Why RPS bikes won't do 80MPH. With numbers

DualSport · 09-19-2018, 04:17 AM

I know the lack of counter-balance shaft and liquid-cooling(unless you have around 100x82(XR 650L) and low gear ratios) would destroy these engines with sustained medium to high rev on long trips(even with oil cooler). But I wanted to compare an RPS Hawk/Magician bore and stroke and drive-train to two sustainable 80MPH(129Km/h) Japanese 250 dual-sports to see why the engine wouldn't produce enough output to do sustainable 80MPH on a flat grade even with sprocket mods.

2018 Kawasaki KLX 250: 72 x 61.2, 14/42 sprockets, ? final ratio(six speed)
(curiousity)2009 Kawasaki Ninja 250R: 62 x 41.2, 14/45 sprockets, ? final ratio(six speed)
2018 RPS Hawk/Magician: 66 x 65, 15/45 sprockets, ? final ratio
2018 Honda CRF 250L: 76 X 55, 14/40 sprockets, ? final ratio(six speed)

Conclusion: Bigger bore supports the shorter arm length that produces higher RPM and ability to gear lower in he top gears without pre-ignition or wrecking valves or over-heating.

Explanation:

You can't modify rod-length of an RPS engine so it's impossible to achieve higher speeds without boring and/or re-gearing the fifth. 34% RPM at 80MPH would require a ratio that would require a bore you can't buy and you can't machine the metal on Chinese sleeves anyway..
Sprockets are too close to matter(just look at before/after results of sprocket mods)
Note the bigger bore and shorter stroke on the Honda; I wonder if this is why Kawasaki did a six-speed and Honda a smaller sprocket?
The Ninja isn't a stroker(not designed for offload required torque) and likely has less torque than an RPS, but has a sixth gear and has about 63% of the stroke of the RPS, so higher RPM through two differences. It probably turns in to a moped on any decent grade though even in the middle of the gears..

**JerryHawk250** · 09-19-2018, 08:03 AM

My Hawk has done 80mph. But I cheated, I was going down hill .

Believe me, you don't want to do 80 on the Hawk. Anything past 70mph it gets a little sketchy with the knobby tires.
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slowroller · 09-19-2018, 08:03 AM

Tread lightly. Get a gps on that klx 250. The forum has some heavy hitters here. With tuning and deep pockets funny things happen. Not many jap 250 dual sports will run 80 on gps some wont with speedo off on knobby tires. Welcome aboard.

ChrisWNY · 09-19-2018, 08:08 AM

A good friend of mine has a newer Honda CRF250L (2016) and it crawls above 55mph, very little to no power. Granted, it gets up to 55mph marginally faster than the Hawk. I've driven his CRF250L on a number of occasions and it is somewhat more powerful, especially in the lower gears...tops out at about 62mph more or less on its stock config. It's definitely not $4000 more powerful.

The problem with high speeds (greater than 65-70mph) on the Hawk goes beyond just the engine overheating/not being able to sustain it. I would imagine the stock wheel bearings could blow out at those speeds, and it's not pleasant to ride that fast on knobbies on pavement.

slowroller · 09-19-2018, 08:13 AM

Probably the closest out there is 1985 to 1989 klr 250 they had 28 hp!!!!!!

Red Hawk · 09-19-2018, 08:32 AM

My 89 KLR 250 did 85 ONCE. I won't try that again. On knobbys it's pretty sketchy for stability.

That said it's got a 6 speed trans, 4 valve DOHC liquid cooled with at least 2x the HP. And it's a 6 speed. See how I did it?

Way to light of a bike to go that fast even on 60/40 tires, just because you can doesn't mean you should. You'll know this too when you've done it.
I'll compromise with 65.

Tashka · 09-19-2018, 03:47 PM

my hawk makes it to 72 pretty good. I often will ride my hawk doing extended high rpm runs. I've commuted with the hawk on the highway, going about 50 mile round trip completely on the highway going 68, with the bike at 7k the whole way there. you can feel the power start to dwindle out at the top end.

My hawk is ported and decked aswell. it doesn't have any problems with extended high speed runs or overheating, and I don't have an oil cooler set up either.

I ride trials tires, they are pretty stable at speeds, but have a light wobble. i dont notice too much.

Most 250f's won't make it to 80 easily either. I've read from CCW that their heists supposedly can cruise at 80mph. They're using the same engine as the hawk, and the bobber they're selling is the same weight or more thsn the hawk.

Ariel Red Hunter · 09-19-2018, 03:52 PM

Quote:

Originally Posted by DualSport

I know the lack of counter-balance shaft and liquid-cooling(unless you have around 100x82(XR 650L) and low gear ratios) would destroy these engines with sustained medium to high rev on long trips(even with oil cooler). But I wanted to compare an RPS Hawk/Magician bore and stroke and drive-train to two sustainable 80MPH(129Km/h) Japanese 250 dual-sports to see why the engine wouldn't produce enough output to do sustainable 80MPH on a flat grade even with sprocket mods.

2018 Kawasaki KLX 250: 72 x 61.2, 14/42 sprockets, ? final ratio(six speed)
(curiousity)2009 Kawasaki Ninja 250R: 62 x 41.2, 14/45 sprockets, ? final ratio(six speed)
2018 RPS Hawk/Magician: 66 x 65, 15/45 sprockets, ? final ratio
2018 Honda CRF 250L: 76 X 55, 14/40 sprockets, ? final ratio(six speed)

Conclusion: Bigger bore supports the shorter arm length that produces higher RPM and ability to gear lower in he top gears without pre-ignition or wrecking valves or over-heating.

Explanation:

You can't modify rod-length of an RPS engine so it's impossible to achieve higher speeds without boring and/or re-gearing the fifth. 34% RPM at 80MPH would require a ratio that would require a bore you can't buy and you can't machine the metal on Chinese sleeves anyway..
Sprockets are too close to matter(just look at before/after results of sprocket mods)
Note the bigger bore and shorter stroke on the Honda; I wonder if this is why Kawasaki did a six-speed and Honda a smaller sprocket?
The Ninja isn't a stroker(not designed for offload required torque) and likely has less torque than an RPS, but has a sixth gear and has about 63% of the stroke of the RPS, so higher RPM through two differences. It probably turns in to a moped on any decent grade though even in the middle of the gears..

I'm not going to rain on this little parade, just drizzle on it a little. By now everyone who reads CR very often knows I used to own an AJS CSR Model 14 that I bought new in 1972, in California. In those days, the English motor cycle press published a magazine with road tests EVERY WEEK! And there were two competing mags every week. I subscribed to one of them, "The Motor-Cycle". So, I'm reading road tests every week. Naturally, I ran across roadtests of the very lively little AJS 250 Model 14. I got more and more interested in what had been originally designed to be a commuter bike to go back and forth to work. But a law was passed that learners (newbies) could not have a bigger bike than a 250. Suddenly, the market changed to "who makes the fastest 250?" The race was on! Up and up went the speeds. Up and up went the bottom end failures! More and more midnight oil burnt to solve the problems. And solve them they did. AJS had the advantage of having the most recent clean piece of paper design. an over-square air-cooled single with very short push rods and big valves. In fact, the cam-pushrod-rocker arm lay out is almost identical to the one in the Hawk. The CSR was the rocket ship of the bunch. Several road tests reported top ends in the low 80's. that's why I bought one. Because of the skimpy 1 quart oil capacity I ran Aero-Shell 40-70 Ashless Dispersent motor oil. And yes, it would run in the 80's mile after mile. I got stopped by a CHP officer once, out in the boonies. "Do you know how fast you were going?" "No, it's only a 250, so can't go too fast, right" "A 250? No way, let me see your license and registration! I clocked you at 85 back there! No kinda' way a 250 can go that fast. Something's gotta be wrong with the police speedometer in my car. I'm going to turn you loose, but hold it down, huh?" "YES SIR". Now there are differences between the Ajay engine and the Hawk engine. The Ajay had more finning on the barrel and much more on the head. It also had dry sump oiling with the oil tank at the front of the right crank case. It had a chain drive primary, 98% efficiency vs. 92% for gears, and a 1 to 1 (direct drive) top gear in the transmission (3% more efficient). Also an inch and an eighth carburetor, more or less 28mm. And battery ignition "Because it allows any spark advance curve you desire"...ARH

**JerryHawk250** · 09-19-2018, 04:06 PM

Quote:

Originally Posted by Tashka

my hawk makes it to 72 pretty good. I often will ride my hawk doing extended high rpm runs. I've commuted with the hawk on the highway, going about 50 mile round trip completely on the highway going 68, with the bike at 7k the whole way there. you can feel the power start to dwindle out at the top end.

My hawk is ported and decked aswell. it doesn't have any problems with extended high speed runs or overheating, and I don't have an oil cooler set up either.

I ride trials tires, they are pretty stable at speeds, but have a light wobble. i dont notice too much.

Most 250f's won't make it to 80 easily either. I've read from CCW that their heists supposedly can cruise at 80mph. They're using the same engine as the hawk, and the bobber they're selling is the same weight or more thsn the hawk.

What sprockets are you running?

ben2go · 09-19-2018, 04:26 PM

I can spout specs and numbers all day. They don't always meet up with real-world experience.

2LZ · 09-20-2018, 02:04 PM

I've run my little bikes up pretty well but 60 is about all I want to do. Spend the vast majority of my time around 45. Very comfy there on our twisties.
I'm with JerryHawk. Anything above 65-70, the bike starts to shrink quickly.

ktigerj · 09-20-2018, 02:25 PM

I don't trust the speedo's on these things at all. My GPS enabled app going down the road is about 10 mph off my bike speedo over about 45. So my phone says I am going 50-53 and the speedo is past 60. This is on a '18 Bashan Storm.

**JerryHawk250** · 09-20-2018, 02:31 PM

Quote:

Originally Posted by ktigerj

I don't trust the speedo's on these things at all. My GPS enabled app going down the road is about 10 mph off my bike speedo over about 45. So my phone says I am going 50-53 and the speedo is past 60. This is on a '18 Bashan Storm.

Yeah, the stock speedos on most of these bikes are way off. My digital speedo is almost dead on with the GPS. You might want to consider switching out to a digital. Cravin01 has a good video on his upgrade. http://chinariders.net/showthread.php?t=21028

timcosby · 09-20-2018, 11:53 PM

jerryhawk250 can verify that my hawk has done 85!

even tho those guys on the fb page still wont read all the comments to know that its true.

DualSport · 09-21-2018, 11:14 AM

Arm length, bore, and gearing are the primary factors in speed. It's a dynamic system of course they don't dictate the whole outcome. Here they pretty accurately correlate with GPS test rides though..

I have GY6 150cc schooters stock that perform almost identical to the Hawk and Magician.. No matter what weight you are you'll be lucky to stay ahead of traffic on most common grades in a 45MPH zone no matter what shifting strategy you use.. Unless someone wants to show one maintaining 50MPH on a 5% or 12% grade without redlining the hell out of the engine..

A liquid cooled six-speed with bigger bore and shorter arm barely does it..(skip to 03:40)

09-19-2018, 04:17 AM	#1
DualSport Join Date: Sep 2018 Posts: 173	Why RPS bikes won't do 80MPH. With numbers I know the lack of counter-balance shaft and liquid-cooling(unless you have around 100x82(XR 650L) and low gear ratios) would destroy these engines with sustained medium to high rev on long trips(even with oil cooler). But I wanted to compare an RPS Hawk/Magician bore and stroke and drive-train to two sustainable 80MPH(129Km/h) Japanese 250 dual-sports to see why the engine wouldn't produce enough output to do sustainable 80MPH on a flat grade even with sprocket mods. 2018 Kawasaki KLX 250: 72 x 61.2, 14/42 sprockets, ? final ratio(six speed) (curiousity)2009 Kawasaki Ninja 250R: 62 x 41.2, 14/45 sprockets, ? final ratio(six speed) 2018 RPS Hawk/Magician: 66 x 65, 15/45 sprockets, ? final ratio 2018 Honda CRF 250L: 76 X 55, 14/40 sprockets, ? final ratio(six speed) Conclusion: Bigger bore supports the shorter arm length that produces higher RPM and ability to gear lower in he top gears without pre-ignition or wrecking valves or over-heating. Explanation: You can't modify rod-length of an RPS engine so it's impossible to achieve higher speeds without boring and/or re-gearing the fifth. 34% RPM at 80MPH would require a ratio that would require a bore you can't buy and you can't machine the metal on Chinese sleeves anyway.. Sprockets are too close to matter(just look at before/after results of sprocket mods) Note the bigger bore and shorter stroke on the Honda; I wonder if this is why Kawasaki did a six-speed and Honda a smaller sprocket? The Ninja isn't a stroker(not designed for offload required torque) and likely has less torque than an RPS, but has a sixth gear and has about 63% of the stroke of the RPS, so higher RPM through two differences. It probably turns in to a moped on any decent grade though even in the middle of the gears.. Last edited by DualSport; 09-19-2018 at 05:54 AM. Reason: 3
	2

09-19-2018, 08:03 AM	#2
JerryHawk250 Moderator Join Date: Oct 2016 Location: Houma, La. Posts: 11,564	My Hawk has done 80mph. But I cheated, I was going down hill . Believe me, you don't want to do 80 on the Hawk. Anything past 70mph it gets a little sketchy with the knobby tires. __________________ 2023 Lifan Lycan 250 Chopper 2023 Venom Evader 2022 Lifan KPX250 2020 Kawasaki Vulcan S 2004 Honda ST 1300 2016 Black Hawk 250 (sold) Keihin PE30 carb,125 main,38 slow.Pod filter,ported & decked head 10:1 CR,Direct Ignition Coil,15/40Sprockets,NGK DPR8EIX-9,De-Cat,Dual Oil Cooler,Digital Cluster 2016 Cazador180 XL 2014 Coolster150 JerryHawk250.com My YouTube Channel
	1

09-19-2018, 08:08 AM	#4
ChrisWNY Join Date: Jul 2018 Posts: 212	A good friend of mine has a newer Honda CRF250L (2016) and it crawls above 55mph, very little to no power. Granted, it gets up to 55mph marginally faster than the Hawk. I've driven his CRF250L on a number of occasions and it is somewhat more powerful, especially in the lower gears...tops out at about 62mph more or less on its stock config. It's definitely not $4000 more powerful. The problem with high speeds (greater than 65-70mph) on the Hawk goes beyond just the engine overheating/not being able to sustain it. I would imagine the stock wheel bearings could blow out at those speeds, and it's not pleasant to ride that fast on knobbies on pavement. __________________ 2018 RPS Hawk 250cc Mods so far: 1. Mikuni VM26 Carburetor w/#115 main jet 2. 17T/45T JT sprockets 3. JT 428 X-ring chain 4. Air box mod 5. Hawk Digital Cluster 6. Aftermarket IMS shift lever 7. Performance Aftermarket Exhaust 8. 295mm Nitrogen Gas Monoshock, 20W oil front forks
	0

09-19-2018, 08:32 AM	#6
Red Hawk Join Date: Jul 2018 Location: NEPA Posts: 273	My 89 KLR 250 did 85 ONCE. I won't try that again. On knobbys it's pretty sketchy for stability. That said it's got a 6 speed trans, 4 valve DOHC liquid cooled with at least 2x the HP. And it's a 6 speed. See how I did it? Way to light of a bike to go that fast even on 60/40 tires, just because you can doesn't mean you should. You'll know this too when you've done it. I'll compromise with 65. __________________ 2018 Hawk P&P Decked .040 off the head. 17/43 D.I.D. 428, NGK Iridium plug, DeCat, Wrapped pipe, Custom S.S. Muffler core, Nibbi PE30 115/35, L.E.D. Lights, Digital Cluster, USB port, Cutting Bord skid plate, Oil cooler w/ custom CRF oil filter inline, 5Wt fork oil, Rear Shock, CNC Back Rack, 30mm FAT bars, Bark Busters, ProGrips, Adjustable levers, Shinko 700’s lots of Loctite!
	1

09-20-2018, 02:04 PM	#11
2LZ Join Date: Mar 2010 Location: Volcano, Ca Posts: 7,092	I've run my little bikes up pretty well but 60 is about all I want to do. Spend the vast majority of my time around 45. Very comfy there on our twisties. I'm with JerryHawk. Anything above 65-70, the bike starts to shrink quickly. __________________ "Light a fire for a man, and you heat him for a day. Light a man on fire, and you heat him for the rest of his life." 2007 Suzuki DRZ400S (SM convert) 2009 Q Link XP 200 1967 BSA B25 250cc Starfire 2022 Royal Enfield Interceptor 650 2023 Royal Enfield Scram 411 1948 Royal Enfield Model G 350
	0

09-19-2018, 08:03 AM	#3
slowroller Join Date: May 2018 Posts: 77	Tread lightly. Get a gps on that klx 250. The forum has some heavy hitters here. With tuning and deep pockets funny things happen. Not many jap 250 dual sports will run 80 on gps some wont with speedo off on knobby tires. Welcome aboard.
	0

09-19-2018, 08:13 AM	#5
slowroller Join Date: May 2018 Posts: 77	Probably the closest out there is 1985 to 1989 klr 250 they had 28 hp!!!!!!
	1

09-19-2018, 03:47 PM	#7
Tashka Join Date: Aug 2018 Posts: 158	my hawk makes it to 72 pretty good. I often will ride my hawk doing extended high rpm runs. I've commuted with the hawk on the highway, going about 50 mile round trip completely on the highway going 68, with the bike at 7k the whole way there. you can feel the power start to dwindle out at the top end. My hawk is ported and decked aswell. it doesn't have any problems with extended high speed runs or overheating, and I don't have an oil cooler set up either. I ride trials tires, they are pretty stable at speeds, but have a light wobble. i dont notice too much. Most 250f's won't make it to 80 easily either. I've read from CCW that their heists supposedly can cruise at 80mph. They're using the same engine as the hawk, and the bobber they're selling is the same weight or more thsn the hawk.
	0

09-19-2018, 04:26 PM	#10
ben2go Join Date: Jun 2011 Posts: 1,335	I can spout specs and numbers all day. They don't always meet up with real-world experience.
	3

09-20-2018, 02:25 PM	#12
ktigerj Join Date: Aug 2018 Location: MD Posts: 20	I don't trust the speedo's on these things at all. My GPS enabled app going down the road is about 10 mph off my bike speedo over about 45. So my phone says I am going 50-53 and the speedo is past 60. This is on a '18 Bashan Storm.
	0

09-20-2018, 11:53 PM	#14
timcosby Join Date: Nov 2016 Location: robertsdale alabama usa Posts: 1,007	jerryhawk250 can verify that my hawk has done 85! even tho those guys on the fb page still wont read all the comments to know that its true. __________________ 1991 harley heritage softail classic 2016 hawk kaw h1 400 tripple 13' long chopper in progress 2009 johnny pag bar hog 2004 hd electra glide ultra classic shriner edition 1997 harley davidson 1200 sportster 1972 harley davidson amf sx250
	2

09-21-2018, 11:14 AM	#15
DualSport Join Date: Sep 2018 Posts: 173	Arm length, bore, and gearing are the primary factors in speed. It's a dynamic system of course they don't dictate the whole outcome. Here they pretty accurately correlate with GPS test rides though.. I have GY6 150cc schooters stock that perform almost identical to the Hawk and Magician.. No matter what weight you are you'll be lucky to stay ahead of traffic on most common grades in a 45MPH zone no matter what shifting strategy you use.. Unless someone wants to show one maintaining 50MPH on a 5% or 12% grade without redlining the hell out of the engine.. A liquid cooled six-speed with bigger bore and shorter arm barely does it..(skip to 03:40)
	1