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[Dackelone]

Originally Posted by VMRWheels

With a 8.5 +45's coming in and 9.5 +50's available, 225/255 at stock height would be perfectly fine.

-Charles@VMRWheels

But... what about 225/255's on stock 18" wheels???

[aerobod]

Originally Posted by Dackelone

With the 225/255 setup wouldn't you have more sidewall flex over a RSC (run flat tire - in the 215/245 size)? This is my main concern. I really do not want to loose ANY steering response with my 135i.

The 225/255 setup seems very temping though.


Also... my local tire dealer here in Germany looked up in a book the max size tires you can mount on wheel widths and size. For the OE 18' M-wheels (7.5" & 8.5"s ) he told me that 225's and 245's are the biggest tire I could safely put on the wheel. That is also what TUV says too. But... I do not have to worry about TUV since I have US tags thru the Army.

Comments?
Dackel

Looking at the datasheet for the Conti DW: http://www.conti-online.com/generato...tasheet_en.pdf

The approved rim width for a 225/40-18 tyre is 7.5 to 9.0" and the approved rim width for a 255/35-18 tyre is 8.5 to 10.0".

[dlong82]

To the original question; is there a down side of the larger sizes? Yes, there are disadvantages. There are also advantages. The issue is, are the disadvantages significant. I have not seen evidence that would indicate one way or the other for the sizes mentioned. As the section width of the tire exceeds the rim width, there is more lateral flex and you need to plan for more clearance to struts and fenders. As the tire width increases in general, there is more of a tendency for the tire to track, e.g., toward the raising side of ridges, as in truck ruts. Potential disadvantages. As the tire size increase, the contact patch gets larger; although at a decreasing rate. An advantage.

Also note that not all tires measurement are the same. A stock Bridgestone RFT has a rounded shoulder and relative narrow contact patch compared, for example, to a Yokohama S.Drive of the same size. I think Gill said the same of the Hankook.

I have seen many autocross and road race cars go for the largest tire for the specified rim width to maximize the contact patch. I have seen the "hot shoe" take the day on narrower tires. In race conditions, the contact patch usually wins. My observations.

[old1]

Originally Posted by Diver

I kind of feel the original point never got discussed fully here as the thread got hijacked by a question about a different tire size. To repeat, the car will have stock wheels & suspension.

I don't know if you've already pulled the trigger on your purchase, but if you are thinking about going with non-RFT's and keeping the stock suspension, I think you will be disappointed with the high speed lateral instability and slop of that combination. I know I was.

[jsublime]

Originally Posted by old1

I don't know if you've already pulled the trigger on your purchase, but if you are thinking about going with non-RFT's and keeping the stock suspension, I think you will be disappointed with the high speed lateral instability and slop of that combination. I know I was.

Which tires were you disappointed with?

[Yogijet]

Originally Posted by jsublime

Which tires were you disappointed with?

Based on my experience in a 335i, I think he's referring to the slop in the stock suspension that suddenly shows up when you move to non-RFTs.

[Dackelone]

Originally Posted by old1

I don't know if you've already pulled the trigger on your purchase, but if you are thinking about going with non-RFT's and keeping the stock suspension, I think you will be disappointed with the high speed lateral instability and slop of that combination. I know I was.

I agree with this statement too. IF you are gonna keep the stock suspension - they stick with run flat tires in the OE size. The steering response is very good with the run flats.

I am still happy I went with Michelin PS3's. But the steering response isn't as good as with the Dunlap run flats the car came with. The PS3's aren't that bad - but not as sharp in steering as the OEM run flats. But the better ride is really nice and the overall perfoamace is very high. Plus I plan on installing a //M3 suspension bits this year.


Dackel

[ND40oz]

Originally Posted by Dackelone

I agree with this statement too. IF you are gonna keep the stock suspension - they stick with run flat tires in the OE size. The steering response is very good with the run flats.

I am still happy I went with Michelin PS3's. But the steering response isn't as good as with the Dunlap run flats the car came with. The PS3's aren't that bad - but not as sharp in steering as the OEM run flats. But the better ride is really nice and the overall perfoamace is very high. Plus I plan on installing a //M3 suspension bits this year.


Dackel

What tire pressures are you running Dackel? Euro PS3s are US SuperSports, is that right?

[burger16b]

Hate to thread jack, but if you lower your car will 225/40-18,255/35-18 fit with out modifications? I want to go with H&R super sport springs. should I keep the stock sizes?

[135CHRIS]

NICE

[top1usa]

Originally Posted by Delta Goose

Why does your site tell me that the 255 Hankook V12's may require fender modification?

I switched over to NRFT's with Hankook V12's 225/35, 255/30 18's Thanks to Gil@Tirerack. Tires came as promised! There were some in availability issues with V12's from their warehouse but quickly Gil contacted me and took care of it for me. Great experience overall....A+++!

I was really impressed with these tires. I made the right choice...

[Dackelone]

Originally Posted by ND40oz

What tire pressures are you running Dackel? Euro PS3s are US SuperSports, is that right?

For now I am running the same pressures I ran with my OE runflats: 2.3 bar up front and 2.8 bar in back. That is 34/41 psi.


The car seems to ride nice like that. Plus I do so much high speed driving (over 100 mph) that I like the way the car feels at speed with higher tire pressure. I was surpised my tire shop also used the same pressure when I picked up the car.

Here are some pics of my PS3's. I don't know what they are called back in teh states. But over here Michelin does make another even more high dollar/euro tire called the PSS: Pilot Super Sports. Maybe you can tell by the tread pattern. ?


Dackel

[Jaguar66]

I have often wondered if the odometer is affected by larger diameter tires. As it does the speedometer. With 225/255s you may record less mileage, and therefore extend the warranty a small amount.

[ZIPNBYE]

Originally Posted by RobMason

I have often wondered if the odometer is affected by larger diameter tires. As it does the speedometer. With 225/255s you may record less mileage, and therefore extend the warranty a small amount.

Actually, I found, via comparison with GPS, that the speedometer and odometer read optimistic (ie: fast) on the oem tire size... Going to 255 in the rear brought it to near perfect...so no more excess speed shown on the speedo and no more odometer clicking away too fast for the mileage.

[Dackelone]

Originally Posted by RobMason

I have often wondered if the odometer is affected by larger diameter tires. As it does the speedometer. With 225/255s you may record less mileage, and therefore extend the warranty a small amount.

You might remember I had my car coded with the M3 digital speedo ("v = kph) that reads true vehicle speed. I have checked it against my GPS and the M3 speedo is dead accurate. The car's speedo reads high by about 3 or 4%.

After I installed my Michelin PS3's in 225/255's I notice my digital speedo now read slightly slower, by about less than 1 kph. That is not something someone would notice if you ask me.

For instance before when I would drive at 100 kph looking at my M3 speedo... the car's speedo would be reading about 104 kph and my GPS would also read 100 kph. Now after the new tires my speedo will read 103 kph and my digital speedo will read 99 kph while my GPS reads 100 kph. Again not somthing to get all worried about.


Dackel

[Gary@TireRack]

Originally Posted by ND40oz

Euro PS3s are US SuperSports, is that right?

No, they are different tires.

[Alpha Trion]

after talking to the boys in service (who are honest and i know well) they say that putting on the wider tyres on the fronts stress the PSteer and even causes issues with the ABS.

[royrathbun]

I had purchased 225/255 Michelin PS2s, based on advice from Gill's FAQ post, to install in my OEM 313 rims, but no one in Stuttgart, DEU, will install the tires on the stock rims. Does anyone else have experience with mounting 225s on 7.5 and 255s on 8.5s?

[fourtailpipes]

Originally Posted by dlong82

As the tire size increase, the contact patch gets larger; although at a decreasing rate. An advantage.

to clarify, the area of contact patch is not affected by tire size. area of contact patch is a factor of tire pressure. a tire inflated to 40psi on a wheel supporting 800 pounds of vehicle weight will result in a contact patch of 20 square inches (40 pounds per square inch x 20 square inches = 800 pounds total supported weight). This will vary slightly based on the stiffness of the specific tire you're using, but not by size. increases in tire width DO affect the SHAPE of this contact patch, however, which can be a significant improvement in mechanical grip and other vehicle dynamics.

Originally Posted by royrathbun

I had purchased 225/255 Michelin PS2s, based on advice from Gill's FAQ post, to install in my OEM 313 rims, but no one in Stuttgart, DEU, will install the tires on the stock rims. Does anyone else have experience with mounting 225s on 7.5 and 255s on 8.5s?

i don't know what to say... the wheels are within the specs of the tire... it's a question of whether the tires are within the published or allowable specs for the wheel/vehicle. here in the states there's no problem mounting whatever tire you want (often regardless of whether it be a good or bad choice haha)

[John_01]

Originally Posted by fourtailpipes

to clarify, the area of contact patch is not affected by tire size. area of contact patch is a factor of tire pressure. a tire inflated to 40psi on a wheel supporting 800 pounds of vehicle weight will result in a contact patch of 20 square inches (40 pounds per square inch x 20 square inches = 800 pounds total supported weight). This will vary slightly based on the stiffness of the specific tire you're using, but not by size. increases in tire width DO affect the SHAPE of this contact patch, however, which can be a significant improvement in mechanical grip and other vehicle dynamics.

What you wrote makes sense at parking speeds, but you are neglecting the stiffness of the steel belt and the centrifugal forces of a rotating tire. At high speed, wider tyres give larger contact area and more grip. If not, can you explain why track cars use wider rubber?

[Dackelone]

Quote:
Originally Posted by royrathbun
I had purchased 225/255 Michelin PS2s, based on advice from Gill's FAQ post, to install in my OEM 313 rims, but no one in Stuttgart, DEU, will install the tires on the stock rims. Does anyone else have experience with mounting 225s on 7.5 and 255s on 8.5s?

Originally Posted by fourtailpipes

i don't know what to say... the wheels are within the specs of the tire... it's a question of whether the tires are within the published or allowable specs for the wheel/vehicle. here in the states there's no problem mounting whatever tire you want (often regardless of whether it be a good or bad choice haha)

royrathbun - The problem is that for the German TUV they say the max size tire you can mount on the rear 8.5 inch wide wheels is a 245 - when they look up the info in their tire/wheel books. My tire shop also pointed this out. But I also told them I do not have to go thru TUV since I am in the Army (with German cover plates and all). Then they were Ok with doing it. It is only 10mm's anyway. I would tell your tire shop what you want to do. I would go to a shop that is near a US Army base and I bet they are more willing to do this or have done this for us Ami customers.

I used ReifenWagoner (tire chain) - IF that helps you at all.



Dackel

[fourtailpipes]

Originally Posted by John_01

What you wrote makes sense at parking speeds, but you are neglecting the stiffness of the steel belt and the centrifugal forces of a rotating tire. At high speed, wider tyres give larger contact area and more grip. If not, can you explain why track cars use wider rubber?

the variables you mention do come into play (specifically the stiffness of the sidewalls and contact area, as well as the weight of the tire, and many others, like the wheel/tire width differential, tension in the sidewalls, shoulder profile, tread pattern etc.), but for the purposes of keeping this discussion somewhat simplistic, the biggest advantages in selecting a wider tire size come from changing the shape of the contact patch. a wider contact patch creates increased lateral mechanical grip and greater lateral stability. this is why camber adjustments can be so important... that's a direct adjustment of the shape of the contact patch of your tires when laterally loaded. this is conceptually similar to why you see drag racers using tall tires... this creates a "long" contact patch, which is most advantageous in fore/aft acceleration and deceleration forces (also a taller sidewall helps with deformation, but thats another discussion).