4g61t.org

On my summit wagon I am using an F5M22 trans from a 1g na dsm. At 70 mph its taching around 3200 rpm's. If I were to go to a larger rim with shorter tires would this make it tach higher or lower in 5th at 70 mph? I'm thinking the smaller diameter will make it tach up higher but I could be wrong.

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93 Mitsubishi Expo LRV 1.8/manual
95 Eagle Summit DL Coupe 1.5/manual
01 Mitsubishi Mirage ES Sedan 1.8/manual

It totally depends on the overall diameter of the tire. What size tire are you wanting to change to? Also, using a different size tire than what the speedometer is calibrated for(which would be the OE size) will result in the speedometer reading incorrectly. If the new tire size is 5% larger than the OE size then the speedometer will read 5% slower than you are actually going as the speedometer gear is driven by the differential itself.

Silly question but if the new tire is shorter when sitting beside the old one then the overall diameter would have to be less wouldn't it?

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93 Mitsubishi Expo LRV 1.8/manual
95 Eagle Summit DL Coupe 1.5/manual
01 Mitsubishi Mirage ES Sedan 1.8/manual

i tried that before..but when u put it on a rim..stretch it to fit then add air it wasnt the same size I thought it was.... either tire rack..or discount tire has a wheel tire calculator to check the diff sizes.



Steve

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Steve 89 colt 2.3 stroker stock top end. evo3@20 psi 13.489@99.30mph 3/10 2012
On drag radials.auto trans.launching @ 5 psi and no traction thru 2nd.

The tires in question are mounted and inflated. Even though the stockers are 14's and these are 16's the 16's are an inch or so shorter. This makes me think they will spin faster causing shorter gearing. Something I don't want if its already taching 3200 rpm's at 70 mph.

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93 Mitsubishi Expo LRV 1.8/manual
95 Eagle Summit DL Coupe 1.5/manual
01 Mitsubishi Mirage ES Sedan 1.8/manual

Shorter tire equals less circumference, that means more revolutions to travel the same distance as a larger tire, making your speedometer read faster than you are really traveling. You would not see a difference in your tach and speedometer because their relationship has not been changed, only the actual speed of your car would be different. This theory is a good way to beat speeding tickets, put a larger diameter tire on your car after you get a ticket then have it calibrated, it'll show your speedometer was reading the speed limit, but the larger tires were making it go faster than you thought

i tried this on my truck to get better mpg. i went from a 245/60/16 to a 265/60/16 thinking that the taller sidewall would increase the overall tire size, which it did. from my understanding the first number is the tire width and the second number is the % of the width to get how tall your sidewall is. third number is rim size. with the truck it gave me a taller tire but also increased the surface area in contact with the ground, thus more friction. mpg didnt change. lol

Not only will the larger diameter affect the speedometer reading it should also affect mileage. If you calculate the circumference which will equate to a roll out distance you can figure the percentage difference of each size tire. Chances are your odometer will say you went less distance than you actually did.

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91 Talon - was 454 whp/440 ft/lbs, now DD
89 C52A - 4G63T To the crusher
91 C52A - 4G63T Up and Running (AWD swap coming!)

On my Colt I run 195/60x15s to get a taller tire for lower rpm. They aren't good for performance as the sidewall is tall and flexible but I did it for mileage. Yes, the odometer will be off. Just measure the accuracy via mile markers on the hwy to get the ratio. I hand calculate mileage every tank and I have to divide by .9428 to get my actual distance traveled.

I did an experiment on my old fwd Talon. I put 4 donut spare tire rims on it with old VW Beetle size tires, 165/80x15s. Of course it handled like stink but I gained 4mpg just from the tires having less rolling resistance.

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'89 Colt GT w/bigger than stock turbo
'91 Talon AWD w/bigger than stock turbo
'05 Dodge diesel w/bigger than stock turbo