Thinking about 235s

Not willing to leave well enough alone, I was curious about slightly upsizing the tires on my CX-5 Sport and
did some analysis of various wheel-tire combinations.

It turns out that the stock tire/wheel combination on the GT is nearly a quarter inch larger in diameter,
or 100.8 percent of the diameter of the stock tire/wheel combination on Sport and Touring. So that
difference you see on the dealer's lot is not just the larger wheels, it's the tires, too.

I'm thinking the 235/65-17 might be an acceptable upsize over stock for Sport and Touring. It would represent
a 1.8 percent increase in diameter over stock Sport and Touring, but just a 1.0 percent increase in diameter over stock GT.

The slightly taller effective gear ratio might affect acceleration, and the 10mm wider tread might
reduce economy, but I don't think either would be by much.

It's common practice to upsize tires on pickup trucks and SUVs, less so with cars and CUVs. I have seen
what a difference just pushing the wheels out a little over stock made my Passat look like a different
car, and for the better. I'm thinking a 235/65-17 tire on a wheel with 5mm less offset than stock might
be just nice without being too much. That would push the outsides of the tires out about 10mm (5mm for
half of the increase in tire width, plus 5mm for the reduced wheel offset). I could do this with the winter
tire set I need to get. If it's great, then when the summer tires wear out, I'll replace them with 235s, too.
If it isn't so great, then I'll live with it until the winter tires wear out and go back to the stock size all around.

And yes I know wider tread on a winter tire is not standard practice. It's not much wider in this case.

Thoughts?

section w (mm) aspect ratio wheel dia w (inches) total dia pct/225/65/17 pct/225/55/19 comment
225 65 17 8.86 28.52 100.0 99.2 stock (T,S)
225 55 19 8.86 28.74 100.8 100.0 stock (GT)

215 70 17 8.46 28.85 101.2 100.4
235 65 17 9.25 29.03 101.8 101.0
245 65 17 9.65 29.54 103.6 102.8
245 60 17 9.65 28.57 100.2 99.4

225 70 16 8.86 28.40 99.6. 98.8
235 70 16 9.25 28.95 101.5 100.7
245 70 16 9.65 29.50 103.5 102.6

This chart might not transfer with the right spacing to this message format but the information is there.

The percent change in diameter is misleading as the circumference of the tire is what effects revolutions per mile, speedomenter change etc. It is 3.1416 times the change in the diameter so if you up diameter 1.8 percent it will change speedometer, odometer and gearing by 5.7%... Take a look at the different tire sizes on tire rack and under specifications look at the difference in revolutions per mile...

Check out the Photos from Miki69:

http://www.mazdas247.com/forum/show...ot-Wheels-and-Tyres/page3&highlight=235+tyres

Thanks Applauso, you beat me to it

Yes, you'll be perfectly fine with 235 on 7" rim width (also Tiguan has 235 on 7" rim width, really no issues). However, for winter driving I would NOT recommend 235, but keeping 225.That's why I have bought separate 17" rims for winter (225/65/17 Pirelli Scorpion Ice&Snow), while having 235/55/19 for summer.

Cheers,
Miki

GAXIBM said:

The percent change in diameter is misleading as the circumference of the tire is what effects revolutions per mile, speedomenter change etc. It is 3.1416 times the change in the diameter so if you up diameter 1.8 percent it will change speedometer, odometer and gearing by 5.7%... Take a look at the different tire sizes on tire rack and under specifications look at the difference in revolutions per mile...

Click to expand...

Gax, percents is percents. Example:

d=100.0 circumference=d(pi)=314.0
d=101.8 circumference=d(pi)=319.7
319.7/314=1.018

And if you carry this out to revolutions per mile or any other unit, it will still show a change of 1.8 percent between the two diameters.

You were mixing up constant units with percentage points. It is true that if we increase the diameter by one unit, the circumference increases by pi units. But because the formula for circumference is linear (i.e. no exponents) if we change the diameter by x percent, the circumference will also change by x percent, which is why percentages are a good way to evaluate changes to parameters independent of the units involved.

Still, even a one percent increase over stock is a consideration.

Miki, point taken on the winters. Have you noticed any differences from stock with the 235s? Do you have any pictures of the whole car?

Thanks all.

Thanks for the correction. If you use 235, you should consider lowering the aspect ratio to keep the same revolutions per mile.

No difference (nothing rubs if that's what you mean), and no need for lower profile. Speed difference is negligible (100km/h on tacho, while actually you're going 97 km/h, who cares?).

As stock tires are rather mediocre (225/55/r19, Toyo proxes r36) new tires are MUCH better (I have 235/55/R19 Continental for summer) and you certainly feel this, especially when driving and maneuvering at higher speeds.

Also I would never go lower than 55 profile for SUV, personally I think this is the best compromise between sport/comfort drive. Anything lower than 55 would put additional (unnecessary) stress to car's driving components, not to mention potholes, road imperfections ...

For winter, 222/65/r17 is good as I like having more "meat" in tires during winter driving.

Cheers,
Miki

I know this is hard to track but did you notice any difference in gas mileage/ fuel economy? Just noticed you have a diesel, which probably won't be as affected by tire differences as much as a petrol engine would in terms of fuel economy.