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[TRZ06]

I don't understand why the 18's would handle better than 19's.

The 19"s have a lower profile sidewall to keep the tire from rolling too much during hard cornering, thereby keeping more tire to the ground. The lower profile makes the car feel more stable and planted with less roll.

I don't get why a 40's series tires is even offered on the M.

Look at all the Ferraris, Porsches, Lambo's, Corvettes, they are using anything from 35 down to 25 series.

They ONLY reason I can see is weight. If you take the weight out of the equation, I would think a 35" 19" would corner better that a 40" 18"

Comments......?

[richardg]

Originally Posted by TRZ06

I don't understand why the 18's would handle better than 19's.

The 19"s have a lower profile sidewall to keep the tire from rolling too much during hard cornering, thereby keeping more tire to the ground. The lower profile makes the car feel more stable and planted with less roll.

I don't get why a 40's series tires is even offered on the M.

Look at all the Ferraris, Porsches, Lambo's, Corvettes, they are using anything from 35 down to 25 series.

They ONLY reason I can see is weight. If you take the weight out of the equation, I would think a 35" 19" would corner better that a 40" 18"

Comments......?

You have to remember that the sidewall measurement is a ratio of how wide the tire is. For all the cars you mentioned they have very wide tires. Especially Lamborghinis and Corvettes. Another example is a bike tire. Most people that do not know how sidewall measurements work would think that a bike has an extremely low profile. In reality a bike has HUGE profile since the tires are almost as thick as they are wide.

Also I would think that the weight you save would work better for you with a smaller wheel. I am not sure but I believe weight that rotates can have a huge affect on the car so every pound counts significantly.

[PunjabiM3]

F1 cars run tires with HUGE sidewalls...I wonder why...

[PunjabiM3]

You will get better overall handling from a 40 series tire than a 30 series in the same width unless maybe you are on a road that is as smooth as glass. Like stated above, the width of a tire makes a huge difference in the fatness of the sidewall. A 285/30 has a fatter/larger sidewall than a 225/30...you can easily tell by just looking at the two tires even though both are a 30 series tire.

[TRZ06]

Ok, I get the sidewall ratio thing, but then why do all exotic supercars use thin sidewalls?

Anybody look at the side profiles (regargless of series) of the new Porsches, Ferrari, Lambo, etc. They are not even close to having the kind of sidewall that the stock 18" tires have on the M3.

Now the 19" sidewalls on the M3 look about right with the supercars, but the 18" don't, their sidewalls are definately taller then the supercars.

My thoughts on the 40 series on the 18" thus far are that once in the corner they stick well, but that initial transition into the corners, you can feel the sidewalls flex and that lessens the quick turn-in response.

[FStop7]

Originally Posted by PunjabiM3

F1 cars run tires with HUGE sidewalls...I wonder why...

because the tire is a very big part of the suspension on those open wheel cars.

Ok, I get the sidewall ratio thing, but then why do all exotic supercars use thin sidewalls?

Because it looks good.

[JAJ]

Who said that the 18's perform better than the 19's? I saw a quote about that earlier when the E9x M3 was first released, but it was unattributed. It might not be true.

I will say that the 18's ride better than the 19's if you don't have EDC. Do they handle better? I have no idea.

[x838nwy]

Originally Posted by PunjabiM3

F1 cars run tires with HUGE sidewalls...I wonder why...

It's in the regulations. Wheel diameters, tyre diameters, widths etc.

Originally Posted by TRZ06

Ok, I get the sidewall ratio thing, but then why do all exotic supercars use thin sidewalls?

Anybody look at the side profiles (regargless of series) of the new Porsches, Ferrari, Lambo, etc. They are not even close to having the kind of sidewall that the stock 18" tires have on the M3.

Now the 19" sidewalls on the M3 look about right with the supercars, but the 18" don't, their sidewalls are definately taller then the supercars.

My thoughts on the 40 series on the 18" thus far are that once in the corner they stick well, but that initial transition into the corners, you can feel the sidewalls flex and that lessens the quick turn-in response.

In my experience a taller sidewall will generally give you a more progressive feeling of the grip limit of the tyre. The taller side-walls will also cope better with bumps including apexes and other circuit furniture.

[sgar0777]

I suspect that it is significantly more complicated than we think, and that you can not make a blanket statement about 18" vs. 19" tires. If we were able to test the two sizes side by side in various road conditions, temps, etc. I would wager that the 18's are better in some circumstances and 19's are better in others ON THE M3. Any conversations about another car brings too many variables in to play that can not be accounted for.

[bigjae1976]

The tires are part of the suspension. Some might do better with an small diameter wheel and larger sidewall and vice versa.

For me it really comes down to cost and selection. There are a LOT more choices at MUCH lower prices for 18" tires vrs 19" tires.

[bobbyd1961]

Originally Posted by TRZ06

I don't understand why the 18's would handle better than 19's.

The 19"s have a lower profile sidewall to keep the tire from rolling too much during hard cornering, thereby keeping more tire to the ground. The lower profile makes the car feel more stable and planted with less roll.

I don't get why a 40's series tires is even offered on the M.

Look at all the Ferraris, Porsches, Lambo's, Corvettes, they are using anything from 35 down to 25 series.

They ONLY reason I can see is weight. If you take the weight out of the equation, I would think a 35" 19" would corner better that a 40" 18"

Comments......?

the 19 rims so much nicer and the car handles fantastic and takes bumps 1000 times better than my 335 xi did with 18s

[Trier Germany]

Did your 335 have RFT? I f so of course there going to feel un comfprtable!

335 18''s RFT versus M3 19''s ps2 = apples and oranges. Go drive an M3 with 18''s oh so comfortable on the road and on the track.


Plus tire manufacyures dont have a huge selection of competion tires in 19''s for the M3 only in 18''s.

[KonigsTiger]

Originally Posted by Trier Germany

Did your 335 have RFT? I f so of course there going to feel un comfprtable!

335 18''s RFT versus M3 19''s ps2 = apples and oranges. Go drive an M3 with 18''s oh so comfortable on the road and on the track.


Plus tire manufacyures dont have a huge selection of competion tires in 19''s for the M3 only in 18''s.

Well, you can find R-Compound/competition tires in 19" such as the Pilot Sport Cup and the Pirelli P-Zero Corsa System (soon to be Pirelli Triumfo). Granted, not a huge collection but as far as I am concerned you only need one for our cars and this fit just fine in 19".

Also, I know the 20" wheels on the M3 leaves sooo little side wall that its difficult for the tire to morph into an appropriate contact area when g forces act on it, this is at least why 19" is better than 20". Now, how much improvement (other than comfort) there is from 19" to 18" I don´t know. There is also the matter of fitting large brakes and not many 18" wheels will allow fitment of competition brakes.

[dcstep]

I'll be using 30-series, 18" tires for my autocross set up next year. I'll be going to a 10" to 10.5" rear wheel to allow as much tire as possible back there, to gain acceleration, since AX is mostly run in 2d gear and I now spin my 19" wheel/tire set at will anywhere on the course. The low profile will give both a wider contact patch and stiffer sidewall. The front tires will also be 30-series and about 20mm narrower than the backs, to maintain balance.

The added advantage of 18", 30-series tires will be that the final drive ratio will be slightly higher numerically, improving mid-gear acceleration.

For street, I'll be staying with the 19" factory option, forged wheels in summer and 18" factory wheels, with snow tires for winter. I think these are the best compromise of ride and handling, where my AX setting is aimed at acceleration and handling with no concern for ride.

Dave

[KonigsTiger]

Originally Posted by dcstep

I'll be using 30-series, 18" tires for my autocross set up next year. I'll be going to a 10" to 10.5" rear wheel to allow as much tire as possible back there, to gain acceleration, since AX is mostly run in 2d gear and I now spin my 19" wheel/tire set at will anywhere on the course. The low profile will give both a wider contact patch and stiffer sidewall. The front tires will also be 30-series and about 20mm narrower than the backs, to maintain balance.

The added advantage of 18", 30-series tires will be that the final drive ratio will be slightly higher numerically, improving mid-gear acceleration.

For street, I'll be staying with the 19" factory option, forged wheels in summer and 18" factory wheels, with snow tires for winter. I think these are the best compromise of ride and handling, where my AX setting is aimed at acceleration and handling with no concern for ride.

Dave

Sorry, how do you figure the 18 x 30 tires will give you a lower profile side wall?

[dcstep]

Originally Posted by BMW-M-Mexico

Sorry, how do you figure the 18 x 30 tires will give you a lower profile side wall?

30-series vs. stock at 40-series, equals lower profile. Maybe I don't get your drift.

Dave

[elp_jc]

There's always a point of diminishing returns on everything. On wheel size, seems like it's between 18s and 19s, depending on track, as previously said; no one tire/wheel combo is best for everything.
By the way, stock 19s are lighter than 18s because they're forged, but forged 18s would be lighter than forged 19s in same design, but a 5-spoke design would be even lighter. Then you have the tire width, aspect ratio, and wheel width to mess with .

[askiles]

Originally Posted by dcstep

30-series vs. stock at 40-series, equals lower profile. Maybe I don't get your drift.

Dave

Depends on the width obviously.

-Andy

[dcstep]

Originally Posted by askiles

Depends on the width obviously.

Duh, really???

Dave

[wea]

Originally Posted by PunjabiM3

F1 cars run tires with HUGE sidewalls...I wonder why...

This is due to Formula 1 Technical Regulations on maximum brake size which is limited to a diameter of 10.9" or 278mm and to limit the cooling potential they limited the rim size. The thinking is that 13" rims (332mm max) would limit ability to cool the brakes because of the limited space. The high side wall is a consequence of the small rims.

FYI, F1 cars were braking 4.5G going into turn 10 at the German GP, so I guess that is limited.

2009 Formula 1 Technical Regulations

Cheers

[ben@tirerack]

Originally Posted by elp_jc

There's always a point of diminishing returns on everything. On wheel size, seems like it's between 18s and 19s, depending on track, as previously said; no one tire/wheel combo is best for everything.
By the way, stock 19s are lighter than 18s because they're forged, but forged 18s would be lighter than forged 19s in same design, but a 5-spoke design would be even lighter. Then you have the tire width, aspect ratio, and wheel width to mess with .

Very good point regarding the point of diminishing returns. I read a test (way back in the early 90's I think) which compared results plus-sizing from a (then common) 15" wheel to +1, +2, and +3 sizing. The +1 was a little quicker around the track, the +2 was quicker yet, but started to feel a little harsher ride, and the +3 was not any faster than the +2, but harder riding.

This was one test of one car by one magazine, but it illustrates the point. In general, a particular vehicle stops gaining performance at a particular wheel size (aside from vehicles with extreme mods that may have special parameters).

Generally, newer cars are engineered around bigger wheels. So tire sizes that used to be silly are now common. 18" wheels on an E36 were 'too big' for pure performance, but are now the smallest thing offered on the E9x.

A little bit of flex makes a tire more progessive, too much sidewall flex makes it sloppy in transition. So there is always an optimal mid point between too big and too small. Honestly I'm not yet sure if it's 18 or 19.

[stylinexpat]

Originally Posted by ben@tirerack

Very good point regarding the point of diminishing returns. I read a test (way back in the early 90's I think) which compared results plus-sizing from a (then common) 15" wheel to +1, +2, and +3 sizing. The +1 was a little quicker around the track, the +2 was quicker yet, but started to feel a little harsher ride, and the +3 was not any faster than the +2, but harder riding.

This was one test of one car by one magazine, but it illustrates the point. In general, a particular vehicle stops gaining performance at a particular wheel size (aside from vehicles with extreme mods that may have special parameters).

Generally, newer cars are engineered around bigger wheels. So tire sizes that used to be silly are now common. 18" wheels on an E36 were 'too big' for pure performance, but are now the smallest thing offered on the E9x.

A little bit of flex makes a tire more progessive, too much sidewall flex makes it sloppy in transition. So there is always an optimal mid point between too big and too small. Honestly I'm not yet sure if it's 18 or 19.

You can get them with 18" or 19" from the factory and an inch must make some sort of difference. Between size and weight I can't see them as pretty close if the weight savings were 5-7 lbs. per corner. If one went to a lightweight forged 18" wheel and saved 5-7 lbs. per corner I would be surprised to see no performance gains..