Optimalius ratu dydis?

Koks optimaliausias ratu dydis kad butu smagu vaziuoti mieste(ir keturiese jei kada prireiks (as apie svori)) na ir kad graziai atrodytu is isores?

man asmeniskai R16 labai graziai ziurisi ir manau neturetu niekur liestis net kai masina prikrauta:)

205/40R17 butu kaip tik. O ar liesis ar ne nepirklauso ar ratai R14 ar R17, priklauso nuo plocio ir padangos profilio

Beje optimalus

Juliau, optimalus, taip kad jeigu maziau\daugiau negu 205/40R17 jau bus blogiau negu sitas variantas. Ar ne?

P.S. nes as galvoju kad R17 jau per daug gal.

O tai pala kokia pas tave masina. Profilyje tai passatas.
va linkas klubas.autos.lt />
irasyk standartiniu padangu matmenis ir ziurek kokie matmenys tinka su R17 diskais
Jei pas tave 185/65R14 tai tada atitiks 205/40R17

OVERSPEED'uose kazkada g idejo toki straipsniuka, as ji visa perkopijuosiu - kas netinges perskaityti gal ir ka nors idomaus supras.

Why bigger is not always better Reply with quote

There is a common misconception afloat that a taller rim will always provide increased lateral grip, but typically result in a weight penalty that hurts acceleration and deceleration.

Well, this is partially true, but it also has to do with the height of the sidewall and its ability to flex enough to hook up with the pavement.

A 17" wheel with a tire sized to fit within the 5G Civic wheel well (for instance) is going to have such a short sidewall that the lack of material to flex is going to have a negative impact on aceleration and deceleration. It could have a positive effect on cornering at steady state on a smooth surface, but in the real world one rarely encounters these conditions. Typically the car is in transition 95% of the time, and road surfaces are rarely smooth. As a result the lack of sidewall will have a negative impact on cornering more than 95% of the time.

Then consider the distance from the rotational axis of a 17" vs. a 16" wheel...even if the 17" wheel was the same weight (which would be unusual, but possible if one was willing to shell out the bucks for an extremely well engineered wheel) then you still have to deal with the fact that the actual outer shell of the wheel was a half inch further from the axis of rotation all the way around. This means it requires more energy to change the velocity of the 17" wheel (either braking or accelerating).

But what about the belief that a shorter sidewall will flex less and provide better handling?

Well that is just not always true. There is a limit. It is just another iteration of a well-travelled myth people who don't know any better recite over and over again.

Yes, a 50 series tire will provide less sidewall flex than a 75 series tire. But that does not necessarily provide better handling...just a different feel, and depending on the construction of the tire carcass, the compound, and the road surface, the 75 series tire could provide better traction. Ever notice that WRC cars use a taller tire on the rough surfaces than they do on tarmac? Do you think that is because they can't afford to buy taller wheels? Or maybe they just don't have the resources to tune the suspensions to handle the rough stuff? Yeah right.

The truth is that one quickly approaches the fine point where the tire's lack of compliance actually results in less lateral grip than a taller sidewalled tire would. I contend that a 215/35-17 (the size tire that would be closest in outer diameter to the stock 175/70-13 tire - on a 5G - and would fit under the fenders of Civic) while providing less flex and a firmer ride than the 215/45-15, will not provide superior predictability or enhanced control. Firmer ride, maybe, but firmer doesn't always mean better.

What does improve handling is increasing the size of the contact patch and/or increasing the coefficient of friction between the tire and the asphalt. The latter can be done with softer tire compounds and things that happen at a molecular level as a particular tread compound breaks down due to friction at the tire/aslphalt interface...but that's not what we are talking about here.

What I am primarily talking about here is maximizing the size of the contact patch and keeping it in contact with the road.

A contact patch's shape is not a constant...it varies depending on the forces (latitudinal and longitudinal) applied to the contact patch due to the amount of torque applied to the wheel by the motor (accel and decel) and the difference between the direction the tire is pointing vs. the direction that corner of the car is travelling (a.k.a., the slip angle). Based on the compliance of the tire (and the tread blocks - this is sometimes referred to as tread squirm), these forces can allow the contact patch to deform in a number of ways that either increase or decrease the total area of tire tread that is in contact with the road surface. We seek to find the way that maximizes the amount of tread that is coming in contact with the road surface.

As a car corners, the suspension compresses on the outside and droops on the inside, which results in all sorts of variations in the orientation of the tire surface to the road (note, we are not focusing on the camber angle which is the angle of the tire relative to the chassis, but rather just the orientation of the tread relative to the road surface).

In a perfect world the outside suspension would compress and add just the right amount of negative camber to that wheel so that it remained perfectly oriented to the road surface such that the contact patch size was maximized (neither the inside nor outside edge would pull up from the road). Likewise the inside wheel would do the same thing but in the opposite direction. Unfortunately since the forces that cause the body of the car to roll, thus creating the compression and droop actions at each side of the car, are actually being applied slightly in advance of the body's ability to adjust and roll as the car is entering a corner and the suspension is yet to reach its steady state, or on corner exit in the opposite degree of compression/droop, we rarely find ourselves in that perfect world.

If one were to take the theory that less sidewall flex resulted in better handling to its extreme, then we would be seeking zero sidewall flex, right? Well, if the sidewall doesn't flex, and the suspension is not able to keep the tire tread perfectly oriented relative to the asphalt, guess what...the tread will lift and only the shoulder of the tire will remain in contact with the road surface. So now the contact patch area has decreased dramatically and you are losing traction.

If you reach and remain in steady state, then a stiffer sidewall can translate into enhanced lateral grip assuming the suspension does utilize spring/damping rates that work with the spring rate of the tire and that it provides sufficient camber correction as well as ackerman to deal with the body roll and the difference in diameters of the circles described by the inside and outside tires (BTW, there is currently no chassis that does that perfectly...certainly not our beloved Civcs which - let's face it - were designed for fetching groceries first).

But in the real world you do not remain in steady state but for a fraction of the time. Even around a skidpad one is typically making adjustments with the wheel or the throttle in an effort to keep the circumference of the circle constant, and these adjustments will cause shifts in the degree of body roll.

Now throw in a bump...let's say there is a .5"x.5" strip of wood lying across the surface in the corner. As your tire encounters this piece of wood, the whole tire lifts off the asphalt and is now resting on the wood...the contact patch has been reduced to whatever the approximate width of the contact patch was before, but only half an inch long. This will produce less lateral grip.

If you've ever experienced a "jittering" sensation when your car was cornering, then you know what it feels like when the tire and suspension is unable to comply quickly enough with variations in the cornering forces or road surface, and the jittering is the result of the tires hooking up momentarily, then losing traction, then hooking up again, etc.

Alright, so let's say we stay away from extremes...let's think about the two sizes I mentioned above (215/45-15 vs. 215/35-17). The 15" tire will have nearly an additional inch of sidewall than the 17. Take weight out of the equation if you wish, and assume that both wheels and tires are the same width filled to pressures where they have the same contact patch at rest.

Once you start applying the forces I described that are present in transitions, and once you throw a few bumps or surface irregularities into the equation, and then factor in the imperfections in the camber curve and ackerman present in the Civic suspension (basically factor in the "real world") you will find that the additional compliance present in the 15" tire will result in improved lateral grip over the 17" tire. At the very least it will provide an enhanced level of predicatbility and control.

So why do all those touring cars have tall rims and short sidewalls? I believe it is primarily due to the desire to run huge friggin' brake rotors (which are free under most touring car rules). These cars make tremendous amounts of horsepower and the drivers do the majority of their passing in late-braking maneuvers going into corners. Nearly every corner entry is a battle for who can break the latest and hardest. Larger brake rotors give them more leverage against the rotational inertia of the wheel, more pad surface, and a greater heat sink. This allows them to charge down the straight, balls to the wall, wait until they see the other guy brake out of the corner of their eye, and then jump on the binders as quickly as possible.

Ever notice how easily a touring car spins? A touch of nerfing and they break loose like tops, and its nearly impossible to catch the cars once they start to break loose. Know why? Because the sidewalls on the tires they run are so damn short that they have very little tolerance for being upset...very difficult to control and can be somewhat unpredicatable (which IIRC was your contention that short sidewalls provided). Its not because the suspensions are set up too stiff...the teams we are talking about - especially the works teams - have development resources coming out the yin-yang. Surely they could design a suspension that was capable of taking a wack from a competitor without causing the car to irreversably lose traction - hell, even NASCAR teams have figured out how to do that some of the time. Nope...the touring car builders are faced with a compromise - since the maximum rim diameters and outer tire diameters are constrained, they have to figure out how to get the most braking capacity built into the cars as possible. In exchange they sacrifice some stability and predictability.

So in conclusion, when selecting new wheels and tires for your car, keep in mind that there is a point at which a taller rim and a shorter sidewall begin to be a detriment to your performance...and not just the ability to put down the power or the extra rotational inertia or the extra unsprung weight either, but rather in the predicability of the car in transitions. Civics and CRXs are especially prone to being "over plus-sized" because of the constraints on the total size of the wheels. Don't be a lemming.

J. Brett Howell
Pebble MotorSports

Puse perskaiciau, atsibodo. Siaip tas aisku, kad reikia pasirinkti tarp isvaizdos ir vaziavimo. As siaip ant savo neplanuoju deti R17 uztenka man ir R16. O siaip nesam mes jau cia tokie sportininkai, taip, kad galim ir R17 uzsimesti del grozio

juk yra matuokle tu ratu NUORODOSE ;)

aha - as irgi pats neiveikiau iskart.
o jei ka uzkniso tai paskaitykit nuo So why do all those touring cars have tall rims and short sidewalls?

is kitos puses kaip rodo patirtis- gauti R17 devetas padangas su normalia mesa turbut paprasciau nei R16 ;)

tik klausimas ar tau tikrai naudotu reikia? ;) jau pabandzhiau praeita zhiema naudotas, baigesi tuom, kad keichiau mashina :D