Tire PSI and Gyro Effect

[redsnapper]

My 2 wheels were running with rather bouncy inflation and I decided to test higher PSI - I'm but a wee lad of 150lbs and I put 45psi in my s1. I was astonished at how significant the effect was on driveability.  At higher pressure the gyro effect of the wheel seemed extreme and it was pretty near impossible to carve from side to side above 10mph. Quick turns seemed very hard to do. Clearly there is less tire in contact with the ground and you are riding on a much thinner band of the tire.  I guess when you change the roll angle to turn on a high PSI tire, it takes more relative roll than on a low psi tire and hence turning seems less responsive. I was really blown away by the effect of high vs low PSI and I quickly went back to a softer inflation. I wonder if others have also found this effect? I wonder what physics can explain this?

[tudordewolf]

100% same experience on my 84V Msuper, at relatively low PSI too; it's not just the turn but my ability to lean it at all. ~30 psi is the highest I can comfortably go before it feels like it's actively fighting my leans, and over 40 psi it feels like it might go into speed wobble because it's so "stiff." 

I think it must be something to do with the contact patch, like you say. Maybe it shifts forwards or backwards when you try to turn in a way that produces a negative-feedback loop in regards to tilt; like if the patch shifts off the centerline and forward, then the motor itself would be trying to straighten you out (maybe?) 

There's more air and therefore more mass around the rim, but I can't imagine it would be enough to make a difference via gyroscopic force.

[redsnapper]

ironically when I bought my 9bot S1 the seller told me he was selling cuz he could not learn to ride the wheel. when the unit arrived all looked ok so I hopped on but within 3 feet I had to jump off. tried again same thing. testing by hand the tire pressure seemed ok but when I put a gauge on it there was only 6psi! the wheel was unrideable... so it must have come from the factory with low pressure and the original buyer never realised it. poor chap never had a hope of being able to ride that wheel :-(

 

[Boogieman]

On a Tesla 16*2.125, the higher the pressure, the zippier it turns (also a lot more nervous going straight).

Running 3.5-3.8 Bar (spec 2.8-4.6Bar / 4-6.5PSI) on my Kenda K924-003 makes it extremely fast turning.

Steering from the hips was never easier.

Edited July 15, 2020 by Boogieman

[Dgar]

 

On 5/16/2020 at 2:36 PM, tudordewolf said:

100% same experience on my 84V Msuper, at relatively low PSI too; it's not just the turn but my ability to lean it at all. ~30 psi is the highest I can comfortably go before it feels like it's actively fighting my leans, and over 40 psi it feels like it might go into speed wobble because it's so "stiff." 

I learned on a KS14D and I just received my V11 a week ago and pumped the tire to 40lbs. I'm 220lbs (100kg). I had a hard time leaning and turning and figured it was just the nature of a larger wheel but it did feel like there was a gyroscopic effect that kept me from leaning side to side sometimes. I kept my KS wheel at 35lbs and got very used to that. I'm sure part of it is the differences in the wheels but your description sounded a lot like my experience. I will need to experiment more with tire pressure to find what I like. After about 10 miles I did get used to the V11 and feel like I can turn on a dime now.

 

[Dgar]

I was just out riding again and noticed that on the berms, or any surface slanted slanted to the left or right, the V11 really wants to tilt that way. I think that might have been some of the difficulty in turning I was referring to above. Now that I am aware of what is causing it I can adjust but it really feels crazy moving from one side of the road to the other and having to adjust quickly right when I cross the middle of the road. I never felt that with my KS14. It might also be caused by the height of the pedals on the V11 or even the type of tire I guess.