Has anyone changed the gearing?

[redbirds_imp]

I think only some trimming of the chain guide at the front sprocket is needed. The details have been shown in an older thread.

[EGAlvarez_imp]

Okay thanks, I'll search for it later. I just want to avoid punching any holes in expensive parts!

[ChipBeck_imp]

In my experience a tooth on the counter sprocket is worth about 400 rpms. Ie: if you are running a given speed at 5000, going up 1 tooth on the counter will net 4600 at the same speed. Conversely it will make it slightly harder to take off, and might require a downshift for going up hill or passing.

Mick,

One tooth(from 18 to 19) on the counter shaft is the maximum that will fit and the chain guard has to be trimmed to even clear that. It slows the engine 200 RPM at 70 mph, not 400. Down 2 on the rear wheel sprocket will net another 200 RPM for 400 RPM total. 7th Gear Designs will make the sprockets out of steel. Almost all aftermarket units are aluminum and they wear out much faster. This is the gearing I have on my '13 CB1100 and it's wonderful. Much more enjoyable. Cheers.

There is a photo of my 7th Gear Designs rear sprocket here.

http://cb1100forum.com/forum/showthread.php?tid=7395

Chip

[Lord Popgun]

Somewhere on here are pics that Chip posted showing exactly how he modified the shield. I don't have time to search for them right now, but they are here.

I didn't see them in the link Chip provided above.
Found it! Wasn't Chip, it was Pekingduck : http://cb1100forum.com/forum/showthread.php?tid=3378

[rbike_imp]

As soon as I get my 19/35 combo from 7GD, I'll be posting my results. I don't expect any problem off the line, only a great reduction at hwy speeds 4,000 will become 3,401. The 14 models do 3300 @ 70. I also expect hwy mpg (@70mph) to go from 43.5 to apx 50. The 3.9G tank will then be matched to performance correctly - IMHO without the need for a 4.4G tank upgrade.

[Django]

As soon as I get my 19/35 combo from 7GD, I'll be posting my results. I don't expect any problem off the line, only a great reduction at hwy speeds 4,000 will become 3,401. The 14 models do 3300 @ 70. I also expect hwy mpg (@70mph) to go from 43.5 to apx 50. The 3.9G tank will then be matched to performance correctly - IMHO without the need for a 4.4G tank upgrade.

It's a common misunderstanding, that lower revs would mean better mpg in every case.

A petrol engine has its best fuel economy at revs at max. torque, which is 5,500 rpm for our CB.

That means, doing exactly the same speed in the same gear at 3,300 instead of 4,000 will reduce mpg. But luckily not much or noticable, as our motor has a very flat torque characteristic.

For the details: https://en.wikipedia.org/wiki/Engine_eff...29_engines

Cited: "Engine efficiency peaks in most applications at around 75% of rated engine power, which is also the range of greatest engine torque (e.g. in most modern passenger automobile engines with a redline of about 6,000 RPM, maximum torque is obtained at about 4,500 RPM, and maximum engine power is obtained at about 6,000 RPM). At all other combinations of engine speed and torque, the thermal efficiency is less than this maximum."

[ChipBeck_imp]

As soon as I get my 19/35 combo from 7GD, I'll be posting my results. I don't expect any problem off the line, only a great reduction at hwy speeds 4,000 will become 3,401. The 14 models do 3300 @ 70. I also expect hwy mpg (@70mph) to go from 43.5 to apx 50. The 3.9G tank will then be matched to performance correctly - IMHO without the need for a 4.4G tank upgrade.

It's a common misunderstanding, that lower revs would mean better mpg in every case.

A petrol engine has its best fuel economy at revs at max. torque, which is 5,500 rpm for our CB.

That means, doing exactly the same speed in the same gear at 3,300 instead of 4,000 will reduce mpg. But luckily not much or noticable, as our motor has a very flat torque characteristic.

For the details: https://en.wikipedia.org/wiki/Engine_eff...29_engines

Cited: "Engine efficiency peaks in most applications at around 75% of rated engine power, which is also the range of greatest engine torque (e.g. in most modern passenger automobile engines with a redline of about 6,000 RPM, maximum torque is obtained at about 4,500 RPM, and maximum engine power is obtained at about 6,000 RPM). At all other combinations of engine speed and torque, the thermal efficiency is less than this maximum."

Django,

The "engine efficiency" referred to above is power production, not fuel mileage. By definition an engine operating AT FULL THROTTLE is most efficient in power production when it is able to make the most power PER RPM. (1 power stroke). Torque is turning force PER REVOLUTION. Horsepower is that torque times the number of revolutions per minute. None of this has much to do with fuel economy especially when operating at part throttle as a car or bike operates 99% of the time. Pumping and internal frictional losses are huge power consumers and they increase in a pretty linear fashion as rpm increases. This is why automakers gear cars to operate at often less than half the rpm where peak torque occurs. When operating at partial throttle (and nobody cruises at full throttle) the lowest rpm that will generate enough power to keep a car or bike at speed, in other words, enough power to overcome frictional losses, pumping losses, and wind resistance, will yield the best MPG as the first two of those three components are directly related to RPM.

I was both a domestic and import car dealer for 25 years and I'm a graduate of the General Motors Institute in Michigan where we studied auto and engine design as well as marketing. The efficiency cited in your example is efficiency to both inhale and completely burn the maximum amount of fuel and air at full throttle. This efficency starts rising above idle and keeps rising until RPM makes intake and exhaust openings too short to allow enough airflow and then it starts to fall off. But again, this is only a measure of torque at full throttle to measure maximum possible power (this is why all dyno runs are made at full throttle) and this is meaningless when it comes to measuring mileage while cruising at 20% throttle.

The bottom line is that my CB1100 gets 3 more MPG at 70 MPH turning 3600 RPM with my new gears than it got turning 4000 RPM with the stock gears. Cheers.

Chip

[Django]

Chip, then, could you please explain, why e.g. the Toyota Celica at that diagram has a better mpg at 60 mph than 55 mph:


(token from: https://en.wikipedia.org/wiki/Fuel_econo...utomobiles )

[rbike_imp]

Quote:The bottom line is that my CB1100 gets 3 more MPG at 70 MPH turning 3600 RPM with my new gears than it got turning 4000 RPM with the stock gears. Cheers.

Chip
Thanks for your details. I was going to run at max rpm in 3rd vs 5th on the interstate to get best mileage - small lol.

On diesels in my area of expertise, I design the systems to run at the peak of the torque curve which is somewhere near 65% max rpm, but only apx 25-30% of the max hp.

Like politics, one has to use the correct CONTROLLING variable in an equation or what they say may be 100% wrong. Many scenarios have many multiple variables and choosing the correct one(s) as the major input factor(s) is critical to a good proper decision.

Your reply to Chip came in after my post - First, I have no idea, but It may have to do with shifting, especially with automatic transmissions and their torque converter specifics. With manual transmissions, it should be nearly linear unless the computer module/epa get involved.