Tire size for 2010 Aspect 30C

Well our spare is old and really will need to be replaced anyway. So that's an extra $250? It will likely be at least another three years before we have to replace the current tires.

Rolin on wrote:
Thanks pnichols. We plan to use the 215/85R16 when we replace our current tires. Good to have some real world feed back before we make the commitment. Looking forward to a little higher gearing on our E450.

If you change to the 215/85R16 tire size ... note that's it's expensive because you have buy 7 new tires instead of only 6!

Thanks pnichols. We plan to use the 215/85R16 when we replace our current tires. Good to have some real world feed back before we make the commitment. Looking forward to a little higher gearing on our E450.

denk wrote:
Bottom line is I'll use 225's as designed.

You should have no problem going from the stock 225/75R16 size to the slightly taller 215/85R16 size.

I had our stock set of Michelin 225/75R16's removed and replaced with Michelin 215/85R16's around 3 years ago on our 24 foot E450 Class C. I got the idea from a friend of ours who has been using 215/85R16's on his 24 foot Fleeetwood Class C for years.

What going to (MIchelin) 215/85R16 tires on our Class C gave us is:

- A speedometer that reads about 0.4 to 0.5 MPH too slow ... this is a trivial non-concern.

- About 0.6 inches of improved ground clearance everywhere on the rig ... this is great for off-pavement exploring and less rear end scraping going into/out of parking lots and driveways.

- Slightly improved gas mileage by partially compensating for the E450's low rear differential ratio ... which is not needed most of the time on a relatively light weight small Class C not doing heavy towing.

- Better cooling of the inner sidewalls on the rear dual sets during hot weather travel ... because of a slightly larger volume of cooling air circulating between the inner walls of the rear dual tires.

- Slightly improved gas mileage because of the Green X rating carried by the Michelin 215/85R16 tires (less rolling friction) .... the Michelin 225/75R16 tires are/were not Green X rated.

- Probably improved straight-line tracking of the front tires. I learned long ago in another vehicle that a wider steering tire tread footprint for any given weight on the steering tires tended to add a bit of a "wander" into the steering.

Thanks for all the input, after looking at my spacing between the 225 duals, I'm not sure this is a good idea and I don't want to try out spacers.

Bottom line is I'll use 225's as designed.

j-d wrote:
Research carefully but I looked at this and I think it'll work. The 85 series is a little taller and a little narrower than the 75. Some of us have used 215/85 in place of 225/75. This change gives a slightly taller and slightly narrower tire with same capacity as 225/75. 235/85 will be still taller (changing effective gear ratio). What requires checking are two additional points:
1. Will the Dual Wheel Spacing be adequate?
2. Will your current Rim Width work with an oversize tire?
Remember, going 215/85 from 225/75 is not a major change. Going to 235/85 is.

This is overall good advice. However, not all 85 aspect ratio tires are narrower than all 75 aspect ratio tires. A 235/85 tire is both taller and wider than a 225/75 tire. Clearance between the two dual tires would be the biggest concern here, I believe. If it's inadequate, there do exist spacers to add more clearance. (Clearance with the fender etc. can also be a concern, but usually on motorhomes there's more than plenty.)

In a tire size, the first number is the tread width (in mm). The second size is the aspect ratio—the ratio of the tread width to the sidewall height. The third number is the rim diameter (in inches). It's a rather bizarre combination of metric, dimensionless, and customary measurements.

Note that your speedometer (and odometer) will be off by about 8% if you use the larger tire unless they're somehow recalibrated—I don't know if that's readily doable on the Ford chassis or not. You'd be going about 5 mph faster than indicated at highway speeds.

Research carefully but I looked at this and I think it'll work. The 85 series is a little taller and a little narrower than the 75. Some of us have used 215/85 in place of 225/75. This change gives a slightly taller and slightly narrower tire with same capacity as 225/75. 235/85 will be still taller (changing effective gear ratio). What requires checking are two additional points:
1. Will the Dual Wheel Spacing be adequate?
2. Will your current Rim Width work with an oversize tire?
Remember, going 215/85 from 225/75 is not a major change. Going to 235/85 is.

Is yours on a Ford E450 chassis?