Last post on Apr 30, 2010 at 10:00 AM
You are in the Chrysler Town & Country/Dodge Grand Caravan
What is this discussion about?
Chrysler Town and Country, Wheels, Van
#10 of 12 Re: T & C "99 16 inch wheel to 17 [xwesx]
Apr 29, 2010 (5:57 pm)
capriracer, xwesx ; thanks so much for your input. Am still unclear on a couple things. 1) what is the mass issue ? Is it the volume, (total area , size of the wheel ) , is it the weight of the wheel ? If stock size is 215/65 / 16 can 205/65 or 70/ 16 be safe ? I notice many SUV s have 17" or 18" wheels and 235/65 so I was wondering how much dammage can occur by going up one rim size 1" Seems like so many vehicles have such oversize tires that have been added after market. Your explanation of what I'm trying to accomplish is right on. But how is it that a larger rim size, with fewer rotations of the wheel does not improve gas mileage.? Is it as so say there is more mass which means ??? Of course there is the stress on other componets ...transmission, suspension,... and all this taken into account can amount to big trouble tha t is just not worth the bother and bottom line simply will not provide better gas mileage. thanks
#11 of 12 Re: T & C "99 16 inch wheel to 17 [timbodey]
Apr 30, 2010 (3:12 am)
Going up in rim diameter, and making the proportional changes so that the load carrying capacity and overall diameter are the same - a process commonly called "Plus Sizing" - makes for a wider, heavier tire and rim assembly.
The loss in fuel economy is partially due to the extra weight that has to be accelerated (and slowed down) and partially because of the larger amount of tread rubber being deflected.
BTW, it is NOT the friction with the road surface that causes rolling resistance in a tire. It's a property called hysteresis. Another way to look at it is the internal friction of the rubber - and since most of the tire - particularly the part the is most involved with deflection - is the tread rubber, this dominates the rolling resistance picture. So more would be worse - meaning wider, deeper, etc.
But the single most dominant factor in rolling resistance is the rubber itself. You can get HUGE differences between tires that are otherwise identical just by changing the tread rubber. Unfortunately, this comes at the sacrifice of treadwear and/or traction.
Plus upsizing tends to put you into lower profiles - and this direction tends to go for traction by sacrificng treadwear (and RR).
So your best bet is to stick with the current size and search out tires that have the best combination of the properties you want.
#12 of 12 Re: T & C "99 16 inch wheel to 17 [timbodey]
Apr 30, 2010 (10:00 am)
But how is it that a larger rim size, with fewer rotations of the wheel does not improve gas mileage.?
After capriceracer's fantastic post, this is likely a moot point, but keep in mind that it is not the rim size that determines the number of rotations, it is the final diameter of the assembly, which is primarily determined by the tire size. For example, I can have a 17" rim and a 16" rim, with 225/55 tires on the first and 225/60 tires on the second, and the rotations per mile are nearly identical (754 versus 757). With a difference of 0.006%, do you really expect noticeable change in fuel economy if all other factors are equal? If I wanted to change the diameter significantly, I could simply put 225/75 tires on the 16" rims and I would have nine percent fewer rotations per mile (689 vs 757); the rim size remains the same - it is the tires that change the overall diameter.