Torque/HP and gearing

[crxtasy169]

I'll try to find it in my MMI notes and post it just for you. I specifically ask my instructor in Suzuki because I got into this same argument with another guy in class. So why don't you call all the instructors there and argue with them too. Since you get symbols so well here:

_____________________________________rpm top 15k


^
stock max torque @7,500

Add more teeth to rear sproket and you get

_____________________________________
^
same torque lower in rpm range.

 

[crxtasy169]

The engine still puts out the same # it just feels stronger because your moving all the torque down the rpm range. the motor does not magically produce more torque.

 

[Sirius815]

I will agree with that, as long as you specify that the torque you mention is at the wheel. And if you read carefully, I NEVER disagreed with that.

"TQ/HP output at the WHEEL is a function of the motor, transmission, and drive-train."

"If you dyno your bike, dyno it in 3rd gear, then 4th, then 5th. The curves will (should) be completely identical, with the exception of the skewed numbers due to the gearing multiplier."

With that said, the actual output of the engine is NOT changed. The gearing is what's giving you more Torque at the wheel.

Additionally - "all it does is shift the torque curve up or down in the RPM range giving the illusion of more torque or horsepower." - is still incorrect. The curve does NOT change.

 

[Sirius815]

The torque does NOT move!! You will get the same gear multiplier throughout the entire rev band - it does not shift one way or the other.

 

[crxtasy169]

So your telling me adding more teeth to the rear sprocket magically gives you more toque to the rear wheel?

 

[Sirius815]

It's not magic - it's mechanical advantage through gearing. Just go out in a car and compare 1st and 2nd gear. You will pull much harder through 1st gear than through 2nd. Doing this is essentially the same as changing the rear sprocket.

 

[upthemaiden]

You guys are getting out of hand!

Lets change this to a simplified example. If I put my stock bike on a dyno it put out say.... 70 rwhp(estimate), and 92 at the motor. If I did a chain conversion and went down a few teeth in the back, making my bike geared taller, and put it back on the dyno, even though my bike will now to go 15mph faster in every gear, will the bike still make 70 rwhp, or will it make less since the rear wheel now has less leverage??

I think people get are going back and forth between two different things. Obviously changing the external gearing has absolutely no way to affect the power coming out of the motor.

 

[crxtasy169]

Yes same amount.

 

[Sirius815]

I'd venture to say - almost the same amount. 15mph is not too drastic of a change. But if you do have a chance for some dyno time, have them do a run with the bike in 3rd gear and look at the numbers.

And, upthemaiden, I apologize if it got a little out of hand - as you say.

"I think people get are going back and forth between two different things. Obviously changing the external gearing has absolutely no way to affect the power coming out of the motor."

Agreed.

 

[crxtasy169]

Sorry guys all apologies for being rude!

 

[buelladdicted]

every thing from the primary gear to the rear tire manage power,they dont create it.If your going racing a tooth on the counter shaft can change your lap times 2 seconds,and because it changes the availability of useable power at the parts of the track you are on at the time.Since we are talking about our street bikes,I would like nothing better than to be going 70 at 3000 like my 99 sportster w/ a 29 front sprocket and 130/90 18"rear tire.