changing the aspect ratio on tires

as you may have already guessed by now, I just got a nice set of VERY gently used Cooper CS4 Touring Tires with less than 100 miles on them for the Low Low price of $296 (if I had bought these tires brand new at Sears, they would have cost me a WALLET SHATTERING $506 mounted, balanced and out the door with tax and all the fees.) the only problem is, the size I got is 185/70/R14, and the Stock Size for our cars is 185/60/R14. I already know my speedo is gonna be 6% too slow, but are there any other problems I should be aware of from changing the aspect ratio by two sizes?

the thing i can say is your tire make up will determine more issues than the size difference. Obvious size difference issues are rubbing, speedo and odometer being off, etc. But when going up to a 70 series tire. I think the biggest "fear" i would have is performance and sidewall buckling under a hard turn. Now if you have the exact same type of tire and same width, but the 10% increase in sidewall (almost 19mm radius or 1 1/2" diameter) than your car can break loose around a bend more easily.

im sure this is some sort of complicated formula for it. But since you changed brands. the side wall composition etc will change that effect anyhow.

Just my $.02: I have an old (1992) sentra that came with 155/80/13. I upsized to 185/80/13 and noticed a few things. 1.) Most stock speedometers are a bit "optimistic" on reported speed. You can verify this on any flat highway with a stopwatch, or use a GPS that you trust. 2.) Sidewall flex was no more noticeable than any other tire if you drive normally. If you spend your days doing slalom maneuvers, just step up to a 15" and be done with it. 3.) Highway cruise rpm will drop (roughly) the same percentage as tire size increased. This could be good and bad, depending on shiftpoints, driving style, terrain, city/hwy...... I'd say "run 'em!".

dustin you went up in size with width, not jut sidewall. there is a fair difference between the two.

i didnt even like how the car would feel loose at stock height with stock tires but then again, i dont drive like many on here.

I just wanted to add that I have used 185/70/14 on the front for several years, and it definitely does affect the cornering, a bit extra ground clearance but no issues with rubbing ever. On a funny note the over optimistic speedo on our car (pretty sure i read around 6-7% stock) with these tires actually reads very close to correct with the larger tire :) Of course the odometer is another story. For some reason I really like this larger tire in the winter when acceleration isn't a priority, it just pulls a little softer in the rev range and seems a bit better for control. I also believe that it improves fuel economy for ppl who do hwy runs to work, but that can be argued, and by improvement I mean like 0.5 - 1.5 mpg, but it adds up.

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Originally Posted by northguest47

I just wanted to add that I have used 185/70/14 on the front for several years, and it definitely does affect the cornering, a bit extra ground clearance but no issues with rubbing ever. On a funny note the over optimistic speedo on our car (pretty sure i read around 6-7% stock) with these tires actually reads very close to correct with the larger tire :) Of course the odometer is another story. For some reason I really like this larger tire in the winter when acceleration isn't a priority, it just pulls a little softer in the rev range and seems a bit better for control. I also believe that it improves fuel economy for ppl who do hwy runs to work, but that can be argued, and by improvement I mean like 0.5 - 1.5 mpg, but it adds up.

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+1 on that. CS4 is a good tire IMHO.

I just got a set of KR21 in stock size. so far, so good.