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-   -   04 X5 4.4i - plus sizing tires (http://www.bimmerfest.com/forums/showthread.php?t=733591)

x_l_r_8 11-05-2013 08:47 AM

04 X5 4.4i - plus sizing tires
 
I'm getting close to needing new tires and considering plus sizing the stock 255/55r18's with 255/65r18's. Well...I guess that would be considered plus plus sizing. :p The stocks are 29" and the 65's would be 31.1" and 3 pounds heavier. My main motivation for this is to get a softer and more compliant ride. The X5 is my daily driver and being on a "truck" platform a bit too rough for my liking for the daily grind. I understand this probably will negatively affect the handling but I'd be willing to take a small hit for a smoother softer ride.

1.) Will these bigger 65 series tires fit on my 04 X5 without rubbing? I've peeked last night and there's plenty of room in the back and the front as well except for the the front shock which currently has about 2.25" of clearance from the stock tire. If I'm thinking about this right the new tires would be about 1" taller on both the top and bottom so I still would have 1.25" clearance from the top of the shock. Is that enough?

2.) Will this setup be OK with the electronics? I'm OK with a speedo change but don't want to mess up ABS, DTC, transmission, etc.

3.) Will this affect gas mileage? The tires will be heavier but the diameter will be larger so less RPM on the freeway? The X5 should also ride 1" higher off the ground. Interesting how this will all play out. The Michelins I'm considering are labeled Green X with low rolling resistance.

3.) I'm currently running Continental DWS that I've been real happy with. They unfortunately don't come in 65 series. I'm thinking about replacing them with Michelin Latitude Tours in 255/65r18. Any others in this size I should consider? It's driven only in Texas on paved roads so no worry about snow or off road capability. I would like a smooth, quiet running tire with good wear.

Thanks in advance for any comments from the pros out there.

white_lancer 11-05-2013 10:56 AM

You can't replace 255/55r18's with 255/65r18's as they have a different aspect ratio with the same tyre width. Your speedo will be incorrect.

x_l_r_8 11-05-2013 11:11 AM

My speedo is off by 5mph at 70mph according to my GPS as is with stock tires so this may actually "correct" it. I'm more concerned about other electronics and the awd system.

white_lancer 11-05-2013 11:37 AM

which way out is your speedo? by increasing the aspect ratio you will be going slightly faster than your speedo said you were before with the smaller aspect ratio. i.e if your speedo registered 70mph before and your gps said 65mph. with the higher aspect ratio when your speedo says 70 mph you may be going at 70mph

x_l_r_8 11-05-2013 12:00 PM

Yes, my speedo is optimistic showing 75mph while going 70mph. Imagine that, a BMW with a correct speedo as a bonus...

white_lancer 11-05-2013 01:40 PM

Quote:

Originally Posted by x_l_r_8 (Post 7938867)
Yes, my speedo is optimistic showing 75mph while going 70mph. Imagine that, a BMW with a correct speedo as a bonus...

yup by increasing the aspect ratio you are increasing the diameter and hence the circumference of your tyres too so for every revolution of the wheel you will go just that little bit further than before so if your speedo is reading 75mph you will actually be doing near 75mph on your gps.

stock wheels and tyres for my truck are 285 45 19 on the rear and 255 50 19 on the front

QSilver7 11-05-2013 03:23 PM

You should try to stay within 3% (+/-) the diameter/circumference of the original tire size. This is not just for speedometer & odometer...but the X5's (early) 38/62 AWD ratio & the later 40/60 "variable" xDrive ratio must be considered in the calculations that tie-in ABS/DSC/Traction Control/AWD/xDrive.

Going beyond the 3% limit could (not saying it will) but could have some affect on the way these features work/perform...and could throw them off as well as the speedometer/odometer.

If you want more "cushion" with a 65 aspect ration...you could go to a 235/65/18 tire. This tire would fit an 18" wheel that is 6.5"-8" wide...as well as meet the criteria of being within 3% (+/-) of the orig diameter/circumference.

A quick pull up of a wheel/tire calculator will show you how close you are to the 3% margin. Just google tire calculator, then input the original tire size as the base reference. The narrower the tire, the higher the aspect ration can go. The wider the tire, the lower the aspect ration should go (if you want to maintain the 3% tolerance).

x_l_r_8 11-06-2013 11:56 AM

Hey QSilver7, thanks for your input. Info much appreciated. Would going to a 235/65r18 really give me more "cushion" or would I end up with just a narrower tire with about the same sidewall height? I would venture to say you can't get more sidewall height and keep within 3% on the same rims no matter what tire size you choose. The proper way I believe to accomplish this would be to step down to smaller 17" or even 16" rims with 65 series tires but I'm trying to avoid the extra cost involved.

I've read somewhere that the 3% rule applies to cars but trucks/SUVs can go up to 18%? Anyone hear something like this?

Curious if anyone out there is running 60 or 65 series tires on 18" rims and would care to comment on their experience.

x_l_r_8 11-06-2013 12:59 PM

Found a post with a pic of someone running 265/70r17's with no rubbing or problems. Those are 31.61" and the 255/65r18 I'm thinking off would be 31.05", over .5" smaller. Stocks are 29.0". Hmmmm....

http://www.xoutpost.com/bmw-related-...-17-rim-2.html


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