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      09-27-2009, 04:08 AM   #1
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aspect ratios and comfort

I've been wondering about this for a long time.

Let's say there's a tire that's 265mm with an aspect ratio of 35 and a sidewall size of 3.7 inches, and a 305mm tire with aspect ratio of 30 with the same sidewall size of 3.7 inches.

Would the 305/30 tire be less comfortable even though both have the exact same sidewall size?
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      09-27-2009, 10:59 AM   #2
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It also depends on what size wheels they're on and what brand tires each is. Both of those factors will make more difference than the width of the tire, but assuming same brand and that neither one is too stretched out, the narrower tire will probably be a bit more comfortable, but maybe not even enough to notice.
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      09-27-2009, 02:38 PM   #3
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The wider tire has to have a little more robust sidewall, even if they're the same height, but as Tlud said, the difference might not be enough to notice.

Last edited by elp_jc; 09-27-2009 at 03:00 PM.
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      09-27-2009, 06:46 PM   #4
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If I just ordered 19x9.0 et22 & 19x10 et20, what tire sizes should I get for max comfort?
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      09-27-2009, 09:33 PM   #5
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Originally Posted by RGuard250 View Post
If I just ordered 19x9.0 et22 & 19x10 et20, what tire sizes should I get for max comfort?
To do it right, you need to get the tire with the same (or as close as possible) circumference as stock, which means 35 aspect ratio or lower (depending on width). If comfort was your priority, you should have chosen 18" wheels . Having said that, you're not going to notice a dramatic difference between 35 and 40 series tires, so don't worry too much about it. Just choose a tire with a relatively soft sidewall, like PS2s.

By the way, if you don't know how to calculate tire circumference, find a calculator online to determine the aspect ratio needed to match stock circumference for the widths you want. Good luck.
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      09-28-2009, 02:05 AM   #6
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Quote:
Originally Posted by elp_jc View Post
To do it right, you need to get the tire with the same (or as close as possible) circumference as stock, which means 35 aspect ratio or lower (depending on width). If comfort was your priority, you should have chosen 18" wheels . Having said that, you're not going to notice a dramatic difference between 35 and 40 series tires, so don't worry too much about it. Just choose a tire with a relatively soft sidewall, like PS2s.

By the way, if you don't know how to calculate tire circumference, find a calculator online to determine the aspect ratio needed to match stock circumference for the widths you want. Good luck.
So would 255/35/19 in the front and 275/30/19 in the rear be good? Or should I make the rear 275/35/19? Thanks!
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      09-28-2009, 02:43 AM   #7
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Quote:
Originally Posted by RGuard250 View Post
So would 255/35/19 in the front and 275/30/19 in the rear be good? Or should I make the rear 275/35/19? Thanks!
Make the rear 275/35 which will clear FOR SURE. 285/35 may not, I wish I could get more feedback on that issue as well.

I have Nitto INVOs and 255/35/19 does rub when locking it full left. I'm going 245/35/19, 295/30/19 for my next set.
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      09-28-2009, 04:18 AM   #8
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Make the rear 275/35 which will clear FOR SURE. 285/35 may not, I wish I could get more feedback on that issue as well.

I have Nitto INVOs and 255/35/19 does rub when locking it full left. I'm going 245/35/19, 295/30/19 for my next set.
I am actually thinking of going with 255/35/19 in the front and 285/35/19 in the rear. I just don't know whether I should go 285/30 or 285/35. Anyone have any recommendations?
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      09-28-2009, 10:13 AM   #9
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Comfort and 19" wheels do not mix...

Unfortunately you won't find any 19" tire size to be "comfortable". Different tires will have different sidewall compliance but they all will be pretty harsh. That being said I though my PS2's were comfortable for what they were-just really loud. An M3 won't ride like a Mercedes CL, ever, and thats ok with me.
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      09-28-2009, 12:30 PM   #10
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Quote:
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I am actually thinking of going with 255/35/19 in the front and 285/35/19 in the rear. I just don't know whether I should go 285/30 or 285/35. Anyone have any recommendations?
Are you lowered? I don't think 285/35 will clear depending on the offset of your wheels but most don't. 285/30 is actually closer to stock size than 285/35. As far as the 255/35, the clearance will depend on offset too. Also, the exact tire you plan to use will make a difference because if at the same size, some tire brands will be wider than others. I believe Nittos are known to have very squared sidewalls so they tend to be a bit wider than most brands.
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      09-28-2009, 04:38 PM   #11
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Thanks man! That was very informative! I know these threads get redundant, but you just want to be safe when it's your tires you're ordering. I just ordered a set of 255/35/19 front & 285/30/19 rear Michelin PS2 (was thinking about the Yokohama Advan Sports though). I'll post a an update once I get them mounted onto my new wheels.

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Are you lowered? I don't think 285/35 will clear depending on the offset of your wheels but most don't. 285/30 is actually closer to stock size than 285/35. As far as the 255/35, the clearance will depend on offset too. Also, the exact tire you plan to use will make a difference because if at the same size, some tire brands will be wider than others. I believe Nittos are known to have very squared sidewalls so they tend to be a bit wider than most brands.
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      09-28-2009, 05:28 PM   #12
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Stock 19's

You are getting the tire size I'm thinking about but I want to put them on the stock 19's. Does anyone know if i'll have issues with that?
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      09-28-2009, 05:52 PM   #13
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255,285 will fit on stock wheels. I believe that is the max.
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      09-28-2009, 06:29 PM   #14
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Quote:
Originally Posted by RGuard250 View Post
So would 255/35/19 in the front and 275/30/19 in the rear be good?
As you read on the many threads after mine, math can't predict if tires would rub or not. That depends on wheel size and offset. Oh, and math depends on wheel width too, as if you cram a tire in a too narrow wheel it'd be taller than the math suggests.

Now to the math. A 265/35/19 tire has 82.634" of circumference. You need circumference to calculate speedometer error. But for clearance, you need RADIUS. It gets simpler here. Every 10mm larger width (275 vs 265, etc) with equal aspect ratio, increases radius by 3.5mm (10mm * 35%). So any size above stock with the same 35% aspect ratio will reduce fender gap by 3.5mm by every 10mm of added width, so tire would look even bigger than stock, and car would travel faster than with stock tires. But if you only go +1 in width (275/35 vs 265/35), you're talking a 1.04% increase in circumference (and 3.5mm less fender gap), which equals 79.2 mph speedo vs 80 real (IF it was accurate ). Hardly anything.

If you go to 30 series, the 305/30 is virtually identical to stock, so anything in-between will be smaller. The next size larger than stock, 275/30, has 3.17% less circumference (82.5 mph speedo vs 80 real, plus factory error ), and is 10.25mm smaller in radius (added fender gap). The 285/30 would add 7.25mm of fender gap; 295/30 4.25mm and 305/30 1.25mm (almost like stock). Hope this helps.
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      09-28-2009, 10:32 PM   #15
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Quote:
Originally Posted by MrHarris View Post
I've been wondering about this for a long time.

Let's say there's a tire that's 265mm with an aspect ratio of 35 and a sidewall size of 3.7 inches, and a 305mm tire with aspect ratio of 30 with the same sidewall size of 3.7 inches.

Would the 305/30 tire be less comfortable even though both have the exact same sidewall size?
Those two sizes can't have the exact same size sidewall. A 265/35 would have a sidewall about .5cm (5mm) taller than a 305/30, so if you're going by numbers on a website, they're either rounded off or inaccrute. But I suppose they're close enough to pose your question. Given the same brand and model tire in both sizes, there would be very little noticable difference. If anything, the 265/35 might feel more forgiving over bumps, but I think you would only notice it if you had a very firm aftermarket suspension. Assuming the sizes in question are what you're planning on running front/rear, Tte difference in sidewall and overall circumference wouldn't even make a huge difference in RPM (rotations per mile). If anything, you want the rear tire to be taller since they tend to wear out faster. That would give then fewer RPMs. That's what BMW did with the stock fitments. The front 245/40/18s are subject to more RPMs than the rear 265/40/18s, thus sort of equalizing the wear timeframes (unless you do a lot of burnouts )
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      09-28-2009, 11:26 PM   #16
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So 295/30 is probably a better option than 285/35? I checked, I don't think I'll rub with 285/35 even lowered on H&R springs but I'm afraid the tall sidewall and overall diameter may throw off the DSC/MDM
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      09-29-2009, 12:56 AM   #17
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Quote:
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Those two sizes can't have the exact same size sidewall. A 265/35 would have a sidewall about .5cm (5mm) taller than a 305/30, so if you're going by numbers on a website, they're either rounded off or inaccrute. But I suppose they're close enough to pose your question. Given the same brand and model tire in both sizes, there would be very little noticable difference. If anything, the 265/35 might feel more forgiving over bumps, but I think you would only notice it if you had a very firm aftermarket suspension. Assuming the sizes in question are what you're planning on running front/rear, Tte difference in sidewall and overall circumference wouldn't even make a huge difference in RPM (rotations per mile). If anything, you want the rear tire to be taller since they tend to wear out faster. That would give then fewer RPMs. That's what BMW did with the stock fitments. The front 245/40/18s are subject to more RPMs than the rear 265/40/18s, thus sort of equalizing the wear timeframes (unless you do a lot of burnouts )
There's also another component here that is not being taken into consideration. While you are comparing overall height there's been no talk about the width and how it affects clearance from the fender and the rear suspension. At 305/30, you might be near stock in terms of overall diameter but you are much wider than stock and depending on the offset of the wheel you could be rubbing the rear suspension components. I don't think I've seen anyone running 305/30 yet and this could be the reason why.
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      09-29-2009, 06:52 PM   #18
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Quote:
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There's also another component here that is not being taken into consideration. While you are comparing overall height there's been no talk about the width and how it affects clearance from the fender and the rear suspension. At 305/30, you might be near stock in terms of overall diameter but you are much wider than stock and depending on the offset of the wheel you could be rubbing the rear suspension components. I don't think I've seen anyone running 305/30 yet and this could be the reason why.
True, but I was trying to address the OP's concern, which was about comfort. Comfort is more affected by sidewall measurement than the width, although more width can cause wandering (tendency follow ruts and shy away from crowns). Plus, I don't think the OP is talking about running a 305/30 tire on the OEM rear wheel, at least I hope not.
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      09-29-2009, 06:59 PM   #19
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Quote:
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So 295/30 is probably a better option than 285/35? I checked, I don't think I'll rub with 285/35 even lowered on H&R springs but I'm afraid the tall sidewall and overall diameter may throw off the DSC/MDM
If you're talking about mounting on OEM wheels, what's wrong with the OEM sizes? What is your objective? Largest possible contact patch? If so, I wouldn't recommend upsixing more than one size on the same wheels So, if OEM rear is 265/40/18 or 265/35/19, then go to 275/35/18 or 275/30/19. try to keep the aspect ratio F/R the same to help ensure a front/rear differentiation similar to OEM.

I can't comment for certain about your concerns regarding DSC and MDM, but I think those electronic systems will do what they do, regardless of tire size. Hopefully, there is already a thread about it somewhere, or somebody listening in on this thread knows for sure.
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      09-29-2009, 10:23 PM   #20
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Quote:
Originally Posted by RGuard250 View Post
I am actually thinking of going with 255/35/19 in the front and 285/35/19 in the rear. I just don't know whether I should go 285/30 or 285/35. Anyone have any recommendations?
from what i can see, you are using the ADvan RS or the RS-D in 19"s
We recommend using the 245/35-19 front and 285/30-19. The 285/35-19 is way too big on the rear and tends to rub with some tire brands.

The best that we have seen is going with 245/35-19 and 265/35-19 YOKOHAMA Advan Sport tires. They are so much more square than the PS2, that they sit very flush.

Hope this helps. Cheers!
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      09-30-2009, 03:19 AM   #21
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Doesn't anyone take into consideration the extra weight penalty of some of these oversized tyres?
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      09-30-2009, 04:29 AM   #22
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My lighter wheels are compensating for the added weight in the rear. 285/295 tires are around 30-31lbs each.
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