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2010 2011 BMW 5 Series Forum F10 F10 Technical Topics Wheels / Tires / Suspension / Brakes relationship between ride quality and rim size
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      03-15-2012, 03:11 AM   #1
darrko
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relationship between ride quality and rim size

Hey all, my car is yet to be delivered and comes with stock 17" RFTs. I chose not to go for bigger 18" or 19" at the time of ordering as I felt the total cost was going way beyond my planned target and I figured I could just get bigger wheels later on.

Some members here advised me to keep the stock 17s till I needed to discard the RFTs and then upgrade and I think that is sound advice. Its just that I see all these gorgeous wheels on the cars here on the forum and I can't help but wonder if I'm even gonna like the 17s on my car.

The thing is: the roads that I drive on are pretty awful with frequent potholes and improperly constructed road bumps. In fact the poorly planned and frequent speed bumps is the main reason I had to forego the M-sport option as the low front bumper would have been totally messed up by the frequent scraping.

So my question is: given the condition of the roads I drive on, does going bigger make sense and offer any benefit other than looks? Does ride quality get better or worse with bigger wheels? I don't see myself going as big as 20" but maybe 19"? Would I still need to replace the springs to lower the car?
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      03-15-2012, 12:04 PM   #2
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The ride quality over bumps and potholes have a direct relation to rims size. The bigger rim the smaller amount of tire sidewall that can absorb bumps.
If you lower it will be even worse.

Larger rims has almost only bad things about it:
lesser top speed
increase in fuel consumption
more roadnoise
easier dent in the rim
risk of scratching rim while parking

Larger rims is only about looks. Unless you drive frequently on a track.
Maybe you can find decent 17" rims you like?
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      03-16-2012, 12:41 AM   #3
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Makes sense. So if I go over just 1-inch to 18" how much of a visual difference will it make and how much will the drive get effected? From what you say 19" and up seems like a bad idea on my roads.
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      03-16-2012, 12:53 AM   #4
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Bigger rim size means lower profile tires with smaller side walls which make a harder ride besides being more susceptible to damage. Unless you are willing to spend a good amount of money in RFT replacements, you would be better off staying with a smaller size rim in Karachi. Another factor to keep in mind would be nails you may be able to pick, again wider the tire the more chance of nail incident.
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      03-16-2012, 01:05 AM   #5
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Well I don't plan on sticking to RFT for very long, only as long as they last. Then I'm switching to non-RFT. Does moving up even 1-inch present a significant deterioration in ride quality and the inherent risks?
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      03-16-2012, 01:46 AM   #6
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depends on which tire you go with. You need to look at aspect ratio. I think the 17's are like 55 and the 19's could go as low as 30 as I have seen on OEM styles. 18" All Season's would be better than the 19" performance ones. I have 17" and I can still feel a harder ride when I compare with my Acura MDX 18". San Francisco is a pothole country but still better than Karachi so you can figure.
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      03-16-2012, 01:55 AM   #7
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I guess I won't really know till I drive on the 17s. Btw, 55 and 30 is what exactly? Tire width?
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      03-16-2012, 01:58 AM   #8
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height of the tire above the rim. Its the side wall. It is the ratio of the tire width, so 225/55/17 means the side wall = 225 x 55/100. Higher the number the more tire can absorb shocks.
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      03-16-2012, 02:07 AM   #9
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Oh, cool. Thank you.

Does going up an inch also means I need to lower the car? And if I had chosen 18" factory-fitted, would the body have been lowered by BMW or do they just replace the 17 with the 18 and call it a day?
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      03-16-2012, 03:40 AM   #10
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seems the configuration and packages are different from where you placed the order so I would not know what comes with the wheel upgrade. Here in the US at least wheel upgrade is normally part of a package rather than a standalone option so any changes would already be part of the package itself
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      03-16-2012, 03:45 AM   #11
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Noted, thank you for the help.
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      03-16-2012, 11:48 AM   #12
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As a general concept and keeping it simple.

The idea is the circumference of the tires and wheel combinations are all the same (or very close) for our 5'ers. Larger rim size means less tire sidewall height. Less sidewall height would be quicker steering and handling inputs BUT less cushion or give, in response to poor road surface.
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      03-16-2012, 02:29 PM   #13
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Racers run larger wheels to run thinner less flexible side-walled tires & also to clear their massive big brakes. It is wise that you opt out the bigger wheels, since vehicle tarriff tax are so high in your country. Use the savings and spend it on some nice 19" staggered wheels. You shouldn't have too much problem with most pot holes as long as you're running strong wheels.

There are guys from Hong Kong, Vietnam, and Malaysia on this forum running 20s and 21s. Those areas have jacked up roads as well.
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      03-16-2012, 04:07 PM   #14
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i went from 19" run flats to 20" non run flat and it is WAY better.
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      03-19-2012, 12:05 AM   #15
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Quote:
Originally Posted by RH512 View Post
As a general concept and keeping it simple.

The idea is the circumference of the tires and wheel combinations are all the same (or very close) for our 5'ers. Larger rim size means less tire sidewall height. Less sidewall height would be quicker steering and handling inputs BUT less cushion or give, in response to poor road surface.
Makes sense, thanks.

Quote:
Originally Posted by JNoSol View Post
Racers run larger wheels to run thinner less flexible side-walled tires & also to clear their massive big brakes. It is wise that you opt out the bigger wheels, since vehicle tarriff tax are so high in your country. Use the savings and spend it on some nice 19" staggered wheels. You shouldn't have too much problem with most pot holes as long as you're running strong wheels.

There are guys from Hong Kong, Vietnam, and Malaysia on this forum running 20s and 21s. Those areas have jacked up roads as well.
Is there a way to tell if a rim is "strong" as you call it?

Quote:
Originally Posted by paulmc View Post
i went from 19" run flats to 20" non run flat and it is WAY better.
20" may be a bit too big but yeah I can see 19" and I can see myself smiling
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      03-19-2012, 12:06 AM   #16
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I would also appreciate some answers about lowering the car. Is it necessary when going for a larger rim? Is replacing the springs the ONLY way to lower the car?
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      03-19-2012, 12:58 AM   #17
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We changed from 17" RFT to 20" Non-RFT last week (F11) and the car handles significantly better. Sure it is not quite as comfy as before, but I think a really important step is to get rid of the RFTs. I assume that changing from 17" RFT to 19" Non-RFT will have no negative impact on comfort but the look is way better and the car handles also much better.

Regarding weight I noticed that the OEM rims with 17" RFT (winter tires) weights more then the 20" BBS CH-R with Michelin PSS. Also a reason for me to get rid of the 17" RFT and get Non-RFT as a replacement.

For bad road conditions, I would not go higher then 18", because of the tire hight, potholes would not be such a big issue then.
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      03-19-2012, 06:26 AM   #18
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I really don't thnk you wil loose much comfort going to 18" or 19".

And you don't have to lower the car if you put on bigger wheels. Yes, you change the springs when you lower it.
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      03-20-2012, 01:39 AM   #19
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Great information, thank you all.
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