Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 Lugging the motor

Might cause another shift prior to sixty slowing down that 0-60 time 😬

That's a good point.

Regardless of the rpms and speed, you just get to "know" when your motor is under more load than it should be for the rpms and speed.

Some people get this and others do not. My ex-father in-law had no concept of mechanical anything. He couldn't even put his lawnmower belt back on without it going backwards.

Some are inherently in tune with the vehicle.

The definitions all make sense to me and one may relate to one person more than another. It's just how you understand this type of thing.

Most of the Harley guys say don't run under a certain rpm in a certain gear as they say that would be lugging the motor. I will say this, that on my old Shovelhead and my '09 Twin-Cam, I typically run in the lower rpm range than most others might do....... But I do know when my motor is under a "lugging" situation and downshift accordingly. There are no set rules for this. It's all situation logistics at the time. But I can cruise back roads at 1800 or 2000 rpms without any fear of lugging the motor.

There is a slight difference between a Harley and the S&S Wedge motors. The Harley uses a multi-piece crank and if you do lug the motor you can possibly scissor the crank and that's a bad thing. On a S&S Wedge they use a one-piece crank similar to the automotive type. The rods are a split main cap design and run side by side versus the Harley which are solid loop rod on the crank pin end and one rod is inside the other forked rod. The two flywheels have to be pressed onto the rod crank pin. Without having the crank trued and welded, a stock crank can get screwed up pretty easily.

Sorry for rambling.

I had many old cars and some smaller European cars, '59 Fiat 500 as an example. All of these small cars had a sweet speed that you just went to and let it run in the zone. My old Shovelhead this is around 55 to 60 mph. Will it run faster, heck yes, but the bars and seat start to vibrate and it just doesn't feel right. Although my wife tends to want me to ride a bit faster. Apparently she doesn't mind the vibration, can't figure that one out, can anyone help with that???

I agree that most of my bikes have had a sweet spot relative to speed. I've yet to notice that on my M3W...it's more about RPM, regardless of speed. It's 3,500, precisely where she's also at max torque. Ecstasy!

Mechanical sympathy is what you need.

Like you said Dan some have it and some don't.

My wife only has to look at something mechanical and it will malfunction or break.

Good job I'm a professional bodger.

I agree Ken.

The thing about V-twins is that 45 degree motors can only be balanced for one rpm "range". Most are in the mid 3's for that perfect balance.

A 90 degree V-twin can be balanced wider range of rpms.

A 56.25 degree still has balance issues like the 45 degree motor and as such it too will have a "sweet" spot in the rpms that it will be velvety smooth.

Now take the Harley "B" motor, it has counterbalance shafts and it can be balanced and mounted solidly in a frame and be perfectly smooth. And for this, it costs hp as all the rotating mass take hp to turn.

I envy all you guys being able to ride in your M3W's while I'm still contemplating the investment that I don't have the funds to undertake. I'm not going to borrow money to get a toy. I'm too close to retirement and I have other priorities at this point.

So I will continue to live out my fantasy through all of you guys having a blast with your cycle-cars.

Dan,

Borrow the money...you're terminal.

In my opinion 0-60 is nothing but pure marketing, they love giving you a one shift to 60 but that's where the benefit stops. If you're only accelerating to 60 then yeah the five speeds are great. If you're going faster a six speed combined with the right rear end gets you past 60 quicker. You might be behind at 60 but by 70 you've caught back up and it's just gains beyond that and more overall time in the sweet spot of the torque curve.

That said that's considering peaks for a Miata which in stock form is hitting peak torque about 1500-2000 rpm higher than the x-wedge.

If anyone knows the ratio of the bevel box and belt pulleys some more maths could be done to see just where it would stand, and that's of course still just theory. Real world performance would eventually be the only way. That said I have friends in Miata clubs with spare transmissions and have already had this thought myself, just need my three wheeler first

https://goo.gl/UPYbdb

I know some numbers are off here mainly the assumed calculation for the bevel box. If anyone knows what the actual ratio is in there please let me know, I haven't found anything here on the forum or online about it. I have to imagine it's higher than what I've given here.

Also I know the front to rear tooth count is off but there are limitations to the tool. It's still a 2:1 ratio so that shouldn't matter what it has fit the tooth count.

You can set the shift rpm and hit auto shift to see a nice little animation of the rpms speeds and shifts.

Ok one more comment. I found an image that Richard Wood posted from garage 56 showing the internals of the bevel box. It looks like it is coincidentally running 30:15 so another 2:1 ratio there giving the combined reduction via the bevel box and rear sprockets at 4:1

I just counted the teeth, not sure why people in the threads about bevel boxes never did that.


So with that based on one of the various setups you can get for gearing in a stock Miata transmission the following link to that calculator linked before shows you the speed at rpm and shifts etc.

https://goo.gl/AK3Pcj

One thing to note with the huge Miata community you can get gears in nearly any setup you want without too much difficulty. So maybe there is an even better setup for three wheelers and just the stock transmission would provide. People with actual racing experience feel free to chime in on that.