I have about 400 miles on my 72 750 Combat with a 19 tooth sprocket and 19 in wheels. Having never had or ridden a British twin I didn’t know what to expect. I’ve been riding mostly secondary roads with posted speed limits of about 40 mph and light traffic. The bike just wants to run, and I find that I’m riding it at 4-6k rpm. This means shifting up from second to third at about 50. I’m trying to be gentle as it’s still in break in, but the engine just seems happier revving. What rpms do you find yourselves riding? Do the 850’s rev differently?
Riding RPM
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robs ss
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Ben
I was pondering about asking a similar question.
I have nearly 600 miles on my "new" 1974 850 and am sticking to an rpm ceiling of 4500 for now.
Top gear at 60mph equates to about 3400 rpm & 70mph is about 4000 rpm.
Seems reasonable - that would make 100mph 5700 rpm and 7000 rpm redline 122mph
So - around town (35mph), top gear is a little low at just under 2000 rpm so I use 3rd gear there.
Other than that it's top gear all the way.
I was wondering how others have their bikes geared for road use?
I was pondering about asking a similar question.
I have nearly 600 miles on my "new" 1974 850 and am sticking to an rpm ceiling of 4500 for now.
Top gear at 60mph equates to about 3400 rpm & 70mph is about 4000 rpm.
Seems reasonable - that would make 100mph 5700 rpm and 7000 rpm redline 122mph
So - around town (35mph), top gear is a little low at just under 2000 rpm so I use 3rd gear there.
Other than that it's top gear all the way.
I was wondering how others have their bikes geared for road use?
Fast Eddie
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Aiming for 70mph at 4000rpm, as a starting point at least, is what I have heard several times. A torquey motor may be happier with higher gearing though IMHO.
I would imagine that gearing lower than that which gives more than 4000rpm at 70mph is going to feel very buzzy / busy, unnecessarily so.
I would imagine that gearing lower than that which gives more than 4000rpm at 70mph is going to feel very buzzy / busy, unnecessarily so.
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My motor is a bit upspecced, and likes to rev higher than it used to. 5k all day. So, even tho it is an 850, it may act a bit more like a 750.
I think a a 19t sprocket is too small for stretching out on the road. Fine for the 1/4 mi.
I always had a 20 on my 74 when I lived in Seattle, and I live on 14 acres now and went to a 21. Happy as.
I think a a 19t sprocket is too small for stretching out on the road. Fine for the 1/4 mi.
I always had a 20 on my 74 when I lived in Seattle, and I live on 14 acres now and went to a 21. Happy as.
Brooking 850
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21 tooth front sprocket is a good alround gearing for our New Zealand conditions, I run a Maney primary belt drive which pushes the gearing up slightly more , although 1st is a little tall at take off, but not annoying over all it ideal for the Commando engine.
robs ss
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Thanks for that - so what's your rpm in top at a speed?
Onder
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It depends a lot on where you live. Im turning 3750 at 70. It would be fine if it wasn't hilly. I'm in hill country so there are times that I think down a
tooth would be better BUT I have a TTI five speed so the jump down a gear is not that much and it works. I am also a small fellow so I weight a lot less than normal people. Also of a certain age so Im not really pressing the issue like I once did.
My Trident (1973) is 4k at 70 or maybe a touch more. Feels like I'm going to blow it up!
...maybe I should ride a Harley! :-(
tooth would be better BUT I have a TTI five speed so the jump down a gear is not that much and it works. I am also a small fellow so I weight a lot less than normal people. Also of a certain age so Im not really pressing the issue like I once did.
My Trident (1973) is 4k at 70 or maybe a touch more. Feels like I'm going to blow it up!
...maybe I should ride a Harley! :-(
robs ss
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No - don't go there!
maylar
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A 19 tooth sprocket and stock tires gets you about 16 mph per 1000 rpm in top gear. You'll find that your Combat motor really wants to rev, and it's a bit unhappy below 4000 rpm. Cruising around town at 30 mph you might find yourself in 3rd gear a lot. But bring it up on the highway at 65-70 or more and that motor will sing a very happy song. Whoever it was at Norton who envisioned the Combat Interstate was a genius.
The 850 has a wider power band and lots of low end torque. My stock 850 & 20 tooth is content at 2500 in 4th and if I twist the grip it responds without hesitation. I do most of my riding below 50 mph, and above 2800 rpm the ISO's are doing their job well. Grabbing a handful of Amals on a highway entrance ramp gets me to legal speed limits before the end of 2nd gear. And it gets there in an almighty hurry.
You're going to find that 2nd gear is a lot of fun on a Norton. Enjoy.
Craig
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‘72 750 here , I tried a 22T but a little too much, dropped back to 21T and it is perfect for my type of secondary road bombing ,3rd gear is still usable around town and high works great once out on back roads rarely see more than 5000 on tach...... unless the spirit strikes me , found 19T not that great except for around town , it was fine then
maylar
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Why? Isolastics work very well at 4000 rpm. My 20T is perfect for my style of riding. 4000 is about 67 mph which is comfortable highway cruising for me. The 850 is just coming on the cam there and there's plenty of passing power. Any higher gearing would put low speed cruising below the iso's threshold.
The OP has a Combat motor and they are perfectly matched to a 19T sprocket. Those motors like to rev.
Timely thread. I'm considering a belt primary for my 850. Notes for the kit state that this change will effectively increase the gearbox sprocket 2 teeth. I currently have a 19 T sprocket, so I should be in good shape to leave it alone. I don't ride aggressively and part of my work commute is about 10 minutes on the highway.
I thought the 19 tooth and the Combat spec was a bit of a problematic combo back in the day.
Fun, but not for long.
Nowadays most detune Combats to stock 750 spec or thereabouts.
Maybe going up a tooth or two on the CS would be a helpful part of the detune?
Or is just upgrading the main bearings enough to make the Combat bullet-proof, leave everything else alone?
Glen
Fun, but not for long.
Nowadays most detune Combats to stock 750 spec or thereabouts.
Maybe going up a tooth or two on the CS would be a helpful part of the detune?
Or is just upgrading the main bearings enough to make the Combat bullet-proof, leave everything else alone?
Glen
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Mk3 850 (SU equipped) 20t seems to cover all bases comfortably for me too..
Fast Eddie
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So, what rpm is a 19T doing at 70mph?
I suspect you are agreeing with me aren’t you? Cruising at 4000rpm (as a starting point) is what I was advocating.
Personally, I would not like my motor to be doing much more than that at a 70mph, largely because I tend to cruise at a higher speed than that and my mechanical sympathy (read paranoia) would kick in.
Different horses for different courses tho.
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Re the mechanical sympathy
- Ive seen the inside of a Vincent ridden by an owner who lacked mechanical sympathy. He believed 100% in his tachometer reading. It turned out that the tachometer had the incorrect drive. It was reading low by about 20%. So he used 3rd gear a lot when he should have been in top and liked to run at 85-90 when in top. This made his tach read where he thought it should.
After 25,000 miles there wasn't much left of that engine.
So there is a sweet spot or range for cruising where a motor will run and run.
Add some revs and you shorten that life up a bit
Add some more and things really start to wear quickly.
Trouble is, with the Norton engine I really don't know where that is.
It does seem that 4000 at 70 is a good all rounder.
It's true that overgearing the Commando means you will spend more time running below the ISOs threshold of smoothening.
So maybe 20 tooth for riders who do a considerable amount of riding in built up areas, 21 tooth for riders who mostly ride in the great wide open?
A 19 is best for quarter mile drags, anyone still doing those today
?
Glen
Gearing chart from the big White Norton book
- Ive seen the inside of a Vincent ridden by an owner who lacked mechanical sympathy. He believed 100% in his tachometer reading. It turned out that the tachometer had the incorrect drive. It was reading low by about 20%. So he used 3rd gear a lot when he should have been in top and liked to run at 85-90 when in top. This made his tach read where he thought it should.
After 25,000 miles there wasn't much left of that engine.
So there is a sweet spot or range for cruising where a motor will run and run.
Add some revs and you shorten that life up a bit
Add some more and things really start to wear quickly.
Trouble is, with the Norton engine I really don't know where that is.
It does seem that 4000 at 70 is a good all rounder.
It's true that overgearing the Commando means you will spend more time running below the ISOs threshold of smoothening.
So maybe 20 tooth for riders who do a considerable amount of riding in built up areas, 21 tooth for riders who mostly ride in the great wide open?
A 19 is best for quarter mile drags, anyone still doing those today
?Glen
Gearing chart from the big White Norton book
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