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      08-19-2012, 05:05 PM   #1
X1blue
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Tire 101: steel v light alloy, wide v narrow, 16 v 19 hub..

I was wondering if someone can help me understand how wheels affect ride quality:

Steel v light alloy hubs: alloy hubs look better and weigh less. Theoretically less inertia means faster acceleration but when you consider the weight loss per wheel against the weight of the car, I wonder if you can really note a difference between the two? And how does less weight affect ride quality (firmer, softer etc)?

Hub size: plus one or two will improve cornering theoretically at the expense of ride quality but does moving from 17 to 19 really make the ride much harder?

Wheel width: I have read on the web that wider tires make for a bumpier ride. I have also read that smaller tires make for a bumpy ride!! Has anyone seen an authoritative source on how tire width affects ride quality? Assuming that rim height is constant (ie 205/55 R17 = 225/50 R17 = 245/45 R17) how does ride quality vary with width?
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      08-19-2012, 05:31 PM   #2
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I can answer some of your questions. Your first one with weight of the wheel: wheels weight is UNsprung weight, which makes a huge difference in total performance of the car with a couple pounds of difference in either direction.

I don't think wheel weight affects ride quality, but I may be completely wrong with that one.

Moving from 17" to 19" would mean that you're getting a tire w/ a smaller sidewall, which is what absorbs a lot of energy from the bumps on the road. Which takes me to your next question: all of those tire sizes decrease in sidewall size, which is what affects ride stiffness or harshness. I don't think tire width has anything to do with it, just the sidewall width. Maybe some tire guru can expand on that and I may be wrong with that too, but I don't think tire width makes a difference.
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      08-20-2012, 03:12 AM   #3
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Quote:
Originally Posted by eVitO View Post
I can answer some of your questions. Your first one with weight of the wheel: wheels weight is UNsprung weight, which makes a huge difference in total performance of the car with a couple pounds of difference in either direction.
Thank you. I see the point about unsprung mass. I guess lighter wheels means less work for the suspension when there are imperfections on the road surface = smoother ride?

We have 17" steel hubs with 225/50 R17 tires on our BMW. 225/50 means rim is 50% of 225 = 113mm. So handling would improve by dropping the hub size to 16" alloy and putting 225/60 R16 tires on..?? (60% of 225 =135 so diameter would be a little big smaller but almost the same - 99.5% of present)

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Originally Posted by eVitO View Post
Moving from 17" to 19" would mean that you're getting a tire w/ a smaller sidewall, which is what absorbs a lot of energy from the bumps on the road. Which takes me to your next question: all of those tire sizes decrease in sidewall size, which is what affects ride stiffness or harshness. I don't think tire width has anything to do with it, just the sidewall width. Maybe some tire guru can expand on that and I may be wrong with that too, but I don't think tire width makes a difference.
I think the tires I quoted for the last part are constant RIM. I wanted to assess the effect of the hub only (increasing or decreasing means you have to change the rim size to keep the wheel diameter similar)
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      08-20-2012, 06:40 AM   #4
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Are wider tires more prone to tramlining in a straight line?
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      08-20-2012, 08:24 AM   #5
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Wheel weight not only applies to unsprung weight but also rotational mass. Rotational mass is anything that is spun by the engine. So less rotational mass results in quicker acceleration and deceleration since it has less weight to spin and stop.
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      09-01-2012, 12:43 PM   #6
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Originally Posted by daixloxbmw View Post
Wheel weight not only applies to unsprung weight but also rotational mass. Rotational mass is anything that is spun by the engine. So less rotational mass results in quicker acceleration and deceleration since it has less weight to spin and stop.
Less weight also for the suspension to dampen.. yet to read anywhere that wheel weight impacts ride quality (soft/ hard). The rubber wall seems to make the most impact, it seems as though tire width has a much reduced impact though wider tires may increase the tramling on the BMW X1 (its pretty bad already at 225..)
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