Losing Weight

newmann
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2/23/2011 3:02pm
Nerd wrote:
Not only that, but the truth of the "weight" thing is that a two-stroke FEELS lighter (which is really the point) mainly because there is much...
Not only that, but the truth of the "weight" thing is that a two-stroke FEELS lighter (which is really the point) mainly because there is much less circulating mass in the engine, so regardless of actual pounds of weight, the two-stroke will feel lighter anyway.
Clotskull wrote:
WRONG.
rmpilot wrote:
how is that wrong?
Because the 250 lb. mass centralized YZ450F feels lighter than a 190 lb. YZ125.....surely you shoud have known.

Mass centralization
Mass centralization
Mass centralization
Mass centralization
Mass centralization
Mass centralization
Erick
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2/23/2011 3:02pm Edited Date/Time 2/23/2011 3:05pm
newmann wrote:
Far be it for me and my high school education to get into a pissing match with anyone who has technical/engineering background.:) Not disagreeing with you...
Far be it for me and my high school education to get into a pissing match with anyone who has technical/engineering background.Smile Not disagreeing with you in the least as everything you stated makes good sense. But modern 4 strokes have huge ass mufflers and that bolt on way up high at the seat mount. That's the bulk of the exhaust system weight as some current bikes already have ti headpipes on them.

There are certain areas where my 4 inch travel vintage bikes handle better than a modern bike (whoops wouldn't be one). Why? My guess would be because it sits lower.

Questions for you though about the titanium springs. Are they sprung or unsprung weight? Or 50/50? And does that differ from the front springs (spring /singular on his 2011 KX250F) to the rear shock spring?
I neither have the purpose of getting into a pissing match Smile

To be honest I havent thought about the weight of the muffler when making the statement about the CG of the exhaust. In that case you are right.

About the springs, the actual mass that is unsprung is theoreticly one third of the mass of the spring itself. This is for a perfect vertical spring, in reality no spring is ideal so the theory is just an approach to the reality. It also differs when the mass to springmass ratio takes radical forms.

The actual unsprung mass is also dertermined by the angle of the spring relative to the surface. Because if the spring is horizontal the unsprungmass of the spring doesn't have an affect on the system (because the force of the unsprung weight of the spring is vertical so this has no effect on the spring which is horizontal).

I hope I made myself clear. It is getting late over here and I am getting a bit tired.


Reference to determining the unsprung mass of a spring:
http://depa.pquim.unam.mx/amyd/archivero/Paraosciladorarmonico_1127.pdf
rmpilot
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2/23/2011 3:54pm
Clotskull wrote:
WRONG.
rmpilot wrote:
how is that wrong?
newmann wrote:
Because the 250 lb. mass centralized YZ450F feels lighter than a 190 lb. YZ125.....surely you shoud have known. Mass centralization Mass centralization Mass centralization Mass centralization...
Because the 250 lb. mass centralized YZ450F feels lighter than a 190 lb. YZ125.....surely you shoud have known.

Mass centralization
Mass centralization
Mass centralization
Mass centralization
Mass centralization
Mass centralization
gosh darnit im too darn stupid to have realized that.
newmann
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2/23/2011 4:03pm
rmpilot wrote:
gosh darnit im too darn stupid to have realized that.
Don't worry, you'll learn all kinds of stuff here.Huh

The Shop

2/23/2011 6:28pm
rmpilot wrote:
how is that wrong?
It was disproven on thumpertalk by a few engineers. The gyroscopic forces of the extra moving parts is negligible. Think of it this way: your bike doesn't stay upright, at a stand still, while the engine is running because the resistance to roll about the axis is minute due to the small diameter of the moving parts.
Erick
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2/24/2011 3:49am
Clotskull wrote:
It was disproven on thumpertalk by a few engineers. The gyroscopic forces of the extra moving parts is negligible. Think of it this way: your bike...
It was disproven on thumpertalk by a few engineers. The gyroscopic forces of the extra moving parts is negligible. Think of it this way: your bike doesn't stay upright, at a stand still, while the engine is running because the resistance to roll about the axis is minute due to the small diameter of the moving parts.
Do you have an reference to that?
newmann
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2/24/2011 6:04am
rmpilot wrote:
how is that wrong?
Clotskull wrote:
It was disproven on thumpertalk by a few engineers. The gyroscopic forces of the extra moving parts is negligible. Think of it this way: your bike...
It was disproven on thumpertalk by a few engineers. The gyroscopic forces of the extra moving parts is negligible. Think of it this way: your bike doesn't stay upright, at a stand still, while the engine is running because the resistance to roll about the axis is minute due to the small diameter of the moving parts.
I'm guessing that extra ten pounds in the cylinder head sitting way up high doesn't give the bike a top heavy feel either?Whistling
burn1986
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2/24/2011 6:36am
There is something to the gyroscopic effect. A light CR500 will be slightly harder to turn than a cr250 even if they weigh the same. Maybe its the bigger crank, but it would make more sense that if you have more moving parts, you will have more gyroscopic effect.
TooOldToPlay
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2/24/2011 7:44am
burn1986 wrote:
There is something to the gyroscopic effect. A light CR500 will be slightly harder to turn than a cr250 even if they weigh the same. Maybe...
There is something to the gyroscopic effect. A light CR500 will be slightly harder to turn than a cr250 even if they weigh the same. Maybe its the bigger crank, but it would make more sense that if you have more moving parts, you will have more gyroscopic effect.
Ok so now I am confused, so would it still be a good thing to build something like this?

Erick
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2/24/2011 8:05am
Ok so now I am confused, so would it still be a good thing to build something like this? [img]http://i371.photobucket.com/albums/oo154/TooOldToPlay/ConceptYZ250EFI2StrokeRevAngle.jpg[/img]
Ok so now I am confused, so would it still be a good thing to build something like this?

That would be very good!

Even better when you place the gas tank on the place where the airbox normally is. But then you would have some problems with the expansion chamber.
hellion
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2/24/2011 8:23am
Clotskull wrote:
WRONG.
rmpilot wrote:
how is that wrong?
newmann wrote:
Because the 250 lb. mass centralized YZ450F feels lighter than a 190 lb. YZ125.....surely you shoud have known. Mass centralization Mass centralization Mass centralization Mass centralization...
Because the 250 lb. mass centralized YZ450F feels lighter than a 190 lb. YZ125.....surely you shoud have known.

Mass centralization
Mass centralization
Mass centralization
Mass centralization
Mass centralization
Mass centralization
You are on crack if you think the YZ450 feels lighter than the YZ 125.
burn1986
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2/24/2011 8:27am
Bad! Where did you get those YZ photos? Man, how cool it will be when they start making these things!

"They'll never make those" in 5...4...3...2..1...
Erick
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2/24/2011 8:38am Edited Date/Time 2/24/2011 8:40am
Yamaha propably wouldn't make it.

But TM, GAS GAS, Sherco, Beta, Ossa, KTM (look at the KTM SX65) or Husaberg wouldn't have a problem with it. I am quite sure a crazy Swede, Spaniard or Italian already has some smart and creative ideas running about a radical two stroke design.
TooOldToPlay
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2/24/2011 8:42am
Erick wrote:
Yamaha propably wouldn't make it. But TM, GAS GAS, Sherco, Beta, Ossa, KTM (look at the KTM SX65) or Husaberg wouldn't have a problem with it...
Yamaha propably wouldn't make it.

But TM, GAS GAS, Sherco, Beta, Ossa, KTM (look at the KTM SX65) or Husaberg wouldn't have a problem with it. I am quite sure a crazy Swede, Spaniard or Italian already has some smart and creative ideas running about a radical two stroke design.
Yeah I am pretty sure the Ossa trials bike motor I stuck in the YZ frame in the the photo probably would not be a great fit......Grinning Grinning Whistling
nytsmaC
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2/24/2011 8:58am
hellion wrote:
You are on crack if you think the YZ450 feels lighter than the YZ 125.
Mass centralization. True story.
nytsmaC
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2/24/2011 9:03am
burn1986 wrote:
There is something to the gyroscopic effect. A light CR500 will be slightly harder to turn than a cr250 even if they weigh the same. Maybe...
There is something to the gyroscopic effect. A light CR500 will be slightly harder to turn than a cr250 even if they weigh the same. Maybe its the bigger crank, but it would make more sense that if you have more moving parts, you will have more gyroscopic effect.
Dunno about that..I think horsepower is directly related to handling. Detune a 500 to under 40hp in a modern chassis and it will turn great too.
newmann
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2/24/2011 9:32am
rmpilot wrote:
how is that wrong?
newmann wrote:
Because the 250 lb. mass centralized YZ450F feels lighter than a 190 lb. YZ125.....surely you shoud have known. Mass centralization Mass centralization Mass centralization Mass centralization...
Because the 250 lb. mass centralized YZ450F feels lighter than a 190 lb. YZ125.....surely you shoud have known.

Mass centralization
Mass centralization
Mass centralization
Mass centralization
Mass centralization
Mass centralization
hellion wrote:
You are on crack if you think the YZ450 feels lighter than the YZ 125.
Oh shit, I've been lied to?Laughing
newmann
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2/24/2011 9:43am
burn1986 wrote:
There is something to the gyroscopic effect. A light CR500 will be slightly harder to turn than a cr250 even if they weigh the same. Maybe...
There is something to the gyroscopic effect. A light CR500 will be slightly harder to turn than a cr250 even if they weigh the same. Maybe its the bigger crank, but it would make more sense that if you have more moving parts, you will have more gyroscopic effect.
Ok so now I am confused, so would it still be a good thing to build something like this? [img]http://i371.photobucket.com/albums/oo154/TooOldToPlay/ConceptYZ250EFI2StrokeRevAngle.jpg[/img]
Ok so now I am confused, so would it still be a good thing to build something like this?

Sweet, I'd buy that!!
Erick
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2/24/2011 9:55am
Yeah I am pretty sure the Ossa trials bike motor I stuck in the YZ frame in the the photo probably would not be a great...
Yeah I am pretty sure the Ossa trials bike motor I stuck in the YZ frame in the the photo probably would not be a great fit......Grinning Grinning Whistling
hehe yeah I know Tongue

Thats why I mentioned Ossa Wink pretty easy job for them, buy yamaha's, cut and weld the frame, heat treatment and you are set Wink
Erick
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2/24/2011 10:00am Edited Date/Time 2/24/2011 10:03am


Imagine a 250 or 125, it would sell like hot cakes

Haha this is turning in another two stroke thread. Only a fool would say two strokes are dead.
2/24/2011 11:00am
Erick wrote:
Do you have an reference to that?
http://www.thumpertalk.com/forum/archive/index.php/t-916617.html


Like KJ790 said in that thread, the major factor is the diameter of a spinning component in determining the angular momentum. The heavier feel is most likely a combination of different factors like frame geometry, cg, and a lot more power.
Erick
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2/24/2011 11:19am
Clotskull wrote:
http://www.thumpertalk.com/forum/archive/index.php/t-916617.html Like KJ790 said in that thread, the major factor is the diameter of a spinning component in determining the angular momentum. The heavier feel is...
http://www.thumpertalk.com/forum/archive/index.php/t-916617.html


Like KJ790 said in that thread, the major factor is the diameter of a spinning component in determining the angular momentum. The heavier feel is most likely a combination of different factors like frame geometry, cg, and a lot more power.
Thank you for the reference Smile

I can see these people are not making wild guesses there. But I am not fully convinced because I fail to see the effect of rotating mass moving in liniear motion on a stick. In this case the stick represents the motorcycle itself. But I must admit I do not know how to calculate the effects of rotating mass in liniear motion on a stick so it kinda makes my opinion irrelevant Wink

Anyway thanks for the link, I bookmarked the forum, I didn't know it had an dedicated engineering section Smile
rohleder644
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2/24/2011 11:43am
I believe fmf did a pretty trick lightweight ktm 300 as well
burn1986
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2/24/2011 11:53am
Pretty interesting article from Thumpertalk. So I wonder if I'm faster on an XR200 or a CR125? I'll have to study it furtherCool
newmann
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2/24/2011 11:56am
FMF 199 lb. KTM 300.

http://www.dirtrider.com/reviews/dirt_bike/141_0911_fmf_racing_199lb_20…

What The Scale Says
Stock Parts (lb) Installed Parts (lb) Weight Saved (lb)
Pipe: 4.45 FMF Special Titanium pipe: 2.90 1.55
Silencer: 3.95 FMF Special Titanium silencer: 2.00 1.95
Rear wheel: 9.05 Round Wheels with heavy-duty spokes: 8.95 0.10
Front wheel: 7.50 Round Wheels with heavy-duty spokes: 6.45 1.05
Rear tire: 10.70 Dunlop 773: 9.95 0.75
Front tire: 8.35 Dunlop D745: 8.05 0.30
Rear tube: 2.05 Tu-Bliss, rimlock is included: 1.60 0.45
Front tube: 1.80 Tu-Bliss, rimlock is included: 1.70 0.10
Brake disc front: 1.10 Braking: 1.05 0.05
Sprocket rear: 0.90 KTM Hard Parts Renthal: 0.70 0.20
Footpeg set: 1.70 Footpeg set, titanium: 1.00 0.70
Spring rear: 3.65 Titanium: 2.05 1.60
Handlebar: 1.60 ProTaper: 1.40 0.20
Subframe: 2.50 Titanium: 1.70 0.80
Seat and base: 2.95 Cycleworks: 2.05 0.90
Chain: 3.85 RK: 3.25 0.60
Chain guide: 0.85 BRP: 0.55 0.30
Full plastic kit: 3.80 Cycra: 3.30 0.50
Installed Parts Savings Total: 12.45 lb
Minus Miscellaneous Trimming: 0.65 lb
Total: 13.10 lb
burn1986
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2/24/2011 12:10pm
Wow, I'm sure they could use a few more if they applied some of the weight saving that was done on the CRF250.
2/24/2011 4:59pm
Erick wrote:
Thank you for the reference :) I can see these people are not making wild guesses there. But I am not fully convinced because I fail...
Thank you for the reference Smile

I can see these people are not making wild guesses there. But I am not fully convinced because I fail to see the effect of rotating mass moving in liniear motion on a stick. In this case the stick represents the motorcycle itself. But I must admit I do not know how to calculate the effects of rotating mass in liniear motion on a stick so it kinda makes my opinion irrelevant Wink

Anyway thanks for the link, I bookmarked the forum, I didn't know it had an dedicated engineering section Smile
Anything spinning is going to produce a gyroscopic effect so the cams at the top of the "stick" will resist change to rotation. As the axis of the cams pivot as the bike leans, they will resist that change because of their gyroscopic effect. But, like was pointed out in that thread, the real determining factor in angular momentum is the diameter and not the RPMs thus the cams are too small to make a difference even if they're spinning at 10,000 RPMs. Again like KJ790 said in that thread nobody complains when they put a heavy duty tube in even though that has a far greater change in angular momentum.
3D
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2/24/2011 5:35pm
So I should be adding lead to the sides of my yz250 motor to make it feel lighter due to mass centralization?
mfowler
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2/24/2011 5:58pm
burn1986 wrote:
Totally good article Newmann. If MXA lost 17 obs on a CRF250, imagine how much you could lose on a 125, or a 150, heck, even...
Totally good article Newmann. If MXA lost 17 obs on a CRF250, imagine how much you could lose on a 125, or a 150, heck, even a 250. Can you imagine losing 17-20 lbs on a 125 or 150? That would almost be worth the money.
ATKpilot99 wrote:
Sometime in the 90s Dirt Bike or MXA, can't remember which built a 167 lb. CR 125.
Sometime in the early or mid 70s MXA had an article about a guy who built a 176 lb CZ. Can't remember what CC it was, someone here might have a copy of that issue.
bigmaico
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2/25/2011 6:21am
Here's a rotten trick my friends dad did to him back in the day.

He was racing a RM 370 & he weighed about 160lbs & keep telling his dad that the bike was too heavy for him.

Dad decided to "fix it" for him & hid about 20 pounds of lead on the bike for practice, he would remove it for race day.

After about 2 months of the "fix" he was no longer bitching about the bike being too heavy & he was blazing fast on it!

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