[PEH]

Hi All,
I am completly new to this forum and was hoping for some advice. I have just picked up a 1981 Honda CM250T and it sits at 60-65 MPH at 8-8.5K revs, I am not sure if this is a bit high to keep the engine for long periods of time (the clocks red line at 9.5)?

Also, is it worth trying to source a slightly larger rear sprocket to keep the revs lower but still achieve 65 - 70 MPH?

Any help would be appreciated.
Thanks,
Paul

 

[Bill H]

You will probably get a lot of advice but from here the Honda motors like to rev. You need to stay above 3500 for the alternator to put out a full charge. Keep it full of good oil and keep it tuned and enjoy it.

Bill H

 

[PEH]

You will probably get a lot of advice but from here the Honda motors like to rev. You need to stay above 3500 for the alternator to put out a full charge. Keep it full of good oil and keep it tuned and enjoy it.

Bill H

Thanks Bill

 

[01-7700]

Hi All,
I am completly new to this forum and was hoping for some advice. I have just picked up a 1981 Honda CM250T and it sits at 60-65 MPH at 8-8.5K revs, I am not sure if this is a bit high to keep the engine for long periods of time (the clocks red line at 9.5)?

Also, is it worth trying to source a slightly larger rear sprocket to keep the revs lower but still achieve 65 - 70 MPH?

Any help would be appreciated.
Thanks,
Paul

A larger rear sprocket (the one on the wheel) will increase rpms for a given speed. The stock ratio is optimum. Using a smaller rear sprocket will stretch out the shifting pattern in the lower gears but will also reduce the top end speed - the engine output is fixed - you can't get more power by switching sprockets.

 

[PEH]

A larger rear sprocket (the one on the wheel) will increase rpms for a given speed. The stock ratio is optimum. Using a smaller rear sprocket will stretch out the shifting pattern in the lower gears but will also reduce the top end speed - the engine output is fixed - you can't get more power by switching sprockets.

Thanks Keith that's great, I was thinking that 65MPH at 8K would be a bit too stressful on the engine, so I was thinking that a slightly larger rear would take a bit of the stress off the engine at the higher speed end, I realise that this would cause a greater load on pulling off, but thought this could be managed by some sympathetic riding.

Thanks again,
Paul

 

[Donthav1]

If you want to lower RPM, you need to go smaller on the rear, or larger on the front. Swapping the front sprocket is easier in my experience.

This website has a pretty handy rpm calculator: Gearing Commander - Motorcycle Speed and Drive Train Calculator v7

I don't see your specific bike listed there, but you should be able to find a similar model to compare it to.

 

[Emil]

I have a CM200T & have put an 18T on the front. It fits well. This thread has a picture of it installed. Top speed remains the same but revs are much lower.

What is the top speed of a CM200T? (1981)

1st, I'd again very much like to thank Dr Acula for this CM200T motorcycle. I have recently installed rectangular mirrors from China, cost $15. I found that the front sprocket 16T was easily replaced for an 18T with plenty of room to spare. Although it couldn't go even 1 tooth more. It works...

www.hondatwins.net

P.S. Welcome to the forum.

 

[PEH]

If you want to lower RPM, you need to go smaller on the rear, or larger on the front. Swapping the front sprocket is easier in my experience.

This website has a pretty handy rpm calculator: Gearing Commander - Motorcycle Speed and Drive Train Calculator v7

I don't see your specific bike listed there, but you should be able to find a similar model to compare it to.

Thanks, Can't think what I was thinking, I'll take a look at front sprocket options. Great advice, cheers.

 

[PEH]

I have a CM200T & have put an 18T on the front. It fits well. This thread has a picture of it installed. Top speed remains the same but revs are much lower.

What is the top speed of a CM200T? (1981)

1st, I'd again very much like to thank Dr Acula for this CM200T motorcycle. I have recently installed rectangular mirrors from China, cost $15. I found that the front sprocket 16T was easily replaced for an 18T with plenty of room to spare. Although it couldn't go even 1 tooth more. It works...

www.hondatwins.net

P.S. Welcome to the forum.

Thanks, looks like a potential option, thanks for the welcome, seems to be some great folks on here.

 

[Montanabill]

How big are you? on these smaller bikes wind resistance makes a difference. I am 6'4" and 200 pounds (about two meters and I don't know how many stone, for our enlishmen) Working in a honda shop I test rode quite a few 250's usually the rebels. They would see 75 on a good day but I would have to tuck in to go that fast. I also currently live at almost 5K feet and that makes quite a difference. When I used to live at 1K feet elevation everything had more power.
Try a one tooth larer front sproicket and see if it works, the cost is reasonable and having the engine more relaxed at speed would be worth it. Just be ready to shift down on any hill.

they are great bikes and the gas mileage is amazing.

 

[Emil]

For every tooth you change the front sprocket, It's relatively equivalent to a three tooth change in the back.
I am 5' 8" about 170 lb and 65 mph is about all I can do on the CM200T (~17HP).
The Rebels (1st generation w/~20HP) , I can get to 85 mph if I truly want to, but there's no way that it's what I would consider to be safe.

 

[Donthav1]

That is an excellent point about the wind resistance. Small bikes don't have the power to overcome it as easily as larger ones. Also, if you have a medium to large sized windshield, that reduces the speed further.

Find out what sprocket is on the front now, it's possible it's already been changed by a previous owner.

I would also recommend only going one tooth larger than stock.

 

[Montanabill]

Just some more background on going as fast as possible on small bikes. Here is a photo of a 175 of another brand that was my first real road bike. I put low clip on bars and a road race fairing on it and did q
uite a few interstate rides. It would go fast enough to get a speeding ticket on a posted 70MPH road. Another time long ago my ex and i took a cheap filght to europe and bought a 175 and a 200 honda twin and rode freeways and all sorts of roads from england to the south of france.
Wide open and tucked in on the faster roads so we didn't get run over.

 

[PEH]

How big are you? on these smaller bikes wind resistance makes a difference. I am 6'4" and 200 pounds (about two meters and I don't know how many stone, for our enlishmen) Working in a honda shop I test rode quite a few 250's usually the rebels. They would see 75 on a good day but I would have to tuck in to go that fast. I also currently live at almost 5K feet and that makes quite a difference. When I used to live at 1K feet elevation everything had more power.
Try a one tooth larer front sproicket and see if it works, the cost is reasonable and having the engine more relaxed at speed would be worth it. Just be ready to shift down on any hill.

they are great bikes and the gas mileage is amazing.

Hi Don,
I am 6' and about 225 pounds. I really hadn't considered the impact of my weight as when I last had a CM250 (which is why I have bought this one) and back then I would have been about 165 pounds! I guess even changing the sprocket would still end up succumbing to the HP issue. with regards to the elevation, I am pretty near sea level so no problem there. Thanks so much for the input

 

[PEH]

That is an excellent point about the wind resistance. Small bikes don't have the power to overcome it as easily as larger ones. Also, if you have a medium to large sized windshield, that reduces the speed further.

Find out what sprocket is on the front now, it's possible it's already been changed by a previous owner.

I would also recommend only going one tooth larger than stock.

Thanks, I will definetly take a look. great input, thanks!