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Discussion Starter · #1 ·
Hey CC Gang! You've all been a great help to me before, and I know you will be again.



I've got a slight issue with my speedometer: it doesn't work. I see this is a common problem with motorcycles when I look on CL I see a bunch of "broken speedometer" stuff.



Now my issue is that I have no idea how fast I'm going, just usually go with traffic, because there's always traffic in CA. The other issue is the freeway; am I really going too slow or is everyone else going fast? I get it up to about 6500-7000 on the freeway max, because the pickup truck driver in me doesn't want the engine to EXPLODE... which I feel is a strong possibility on a 30 year old bike that's had a broken speedometer for 8 years that has been stuck at 40k miles, for 8 years. I guess what I'm asking for is benchmarks kinda. How fast is 4500 in 4th gear? How fast is 4500 in third gear? What gear/RPM is 65MPH? Y'know, those typical things.



I'm always just a little shy on the freeway and my heart gets a little heavy when I go over 5k, just from other vehicles experience.



What might help is that it's an 81 CX500 Custom with what I'd assume is a 16" rear... which leads me to ask, what could I do to to make the top speed a little easier attainable? Could I switch to an 18"?



Thanks guys
 

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Hey CC Gang! You've all been a great help to me before, and I know you will be again.



I've got a slight issue with my speedometer: it doesn't work. I see this is a common problem with motorcycles when I look on CL I see a bunch of "broken speedometer" stuff.



Now my issue is that I have no idea how fast I'm going, just usually go with traffic, because there's always traffic in CA. The other issue is the freeway; am I really going too slow or is everyone else going fast? I get it up to about 6500-7000 on the freeway max, because the pickup truck driver in me doesn't want the engine to EXPLODE... which I feel is a strong possibility on a 30 year old bike that's had a broken speedometer for 8 years that has been stuck at 40k miles, for 8 years. I guess what I'm asking for is benchmarks kinda. How fast is 4500 in 4th gear? How fast is 4500 in third gear? What gear/RPM is 65MPH? Y'know, those typical things.



I'm always just a little shy on the freeway and my heart gets a little heavy when I go over 5k, just from other vehicles experience.



What might help is that it's an 81 CX500 Custom with what I'd assume is a 16" rear... which leads me to ask, what could I do to to make the top speed a little easier attainable? Could I switch to an 18"?



Thanks guys


From what I know an 18" rear-wheel CX would go 11 mph / 18 kph @ 1000 rpm in fifth. A 16 "-er would rev just marginally faster (~3-4 %) at the same speed.



I don´t recall about other gears, but have a printed diagram somewhere (old American Honda CX 500 test) which I can look up when I´ve dug that mag out from somewhere.



Maybe others are going to fill in before??



Sture
 

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marshall,i put an 18 wheel on my gl back last may.best thing i did.

more mpg

cheaper and a better selection of tyres.

range on the tank increased dramatically.

lower revs.

anyway,my gl does 10 mph more than the revcounter shows.......

4000 rpm equals 50 mph [in top gear]

5000 rpm equals 60 mph.....and so on.





4th gear equates the rpm same as mph..

example ...4000rpm equals 40mph

...........5000rpm equals 50mph

HTH
 

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Put a GPS on it. You'll have an accurate speedometer and accurate mileage counter to calculate MPG from. Plus when you get lost joy riding on back roads you can always find your way home. If you take cross country trips many GPS units can also inform you of gas station locations.
 

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Both the previous posts are excellant ideas, the 18 wheel alters the gearing and will give a usable increase in both speed and mileage. A GPS will give you totally accurate chassis speed and is a great boon in speed controlled area's

If you want to know more about speeds at rpm's etc, pm me and Iwill send you a simple automatic excel program that shows the effect of modifiying any gearing and all speeds at 1k intervals in every gear
 

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Good morning everyone, Hey that's interesting I have a 1980 cx500 never understood why they make them with smaller rear tire and sux/good at the same time that we have driveshafts. But never thought to find a bigger tire would i have to change the rim also ? if we had chain driven bikes i would have already changed the sproket in the rear for better rpm's and mpg enjoy the day
 

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People swap the tires all the time but in reality the conclusion seems to be that it isn't a huge difference, selection of brand & model of tire make a difference too.



Somewhere there's a formula for figuring out rpm vs speed, but even this can't be relied on because the tach isn't all that accuate either.



If it's any consolation tachs and spedometers only come in a couple of ratios relating to input shaft vs inidcation speed, you canswap a lot of diffferent ones in there. They also come and go in our buying/selling section as well as eBay.



You will mainly see the 80 mph ones, the 120 mph ones like I have are more difficult to find. Mine is a buit tempermental when cold (as is my tach) so some day I'm going to take them apart for a complete cleaning and relube along with removing and putting locktite on the screws that hold the faceplates on.
 

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Hey CC Gang! You've all been a great help to me before, and I know you will be again.



I've got a slight issue with my speedometer: it doesn't work. I see this is a common problem with motorcycles when I look on CL I see a bunch of "broken speedometer" stuff.



Now my issue is that I have no idea how fast I'm going, just usually go with traffic, because there's always traffic in CA. The other issue is the freeway; am I really going too slow or is everyone else going fast? I get it up to about 6500-7000 on the freeway max, because the pickup truck driver in me doesn't want the engine to EXPLODE... which I feel is a strong possibility on a 30 year old bike that's had a broken speedometer for 8 years that has been stuck at 40k miles, for 8 years. I guess what I'm asking for is benchmarks kinda. How fast is 4500 in 4th gear? How fast is 4500 in third gear? What gear/RPM is 65MPH? Y'know, those typical things.



I'm always just a little shy on the freeway and my heart gets a little heavy when I go over 5k, just from other vehicles experience.



What might help is that it's an 81 CX500 Custom with what I'd assume is a 16" rear... which leads me to ask, what could I do to to make the top speed a little easier attainable? Could I switch to an 18"?



Thanks guys


4500 in 4th gear is around 40mph. Anything under fifth gear is hard to guess. In fifth gear take the rpm and add 500 to it and divide by 100. 6500 = 70mph, 4000= 4500. 4th gear is opposite of that so rpm -500 divided by 100. 4500= 40mph



If you switch it to an 18 inch rim you will go faster but it may take longer to go faster because you're adding size that affects torque. But it might not be effected in any way.



Feel free to crank the bike up. It doesn't mind. I usually don't go over 8-9000rpms but there is no worry about blowing the bike up.
 

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If your brakes are not dragging or clutch slipping, in stock trim, figure 11 mph for every 1000rpm. in top gear... 6000rpm =66 mph rough but close enough for Jazz and Radar




A strong headwind will reduce top speed pretty drastically.



I'm not sure about the other gears, but there are many forum members with Parts for sale at reasonable prices and I bet you could get a new speedo for a song.. might even take 20-30k off the od reading




Sure it's not just the cable ( easy fix) ?



Putting an 18" rim is one way to get a taller gear... tire profiles are also different.



You could end up with a lower profile fatty tire on the 18" and not gain much.



Your Bike will not blow up at 7k... they like to rev and mine sees 7k to 9k fairly often. I've blown speed shifts running it up to 10.5... not good, but good It ain't a harley
 

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I think this is true although it sounds like a bat out of hell our redline is like almost 10 or 11 grand at 75 or 80 on highway i am reving like 7 grand on the rpm's but again the bike seems to like it that way. and then again it just wastes more gas 55 60 is just a fine cruising speed heck even at a steady 70 cars a still flying past ya lol
 

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I think this is true although it sounds like a bat out of hell our redline is like almost 10 or 11 grand at 75 or 80 on highway i am reving like 7 grand on the rpm's but again the bike seems to like it that way. and then again it just wastes more gas 55 60 is just a fine cruising speed heck even at a steady 70 cars a still flying past ya lol




when i am going down the super slab my gas mpg drops by 10 or so but i think that has to do with me making sure i pass everything in sight in other words running 100mph to 105 (its real fun) and i am pegged out at red line or at least sitting at or close to 10 grand call me crazy but to me my bike seems to love to run like that (and i love making her run like that) but thats my bike your could differ
 

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Your gearing will vary slightly dependant upon which make, model, and size of tyre you run (even tyres of the same size can vary on width and diameter quite markedly)but in top a cx will make 11.6mph per 1000rpm in 5th, 8.5mph per 1k in 4th,7.6mph per 1k in 3rd, 5.85mph per 1k in 2nd, 3.96mph per 1k in 1st running a 130/90-16 and 12.22mph per 1000rpm in 5th, 8.92mph per 1k in 4th,8.03mph per 1k in 3rd, 6.15mph per 1k in 2nd, 4.16mph per 1k in 1st running a 120/90-18 so cruising in 4th and 5th are quite altered in comparison

To answer your question (using a 130/90-16) 4500 in 4th is approx 40mph, and 35mph in 3rd

65mph is 8000 in 3rd, 7200-ish in 4th, and 5400k-ish in top

you can further reduce revs by fitting the 650 clutch and primary gear raising the ratio to 2.056 from 2.242 (36/74 from 33/74)



Lots of Honda ( in fact all japanese manufactures) use 1.4:1 ratio speedo's and most most tacho's are interchangeable so you can basically run what you want. Some Suzuki Guages not only look good, but are much higher quality than standard Honda units

these motors were made to rev and love doing it so dont be afraid to rev it all day long
 

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I'm always just a little shy on the freeway and my heart gets a little heavy when I go over 5k, just from other vehicles experience.



It has been said many times - these engines like to rev. I know what you mean when you say that the trucker in you doesn´t like to let it spin faster than ~ 5000 rpm. Smooth and relaxed!



But believe me - if your engine is sound and well maintained it´ll cope with continous high revs far better than one would imagine. I´ve been sitting at constant 7500 - 8000 in fifth on German Autobahn for quite some time (around one hour) - and nothing made me believe that the bike wouldn´t want it repeated, if necessary. It´s liquid-cooled, rather short-stroked and proven to stand it.



My bikes are also nearing 30 years. I´m revving them into red, occasionally, without slightest hesitation. Ideal shifting point (full throttle) would be just under red.



Edit:



I´ve scanned a diagram from the Swedish CX 500 standard model (18" rear) owner´s manual.



A 16"-er would be just slightly off.







Sture
 

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Bump - for linked rev-chart
 

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For anyone wanting to know how fast they're traveling just fit a cheap ($30.00) bicycle computer. It will give you much more than simple speed usually 8 to 12 functions and very accurate providing you set it up accurately. Usually the code is the tire circumference in millimeters. Install the magnet on the wheel and the computer on the handlebars. Inflate your front tire to you usual PSI and mark the pavement and tire sit on the bike and have your wife (ha ha ha) friend push you one tire revolution. Mark and measure very carefully, enter the number into the computer and that's it. Example of my race bike (bicycle) is 2054 mm Poor man's data accusition.

Cheers, 50gary
 

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Discussion Starter · #16 ·
Awesome, thanks for all your help guys, and thanks for that graph Sture. Now it sounds like an 18" is the way to go, how would I go about obtaining one? They on ebay easily or does anyone want to sell one on here? Bandit, you said you put an 18 on recently, did you have to do anything to the rear suspension to make more travel room or is it enough play there already?
 

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Awesome, thanks for all your help guys, and thanks for that graph Sture. Now it sounds like an 18" is the way to go, how would I go about obtaining one? They on ebay easily or does anyone want to sell one on here? Bandit, you said you put an 18 on recently, did you have to do anything to the rear suspension to make more travel room or is it enough play there already?
marshall,its a straight swop,no extra work to do.just,id say,,,,while the wheels off,service the brakes and the spline.clean everything up well,bolt the wheel on and ride.enjoy the lower revs,the extra cash in your pocket....you will notice the difference.

the only thing i did later was to fit a piece of steel to the side stand....it lent over a bit too far for my liking
 

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Awesome, thanks for all your help guys, and thanks for that graph Sture. Now it sounds like an 18" is the way to go, how would I go about obtaining one? They on ebay easily or does anyone want to sell one on here? Bandit, you said you put an 18 on recently, did you have to do anything to the rear suspension to make more travel room or is it enough play there already?


Shipping won't be cheap no matter how you go, first place I'd ask would be in out 'Parts for sale/wanted" forum. AN alternate might be a salvage yard but I'd be darn sure the wheel was straight.
 

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You should also verify that they are switchable between KM/h and mph if needed.
 
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