Significant drop in gas mileage

[Redfish Hunter]

...You said the front wheel does not even make one revolution? There is no good reason for that. I would double check the front brakes. The front should spin fairly easily if everything is correct.

Actually, on the FJRs I've played with neither the front or rear wheels spin really freely. If I pull the calipers off and assiduously clean the pistons and everything else related to the caliper really good the front wheel will spin fairly freely but after a few days of riding, not so much again. Perhaps it is simply the piston seal design that causes this. The rear wheel has to turn the ring & pinion and right angle drive so it doesn't spin very freely either. Neither did the shaft driven rear wheel of my Honda V65.

I have learned from personal experience that arguing with you always results in me feeling and looking really stupid. Sooo, not arguing, just asking. Aren't the front calipers on your Gen1 different from the calipers on the Gen2? Do they act the same way? I honestly do not remember checking this on Dad's bike before. If I get time today I will go by Dad's and check his. Also, I did note in my post that the rear wheel was turning the drive train and would probably not spin freely.

 

[ionbeam]

I have learned from personal experience that arguing with you always results in me feeling and looking really stupid... Aren't the front calipers on your Gen1 different from the calipers on the Gen2? Do they act the same way?...

Very sorry to read the first line, I sure don't intend for it to happen like that. Something for me to watch in future posts.

You are correct, Gen I calipers are apples to oranges with Gen II. I have had a chance to spin a few Gen II front wheels also and I thought they didn't spin as freely as my Gen I. The unknown here is my maintenance vs the Gen II owners. While my FJR (Pig Pen) may not be clean, the important items are well maintained.

That said, I doubt that brakes are the reason for mileage dropping. One fast way to get an idea of dragging brakes is to go for a short ride using only the back brake and then come to a stop using only the back brake lightly. Carefully tap the front rotors with a finger tip to gauge rotor temperature. If a quick tap results in burn blisters the brakes are probably guilty of contributing to the mileage drop. If the rotors don't blister your finger they are exonerated. Repeat using the front brakes only and 'measure' the rear rotor. It's normal for the rotors to be warm even when not used but they shouldn't be blistering hot. If some of the Sun Shine Boys on the left coast are looking for an excuse to ride they could bring along a cooking thermometer (don't let your wife catch you) so we could compare actual numbers. It won't be the first time we over think a 'problem'

 

[SkooterG]

I guess it all depends on what the definition of 'spins freely' is.

I checked the other day, and the rear on my 09 spins 1 - 1.5 turns with a solid tug. It seems to be spinning 'freely'. I assume temperature (viscosity) of the final drive oil could have a minor impact on that. I haven't had a helper to check the front yet. I know that when removing the front wheel and the calipers are removed, it will spin and spin and spin. I am guessing 2-3 rotations with the calipers installed and the brakes slightly dragging.

 

[Redfish Hunter]

I have learned from personal experience that arguing with you always results in me feeling and looking really stupid... Aren't the front calipers on your Gen1 different from the calipers on the Gen2? Do they act the same way?...

Very sorry to read the first line, I sure don't intend for it to happen like that. Something for me to watch in future posts.
they could bring along a cooking thermometer (don't let your wife catch you) so we could compare actual numbers. It won't be the first time we over think a 'problem'

Ionbeam, it is not your fault I feel dumb when having a discussion with you!

That is all on me. I truly appreciate having you and FredW around when I get confused.
The cooking thermometers in this house all belong to me. And I am not putting them on a brake rotor. We have some handy little temp reading guns at work that I can borrow. Just aim, squeeze trigger, digital readout. We use these when looking for hotspots in switchgear and other process related troubleshooting.

Us? Overthinking a problem? No! It has never happened...

Okay, I rode over to Dad's, put the FJR on the centerstand ('07 Gen2, well maintained) and spun the front tire. Well, I mean I tried to spin it. I could not get one revolution out of it. Of course, I was holding the front end up with one hand but 3 attempts were more than enough to convince me that, once again, you were correct. At least I don't feel as dumb this time.

Edit: I did the same test on the front of my ST1300 and it spins relatively freely. I could hear a slight rubbing from the brakes but the wheel spun easily.

Oh and FWIW, I agree, it would take quite a bit of brake drag to adversely affect fuel mileage and that it would show up in other aspects as well.