Cruising RPMs

[kerryb]

So I took Wilma out for a romp to gather data for this thread. Near top speed of 83 at what appeared to be 3700 on the tach. Speedo was reading 2-3 mph high at 45mph compared to a gps unit. Tach appeared close enough when compared to a bench mounted tach/dwell meter. I wouldn't cruise at that speed but it did feel quite comfortable. That wasn't top speed on level ground but Im sure it was close to it. More background info: wilma has a 1970 1600cc motor, later dual port heads with 34pict carb. Mid 70's tranny that someone called a freeway flyer. And last but maybe more important, giant rear tires! I measured a circumference of 2030 millimeters to calibrate the new speedo. I think these tires, combined with the later ( maybe modified ) transaxle help account for lower rpms at speed and the need to downshift to climb hills that don't seem that steep.

So...my question is...would putting on smaller diameter rear tires be much of an advantage? I could regain a little torque for climbing hills, but would the trade-off of less than 36mpg be a good compromise?

What would you do?

[sonny8l3]

Hello, Thanks a bunch for all the info. folks. I just got back from the mechanics. He put the tach on a meter to check accuracy and said it's pretty close, which is close enough for my purposes. Since I don't hear real well any more, I asked him to take it down the road and listen to it and compare it to the tach. He took it down the road and said on my speedometer, which reads about 3 mph above my ground speed, 70 to 73 is fine for cruising. 75 is ok, but not for a long time. Since I usually run surface roads under 65, this is going to work fine. 70 on the interstate is going to feel like really hauling @**. For $59.95 to my door, one wire connection, and easy mounting options, the Trail Tech Tach is going to work fine for my riding style. And if a scooter show happens in the Vicksburg area, Mable and I would make plans to get there and probably bring a friend with a pretty VW trike.

[Fowler]

This morning I was doing 75 and the tach was reading about 3700

I should not have been doing 75 but I wanted to see the RPMs

The fastest I have gone on my trike is in the high 90 MPH

one thing I found out is a set of bumps I normally slow way down for if I do 75 over them instead it is not that bad

[sonny8l3]

I think I read somewhere that big bumps and 75+ is required to pre-qualify for a pilots license. :-)

[rhino 2]

This morning I was doing 75 and the tach was reading about 3700

I should not have been doing 75 but I wanted to see the RPMs

The fastest I have gone on my trike is in the high 90 MPH

one thing I found out is a set of bumps I normally slow way down for if I do 75 over them instead it is not that bad

Its like riding on abandoned rail road lines......The faster you ride between the rails in the ties with ATV's the smoother the ride......I kid you not....

[Fowler]

Its like riding on abandoned rail road lines......The faster you ride between the rails in the ties with ATV's the smoother the ride......I kid you not....

They actually did a test on that on Myth busters. They found the faster you go over bumps the less your vehicle moved up and down.

I liked the Myth Busters wish they were still on