MF Review: M7 Under Strut System

Could it be possible that the R50/R53 MINI coupe, a car with twice the structual rigidity of the current BMW M3, could use some further structural reinforcment? As anyone who’s pushed the car hard on the track can tell you, it feels incredibly solid and stable in corners with no obvious need for an upgrade in this area.

However the aftermarket MINI tuning company M7 felt that an improvement could indeed be possible. So they designed a system of understruts that reinforce the chasis by spaning the width of the car upfront and near the center.

On the face of it this system would seem ideal for the MINI convertible. As with any car without a roof, the MINI convertible is decidedly less stiff than it’s coupe counterpart. However reviewing the Under Strut System on an open top MINI would just be too easy. So instead we put it to the test on the already stiff MINI coupe to see if there could be any real benefit.

Installation is fairly straightforward but easier accomplished with the help of a lift. Specifically it’s important to make sure you’re level during installation as you want to make sure the two required holes are drilled at the correct angles. Otherwise it’s simple process that doesn’t take too long with the included instructions.

Immediately after installation I took some time to drive around some of my favorites roads in Chicago however I didn’t have time to do any back to back testing. In fact the difference (based purely on memory from the car without the USS) seemed quite subtle. However that all changed once I got a chance to drive the car aggressively back to back with another MINI without the USS.

The difference was obvious entering and exiting several slightly cambered corners. Where the stock MINI felt good, the MINI with USS felt incredily composed and infinitely solid on the exit. It’s almost a hard thing to articulate but the car feels more planted and quicker to respond. The USS allow a driver who may have missed the turn-in point, to recover much easier. The car seemed to have quicker reflexes and in turn greater exit speed.

The stock MINI feels like a go-kart from the factory. With the USS, it becomes utterly point and shoot to a level that is entirely addictive.

The difference isn’t night and day mind you. It’s something that only rears its head in tight corners and aggressive driving (best done at the track). However if you are an aggressive driver than regularly participates in track days or autocrosses, the M7 Understrut System is a worthwhile upgrade that truly improves the feel and composure of the MINI.

MotoringFile Rating: 4.5 (out of five)

Where to Buy: The M7 Understrut System are available from M7 Tuning for $349 plus shipping.

Written By: Gabe

  • MCV

    This system has a flaw. The frame under the motor is made to collapse in a collision. This provides resistance to that function of the frame. I’d hate someone get hurt because their motor came more into the passenger compartment than under the car in a collision.

  • badburro

    Gabe -

    Thanks for the review. I was looking to put one of these on my MCSc and was waiting for your review on it. Lots of forums and banter on it, but I was afraid they may have been biased. This site has become my number one MINI site for both its contents and trusting its reviews.

  • Rocco Rocket
    This system has a flaw. The frame under the motor is made to collapse in a collision. This provides resistance to that function of the frame. I’d hate someone get hurt because their motor came more into the passenger compartment than under the car in a collision.

    Can you qualify your ability to make such a statement? Do you have an engineering background? Just a guess but, the bolts and joints would probably break when put under stress from that angle. It’s a rigid system designed to connect the frame. I feel it would break before bending. I’m not an engineer just a gear head car guy that has in stalled an m7 USS.

  • http://www.motoringfile.com/ Gabe

    I concur. The idea that a few bolts (how the USS is attached to the frame) would hold back a heavy iron block engine in the event of a crash is a bit far-fetched.

  • iNomis

    Anytime you add a mod you’re playing with the original engineers design and you have no way to know the effect. MCV has a valid point but if you’re a safty nut then you’re probably not in need of such a device, anyway.

    Gabe, how much does all this weigh? What was the milage on both cars in the comparison and how were they setup? How much could normal differences between the cars account for the differences you felt?

  • http://www.motoringfile.com/ Gabe

    Gabe, how much does all this weigh?


    What was the milage on both cars in the comparison and how were they setup?

    Cars tested: With USS: 15,000 miles Without USS: 200 miles

    How much could normal differences between the cars account for the differences you felt?

    Put it this way… I had a passenger who owns the same car with less miles (same wheels even) who felt the difference at turn-in.

    Let me be very clear about one thing. I was somewhat skeptical that the USS was actually going to make a noticable difference on a MINI coupe. My experience since install (especially driving the two cars back to back) has really surprised me.

  • http://www.newminiclub.nl Berthil

    Yes, what does it weigh? The gain in handling decribed I also noticed with the OMP chassis brace under the engine and additional directer turn-in. I wonder if the points mentioned for the M7 under strut system will also be that noticable if one has a front under strut brace from OMP. In addition I wonder how much of the described gain can also be accomplished with a upper strutbrace behind the backseat?

  • iNomis

    Yes, went to the web site and found the less than 10lbs also and was surprised by that until I saw it was aluminum. I just figured it was steel from the black paint.

  • MCV

    I’m sure the bolts would break. I too have this installed on my MINI and love the way it makes the car feel. I was just trying to bring attention to the fact that it could possibly hinder what the engineers were trying to accomplish with the front end.

  • http://dcmini.blogspot.com/ DanC

    good point MCV. Perhaps an engineer could chime in or M7 should have it at least reassured by one that it indeed does not hinder what the engineers were trying to accomplish.

  • http://www.gbmini.net Ian C.

    But why are all the pics labelled “R56 Cooper S”?

  • rkw

    If the rating is 4.5 for a hardtop, then it should be 5.0 for a convertible. The M7 USS transformed the handling on my cabrio. When I first got the car, I thought the handling was fine but nothing special. I didn’t understand all the hype around MINI “go-kart handling”. I just figured that it was the reaction of most owners after changing from a larger, heavier car. Driving home after the USS installation, the difference was immediate and obvious. The first time I did a lane change, quickness of response took me by surprise. The handling became much more immediate and precise. By comparison, the handling previously was accompanied by a delayed response and looseness. I would attribute this to the body flex of the convertible. Now I feel that I really do have go-kart handling.

    By the way, I previously had an OMP lower frame brace and the change to the M7 USS still made a big difference.

  • http://www.newminiclub.nl Berthil

    Thank you rkw for that info, maybe the difference is less on a hatchback but probably the M7 USS will do good work together with the OMP. 10 lbs is not too bad, I’ll get the aluminium GP rear trailing arms, saves 15 lbs :)

  • BrianBlack

    How do you mean more composed? More predictable? I guess I can’t believe this until I test the difference first hand. I can understand why some people would feel a difference. They spent the $350 for a couple pieces of aluminum, of coarse they are going to want to feel something.

    I am not trying to discredit anyone who has one, but just ask the question could it be mental?


  • rkw

    Berthil, the M7 USS and OMP lower frame brace cannnot be fitted together at the same time. Unless you meant an OMP upper strut brace.

  • http://www.motoringfile.com/ Gabe

    How do you mean more composed? More predictable? I guess I can’t believe this until I test the difference first hand. I can understand why some people would feel a difference. They spent the $350 for a couple pieces of aluminum, of coarse they are going to want to feel something.

    That’s understandable because I didn’t really believe it would be noticeably beneficial for a coupe until I tested first-hand. Again I was really surprised at the difference. It’s not huge but it’s undoubtedly there and it’s unquestionably an improvement.

    I’m sure anyone who spends the money on anything will want to believe it works. However in this case we were given a unit to review so I can assure you that was not a factor in this review. It’s all about the product and whether it does what it claims to do.

  • Vanwall

    This seems more like a track oriented mod, but a street MINI would undoubtedly benefit – I like the idea, and the product seems to live up to the promise. Stress transfers would hopefully be minimal for the life of car.

    I’m not so sure anyone should be throwing around opinions best left to structural engineers regarding the crash-worthiness, or not, of any product – just about any performance mod changes the dynamics of a car, so adding anything is your responsibilty, regardless.

              Rob in Dago
  • Earl Harris

    Has anyone tried it on a convertible Mini? I had a Mini S convertible and sold it because it had to much flex if this would fix most of the flex I would buy another one because I love the car. Thanks

  • csdmmnt

    Oiy! …

    Was the atmospheric pressure at the time of each run the same?

    Was the decernable percipitation and humidity during each run the same?

    … good lord guys.

    Nice review, thanks for the information it covers the basic knowledge one would want to gain I think. For the race nut they’d already know or would seek their own further investigation for the finer facts.

  • alpinamike

    I need the one for my R52. Hey M7 want to throw me a free one…lol Then I can test it before and after.

  • rkw
    Earl Harris Oct 19th, 2006 Link Has anyone tried it on a convertible Mini? I had a Mini S convertible and sold it because it had to much flex if this would fix most of the flex I would buy another one because I love the car. Thanks

    See my comment above

  • Kennedy

    Nice review Gabe. I have had my eye on the USS for a while too, no matter how stiff and great the MINI is, I have always thought that you can never go wrong with stiffer… I know there’s a joke in there somewhere, but that wasn’t what I was going for. I’m sure one will be in my future, once I get caught up with the rest of the mods wish list.

  • Kennedy

    Having said that, I have a few comments to the comments. Actually, I AM a mechanical engineer who happens to work as an auto-safety engineer. I can understand the comments about the safety concerns and I will say that really I shouldn’t comment, nor should you fully take what I say as gospel. The simple answer is (as someone else pointed out), that MINI’s chassis engineers specifically designed the car to perform a certain way in a crash. This is not only to have the vehicle crush in a certain manner, but also control the way it slows down as it is crushing. For example, if it slows too suddenly, by the time your seat belts fully “catch” you, you’re traveling much faster than your car and experience a more sudden stop. Compare this to the scenario where the vehicle begins to slow gradually at first, allowing your seatbelts time to “catch” you, and you ride the rest of the crash down “more gradually” (everything is relative when you’re talking about a serious crash) with your car.

    While almost all modifications that you make to your car fall into the category of not affecting your vehicle’s crashworthiness, this one most certainly does fall in the category of POTENTIALLY affecting the crashworthiness. HOWEVER, in almost every vehicle design, the car is designed to crush from the front to the back. That may seem pretty obvious, but generally a car first crushes at the bumper, the radiator and on back, etc. One of the many reasons for this is to protect the integrity of the occupant compartment. Simply put, you need space to survive; you need as much space to slow your body down as gradually as possible. The USS as I understand it, mounts from the front wheels back, and also has a stiffener about mid-point along the wheelbase. So it shouldn’t dramatically change the INITIAL response of the car in an accident.

    Now, once you get to the wheels (to the USS) then yes, perhaps it could start to change things. Regardless of whether the bolts fail or not, the brace is going to have to go somewhere as it crushes. I not sure exactly of everywhere it attaches to the car and specifically how strong each of those connections are, but it will either A) pull or shear the bolts off, or B) crush with the car. I’m pretty sure those are the only two potential answers. If it is A, then it’s likely it will not be a big player in changing things. If it is B, then I would assume the long bars, the actual “understrut attachments,” will probably buckle and bend out of the way. If intact, then it will likely make the rest of the crash even slightly stiffer, thus a bit of a “harder” ride down, but by how much, it is impossible to say. Also, that additional rigidity would likely help to keep the occupant compartment more intact, which would potentially benefit the occupants, but again, it is impossible to say.

    Ultimately, there is only one way to truly know the answer to how this will affect the MINI in a crash, but that would require resources far beyond what M7, as an aftermarket company could be expected to provide. I think putting something such as this on your car classifies as implied consent to changing your vehicle’s structure. It is unavoidable that this may change some of the crash dynamics. You can only answer for yourself how comfortable you are with that… but it’s on my wish list.

  • Kennedy

    Was just thinking, I don’t want to confuse anyone. The USS doesn’t attach to the bottom of the strut or anything, so when I say “get to the wheels” etc. I only mean that the front of the USS attaches approximately at the same location as the front wheels. I think actually just a bit further back, but I am not certain.

  • MINI Fireman

    I did the suspension mods to my MINI one at a time so I could better evaluate the effect of each change. I felt like the USS made my car more settled, particularly during aggressive cornering when I am really throwing the car around. All in all a nice addition. Your review reinforces my observations.

  • Vanwall

    Thanks for the analysis, Kennedy, it’s what I was thinking generally, but you’ve done an excellent job of explaining. I see on their website the bolts are stainless steel, (not my choice for anything but trim applications, though), prolly A-2 grade button-head socket caps, so the usual calcs for automotive fastener tensile strengths are out window, as far as I’m concerned, (I’m a big graded bolt fan for automotive uses), but the inserts in the sheet-metal are prolly the weak link, anyway. Hopefully when the moving object meets the redirecting force, it’s a non factor. This is on my wish list, too, anyway – I like the idea and M7’s finished product seems to be the real goods.

           Rob in Dago

    Kennedy, Thanks for your comments. Hope your doing well in Winston

    Tar Heel MINI Motoring Club

  • http://dcmini.blogspot.com/ DanC

    Nice analysis Kennedy! Very eloquent, informative and reassuring. You have my vote for comment of the month… if there is such a category. ;-) thanks

  • Kennedy

    Vanwall – Thanks for the comments. I’m with you 100% about both the appreciation of a nice, quality bolt! I also agree that it seems stainless is probably fine, as evidenced by the performance of the USS in the review, the bolts are good enough to do the job as intended, plus corrosion resistant (and a little under-chassis bling). I think you are right, that whatever the insert in the sheet metal is, it is likely the weak link….

    Twister – Thanks, I am back at Tech these days, but looking forward to catching up with the Tar Heels sometime soon. Just not the basketball team, go Terps (and Hokies)! 

    DanC – ha, thanks for the vote. I wonder if that nomination would look out of place on my resume? 

    Also, as an afterthought… If this were being sold at WalMart/Target, etc. and it was a car-seat, kids toy, or some other device sold to the everyday consumer, I would feel much more adamant that the mfg. company would be obligated to completely ensure that the product was safe in all aspects of its intended application. However, this is a product available to a small group of enthusiast owners, a small sub-set of owners of a particular car, I think it seems a well-intended solution to a specific issue. Like I said, you have to realize if you put this on your car, it is advertised specifically to affect the structure of your car. If it were more mass-market, I would definitely have a different stance on the issue.


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  • tomm9050

    I have the M7 USS installed and have had one incident with it worth reporting. I managed to scrap the underside of my MCS on a piece of pipe (took a wide turn into Long Beach Mini’s drive, over the curb, poorly marked obsticle which they have since fixed). It hit the USS front bar and rotated the one of the brackets 45degrees.and ripped up the front bar, which is rather thin and hollow extruded aluminum. The corner brackets are solid.

    M7 sent a replacement front strut bar for about $30. shipped.

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