175/65/15 vs 185/65/15
 

Does anyone know why Mini (BMW) opted for 175/65 tyres on the 15" rims?

Whilst looking for winter tires to fit to some Rotator 101s I looked at the Mini winter wheel sets and they use 175/65/15.

This size gives smaller rolling radius than the 16 / 17" wheel options - ca 1-1.5% more rotations per mile. Thats no big deal but from my calculations 185/65 seems almost the same as the 195/55/16 summer tires i have fitted on the Blaster wheels. The extra width would provide a little more kerb protection, the extra sidewall height will add to ground clearance for snow and a better ride / pothole absorption.

Other than the fact it keeps within Mini's guideance I can't see why the small tire size ?

I pondered whether it was for snow driving performance (narrower 175mm being better) but then the summer/all season tires fitted as stock to 15" rims are the same size.

Maybe it was purely on costs grounds when negotiating long term supply contracts with the tire companies ?

One other thought was whether the smaller overall diameter was a marketing / sales plus, helping the acceleration feel of the lower powered cars, albeit at the expense of fuel economy once up to speed ?

Reading winter tire threads here its clear that 185/65 is a popular choice and creates no issues in use. Warranty related claims might be a little awkward though ? :confused:

Anyone got any inside insight ?

Tyre width is surprisingly important for aero drag, so when manufacturers are fighting for every mpg they can claim, fitting wider tyres to the base model (which makes the good numbers) is undesirable.

Just going from 175 to 185 would probably make fuel economy as much as 1mpg worse at high speed.

Thats a good point Angib - I'd forgotten about that aspect :roll: I suppose the 6mm lower ride height migt help the aerodynamics too !

I run 195/65/15 winters on steelies on another car, versus its normal 225/45/17 summer alloys and the mpg is 10% better on the winters (over 4 winters, 35k miles) - maybe the drag, maybe better rolling resistance or perhaps the fact the winters weigh a heap less than the summer wheels :eek:

You'd have to ask the MINI/BMW engineers why they selected that 15" tire size, obviously there are multiple options.

175/65-15
Pros
Low rolling resistance, better mpg
Lower tire weight, easier to accelerate
smaller tire diameter relative to other sizes, slightly lowered gearing
generally lower cost
Works for all season tire classes
Tall sidewall height gives more ride comfort
Fits OEM 15x5.5" wheels well

Cons
Somewhat limited number of possible tires to choose from vs other tire sizes
Not as much tread width for better handling
Not aggressive looking

In the end for street driving the MINI on OEM 15" wheels will do fine with many of the possible tire sizes. For winter, narrow is better. For long commutes, narrow is better.

Take your pick.

Indeed, although the fact the rolling radious is 2% smaller suggests the economy argument is a mute one, engine running faster for any given road speed (I know, marginal, but it all counts :wink: )

!85/65/15 winters fitted this morning so looking forward to the extra comfort of the higher sidewall and lighter weight over the summer 16" runflats.

Every year when I mount my 15" snows on OE holies I am struck by how much lighter they are then my 16" Michelin Pilot Exaltos on R84s.

Yes surprising the differences in wheel weights..

summer R103 Blaster with 195/55/16 Goodyear Excellence RF - 40.3lbs

winter R101 rotator with 185/65/15 Dunlop WinterSport 3D NRF - 34.3lbs


I run my Audi A3 on 15" steelies in the winter - not sure how much lighter they are thant he 225/45/17 shod summer alloys but its very noticeable when swapping wheels - maybe 8-10lbs each ?

Amazing thing is the r84 x-lite is among the lightest OEM 16 rim....
Can you imagine the feel with the heavy 17 s-lites or most any 18" rim?!
And those 15 imola rims (holies) are light for ANY rim, OEM or not! Once they were a dime a dozen...but as folks running autos have realized they are so light and strong...they are much more $$ and harder to find....

yep - love my imolas. running 195/65-15 on them right now for lower rpms at highways speeds, but will probably go to 185/65-15 next time

Imagine the difference I felt years ago when I went from 17" S-lites with run-flats 3 seasons of the year to the 15" with snows in the winter. I bet it was almost 15 lbs difference at every corner. Like I suddenly found an extra 30 hp.