Over the winter I swapped the stock gearing of my '84 FJ over to the 18/38 combo in search of some more MPG. However, at the same time I did a number of other mods that could have an effect on mileage as well. I put on a 17" later FJ front wheel and the 17" GSXR rear wheel. I also switched to blue spot calipers. Oddly enough, my mileage went from about 38mpg before the mods to around 33mpg afterwards. I have a adjustable bicycle speedometer that I calibrate using the mileage markers on the interstate. It was accurate before the mods, and I recalibrated it afterwards. I understand that there are a huge amount of variables here, but has anyone heard of mileage going down after making the gearing taller on our bikes? I ride it in the same manner as I did before I did the mods. That is, medium-aggression, mostly 75mph, highway riding.
I thought that I'd pick up a few MPG, not drop 5. Any ideas? One thing that occurred to me is that maybe the lower RPM has put the engine into the less efficient midrange with my 4-1 exhaust.
[edit] I corrected the title of the post from 18/83 to 18/38. Hope you don't mind Sgt.
you should measure overall diameter of the new tire and old tire.
chances are your new overall tire diameter is smaller now with a lower profile tire, even though its a larger rim.
after the sproket and chain your tire diameter will influence working rpm vs mph
Changing the gearing like that shouldn't lower the MPG. Must be some thing else. I like the wheel circumference question. How is the jetting? Hope this helps? :scratch_one-s_head:
Kurt
I agree with Kurt, something else is going on.... Have the carbs been sync'ed lately? Fresh plugs? If not, then perhaps it's time.
I would run several tanks of gas thru to get a good base mileage data.
I've been running 18/38 for a wee while now.FJ1100 with 1200 motor and 17"wheels,standard pipes and airbox. Normal work commute in town and 80mph on the M-way gives me 55mpg (uk gallons).Same route on my fj1200 engined z900 with filters and 4into1 gives me 43mpg.It was 38mpg before I played with the needles.18"wheels on the zed and a 33 rear sprocket/17front.70mph at 4000rpm ish on both.
My chain and sprockets are nearly due for replacement. Am I correct in thinking that the standard gearing for a 1990 3cv is 17/40?
Well that's what it shows on here. http://www.gearingcommander.com/ (http://www.gearingcommander.com/)
Eliminator: Yes, 17/40 is stock for the 89-90 US models.
A drop in mileage right at the same time you changed brakes? I know where I'd be looking first, a dragging brake can easily trash your mileage as well as your brakes. That said, the idea that you're running less rpm and the engine isn't as efficent down low is also possible. Also, to get the same amount of oomph will require a lot heavier use of the throttle, which won't help either.
oooooh, very good Andy....a dragging brake pad.....good catch amigo! :good2:
I had thought of the dragging brake thing, and there might be something there. I can hear the pads slightly dragging when I roll the bike around the garage, and it seems to be just a bit harder to push than it was with the old brakes.
However, I can't notice any dragging while the bike is coasting, and there's no undue heat from the brakes or unusual wear. Is it normal to be able to hear the pads dragging (while rolling the bike with the engine off) with the blue spots?
yep, with the HH pads I run there is a slight dragging noise when I push my bikes around....that's no biggie.
Coast to a stop and feel the rotors...if they are hot, then a pad is dragging, a piston is not retracting.
Safer, and easier:
Come to a stop using the rear brake, check the feel of the fronts. Check rear brake after using fronts to stop.
A little bit of contact is normal, as they don't have little retractor springs to pull the pads back, though some (car?) calipers have had that feature I understand.
I dunno though. My daily ride gets about 45mpg in normal riding, and 51mpg if I ride like my hair's on fire. Needle settings are actually slightly rich (intentionally) on it, too. I can only think that the motor is running up in a more efficent area when I'm out hooning about like that, so it's getting better mpg.
So,
A slight drag on the breaks is typical and actually good, they wear more evenly if they make proper contact and a slight drag means that. a simple test is just to mash the break hard and if its difficult to roll at first that's a problem.
Back to my first post
If all being equal the stock vs stock tire size for fj and a 94 gsxr 600 are 150/80r16 and 185/55r17 with od's of 79.95 and 78.58, respectively. So, unless your tire sizes were much different I feel like your cruising at a higher rpm than before per given MPH even with the new sprockets because there pretty close to stock, equivalent to a tooth smaller rear with stockers. 1 tooth wont make up for 1 and 1/4 inch tire difference.
This is all subjective to tire size however, of new and old tires. check it out!!!!
http://www.tacomaworld.com/forum/tirecalc.php?tires=150-80r16-185-55r17 (http://www.tacomaworld.com/forum/tirecalc.php?tires=150-80r16-185-55r17)
looks like OD is about 1.7% difference you be the judge :sorry:
did you switch to radial tires?
what pressure are you running?
Quote from: rexsk8er on June 13, 2012, 11:45:37 PM
So,
A slight drag on the breaks is typical and actually good, they wear more evenly if they make proper contact and a slight drag means that. a simple test is just to mash the break hard and if its difficult to roll at first that's a problem.
Back to my first post
If all being equal the stock vs stock tire size for fj and a 94 gsxr 600 are 150/80r16 and 185/55r17 with od's of 79.95 and 78.58, respectively. So, unless your tire sizes were much different I feel like your cruising at a higher rpm than before per given MPH even with the new sprockets because there pretty close to stock, equivalent to a tooth smaller rear with stockers. 1 tooth wont make up for 1 and 1/4 inch tire difference.
This is all subjective to tire size however, of new and old tires. check it out!!!!
http://www.tacomaworld.com/forum/tirecalc.php?tires=150-80r16-185-55r17 (http://www.tacomaworld.com/forum/tirecalc.php?tires=150-80r16-185-55r17)
looks like OD is about 1.7% difference you be the judge :sorry:
I think you mean circumference not O.D. 1.25"difference in circumference is nothing to worry about.
I reckon it's because since you hotted the bike up, you're getting up it more.
You are more confident and riding it harder.
This maybe unlikely but could your pilot jets be lean witch causes you to open the throttle a little more hence forth using more fuel. Hope this helps?
Kurt
Gentlemen,
Right on the money Kurt.
Many miles ago I also geared as high as possible.
As my original carbs wore out, the mileage began to drop off until at normal highway speeds (mid-70's) mileage was in the high 30's.
When I replaced the carbs (mainly because of the costs of new diaphragms) the gentleman from RPM rejeted to larger than stock.
Since then, the milage at normal highway speeds is at least in the 42 mpg range. The lowest I ever get is 38 mpg, no matter how I ride (including road conditions, time of day or temperature...?!).
Cruising Highway 50 on my way to Gunnision last week, at night it was quite cool, probably in the 40's, and at cruise speeds in the 90 mph range, I averaged 38 mpg. On my return during the day and warm temperatures, the same mpg.
Also check the float levels as well, the wrong setting will use more fuel, even to the point of your engine running on 3 cylinders (regardless of the temperature, road conditions or time of day). randy at RPM has tips on the proper method(S) to use. And believe it or not, the correct float level will keep you from getting kicked out of hotels...! Apparently not a problem at the KOA.
And as an aside, because of an upgraded oil cooler, not a big difference in oil temperature either, day or night.
Stay in good humor & Ride carefully,
Mike Ramos.
Right on Mike! You a funny, funny man!
Hi Pat,
Funny? Not true! But I am Goofy (and have the ears to prove it).
As the record shows, there is an ex-wife who unequivocally sates that I am " [expletive deleted] Goofy!"
Ho hum...
Ride safe,
Mike Ramos.
I just checked gas milage again on the last two fill ups. I'm getting 46 - 48 MPG. 18 tooth front, 38 tooth rear. GSXR rear wheel, new carbs, recent valve adjustment, carbs synced, new wheel bearings, new blue spots. I very rarely go much over 5000 rpm. 91 octane if it matters. 60,000 mi on the odometer.
Back when I first got the bike and was getting on it at every opportunity, I was getting in the 36 to 38 MPG.
YMMV.
My brain is frazzled trying to work that out.
1Imperial gallon is 1.2 US gallons. Your rear tyre is a 17", mine is a 16"................ melt down!
I was getting the similar milage - mid + 40's -- with a 16" rim. The tire circumferences between the 16" and 17" tires aren't much different. The 16" has a higher sidewall. I am enjoying the lower rpms with the 38 tooth rear sprocket especially when cruising, so I'd advocate for a 38 tooth rear.
I guess my point would be that my milage varied more by the way I drove(accelerated etc) than by changing the ratio of the sprockets. Again, YMMV.
A stock rear wheel/tire combo is about 25.5 inches high.
a 180/55x17 wheel/tire combo is about 24.8 inches high.
So, the circumference of each is (pi * D) is 80.1" OEM and 77.9" with the 17" wheel.
This gives you a difference of ~ 3% pretty close to the 4-5% change of a single tooth on the rear sprocket.
Hope this helps your argument :-)
Arnie
Yes the big front sprocket and small rear are great for cruising, but the small front and large rear make the front end real light and save on front tire wear this can be hard on fork seals. Too much fun :yahoo: !!!!
Kurt
I've noticed my MPG is the same or slightly lower since I've switched to 18/38 from 17/38. I know it doesn't make sense and this is only over 5 or 6 tanks of gas. For what it is worth, I've been commuting and cruising at 3000-4000 RPM with the 18/38. If I recall from last summer, some of my best mileage was on a trip that I was cruising faster and with the 17/38 gearing, the RPM's were more in the 4000- 5000 + range.
I still enjoy the lower RPM's.
Quote from: markmartin on June 11, 2013, 05:03:41 PM
I've noticed my MPG is the same or slightly lower since I've switched to 18/38 from 17/38. I know it doesn't make sense and this is only over 5 or 6 tanks of gas. For what it is worth, I've been commuting and cruising at 3000-4000 RPM with the 18/38. If I recall from last summer, some of my best mileage was on a trip that I was cruising faster and with the 17/38 gearing, the RPM's were more in the 4000- 5000 + range.
I still enjoy the lower RPM's.
I to enjoy the comfort level of lower RPM's. But the engine efficiency is probably better closer to the peak TQ RPM. I think she likes to spin.... :lol:
George
I have the same mods as move on and markmartin, my mileage has dropped from the 40 to 42 range to 38. However; I'm riding a lot more aggressively! So Im sure that is a lot my lower mileage. May take her out for 400 mile rode trip this w/e, so I'll see what she does on the open rode. I can see the lower rpms making the engine work harder do to lower torque. However at higher highway speeds (75 to 80) it may be back into power band of the engine??? Makes sense but I'm just guessing, haven't actually calculated anything out.
volumetric efficiency is the key .
I went on a 350 mile ride over the weekend. I have the 18/38 sprockets with a FZR750R front wheel w/standard size tire. A GSXR rear wheel out back with a 180/55/17". My mileage used to be between 40 to 42 mpg. Saturdays ride gave me 44.8 mpg which would give me 260 miles on 5.8 us gallons.
Fred