Speedometer/Top Speed on DOHC

doodsaibot

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I noticed the other day that my speedometer is off by 5 miles per hour. I figured this out after looking at the radar detector in a nearby subdivision. I think the tires I have are a bit larger than the stock tires so I don't know if that has something to do with it. Also, I got my Maxim up to the its' top speed of 80 MPH (more like 75 because of the messed up speedo). It was only pushing 7.5 RPMs at the time. I don't normally ride that fast so I was wondering if it is okay to run this engine at that speed for a prolonged period of time. I know my bike loves high revs but I suppose I just need some input from DOHC riders that are more experienced with longer distance, higher speed riding.
 
The speedo error is generally increased as speed increases (think percent error); the faster you go the more error there is. the larger tires will do that, but most bikes are off by some modest amount; you need radar or gps to be accurate.

I don't know what the redline is on a DOHC, so I can't give you an exact number, but in general I would not want to sit at greater than two thirds (2/3) of maximum rpms for a prolonged period of time. For me this is around 6,000 since I max out at a little over 9000. Anything at or around 6,000 is my target give or take.

If your max is 10,000 around 7,000 sounds fine give or take.

Don't take this as gospel for any bike because it varies based on other factors, but these old parallel twins don't mind sitting in that range for longer distances; you won't really have a choice if you're going to be doing much riding on the freeway if you want to keep up with traffic.
 
Yes, the bike does redline at 10 grand. The road I was cruising on was the tollway and the speed limit there is 80 MPH, which is the ceiling on my 5 speed DOHC. I don't ride that tollway much but for me it is a more efficient route to my buddies house and it is only for about 15 minutes that I travel on it. All things considered, the bike did well and it gave me a good exercise.

I did more research on the speedo and inadvertently stumbled upon some info about that redline on the speedometer that starts at 55 MPH and goes up to its' max of 80. I never knew what that meant but I found that the national speed limit here in the U.S.A. in the mid 70's to the late 80's (my bike is an 83) was 55 MPH and that there had to be a highlight of some point on the 55 MPH of the speedo for all vehicles. After they repealed the speed limit law, the highlight was no longer needed for any vehicle. Now it seems even in 65 MPH zones I am almost maxing out my speed just to compete with everyone else on the highways.
 
Indeed, these bikes are not well suited for longer highway rides. Once you get above 65 mph or so you'll tend to experience harsher vibrations because the engine needs to work hard to stay there. Going over the "happy zone" of 6,000 or 7,000 rpms is fine for shorter rides though; I wouldn't flinch at 15 minutes.

Just be careful out there; in my experience it is safer to be going 5 or 10 mph over the speed limit than to be going at or below it on the highway; you don't want people constantly overtaking you.
 
With the size of these bikes, your weight plays a huge role as well. I'm 6ft, 150lbs soaking wet, and these small bikes fly with me on them. But at high speeds, my small frame causes these bikes to be unstable as all hell
 
I've found that the speedo error on my Maxim isn't consistent. The error increases with speed, ambient temp also effects it, as does how I've been riding. If I spend a lot of time at highway speeds, the error at higher speeds is reduced. If the bike has been parked for a while, or only seen low speed rides, the error at high speed is greater. Regardless, I don't trust the speedo, and the faster I go the more this is true. When I'm concerned about my actual speed, I use my phone and a speedometer or GPS navigation app.

I don't like to spend a lot of time above 120 kph (75 mph) simply because the bike is working rather hard to maintain these speeds. And there isn't much power left to get out of harms way, if needed. That said, 7000 rpm is about where my bike comes onto the main jets and becomes rather invigorating, in the lower gears anyways. A 400 is a 400, no matter how hard one rides it...
 
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