Tire choice 215/40/17 or 215/45/17?

[Losiracer2]

I have an opportunity to get some 215/40/17s for a pretty good price but I'm worried that might be too thin of a sidewall for our CB7s. Right now I've got the 215/45/17 size on there but they kinda rub in back during hard cornering, even with my fenders slightly rolled. Offset of my 17s is +42

Anyone running the 40 series? your thoughts about it would be great.

[F20A CB7]

You will b fine man! 215 40s won't b to thin.

If it was 205 id say think for me.

[CB7H22Los]

i actually have 215/45/17 on right now with no rubbing at all..but im thinking of going to 40 if i can find a good set

[Losiracer2]

ok cool. now the only problem I see now is rubbing my Legend lip more when going up my driveway haha. But I guess I could rail my GC coilovers a bit in front to clear.

[owequitit]

I have an opportunity to get some 215/40/17s for a pretty good price but I'm worried that might be too thin of a sidewall for our CB7s. Right now I've got the 215/45/17 size on there but they kinda rub in back during hard cornering, even with my fenders slightly rolled. Offset of my 17s is +42

Anyone running the 40 series? your thoughts about it would be great.

If you actually do the math, 215/40-17 is the closest to ideal size for our car.

[Losiracer2]

If you actually do the math, 215/40-17 is the closest to ideal size for our car.

well I used the miata tire calc found online and the 215/45/17 was i think 1.8% too slow and the 215/40/17 was 1.7% too fast, so regardless, they'd both be off by like 1mph. 205/45/17 was actually the best tire size to keep the speedo calibrated most correctly

[owequitit]

well I used the miata tire calc found online and the 215/45/17 was i think 1.8% too slow and the 215/40/17 was 1.7% too fast, so regardless, they'd both be off by like 1mph. 205/45/17 was actually the best tire size to keep the speedo calibrated most correctly

I did mine by hand. The overall diameter on 215/40-17 is almost identical to 195/65 R15. 215/45R-17 is notably larger.

Did you think I would be making it up?

[Losiracer2]

I did mine by hand. The overall diameter on 215/40-17 is almost identical to 195/65 R15. 215/45R-17 is notably larger.

Did you think I would be making it up?

195mm(.65)x2 / 25.4mm + 15" = 24.98" dia.

215mm(.40)x2 / 25.4mm + 17" = 23.77" dia.

idk, quite a bit off from identical to me

a 225/45/17 would be closer to the 195/65

225mm(.45) x 2 / 25.4mm + 17" = 24.97" dia.

[uslspct]

The OE size tire should be about 24.2" Which are equal to:
185/70-14
195/60-15
205/50-16
205/45-17

owequitit, the numbers you mentioned don't add up. 215/40-17 is more than an inch smaller than 196/65-15, like he shows above. Maybe you typed the wrong thing.

These 2 sizes you Losiracer2, mentioned, are equally off from a stock size. So, who cares. Buy the 45 series unless your state has great roads. Pretty stupid to do a 40 where I live. Also getting that bigger tire will full your wheel wells and raise you off the ground that little bit more, if you care. I don't see why they even make a skinny 205 tire for a 17" rim.

[Losiracer2]

yeah...I went to go look at those tires today, 3k miles my ass....2 of them were from 06' and 2 were from 01'. I don't understand why people hide the truth when I'm going to find out anyways. No way in hell I'm going to buy 10 yr old tires.

[owequitit]

195mm(.65)x2 / 25.4mm + 15" = 24.98" dia.

215mm(.40)x2 / 25.4mm + 17" = 23.77" dia.

idk, quite a bit off from identical to me

a 225/45/17 would be closer to the 195/65

225mm(.45) x 2 / 25.4mm + 17" = 24.97" dia.

The problem that you also run into is that tire diameters vary slightly. Did you account for that? And yes, it can be a significant source of error. For instance, my 215/45-17's are quite noticeably larger than the stock 195/65-15's I have sitting in the garage, even though mathematically, that should not be the case. It is also why you get different revs per mile from different tires (if overall diameter were exactly the same, the revs per mile would not vary).

215(.45) x 2 /25.4mm + 17" = 24.61"

Don't go changing the variables. 225 never entered it.

While mathematically 225 or 215/45-17 would actually be the closest, you would actually need to get the actual figures on your spefic tire and go from there. You would be surprised at the variance. In my case, the several tires I compared, put 215/40 closest to what I needed, but it was uncommon and I liked the look of 215/45 better.

Also keep in mind that it is measured by the factory on a specified wheel width. Vary from that, and you are also changing the values slightly.

Finally, as long as you remain within 3-5% of your original size (which ALL three tires do) you will not throw your speedo calibration off enough to make a significant difference, as most have a variance of ~3-5% anyway.

[quote=uslspct]The numbers add up fine. The difference between a 195/65-15 tire (the stock EX size) versus the 215

[Prez808]

195/60-15 is the correct stock size for the ex wheel.

[owequitit]

195/60-15 is the correct stock size for the ex wheel.

Even still. My 195/65-15 are smaller than my 215/45-17's, which means that 195/60 would be even smaller.