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  1. #1
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    My Experiment: The Mach 4.7

    I've always liked my Mach 5, but there have been some things that have kept the bike from being fantastic. This bike is tall, it's always had a tippy, unstable feeling when maneuvering around tight turns and switchbacks, and the front end gets very light on climbs. When getting the speed up it wanders a bit, and doesn't carve turns well. In short, the bike just isn't "settled". So, how to lower the bottom bracket height?

    The M5 stock shock is a Fox 200x57mm (7.875x2.25"). Fox also makes a 190x51mm (7.5x2")...hmmm. Doing some math, the travel would go from 137mm to 122mm, just shy of 5" and plenty for most of my riding. Definitely worth it for over a half-inch drop of BB height! Running 25% sag on the shorter shock would put the sag point at about 40% of stock, which should be fine.

    The biggest question: since shorter shock allows another 4mm stroke past stock, is there enough frame and tire clearance?

    Short story, on my bike there is. I drilled a wood block to simulate the shock max and min length, installed it, and tested the bike with the cranks on and off, with the front derailleur on and off, checking the swingarm, checking the linkage, and everything works with no binding or contact. With a Nobby Nic 2.25 Tubeless, there's about a quarter-inch of tire-seat tube clearance left.

    Here are theoretical numbers, with a RockShox Pike 454 DA and Schwalbe Nobby Nic 2.25" tires:

    Mach 5 original specs w/ 140mm fork:
    BBH: 13.85"
    HA: 69 / SA: 72
    Travel: 137mm/5.4"
    Shock: 200x57mm/7.875x2.25"
    Ratio: 2.4:1
    Min Length: 143mm
    WB: 43.375"

    Mach 4.7 w/ 120mm fork:
    BBH: 13.25"
    HA: 69 / SA: 72
    Travel: 122mm/4.8"
    Shock: 190x51mm/7.5x2"
    Min Length: 139mm
    Sag: 25% = 39.8% of original sag

    Thanks to the help of another MTBR member (thanks Jdub!) I got my hands on a Fox RP3. Setting sag to 25% only required 150psi, about the same as the stock shock. I lowered the fork to 120mm by increasing the negative pressure. For the test ride, I used a nearby trail that I've ridden several times with the stock setup. It's not technical at all, but has lots of g-outs, turns, and water bars that make great little jumps. I had no bottoming issues on the initial ride, and the cornering was amazing. So far everything's been perfect, and the RP3 is much plusher than the stock RP23, so no regrets there either.

    With it being winter in Colorado, I haven't had many chances to ride, but the rides I've gotten in have been stellar. No bottoming issues, the cornering and maneuverability are noticeably better, and I have no interest in going back to the stock shock. I haven't had any pedal strike issues, but haven't had the chance to ride on anything really rocky yet. I can see why the lightweight, slack 120mm bikes are becoming so popular, they're just really, really fun.

    As a side note, doing some quick and dirty math the new Mach 5.7 should have a slightly lower sagged BB height than my bike...which really makes me want to test ride one this spring.

    All this has been done on my bike, an early 2008 Mach 5. I can't say the same for anyone else's bike, so if you choose to check it out, do so at your own risk.
    Attached Thumbnails Attached Thumbnails My Experiment: The Mach 4.7-m4.7.jpg  


  2. #2
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    You would want one if you rode it. I think the new Mach 5.7 solves all of the problem you mentioned above. Two years ago I demoed the Mach 4, Mach 5, and the Mach 429. I choose the Mach 4 over the Mach 5 for most of the reasons you stated above. Now I want a bike with more travel than the Mach 4. I have demoed the Mach 5.7 and I love it. It is near perfect in my opinion. I am looking at getting one this year.

  3. #3
    it's the ride....
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    Quote Originally Posted by coolhandluchs
    I've always liked

    All this has been done on my bike, an early 2008 Mach 5. I can't say the same for anyone else's bike, so if you choose to check it out, do so at your own risk.
    An interesting experiment recalling the similar initiatives of the Homers on their heydays . Kudos for you for the trial (and without the error). I wonder how different the 4.7 to the revised 5.7 (apart of 1" gap). Keep us posted on your riding impression.
    Mach 5 was one of my plan for upgrade to dw-Link realm but knowing it is still too XC than AM I refused to let my 2004 Turner 5Spot HL go and keep it as my main trail bike.
    Now the Mach 5 is on sale, but then the 5.7 is here with all the hype.
    Ulating blencong sejatine tataraning lelaku...

  4. #4
    Black Lion
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    cool modification. Glad you got your M5 running the way you like.

    I however can't imagine my 2010 M5 feeling any better. I love the BB height and head angle using a 160mm lyric. The bike rips, and climbs my terrain (New England) exceptional well


    Greg
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  5. #5
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    Quote Originally Posted by yogreg
    I however can't imagine my 2010 M5 feeling any better. I love the BB height and head angle using a 160mm lyric. The bike rips, and climbs my terrain (New England) exceptional well
    Greg
    When I first saw the bike's spec in 2007/08, my first thought was: short wheelbase + tall BB = great Northeast bike! I grew in in central PA, so I can related to having the tall BB going over all the rocks and roots.

    I've heard the 2010 M5 and M5.7 are pretty plush, that's not the case with my 2008 though. I'm pretty sure the shock's overdamped, and with the new setup, I don't see any reason to get it Pushed now.

    The 5.7 is on my list of demos, just for comparison. I won't be getting a new bike anytime soon, and I can't decide if I want something lighter and about 120mm, or something bigger, slacker and able to handle rougher trails. I've had three different 5+ inch travel bikes, and while they're good at everything, they're not great at anything. A bigger bike is overkill for most of my trails, but would be nice for Moab and such. A lighter bike could push me to try out some racing, so it's a tough call either way, but I have plenty to time to enjoy the indecision.

  6. #6
    it's the ride....
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    chl, good to see you are enjoying the evolution of your Mach 5 and your observation was also something make me wonder if my effort to acquire M5.7 is the right way.

    I own 5.7" HL 5Spot (yupp... it's Push rocker modified), I am retiring my 4' Maestro bike, and it was a long while also since I sold my SC Blur (original version). I have also owned a GT i-Drive, Titus Motolite, Intence Tracer (HL prior to VPP), Kona 4-bar, and few others so clearly it's a tall order to own a DW-Link bike. The bad thing of having ridden so many different type suspension is a higher expectation on a new thing since I will always benchmark it to some good (and bad) experience in my head..

    Will be interested to hear from your Mach 5.7 ride test....
    Ulating blencong sejatine tataraning lelaku...

  7. #7
    DLd
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    Quote Originally Posted by coolhandluchs
    When I first saw the bike's spec in 2007/08, my first thought was: short wheelbase + tall BB = great Northeast bike! I grew in in central PA, so I can related to having the tall BB going over all the rocks and roots.

    I've heard the 2010 M5 and M5.7 are pretty plush, that's not the case with my 2008 though. I'm pretty sure the shock's overdamped, and with the new setup, I don't see any reason to get it Pushed now.

    The 5.7 is on my list of demos, just for comparison. I won't be getting a new bike anytime soon, and I can't decide if I want something lighter and about 120mm, or something bigger, slacker and able to handle rougher trails. I've had three different 5+ inch travel bikes, and while they're good at everything, they're not great at anything. A bigger bike is overkill for most of my trails, but would be nice for Moab and such. A lighter bike could push me to try out some racing, so it's a tough call either way, but I have plenty to time to enjoy the indecision.
    Have you considered getting the shock modded to have the HV air canister on it to get the plusher feel of the 2010 M5, or is that not the direction you wanted to go? Cockpit setup can have a big influence on how tippy a bike feels, or front end wandering too.
    "Great things are not accomplished by those who yield to trends and fads and popular opinion."-Jack Kerouac

  8. #8
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    Quote Originally Posted by DLd
    Have you considered getting the shock modded to have the HV air canister on it to get the plusher feel of the 2010 M5, or is that not the direction you wanted to go? Cockpit setup can have a big influence on how tippy a bike feels, or front end wandering too.
    I put an HV sleeve on the stock shock over a year ago, and while it helps the overall suspension feel, it does nothing for the small bump compliance. I was thinking about spending the money to get it Pushed, but that wouldn't have solved the "tallness" of the bike. The shorter shock, even though it's older and a standard sleeve, is much plusher.

    In the three years I've had it, I've tried stems ranging from 60-100mm and bars from 24-27" wide. The current setup with a 90mm stem and 27" bar is really nice. I don't feel like the cockpit's holding me back, It's been the overall handling: the bike's just kind of tippy, never quite balanced. Not enough to keep me from riding it or liking it, just not great. The current lowered setup has made a much bigger change than any cockpit mods and is a big improvement for my riding.

  9. #9
    DLd
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    Quote Originally Posted by coolhandluchs
    I put an HV sleeve on the stock shock over a year ago, and while it helps the overall suspension feel, it does nothing for the small bump compliance. I was thinking about spending the money to get it Pushed, but that wouldn't have solved the "tallness" of the bike. The shorter shock, even though it's older and a standard sleeve, is much plusher.

    In the three years I've had it, I've tried stems ranging from 60-100mm and bars from 24-27" wide. The current setup with a 90mm stem and 27" bar is really nice. I don't feel like the cockpit's holding me back, It's been the overall handling: the bike's just kind of tippy, never quite balanced. Not enough to keep me from riding it or liking it, just not great. The current lowered setup has made a much bigger change than any cockpit mods and is a big improvement for my riding.
    Well, sounds like you've found your sweet spot.
    "Great things are not accomplished by those who yield to trends and fads and popular opinion."-Jack Kerouac

  10. #10
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    Another option?

    I was surfing the net this morning and found the following article on dirt.mpora.com that details an aftermarket offset shock bushing that effectively reduces the length of your shock without decreasing travel. It appears that you have spent some time calculating the effect for your Mach 4.7. Can you make a guess on the HA and BB height impact on a stock Mach 5 with a 140mm Fox fork if you have 4mm less effective shock length? I would like a little slacker version of my Mach 5 without reducing travel. I am thinking about the new angleset that comes out this April, but maybe this is a better option.

    http://dirt.mpora.com/news/slacken-head-angle.html

  11. #11
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    Quote Originally Posted by davemk
    Can you make a guess on the HA and BB height impact on a stock Mach 5 with a 140mm Fox fork if you have 4mm less effective shock length? I would like a little slacker version of my Mach 5 without reducing travel.
    OK, I think my math's good enough to do this.

    Losing 4mm of overall shock length x 2.4 (suspension ratio) = 9.6mm of rear axle "lift"
    So, the rear axle will be about 10mm higher, which should slacken the bike by about half a degree.

    On my bike, putting the axle 24mm higher lowered the BB by about 15mm, so BB drop is .635 of axle lift. I would guess (9.6 x .635 = 6.1) that you'd lower you BB by about 6 mm or a quarter inch. The only fly in this is that I lowered my fork by 20mm as well, so you may not see as much of a BB drop if your fork stays the same length.

    So, half a degree slacker and not quite .25" lower? Just a guess, but it seems right.

    Using the angleset would also drop the BB very slightly since the effective axle-to-crown would be shorter with the slacker head angle.
    Edit: found the old thread. Using the angleset would (probably) lower the front end by 3-4mm.

  12. #12
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    Quote Originally Posted by coolhandluchs
    Using the angleset would also drop the BB very slightly since the effective axle-to-crown would be shorter with the slacker head angle.
    Thanks for the help, 1/2 degree and .25 inch drop was about what I was guessing based on your before and after geo. I think the angleset only drops the BB by 1-2mm. My goal was to end up with a 68 degree HA, I guess I could do both this and a .5 degree Angleset and have both a slacker geo and lower BB.

  13. #13
    North Van/Whistler
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    Never been ecstatic with the geo of the Mach 5 for the same reason mentioned as the OP - would prefer the M5 to be a trifle more downhill-biased.

    Just adding some data here. I tried this experiment and came up with a 66 degree HA using a Fox 36 160 on my Mach 5 (measured using a ghetto phone app so it's approximate).

    I've got a Magura Thor 140 so might try that instead on the front end as that's a bit slacker than I wanted. Either that or drop the Fox 36. Assuming that 20mm decrease in fork length will approx 1 deg HA that would put me around 67 deg which is where I'd like this to be..

    Replaced the stock RP23 (XL rebound tune, L compression; 130psi for 30% sag) with a 2012 Fox RP23 kashima (F rebound tune, L compression; 110psi for 30% sag). 160 lb rider

    Bears mentioning again that these settings and measurements are just riding around in the driveway and are therefore approximate
    Locals' Guide to North Shore Rides http://mtbtrails.ca/

  14. #14
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    Good job! New Shock

    Did my first ride with a new shock today, a Rockshox Monarch RT3 (190x51mm). I got the low compression tune with the medium rebound tune and what a difference! The rear wheel just sucked everything up and stayed glued to the ground. No more rear wheel chattering over the bumps, no more hardtailesqueness over the small bumps. Just butter. Probably still in the honeymoon period, but so far, it's amazing! Did a typical ride for me, (Alderfer Mtn and 3 Sisters for those in the area) with high speed, low speed, lots of bumps, little jumps and g-outs. Shock handled everything on the trail and left over .25" of shock shaft unused. Final shock pressure will probably be between 145-150 psi for a 180 lb rider (no gear).



    I also plotted out the pivot points and ran them through linkage. I just have the free version, so no charts or anything, and I couldn't get the print screen to work. Some data for those who like such things:

    With a 190x50.8 shock, I get 114mm of travel, for an overall ratio of 2.24:1. The leverage ratio starts out at 2.21:1, drops to 2.16:1 at 23mm of travel (28.5mm is 25% sag), stays at 2.16:1 until 38mm of travel, then tops out to 2.5:1 at 114mm. Total chain growth is 19mm.

    I wrote down all the pivot point locations relative to the BB, so if anybody out there would like to run my numbers through Linkage or another program and post the results, PM me and I'll send them along.

    So far, no issues with frame interference or bottoming the shock. Not really missing the extra 14mm of travel with the shorter shock, but definitely enjoying a properly valved shock!

    Edit: Oh yeah, shameless plug: thanks to Dave at Full Service Bicycle for hooking me up. The new shock is the best thing I've put on this bike.

  15. #15
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    Anyone else hoping for a 27.5 Mach 4.7? With any luck there's already one in the works- would appear to be a pretty obvious follow up to the Mach 6 (witness the way the Burner was followed by the Flux, Bronson by the Solo, Altitude by the Thunderbolt).

    All intriguing bikes, but the Mach 6 really seems to stand out to me; I could see a shorter travel option doing the same.
    A government big enough to give you everything you want is a government big enough to take from you everything you have.

  16. #16
    650b me
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    Quote Originally Posted by miles e View Post
    Anyone else hoping for a 27.5 Mach 4.7?
    Yes, I am. I fear my fingers are permanently gnarled from keeping them crossed for too long. Good thing I can't afford a new bike right now or I'd probably buy a Mach 5.7. As someone else mentioned, that bike is damn near perfection IMO.

    Still loving my Mach 4, but I'd like a bike that's just slightly more capable all-around.

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