33 mpg highway @ 85??? (55 swap)

[mlarivie]

Bike is an 09' I recently did the oversize 55 swap and though its geared down a tiny bit have noticed my gas mileage has suffered horribly. I am running 37 PSI in front and back. I usually travel at 85mph on the highway here in New england and the computer reports a steady mpg of 33... Typically when my road star got this bad it was time for a valve adjustment and TB sync... I'm at 11000 miles currently.

2 Questions...

Am I due for some maintenance, frame bolt check?
Has anyone switched to a smaller tire (if available) for taller gearing?

[Rhino]

Not sure I ever got as low as 33 mpg but I do notice my mileage goes way down above 80 mph. Will be putting a 55 on this week for the first time. I wouldn't expect any difference in mpg but will be looking out for it.

[mlarivie]

So far I've noticed the lean in is nicer, but when its raining the bike feels looser.

[Conrad]

Just for grins. Air your tires up to 42 and slow down just a tad and see what happens. I'm not trying to tell you that you're going too fast, so don't get me wrong there. I'm the same way and I satisfy my need for speed every day that I ride.

[p07r0457]

I would definitely say air up your tires a little more, I ran 42 psi on my last ride to Crater Lake and I noticed a several mpg increase (despite riding uphill at a fast clip).  Only downside is the ride is considerably more firm.

[chap]

I went from 42 to 39 US MPG with the 55 tire swap. I am running the Michelin PR3's. This is the indicated MPG only, dont forget your computer is still figuring distance related to the stock tire. You will also notice your speedometer is reading about the right speed now, not the factory set 2 - 3% high. Your odometer will read a similar percentage lower. If you really want to check MPG use a GPS for distance, and the fuel station pump reading for Gallons. Or just allow for the 2 - 3 % it is reading low. I would think 33 is about right for those speeds and low tire pressure. Don't forget your ECO Mode doesn't work at those speeds (not sure if 2009 has ECO Mode).

[mlarivie]

Im going to have it nitro filled at 42 this afternoon like I do on my C5 vette. It's worth every penny. I will report back later, but wish I bought a 50 tire!

[Conrad]

Im going to have it nitro filled at 42 this afternoon like I do on my C5 vette. It's worth every penny. I will report back later, but wish I bought a 50 tire!

We've had the nitrogen discussion here before and the consensus? Snake oil.

[mlarivie]

I can see that, I guess it matters when youve got 4 to balance out (left and right). I'll just air it up to 42! Thanks

[cablebandit]

Your windshield, and it's position, will have more of an effect on gas mileage than a slightly taller tire will.

[galaxieman]

Alternately, on the next rear tire swap you could go for a 180/55, which is has a sharper profile, is slightly taller than the 190/50 stocker, is lighter, and less expensive.  There's no real gain in going with a 190-width tire over a 180 on these bikes.  Just my $.02...

Oh, and on the current tire, 37psi is way too low.  Based on the manufacturer recommended 42psi for the stock sized tire and the change in surface area of the new tire compared to the old one, 41.3psi will give the same % of the tire as a contact patch.  In other words, in order to keep the percentage of the available surface in contact with the ground (thus slightly increasing the size of said tire patch), you need to reduce the pressure by less than a pound.

[wally_games]

Your windshield, and it's position, will have more of an effect on gas mileage than a slightly taller tire will.

DEFINITELY!

[mlarivie]

I expected that as well, so I tucked in- shield down, with about 34 reading on the dash. I have a shad 50 on the back as well.

[wroman]

 My Aeroflow shield seems to affect fuel mileage less than any I have ever used before.  Also the hotter it is the better my mileage is. I got actual 48 MPH on the highway a few weeks ago during the recent heat wave.

[eng943]

Aeroflow tall, Guhl reflash and Area P pipe, BMC Filter.

About 36 mpg when cruising around 80 ish. MPG has always been a bit disappointing.

[Cuda]

Need to buy a TDI

[mlarivie]

This is all new to me, just checking with the crowd to see if it sounds norm!

[B.D.F.]

That tire pressure is a bit low I think- try between 40 and 42 PSI cold.

The larger rear tire should not hurt mileage. In fact, at highway speeds, it should improve it slightly. All else being equal, and assuming the engine is running beyond the lugging range (which is quite low on a C-14), mileage will increase as engine speed drops (by using higher gears for the same speed). At 85 MPH, you are absolutely NOT lugging that engine- it will be turning just over 3,500 RPM.

The other big differences in mileage will come from the load the bike is carrying  (weight) and headwinds. The absolute worst mileage I ever got on a C-14 was in South Dakota, fighting headwinds that seemed to be about 200 MPH. Instantaneous mileage dropped from an indicated 43.X to 29 MPG! But I doubt you have anything like those conditions in New England unless you are riding on top of Mt. Washington.

You should be able to do a bit better than 33 MPH but that also assumes you are riding a steady 85, not an average of 85 with large throttle openings used here and there, for example passing cars. Accelerating from 85 MPH will absolutely kill your average mileage if it is done at all regularly on a ride.

Brian

Bike is an 09' I recently did the oversize 55 swap and though its geared down a tiny bit have noticed my gas mileage has suffered horribly. I am running 37 PSI in front and back. I usually travel at 85mph on the highway here in New england and the computer reports a steady mpg of 33... Typically when my road star got this bad it was time for a valve adjustment and TB sync... I'm at 11000 miles currently.

2 Questions...

Am I due for some maintenance, frame bolt check?
Has anyone switched to a smaller tire (if available) for taller gearing?

[Conrad]

Need to buy a TDI

+1

[maxtog]

Bike is an 09' I recently did the oversize 55 swap and though its geared down a tiny bit have noticed my gas mileage has suffered horribly. I am running 37 PSI in front and back. I usually travel at 85mph on the highway here in New england and the computer reports a steady mpg of 33... Typically when my road star got this bad it was time for a valve adjustment and TB sync... I'm at 11000 miles currently.

2 Questions...

Am I due for some maintenance, frame bolt check?
Has anyone switched to a smaller tire (if available) for taller gearing?

Like others say...

1) Gas mileage will suffer greatly at speeds in the 75+ range
2) You are running your tires way too low in pressure.  They SHOULD be around 42.  Running them 37 will create a lot of extra friction (and wear) and affect gas mileage.
3) Changing the tire size slightly will not affect MPG.  But if it is not the correct (OEM) diameter, it will affect both the speedometer and odometer, changing your computations.
4) Inflating with Nitrogen will not affect performance, wear, or mileage.