Mud Flaps--Initial Impressions

I installed my mud flaps, purchased from ToyotaTown (a PriusChat Sponsorer) 2 days ago and already am able to give some opinions/observations that I think might interest others considering buying these.

Appearance: They look nice, quite OEM, non-intrusive and don't signficiantly break up the natural lines. It would be nice if they were smooth/convex on both sides, but it's not a big issue and the cost differential is probably signficant.

Effectiveness: Not bad. They definately reduce/eliminate the bad spray that occurs right behind the wheel well area. I'd hoped they would stop the spray from hitting the rear-view mirrors, but they don't, that comes off much higher than the mud guards go.

Affect on Mileage: Unfortunately I think this is going to be more significant that was previously reported. I don't have enough miles to say exactly what the percentage or absolute mileage impact will be, but I have seen a DEFINATE downturn in my mileage over the past 2 days that is not attributable to any change in weather, driving habits, route, weight carried or any other changes in the car. At 370 miles into the tank I showed a 58.3mpg average for the tank--I had not dipped below 58.0 at any time during that period. Since adding the mud flaps I've seen a steady slow decline in the displayed average to 57.7 at 425 miles. So, over a 55 mile stretch of driving my mileage has been reduced by over 1/2 mpg. Over a tank of gas I have to think it's going to be even more.

Conclusions: Draw your own, and at $45 for a set of these plus an hour of your time to install them it's worth buying them and making up your own mind.

For me, I'm leaving them on, at least for now. If I find that I can't get my mileage up to where I think I can/should be and I'm not satisfied with the job they're doing I'll take them back off of the car (should be very easy and take maybe 15 min to do that). I have to say that I'm concerned about the reduced gas mileage, esp. after becoming so optimistic over the past 1000 miles of driving that I could consistantly get in the 55-58mpg range. I don't mean to discourage anyone else from getting the flaps, their benefits probably outweigh the loss of performance, but I wanted to make folks aware of that impact.

 

Just to add a little update, the mileage hit is real and it's going to be pretty significant. I've dropped from 58.3mpg @ 360miles in the tank to 57.4 at 480 miles into the tank...and I've been driving very carefully to keep it that high!

Again, I haven't decided if that will be important enought to me to take the flaps off yet, I'll probably give it a couple more tanks before I do decide, but if one of your 'big things' is squeezing every possible mile you can out of a gallon of gas then be aware that this will affect that mileage. And that makes sense, let's face it, if those little grooves in the roof and the rings on the wheels affect aerodynamics then adding 4 1 square foot air scoops to the car will definately have an impact.

FWIW on a more techy note, I've found it much harder to 'dead band' with the flaps, I can't get into a no-arrows coast and sustain it nearly as long as I could before. The increased drag forces me to engage the ICE again much sooner than I had to before.

 

Thanks for the great comments. The flaps are, for the time being staying on. I like the look, the decreased spray, etc. I'm not 100% convinced that they'll really ever save me anything when it comes to rust and such (I think those body panels are plastic anyway), but I do see the positive affect of the panels.

I just wanted to give a little equal time to the aerodynamic/fuel economy impact.

I now have almost 6800 miles of driving in on my Prius. I've adjusted and changed my driving style a number of times over the last 6+ months and only over the last 1000-1500 miles have I really gotten a 'feel' for the car. I can feel when I'm in the 'dead-band' even when I'm not on the Energy screen. I can tell when to back off the pedal pressure and feather into stealth. I know this probably sounds like BS voodoo stuff to some of ya (probably related to that Prius Cult we've been involved in), but I promise, you're going to find it as well when you've gotten enough miles in.

Anyway, much of my sense that the mud-flaps are having an impact comes from a change in the response I'm getting from the car in those very subtle situations where without flaps dead-banding would work, but with them there's too much drag to sustain the speed. I drive, as most people do, the exact same route over and over. I know when to back off the gas and when I can feather into stealth, those parameters changed with the flaps...I can feel it and see it on the speedometer and mpg read out for individual sections that I drive.

Still, I'm gonna have to see. I filled this tank today at 505 miles with a 57.1computer mpg. I'd expected more like 550 miles at 58.4. But rain last night and today then a trip with all 4.5 family members (my wife is 28 weeks pregnant) today in the rain dropped me from 57.4-57.1 in just 20 miles and gas prices are on the rise but hadn't hit my local Wal-mart yet so I thought it best to fill up--the add fuel had been flashing for about 16 miles.

If I can continue to get 57mpg, with flaps, and my normal driving routine, they'll stay on forever. But, if this tank drops me down to the low 50s, even sub-55 range with good driving weather I really will consider removal--at least as a trial.

Someone asked if my design was different than their Canadian flaps. I doubt it, these say "made in Canada" on them, and I bought them from ToyotaTown--a Canadian dealer. They do not have a particularly pronouced profile, but they're still scooped and stick out behind--they obviously catch a lot of air that would otherwise slide by--I know that b/c they catch the much and spray that would otherwise slide by/stick onto the side of my car!