Mazda 6 Forums banner
1 - 10 of 10 Posts

·
Registered
Joined
·
1,996 Posts
Discussion Starter · #1 · (Edited)
Wheel/Tire Weight Effects for 3rd Gen Wheel/Tire Upgrades Considerations

Lots of Awesome Links cross posted here:
http://forum.mazda6club.com/wheels-tires/144380-effects-wheel-size-weight-performance.html

Some summary takeaways:

  • For wheels and tires of a same diameter the difference in acceleration/braking is 1lb wheel/tire weight is equal to ~2.5 lbs of vehicle weight (1.5 lbs rotational + 1lb translational)
  • Going up or down in wheel Diameter changes effective rotational mass dramatically: Radius^2. That means a 19 wheel has to be closer to 20lbs to have the same rotational inertia as the stock 26lb 17inch wheel
  • Similarly, where the mass is distributed on the wheel is roughly as important as overall weight which is why the flow form technology wheel weights, which reduce weight out at the rim should be considered differently than regular cast or forged wheel weight for acceleration and braking purposes.
  • Going up or down in tire diameter is a different story because the larger the tire diameter the slower the entire wheel/tire mass turns and accelerates which counteracts the ill affects of the tire mass being father from the center. So today's modern wheels which are larger tend to run larger overall tire diameters which reduces the ill affects of extra weight, and reduces rolling resistance due to the shallower angle of attack of the tire and pavement
  • Unsprung Weight, which ignores rotational impacts is pretty straightforward and can reduce the "crashiness" of a suspension and increase the ability of the rubber to maintain more consistent pressure on the pavement maximizing traction at the limit of adhesion on any road that is not newly, perfectly paved

I think this may need to be a sticky for quick reference, maybe not. Please weigh in.
 

·
Registered
Joined
·
1,996 Posts
Discussion Starter · #3 · (Edited)
It's 30.4lbs per a post somewhere before on this forum I can't locate. Stock tire is pretty light at 24lbs per tirerack.com. 17 inch stock is 25.8lbs and the tire is 25lbs per TireRack,com. So from an un-sprung weight comparison there is only a 3-4lbs difference between the two per wheel/tire, but from a rotational mass perspective it's probably equal to a 60-70lb difference in vehicle weight between all four wheels/tires.
 

·
Registered
Joined
·
1,996 Posts
Discussion Starter · #5 · (Edited)
I just ran accross this link which shows parasitic losses on a dyno from different wheel/tire weights.
Dyno Runs - The effects of wheel/tire weights on wheel horsepower - MBWorld.org Forums

I honestly didn't think that inertia losses would show up on a dyno, I thought only friction losses would. Maybe they dyno'd in 1st gear or something or the mass of the dynometer was low enough that very rapid acceleration occured (faster than the car could be accelerated down the road) which exagerated the change.

Anyways it's proof wheel and tire weights affect power, although the amount is debatable.

I still think that multiplying the weight drop at 1 wheel times 10 (4 wheels x 2.5 factor) then divide that by the power to weight ratio of your car (3150-3300 depending on model and options, and 184hp) will give a conservative estimate of the power gain felt by lightening up wheels and tires.

My car is about 3080 weight and about 200hp so I'm at 15.4 lbs/hp and if I go with 22lb konig oversteers in place of the 30.4 factory 19s and same weight tires, I'll save 8.4 lbs per corner or 84lbs total, which when divided by 15.4 is 5.45 hp peak or about a 3% gain at every rpm at all throttle loads. Also it will give the same 3% reduction in braking distance.
 

·
Registered
Joined
·
465 Posts
Car and driver has been an excellent source of engineering information. Just from my experience the amount of gain from lighter rotating mass differs from car to car, there are so many variables. And do we want give up the big wheel , full wheel well look, for the gain and spend easily $3k on new wheels and maybe tires that save us tenths of a second or another mile per gallon. Racing , yes, everyday commute I dont know . OLdvet
 

·
Registered
Joined
·
1,996 Posts
Discussion Starter · #9 ·
Car and driver has been an excellent source of engineering information. Just from my experience the amount of gain from lighter rotating mass differs from car to car, there are so many variables. And do we want give up the big wheel , full wheel well look, for the gain and spend easily $3k on new wheels and maybe tires that save us tenths of a second or another mile per gallon. Racing , yes, everyday commute I dont know . OLdvet
The mazda 6 wheel with a relatively large overall diameter for a passenger car and relatively light internals for skyactive would probably be towards the makes very little difference end of the spectrum.
 
1 - 10 of 10 Posts
Top