Re: How fast?

Technical Help Forum

How fast?

fsjcjd 05-09-2008, 9:43 AM
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?

Re: How fast?

Abes_CW 05-09-2008, 10:31 AM

My 81 GL is just like your '82. 55 rpm @ 62mph (100km/hr), Not to point out the obvious, but your Euro bike likely is readking KM/hr, I bet 60 km/hr is around 4000 rpm....

Re: How fast?

fsjcjd 05-09-2008, 10:52 AM
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.. . . . .

Re: How fast?

Reg in Bristol 05-09-2008, 10:57 AM
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

Re: How fast?

MartinUK 05-09-2008, 11:38 AM
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

Re: How fast?

Graywolfs02 05-09-2008, 11:39 AM
I have a '78 "basic" here in the states (Minnesota) and I am running 4 grand @ 60 MPH

Greg

1978 CX 500
Minnesota

Ride Safe, Ride Fast, Ride Far

Re: How fast?

Anonymous 05-09-2008, 11:50 AM
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.

Re: How fast?

Randall-in-Mpls 05-09-2008, 1:53 PM
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.

Re: How fast?

Graywolfs02 05-09-2008, 2:54 PM
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

Ride Safe, Ride Fast, Ride Far

Re: How fast?

dozer1 05-09-2008, 3:44 PM
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

Re: How fast?

makenzie71 05-09-2008, 6:01 PM

dozer1 wrote:
...and what's the difference going to be?

About two inches.

direct swap...however, it won't make much difference. You've only got so much clearance for a taller tire.

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Re: How fast?

t053376 05-09-2008, 6:08 PM
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

Re: How fast?

makenzie71 05-09-2008, 6:16 PM

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.

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.

Re: How fast?

t053376 05-09-2008, 8:18 PM
Why does the direct switch suck!! What trouble did you encounter??

tuy_kat

Re: How fast?

makenzie71 05-09-2008, 8:52 PM

t053376 wrote:
Why does the direct switch suck!! What trouble did you encounter??

Because tires suck for the 18" wheel.

Re: How fast?

Randall-in-Mpls 05-09-2008, 10:50 PM

Graywolfs02 wrote:
I am turning 5 grand @ 50 MPH

... 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?

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??

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.

Re: How fast?

dozer1 05-10-2008, 8:17 AM
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

Re: How fast?

vitter 05-10-2008, 8:52 AM
<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.

Re: How fast?

Randall-in-Mpls 05-11-2008, 9:23 PM
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.

Re: How fast?

dozer1 05-11-2008, 9:54 PM
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

Re: How fast?

Randall-in-Mpls 05-11-2008, 10:58 PM

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.

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.

Re: How fast?

makenzie71 05-12-2008, 4:21 AM
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.

Re: How fast?

dozer1 05-12-2008, 6:02 AM
Yea, I seriously doubt an 18" rather than a 16" is going to give you that much more top end. Maybe a few hundred rpm in top gear i'll belive, but 1,200? I would say it is probably your speedo saying your going a bit faster than you actually are.

1980 CX500 "Stella"
Dozer1 AKA Snowplow

Re: How fast?

wridley 05-12-2008, 7:28 AM

Randall-in-Mpls wrote:
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

One thing to remember is that the speedometer is connected to the the front wheel. If you don't have the proper size on the front it will affect the shown readings.

Willy
1982 CX500C
1980 CX500D
1981 GL500I (wife)

Re: How fast?

Randall-in-Mpls 05-12-2008, 1:41 PM
I'm actually seeing lower gearing than the original poster on his British '79 Standard:

fsjcjd wrote:
I run the bike at 60mph and the tach reads around 4000rpm.

My front wheel is stock, and the tire is spec, so I don't expect any distortion there. I don't know. I'll have to dig around for that old thread.

R

'78 CX500 - The Black Maggot

My mid-life crisis has two wheels.

Re: How fast?

Anonymous 07-07-2008, 8:49 PM
well i have an 81 honda cx 500, and when i'm on the highway doing 55 the engine does seem to be reving quite fast, my tac is not working cause it needs a new cable.
But when i'm doing around 55 to 60 i feel a bit uneasy, cause it makes me think my engine is reving way too fast, at the red line, which would be around 7.5 k to 8k

how ever i can't be sure what the real tac is, until i replace my cable.
when i'm doing 60 mph and let the throttle go the engine does seem to slow the bike down quite a bit with out hitting the brake, probably from 60 mph to 45 with in 5 sec
any way if any of you know, does that sound normal for hte engine to sound like it's reving very high at 60 mph?

Re: How fast?

dozer1 07-07-2008, 9:33 PM
rev the snot out of your CX, dont worry about the engine, ever.

1980 CX500 "Stella"
Dozer1 AKA Snowplow