Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Aspect ratio

Aspect ratio

Aspect ratio

Is it ok to replace a tyre with aspect ratio 55. The specification is 50.

E90bmw tyres original spec 225/50 R16
Market 225/55 R16.

What side effects could arise from this slight change?

RE: Aspect ratio

The speedometer will likely read lower mph or kph than actual and the odometer won't read quite as many miles/kms traveled.

The 55 profile tire is slightly taller, reducing vertical clearances slightly.

Acceleration will be slightly 'softer' for any given pedal input.

Ride quality will probably improve, but cornering response may be softer and less precise than you're used to with 50-profile tires.

Load capacity @ inflation pressure probably goes up, meaning that you could run slightly lower inflation without compromising the mfr's intended tire load rating. There are tables for this. Cornering response and precision may be reduced if you do, tire center tread wear rates could be increased if you don't.


RE: Aspect ratio

There is a limited amount of space under the fenders. So going physically larger might result in a tire rub - very bad!!

However, my experience is that you can go up 2 units (either width or aspect ratio) and there is enough clearance in most cars. There is usually more clearance in pickup trucks.

But the question I think you are really asking is about how much difference there would be in the way the tire performs - and the answer is that changes in tire size are minor compared to the difference between tires (meaning make and model). Put another way, changing make and model of tire can result in a HUGE!! change in the wear/traction/handing/fuel economy, but changing tire size in the same make and model results in a small change.

Careful selection of make and model of tire is critical to achieving your goals.

RE: Aspect ratio

The problem you really face is that the OEM tires on your BMW (MIC, CON, GDY, BRI) are a special construction and you won't be finding tires even in the brand and exact size that match the factory tires UNLESS you can get them from the factory or from a dealer with special connections. You can identify them as having a coin sized 5 pointed star on the sidewall. Then again, you may not be able to differentiate between a new star tire and a new non-star tire anyways. Most people are just thrilled by comparing a new tire with their worn out meats and so life goes on. Sometimes the driver is better than the car, sometimes the car is better. It all depends on you and your budget.

RE: Aspect ratio

Cibachrome brings up a good point - but I don't think it is the one he was trying to make.

The original tires on your BMW were RunFlats. Those are quite different than regular tires and if you change out of those, there will be quite a few differences on top of what normally occurs when changing tires.

However, I am going to disagree with Ciba in that:

1) If the exact tires are still in production (not likely due to the age of the car!), they will be generally available - as in if the tire dealer doesn't have them he can order them - and the BMW dealer is not the only source.

2) If the exact tire is out of production, suitable replacements (RunFlats) will also be generally available. The car dealer is not the only source.

But you haven't responded since the first post, so we don't know much about what your goals are in the change. If you read this, please let us know what you'd like to have in a tire. That way we can perhaps advise you better.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close