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Old 02-14-2013, 03:44 AM   #1
tommyvdv OP
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why not ride an mx bike long distance

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!
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Old 02-14-2013, 05:08 AM   #2
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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.
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Old 02-14-2013, 05:56 AM   #3
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In the case of a 2-stroke, because of cylinder and main bearings lubrication.
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Old 02-14-2013, 06:20 AM   #4
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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.
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Old 02-14-2013, 07:00 AM   #5
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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?

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Old 02-14-2013, 07:18 AM   #6
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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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Old 02-14-2013, 07:27 AM   #7
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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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Old 02-14-2013, 08:03 AM   #8
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In the case of a 2-stroke, because of cylinder and main bearings lubrication.
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.
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Old 02-14-2013, 08:10 AM   #9
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Originally Posted by tommyvdv View Post
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.
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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Old 02-14-2013, 08:23 AM   #10
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Originally Posted by Foot dragger View Post
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.
Would replacing the Ti valves with stainless steel ones help to prevent disaster?
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Old 02-14-2013, 08:32 AM   #11
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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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Old 02-14-2013, 08:47 AM   #12
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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.....
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Old 02-14-2013, 01:01 PM   #13
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So I think everyone trying to say something here....

Get a KLR!

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Old 02-14-2013, 01:47 PM   #14
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Originally Posted by davesupreme View Post
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.....
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.
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Old 02-14-2013, 01:55 PM   #15
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just do...

.................................................. ............................................this
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