wheel width went from 175 to 205 - fuel efficiency went down.

londonTiger

I put on some cheap alloy wheels on my car to get away from the cheap hub cap look. Bought all 4 alloys for 97 quid, they're oz racing alloys but probably one of their lowest rating alloys.

I dont know how much the rims weigh, but the overall wheel weight is 19.3kg (including tyres). The previous steelies weigh 16kg all in.

There's been a noticeable difference in mpg - dropped by 1 I think.

I was wondering whether the alloy wheels were the culprit and whether it was more the weight or the wider threads leading to more rolling resistance that's causing it.

previous wheels 175/80 r14
new wheels 205/50 r17
Correction: is 50 not 45

I suppose I could drop from 205 to 185 because I dont need these big wide tyres for a modest 105hp car. Any idea how much weight I could shave off the wheel by dropping the width?

picture of aloys (not my car)
http://www.4tuning.ro/images/jante-oz-polaris-17/jante-oz-polaris-17-12bfb6a68c7826a6b-0-0-0-0-0.jpg

londonTiger

never mind 185/55/17 are impossible to find, i think minimum is 195 but the profiles dont add up the right circumference, i would need to get 205 minimum to get the right profile to match my cars computer.

skivenov

It's not about weight as such, it's about rolling resistance. Loosely speaking (someone's going to correct me with science - I know it), more tyre on the ground means there's more grip, meaning more energy is needed to turn the wheel.

harleq1962

i bought an 02 2 door focus when i got it it had 225 tires on it, got they where mondeo wheels, swapped this for a 4 door focus with similar mileage similar condition but with 195 and i recon im getting about 60 miles more to the tank, i also had to replace 2 good tires on the front as the wide wheels pulled the tracking out,

Norman_Castle

There's been a noticeable difference in mpg - dropped by 1 I think.

You've noticed a 1 mpg drop?. Possibly rolling resistance, but more likely to be different circumference.

maninthestreet

londonTiger wrote: »

There's been a noticeable difference in mpg - dropped by 1 I think.

That doesn't sound huge to me - it's well within the margin of error when it comes to calculating a vehicles mpg.

londonTiger

Norman_Castle wrote: »

You've noticed a 1 mpg drop?. Possibly rolling resistance, but more likely to be different circumference.

if you took a bash at a wheel size comparer you will find that the circumference is the same - i intentionally went for 205 rather than 195 because 205 fits the circumference perfectly. 195 doesn't quite work, in the case of 195 the height should be between 50% and 55% - they either don't exist or are very rare tyres which would attract a price premium

Chopper_Read

I hope you torqued up the wheen nuts.

londonTiger

skivenov wrote: »

It's not about weight as such, it's about rolling resistance. Loosely speaking (someone's going to correct me with science - I know it), more tyre on the ground means there's more grip, meaning more energy is needed to turn the wheel.

Surely weight plays a part with rolling resistance - especially start stopping in city driving.

I know that it will also affect the braking distance because there's more mass being spun around therefore it will be harder for the brakes to stop the motion. I don't know whether the increase/difference in weight will cause changes in resistence when the car is moving at a constant speed - say 50mph

skivenov

I've read your post properly now

I wouldn't worry about a 1mpg difference, there's so many things you can't change that can make more of a difference than that (quality of fuel, ambient air temperature, change of driving pattern). A slight change of rolling radius, which to some extent, you will have caused when you changed you wheels can alter the accuracy of your odometer as well.

Running the same van on the same tyres, with the same service schedule and the same driving technique, I can get a 5mpg fluctuation.

Rolling resistance is about a lot of things, wheel weight is one of them, but nowhere near as much as tyre choice.

StrongWork

Your mpg has dropped by 1mpg?

Non story is non story.