 I just swapped to 11/46.

I just ran some numbers.  Using the oem 1972 sales brochure I had the internal gearbox ratios.  Based on the numbers, it does seem the current 11/46 second gear was taller than the 12/46 first gear by about midway between 1st and 2nd.

I suppose, the true question is, how low is too low for 1st.  My minimal experience has me considering using second almost as my main gear, with first for very slow sections.  The current setup would make first still more commonly used, as second is probably too tall with 11/46.

Just asking, not debating what is best.  I honestly do not know.  Just riding around the yard, the 11/46 first gear is easily ridable for slow no dab cornering and so forth.  Almost leading me to think, even lower may not be an issue.

Stock 12/46 gearing = 3.83:1

11/46 gearing = 4.18:1

10/46 gearing = 4.6:1

Internal gearbox ratios are listed as

1st = 4.31:1

2nd = 3.24:1

3rd = 2.40:1

Overall gearing with 12/46

1st = 16.50:1, 2nd = 12.40:1. 3rd = 9.19:1

With 11/46

1st = 18.01:1, 2nd = 13.54:1, 3rd = 10.03:1

With 10/46

1st = 19.82:1, 2nd = 14.90:1, 3rd = 11.04:1

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13 hours ago, trialsrfun said:

11 / 46 on my OSSA TR77 Verde, original fitment would I think have been 11 / 42. 

Any idea if the gearbox internally, as far as ratios, is the same between your TR77 and my, TR72 I think it is, 1973 MAR?

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2 hours ago, pmk said:

Any idea if the gearbox internally, as far as ratios, is the same between your TR77 and my, TR72 I think it is, 1973 MAR?

I am unsure about that but the ratios fitted to the different models are probably about the web somewhere. The 11/46 seems good to me as you do not have the hassle of the reduced nut which is required for a 10t gearbox sprocket or a massive rear sprocket and the overall performance seems ok for the sections I have ridden.

Does your bike have the dished rear sprocket or a flat sprocket conversion.

Edited by trialsrfun

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41 minutes ago, trialsrfun said:

I am unsure about that but the ratios ifitted to the different models are probably about the web somewhere. The 11/46 seems good to me as you do not have the hassle of the reduced nut which is required for a 10t gearbox sprocket or a massive rear sprocket.

Does your bike have the dished rear sprocket or a flat sprocket conversion.

Currently dished oem 46t rear.

I sent an email to Pete at In Motion regarding the spacer bushing that goes between the countershaft sprocket and gearbox.  They sell Talon countershaft sprockets, that may be stepped, so I wondered if the spacer is shorter.

Yes, the modified nut is needed, plus the 10 tooth may require installing a chain slide on the swingarm.  Can be done, just a bit more work.  No doubt the ever so slightly longer rear shocks will make this worse on my bike bike.

As I mentioned, it feels too low in 1st now at times, but other times no, but second is a bit too tall when first seems to low.  I know, ride and enjoy...

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Rode a bit more.  Will give the 11/46 a chance.  Not bad, just considering a bit slower in first could be a benefit and allow second to work better.  Time will tell after the upcoming event.

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So, with two events on the 11/46 gearing, certainly better for what they have us ride but maybe not quite there yet.

Locally they run two vintage specific classes during an event.  An event is focused on the modern bikes, but they offer a vintage B class that rides the intermediate lines.  The other class rides the novice line.

Without doubt, the very experienced guy that always sees the lowest scores rides well.  He is riding a TL125 with modified engine, kind of stripped down to bare minimum, and I beleive has had the frame headtube angle steepened.

At the last event, I watched him ride a section.  The first portion he seemed to ride in third gear.  I say this based on him downshifting twice as he rolled out of the begining portion and into the second portion that involved a right hand 180, into a left hand climb of 6 feet while turning up the steep climb, followed by completeing the left turn as you crested the climb onto the flat.  Seems he entered the section in 3, then as he approached the twisty section and climb, selected first.

Riding the MAR, the entire section was ridden in first, including the climbs, and to have control required a bunch of clutch work.  The TL did see some clutch use, but almost none.

Reconsidering going with a 10 tooth countershaft sprocket, or possibly converting to a 50 rear 10 front and using second more, with first gear for these previously described sections.

FWIW, his TL is geared so low, the rider accidentally started in gear with clutch out.  With barely a kick, the engine fired and it immediately without bog had the front wheel skyward.

Just revisiting it as discussion, not saying any one setup overrules a other.  Curious on opinions from others that have tried a 10/46 setup, even if they went back to something else.

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On 12/23/2017 at 11:25 PM, pmk said:

So, with two events on the 11/46 gearing, certainly better for what they have us ride but maybe not quite there yet.

Locally they run two vintage specific classes during an event.  An event is focused on the modern bikes, but they offer a vintage B class that rides the intermediate lines.  The other class rides the novice line.

Without doubt, the very experienced guy that always sees the lowest scores rides well.  He is riding a TL125 with modified engine, kind of stripped down to bare minimum, and I beleive has had the frame headtube angle steepened.

At the last event, I watched him ride a section.  The first portion he seemed to ride in third gear.  I say this based on him downshifting twice as he rolled out of the begining portion and into the second portion that involved a right hand 180, into a left hand climb of 6 feet while turning up the steep climb, followed by completeing the left turn as you crested the climb onto the flat.  Seems he entered the section in 3, then as he approached the twisty section and climb, selected first.

Riding the MAR, the entire section was ridden in first, including the climbs, and to have control required a bunch of clutch work.  The TL did see some clutch use, but almost none.

Reconsidering going with a 10 tooth countershaft sprocket, or possibly converting to a 50 rear 10 front and using second more, with first gear for these previously described sections.

FWIW, his TL is geared so low, the rider accidentally started in gear with clutch out.  With barely a kick, the engine fired and it immediately without bog had the front wheel skyward.

Just revisiting it as discussion, not saying any one setup overrules a other.  Curious on opinions from others that have tried a 10/46 setup, even if they went back to something else.

My 250 OSSA runs 10/52 gearing. I never use the clutch and I don't remember ever riding a section in anything except first gear. I remember having to make some sort of spacer for the front sprocket to provide clearance for the chain with the 10T sprocket, maybe to clear the sprocket nut.

Be aware that gearing is to suit the rider's own riding style. Just because someone else has a certain gearing doesn't mean it is right for you.

If you have a clutch with a light, fast and predictable action, you can usually ride in whatever gear best suits the fastest part of the section. If you have a twinshock clutch that has a soft takeup, or an unpredictable takeup, or a wide takeup, or a delayed takeup, it is usually better to ride (in the old-fashioned way) without touching the clutch. You would probably find that your "very experienced guy" with the custom TL125 has a clutch that works like a modern bike. OSSA clutches while predictable are usually a bit heavy with standard leverage ratios and have a wide take-up if you increase the leverage enough to make them light.

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9 hours ago, feetupfun said:

My 250 OSSA runs 10/52 gearing. I never use the clutch and I don't remember ever riding a section in anything except first gear. I remember having to make some sort of spacer for the front sprocket to provide clearance for the chain with the 10T sprocket, maybe to clear the sprocket nut.

Be aware that gearing is to suit the rider's own riding style. Just because someone else has a certain gearing doesn't mean it is right for you.

If you have a clutch with a light, fast and predictable action, you can usually ride in whatever gear best suits the fastest part of the section. If you have a twinshock clutch that has a soft takeup, or an unpredictable takeup, or a wide takeup, or a delayed takeup, it is usually better to ride (in the old-fashioned way) without touching the clutch. You would probably find that your "very experienced guy" with the custom TL125 has a clutch that works like a modern bike. OSSA clutches while predictable are usually a bit heavy with standard leverage ratios and have a wide take-up if you increase the leverage enough to make them light.

Awesome reply.  

10/52, great info, as I was considering maybe 10/50.

The TL rider is without doubt experienced at the craft of trials riding.  His skills and even his bike are purposely built.  The TL is no show winner, but rather the sum of mods based on experience and preference.  As a rider, and the sections we ride, he seldom uses the clutch.  Like a stump pulling tractor, the machine thumps along, very controlled with little bits of throttle just above idle.  His setup is so controlled and predictable, and I suspect the ultra low gearing adds a lot to help this.

In regards to my MAR, and my riding buddies.  We both have a reasonably light clutch pull, with a soft controlled engagement.  Without that, the previous 12/46 and now 11/46 would be impossible to ride sections slow or manage the corners / features.

Overall, it just seems, the OSSA is just too fast at times in the technical stuff, and becomes very dependent ypon clutch control while holding a steady throttle.  In short, using the clutch to manage speed, grip, and even braking.

Understand also, this is simply local events, not a national championship, so if nothing were to be changed, the fun factor still remains.

As a lower cost test, I will try a 10/46 setup.  Provided the gearing still allows floating the front wheel over or onto stuff, this should be a good indicator to see if it helps.

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 I take it you are riding vintage b class, which is actually set as modern sections. I would try the 11/50 combo before going to the 10. 

 If you get a chance, you should try to ride a dew if the ITSA events.

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30 minutes ago, lineaway said:

 I take it you are riding vintage b class, which is actually set as modern sections. I would try the 11/50 combo before going to the 10. 

 If you get a chance, you should try to ride a dew if the ITSA events.

Yes, Vintage B, which does the modern lines along the intermediate course.

The 10/46 may happen as a test.  Easier to get.  

Once sorted out, I can decide on what sprocket set to run.

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Yes, if you are still running the dished sprocket.

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18 hours ago, feetupfun said:

My 250 OSSA runs 10/52 gearing.

 

10/52..?  Really or was that a typo for 10/42.  I found 10/42 about as low as I would want to go,  10/52 would be far too low for me to even use first

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