Airhead on the Interstate

[bluehole]

I am down to one motorcycle. It is a 1972 R75/5. I love the bike, but it is much different experience than the Oilheads I owned. Those riding multi generational BMW models will appreciate what I mean.

Here is the situation:

I seldom ride interstates much on my Airhead. This motorcycle has been used primarily for riding secondary roads. However, this is now my primary bike and there are times I prefer the interstate to secondary roads. In this area, the interstate speed limit is usually 65 or 70 mph. Last week I was on the local interstate on Ol' Red and at a GPS indicated 65 mph the tach showed 4,500 rpm. At 70 mph the rpm was just under 5,000...maybe 4,800. The Airhead is happiest a bit on either side of 60 mph. Naturally, my Oilheads cruised the interstate effortlessly at a lower rpm... perhaps 4,000 rpm at similar speeds.

Here is the question:

The R75/5 feels busy on the interstate. I usually limit my interstate riding because I am concerned it may be detrimental to the engine run the R75/5 at the higher speeds for long distances. Is is wise to limit high speed interstate riding or am I needlessly babying the R75/5? I understand part of what I am dealing with is the transition between riding on an Oilhead as opposed to an Airhead. The Oilhead will feel more relaxed. I want to be sure I am doing the right thing. I do not want to strain...damage Ol' Red. I believe keeping the rpm down is better for the engine. What are your thoughts?

 

[RAColeman]

Ride it!

 

[20774]

I personally don't like Interstates because of how boring they are...but I'll ride them if it's the best option to get to a spot where I can take secondary roads or if I need to make some time.

But the R75/5 should have no troubles doing high interstate speeds virtually all day long. If the bike is in a good state of maintenance, I really don't see any issues. My /7 has a "low" rear end, so my freeway speeds are somewhat reasonable. Not sure what your /5 has but it might result in slightly higher RPMs at say 70-75. But still very doable. IMO and YMMV.

 

[dennisdarrow]

To me, you should be doing 70 mph at 4000 to 4500 RPM. At least that is what I remember my old /5 doing that day after day. Coast to coast, down into Mexico, OKC to parts unknown and parts known. My /6's do/did the same thing so it isn't a case of wanna be memory. Often the bike would be ridden at 75 to 80 mph with NO problems....No oil useage, no worn out parts, or parts abused by these speeds.....BMW's have always been designed and engineered for FAST touring or spirited riding.....NOT sloughing along with the Buick crowds......
Two things.....again, nothing is wrong with keeping that engine above 4K RPM. 5K is just right. Below 4K is when folks start having problem......Another thing, you mention that you are doing 70 at 5K RPM. To me, something is off there. Either the speedo is off, way wrong tires, or the rear end has been swapped out. How long have you had this bike???? Has it always been this way????

As far as Interstate riding goes......that's what we used to GET someplace.....80 mph was/is what you do to get there....If you want to put along, that is just fine; but just maybe try to keep the RPM's up a bit.....God bless....Dennis

 

[bluehole]

Update: This bike has a /6 5 speed transmission. I don't know if the final ratio is different from a standard /5, but offer it for what it is worth.

I notice Bob and Kurt have high performance, super powerful later model Airheads, where as I have but a modest /5.

 

[bluehole]

.NOT sloughing along with the Buick crowds......

I don't want to be that guy...the guy traveling slowly, impeding traffic and incurring the wrath of others on the interstate. One of my interstate strategies has been to find someone traveling a little more slowly than everyone else and slide in behind them. "Hey, the guy in front of me is holding up the show, not me"

You might be right about something there. 4th and 5th feel like they are pretty close. I will get that checked.

 

[gromulin]

I feel ya. Always felt the same way on my 72 /5 at anything over 70MPH for a long distance. Just felt like the engine was too wound up, which made me feel too wound up and made for a less enjoyable ride. Always wanted that 5th gear, interested to see what you find out.

 

[Friedle]

Interstate Airhead travel

Check the rear end ratio of your bike. IIRC the stock 75/5 rear end was 32:10. Perhaps it has been changed over the years. I have hundreds of thousands of miles on my 70 R 75/5 with a 32:10 rear on everything from Interstates to jeep trails and I still enjoy riding that bike today. BTW, don't lug the motor, no trouble running 4-5 K revs all day long until you get to your destination for the day.

Friedle

 

[Friedle]

Interstate Airhead travel

I forgot to mention that I believe the gear ratio for top gear in the /5 transmission (4th gear) is the same ratio as for top gear in the /6 transmission (5th gear).........1 to 1........so it really should make no difference at freeway speeds which transmission is presently installed in the machine.

Friedle

 

[20774]

^^^ What he said!

 

[72r60/7]

Airhead Travel

BTW, don't lug the motor, no trouble running 4-5 K revs all day long until you get to your destination for the day.

Absolutely.

Rode /5 and /7 600cc powered bikes for 20 yrs loaded 2 up to solo.
You could run them at 5500 rpm's all day. Not just my personal opinion, it was backed up by fact or rumor that the oil supply was sufficient by factory testing. I would venture to guess that if a German had had engine problems with continuous Auto Bahn engine speeds, you would still know about it 45 years later.
For me 5500 rpm was a sweet spot where the engine felt it was in equilibrium between pulling and pushing.
Now that's character ! Wish I still had one.
Charlie

 

[fawudd]

My R75/5 is not too far from your numbers - 4000 at 70 and 5000 at 80mph. AFAIK it is stock gearing and rear end. However, it does not feel stressed at 5K, so perhaps that is just a subjective thing. I don't seek out highways, but I don't fear them either. I would not want to run an 800+ mile day on the interstate in warm weather, but that is more due to boredom, and running any 40+ year old machine that hard. Commuting, no problem. Cheers


Sent from my iPad using Tapatalk

 

[beemeruss]

Needles

I,too, have fond memories of my '70 R75/5 bought in '72.I put 30,000 miles on it in 1 1/2 years including a trip to Europe (airfreight) and lots of Autobahn high speeds.A really neat touch of German engineering is the tach/speedo combo.The bike was in its groove when the tach and speedo needles lined up.IIRC 78 mph and about 4800 rpms were the norm.Can anybody confirm this?
Russ












needles

 

[gromulin]

I forgot to mention that I believe the gear ratio for top gear in the /5 transmission (4th gear) is the same ratio as for top gear in the /6 transmission (5th gear).........1 to 1........so it really should make no difference at freeway speeds which transmission is presently installed in the machine.

Friedle

No kidding? Well, so much for looking for a 5 speed. The only reason I wanted it was a taller top gear. Checked the rear end last night, it's a 32/10.

 

[terham]

One of my interstate strategies has been to find someone traveling a little more slowly than everyone else and slide in behind them. "Hey, the guy in front of me is holding up the show, not me"

Now I know why you insisted on me leading our interstate ride at the RA rally last year.

I don't think you have anything to worry about, especially since you maintain Red in top shape. I ride my /5 four speed on the interstate at 65-70 when needed and haven't had any issues.

 

[PGlaves]

Here is the question:

The R75/5 feels busy on the interstate. <> What are your thoughts?

I have a hunch that the bike feels "busy" because the bike feels buzzy because the bike may be slightly out of tune. I think a careful valve adjustment followed by carefully synchronizing clean carburetors will make the bike feel much smoother and less busy. It ought to feel smoother at 5,500 rpm than it does in the 4,000 to 4,200 range which is a common buzzy range due to secondary balance harmonics.

 

[barryg]

I ride my '71 R50/5 on the interstate quite a bit. Pretty much maxed out at 70 mph. I get over in the right lane and usually hold the throttle at wfo with a smile on my face. It'll do that all day long over in this flat land, no problem. Ya get over in the Ozarks or Ouchita's and it's a different deal altogether. Generally run US, state, county roads at a slowe pace. I find that you leave a little earlier and ride a little later and you get there on time. It's usually a great ride at a more relaxed pace.

 

[barryg]

Then again, when I ride my R90 I can easily run 80-90mph on the interstate loaded when I ain't worried about tickets. The real limiting factor is braking at those speeds.

 

[galaxie]

airhead on interstate

My 86 R80RT is running at 4800 rpm's at 70 mph,have run it for 400 miles at that speed does not seem to bother it,the R80 are geared lower than most BMWs.

 

[bluehole]

My 86 R80RT is running at 4800 rpm's at 70 mph,have run it for 400 miles at that speed does not seem to bother it,the R80 are geared lower than most BMWs.

Interesting. That is about where mine is running.