964-C2

I have heard that you have to multiply the wheel wheight by 4 to get the same effect as loosing/adding sprung weight to the car.

Will reducing the wheight at each wheel with 4 kilo reduce the lap times as much as reducing the sprung weight by 64kilo? (4 kilo x 4 wheels = 16 kilo x 4 =64 kg)...

Any experiences with this?

Thanks.

Bill Verburg

The actual # is debatable and will vary depending on external conditions like track configuration, traction, actual maneuvers on track etc. but there is question that dropping 4kg/ wheel will allow the car to brake, accelerate and turn more quickly. I routinely go between street wheels and track wheels which are the same size and have the same size tires, you can feel the difference in liveliness of the car when the light track set goes on.

One condition where the lighter wheel may not help is where there is limited traction, the heavier wheel can function as a sort of traction control absorbing some torque that would other wise be wasted in wheel spin

M758

I was able to feel the differnce in weight of worn down RA-1 vs a new full tread RA-1 (225/50 R15).

The new RA-1 were about 1-2 llbs more per tire. On track the car felt ok, but it not have the accerlatoin. It was felt a little off. Steady state grip was fine, but lap time were off and the car did not see to pull as well. Part of that due to more rubber = taller tire and all that weight is on the outside of the tire.

Tedster

I can feel the difference between my stock 6GT3 wheels with PS2 vs Fikse and MPSC. I think the weight difference is about 5-7 lbs per corner. With the Brembo floating rotors vs stock iron rotors thats another 2 lb per corner. The car feels like it is wearing running shoes!

IcemanG17

I went from 225/50-16 street tires (Dunlop Direezas 26lbs) to 245/45-16 BFG R1's (22lbs) and the difference was AMAZING....yes the tire is slightly shorter 24.7" vs 25.0..but the car just felt SO Much better.....I was stunned at the improvement...

I'm not exactly sure how much the 16lbs of sprung weight helped...but I was debating going to 18" rims & tires but that will gain nearly 60lbs of sprung weight...which is a big part of why I haven't done it

sig_a

Smaller diameter wheels steer faster, spin faster, stop faster than larger diameter wheels. On the other hand, gearing, braking and traction can be goofed up. Weight saving with smaller wheels is another plus.

mark kibort

Guys, you are not going to feel it. You may think you can, but you cant. the ratio is a little more complicated than just , 4:1 or something, because it depends on where the weight comes from.

Its as simple as this. if it is on the tire, (say 17" rim or so), the weight spinning has an effect on acceleration , as if 2x that weight was in the car. If you want me to post the formula, its pretty simple and it proves this beyond a shadow of a doubt. so, if you loose 2lbs of spinning tire weight, that's equivilent to 4lbs as if it was in the car, and so that is like if you pullled 16lbs out of your car. In other words, 10lbs is like you just gained 1 hp!! can you feel 1.6hp????? Maybe you think you can.

edit: If the weight was on the wheel and not the tire, change that 2x factor to more like 1.5x as if the weight was sitting in the car for the full acceleration effects, assuming that the weight is evenly distributed.

mark kibort

Dont confust R compound test, to diameter or weight changes of a tire what you felt was ALL stick differences, not acceleration differences. on a smooth , straighter track, the unsprung weight difference will be much less noticable.

mark kibort

so, you are able to tell 1 to 2 lbs difference a tire difference? thats like detecting 1/2 to 1hp difference. anyway, what you probably felt was lack of grip as anyone that was running a full tread tire would feel. you will come off a given corner faster and have more top speed down the straight, but its due to the tire, not weight or size of it.

telemetry will tell all in a comparison.

remember the comparison of the guy with the telemetry output from Cal speedway? when we looked at it, you could see that throttle application was differenent on the approaches and through the turns, yielding different straight line top speeds. It was very clear from the data.

mark kibort

I also routinely go from 305s up front to 275s up front and brand changes from Hoosier vs Toyo (which are about 4lbs heavier). the only real difference I feel is the greater grip of the hoosiers, and there is a heavier steering wheel feel for the 305s up front vs the 275s or even the 225s I drive in a similar car but different venue. With the power assist steering, its really hard to tell, but there is a difference. as far as acceleration, not going to matter. You can put the car on the dyno and check that, and in fact, you could calibrate the dyno by the values of the weight changes, size and acceleration times to final RPM.