I've got a 2008 Honda Civic and need new front tires but the rear ones still have some tread left. My mechanic said I could get away with different sizes front and back to save money, but I'm not sure if that's actually okay. Would this affect my handling or transmission?
I've seen this cause real problems with how a car tracks and pulls, plus it does mess with your transmission and differential since they're trying to compensate for wheels spinning at different speeds. Instead of mixing sizes, check if any local tire shops have used tires in your size - you'd get a matching set for way cheaper than new ones, and your Civic will handle like it should.
Mismatched tire sizes between axles can mess with your car's handling, traction, and potentially damage your transmission and differential - it's not really a safe money-saving move. Your best bet is replacing all four tires at the same time, or at minimum doing both fronts or both rears together to keep things balanced.
Your mechanic's not giving you great advice here - mixing tire sizes front to back really does mess with how your car handles and can actually strain the transmission and diff over time. Instead of going that route, check if there's a tire shop doing a sale or if you can find a decent set of used tires with matching tread depth on all four wheels. You'll spend maybe a bit more upfront but you're saving yourself from potential repairs that'll cost way more down the line, and your Civic will feel way more stable on the road.
Running different tire sizes front and back throws off your speedometer and forces your transmission to work harder trying to match wheel speeds - it's a false economy that'll cost you more down the road. If budget's tight, get both front and rear replaced with the same size (your Civic manual lists the right spec), or rotate your good rears to the front and replace just those, then do the back ones next month. Either way you'll actually save money by avoiding transmission work later.
Going with mismatched sizes is a genuinely bad idea, and your mechanic's reasoning doesn't add up - you're not actually saving much money if you end up replacing the drivetrain components early. I had a friend try this on his older car to stretch his budget, and within a few months his transmission started shifting weird because the front and rear wheels were effectively rolling at different rates, making the system work overtime to compensate. Your transmission and differential don't handle that kind of mismatch well, and your car will also pull to one side and feel twitchy in corners. Just bite the bullet and replace all four tires at the same time, or at minimum get matching pairs for each axle.
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