Ive been looking at reducing weight in my car, without losing the A/C and other essential homely features as heating and stereo etc..

When I first swapped my OEM 17" Subaru wheels for TD Monza 18"'s, I noticed a 3MPG drop on the trip computer. I kept the monzas, much better looking wheels.

Meanwhile... Ive got rid of my spare and jack, changed the bonnet to a fibre glass carbon coated bonnet, frp front bumper, lightened flywheel and some other bits which make little contributions to my overall weight savings.

Ive read online that wheel savings equal x 10 the savings on the car weight momentum. i.e. to do 40mph with lightweight wheels uses less fuel than 40mph using the heavy wheels, not just because of the actual weight difference in wheels, but the amount of effort the engine has to put into making 40mph.

I havent got a clue how heavy my wheels are, but according to the blab above, if I can cut 5kg off each wheel thats 20kg of the stationary weight, its an equivalent of 200kg's off the weight momentum.

Id love to see some figures on this if anyone has gone through the excercise. Unfortunately, I only have the one set of wheels so I cant do this experiment. I definitely know it does make a difference as I lost 3mpg, which is quite a bit for wheels. If I could squeeze 5mpg just on lightweights that would be great. Not just for petrol savings but in improved acceleration and handling.

 

i think i have overestimated the 200kg and its more like 80kg savings (which still is loads)

 

I'm only speculating but I bet theres not much in it;
Your computer is saying 3mpg less but what it doesn't know is for every revolution of your larger wheels you are actually travelling further than every revolution on 17's so it probably evens out somewhere along the line. It depends upon whether you have lower profile tyres to compensate for the increased wheel diameter.

There will definitely be handling advantages to any reduction in the unsprung weight on each corner.

 

I dont think thats correct. When you go up a wheel size you usually come down a side wall size so the circumference stays the same does it not?

 

I just go to the loo before heading out, saves a load of bother

 

Nah don't believe you, you're full of ****.

 

It's all about unsprung weight Carl.

This may help with the wheels.

http://www.wheelweights.net/

 

Unsprung weight reduction is around 6 times more effective than removing weight from the rest of the car.

 

Well i have one of the lightest wheels available on my sti (oz superlegera) and its still shocking on fuel

Average 18 mpg

 

Not necessarily the case but I did say "It depends upon whether you have lower profile tyres to compensate for the increased wheel diameter."

I think you're right in that there is very little in it either way. Main point is reduced un-spring weight is a good thing!!

 

It'll get a lot less to the gallon if you get a flat tyre and have no spare or jack!!