mark kibort

We dont want to turn this into a gearing discussion, but lower gears, especially 1st , is sometimes more effective out of the start, BUT, gearing doesnt make hp , only more effective use of the HP you have available. It all depends on your operational speed range. This is easly seen with the drag simulators by doing a gear change and seeing the effects over varied speeds.
Lots of trade offs through the gears. 80 to 120 might be a sweet spot for a certain gear ratio, you only can get with a taller rear end. gear spacing doesnt change, but when it does, like in the Cup car GT3, you get better use of the available hp through closer gears, not lower gearing. I dont think this is an issue here as its only a 1.5% max difference in diameter we think. (although he has stated that there is no difference in diameters)
anyway, you dont nessarily get better acceleration overall with lower gearing. It depends on the speed range. generally, we want to just hit the rev limiter at the end of all main straights. I think with autocrossers, they can pretty much use only 1st gear and maybe 2nd, as their top speeds never are faster than 60-70mph I would imagine.

MUSSBERGER

Hey guys! Did I miss anything?

mark kibort

You didnt tell me if you are having to input the new tire diameter for speed sensing or is it all GPS. Any accelerometer readings? If the GPS and ground speed match up, how are they correlated with tire size. (I understand that the GPS part will be based on how you are tracked via satalite) I guess it really doesnt matter if the time to a certain postion on the track is now different and we want to know why. I cant think of anything else right now.

Im really leaning toward some type of engine power issue or difference.

mk

Brinkley

Regarding ground speed, I actually don't know how the sensor measures speed. I assume wheel speed indicated from abs system?

Circuit Motorsports

Consistent lap times /= consistent laps.

Show me the data to prove they are consistent

Circuit Motorsports

Easiest way for me is to hit the "print screen" button.

Go to MS Paint.

Edit--Paste

Save the pic and then post on here. If you have trouble posting you can send it to my email address and I'll get it up for you.

mark kibort

Like speedo input?? If so, you will be off there by the amount you might be concerned about. as I said, I just happen to have the exact same tires on the same sized rims as you do! 26" exactly is the diameter of the tire with a bubble level. If the speed sensor is for the stock tire on the car, certainly that would be an overall issue. I forgot the hight of my 275s, but they were well under 26".

Now, hard to argue with the time clock and GPS . Stilll puzzled.

mk

GT3CAR

I am pretty sure I also saw Brinkley drinking a Monster Power Drink while mounting the 18s....hmmm

2BWise

Just do a print screen of the i2 window showing the pertinent data. Even if you can't post it up maybe you could email it to me and I'll take a look. I've got the i2 pro software.

I know Motec calculates ground speed from wheel speed, but GPS as well, is there a GPS input? I never tried using one with the Motec.

What is considered matching up well? Almost dead nuts or off by a bit. Any error will easily show up as 2 mph. They should be nearly identical.

The other thing I've noticed with the Motec, if calculating track map from wheel speed and lateral accel, is that there will definitely be an error associated with sizes. Therefore if your ground speed isn't correct then you're track maps won't match up either. Are your distances for the straight identical, they should be?

2BWise

Its measured by measuring the number of rotations of the wheel. Therefore its back calculated using the rolling radius to give you wheel speed. If the radius you've entered isn't correct then the calculated wheel speed won't match the actual ground speed.

Brinkley

I mainly use gps speed and don't worry about changing wheel size imputs to maintain correct ground speed.?.
Joe, while in i2 I tried hitting the print scrn button and nothing happens. It does not give me a window to save that screen or anything.
I don't have MS Paint.

Circuit Motorsports

When you hit print screen it just saves it like hitting Copy in a program.

Then you just need to open up a graphics program and hit Paste and it should pop up.

MS Paint comes batched in all the Windows machines I've ever used.

Hit the Start Menu
All Programs
Accessories
It should be there. The name on my computer is just 'Paint' If not you could try another graphics program but I haven't ever checked to see if it worked on anything other than MS Paint

Brinkley

Here is a screen print from Sebring red speed line is 18's vs. black is 17's. thanks for your directions Joe.

Brinkley

Here is a zoomed in trace of Tower turn and Bishops Bend. Red line is 18's vs. Black line 17's

Brinkley

This is a larger image of the full lap and you can see how the 17's are faster at the end of each straight.