Low down bum

Corvus · Post by **Corvus** » Sun Feb 07, 2016 9:48 am

http://thekneeslider.com/homebuilt-recu ... ned-event/

Is the low c of g a benefit or hindrance in racing? The frontal area will nearly halve, l guess, but what about the fast cornering? Won't you need a lot more lean angle?

I like anything different and this is different! Plus, hats off to the guy for sheer determination, to say nothing of sheer ability. I love it for that.

SP250 · Post by **SP250** » Sun Feb 07, 2016 3:06 pm

Seem to remember Royce Creasey or Malcolm Newell back in the 1970's using a Quasar in the IOM during TT week.
With only about 40 HP from the Reliant engine, they were leaving the sportbikes of the day for dead through the twisty bits and then getting caught and passed on the straight bits.
All reported in Motorcyle Sport IIRC.

Bit like VHS and Betamax.....the better system lost out to cheaper pricing and fashion / marketing, reluctance to change.

John

Blackal · Post by **Blackal** » Sun Feb 07, 2016 3:26 pm

Low CoG beneficial?

Must be a rhetorical question?

Take moments about the contact point (tyre on tarmac) - that will convince you.

Al

Corvus · Post by **Corvus** » Sun Feb 07, 2016 5:04 pm

Blackal wrote:Low CoG beneficial?

Must be a rhetorical question?

Take moments about the contact point (tyre on tarmac) - that will convince you.

Al

Non rhetorical.

If pressed I'd have to guess that there'd be trade off's? Gotta be, surely? What are they?

Taking the moments seems to suggest a greater angle of lean for a very low centre of gravity? But I'm not sure.

It would be difficult to hang off of such a machine I'd imagine. But why hang off in the first place?

Would such a machine be able to switch from extreme angles of lean (ie extreme changes of direction) more easily?

The frontal area must be lessened?

I'm assuming the wheelbase would increase?

If low c of g is overall a great asset, why aren't we seeing moto gp machines with things like underslung suspension and fuel tanks?

Dog Tyred · Post by **Dog Tyred** » Sun Feb 07, 2016 5:04 pm

LcG bound to be an advantage but not sure about the increased wheel base ?

DT

Boxered · Post by **Boxered** » Sun Feb 07, 2016 8:36 pm

Hmm swings and roundabouts I think, it's gotta be difficult trying to shift your weight on a recumbent? would you still need or want to load the front/rear for corners? It would certainly make for interesting racing on the Moto GP grid.

Steve

Hayden · Post by **Hayden** » Sun Feb 07, 2016 8:46 pm

its the riding position for me, I just cannot imagine it being as fun/involving as a normal bike, especially a sport bike.....its more like extreme cruising?

Also, in the event of a crash theres a good chance the engine would be forced up your jacksie

Corvus · Post by **Corvus** » Mon Feb 08, 2016 6:31 am

Hayden wrote:its the riding position for me, I just cannot imagine it being as fun/involving as a normal bike, especially a sport bike.....its more like extreme cruising?
Also, in the event of a crash theres a good chance the engine would be forced up your jacksie

I agree on both points there. Modern sport riding and especially racing is, bodily, quite dynamic and the recumbent position doesn't suggest that it lends itself well to this. But, having never ridden one, I'm speculating. It'd be good to hear from someone who has actually designed and ridden one.

The crash scenario is a good point. Sliding off, probably able to bale out, but any scenario where you're thrown forward might be grim!

Regarding c of g in height terms, I must admit that, whenever I carry luggage I much prefer throw over panniers to a tank bag and I despise top boxes. So maybe this is telling me something. Maybe, though, there's a "sweet spot" for c of g and I just can't help feeling this type of machine has it below that "sweet spot".

Blackal · Post by **Blackal** » Mon Feb 08, 2016 6:40 am

For change of direction ability - think

a) Metronome

b) Polar momentum in cars like Porsche 928 vs Toyota MR2

Al

Corvus · Post by **Corvus** » Mon Feb 08, 2016 7:01 am

Page 49 motorcycle design and technology, gaetano cocco.

"By raising the centre of gravity along with the radius of curvature and speed of travel, the motorcycle does not have to be as steeply banked.

A rather surprising fact , indeed!"

Rapid changes of direction I'm inclined to believe blackal's last post.

SP250 · Post by **SP250** » Mon Feb 08, 2016 9:42 am

With the carbon framed singles that Hejira used to race, we found that an under engine or under seat fuel tank gave better braking stability. But they were very much harder to get to change direction in S bends. The CG being up higher with a conventional above engine fuel tank gave the rider some weight to leverage against and then the bike would flick from side to side easier once the inertia was overcome. Always a trade off.

John