Wheel & Tire Weight Input

[Donbrz]

Looking at wider wheel and tire combinations for 2015 Brz to replace stock, and seeking input as to whether 4 lbs incremental weight per wheel/tire (16 lbs total for car) is significant to power or handling and whether something I should be concerned about in considering replacement? Insights would be appreciated.

[NWFRS]

D@am.

I've had a hundred different answers to that same question in the last year.

The unofficial consensus was that I'd never feel a difference. I was told to buy what I wanted, regardless of weight because I'll be looking at them for a long time.

That said, anytime I've swapped wheels, I've always gone LIGHTER on the basis that the original engineers and road testers knew what they were doing. I also figured that with the FA20's relative lack of torque, it certainly wouldn't hurt to go lighter.

I recently settled on a 16x7.5" wheel weighing 17.9lbs.

I think that means I've saved 2.2lbs.

My priorities were:
Attractive design.
Lighter than stock.
Relatively inexpensive.
16" for less harshness.

What are YOUR priorities?

[Donbrz]

Priority is handling in curves without noticible impact on acceleration. Thus, considering wider wheels and tires than stock. Down to 245/40/17 PSS (23 lbs) or Bridgestone RA-11 (27 lbs). RA-11s favorable reviews, but reviewers seem to be porche owners with substantially higher hp than brz

[ApolloSki]

http://www.ft86club.com/forums/showthread.php?t=32858

[continuecrushing]

Find/buy the lightest wheels you can, and wrap them in good rubber.

Don't worry about the weight of tires themselves, I was determined to find something "lighter" than the others, but what I found is that all the "good" tires that weighed more generally had stiffer sidewalls.

The RE-11a is going to be a more performance oriented tire than the PSS. If you favor performance more than longevity of the tire, go with the RE-11a. Both are great tires though, just slightly different priorities.

[Donbrz]

Great input. Went with RE-11A and Enkei RPF1 17x9 +35. No noticible impact on acceleration. Thanks for feedback !!

[ss3gt]

This is my speciality. Yes, a lighter rim and tyres is one of the easiest and most effective modifications to your car. My 1998 SS3 Celica gains another 9 HP than an FT 86 on this mod alone, as well as improved handling.

I've had and won 59 illegal road races and have beaten Wrx,s, Skylines and Evos.
Ive also written a book on how to increase power and handling from non turbo cars.
Let me explain.

Tyre and rim weight are centrifugal weight connected to your drivetrain along with pistons, driveshaft and flywheel. The more weight on the outside of the rim..the greater power needed to turn it. When i say I've gained another 9 HP on this mod than a Brx i mean I've freed up 9 HP..it no longer has to turn that weight and is now available for pure acceleration.

The first thing you need to do for your car is this. Divide its weight 1250 kg by its HP 190. This shows that each HP is pulling 6.5kg of weight..or for every 6.5kg of weight you shed 1 HP is freed up

For the wheels even more is gained. Roughly its a 4:1 ratio for rims and a 5:1 ratio for tyres. So 1 kg less on tyres weight is equivalent to 5 kg of body weight x 2 for your rear tyres = 10 kg or 1.5 HP on your tyres.
A one ply sidewall tyres is lighter than a two ply. The lightest are Toyo T1R,s. There is a reason why they used these tyres on Fast and Furious 3 Tokyo Drift.

If you run a 17" rim I'm guessing its around 9kg? A 16" Volk TE37 for around $800 2nd hand will weigh 5.3kg or 6kg for a CE28.
So now you're looking at a 3.7 kg saving for each wheel. That's 7.4kg for your front wheels and for the rear .. 3.7 x 4 = 14.8kg 1kg x 5 = 5kg = 19.8kg x 2 for both driving wheels = 39.6kg + 7.4kg =47kg or a 7hp increase in freed up HP

As for handling the lighter wheel means that your suspension rebound is able to work better at keeping that wheel in contact with the road. Heavy wheels tend to bounce on uneven surfaces.

This will be more beneficial on bumpy roads in the wet and less noticeable on freeways.

The other benefit of a light rim is a smoother ride and a quieter ride with a smaller rim

[stugray]

Originally Posted by ss3gt

The first thing you need to do for your car is this. Divide its weight 1250 kg by its HP 190. This shows that each HP is pulling 6.5kg of weight..or for every 6.5kg of weight you shed 1 HP is freed up

Interesting "rule of thumb" but far from scientific.
The fact is that the car will accelerate (on level ground) exactly the same if you removed the same weight from anywhere else on the car.

The 'rotational mass' of the system is FAR outweighed by the 'total mass' of the car.
The total mass is by far the dominant factor in calculating acceleration based on hp. The rotational mass difference is in the noise.

Based on this link:
http://www.w8ji.com/rotating_mass_acceleration.htm

If you could take off the 30 lbs driveshaft, and replace it with one that weighs ZERO, you get a whopping 1/4 hp equivalent difference.

Edit: Now when talking about reduction in rotating mass, removing it from the flywheel, or around the perimeter of the wheels (rims/tires) makes the biggest difference in rotational mass.
In fact worn tires versus new tires makes a MUCH larger difference in rotational inertia than the great "Pulley upgrade".
SO if you want to feel a bigger difference on the butt dyno than a LWCP, just have your tires shaved.

[BRZ NA]

Interesting,I would like to know too