The ton plus 10, what could be the problem?

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Craig said:
so in real life with much experience here .... roughly how fast should a '72 Commando be going at 5000 RPM ..... standard size tires both ends K81 4:10 X19" , stock rear sprocket , with 21 tooth counter shaft sprocket , 180lb rider ..... Big Thanks !!! for anyone skilled at the math and takes time to answer .... I have downloaded a speedo app on phone and am curious but still a couple wks out from actual test , due to weather and road conditions here ....
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From page 1 of this thread.
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Thanks very much Kurt , much appreciated.... my speedo bounces around 90 mph under and over , so if anything maybe a little optimistic... will be interesting to see what the speedo app. say once out on road .... like the graph too as it has all info I need too !
 
Craig said:
Thanks, surprisingly have heard that all before .... not sure how state of tune affects this question though as 5000RPM can be maintained no problem .... I had my original speedo repaired several years ago and it bounces a bit .... after all the talk ‘bout speeding and the resulting tickets thought I would ask those more knowledgeable how I was doing at 5000RPM .... maybe save myself a few dollars plus just kinda nice to know how true the speedo is .... really didn’t mean to stir anything up ... just an ask , that it ....
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Not all speedos or tacos will give true readings even from new or rebuilt, you haven't stirred things up at all, may be the only way to get a true fix on things is a GPS or something simlar who knows and when we get pulled up for speeding how do we know that the device the cops used to get you is giving a true reading, its their word against ours, same as wind speed affects readings, so there are a lot of things that can effect your speed to RPMs, so really nothing in this can be 100% accurate in what ever is used.

Ashley
 
Craig, you go here: https://www.gearingcommander.com/ You chose the norton commando from the database. In the green line you can alter the stock specifications for the modifications that your bike has, such as rear wheel size or sprocket sizes to have the database results to show the corrected specs that include your modifications.

As you scroll down the page, you can look at your bike's specifications in numerous ways. It even gives drive chain to sprocket alignment patterns which can help predict chain and sprocket wear problems... It's a very interesting site.

Occasionally, I ride with my GPS on my handlbars and it confirms the accuracy of my speedometer. My tachometer is totally whacked lately, but the speedo is working...
 
Thank you Frank and Ashman .... I have tried with the GPS ... sadly my eyes can’t see the small digits and can’t wear specs while riding/driving ... why I found the speedo app for phone the numbers are screen size so should be able to clearly see them ... I will also check out the link you posted Frank , thanks again to all for the info ....
 
I guess that gearingcommander web site is pretty accurate. My rev limiter is set at 6800 so the most I could have gone in 3rd gear is 104mph. At 5300rpm I would have been at just under 100mph. If the engine had the guts to redline in 4th I would be doing 126mph!

I really appreciate all the replies. There is probably not much that can be done to my engine to make it go faster in it's present set up. I'm happy to be able to cruise all day at 80mph at 4350rpm. And just think, my transmission will last a long time.
 
Dunno... Seems to me like a trans might last longer with the lower 19T gearing. It would spin faster but have less load on it.
 
Best way to make the trans spin faster at any given road speed is to raise the primary gearing.
 
ashman said:
In the 60s, 70s as well the 80s was all about going flat out to prove your manhood, to prove who had the fastest bike around, but now I have nothing to prove, I know what my bikes can do , how they perform..
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That may be so, but these days, I love to feel and hear my bikes wind right out and sing at or near their max, on wide open, empty roads (we have LOTS of those, and the cops could care less out there). NOTHING to do with proving anything, just me and my bike. I don't even ride like that with my sons any more, but they were great days and also not proving anything.
 
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baz said:
I had a 23 gearbox sprocket on an 850 it was a performance killer I soon dropped it back to 21
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I currently have a Norvil belt drive. With it a 19T sprocket is roughly equivalent to a 21T with a chain primary drive. I briefly ran a 21T sprocket with this setup and it seemed a bit sluggish in acceleration but I'm not sure about top speed. I'm currently running a 20T, probably equivalent to a 22T sprocket with a stock primary. It seems to accelerate pretty well off the line, probably not as good as a 21. At 90+ it feels at least as good as it did with the 21T.

The strongest incarnation of my bike was when I put a freshly done cylinder head on a bottom in that had probably 35,000 miles on it. i didnt touch the rings or anything else. The compression felt kind of weak when I would kick it over, but it pulled really strongly. I ran that with the belt primary and a 20T sprocket. I never tried to do a true top speed run but I had it up over 100 a few times and it felt like it would have done quite a bit more, probably close to 115. I ran it like that for about a year and then at ate a carburetor slide.
 
grandpaul said:
That may be so, but these days, I love to feel and hear my bikes wind right out and sing at or near their max, on wide open, empty roads (we have LOTS of those, and the cops could care less out there). NOTHING to do with proving anything, just me and my bike. I don't even ride like that with my sons any more, but they were great days and also not proving anything.
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Paul I am the same I ride my bikes hard and still push then to their limits when I get the chance on some outback roads as well in the twisties, I still haven't grown up yet and one of the reasons I just brought a new Triumph Thruxton 1200 its not the fastest bike around but very torquey and gets up there very quick, I have nothing to prove but its just the way I have always rode, coming up to 60 years old I haven't slowed down but the bastards are still trying to get us here, just got to be more smart about it, I still ride my CRF450X dirt bike flat out when I take it out in the bush, it makes me feel young.

Ashley
 
Once out on road , I will post up results of the phone Speedo app ... Ashley I am well past the 60 Mark , and will disregard your earlier post ‘bout why folks ride fast , as you answered your questions in above post , have a good one ....
 
Everybody needs two motorcycles - one for commuting and touring, the other for track days on road race circuits. I gave up riding on public roads at age 29 and went road racing. I was having too many near-misses.
 
Near misses can make you feel very alive, 3 bikes here all on road , always good for the heart to stick your neck out occasionally, can’t let the big head run everything.... nothing better than a good laugh over a close call when no damage to riders , drivers or bike
 
until you face the left turn in front of you, fun & games then end there
 
True enough , but it the fun and games we all ride for , or did .... riding a bike still gets me going like nothing else , now the hockey and rugby done it makes for long winters , thank the Gods for 2 wheels and still able to go
 
Craig said:
Once out on road , I will post up results of the phone Speedo app ... Ashley I am well past the 60 Mark , and will disregard your earlier post ‘bout why folks ride fast , as you answered your questions in above post , have a good one ....
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Craig I still ride all my bikes hard but these days knowing how fast my bikes will do flatout in top gear on the road is nothing to gane as I already know from my younger days but giving them a big blast past the ton a few times keeps me happy knowing they still pull past it plus it is a rush, what does effect me is hearing about the young inexperienced that have wiped themselfs out trying to prove to themselfs or their mates, my youngest daughter has lost a few friends this way and they do it in the wrong places, but some take their friends with them hence the crack down from the GOVT and the law, we are becoming a nanny state, but the young still do stupid things on the road without thinking about it and we all suffer for it.

Ashley
 
All very true, history keeps repeating itself .... however my original question was speed of my bike at 5000rpm .... never asked ‘bout top end or state of tune , I got very useful info here and I appreciate that very much .... my point on close calls was .... everyone that rides a bike accepts the risks regardless of how good , how fast etc. they are , just nature of the hobby .... example hockey players get cut , I lost track of stitches but really enjoyed the playing .....
 
On my orginal commando in the early days at 4,000 rpms my speedo would be between 60 to 65 mph and I think around 5,000 rpms it would have been 85 to 90 mph but that was a long time back and I never kept records only what has stuck in my head from 43 years, I know I can ride around town in top gear at 40 mph any lower my hot cam will jurk the bike around and labour the motor but my hot cam doesn't start to work best till it hits around the 4,500 rev range and will rev freely till something goes bang, just got to know how far to push it lol.
When I do high speed runs I don't even take notice of my speedo or taco I am to busy watching whats in front of me or around me, things can happen very quickly at high speeds and the speeds some of these high powered sports bike can do 300ks plus compared to our old bikes, scares me what could happen and I have mates that do it every time they are out on their high powered sports bikes, their way of thinking is we will just out run the cops, they are ticking time bombs waiting to go off.

Ashley
 
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