255 45 17 Tires - Mercedes-Benz Forum
 
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#1 (permalink) Old 03-14-2007, 06:20 AM
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Smile 255 45 17 Tires

Hello guys,

I bought four used 17 inches rims. Each of them came with tires size 255 45 17.When I put them in my car (1990 300E) the front tires start rubbing the fenders, the rear ones were ok. I would like to know if buying a tire with a ratio of 40 instead of 45 will help me with this, or if I can just put another tire size on these rims.

I appreciate your comments. Thanks.

Carlos.
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#2 (permalink) Old 03-14-2007, 06:37 AM
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Carlos,

Go to TireRack.com and use the guide they have for +1, +2 wheel/tire sizes. Also, there is a search function here on the site that will provide you about a million threads on the subjects of how big, how wide, no rub questions.

Good Luck,

Jayare
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#3 (permalink) Old 03-14-2007, 12:48 PM
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i have a 91 300E with the same tires, 225/45/17 and no rubbing issues, in fact i have alot of clearence. the more i read about this topic the more i think these cars are all unique when it comes to tire and suspension setups. ive heard people getting a 1.6" drop with no problems and then ive herd even people putting a drop of 1.2" with rubbing issues. it seems these cars are all very picky when it comes to these issues. and at the end of the day, its mostly just a trial and error routine.

note: going from a 45 profile to a 40 your only making a change of half a centimeter (5mm) which is not a real big difference. you may want to concider going to a 215/35/17 that may solve your problem, but its still not a garantee.

good luck

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#4 (permalink) Old 03-14-2007, 01:29 PM
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Olsb says his new wheel/tire combo came with 255/45 - 17's. Different animal than 225/45's. Tire rack says 215/45's on 17 X 7.5" rims. Olsb also doesn't mention rim width or offset.

Jayare
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#5 (permalink) Old 03-14-2007, 04:20 PM
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Quote:
Originally Posted by pyro_la
i have a 91 300E with the same tires, 225/45/17 and no rubbing issues, in fact i have alot of clearence. the more i read about this topic the more i think these cars are all unique when it comes to tire and suspension setups. ive heard people getting a 1.6" drop with no problems and then ive herd even people putting a drop of 1.2" with rubbing issues. it seems these cars are all very picky when it comes to these issues. and at the end of the day, its mostly just a trial and error routine.

note: going from a 45 profile to a 40 your only making a change of half a centimeter (5mm) which is not a real big difference. you may want to concider going to a 215/35/17 that may solve your problem, but its still not a garantee.

good luck
Completely incorrect. the difference in tire height is not 45 - 40 = 5mm

P-Metric tire sizing works as follows:

Section width (in mm)/ Aspect ratio - rim diameter (in inches)

Sections width: width of the tire from sidewall to sidewall
Aspect ratio: height of the sidewall experssed as a percentage of the section width.
Rim diameter: self-explanatory

With the numbers:
255/45-17

255 = section width
45 = aspect ratio
17 = rim diameter

to figure out the overall diameter:

255 + (255 x 0.45) + (17 x 25.4)
= 255 + 114.75 + 431.8
= 801.55mm = 31.56"

as far as the difference in height of a 255/45-17 vs. a 255/40-17

255 x 0.45 = 114.75mm
255 x 0.40 = 102.00mm

The difference in height between the two is 12.75mm or 1/2". Not 5mm

If you were to take the difference between a 225/45-17 and a 255/45-17 you're looking at 43.5mm (758.05 vs. 801.55) or almost 1-3/4"

People typically run into rubbing issues because they don't understand that there is a lot more to tire and rim selection than they think.

Rims

Not only are width and diameter important but also offset and the shape of the BACKside of the rim.

Offset (ET) is defined as the distance from the centre of the rim to the mounting face expressed in millimetres. If a rim had an ET of 0mm this would mean that the part of the rim that contacts the hub is exactly 1/2 way in between the two outside edges of the rim.

A rim with ET = 34 means that the mounting face of the rim is 34mm OUTBOARD of the centreline. in other words, the rim sits 34mm further in than a rim with ET = 0. However, you have to realize that ET is an absolute measurement. which is to say that a rim which is ET 34mm does NOT sit 34mm further in than a rim which is ET 12mm. In this particular case, the ET 34 rim sits only 22 mm further in.

Another thing to keep in mind when you're trying to figure out how much further out/in a rims sits in comparison to another the rim width.

Here's an example:
OEM rim for a 190E 2.3-16 is 7x15 ET44
OEM rim for a 190E Evolution is 8x16 ET34
How much further in/out will the EvoI rims sit than the OEM 16v rim?

ET44 - ET34 = 10mm further out
BUT you have to take the difference in rim width into account as well.
The EvoI rim is 1" wider overall. Divide by 2 (because 1/2 of the difference goes to each side of the rim's centreline.) and convert to mm = 12.7mm

So 10mm + 12.7mm = 22.7mm further out.

On the flip side (literally) you have to consider that there is a change to how far in the INSIDE edge of the rim sitsbecause we needto make sure there is clearance to the steering and suspension components.

in this case, the difference in ET moves the INSIDE rim edge 10mm OUT, so you get more clearance but the additional width brings that edge 12.7mm back in. SO, the net result is the inside edge sits 2.7mm further in towards the middle of the car.

Furthermore, you also have to consider if the shape of the caliper well (the backside of the rim that would sit in front of the brake caliper allows enough clearance for the caliper. ESPECIALLY if you're going to bigger brakes.

Tires

I've already broken down P-metric sizing and how to interpret it. The most common mistake people make when changing rims to a larger size is that they just carry over the numbers from the previous tire size and get tires with the same section width and aspect ratio, but for a larger diameter wheel.

To illustrate the point:

OEM tire size for a 2.3-16 is 205/55-15
Working the math you get a diameter of:

205 + (205 x .55) + (15 x 25.4)
= 205 + 112.75 + 381
= 698.75mm

if we were to make the common mistake when going to a 16" rim, we'd incorrectly order a tire that is 205/55-16. Since the other numbers stay the same, logic would say that the overall diameter would be 1" (25.4mm) taller. I won't go through the equation here, but feel free to try it out.

So, obviously a tire that is 1" taller is an issue. This is where plus sizing comes in. Plus sizing means increasing the rim diameter while maintaining the same overall diameter. Plus-1 means an rim diameter increase of 1", Plus-2 is 2" etc.

the way to figure out proper plus sizing is just simple algebra. using the numbers from above we know that the 2.3-16 OEM tire/rim package has an overall diameter of 698.75mm and we know that we want a 16" rim. assuming that we are happy with the tire section width, we have 3 of the 4 numbers. all we need to figure out is the aspect ratio:

205 + (205 x X) + (16 x 25.4) = 698.75
205 + 205X + 406.4 = 698.75
205X + 611.4 = 698.75
205X = 87.35
X = 0.426

(To those proficient in math: Yes, I know the steps I took were cumbersom, but I did it that way for the benefit of those who may not be as proficient with algebra.)

Since there are no 42.6 series tires, the closst we can hope for is a 40 series tire, but it will be marginally undersized.

"But what if someone wants to change the tire width as well? after all, a 205 tire is really narrow. "

Well, if you know what width you want to go to, be it 225, 245, 255, or even 285, you can figure out the proper aspect ratio to keep the overall diameter the same. Just substitute the numbers you know/want and solve for X.

CAVEAT: this does NOT guarantee that a given tire/rim will fit. This just explains what thought process and math you need to be able to properly compare one rim/tire combo to another. There are other factors to consider such as additional tire width will require more clearance under the bodywork for turning. also watch out for clearance to the shock, tie-rods, etc

'93 W124.036 199/040; parts car
'93 W124.036 481/040; euro delivery
'94 W124.036 249/040
'88 R107.048 441/409
'87 W201.034 199/040
'70 R113.044 050/526

Last edited by yvrbenz; 03-14-2007 at 04:51 PM.
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#6 (permalink) Old 03-14-2007, 04:55 PM
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Well I guess this post definitely answers my question for putting 245/45/17's on my rears !! IT FITS !!! YAY !! I plan to put 225's on the front anyways, just was worried about the rears !! Staggered setup so yeah !!

Well if your wheels came with 255's those must be 17x8.5 or 17x9 and there is no way you can put 215's on them. Let alone 225's. You can put 225's but its going to stretch the tires out. You wheel will stick out more than your tire. Its more of an euro look. Try 235/45/17's on the front and you should be good.

But then again, its all relevant to what offset your rims are. Find out the proper specs on the rims and everyone will be able to help you out more.

And post pictures too

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#7 (permalink) Old 03-14-2007, 04:58 PM
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Quote:
Originally Posted by yvrbenz
Completely incorrect. the difference in tire height is not 45 - 40 = 5mm

P-Metric tire sizing works as follows:

Section width (in mm)/ Aspect ratio - rim diameter (in inches)

Sections width: width of the tire from sidewall to sidewall
Aspect ratio: height of the sidewall experssed as a percentage of the section width.
Rim diameter: self-explanatory

With the numbers:
255/45-17

255 = section width
45 = aspect ratio
17 = rim diameter

to figure out the overall diameter:

255 + (255 x 0.45) + (17 x 25.4)
= 255 + 114.75 + 431.8
= 801.55mm = 31.56"

as far as the difference in height of a 255/45-17 vs. a 255/40-17

255 x 0.45 = 114.75mm
255 x 0.40 = 102.00mm

The difference in height between the two is 12.75mm or 1/2". Not 5mm

If you were to take the difference between a 225/45-17 and a 255/45-17 you're looking at 43.5mm (758.05 vs. 801.55) or almost 1-3/4"

People typically run into rubbing issues because they don't understand that there is a lot more to tire and rim selection than they think.

Rims

Not only are width and diameter important but also offset and the shape of the BACKside of the rim.

Offset (ET) is defined as the distance from the centre of the rim to the mounting face expressed in millimetres. If a rim had an ET of 0mm this would mean that the part of the rim that contacts the hub is exactly 1/2 way in between the two outside edges of the rim.

A rim with ET = 34 means that the mounting face of the rim is 34mm OUTBOARD of the centreline. in other words, the rim sits 34mm further in than a rim with ET = 0. However, you have to realize that ET is an absolute measurement. which is to say that a rim which is ET 34mm does NOT sit 34mm further in than a rim which is ET 12mm. In this particular case, the ET 34 rim sits only 22 mm further in.

Another thing to keep in mind when you're trying to figure out how much further out/in a rims sits in comparison to another the rim width.

Here's an example:
OEM rim for a 190E 2.3-16 is 7x15 ET44
OEM rim for a 190E Evolution is 8x16 ET34
How much further in/out will the EvoI rims sit than the OEM 16v rim?

ET44 - ET34 = 10mm further out
BUT you have to take the difference in rim width into account as well.
The EvoI rim is 1" wider overall. Divide by 2 (because 1/2 of the difference goes to each side of the rim's centreline.) and convert to mm = 12.7mm

So 10mm + 12.7mm = 22.7mm further out.

On the flip side (literally) you have to consider that there is a change to how far in the INSIDE edge of the rim sitsbecause we needto make sure there is clearance to the steering and suspension components.

in this case, the difference in ET moves the INSIDE rim edge 10mm OUT, so you get more clearance but the additional width brings that edge 12.7mm back in. SO, the net result is the inside edge sits 2.7mm further in towards the middle of the car.

Furthermore, you also have to consider if the shape of the caliper well (the backside of the rim that would sit in front of the brake caliper allows enough clearance for the caliper. ESPECIALLY if you're going to bigger brakes.

Tires

I've already broken down P-metric sizing and how to interpret it. The most common mistake people make when changing rims to a larger size is that they just carry over the numbers from the previous tire size and get tires with the same section width and aspect ratio, but for a larger diameter wheel.

To illustrate the point:

OEM tire size for a 2.3-16 is 205/55-15
Working the math you get a diameter of:

205 + (205 x .55) + (15 x 25.4)
= 205 + 112.75 + 381
= 698.75mm

if we were to make the common mistake when going to a 16" rim, we'd incorrectly order a tire that is 205/55-16. Since the other numbers stay the same, logic would say that the overall diameter would be 1" (25.4mm) taller. I won't go through the equation here, but feel free to try it out.

So, obviously a tire that is 1" taller is an issue. This is where plus sizing comes in. Plus sizing means increasing the rim diameter while maintaining the same overall diameter. Plus-1 means an rim diameter increase of 1", Plus-2 is 2" etc.

the way to figure out proper plus sizing is just simple algebra. using the numbers from above we know that the 2.3-16 OEM tire/rim package has an overall diameter of 698.75mm and we know that we want a 16" rim. assuming that we are happy with the tire section width, we have 3 of the 4 numbers. all we need to figure out is the aspect ratio:

205 + (205 x X) + (16 x 25.4) = 698.75
205 + 205X + 406.4 = 698.75
205X + 611.4 = 698.75
205X = 87.35
X = 0.426

(To those proficient in math: Yes, I know the steps I took were cumbersom, but I did it that way for the benefit of those who may not be as proficient with algebra.)

Since there are no 42.6 series tires, the closst we can hope for is a 40 series tire, but it will be marginally undersized.

"But what if someone wants to change the tire width as well? after all, a 205 tire is really narrow. "

Well, if you know what width you want to go to, be it 225, 245, 255, or even 285, you can figure out the proper aspect ratio to keep the overall diameter the same. Just substitute the numbers you know/want and solve for X.

CAVEAT: this does NOT guarantee that a given tire/rim will fit. This just explains what thought process and math you need to be able to properly compare one rim/tire combo to another. There are other factors to consider such as additional tire width will require more clearance under the bodywork for turning. also watch out for clearance to the shock, tie-rods, etc
Good post !! Very informative !!

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#8 (permalink) Old 03-14-2007, 05:06 PM
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[QUOTE=zudeck]Well I guess this post definitely answers my question for putting 245/45/17's on my rears !! IT FITS !!! YAY !! I plan to put 225's on the front anyways, just was worried about the rears !! Staggered setup so yeah !!

With 245's on the rear, you will need to roll your fenders & make sure you get a good alignment. I have the same set up with a lowered suspension - no rubbing issues.
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#9 (permalink) Old 03-14-2007, 05:09 PM
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sorry guys, i thought he had 225 tires not 255, i guess im still feeling it from last night, my bad!
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#10 (permalink) Old 03-14-2007, 05:16 PM
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[QUOTE=bahnstormer]
Quote:
Originally Posted by zudeck
Well I guess this post definitely answers my question for putting 245/45/17's on my rears !! IT FITS !!! YAY !! I plan to put 225's on the front anyways, just was worried about the rears !! Staggered setup so yeah !!

With 245's on the rear, you will need to roll your fenders & make sure you get a good alignment. I have the same set up with a lowered suspension - no rubbing issues.

Oh sweet, now I found another person as the same setup.

I got 17x7.5 ET 35 for the front and 17x8.5 ET 30 for the rears !! Im planning 225's on the front and 235's on the rear. I know I can go 245's but my concern is, Does acceleration and fuel economy suffer ? What have you noticed so far?

I wont need to roll my fenders. Not yet, since its not lowered !! But in the future yes.

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