Average MPG drop :( - Fuel Economy, Hypermiling, EcoModding News and Forum

Eddles · 08-10-2009, 05:45 PM

Am well disappointed. Before doing the following, I've been getting 63MPGus average. But now after fitting new tires on the front of my car & inflating all tires to 50PSI, put back in my seats and installing cruise control, now my FE has suffered - the average has fallen down to 60MPGus. Does new tyres and the extra weight from the seats really do make that much difference? I miss the 70MPGus I got a while ago...

Or could it be all the rubbish weather we're getting in the UK lately...?

Matt Herring · 08-10-2009, 05:55 PM

Depends what type of tire you deleted and what type of tire you added. If you removed LRR tires and added a HRR tire you will lower mpg. If it's the same tire you will have a breaking in period for the new tires that will lower mpg. Are all the tires the same size (just asking as they could throw off the odometer as well...hoping they are all the same size).

Also, any added weight in the car will lower FE. Your seats could be an extra 50, 75, 100+ lbs. that you are dragging around in the car now.

Both of these events (plus any bad for FE weather) can all have negative effects on your FE.

Eddles · 08-10-2009, 06:00 PM

Quote:

Originally Posted by Matt Herring

Depends what type of tire you deleted and what type of tire you added. If you removed LRR tires and added a HRR tire you will lower mpg. If it's the same tire you will have a breaking in period for the new tires that will lower mpg.

Old tires weren't fuel savers, while the new ones are.

Quote:

Also, any added weight in the car will lower FE. Your seats could be an extra 50, 75, 100+ lbs. that you are dragging around in the car now.

Is there any rough figure of how many less MPG for each lbs that are added on? I.e. 1% less MPG for 50 lbs added on?

Thanks!

SVOboy · 08-10-2009, 06:03 PM

New tires also have higher rolling resistance than worn in tires. Give them some time to break in and your MPG should go back up.

Also, cruise control, in my experience, isn't as good for fuel economy as driving with load and paying careful attention, so that might have some bearing on the situation.

Matt Herring · 08-10-2009, 06:04 PM

That being the case on the new tires I would give them some time to break in before making any judgments on their effect on FE. What are the specs on the tires that are on the car now (front and back) and what did you replace with them?

Check this thread out about weight reduction in the car...read down through the posts to see what others have seen in FE in regards to weight...

http://ecomodder.com/forum/showthrea...tion-3482.html

MadisonMPG · 08-10-2009, 06:10 PM

Weight does very little on the highway. I can't remember the "formula" for weight added and gas mileage.

Eddles · 08-10-2009, 06:11 PM

Quote:

Originally Posted by SVOboy

New tires also have higher rolling resistance than worn in tires. Give them some time to break in and your MPG should go back up.

I guess so. How long is a break-in period, normally?

Quote:

Also, cruise control, in my experience, isn't as good for fuel economy as driving with load and paying careful attention, so that might have some bearing on the situation.

The motorways between the city where I live and where I work are completely flat - and I mean flat. The cruise control holds the speed much better than I do - it rarely devitate from the set speed more than 0.5mph, where I deviate from the set speed a lot more so I spend my time accelerating/deaccelerating to keep to the set speed. I guess I could do a tank without CC to see if there's any difference, however holding the accelerator pedal in the same place for 800 miles a week isn't forgiving to my ankle!

Quote:

Originally Posted by Matt Herring

Check this thread out about weight reduction in the car...read down through the posts to see what others have seen in FE in regards to weight...

Thanks for link, much appreciated!

Eddles · 08-10-2009, 06:14 PM

Quote:

Originally Posted by Matt Herring

Check this thread out about weight reduction in the car...read down through the posts to see what others have seen in FE in regards to weight...

Hmm. I suspect the seats in my car are about 60KG for the front passenger and all rear seats. That would translate into 130lbs and that's a 5% weight reduction for my car, which might translate into 0.5-1MPG. Might need testing, but getting 800 miles out of a tank means really long test periods!

Thanks again for help.

Matt Herring · 08-10-2009, 06:14 PM

800 miles of holding a constant speed certainly is a little painful...but how about breaking your 800 miles into smaller segments if your ankle doesn't allow for it over 800 miles of driving. Something like 20 miles of cc then 20 miles of your foot.

Do you have any instrumentation to monitor FE? This would show you exactly how your cc is doing for you vs. your foot.

Eddles · 08-10-2009, 06:19 PM

Quote:

Originally Posted by Matt Herring

Do you have any instrumentation to monitor FE? This would show you exactly how your cc is doing for you vs. your foot.

Very good suggestion. I've brought a MPGuino and have assembled it but haven't installed it yet. The amount of wiring in my car is scaring me! I haven't figured out where to tap the MPGuino into - I don't have the correct wiring information for the engine and to get that might take me a lot of time. I might get around to installing it in early September when I get back from my holiday in late Aug.

And unfortunately no, I can't have a OBDII based display as my car doesn't have an OBDII port.

Probably best if I wait until I install a MPGuino and check the thermostat (the engine takes over 10 mins to warm up) before asking for help here I guess.... Sorry!