why not ride an mx bike long distance

Discussion in 'Thumpers' started by tommyvdv, Feb 14, 2013.

  1. tommyvdv

    tommyvdv Been here awhile

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    hi
    I've been stumbling upon the advice not to take an mx bike for a ride on a main road or a long stretch. but haven't found an answer as to why exactly. so here goes:

    why exactly is it a bad idea to ride an mx bike at a constant speed on a long stretch?

    feel free to get technical

    thanks!
    #1
  2. RFVC600R

    RFVC600R SAND EATER!

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    maybe cuz those engines aren't designed for that and of course true MX bikes require more maintenance and they're light so they probably handle like crap on the freeway. There are plenty plated dirt bikes, I've seen true MX bikes that are ready to go on and off road at anytime. And I guess it depends on what you consider "long distance." That's all I can think of but I ain't even close to an expert. :D
    #2
  3. cat

    cat Long timer

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    In the case of a 2-stroke, because of cylinder and main bearings lubrication.
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  4. Grreatdog

    Grreatdog Long timer

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    With mine it really depends on the speed you want to run. MX bikes typically have close ration transmissions and pretty short gearing. Even running the biggest countershaft sprocket I can fit (15 tooth) and a pretty small real sprocket my MXC is still getting into the rpm range where it comes on the pipe at highway speeds.

    Which makes for an interesting ride at 60 to 65 mph. But slow it down to 50 to 55 mph and I would be willing to ride the bike any distance I would ride any other dual sport. Well any distance that featured closely spaced gas stations. Three gallons doesn't last very long on a two stroke MX bike with the throttle nearly pinned.

    Back in the day we used to pull the choke out a bit on two strokes when we were bombing down long stretches of road. But that doesn't seem to be an issue with modern two stroke oils. When my MXC was rebuilt last winter after several years of dual sport use the top end was nearly perfect. It has never even hinted at seizing.

    Also, to me, the size and weight of the bike make zero difference on the highway. But then in 35 continuous years of riding I have yet to own either a dirt bike or a street bike. All I have ever owned are dual sports and plated dirt bikes. So what seems normal to me would probably be unacceptable to somebody used to an actual street bike.

    What you really have to sweat when riding an MX bike on the street is keeping your license. When ever time a signal turns green it seems like a gate drop at the track and every shift brings the front wheel up the hooligan factor is off the charts.
    #4
  5. VxZeroKnots

    VxZeroKnots Long timer

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    Yeah on a four stroke I don't understand the whole "they don't like to sit at one RPM" thing. How exactly is that bad for the engine? On a two stroke it most certainly make sense, but just because an engine is designed to accel and decel fast, what harm would come to it operating at a constant RPM?

    :ear
    #5
  6. tommyvdv

    tommyvdv Been here awhile

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    wow. impressed by the answers.
    I'm talking about a Honda crf 450r or any four stroke like it.

    I understand that the gearing is short and running highway speeds equals being in the red zone constantly. but let's say I ride it slower so that the engine is not maxed out in the rpm department.
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  7. Grreatdog

    Grreatdog Long timer

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    As I said, riding it more slowly and at rpm under the big hit is your (and the bikes) key to survival. Some of the four stroke MX bikes hit almost as hard as a two stroke. They are just smoother getting to that point and not as instantaneous. That big hit of power is where you run into issues. It makes the bike difficult to ride in that rpm range and drinks fuel.

    So, again, it comes down to the top speed you want to sustain. Stay below the big hit and everything is cool. And it isn't just sustained cruising. In traffic you really have to be cool because MX bikes are made to launch you off jumps and over whoops with a crack of throttle. That instant power is really fun. But it can also make for a hairy ride in traffic.

    But there are many things you can do to mitigate that. A different pipe and muffler, different gearing and flywheel weight all make the bike more civilized. But at some point it all defeats the purpose of owning an MX bike in the first place. I have limited the mods to my MXC to just taller gearing and a little extra flywheel weight. I want it to remain unruly.
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  8. Foot dragger

    Foot dragger singletracker

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    Two strokes have lubrication right in the fuel,fresh all the time. Why would that be a problem?
    If they're jetted right they can run as far as you want to go down the road.

    Wouldnt be pleasant but lubrication isnt the issue.
    #8
  9. Foot dragger

    Foot dragger singletracker

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    Honda wants that bike torn down and inspect the top end pretty often,putting 100 hours on one with out checking the piston/valves is asking for troubles.
    My buddy that races one has figured out that 1 valve adj is all you get,after that the magic coating on the Ti valves wears away and the valves are shot soon after.
    Also those bikes are known for blowing the crankcase oil out through the breather at hiway speeds,they dont hold much oil so losing much can lead to imminent disaster.

    Sorta like using an F1 car to fetch groceries.
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  10. tommyvdv

    tommyvdv Been here awhile

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    Would replacing the Ti valves with stainless steel ones help to prevent disaster?
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  11. TNC

    TNC Candyass Camper

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    You don't get 50-60 horsepower out of 450cc without some compromises, and I think there are longer term reliability issues connected to any engine that's somewhat "on the edge" of its maximum power potential. The valvetrain is one them, and there are practically no piston rings in many of these types of engines...as well as super short piston skirts. That's all fine and dandy for what these engines were designed to do, but cruising on the highway is not their bailiwick. The gearing issue has already been mentioned.

    If you tried driving a street car with a AA Fuel dragster engine installed, it would become very apparent how an engine designed to produce max power is almost unusable on the street. And while one would be correct that it's an extreme comparison, the modern 450cc MX engine for the most part is running at a decently high percentage of its power potential. It would go down the highway, but it would be dying at an accelerated pace compared to just about anything else with a more moderate powerband. That lovely power is not free. Depending on your willingness to perform much quicker, major service intervals, the bike/engine will do it, however.
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  12. davesupreme

    davesupreme grand poobah

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    i've ridden my KTM 450 SMR across fla. a couple of times, and it didn't miss a beat.... proper gearing is essential, and i got the close ratio gearbox.... an EXC wide ratio box would actually be even better, so.... you just gotta keep up on the maintenance on these bikes, and change the oil alot.... 500 mile oil changes worked fine on mine, especially for road riding, probably go more, but why?.... but like alot of the constituency here, if you're daunted by changing 'yer oil, maybe you better get a KLR..... :evil
    #12
  13. RFVC600R

    RFVC600R SAND EATER!

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    So I think everyone trying to say something here....

    Get a KLR!

    :hide
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  14. TaterHarry

    TaterHarry Redneck Emeritus

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    This. Is the main reason you don't want to ride a MX bike on the highway. The oil capacity is typically on the order of a quart, and the oil shears out of grade and wears out very quickly. More than one person has blown their "street legal" Husky or KTM motor by ignoring the need for fresh oil on a regular basis.
    #14
  15. zokalr13

    zokalr13 Been here awhile

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    [​IMG] ..............................................................................................this:D
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  16. Grreatdog

    Grreatdog Long timer

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    Don't listen to the naysayers. Yes, it vibrates. Yes, it is hard to ride. Yes, it drinks fuel. And, yes, it is stupid on several levels. But it also never fails to have me laughing out loud inside my helmet. So much fun it should be illegal. Oh, wait a second.......


    [​IMG]
    #16
  17. Adv Grifter

    Adv Grifter on the road o'dreams

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    How far do you intend to go on your CRF450R? Having toured Europe quite a bit ... it looks to me like you'd have to ride down to Southern Spain ... or Morocco to find legal trails to ride.

    Where can you ride in Belgium besides on a PAY to USE Moto Cross track?
    Is there extensive open land there to ride on?

    There are lots of reasons why your RACE bike (key word: RACE) is not good for longer street rides. Not only are you likely over revving the motor but since your machine has no Cush Drive cushion system ... you may be stressing the gear box as well. Then there is the comfort issue, luggage and all the other trappings of making a bike street and travel ready.

    The CRF450R is a GREAT off road bike. Of course early ones had serious top end problems ... and worse. Different valve kits are common. Newer CRF's seem to be holding together better. I love that bike but bought the Yamaha because they hold together. Keep in mind that HONDA recommend
    a complete rebuild on that bike at something like 25 or 30 hours, (IIRC).

    In '07 I did a two week Baja ride with 5 of 6 other guys. The only bike that did not make this 2000 mile, mostly off road ride, was the poor guy on the CRF450R. Cam follower bearing in the top end cam apart near Bahia de Los Angeles, trashed the valve gear. Hitched a ride in an empty trailer. Lucky.

    But the WR250F and 2 WR450F's both made the trip. The WR's were revving like mad on our paved road sections. Not happy ... and we were only going 50 to 55 mph! (about 80 kms) My old school Honda XR250R with it's wide ratio 6 speed, was better on the roads. Cruised comfortably at 60 mph without over revving. Off road, the "real" dirt bikes
    took off ... never saw them! Much better than my poor little XR. :cry
    #17
  18. The Letter J

    The Letter J lost in the 690 mega

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    Arrrgghh!!!

    I typed out a very long, drawn out response and then my computer froze, so you will have to settle for my cut-and-paste response from another thread!

    #18
  19. Adv Grifter

    Adv Grifter on the road o'dreams

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    Considering the mileage covered I'm thinking you did damn good on your CRF :clap 12,000 is huge on that bike.

    Nonetheless, no motocross bike for dual sport for me.
    #19
  20. tommyvdv

    tommyvdv Been here awhile

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    i'm not in the planning stages of a trip with that crf. I'm trying to wrap my head around the problems and weak points of that or a similar bike.

    I have no or very little experience working on a bike and I'm learning with every reply.

    @adv grifter
    what year is an early crf?

    I've heard that the newer (injected) versions have a lot of starting issues. but that's just one case
    #20