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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Tracking, Autocrossing, Dragstrip, Driving Techniques > Trap speeds with 335i



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      04-10-2016, 03:18 PM   #1
Grand_hustle17
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Trap speeds with 335i

Ok so ive tracked my car a few times and felt like maybe the track was off with the mph it lists on the slip, so ive kind of brushed it off. I went over the past weekend and had someone drive the car for a pass to see if he can see wth is going on with my clutch, when he came back, he surprisingly raised a concern or observation which put the thought back to the fore front of my mind, he said while going down the track he was looking at the speedo to kinda gauge how well he did (mind u this guy ive known for at least 8yrs and is religiously a track head, there with his GTR) he said he saw a trap of 120 which made him almost positive it was a 11.xxx pass but when he got the slip it was a measly 114mph and 12.9.. He said its weird how the mph was that far off... I wanted to lean maybe towards tires and specs but car is stock suspension and stock wheels and tire spec.

I say that to ask sould i be concerned about speedo calibration or is this normal?.. Most ive seen was 118mph and even then it felt like a 120+ trap.

This most def isnt my 1st time at the track but this is my 1st time where the traps seem at least 6mph off that what speedo is reading.
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      04-10-2016, 10:49 PM   #2
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Speedo error of 5 to 6 percent is pretty much the norm with these cars.

You can do some coding and unlock a function that displays your actual speed in the center dash display.

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      04-11-2016, 02:23 PM   #3
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The analog speedo is useless as an accurate speed indicator. Code in the digital speed readout with the corrector turned off to get a true speed. I'd still say the trap lights will be more accurate than either if it's a legit track.
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      04-12-2016, 11:01 PM   #4
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Great. Will do
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      04-19-2016, 11:35 AM   #5
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Yeah I'd expect to read around 125 on the speedometer when trapping at 120.
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      04-24-2016, 09:10 AM   #6
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Yeesh. Is it that bad?
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      04-24-2016, 03:13 PM   #7
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Quote:
Originally Posted by Grand_hustle17 View Post
Yeesh. Is it that bad?
The higher the speed, the larger a 5-6% difference becomes. Two mph is 5% at 40 mph, 6 mph is 5% at 120 mph.
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      04-30-2016, 07:19 PM   #8
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Woow.
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      05-12-2016, 11:39 PM   #9
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I laugh when I hear people talk about this subject. We learn from a young age that speedometers now days are digital (not like analog speedos) and most vehicles now days are coded from factory to read optimistic. Run your phones GPS with a speedometer app and watch for yourself the difference between your "true" speed and whats indicated. Yes that's perfectly normal to answer your question.

Note: some people say its a percentage (which is true in most cases) but some read a specific set amount, say 2-3mph over. (E46's are this way).

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      05-12-2016, 11:43 PM   #10
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Quote:
Originally Posted by gavronm View Post
Speedo error of 5 to 6 percent is pretty much the norm with these cars.

You can do some coding and unlock a function that displays your actual speed in the center dash display.

:

Yep, I have this and can confirm even at 195mph it was within a mph from my GPS. Its very accurate (as it should be) If you want proof I can show you the video but I'm not trying to get flamed for it lol
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      05-26-2016, 08:22 AM   #11
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Vids plz
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      05-30-2016, 11:58 AM   #12
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Quote:
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Vids plz
+1
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      06-10-2016, 05:51 AM   #13
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This car the stock speedo reads way to fast with stock 25 inch tires. Get 275/35/18 and the speedo will read accurately.
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      06-26-2016, 05:51 PM   #14
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Quote:
Originally Posted by Riceball777 View Post
This car the stock speedo reads way to fast with stock 25 inch tires. Get 275/35/18 and the speedo will read accurately.
275/35r18 will still read fast by 2-4% from my experience.
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      08-02-2016, 12:29 PM   #15
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Quote:
Originally Posted by Grand_hustle17 View Post
Vids plz
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      08-07-2016, 08:14 AM   #16
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