Highway Driving.

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jsouthard

jsouthard

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Here in michigan we have a 70 mph speed limit on the highways which really means you
have to be prepared to drive 80+ to keep up with traffic.

My 850 commando runs 4000 rpm's @ 60 mph's.

I am concerned a little about running 5,000 - 7,000 rpm's for 30-40 minutes on my commute to work.

At what speed / rpm's are you guys riding? Anyone see a problem running her that hard?

joe
 
If you're truly running 4000 at 60 mph, then you must have a 19t gearbox sprocket fitted. In my opinion this is too small for an 850 on fast roads. A 21t sprocket would give you a much more pleasant machine and would put you at 68mph at 4000 rpm and 5000 rpm which is comfortable would equate to 85 mph.

Aceleration is not a problem and this is still lower geared than the later 850s for the european market.
 
I just counted the sprocket on my friends bike today - 23. Needed to keep to keep up with the Harley boys, he's finding it tough in city traffic though. I run a 20 (or is is 21..?) and find it quite a nice compromise.
 
20t is still quite busy at 8o-85 mph,70-75 is good right in the power range,nice in the hills to.
 
Not Dead sure what I run, 21 or 22 I think, but someone told me the RGM belt drive I run with changes things slightly.
I do know that at 4000 rpm I am doing just over 75mph, which is great for touring. The bike performs OK around town and under accelleration.
Stuart.
 
Have a Norvil BD with 35/72 giving 4.114:1, that's a little higher than stock primary with 22T gearbox sprocket. Gives about 18.1/1000 in top with 110/90 BT45 and ran a 13.62/102 last year. Your 850 will easily pull a 22T on the box.
 
I run a 22T. Reasonably adequate around town, not too busy on the highway. I know a guy in Melbourne (FL, not AU) who runs a 25T on his Interstate. He turns just over 3000 RPM at 65, and 85 is right around 4000 RPM.

I turn around 3500 at 65, and about 4600 at 85.
 
Factory gearing for the 850 Roadster was a 20 tooth sprocket, which gives you 16 mph per 1000 rpm. At 4000 rpm that's 64 mph and that's where my Norton and I are both comfortable. If I needed to maintain 70+ every day I'd up to a 22 tooth sprocket which should give you 80 mph at about 4500 rpm. But you'll lose the ability to chug along at 35 mph in top gear and still have throttle response.
 
We ran the prototypes on a test track at 100-105 mph for 10 hours a day for several weeks during our development testing endurance runs. Had one problem when the final drive chain snapped and the resulting over-rev blew the engine apart. Other than that, and lncluding lots of high-speed freeway miles, we didn't have any engine problems. If I remember correctly, we put about 30,000 miles on each of the two prototypes, and it was all hard riding once they were broken in. A typical day for a rider was 400 miles or more in 8 hours, and we ran two 8-hour shifts a day on each bike.

Things did break, but not usually in the engine.

For a typical hobby bike, with trips on weekends rather than long daily commuting runs, you're unlikely to have serious issues with bursts of high rpm running.
 
And after you tortured them Frank, idiot kids like me bought them and buzzed them up and down like yo yos.
 
I have a 22 tooth sprocket and it makes for very relaxed highway cruising at 70 mph. Not exactly sure how many rpms I am turning as my tach surely reads high. This sprocket replaced a 20 tooth which I assume was original. I need to slip the clutch a bit to get going but acceleration is still quite adequate. Some people say the larger sprockets put extra strain on the gearbox but it probably depends a lot on how your ride. I think that a 21 tooth is the best overall sprocket for an 850 and I will probably drop a tooth when I get a chance as most of my riding is on backcountry roads rather than freeways. However, for extended freeway cruising the 22 could work well for you.

Do you know if your tach reading accurately? I suspect mine is at least 500 rpm high. My speedo reads about 10 mph high at 60 mph according to my electronic bicycle speedo.
 
Don't know about other markets but my understanding was that 750s ran a 19 tooth, MK1 and MK2 850s and 750 Combats ran a 21 tooth and MK3 850s ran a 22 tooth.
750s have always seemed a bit busy to me with first gear only good for taking off. The 850s were better, but really, 1st and 2nd gears weren't much use. I remember taking normal suburban corners in 3rd and only using the two lower gears for takeoffs. With a 23 tooth on my MK1 850 I now find that 1st and 2nd are much more useful and I even use 1st for small roundabouts. 3500 revs at 75mph makes for relaxed touring with more than enough grunt to overtake.
100mph comes up at 5000rpm. Obviously it won't do 7000rpm in top but who cares?
 
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