Harry's GPS Suite Forum

Hi all,

The gear position is most of the time wrong after the 2nd gear. Typical behavior reports the gear in use as one gear lower than actual.
My car is a Cayman R PDK and I use the following settings:

Gear ratios: gearbox PDK
1st gear 3.91
2nd gear 2.29
3rd gear 1.65
4th gear 1.30
5th gear 1.08
6th gear 0.88
7th gear 0.62
Final drive ratio: 3.25

Source: http://www.motorshow.me/GalleryDocs/Doc4133.pdf

Note: I also checked the size of my wheels.

There is one parameter from the specifications that I did not use: Constant ratio 1.114. Do I need to use this one?
Any other paramater to set to have a correct car setup for Harry's LapTimer?

Note 2: Tested with v20.0

Thanks!

Hi,

Except the factor, it looks o.k. I do not know what the constant ratio is either, but I assume it is another ratio to multiply. So please try 3.25x1.114 = 3.62 as the drive ratio. If I get it right, this should raise the resulting gear...

- Harry

Thanks! I will give a try tomorrow.
I also noticed that the speed reported on HLT is a little bit lower than the digital speed I get from my car. Do I need to check another parameter?

By default, LapTimer displays the value it receives from the bus. It can be calibrated to the (correct) GPS speed by setting a multiplier in LapTimer's expert settings. The car's dashboard display always needs to be the same or higher than the real speed. This is to make sure speed limits are kept. Or the other way around: GPS (at constant speeds) is the most precise value. OBD delivers a sensor value which may be above or below the real value. Ideally you calibrate it using the named multiplier and GPS speed. This merges the best of two worlds: GPS precision and wheel speed sensor dynamics. Finally the dashboard value is a tactic or politic value you can't trust.

- Harry

Harry,

Is there a way using HLT to display both the GPS speed and OBD speed so I can calculate the multiplier value?

The best way to adjust OBD wheel speed to GPS speed is to compare your odometer to a GPS distance traveled. The longer the distance, the better the result. You need to do this on the highway. Stopping may cause the GPS distance reading to drift if it doesn't filter out very low speeds. I've had this problem with GPS Buddy. If I left it running when the car was parked, the distance slowly increased. Or at least it did in the past.

When calibrated, the OBD wheel speed is accurate. The dash display is not.

Another problem is that the tire size may not be giving you the correct number of revolutions/mile or km. I can't remember if I've requested being able to enter revs/mile as an alternative to tire size.

Edit: Yes, I did request that feature.

Yes, try the speed chart in Data Recordings for any lap recorded with OND. We had some discussions here on the forum too, so please try the search function.

Harry

Another way, if you have a spreadsheet program, is to export a lap in .csv format and plot GPS wheel speed on the Y axis and OBD wheel speed on the X axis. Fit a line to the data and the slope of the line is the correction factor. You may want to use a fixed intercept of zero, but it shouldn't be necessary.

Hello,

FYI using constant ratio as a multiplier has worked. So my initial problem is solved! Thanks

Hello,

While debugging some freeze issues (see viewtopic.php?f=8&t=4142&p=21401#p21401) I noticed that GPS buddy application correctly displays the current gear while I did not enter any data related to my car. Does that mean that I don't need to set the gear ratio anymore?

Thanks!