[Sankar]

Not talking about profiles, cars and all. A big wheel for example Bullet's 19" wheel provides more comfort especially on broken roads when compared to a Bullet with 18" wheel.

Problem is with a bigger wheel your speedo and odo readings will be way off the mark. But then is it? Most manufacturers calibrate the speedo to show more speed than the actual speed. So with a bigger wheel the speedo might show you the actual speed speed But it depends.

[aaggoswami]

Originally Posted by ritz830

Nice picture. So bigger wheels with bigger tires do improve ride quality. I think many budget cars like swift,vista have improved their suspension by just upgrading their wheels

OK, here it gets a bit confusing. A wheel = wheel rim + tyre. Correct me if I am wrong.
And yes bigger wheel will contribute to ride quality. But then there are certain negatives also.
For example, the unsprung mass will increase with bigger rim. If we are able to increase the rim size and keep the tyres low profile, then the unsprung mass increase wont be much. But if on bigger rims we put in tyres that are high profile, then we have to make modification to suspension as the unsprung mass is increased.

[Guna]

Simply increasing the overall dia of the wheel is going to change the CG and is bound to affect the dynamics of the car. It will result in speedo/Odo error. Even with the same unsprung weight, bigger wheels need more torque for spinning.
In auto reviews I have seen remarks like 'wheel arches are so big, they can take much bigger wheels..' etc. I wonder if it is that simple.

[S_budhiraj]

Well seems this debate will be very intresting.

The correct size on my new Ikon TDCI is tube type 175/70/R13 Goodyear.

[rjvora_2000]

I had M.Versa dx2 modal.

The day on which I bought the car I found that the car was bobbling. I got the tyre changed from the original to radial tyre. and the problem was solved.

[ritz830]

Originally Posted by aaggoswami

OK, here it gets a bit confusing. A wheel = wheel rim + tyre. Correct me if I am wrong.
And yes bigger wheel will contribute to ride quality. But then there are certain negatives also.
For example, the unsprung mass will increase with bigger rim. If we are able to increase the rim size and keep the tyres low profile, then the unsprung mass increase wont be much. But if on bigger rims we put in tyres that are high profile, then we have to make modification to suspension as the unsprung mass is increased.

Cool, this is something new...

To summarize, there are two factors which jointly affect the ride quality w.r.t the wheel size
1) bigger wheels with bigger tires improve ride quality (suspension need to be adjusted as per the new size).
2) Unsprung mass, read this "http://en.wikipedia.org/wiki/Unsprung_weight"
The article explains how lighter unsprung mass improve ride quality.
For example The car's wheel is called the unsprung mass, so using alloy wheels will reduce the weight and hence improve ride quality.

[theEnd]

I think greenhorn hit the nail on the head.

Anyone changing their wheels/tyres would be advised to maintain the same overall diameter (OD). Supposed the OD is 20 inches (20"), and the wheel diameter is 14", that leaves you with 3" of sidewall on either side (3" + 3"). Now if you go and get some shiny looking 16" wheels, and upgrade your tyres while keeping the same OD, you've only got 2" of sidewall on either side (2" + 2").

More sidewall = more absorption of bumps, nice cushy ride for the bada sahib who likes to sit in the back seat
Less sidewall = less lateral flexing of tyres, better cornering and overall driving dynamics, but you feel every single bump on the road (and sometimes even painted lines)

Upgrading the wheels/tyres to a different OD is a whole different thing and generally not advisable unless you really know what you're doing. The speedo error is not the key reason, its more of an indication.

[anupmathur]

Originally Posted by Shan2nu

Generally a bigger wheel is said to be comfortable but lets say you upsize from 175/70 R13 to 195/60 R14, whats happened here is that while the wheel size has increased from 13 to 14, the tyre profile has reduced from 70 to 60.

So technically, your overall diameter is still the same and you've ended up with a lower profile tyre.

On the other hand if you compare 175/65 R13 vs 195/65 R14, the 14" setup not only has a wider contact area and a bigger overall diameter but it has also maintained its tyre profile, which is bound to improve ride quality. But doing this will cause the wheels to touch the wheel arch and makes for a very unpractical upgrade.

Shan2nu

Shan2nu, your arithmetic for these calculations seems to be flawed.
The sidewall height is very different from the 'profile' that you are using as the height of the sidewall.
175/65 has a sidewall height of 113.75 and 195/65 has a sidewall height of 126.75 mm.

[ritz830]

Originally Posted by theEnd

I think greenhorn hit the nail on the head.

Anyone changing their wheels/tyres would be advised to maintain the same overall diameter (OD). Supposed the OD is 20 inches (20"), and the wheel diameter is 14", that leaves you with 3" of sidewall on either side (3" + 3"). Now if you go and get some shiny looking 16" wheels, and upgrade your tyres while keeping the same OD, you've only got 2" of sidewall on either side (2" + 2").

More sidewall = more absorption of bumps, nice cushy ride for the bada sahib who likes to sit in the back seat
Less sidewall = less lateral flexing of tyres, better cornering and overall driving dynamics, but you feel every single bump on the road (and sometimes even painted lines)

More sidewall does not assure you better ride quality. The speed of the car also matters. At high speed the car will give a bumpy ride if it has a thick sidewall. Only if the driver prefers to brake and reduce the speed will he get a cushion like ride.

On the other hand less sidewall will be the best for highway cruising. That could be the reason why sports cars have alloys wheels fitted with tires having less sidewall.

[lancer_rit]

As some posters have mentioned, when you upsize wheels on a car, you keep the OD constant (+/- a couple of mm). This is not only because of speedo error, but the whole drive ratios of the car change if OD is altered, and there is more stress on the suspension components as well as the chance of the tyre fouling up on the suspension or wheel well due to the larger OD.

For any given OD,
1) larger wheels means lower sidewall profile
-> Better handling of the car
-> Worse ride quality

Now, if the tyre width is increased (for eg. 175 -> 195), handling improves (in dry conditions) and also ride can improve marginally.

Finally, the make and model of tyre also determines ride comfort depending on how hard compound is used in the tyres. So, comfort oriented tyres of the same spec will provide more ride comfort than performance oriented tyres (Eg. Michelin MXV8 vs Michelin Pilot Preceda 2)

Other factors which matter are the car's suspension setup based on which higher or lower sidewall may work better.

Cheers,

[lancer_rit]

Originally Posted by ritz830

More sidewall does not assure you better ride quality. The speed of the car also matters. At high speed the car will give a bumpy ride if it has a thick sidewall. Only if the driver prefers to brake and reduce the speed will he get a cushion like ride.

On the other hand less sidewall will be the best for highway cruising. That could be the reason why sports cars have alloys wheels fitted with tires having less sidewall.

More sidewall does normally mean better ride quality. What you mean is handling of the car may suffer. Sports cars dont have comfortable ride quality, they are sprung firm to provide great handling and cornering at high speeds.
Ride quality and handling of the vehicle are different aspects!
You can refer to the Car and Tyre Bible for more details about wheels and tyres
http://www.carbibles.com/tyre_bible.html

[ManneAtWheelz]

Originally Posted by Sankar

Not talking about profiles, cars and all. A big wheel for example Bullet's 19" wheel provides more comfort especially on broken roads when compared to a Bullet with 18" wheel.

Problem is with a bigger wheel your speedo and odo readings will be way off the mark. But then is it? Most manufacturers calibrate the speedo to show more speed than the actual speed. So with a bigger wheel the speedo might show you the actual speed speed But it depends.

Little off topic with the thread, My vespa scooter has 10" & 9" for front & rear respectively and I'm going to change them to 14" & 13" for better road handling & comfort. My rides are confined to strictly city use only. So, I feel no issues in doing so.

[Aroy]

There are two aspects to consider

1. Outer Diameter. The larger the diameter, the less will it be affected by potholes. For example a 12" OD may go into a 14" pothole,while a 15" OD will not, thus jerking the vehicle less.

2. Sidewall height. The more sidewall height the more air there is to cushion the ride.

If you upsize the rim diameter while keeping the outer diameter of tyre the same, you reduce the sidewall height, thus less air cushioning. It helps by reducing the overall tyre weight thus giving better high speed, but you get a bumpier ride n brocken roads.