How much RPM is good to cruising speed 250cc

rockridex · 07-21-2021, 09:28 PM

Hi everyone!!

The original engine of my yamaha tzr 250 no longer works so please do not ask me about it.

Instead I bought and instaled this OHC LIFAN 250cc engine, and I want to travel with it but I would like to know how many revolutions it is advisable to take it to?

I say this because my current tachometer and speedometer tells me that in the 5th gear at 5,000 revolutions it throws me 80 kilometers per hour and at 6500 revolutions it throws me 100 kilometers per hour.

But I don't know if my tachometer and speedometer are lying to me or I'm really reaching that speed at those revs.

It is worth mentioning the following:
- Weight 70kg
- My rear rims are thin (130 thin profile)
- I put a 17 tooth pinion on the engine and I put 42 teeth on the rim crown.

It has a conical air filter and free exhaust.

help me please I don't want to spoil the engine.

franque · 07-22-2021, 12:29 AM

Welcome! I take it from the TZR that you're not in the States? The RPMs will be different based on the internal gearing, primary drive ratio (also internal), and then the sprockets you use. One of those motors should be good for at least 7-7.5k continuous RPM, but that won't necessarily correspond to the revs that you've ran with the old motor.

If you look at a service manual for the TZR you can compare the gearing in your old motor vs. the new one.

For the Lifan with a 16/50 secondary reduction (the sprockets, which are geared for off-road) on a bike with the same primary drive ratio as the new motor, you're looking at around 13.43 km/1000rpm.

You'll probably be running a smaller rear sprocket, so if you ran, say, a 17/40 ratio, you'd be getting 17.83 km/1000 rpm, with roughly the same, maybe slightly larger diameter rear tire.

It also depends on what size chain you're running, because a 520 chain creates larger diameter sprockets with fewer teeth, but you should be able to calculate correspondingly.

This is assuming your Lifan is the 6-speed, if it's a 5 speed, final numbers would be around 15.69 km/1000 RPM.

You should post up pics of the install, we'd love to see it here, and don't hesitate to ask any questions!

rockridex · 07-22-2021, 02:52 AM

Quote:

Originally Posted by franque

Welcome! I take it from the TZR that you're not in the States? The RPMs will be different based on the internal gearing, primary drive ratio (also internal), and then the sprockets you use. One of those motors should be good for at least 7-7.5k continuous RPM, but that won't necessarily correspond to the revs that you've ran with the old motor.

If you look at a service manual for the TZR you can compare the gearing in your old motor vs. the new one.

For the Lifan with a 16/50 secondary reduction (the sprockets, which are geared for off-road) on a bike with the same primary drive ratio as the new motor, you're looking at around 13.43 km/1000rpm.

You'll probably be running a smaller rear sprocket, so if you ran, say, a 17/40 ratio, you'd be getting 17.83 km/1000 rpm, with roughly the same, maybe slightly larger diameter rear tire.

It also depends on what size chain you're running, because a 520 chain creates larger diameter sprockets with fewer teeth, but you should be able to calculate correspondingly.

This is assuming your Lifan is the 6-speed, if it's a 5 speed, final numbers would be around 15.69 km/1000 RPM.

You should post up pics of the install, we'd love to see it here, and don't hesitate to ask any questions!

Thanks for your answer.

Sorry, i'm not using the original tzr250 tachometer i'm using this universal tachometer.

And my Lifan engine is 5 speed.

My rear sprocket is 42 teeth
My engine sprocket is 17 teeth
Chain size 428H

Please help me

The principal reason is i wanna know how much rpm i need to be cruising speed. Its 2:13am in the morning i'll sent images for the instalation.

Bruces · 07-22-2021, 01:50 PM

The tz is a race bike you can order from the dealer ,not road legal ,2 stroke ,up to 750ccthat I know about ,you are asking about “cruising speed “ ,what are you trying to do with this bike ?it used to go 100 mph on a race track ,with the lifan 75mph is probably about it ,are you trying to make it street legal or are you going to road race it ? It’s somewhat rare and valuable ,I would think seriously about modifying the bike ,and certainly wouldn’t put in a lifan 250 .

franque · 07-22-2021, 02:30 PM

That's a TZR, not a TZ... they didn't make it to this side of the Atlantic. The TZR was a road legal model.

It depends on how small of a sprocket you can get for the rear, but with that combo, I would think at least 90km/h would be a reasonable all-day cruising speed with your current gearing. It's pretty light though, so if you can get a smaller rear sprocket, you could easily cruise at 130 or so assuming you're relatively light yourself. 7500 is a good max cruising RPM.

Make sure you change the oil before you run it, they ship with cheap stuff in the crankcase that is little more than a rust preventative.

Where are you located?

Bruces · 07-22-2021, 04:09 PM

So ,it’s an RZ ? We had those in Canada ,but only as 350 and 500 cc bikes .

franque · 07-22-2021, 09:08 PM

Nope, the RZ was strictly a sporty road bike, we got them in the States too. The TZRs were 250cc Yamaha homologation specials/2t sport bikes, much like the Honda NSRs, Suzuki RGVs and Kawasaki KR-1s... Most were V-Twins with the exception of some TZRs and some if the Kawasakis, and they were sold for production racing/marketing the proddie bikes. NA never received any of the 250cc 2t homologation specials/race bikes of the 80s and 90s, with the exception of the Aprilia RS250, which used a Suzuki motor.

07-21-2021, 09:28 PM	#1
rockridex Join Date: Jul 2021 Posts: 2	How much RPM is good to cruising speed 250cc Hi everyone!! The original engine of my yamaha tzr 250 no longer works so please do not ask me about it. Instead I bought and instaled this OHC LIFAN 250cc engine, and I want to travel with it but I would like to know how many revolutions it is advisable to take it to? I say this because my current tachometer and speedometer tells me that in the 5th gear at 5,000 revolutions it throws me 80 kilometers per hour and at 6500 revolutions it throws me 100 kilometers per hour. But I don't know if my tachometer and speedometer are lying to me or I'm really reaching that speed at those revs. It is worth mentioning the following: - Weight 70kg - My rear rims are thin (130 thin profile) - I put a 17 tooth pinion on the engine and I put 42 teeth on the rim crown. It has a conical air filter and free exhaust. help me please I don't want to spoil the engine. Last edited by rockridex; 07-21-2021 at 10:01 PM.
	0

07-22-2021, 12:29 AM	#2
franque Join Date: Nov 2017 Location: Marseille, France -> Conakry, Guinea Posts: 1,481	Welcome! I take it from the TZR that you're not in the States? The RPMs will be different based on the internal gearing, primary drive ratio (also internal), and then the sprockets you use. One of those motors should be good for at least 7-7.5k continuous RPM, but that won't necessarily correspond to the revs that you've ran with the old motor. If you look at a service manual for the TZR you can compare the gearing in your old motor vs. the new one. For the Lifan with a 16/50 secondary reduction (the sprockets, which are geared for off-road) on a bike with the same primary drive ratio as the new motor, you're looking at around 13.43 km/1000rpm. You'll probably be running a smaller rear sprocket, so if you ran, say, a 17/40 ratio, you'd be getting 17.83 km/1000 rpm, with roughly the same, maybe slightly larger diameter rear tire. It also depends on what size chain you're running, because a 520 chain creates larger diameter sprockets with fewer teeth, but you should be able to calculate correspondingly. This is assuming your Lifan is the 6-speed, if it's a 5 speed, final numbers would be around 15.69 km/1000 RPM. You should post up pics of the install, we'd love to see it here, and don't hesitate to ask any questions!
	0

07-22-2021, 01:50 PM	#4
Bruces Join Date: May 2018 Posts: 1,591	The tz is a race bike you can order from the dealer ,not road legal ,2 stroke ,up to 750ccthat I know about ,you are asking about “cruising speed “ ,what are you trying to do with this bike ?it used to go 100 mph on a race track ,with the lifan 75mph is probably about it ,are you trying to make it street legal or are you going to road race it ? It’s somewhat rare and valuable ,I would think seriously about modifying the bike ,and certainly wouldn’t put in a lifan 250 .
	0

07-22-2021, 02:30 PM	#5
franque Join Date: Nov 2017 Location: Marseille, France -> Conakry, Guinea Posts: 1,481	That's a TZR, not a TZ... they didn't make it to this side of the Atlantic. The TZR was a road legal model. It depends on how small of a sprocket you can get for the rear, but with that combo, I would think at least 90km/h would be a reasonable all-day cruising speed with your current gearing. It's pretty light though, so if you can get a smaller rear sprocket, you could easily cruise at 130 or so assuming you're relatively light yourself. 7500 is a good max cruising RPM. Make sure you change the oil before you run it, they ship with cheap stuff in the crankcase that is little more than a rust preventative. Where are you located?
	1

07-22-2021, 04:09 PM	#6
Bruces Join Date: May 2018 Posts: 1,591	So ,it’s an RZ ? We had those in Canada ,but only as 350 and 500 cc bikes .
	0

07-22-2021, 09:08 PM	#7
franque Join Date: Nov 2017 Location: Marseille, France -> Conakry, Guinea Posts: 1,481	Nope, the RZ was strictly a sporty road bike, we got them in the States too. The TZRs were 250cc Yamaha homologation specials/2t sport bikes, much like the Honda NSRs, Suzuki RGVs and Kawasaki KR-1s... Most were V-Twins with the exception of some TZRs and some if the Kawasakis, and they were sold for production racing/marketing the proddie bikes. NA never received any of the 250cc 2t homologation specials/race bikes of the 80s and 90s, with the exception of the Aprilia RS250, which used a Suzuki motor.
	0