what is the advantage of 18s....is it oly cosmetic..... more weight...... longer to get moving etc.... they do look cool

 

Yup, only cosmetic.

 

Bling Bling

 

thought so...... look cool but not for me..... the only reason I have 17s is to fit over my brakes

 

18's will mostly just be for looks, you can find lightweight 18 inch wheels which can help performance but will they weigh in less than 16's or 17's??? Doubtful....stick with 17's. You can fit 20's on Coopers if you just want the look.

 

More metal > less rubber

 

Really depends on how much money you want to spend. If you have $4K then a set of BBS or Jongbloeds in 18 would be primo.
One thing I have found that in racing, you have a huge selection of 18" slicks and a very slim selection in 17"
In a Mini though, being a relative low power car, stick with a 16, then 17 and then only an 18 if you are just out for looks or if you are a serious all out race car.

 

I have read some comments about Walter Ruehl (sp) taking a Cayman around the ring and that the 19" wheels are the best to get the quickest times but the 18" wheels were the best for the average driver around town (talking comfort)

So why are larget wheels in the MINI a "bad" thing but a "good thing" for the Porsche.

Similarly, Porsche sells as OEM wheel spacers as a option I thought wheel spacers were a "bad" thing you only do to clear the front brakes?

 

19"...18"... it's all mute unless you talk about what tires were on each.
Cayman has lots'a power, Minis don't.
Wheel spacers are not 'bad', but you need to understand what you are doing with scrub and also with bearing and driveshaft wear. Also you might create 'push' with them on a Mini, where as on a P-car it's not such a concern

It's apples and oranges kinda thing. The Mini and P-car couldn't be much more different from each other.

 

you can get a larger contact patch with the larger wheel/tire combos and enhance cornering grip. The price paid is reduced (effective) torque and increased unsprung weight. Depends on the details as to whether it will make a difference in a good way or a bad way for how you drive your car.

19s going faster around a track is probably due to the improved contact patch. But not fun on the street because of the very short tire sidewall. Look at all those that live in pot-hole cities (like Manhatten) that have better experience when going to a 16 or a 15 from the 17s on the minis....

Matt

 

Thanks! Got it.

And the tire patch thing makes sense too, Dr. O

 

Ok... I'm summoning up the courage to question the Dr.

I don't really get the whole "more rubber on the ground increases grip" argument. Sure, increasing the width of a tire puts more rubber down, but does so with less force, since the same weight is distributed over more area. In road racing, isn't the primary benefit of a wider tire improved resistance to heat/wear, because each square inch of tire has less work to do?

A separate but related topic is the tire aspect ratio. Larger wheels are generally used in conjunction with a tire that has a reduced the aspect ratio (same or increased width with a shorter sidewall). This change in aspect ratio results in a car that responds quicker to steering inputs because the tires deflect less when cornering. It also transmits more of the road (cracks and potholes) to the car. Keeping the aspect ratio the same, I can't see why simply running 19s vs. 18s would have any benefit.

 

Been arguing this exact subject with regard to the motorcycle world for about thirty years now. With bikes, it's different to some degree because of the huge variety of tire sizes and shapes available and the different demands that bikes put on tires than cars do.

But, having said that, in the bike world, it's the captured air (or nitrogen, or helium, or peanut butter if that's what you've got in there) that supports the bike/car. The size and shape of the tire gives shape to that air and controls how it's distorted when you accellerate/decellerate/turn/fall off/whatever. Given the same weight bike and the same air pressure in the tire, a 21" wheel and skinny tire will have the same size contact patch as a fat 16" wheel and tire. What's different is the shape of the contact patch. A tall, skinny wheel and tire will have a long narrow contact patch that runs in the same direction as the vehicle does, while a shorter wider tire will have a contact patch that's shorter front to back and wider side to side. Aspect ratios will influence that to a great degree, but at least in the motorcycle world, what you're manipulating is essentially the shape of the contact patch.

YMMV.

 

Alex

 

If that is the case, and it appears that Alex agrees, then I thought it was fairly well known that for winter driving you want a long, thin contact patch (Not a fat wide one). And for maximum traction in the dry you want a wide tire and not a skinny one. Hence the 19" wheels much better in my example and perhaps the reason Walter Ruehl made that comment.

 

When you first do friction calculations, you end up in a situation where the friction force is independant of contact area. Precisly because of the reason stated above: More contact but less pressure.....

But the rubber on tires does something called "intimate contact", which is the interlocking of the rubber and tread with the surface imprefection of the surface of the road.

This leads to a very complex relationship between contact area, contact force, and sustainable loads.

Matt

 

When there's snow or water on the road, you don't want your tires to "plane" over it - you want them to maintain contact with the road. A thinner tire is able to cut through better because it is bearing the same weight but displacing less snow/water. Other than that, I imagine the same wider-is-better logic could apply in wintertime.

Wider could be better because of the "intimate contact" Dr. O. described, however, the width to height aspect ratio of the tire has nothing to do with the size of the wheel on which it is mounted. I doubt that, aspect ratios remaining equal, there's any benefit to larger wheels.

 

Cool. Makes me think of spider-man. It is kinda the same thing, right?

Care to share any thoughts on the practical limit of wide-ness? I imagine it varies considerably with vehicle weight, wheelbase, track width, suspension design, horsepower, road/track conditions, and probably a few others I'm not thinking of... as you said, complex.

 

The difference between pure F=μN and also having the load transfered through bearing on surface imperfections.

 

Ok, not to get technical here. I had S-Lites and just got JCW 18's. Both had/have RFT's. I feel the difference in the overall handling/ride for the MINI. The JCW's feel better and seem to stablize the MINI more effectively.

 

What was the aspect ratio of the tires on the S-Lites? The JCWs? It seems to me that wheel diameter (17 vs. 18 vs. 19) is pretty much irrelevant to handling... it's the change in the tire width and sidewall height that is making the car feel more stable.

 

Just to make things even more complicated, some tires have stiffer sidewalls than others, so tire A in an 50 series 16" size may in fact have a stiffer sidewall than tire B in a 40 series 17" size.

 

Is there really a larger contact patch. I thought that all of the wheel/tire combinations all ended up around 24" diameter regardless of the wheel diameter. As Scooby said: "more metal > less rubber".

If that is true then why would the size of the contact patch change, given equal width tires?

I understand the benefits of smaller diameter wheels in terms of moving the weight closer to the center of rotation. The advantages of lighter wheels as it effects the preformance of the suspension over uneven pavement, under acceleration and braking has been well discussed here before.

I'd appreciate hearing your thoughts on this.

 

ummmmm... there's a lot of goblety-gook here...
There are just way too many variables in wheel AND tire selection to come up with "what's better, 17 or 18".
I'm not sure that there is a race team out there that would choose a larger diameter wheel then they needed to fit over the front brakes.

Not sure bike wheels and tires can relate to any of this.

 

The S-Lites were the OEM Dunlop RFT's. I believe the were 205/45/17. The JCW's are 205/40/18 Dunlop RFT's.