Bigger Wheels = Bumpier ride?

[2legit2quit]

Hey I own a 7th generation celica (2003) and i was wondering if bigger wheels on my car (thus smaller tires) would make a bumpier ride as well as making my car slower on turns. There has always been the rumor that if you put bigger wheels on your car, it'd make it slower.. Does anybody have opinions on this?

I am debating to put 20" wheels on my car and it will kind of look like this:

http://images.autotrader.com/images/..._A.565x377.jpg

as you can see the tires are alot smaller than normal stock tires, but the rims & wheels are huge.. to what extent would this affect my driving? would it be better if i used small 17" wheels?

[bobbyex]

Bigger wheels = bumpier ride, worse cornering/turning, worse fuel mileage

and it's not a rumor, bigger wheels does make your car slower, the motor has to work harder to turn the wheels. 17's would be much better.

[stepho]

There are multiple factors here.

The first was assumed by bobbyex.
If you make the total diameter bigger (including both rim and tyre) then you have changed the leverage that the engine can supply to the edge of the tyre.
The tyre has a larger circumference, hence one turn of the tyre will take you a further distance, hence the car will go faster for a given RPM.
This is paid for in that the engine requires more torque to turn the wheel a single revolution, so acceleration will suffer.
This is simple high school physics.
Summary: bigger total diameter means higher top speed but lower acceleration.

The other factor is what was said by 2legit2quit.
A larger rim with a lower profile tyre (ie same total diameter including both rim and tyre) will not chance the top speed or acceleration.
You will get a firmer ride (less tyre to absorb the bumps).
If you firm up the springs and shocks too much the tyre will actually spend too much time skipping into the air on every bump.
It might be less than 1mm but the tyre is not gripping the ground and so can't steer or push the car.
But you can't firm up a tyre any where near that amount unless you run solid plastic tyres.
So just using lower profile tyres on larger diameter rims will just give a firmer ride that might be slightly more uncomfortable but will generally distort less and hence will corner better.
Summary: everything is good except for the slightly harsher ride.

The third factor is if you also widen the tyre (ie left to right).
This puts more rubber on the road.
In dry conditions this gives allows the wheels to turn or push the car more before they find their limit.
In wet conditions a wider tyre tends to aquaplane.
This is when water underneath the tyre can't get all the way out to the edge and so the tyres floats on a film of water.
The car is liable to crash.
Wider tyres also take more energy to change their rate of spin, so acceleration is ever so slightly less - you will be hard pushed to tell the difference on a road car.
Wider tyres also have more drag, so fuel economy will suffer a very small amount.
Summary: good in summer, bad in winter.

In my opinion:
1) a 1" or 2" bigger rim with a corresponding lower profile (ie same total diameter) is always good for enthusiasts but usually not enjoyed by the rest of the family,
2) factory width is best in winter,
3) 10-20mm is good in summer on anything short of a race car,
4) anything else is usually just for show and/or dangerous.

- Stepho

[roushians]

My 5th gen is lowered w/ low profile tires on 17" alloy rims.

In my case, ride is super, super rough :P pot holes knock the wind out of me literally! It's insane. Maybe it just seems extreme to me because I was never used to driving a vehicle setup like this, but it does handle amazing and corner beautifully. I absolutely love driving it (when the road is smooth).

Definitely notice way more hydroplaning as my tires are very much wider than stock!

[Pineapple]

Big wheel = less side wall = less rubber to absorb bump = rough ride.
You will have better cornering with a lower profile tire. High profile (50+) tire will bend and run on the side walls under heavy cornering. Not a good thing.
The other factor is weight. Big wheel tends to be heavier. Forged and 2-3 piece wheels are usually light. Put them on a scale to compare. Check weight of your stock rim with tire and air. Usually cheap rims are heavy.
Less side wall will also mean avoid all pot holes. You'll bend the rims with a good bump. Also stay away from curbs.

[2legit2quit]

Okay so basically those 20" wheels would

1. Make acceleration slower
2. Make top speed higher
3. Make ride more rough

About how much slower would it make the acceleration/how much would it increase the top speed?

So pretty much its a bad idea to put wheels (as shown in picture) on the car unless for show. I've noticed alot of the celicas (and other cars) have big wheels when they are on show and sometimes when racing (?). So just casual driving and some racing (a little :P) i should keep with the smaller wheels/bigger tires?

I pretty much know about the whole car becoming slower in acceleration with bigger wheels.. but how big of a difference does it make?

[Pineapple]

1,2: depends. 3: yes you're correct, due to lower profile tire.
1: True only if the rims plus tires are heavier then your stock rims + tires. If you can get lighter rims, you'll gain performance.
2: Depends on the tire you chose. With correct tire, you'll get same thing as stock. Use this to find right size tire: http://www.miata.net/garage/tirecalc.html

[stepho]

Acceleration and top speed difference is proportional to the change in tyre diameter.
It doesn't matter what rim size or profile you use.
If the old tyre diameter was 80cm (not a real size, just a number off the top of my head) and the new tyre diameter is 83cm, then the new top speed is
OLD SPEED times 83 divided by 80

Likewise, acceleration would be
OLD ACCELERATION times 80 divided by 83

Also, the speedometer will read wrong by this proportion as well.
(the speedo converts revs of the drive shaft - it doesn't know about changes to tyre diameter).

Ride firmness is dependant only on tyre profile.
Lower numbers meaner firmer.

As Pineapple said, you can select a rim size and a tyre profile so that the total tyre diameter can be stock size - or any other reasonable size you want.

I generally prefer to increase the rim diameter by 1" (eg 14"->15" on my 1977 Celica) and then choose a profile which makes the tyre diameter match the stock diameter.
Increasing by 2" and choosing an appropriate profile also works.
Increasing by more than 3" is generally a bad idea because really low profile tyres are really expensive and your fillings will rattle out.

- Stepho

[hatchy_gt-s]

^ very nice explanation but to make it simple you dont gain top speed the speedo just lies to you and accel. will not be noticeable
its like putting higher octane in your car your car it doesnt make it go any faster, you dont gain hp from it.

[stepho]

Actually Hatchy_gt-s got it back to front.
The real speed changes (say, higher for bigger tyres) but the speedo tells you what the old speed would have been (ie it reads low compared to the real speed).

- Stepho