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      01-25-2017, 09:29 AM   #1
JMBNaples
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Tire size Q - 235 replace a 245?

I am driving a 2013 X3.

My front 2 tires are almost done and will need to be replaced this spring before the Florida rainy season starts.

I started looking for new tires.

Tire Rack recommends the Bridgstone DriveGuard RFT. Reviews look strong.

However, they do not come in 245/50RF18 - the size of my current Eagle RFTs. They only come in 235/50RF18. Tire Rack is clearly ok with the size difference.

Any thoughts on the size difference?

Or any experience with this tire on an X3?

Thanks.
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      01-25-2017, 12:48 PM   #2
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is it summer tire or grand touring tire?


plenty of tires that you can select without having to change tire size.
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      01-25-2017, 02:18 PM   #3
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The quick answer is yes you can replace 245/50-18 tyres with 235/50-18 but they will have 10mm (0.4 in) smaller overall diameter. Will only slightly effect speedo and odometer - ie speedo will read about 1.5% high.

Other option is to replace the 245/50-18 with 235/55-18 but in this case the overall tyre diameter increases by 13mm (0.5 in) to result in your speedo and odometer reading about 2% low.

Tony
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      01-25-2017, 03:05 PM   #4
JMBNaples
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I thought 235 is the width in mm.

So the diameter would be nearly the same.
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      01-25-2017, 03:30 PM   #5
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Quote:
Originally Posted by JMBNaples View Post
I am driving a 2013 X3.

My front 2 tires are almost done and will need to be replaced this spring before the Florida rainy season starts.

I started looking for new tires.

Tire Rack recommends the Bridgstone DriveGuard RFT. Reviews look strong.

However, they do not come in 245/50RF18 - the size of my current Eagle RFTs. They only come in 235/50RF18. Tire Rack is clearly ok with the size difference.

Any thoughts on the size difference?

Or any experience with this tire on an X3?

Thanks.
These are the specs on the 2 different sizes:

Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
245/50-18 4.8in 13.8in 27.6in 86.9in 730 0.0%
235/50-18 4.6in 13.6in 27.3in 85.6in 740 -1.4%


Width would go 9.6" to 9.3".

If you went all 4 new in this size then there is no doubt it'd be fine. Speedometer would be off approx .5mph (actual speed would be that much less than what shows on speedometer).

You'd be basically gearing the truck down a little by going to a shorter tire.
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      01-25-2017, 03:45 PM   #6
JMBNaples
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But there would be no issue using the same rims on the slightly smaller width tire?

Said another way, they are not going to fall off or anything?
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      01-25-2017, 06:27 PM   #7
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Nope. I'ves swapped tire sizes on many of my cars...as long as you're ok with a small speedometer/odometer error and you don't go crazy in changing the overall diameter where it'll screw up the ABS system, you're fine.

I'll need tires for my wife's X3..I want to go go something wider rather than narrower...mostly for looks.
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      01-26-2017, 07:37 PM   #8
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Yep no issues with 235's.
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      01-29-2017, 06:48 AM   #9
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Quote:
Originally Posted by JMBNaples View Post
I thought 235 is the width in mm.

So the diameter would be nearly the same.
235 is the width, but the subsequent measurement is a percentage of that width.
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      11-15-2018, 05:41 AM   #10
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Quote:
Originally Posted by malicem3 View Post
Yep no issues with 235's.
Hi, do you rund 235/55? If so, do you have any pics?
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      11-15-2018, 07:53 AM   #11
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Quote:
Originally Posted by E60525d View Post
Hi, do you rund 235/55? If so, do you have any pics?
https://tiresize.com/calculator/

I have 225 for winter on oem wheels.

Europe and NA dont get the same wheel setup.

Originally , I have 245-45-19 on all 4 corners.

Now I have 245-40-19 back, and 225-45-19 front. 1% outer diameter diff r/f. speedometer 5% off.

I got some nokian for a steal , so I will live with this difference. Planning to do 1000km local drive this winter, not more.

It looks just like OEM. No visible stretch at all. I was surprised.

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      11-15-2018, 06:47 PM   #12
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The only concern one might have with the Bridgestones in 235/50-18 (vice 245/50-18) is the load rating of the 235's. According to tirerack, that size has a load rating of only 97 compared to 100 for the 245's. Technically, the 235's might not be designed for the weight of an X3. I am no engineer, but you might want to ask the folks at Tirerack if this would be an issue.
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      11-16-2018, 09:22 AM   #13
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Quote:
Originally Posted by TEF View Post
The only concern one might have with the Bridgestones in 235/50-18 (vice 245/50-18) is the load rating of the 235's. According to tirerack, that size has a load rating of only 97 compared to 100 for the 245's. Technically, the 235's might not be designed for the weight of an X3. I am no engineer, but you might want to ask the folks at Tirerack if this would be an issue.
That is incorrect.

The load rate is lower, but it isn't a concern.

The main concern with mismatching tires on both axles is the difference in diameter, which puts it dangerously in the range of diameter difference that would make the transfer case work too much. It overheats and breaks.

You always want to have same diameter tires on all 4 corners of the car.
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      11-16-2018, 03:54 PM   #14
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If a stock tire has a load rating of 100 and a replacement has one of 97, what is incorrect: the absolute number or that load ratings do not matter? if it's the latter, than why have them. I am not incorrect, it's just another reason that the tires are not equivalent. Just because you point out that tires must be the same on all corners doesn't make my comment any less valid.
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      11-16-2018, 04:04 PM   #15
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Quote:
Originally Posted by TEF View Post
If a stock tire has a load rating of 100 and a replacement has one of 97, what is incorrect: the absolute number or that load ratings do not matter? if it's the latter, than why have them. I am not incorrect, it's just another reason that the tires are not equivalent. Just because you point out that tires must be the same on all corners doesn't make my comment any less valid.
You said "the only concern one might have is the tire load".

That's a concern you have.
Far from being the "only" concern. It may be a concern to some, as proven by you and your own, but it may as well be the "least" concerning piece, not the "only one".

Your point is valid though otherwise. Being that the thread topic is about mixing tires of different diameters, I maintain my post in its entirety and excuse myself of further commenting to not seem like I'm arguing, which isn't the intent.
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      10-28-2019, 12:43 PM   #16
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Quote:
Originally Posted by CalCarNut View Post
Nope. I'ves swapped tire sizes on many of my cars...as long as you're ok with a small speedometer/odometer error and you don't go crazy in changing the overall diameter where it'll screw up the ABS system, you're fine.

I'll need tires for my wife's X3..I want to go go something wider rather than narrower...mostly for looks.
curious to know if you ever switched tires for your wifes X3?

i have a 2011 X3 with 245/55 r17 runflats. I want to switch to a regular tire but there arent any in that size. Tirerack is telling me that 235/60 r17 is guranteed to work for my vehicle. The diameter difference is 1.75%.

Will it be safe to make the switch? will the suspension or ABS get out of whack if i switch to the different size?
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      10-28-2019, 01:09 PM   #17
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the speedo already runs high from the factory, so changing tire size that makes it run a little low brings it closer to actual speed.
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      10-29-2019, 05:12 AM   #18
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Load rating on tires is based on the gross vehicle weight rating or the weight when fully loaded. GVWR varies a bit year by year. Post LCI seems to cap at 5160 lbs. Pre LCI at 5214. Tire load index is the amount of weight a single tire can carry. Let's use 5250 as our target number. That's 2625/axle assuming a 50/50 distribution or 1312.5/tire. A load rating of 90 (1323 lbs) would be all you needed. However once a car is in motion axle loading is subject to acceleration and braking weight transfer. Let's assume worst case of 60/40. Now loading is .60x5250=3150/axle or 1575/tire. Now a load rating of 97 (1609 lbs) is recommended. The lowest I know of BMW using is 98 (1653 lbs) so that's the minimum load rating I'd use.

TL/DR
A 97 load rating is probably OK, but I'd recommend at least a 98.
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      11-05-2019, 09:44 AM   #19
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IMHO 100% not worth it. Just find 245's. Apart from anything else you should never mis-match tyres.
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      11-05-2019, 01:58 PM   #20
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i recently switched on my 2011 x3 from the OEM 245/55 17 runflats to 235/60 17 based on tirerack.com recommendation, a diameter difference of 1.8%. no issue at all and the ride is much better with non-runflats. The only possible concern is if a taller tire might rub with the fender or other parts. Tires are much cheaper, the OEM tires were $250 a piece.

In my case the difference in height of the new tire was half an inch and there was more than enough clearance to handle that.
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      11-05-2019, 05:11 PM   #21
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Quote:
Originally Posted by nyboy42 View Post
i recently switched on my 2011 x3 from the OEM 245/55 17 runflats to 235/60 17 based on tirerack.com recommendation, a diameter difference of 1.8%. no issue at all and the ride is much better with non-runflats. The only possible concern is if a taller tire might rub with the fender or other parts. Tires are much cheaper, the OEM tires were $250 a piece.

In my case the difference in height of the new tire was half an inch and there was more than enough clearance to handle that.
Just did new wheels 17x7.5 et32 (OE fitment) and 235/60/17 snow tires for mine. No problems at all. You can run those tires anywhere from 6.5-8.5" wheel width. Great size for winter tires.
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