fuel economy

bladeracer · 06-02-2008, 9:34 PM

Fuel prices here have only climbed over the last couple of years.
A few weeks ago we were still under A$1.50/litre for 98RON - Aussie dollar is pretty close to the US now. Last weekend though I paid $1.67.
I can't imagine 7000 miles out of a tyre :-)
I was amazed to get around 11000kms out of a set of Dunlop slicks I ran in '06 on the road and track days including a trip across Australia. I've never seen that sort of mileage out of my tyres before.

curt248 · 06-02-2008, 9:39 PM

isn't 11000km the same as 6820 miles?

bladeracer · 06-03-2008, 5:45 AM

Possibly :-)
As I said though I was amazed as that was probably double what I'm used to.
That particular set wore very well and never actually got down to the canvas although all the wear markers were gone from both tyres for a long while before I had to replace them with fresh rubber for the start of the race season. I still have them on my tyre rack - maybe I'll get a few more thousand out of them sometime :-)

yeller929 · 06-04-2008, 1:41 AM

I get 37-40 and it doesn't matter how i drive. 00 929

conor · 06-18-2008, 6:42 AM

Just got back from a 3650km ride from Dublin, Ireland down through France to Catalunya and back again.

In the Pyrenees I was using mostly 2'nd and some third gear, 10 to 11,000 rpm zone, was getting 170 km's (at worst) before the red light would come on.

On the autoroute (at ludicrous speed), it would come on at 198 km's.

City riding (in Dublin) it comes on at 180km's and that's at the speed limit all of the time. So I guess living in Ireland gets crappy fuel economy due to out super twisty and stop / go type roads. Where as in Spain & France, no matter how nuts we rode, and it was nuts (in 25C to 35C heat), the economy was vastly better.

I would have thought that riding in cooler climates would have improved the perf. Apparently not.

Conor.

RDRACR · 06-21-2008, 4:16 AM

... this is going to sound ridiculous, but my '95 CBR900RR is getting around 50 MPG, and it has a FACTORY I Jet Kit with the stock air box, a K&N Filter and a full SS Two Brothers pipe... but then again my fuel pump wasn't putting out like she should have, lol! But really, around 50MPG.

ghbzorro · 06-21-2008, 4:31 AM

Quote:

Originally Posted by conor

I would have thought that riding in cooler climates would have improved the perf. Apparently not.

Better performance, meaning more power, can be had with colder air. But I guess the poorer peak power and less dense air to push through with higher temperatures improves mileage? Does that make sense? If it does then I should be getting 100 miles per Imperial Gallon!

Quote:

Originally Posted by RDRACR

around 50 MPG, ...stock air box, a K&N Filter

Hmmm. I wonder if the major restriction in airflow from your K&N

and its corresponding reduction in maximum power, is giving you a mileage benefit?

curt248 · 06-21-2008, 9:20 AM

In the mountains of Colorado I consistently got 47mpg riding 2 up.

I normally get 40mpg in Illinois.

The thinner air with less oxygen allowed for less power and more fuel economy.

danny_isr · 06-21-2008, 4:51 PM

i'm getting 45mpg all the time in Colorado.

"The thinner air with less oxygen allowed for less power and more fuel economy."

i would think it's the opposite. less oxygen ends up with you using more gas to get the same power

curt248 · 06-21-2008, 6:59 PM

But you don't get the same HP in the mountain elevation. I'd say at 8000ft my bike was probably putting out closer to 100hp vs 130 at close to sea level.

There is a ratio for gas to burn. There is an exact number, but I think it's around 14:1. So less air (mountains or hot) needs less gas and more air (think cold or low elevation) needs more gas. Of course with less gas you get less power and vice versa.

danny_isr · 06-21-2008, 8:54 PM

i just think if you go 70mph at sea level , you need less gas then if you want to keep the same speed in high altitude. because your engine generate more power. so you end up giving more gas = consume more

bladeracer · 06-21-2008, 9:41 PM

I've never had the opportunity to test it myself but I believe the lower air pressure reduces the actual measured compression in the cylinders.
For example, 15psi at sea level gives you compression of 165psi at 11:1.
At 14,000ft air pressure is much lower - around 8psi? - so your 11:1 compression ratio only gives you around 90psi.
Anybody ever done a compression test at sea level and at altitude?

curt248 · 06-22-2008, 12:55 AM

That makes sense. When you are in the mountains they have gas at 85 octane and everything runs fine on that.

Sense raising the compression ratio increases the requirement for a higher octane rating, vice versa should be true.

bladeracer · 06-22-2008, 1:15 AM

There you go then. Not having any mountains around here it's not something I'm ever likely to be able test for myself :-)
Keep in mind though that the higher octanes are more than just a higher detonation resisitance - they also have additives to improve mileage and efficiency (otherwise they'd never be able to sell it except as race tracks). I routinely run 98 which is our highest pump gas and the only reason I do is for the extra mileage it gives me.

curt248 · 06-22-2008, 1:19 AM

I wonder what additives can increase fuel mileage? I've noticed improved fuel milage of 3mpg when using premium 93 octane in my car. It seemed to give 2 or 3 mpg to my bike as well.

If they can just put in an additive to increase fuel mileage, why wouldn't they just put it in all levels of gas and reduce the amount of gas we need to buy (I may have answered my own question lol).

bladeracer · 06-22-2008, 1:30 AM

Cost is my guess.
Millions of people refuse to run the higher octanes purely on cost basis without even testing it themselves.
It costs me no more to run it in all my vehicles as the extra mileage offsets the extra cost.

curt248 · 06-22-2008, 1:40 AM

lets see $0.20 more per gallon and 3mpg. lets say mileage goes from 17 to 20. 17/20 = .85. So that's a 15% increase in gas mileage. Gas here is 4.17 for 87 octane and 4.37 for 93 octane. 4.17/4.37 = 95.4 for an increase of price of 4.6%.

I guess your right for my car that gets 17mpg city (it's a v8) a 15% increase in mileage for a 4.6% increase in price is worth it.

Now back to the bike. 37mpg on 87 octane and 40mpg on 93 octane. 37/40 = 92.5. So that's a 7.5% increase in mileage for a 4.6% increase in price. That's a good deal as well. Hmm I just started to use 87 octane since the manual says you can you 86 octane. To think I was happy about this. I guess I had nothing to be happy about.

What has been your experience with gas mileage compared to octane rating?

bladeracer · 06-22-2008, 1:51 AM

I've always run it in my bikes for the fuel economy. In the dry I get from 7.8kpl to 8.4kpl depending on the circuit. On the road I was getting 13.5kpl - I've just stripped out all the road accoutrements so don't expect to be riding the 929 on the road again until the end of the season. What I was getting on the lower octanes I'd have to dig back through years of data to find out but I think it's about 10% under the good stuff.
In the car (1300cc Suzuki Swift) we get around 13.5kpl on 98 and from memory just under 12kpl on 91. If we only let my girlfriend drive it she's gets heaps better mileage than me :-) I've only run one tank of 91 since I built the engine last year just to see if the compression was high enough to cause detonation - which it was :-)
I couldn't even tell you what 91 is selling for at the moment but I paid $1.72 per liter last week for 98.