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Old 05-09-2022, 08:05 AM   #1 (permalink)
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New french member

Hi guys! I'm Benjamin, 32yo from France
I've been saving fuel for some time now but I do believe that I'm ready to level up a bit

I drive a diesel Fiat Multipla 1.9 jtd 120hp. Doing 5.27l/100km (44.63mpg)
I have very old tires on the car, 195/60/15
I will go for narrower tires asap (185/65/15), that's the smallest I can put on legally and chose a A ranked energy saving tire.
Do you guys did that already? Any idea of how much I can decrease my consumption just by doing that?

I want to remap my ECU too, here is what I can get, a looooot more torque. Is this bit of extra torque in low rpm will help me to reduce my consumption too? Any idea of how much I can save?
(I can't post a link yet because I'm a new member. All the data's can be found by searching "Fiat Multipla 2002 2010 1.9 Multijet stage 1 - BR-Performance on Google"

Thanks for your help!
Let me know if it's better to open one or two threads for each topics!

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Old 05-09-2022, 10:35 AM   #2 (permalink)
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Bienvenue, Benjamin!


I've changed your account so you can now post links/pictures.


As for your question about tires:



If the old tires are NOT low rolling reisistance, then you will notice a big difference in how easily the car coasts in neutral. That can save you a few percent in your fuel use. It can save you MORE than a few percent if you can change your driving techniques to take advantage of opportunities to coast longer before turns & stops. (Depends on traffic, too.)



Torque mapping:



As for changing engine characteristics, my feeling is that would be most useful if it allows you to change to top gear sooner than you can now.



Similar situation: I installed an "economy" camshaft in my gasoline engine that makes more low-end torque, so I can up-shift earlier.
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Old 05-09-2022, 11:51 AM   #3 (permalink)
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Thanks!

Here you can find some details about the possible remap:
https://www.br-performance.be/en-be/...-1-9-multijet/

We can see that they provide eco remap or stage 1 remaps. Both gives the same extra torque, so I guess the torque curve is the same that the one we can see in the stage 1 section
They claim 35% less fuel consumption, sounds completely irealistic, it means going from 45mpg to 68mpg...

For the tires, we have in Europe a specific label that gives infos on tyre noise, wet braking and rolling resistance. I think that my actual tires are ranked C and E, or E for all 4 tires. I'll get A ranked tires, but will I really decrease my consumption by 0.45l/100km as it is claimed? Seems huge! ( It means that I'll go from 45mpg to 49.5mpg! )
Here is the details about this label and the consumption
https://www.tyreleader.co.uk/tyres-a...ar-tyres-label
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Old 05-09-2022, 03:24 PM   #4 (permalink)
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Hi Benjamin!
Welcome to EM

According to tire size calculator, if you go from 195/60R15 to 185/65R15 then the new tires will be ~5% narrower, slightly reducing aero drag. Also, the the diameter and circumference will be ~1.2% larger, which means that when cruising your engine will be at slightly lower RPMs.

Pumping the tires to a higher pressure will also reduce rolling resistance. I pump mine to the max pressure printed on the tire's sidewall, but if you want to start off safe then try 10% less than max sidewall.

As for chip tuning your engine's ECU, more torque at low RPMs will help reduce fuel consumption, as MetroMPG stated, but will it save enough to make up for the cost for the mod?

I would suggest you look into cleaning up your car's aero.
Also, since it is a diesel, covering the radiator/grille and insulating the engine bay will help retain heat as your efficiency improves.

How do you usually use your car? Daily driving in city traffic, high speed travelling on the expressways, etc.?
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[Old] Piwoslaw's Peugeot 307sw modding thread
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Old 05-09-2022, 04:50 PM   #5 (permalink)
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Overpumping tires won't ruin the middle of the tire?

I'm thinking of making a blocked grill too, for the aero I won't do that much, except maybe a bigger front air dam and a belly pan, but it's definitely a long term project.

I live in the countryside, so here no traffic jam, no traffic lights... Just empty roads going uphill and downhill with a 90km/h speed limit

I often do longer trips (650 with return, or 900km with return but most of the time I drive on secondary roads, I try to avoid highways and when I have to use one, I never drive faster than 110km/h
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Old 05-09-2022, 08:18 PM   #6 (permalink)
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Welcome.
Quote:
Overpumping tires won't ruin the middle of the tire?
That was true of bias ply tires. Pneumatic structures admit cylindrical forms. The belts make it happen.
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Old 05-10-2022, 02:52 AM   #7 (permalink)
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Quote:
Originally Posted by MorvanBen View Post
I live in the countryside, so here no traffic jam, no traffic lights... Just empty roads going uphill and downhill with a 90km/h speed limit

I often do longer trips (650 with return, or 900km with return but most of the time I drive on secondary roads, I try to avoid highways and when I have to use one, I never drive faster than 110km/h
That sounds ideal for adding a Kammback, or even a boattail.
The Kamm I made for my previous Pug307sw reduced fuel consumption by 7-8% in the 70-100 km/h range, based on testing at a steady speed.
But that gain almost doubled, because better aero allowed for much longer coasting between pulses. If you have long but not steep downhills, you may also want to add an engine kill switch to save more while coasting.
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[Old] Piwoslaw's Peugeot 307sw modding thread
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Old 05-10-2022, 04:08 PM   #8 (permalink)
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Quote:
Originally Posted by MorvanBen View Post
I will go for narrower tires asap
Some folks who often are not really good drivers are fooled to believe a much wider tire may save their arses, as if they were driving a race car on the streets and really needed all that drag, yet sometimes a narrower tire may actually be better to prevent issues such as aquaplaning.
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Old 05-12-2022, 06:47 AM   #9 (permalink)
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I'm afraid I can't lower that much my cx (cd in the US?).
Got .35, maybe I can improve a bit the airflow with a blocked grill, narrow tires, maybe I can search in fiat parts if I can put some other side mirrors (mines look like truck mirrors! :O )
I can work on the air flow underneath the car, but for the car body itself, because of it's "box" design, I'm afraid I can't do that much
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Old 05-12-2022, 07:35 AM   #10 (permalink)
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First, welcome aboard!

Quote:
Originally Posted by MorvanBen View Post
I'm afraid I can't lower that much my cx (cd in the US?).
Got .35, maybe I can improve a bit the airflow with a blocked grill, narrow tires, maybe I can search in fiat parts if I can put some other side mirrors (mines look like truck mirrors! :O )
I can work on the air flow underneath the car,
Second, there is a lot of things one could do with modifying the underbody air flow. I've been looking for this for my Opel Zafira this morning. Found this image in this forum, for instance. Mercedes apparently did a lot of research into making their CLA class more aerodynamic. So I found the original image



on the intertubes, and then did close-ups of the parts I found interesting and screen-shotted them.






Quote:
Originally Posted by MorvanBen View Post
but for the car body itself, because of it's "box" design, I'm afraid I can't do that much
I'm going to look at making some sort of rear spoiler, like this one


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