Tire Pressure vs Speed

delagem

We were having some fun today with a new toy, the Stalker ATS II graphing Radar gun. This is the same gun that magazines and tuning professionals are using to gather their data with, unless they still have the old ATS I gun...



We tried a variety of runs, using different tire pressures, to see if there really was a significant difference on pressure vs speed on a stock setup.

For the record, Stalker Radar gun calibrated by Stalker within the past 2 weeks. Pressure gauge calibrated by Michelin tire vendor at the race track last year. Battery voltage at 49.0v, approximately 60% charged, at the start of the test. Only 0.1v drop from before the test, until after. Student driver, Michael Jr, at the wheel...

We started at 50 psi, and made passes of about 100 yds, lowered the tire pressure by 10 psi, and made another run. Due to a screw-up in logging the data, the 50 psi run had to be repeated, but the results were the same.... This also proved that the runs were consistent, getting the same speed at both the beginning and at the end of the test.





What does all this mean? Well, it would appear that pressures in excess of 30 psi are statistically insignificant, speed-wise. We were quite nervous that a bead would pop during the 50 psi tests, but there were no problems. The test pilot commented on how much more jarring the ride was above 30 psi, and how hard and mushy the steering was at 10 psi.

Also, this goes to show that GPS isn't as accurate as I would have hoped. I got many 16mph and a 17mph GPS run on this cart, but nothing that high was recorded today!

BGW

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gornoman

"The data on the Mig is inaccurate." Top Gun

The difference between previous GPS runs and your current radar runs does not exhibit controlled conditions. Having the GPS onboard WHILE doing the radar runs would show definitive results.

The nice part about using GPS data for speed comparisons is the fact that we ALL can use the same criterea (the satellites) to take seperate measurements, therefore supporting the "apples-to-apples" scenario.

Overinflating a tire COULD reduce the size of the contact patch so much that traction is being LOST, and the cart is slower. I'm not saying that is what happens, it's just a possibility. Thanx for sharing your results.

TerryH

I'd say that the results are all about the roll out of the tire. As the pressure increases, the tire becomes taller and harder leading to more roll out per revolution and therefore faster speed at the same motor rpm. Of course, I could be wrong.

shadowman

does it really matter that much?.....isn,t the person usisg it supposed to be certified also? don,t know why..........i had a security guard at camp hit me with a radar gun while i passed someone on my cart......the place was empty but his excuse was i could have hurt a child ( there were none anywhere to be seen ) i said ok barney fife how fast was i going and where,d you hide your sickle......i think i pissed him off..........................

delagem

I hold an FCC General Radiotelephone Operator License, a GMDSS Maintainer license, and a Radar endorsement. I'm qualified. If it matters that much!

Honestly, though, this was just about having some fun with my son. I had read some posts here about improving speed via raising tire pressure, and, to a limited extent, it does appear to be true.

Just like gearing on a racebike, within limits you can improve upon speed or acceleration. But there comes a point when you go past what the available power can move. It would appear that this limit comes pretty early on a 3hp stock electric motor!

shadowman

dosn,t matter a bit to me but to be honest i think using a radar gun on a golfcart is silly but thats just me........after all there golfcarts not race cars.................

kernal

I found it interesting. Thanks for taking the time to post the data.
I'll bet it was fun for your son!

I've been running 22-25 psi in my carts for years and your tests validate that I've been on the right track.

Stevegrmich

scubabud

delagem... out of curiosity what were the tires rated at... max PSI.

Thanks for your input as well...

delagem

Um, yeah. About that. 22psi max, according to the sidewall. Carlisle Links brand tires. I certainly wouldn't recommend running the tires as high as we tested, but we wanted to see if there were any improvements as we went higher.