RPM question

[Mortman22]

Yeah, I was just wondering what kind of RPM's you guys are turning in 5th gear at around 60 mph. I just had her out for the first real ride of the year a couple of days ago and I was at 4000 on the tach @ 60mph. It idles fine right at 1000. I did do some work over the winter, K&N pods, Dynatek coils, and slip-on mufflers, and I did know I may have to rejet but this is the only malady since I did the work. I just don't remember the RPM's being that high last year. Granted, I didn't get to ride her alot last year. Well, anyway, Any help would be great.



Thanks,

[John]

Your RPMs are right on the mark. 4000 rpm for 60 mph is normal, but if you swap to an xs750-850 final drive you can get a taller gear, and lower the engine speed at 60 mph to around 34-3500 rpm AND give about a 5 mpg increase in gas milage.

[Mortman22]

well thanks I feel better now.

[skids]

I didn't get the improved mileage, but it is a lot nicer, one-up doing 70 plus Mph.

Originally posted by John
Your RPMs are right on the mark. 4000 rpm for 60 mph is normal, but if you swap to an xs750-850 final drive you can get a taller gear, and lower the engine speed at 60 mph to around 34-3500 rpm AND give about a 5 mpg increase in gas milage.

[red bandit]

My mileage didn't change any after the 850FD swap either.

[TADracer]

4,000 at 60 mph sounds about right. Providing your clutch is not slipping and you have not changed to some radical rear tire that is not as tall.

The revs should remain the same since it is just numerical gearing. Maybe what you are noticing is just the change in the power band since you did your mods.

[John]

Originally posted by skids
I didn't get the improved mileage, but it is a lot nicer, one-up doing 70 plus Mph.

My milage on my daily commute went from 30 mpg to 34 mpg and most of that is around 70-75 mph, and at speeds around 50-55, I can now get around 40 mpg. That bike never got that kind of milage before the swap.

[HobbyMan]

I have the goods yet havn't done the swap yet. I like the low end torque right now. I bet I would easily get 55mpg on the road. I get 40 daily in heavy traffic

[skids]

My question to you John, is what gear are you in when doing 50-55 mph? I would think that the rear end would not have anything to do with better fuel economy unless you are traveling at high speeds(?)

Originally posted by John

My milage on... and at speeds around 50-55, I can now get around 40 mpg. That bike never got that kind of milage before the swap.

[John]

5th gear of course. Wouldn't it make sense that if the engine is turning around 500 rpm less at speed, that it would use less fuel? Think of a car for a moment... Which gear ratio do you think would give you better milage, a 3.73:1 or a 5.56:1? They both will propell you to your desired speed, but with the taller gear, the engine is turning much slower, thus the increase in fuel economy. My bike has an 1179cc big bore, Jardine 4-2 Spaghetti pipes, and a Uni foam filter, with the 78 E carbs jetted to 140's on the mains. Before the big bore, I was getting 33 mpg on my daily commute. After, I was getting 30. After the F/D sawp, I checked the milage after my first commute, which is 33.6 miles...and I used .94 or .95 gals. Thats 34 mpg to me. Back when we had the 'Meeting O' Da Minds' in March, Wildkat, and I escorted trbig back to Oklahoma, on back roads, obeying the 50-55 mph speed limits, and when we gassed up in Merrietta, OK, my milage was 40 mpg! trbig can vouch for that one. I can only speak from m experiences, and Maximan has also claimed to have an increase of 5 mpg also.
This sounds like a topic for a new poll...

[skids]

Mine runs rich at 3000rpms and I think my economy would suffer there, however, at 2500 rpms it would be a different story. Its not that I didn't believe you...I just don't believe that mine would do as well in that rpm.

[pggg]

Ah yes, I'll just put on my flak jacket and come stomping into this discussion with all guns blazing, now just because the engine's turning a lower rpm it doesn't mean point blank that the fuel economy will increase, as there's more to it than that, riding conditions, air/wind resistance, slopes/hills, power curves, state of tune, my example is my XS geared at 3000@60mph - on a long highway cruise in a tailwind, or benign riding conditions, I was getting better economy for sure, an improvement over stock 4000@60mph. A 3 or 4 mpg improvement sometimes. Definitely noticeable on tank fills.

BUT, yes BUT - even in the slightest of headwinds, or on consistently hilly roads, there was never any difference in fuel economy over stock gearing, and the truth was I'd actually be using more gas with the taller gearing in headwinds, as to get good efficiency from the motor I'd need to be sitting on 3500 or over in 5th, which always meant faster speeds. Other option was to drop down to 4th and not use 5th at all, except for heading downhill. Pointless exercise in having it overgeared ain't it?

Currently my XS is geared at 3700@62mph, and, FOR ME, any lower revs than that is pretty much a backward step rather than an improvement, the noticeable drop off in all-round performance just doesn't make a 1 or 2 mpg increase worth bothering with. I'll probably cop howls of protest from my comments John, but hey, as usual, just one persons opinion