Ride Quality, Handling on 17" vs 18"

[Sasquachulator]

Originally Posted by Racecomp Engineering

The tire type itself makes the most difference IMO. More than weight and sidewall (within reason).

I always caution against ultra-light wheels if your roads are extra crap because wheels can and do bend.

- Andrew

This.

My BMW X1 with the sport package came with 225/45/19 Bridgestone Potenza Summer tires.
They are a stiff hard riding tire.

We switched them out with Continental ExtremeContact DWS UHP All seasons for winter and they are noticeably WAY softer.

[alex87f]

I bought my 1st gen 86 with Gramlights 57C6 in 18x7,5 with 225/40/18 PSSs (which looked amazing). Later switched back to the stock wheels & tires and definitely felt a difference in:

-noise level
-harshness (per my GF - "it's less unpleasant when you need to pee")
-agility and fun, but that's probably down to the lower grip tire

I never put the gramlights back on.

[Blighty]

Originally Posted by SuperTom

That plus you will throw off speedometer and slower acceleration with larger diameter tire.


Yep its all about the weight. Especially on the outside perimeter. On a 17 the weight of the barrel is pulled in closer.

Isn't the OEM 17's heavier than the 18's?

Just remember this from C&D. It is the BRZ 18 vs the GR86 17, but I assume those weights are the same for each car.

I would of though compound and sidewall stiffness is that primary changes to the ride (all other things equal).

[NoHaveMSG]

Originally Posted by Blighty

I would of though compound and sidewall stiffness is that primary changes to the ride (all other things equal).

Put 1 bar of air into a 1 liter container and 1 bar of air into a 2 liter container. Compress the sides of each container 25mm. Are they going to have the same pressure in the compressed state?

[OkieSnuffBox]

Originally Posted by Racecomp Engineering

The tire type itself makes the most difference IMO. More than weight and sidewall (within reason).

I always caution against ultra-light wheels if your roads are extra crap because wheels can and do bend.

- Andrew

Yep. More performance oriented you go, the stiffer and stiffer the sidewalls get to aid in performance and turn in.

[Blighty]

Originally Posted by NoHaveMSG

Put 1 bar of air into a 1 liter container and 1 bar of air into a 2 liter container. Compress the sides of each container 25mm. Are they going to have the same pressure in the compressed state?

Can I take a guess without googling I wonder?

There is probably some physics here about thickness of the wall, its own ability to compress, and the relative compressibility of a larger area of air vs a smaller one vs the amount you are trying to compress - but certainly 1 bar is still one bar pushing back on you - and the lower the pressure of the air inside, the more that pressure would define the overall effect - as things like the wall would be more relatively firm and therefore only come into the equation when the pressure needed to overcome the air pressure start to get high enough that there is also a difference in the compressibility of the wall.

[Spektyr]

Originally Posted by Blighty

Can I take a guess without googling I wonder?

There is probably some physics here about thickness of the wall, its own ability to compress, and the relative compressibility of a larger area of air vs a smaller one vs the amount you are trying to compress - but certainly 1 bar is still one bar pushing back on you - and the lower the pressure of the air inside, the more that pressure would define the overall effect - as things like the wall would be more relatively firm and therefore only come into the equation when the pressure needed to overcome the air pressure start to get high enough that there is also a difference in the compressibility of the wall.

The better way to illustrate this principle is a piston/cylinder like those plastic "flavor injectors" for cooking. Basically a syringe with a removeable needle.

Take the needle off, pull the plunger out as far as it will go. The seal the end with your thumb and push the plunger in as far as you can without breaking the seal.

Repeat, but this time start with the plunger in the middle.

The larger the starting volume the more compression it takes to equal the input force (assuming all other variables are constant).

Of course applying this to tires/suspension means you're almost certainly changing at LEAST one other variable in every given experiment, which muddies the waters considerably.

[NoHaveMSG]

Originally Posted by Spektyr

The better way to illustrate this principle is a piston/cylinder like those plastic "flavor injectors" for cooking. Basically a syringe with a removeable needle.

Take the needle off, pull the plunger out as far as it will go. The seal the end with your thumb and push the plunger in as far as you can without breaking the seal.

Repeat, but this time start with the plunger in the middle.

The larger the starting volume the more compression it takes to equal the input force (assuming all other variables are constant).

Of course applying this to tires/suspension means you're almost certainly changing at LEAST one other variable in every given experiment, which muddies the waters considerably.

Yeah, it isn't the only factor, but it is one. Given all things equal, they still are not going to be exactly equal.

[new2subaru]

Tires being equal, more sidewall = more comfort. Less harshness over small bumps imo. More sidewall protects the rim too. I run 225/55 R16 on street.

See if you can get a ride in someone's car with decent 17's