By on January 10, 2017

2016 Lincoln MKT painted wheel, Image: Lincolnsouthcoast.com

Austin writes:

Sajeev,

So, a while ago I asked Bark and community what to replace my broken Audi‎ wagon with. I ended up purchasing a 2010 Lincoln MKT Ecoboost. So far, it has meet all my needs and — more importantly — my expectations, with one minor but irritating issue. At speeds around 70 mph and up, I notice a constant “twitch” in the steering on some highway surfaces — a sensation of vibrating left and right just enough to be noticeable, but not enough to change the actual t‎rajectory of the car.

Thinking that it was an alignment issue, I ran to discount tire (free rotations and balance because of my previous purchase history), where it was pointed out to me that the aftermarket wheels the car came with (future note: check the width and not just the diameter) did not align with what their computer system said I should have.

A stock tire on an Ecoboost MKT is 255/45-20 Goodyear Eagle RS-A. The tires on my car are 235/60-18 Michelin Premier LTX. The gentleman explained to me that my tires were basically an inch narrower than ‎stock, and while the ratio for the tire and the wheel was correct, because of the prodigious power output of a front-wheel-drive Ecoboosted car, my front tire might be “slipping” on some surfaces at higher speeds due to smaller tire contact patches. It’s not enough to get the AWD system to kick in but enough to get the vibration sensation when driving at higher speeds.

He said the best solution would be to get wider wheels and tires. Now, I consider myself somewhat knowledgeable on the benefits of higher-profile tires in terms of ride, snow traction, and towing performance, I have no experience with tire width. The cost of a wheels and tires swap-out for a stock setup is about $2,000. Thus, I would like to know what the community and yourself thinks before I start looking for ways to part with a sum of money that, in theory, could get me into old but reliable Civic or Camry.

Sajeev answers:

“The gentleman explained…because of the prodigious output of a front wheel drive Ecoboosted car, at higher speeds because of the smaller tire contact patches, my front tire might be “slipping” on some surfaces.”

Never. Double the power and it’ll still hook up at highway speeds at throttle inputs soft enough to not activate the power take-off unit. Your vibration is related to aftermarket wheel quality, not throttle input.

The circumference difference is only 0.3 percent (91.2 inches vs. 91.4 inches), so the tire choice is valid. My relationship with aftermarket wheels is still love/hate, since my Fox-body Cougar is daily driven: the reproduction Cobra wheels vibrate at around 40-50 mph on certain paved surfaces, even after switching to factory lug nuts.

I’m sick of it, and I feel your pain. We both need higher-quality aftermarket, or factory, Ford wheels. I should grab some 15×7-inch factory turbine wheels and you should consider a set of “take-off” hoops from an MKT, MKX, or perhaps that newfangled Town Car thingy.

[Image: Lincolnsouthcoast.com]

Send your queries to [email protected]com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice. 

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83 Comments on “Piston Slap: To Love, To Hate Aftermarket Rimz (Part III)...”


  • avatar
    Gardiner Westbound

    Could one or more of the tires be slightly out of round? Regardless, Austin should look to the retailer to right his problem.

    For what its worth, I have had no difficulty with aftermarket wheels sourced from TireRack.

    • 0 avatar
      AVT

      Had I bought a set of aftermarket wheels after I bought the car, I would completely agree with you. Unfortunately, they came with the vehicle at the time of purchase. I only have the records for how much they cost along with the tires and the mounting date.

      • 0 avatar
        tedward

        It could just as easily be the tires. It sounds like a manufacturing defect or damage since installation. There’s simply no way that going 10mm wider or narrower has any effect. Manufacturers routinely bridge much wider width differences on different trim levels of the same model, and neither of your sizes are narrow.

        I had a vibration that was crazy annoying on a set of aftermarket wheels and tires. It eventually went away and it was either the hub centering rings or the tires themselves that caused it (replaced both at the same time). It’s too expensive with tires to thoroughly trouble shoot, just replace the hardware and, if that fails, move them around the car until you isolate the problem to a corner. Then go hard on that one wheel with diagnosis and replacement therapy. It’s the least satisfying of repair processes in my opinion.

        • 0 avatar
          AVT

          Well according to Lincoln, the non ecoboosted models come stock with 19 inch 245 series tires. Heck, my A6 Avant I had before this had 245 series tires all around. So maybe the current set of tires I have are really pushing the limits of the manufacturers specifications.

    • 0 avatar
      redmondjp

      Aftermarket wheels, likely with a hub centerbore that is larger than the OEM hub. This means that you are relying only upon the lug nuts to perfectly center the wheel onto the hub. This often causes the wheel to be slightly off-center, and bingo, there is your slight vibration (which of course the tire shop can’t fix).

      Try switching to OEM wheels that have the proper centerbore diameter. You can use the plastic hub adapter rings on aftermarket wheels, but those have to be perfectly-sized or they are useless.

      • 0 avatar
        never_follow

        This is quite likely the correct answer. Hubcentric wheels need to fit correctly on the hub. If the wheels balanced out and have no visible damage, there’s little to no reason for any issue.

        Confirm by swapping front to back, and then you can be 100% sure.

  • avatar
    notapreppie

    I don’t know what your tire guy does for balance but if it isn’t a “road force” balance, it’s crap.

    It’s possible that the wheel is out of round or the tire (or both).

    I have a buddy that lets me use his tire mounting and balancing equipment. They make it so stupidly easy to use that even a pedantic computer-nerd-turned-chemist can solo on the machines after the first tire.

    It’s also possible that the bolt pattern on the wheel is just slightly off. I’ve seen cases where people have tried to use 5×114 wheel on 5×114.3 hubs (or something like that, I forget the exact numbers) and the wheels never get centered properly even with the correct hub rings and wobble lugs.

    I’ve had aftermarket wheels on 5 of my last 6 cars and the only problems I’ve ever had with them were my ignorance (or occasional downright stupidity).

    • 0 avatar
      AVT

      The place I go to for tire rotations does use road force balance setup for all wheels. I looked at all the tires myself and did not see any issues, uneven wear, or obvious defects. Since the tires are new and still under warranty, the gentleman said he could have their michelien representative look at it when he comes buy next.

      • 0 avatar
        notapreppie

        I suppose it’s possible but my mechanic friends tell me that Michelins are almost never out-of-round.

        I saw you said the problem remains even after rotating the tires. I wonder if you’ve got another suspension component out of whack…

  • avatar
    iNeon

    Every car I’ve ever owned has been ‘twitchy’ with a just-perceptible feeling of oscillation at cruising speed. None has ever been as smooth as I expected them to be.

    None of them have ever been as quiet as I expected, and they’ve all rattled and buzzed at certain speeds/conditions.

    It’s been a half dozen Chryslers, a half dozen MBs, trucks, a Volvo– another half dozen old Beetles.

    You’re going to have a heck of a time getting a straight answer from any technician– as I feel this is a perception issue, not a mechanical one. The car’s likely to be within specs and no one is going to want to chase demons only you can ‘see’ :(

  • avatar
    MrGrieves

    It sounds like the problem he is describing is known as “Tram-Lining” and going to wider tires will only make it worse. It’s dependent on tire width, road surface smoothness and condition, tread pattern… etc. Tends to be much worse on grooved highways at elevated speeds because the tread grabs the pavement grooves and points the front wheels from side to side as you are driving.

    I also am a big advocate of road force balancing but most places don’t do it.

    • 0 avatar
      AVT

      Most of the highways in northern minnesota are grooved. I especially notice it when I’m going from the Twin Cities towards Alexandria. That’s a nasty bit of road in the winter time. Though I have noticed now with winter present in full force, the issue does not seem to occure as much. Though I thought that could be the change in tire pressure going from 15 degrees to negative 18. Not inluding wind chill.

    • 0 avatar
      Flipper35

      This. We had Eagle LS tires with a very square shoulder and they did it terrible but the new Comp TA don’t do it at all.

      It was especially bad when passing. Crossing the centerline under full throttle made for a handful as you passed over the grooves.

      • 0 avatar
        AVT

        Would this be worse on a heavier vehicle like mine, 5000 ibs with me in it, on skinner tires, meaning more “static” pressure on each tire patch, thus more likely to dig into the pavement, especially with michelins and their deep treads.

        • 0 avatar
          Flipper35

          I am not sure how much weight plays into it. I have a 2000# car that did it terribly with the Goodyear Eagle bias ply racing tires and the 3200# car was worse with the LS radial tires. Track width may play a part in it compared to the ruts in the road since it is the read trying to climb up the ruts.

          When it happens, is the road rutted more than the road when it doesn’t happen? If it does it on perfectly flat roads it is not a tramline issue.

    • 0 avatar
      nvinen

      I had a set of Dunlop Sportmax tyres that tramlined like a tetchy female dog. They had noticeably curved sidewalls. Replaced them with Michelin Pilot Supersports with a much more square profile – problem totally solved and a LOT more grip, especially on wet roads.

  • avatar
    jimmyy

    Buy a set of stock wheels and put them back on the car.

    Try to sell the aftermarket wheels to someone on craigslist.

    • 0 avatar
      spookiness

      This is the correct answer. For an MKT you can probably use pull-offs from any number of plentiful cars at the local u-pick-it recycled parts garden.

      • 0 avatar
        OldManPants

        Here’s what I’d try for, maybe sans the red stripe:

        allfordmustangs.com/wordpress/wp-content/uploads/2016/05/dogdish-01.jpg

      • 0 avatar
        28-Cars-Later

        I seem to recall a difference between FWD and RWD wheel sets regardless of bolt pattern (maybe I have been misinformed all these years?). So you would need Ford FWD if I am not mistaken (as opposed to any random Ford bolt pattern).

        • 0 avatar
          Adam Tonge

          previous gen MKX, MKS, Flex, Expo, MkT, or Edge are the best bets.

          I am currently looking for Explorer Interceptor wheels. If I can get a set for $600, I’m going to pull the trigger.

        • 0 avatar
          AVT

          I believe that would only apply in cases of staggered tire size, skinny ones up front and fatter ones at the rear for most sport sport cars. Lincoln MKT’s have the same tire size all around.

        • 0 avatar
          Scoutdude

          Yes the offset is important and virtually all FWD based vehicles have a high offset while many RWD vehicles have zero or low offset but not all, For example 2005+ Mustangs and 2003+ Panthers have high offset that is the same or greater than some FWD vehicles.

  • avatar
    PRNDLOL

    Have the wheels been rotated and this issue still occurs? I would first rule out a problem with the front pair of rims or tires by moving them to the back if they haven’t been already.

  • avatar
    Truckducken

    I think the correct answer is a set of 24″ spinners. But seriously, your first step is what PRND said. Lotta other good advices above too, depending on what step 1 reveals.

    • 0 avatar
      AVT

      I think the 24’s would look better on my girlfriends 2012 Jaguar XJ than my Lincoln. Of course, when I’m getting the rare chance to drive that animal, things like ride quality and tire noise don’t seem to bother me as much as constantly looking in the mirror for cops.

  • avatar
    Adam Tonge

    Sajeev is right. Get some MKX/MKS/MKT 18″ take offs. As a fellow MkT owner, I get wanting to drop the wheel size. You are basically stuck with the Goodyear RS-A or Hankook Optimo with the 20 inch blades. There are other options, but those are, by far, the most common. The RS-As seem to last forever though.

    • 0 avatar
      AVT

      Thanks for the advice. PTU was checked out at time of purchase and is covered under warranty.

      • 0 avatar
        Adam Tonge

        It could be other things. I don’t think the tire width should be an issue though. I’ve run skinnier winter tires/wheels on my last MkT, also a 2010, and didn’t have an issue.

        I don’t know if your vehicle is part of the power steering recall. I don’t think it is, but I’d check through TSBs. Look on Flex forums, because there are fourteen other MkT owners.

        • 0 avatar
          AVT

          I’ll call the dealer today and ask. It should be fixed at no cost to me as that should have been resolved at time of purchase according to the documentation I have. It stated all recalls and relevant tsbs had been performed.

          • 0 avatar
            Adam Tonge

            They probably were. But I’ll give you an example of an issue I had:

            Our 2013 MkT had the power steering recall already performed. However, sometimes instead of being reprogrammed, the whole EPS module needs to be replaced. They always do the flash first. It could be something like that, or it could also be something that the dealer wasn’t made aware of.

        • 0 avatar
          Flipper35

          I never thought of that, but we rented an Elantra when visiting family at Christmas and at 60mph or more you could not hold it on center. It felt like there was a cam or catch (or a toggle switch spring ball) on center and you could go to one side or the other but not on center. At low speeds the rack felt smooth so it had to be in the programming for the power steering.

          Had that been a car I purchased it would have gone back until fixed or refunded.

    • 0 avatar
      OldManPants

      What does “take off” mean in wheel context?

      OEM wheels taken off their original vehicle?

      • 0 avatar
        AVT

        Stock tires off another vehicle that is the same or based on the same platform.

      • 0 avatar
        28-Cars-Later

        Correct, urban folk buy new[ish] cars and then drive them to the rimz shop for new wheelz. The factory wheels are take offs.

      • 0 avatar
        OldManPants

        Thanks, both.

        “urban folk”

        I don’t think metals can transfer cooties. I’d buy ’em.

        Wouldn’t buy seats, though.

        • 0 avatar
          28-Cars-Later

          According to the US branch of the Cooties Resource Council (USCRC), cooties can live on metal surfaces for up to 72 hours.

          • 0 avatar
            OldManPants

            I believe in bleach, always have plenty around. Flush the half-basement-perimeter drain line on my furnace’s condensate pump with it.

            Bleach IS civilization.

          • 0 avatar
            Adam Tonge

            Gotta bleach that condensate pump. I have a reminder on my phone.

          • 0 avatar
            30-mile fetch

            “Bleach IS civilization”

            This is truth and has been for some time. How this has escaped historians I do not know, but there was a Greek god named Hypochloripides.

      • 0 avatar
        Scoutdude

        Yes you will see wheels and wheel + tire packages marketed as NTO or new take offs which were taken off of brand new cars. Either because the dealer put the aftermarket units on or the new buyer went straight to the tire store and put on crappy aftermarket wheels and cheap tires. I recently picked up some 2016 F250 NTO’s for my 06 F250 for less than the tires alone.

    • 0 avatar
      Corey Lewis

      The RS-A is an awful tire for noise and ride quality, and I wouldn’t wish them on anyone. They also tend to follow grooves in the road as you go along.

  • avatar
    cgjeep

    Might not be the tire/wheel combo at all. Could be an axle or CV joint starting to go bad. The previous owner was probably a car guy, hence wheel/tire change and car guys (or gals) tend to be harder on cars.

  • avatar
    Adam Tonge

    Has the PTU been cracked open or replaced yet?

  • avatar
    dougjp

    never been mentioned yet – Check to see if there has been a TSB of any kind about the power steering on this car.

    • 0 avatar
      Adam Tonge

      There was a recall but it doesn’t cover 2010MY. There is probably some sort of TSB though. Here’s the problem: with the aftermarket rims, the dealer is going to give him a hassle about any TSB.

      • 0 avatar
        AVT

        Good point, but the car came equipped with the aftermarket tires at time of purchase. Thus if they knew that the rims could be causing an issue they have to potentially warranty later, you’d think they change them out for stock setup.

        • 0 avatar
          Adam Tonge

          I think the previous owner probably added them because he/she was running winter tires and didn’t want to spend $300/tire on 20″ winter rubber. Or they just wanted the taller sidewall in Minnesota.

          OR….they didn’t get the tire insurance, [email protected] up a blade or two on a pothole/curb, and then realized that it was cheaper to replace everything with 18s and tires. The OEM wheels cost $800+ from Lincoln.

          I bought the TireCare. We had a rim and tire replaced because they weren’t sealing 100%. Had a really slow leak. But the temp really affected it. I think our bill would have been $1300. I only got the tire care because my wife has the propensity to hit curbs.

          • 0 avatar
            AVT

            My girlfriend has tire care included with her jaguar. So far it’s saved her about 3 grand. 2grand of that on tires that got mangled by our roads (though the rears were probably more my fault that mother natures). The other grand on 2 bent rims, one of which started to rust shortly after. Minnesota is not a nice place for rims and tires given out rough roads and salt and temperature swings.

  • avatar
    energetik9

    This is not my area of expertise, but reading the comments, is it worth it to go to a different shop to see what they say about the issue? A second opinion?

  • avatar
    tommytipover

    OMG. The first clue is the Tire Guy is high on exhaust fumes. That is your sign to stop taking your car there. Find somebody else to look at it. It may very well be the wheels, but for God’s sake it isn’t because they are breaking loose at highway speed.

  • avatar
    pwrwrench

    I am in agreement with those that diagnose this as a tire/road surface issue. All vehicles will ‘twitch’ in some degree on certain pavements, grooved/seamed surfaces being the worst.
    A possible improvement for the symptom would be different tires, but that could be an expensive job to keep buying tires searching for a brand/type that was the best.
    Another possibility is that the OEM wheels and tires were replaced because of damage due to hitting something like a curb. This can cause damage to suspension, steering and sub-frames etc that may not be easy to find. If the wheel alignment has been found correct that should have found those problems.
    Bent or out of round wheels and hubs, or unbalanced tires, or tires with loose belts, out of round or other problems, will cause vibrations. This will usually be speed related, happening at some speeds and not others or getting worse at higher speed.

  • avatar
    30-mile fetch

    Interesting post. Considering aftermarket wheels from Tire Rack for our Altima so we don’t have to keep paying the tire shop to mount and balance twice a year when we swap out the snow tires, and this concerns me a bit. It’s hard to want to spend the extra on OEM wheels for a 5-year old basic midsizer.

    • 0 avatar
      JMII

      Hit up Craigslist or the local salvage yard. OEM wheels are easy to come by as the “cool” kids go aftermarket leaving plenty of OEM take-offs collecting dust. Also check various years and models of your vehicle. Bolt patterns and sizes rarely change so you should have plenty of choices. For example on my ’03 Nissan Z I am running ’08 rims which are wider. Then on top of that I put even wider, sticker rubber since I track my car. For ABS and traction control to work properly you need to maintain the correct height and ratio (I’ve got RWD thus a staggered setup) but beyond that you have tons of options including different offsets. Good aftermarket rims should not be a problem either, but the cheap knock off brands aren’t built to those high standards. Another issue is the tire pressure monitors, you’ll need to learn how to reprogram the swapped set so the light on the dash isn’t on all the time.

    • 0 avatar
      AVT

      Ya, problem is the rims are actually the cheap part of the equation in this case. Those 55 series 20inch tires cost more than the set of rims themselves. See even if I replace the rims, I have to get tires for them. When you start doing the math, it comes out to almost 2 grand with tax in minnesota. That’s a lot of dough to spend on a wearable item for a vehicle. If it was my girlfriends jaguar, I have less issue paying that cost for good summer tires, because the performance they provide is worth it. On a 5000 ilb suv with a somewhat squishy suspension, the ability to justify that for me personally is harder to do, especially when it impacts tire noise and ride quality.

    • 0 avatar
      Scoutdude

      Then don’t buy new OE wheels buy used. Wheels don’t wear out per se so find out what other Nissans use the same bolt pattern, offset and pilot diameter and start cruising craigslist, ebay, wrecking yards and the used tire and wheel places. You can usually pick up a good set for less than the cheap steel wheels that the tire store will sell you.

      • 0 avatar
        AVT

        I suppose it would be the time of the year to do it. Plenty of wrecks this year on the road. Heck we had a foot of snow fall today all ready. I’m sure more have been added.

    • 0 avatar
      30-mile fetch

      Great advice, folks, thanks.

  • avatar
    Scoutdude

    As some others have mentioned the tire guy is full of it, the tires aren’t slipping while cruising down the road at a constant speed.

    You do mention that the roads in your area are grooved and some tread patterns do “lock” into those grooves and if the grooves aren’t cut perfectly parallel to the direction of travel it can cause the wiggle problem.

    A broken belt in the tire can be the problem. Yes as others have mentioned that is not a common problem with Michelins but a good impact on a curb or pothole can break a belt on any tire. Someone who knows their stuff can visually spot the problem or just by running their hands around the circumference of the tire however good luck finding someone with that knowledge and ability at your average tire store today. You certainly won’t find that at a big chain stores who employee anyone with a pulse and churn through employees. Rotating the tires may cause it to go away and if it does then one of the ones that was on the front is not true and round.

    It is possible that it is a wheel problem as many aftermarket wheels are not the exact right dimensions for the vehicle. You often find them selling wheels that aren’t hub centric for vehicles that are designed for hub centric wheels. You also see offsets that are close but not exact and the same thing for bolt pattern. Look for any marking on the wheels themselves and find out the exact specs and compare those to the factory specs.

    But yeah find a new tire store.

    • 0 avatar
      AVT

      Thanks for the advice. I will be hitting up 2 other shops this week to see what their take on the issue is. As for the grooves in our roads aligning with the direction of travel, their usually is noticeable variation in regards of them remaining strait.

    • 0 avatar
      Fordson

      The more I read of this thread the more convinced I am that the wheels are lug-centric on a car that wants hub-centric, or that these wheels are hub-centric but they don’t have any or do have incorrect hub rings.

      If you determine that it needs rings, get the aluminum ones and not the plastic ones. I think Discount Tire Direct sells nice aluminum ones.

  • avatar
    jpolicke

    I am assuming that you’ve already done the switching from front to back to see if you can isolate the problem.

    It could be the tires. We had Pirellis on our Touareg that were great at first; at 30,000 miles they developed a vibration that could not be balanced away. They were replaced with half their tread left because they became intolerable.

  • avatar
    APaGttH

    …“The gentleman explained…because of the prodigious output of a front wheel drive Ecoboosted car, at higher speeds because of the smaller tire contact patches, my front tire might be “slipping” on some surfaces.”…

    Wut der furk?!?!

  • avatar
    MikeP20

    I would suggest checking the runout of your front hubs/ wheelbearings with a dial indicator. Check both fronts with the brake rotor on and off. Rust under a brake disc can push it out of plane enough you could feel it at higher speed. Remove the rust and paint the hub face with antisieze before reassembly. Being an older car it may not have the original rotors and the center flange of one could have been manufactured unlevel/out of spec and a little excessive runout at the flange face telegraphed over the radial distance to the tread could be enough to feel/shake at higher speeds.

    Also does shifting down a gear or 2 at 70mph+ speed make it go away ?

    A tall top gear combined with a lugging engine and older/worn engine mounts can cause funny and hard to find shakes/shimmys. I have found “luxury” cushy/ quiet engine mounts fail/wear out much quicker than normal mounts.

  • avatar
    carlisimo

    Isn’t the most likely problem simply a bent wheel or two? Happens all the time, stock or aftermarket (though more so with cheaper wheels).

  • avatar
    rpn453

    “The gentleman explained to me that my tires were basically an inch narrower than ‎stock, and while the ratio for the tire and the wheel was correct, because of the prodigious power output of a front-wheel-drive Ecoboosted car, my front tire might be “slipping” on some surfaces at higher speeds due to smaller tire contact patches.”

    Ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha!

    Yes, I’m sure the 30 hp required to run at 70 mph is overwhelming the tires.

    Find a new tire shop. This one is completely clueless.

    Some possibilities:
    – The wheels are not hubcentric and are not perfectly centered on the hub. Non-hubcentric wheels need to be installed very carefully, and even then could be a little off. Get some centering rings or different wheels if this is the case.
    – A tire is defective, damaged, or flat-spotted.
    – A tire is poorly balanced.
    – A rim is bent.

    I’d be swapping the wheels around to different positions to see if I could narrow down the possibilities and hopefully isolate the problem wheel.

  • avatar
    jthorner

    I had an America’s Tire counter person try to sell me aluminum wheels for our daughters’ steel wheeled Hyundai Sonata as a way to improve fuel economy. While there might be some theoretical gains from a slight reduction in rotating mass, I don’t think anyone has ever measured it in the real world. Said counter dude also knew nothing about rolling resistance of tires, which can have a measurable impact on fuel economy.

    Sadly, many of the people working at parts counters, tire dealers and other repair shops either don’t know what they are talking about or are just saying anything in hopes of making a sale.

    That said, I generally hate aftermarket rims for a host of reasons. Unless you are buying top-of-the-line stuff they are often not designed and built to the standards of OEM parts.

    • 0 avatar
      Scoutdude

      Lighter wheels will absolutely improve fuel economy, the old racer’s rule of thumb is that every 1 lb of rotating mass you remove is roughly equivalent to removing 4 lbs of not rotating weight. Breaking will also be improved with the lighter weight. However the improvement would be so small that it amounts to a rounding error or the normal variation from tank full to tank full caused by variances in traffic, weather and vehicle load. Switching to, or from LRR tires on the other hand can have a repeatable, measurable, statistically significant effect on MPG.

      • 0 avatar
        rpn453

        That might be a rule of thumb for the effect of unsprung weight on the suspension.

        In terms of rotating mass, a solid disc has an equivalent mass factor of 1.5, and the factor is 2 for a thin ring. So an automotive wheel/tire combination would have to fall somewhere in there.

        Tire choice can indeed have a much greater effect than wheel choice, unless you’re dramatically changing the wheel mass. With tires, tread mass is the biggest factor when it comes to rolling resistance.

  • avatar

    Sajeev is spot on and the tire counter guy is way off base. Your tire sizes are very close and even closer than a lot of winter setups that people run. My first hunch is that the aftermarket wheels may have a bigger center bore and if you are not running centering rings then one may be slightly off center on the hub. I would check that first and order some rings if none are installed.

    The next issue is the quality of the aftermarket wheels. They may not be of equal weight or equally balanced. Like Sajeev says, the easiest thing to do would be to swap to some 18 OEM wheels from another Lincoln.

    The original 20 wheels on your MKT were 20×8 inches with 39 offset

    The closest match in 18 is a 2nd gen MKX wheel which is 18×8 with 40 offset

    Here what specs look like when switch to the MKX wheel and transferring over your current tires:

    Spec | MKT 20 | MKX 18
    Diameter 737.5mm 739.2mm
    Circumference 2316.9mm 2322.3mm
    Poke 62.6mm 61.6mm
    Inset 140.6mm 141.6mm
    Speedo error 0% -0.23%
    Reading at 30mph 30mph 29.93mph
    Reading at 60mph 60mph 59.86mph
    Ride height gain 0mm 0.85mm
    Arch gap loss 0mm 0.85mm

    As you can see, the offset and size of the MKX wheel is almost a perfect match and your current tire is only slightly wider than the stock MKX tire so it should fit without issue. If you need to swap tires then I would recommend going for the 245/60-18 tire that is found on the MKX as that will bring you even closer as far as speedo match.

    Diagram: https://goo.gl/YGpDBb


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