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Technical Help Forum
Started by fsjcjd at 05-09-2008 9:43 AM. Topic has 26 replies.
  
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 05-09-2008, 9:43 AM
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fsjcjd
Joined on 01-01-2008
Posts 6
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When I rode my 1982 CX500 Custom in New York, 60mph was around 5500rpm on the tach. I've moved to England and left my '82 to a friend and bought a '79 CX500 here. It's the basic model, not a Custom. I run the bike at 60mph and the tach reads around 4000rpm. It doesn't feel like 60 either. Is this normal or is my speedometer off? Where should it read in relation to the tach?
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05-09-2008, 10:52 AM
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fsjcjd
Joined on 01-01-2008
Posts 6
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Nope. It's definitely in mph. I had to go check though, just to be sure. It's like getting halfway to work and can't remember if you turned the stove off! Definitely m.p.h.. . . . .
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05-09-2008, 10:57 AM
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Reg in Bristol
 
Joined on 03-11-2006
Bristol UK
Posts 251
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Sounds normal to me
I've seen discussions on this here (in the UK) before
and it seems the standard CX revs lower at any given speed in 5th
Its been a while but I think its about 10 mph per 1100 revs
Down to one project/rat bike now, when I get a 'round tuit'
Member of the UK CX-GL MCC at
http://www.cx-gl.org.uk/index.html
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05-09-2008, 11:38 AM
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MartinUK
Joined on 04-19-2008
Oxfordshire, UK.
Posts 14
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That sounds about right to me. Though I'm not sure I'd describe the CX500 (non-custom) as the 'basic' bike  .
The custom has a smaller rear wheel doesn't it? It makes sense to me for the 'Normal' CX to have longer gearing anyway, as with the lower bars you don't feel the wind so much & with the bigger tank it is a better tourer / allrounder. (Not wishing to to upset my Custom riding friends, of course  .)
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05-09-2008, 11:39 AM
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Graywolfs02
Joined on 09-08-2007
Coon Rapids Minnesota
Posts 149
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I have a '78 "basic" here in the states (Minnesota) and I am running 4 grand @ 60 MPH
Greg
1978 CX 500
Minnesota
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05-09-2008, 11:50 AM
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Anonymous
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Just seen this on Robs site
The ZAB and EC 500s do 6,000 rpm
at 70 mph but the 500 Customs and GL500s rev higher - about 6,250 - due the
small 16" rear wheel. The ZAB 18" rear wheel drops straight in, if
you want to reduce the revs at motorway speeds.
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05-09-2008, 1:53 PM
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Randall-in-Mpls
Joined on 07-06-2007
Minneapolis, MN
Posts 893
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In the US, we only got the 18" rear on the '78. After that, with the Custom, Deluxe, and GLs, everything was 16". I think in Euroland, they only got the 16" on the Custom (and in relatively low numbers, unless I'm mistaken.)
R
'78 CX500 - The Black Maggot
My mid-life crisis has two wheels.
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05-09-2008, 2:54 PM
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Graywolfs02
Joined on 09-08-2007
Coon Rapids Minnesota
Posts 149
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After being out riding a bit today, and paying closer attention, I'll have to amend my previous information....
I am turning 5 grand @ 50 MPH 
Greg
1978 CX 500
Minnesota
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05-09-2008, 3:44 PM
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dozer1
Joined on 05-26-2007
Boston, Massachussetts
Posts 448
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I have found that about 1000 rpm per 10 mph is about right. From what I understand any post '78 CX in the US has a 16" rear? Is that just a simple swap to an 18", and what's the difference going to be?
1980 CX500 "Stella"
Dozer1 AKA Snowplow
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05-09-2008, 6:01 PM
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makenzie71
Joined on 03-30-2007
TX
Posts 303
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 dozer1 wrote: | | ...and what's the difference going to be? |
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About two inches.
direct swap...however, it won't make much difference. You've only got so much clearance for a taller tire.
Available from EssGlass ATV/Motorcycle Fabrication
~Preload adjusters (CX5/applicable): $55 + core caps
~310mm big brake kits (CX5/applicable): starting at $125
~Left exit divorced exhaust: $225
for info email me!
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05-09-2008, 6:08 PM
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t053376
Joined on 03-03-2008
Posts 68
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So, has someone successfully swapped the 16inch out to 18?? I would like to drop RPM at 60mph. Easier on the engine. 82 CX500 Custom.
tuy_kat
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05-09-2008, 6:16 PM
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makenzie71
Joined on 03-30-2007
TX
Posts 303
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| t053376 wrote: | So, has someone successfully swapped the 16inch out to 18?? I would like to drop RPM at 60mph. Easier on the engine. 82 CX500 Custom.
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I went the other way. Tires suck for the 18. It's a direct swap. I'll sell you my 18" wheel if you really wanna try it.
Available from EssGlass ATV/Motorcycle Fabrication
~Preload adjusters (CX5/applicable): $55 + core caps
~310mm big brake kits (CX5/applicable): starting at $125
~Left exit divorced exhaust: $225
for info email me!
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05-09-2008, 8:18 PM
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t053376
Joined on 03-03-2008
Posts 68
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Why does the direct switch suck!! What trouble did you encounter??
tuy_kat
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05-09-2008, 8:52 PM
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makenzie71
Joined on 03-30-2007
TX
Posts 303
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| t053376 wrote: | Why does the direct switch suck!! What trouble did you encounter??
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Because tires suck for the 18" wheel.
Available from EssGlass ATV/Motorcycle Fabrication
~Preload adjusters (CX5/applicable): $55 + core caps
~310mm big brake kits (CX5/applicable): starting at $125
~Left exit divorced exhaust: $225
for info email me!
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05-09-2008, 10:50 PM
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Randall-in-Mpls
Joined on 07-06-2007
Minneapolis, MN
Posts 893
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| Graywolfs02 wrote: | | I am turning 5 grand @ 50 MPH |
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... In fourth gear. In fifth, the 5500 at 60 stated in the original post is about right for our '78 Standards.
That's how I know what gear I'm in when I lose count. In third, the tach reads a bit higher than the speedo. In fourth, they're about 10mph per 1,000rpm. In fifth, the speedo is a bit above the tach. But, again, that's on a '78 with the 18" rear.
| dozer1 wrote: | | Is that just a simple swap to an 18", and what's the difference
going to be? |
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Standard vs. reverse Comstars. The US market never saw the 18" reverse Comstar from the A and B models. (Something I'll be looking at importing if I ever do a cafe project based on a later model.)
I'm pretty sure the rear is a straight swap, but I don't think the front is. At least, the fork ends and wheel spacers are different. So, if you did the rear swap, you'd have mismatched wheels.
Ask Rodent about the front. He had reverse Comstars on a '78 frame, if I remember correctly. He may have had later forks, though.
| t053376 wrote: | | Why does the direct switch suck!! What trouble did you encounter?? |
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There aren't as many 18" options in the fancy racing tires he thinks he needs. If you want decent touring tires, there are plenty available.
R
'78 CX500 - The Black Maggot
My mid-life crisis has two wheels.
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05-10-2008, 8:17 AM
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dozer1
Joined on 05-26-2007
Boston, Massachussetts
Posts 448
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Yes, Rodents front end is from a different vintage as well. I dont suppose it would really matter to me if i had mismatched wheels, but i would rather have an 18" reverse comstar. It's not an urgent change, I suppose, let me know when you import some : )
1980 CX500 "Stella"
Dozer1 AKA Snowplow
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05-10-2008, 8:52 AM
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vitter
Joined on 04-29-2006
Ontario Canada
Posts 84
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<BLOCKQUOTE><table width="85%"><tr><td class="txt4"><img src="/cs/Themes/default/images/icon-quote.gif"> <strong>t053376 wrote:</strong></td></tr><tr><td class="quoteTable"><table width="100%"><tr><td width="100%" valign="top" class="txt4">So, has someone successfully swapped the 16inch out to 18?? I would like to drop RPM at 60mph. Easier on the engine. 82 CX500 Custom.<br></td></tr></table></td></tr></table></BLOCKQUOTE>
I installed an 18" standard comstar in place of the 16" rear on my '81 GL. Makes a small reduction in revs at highway speeds. Can't remember how much; I'll be riding today so may post later, but it doesn't bring the revs down significantly. Clearance for tire height is not an issue. Very few people notice the rim difference between the reverse Comstar front and standard Comstar rear on my bike. I'll stick with it since anything that brings the revs down is ok with me. There are many threads on this board on the subject or reducing revs.
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05-11-2008, 9:23 PM
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Randall-in-Mpls
Joined on 07-06-2007
Minneapolis, MN
Posts 893
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I got in a little highway time this afternoon to double check what I stated earlier. Most of my riding is on city streets at relatively low speeds. What I found in my highway tests is a little surprising. I guess it's easy to read 2900 rpm at 32 mph as 3k at 30, 'cause I didn't find the 10 to 1 ratio in 4th at higher speed.
My first run, I was turning 4500 rpm at 60 mph in 5th gear. For comparison, pulling away from the next traffic light, I noted the speeds of the other gears at 4500 rpm, much to the annoyance of the driver in the pickup behind me. The results were, within 1 or 2 mph:
1st: 21 mph @ 4500 rpm (about 4.5 mph per 1000 rpm)
2nd: 29 mph @ 4500 rpm (about 7 mph per 1000 rpm)
3rd: 39 mph @ 4500 rpm (about 9 mph per 1000rpm)
4th: 49 mph @ 4500 rpm (about 11 mph per 1000rpm)
5th: 60 mph @ 4500 rpm (about 13 mph per 1000rpm)
There was an old discussion on here regarding the spec gear ratios, but I don't know if it was translated to actual speeds.
What's the stated top speed for the '78 CX? My test suggests 120 mph at 9000 rpm, which is still short of the redline! Of course, it would have to be a much smaller jockey than me. I'm discovering that I'm not very aerodynamic.
R
'78 CX500 - The Black Maggot
My mid-life crisis has two wheels.
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05-11-2008, 9:54 PM
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dozer1
Joined on 05-26-2007
Boston, Massachussetts
Posts 448
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Randall, those numbers make me think your speedo is on the eager side. The top speed of a CX500 is about 105, and thats on flat land with a tailwind., and your bars are vibrating quite a bit. At least thats what they tell me. Elsewhere I read that it is aprox 1100 rpm per 10 mph in 5th, and I've found that to be pretty accurate.
1980 CX500 "Stella"
Dozer1 AKA Snowplow
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05-11-2008, 10:58 PM
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Randall-in-Mpls
Joined on 07-06-2007
Minneapolis, MN
Posts 893
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| dozer1 wrote: | | Elsewhere I read that it is aprox 1100 rpm per 10 mph in 5th, and I've found that to be pretty accurate. |
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That's with the 16" rear. Would +2" diameter make that much difference?
If my numbers are correct, it's like a whole extra gear with the 18". You're turning 6600 rpm at 60 mph in 5th, while I'd only be turning 5400 rpm at 60 mph in 4th.
Doesn't seem like it should make that big a difference. Maybe my tach is dragging a little.
R
'78 CX500 - The Black Maggot
My mid-life crisis has two wheels.
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05-12-2008, 4:21 AM
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makenzie71
Joined on 03-30-2007
TX
Posts 303
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That 2" is only applied to the diameter of the wheel it's self, not the tire. The tire isn't anywhere near that much taller.
Available from EssGlass A | | | | | |