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Author Topic: C5 and G5 speedometer question  (Read 1056 times)

GSS

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C5 and G5 speedometer question
« on: May 01, 2011, 12:36:55 AM »
Does anyone know if there is any difference in the speedometer gear ratios at the front tire hub between the C5 and G5?  Did RE slap on the same parts on both bikes despite the difference in tire/wheel sizes?  It might explain the somewhat optimistic speeds I am seeing with my C5.....
2014 GT - Red
2010 C5 - Teal
It's a Jeep thing......you wouldn't understand.

olhogrider

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Re: C5 and G5 speedometer question
« Reply #1 on: May 01, 2011, 01:45:40 AM »
A dealer could check the part numbers but I suspect that is the case. I have heard that some European countries levy heavy fines against manufacturers if they are even 1 kph BELOW the actual so they all err on the high side.

singhg5

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Re: C5 and G5 speedometer question
« Reply #2 on: May 01, 2011, 03:48:02 AM »
...  It might explain the somewhat optimistic speeds I am seeing with my C5.....

Most of the speedometers on REs are optimistic, reading about 5-10% higher than actual speed.  I had tested my G5 with a GPS and posted the results in another thread in 2009.  Here is a copy of part of the thread.

"Just bought a TomTom on Thanksgiving.  So l thought of checking speedometer readings on my G5 versus GPS.  Here are my results."

                              RE Speedometer       GPS (mph)

                                  20  mph                       18

                                  30   mph                      28

                                  40   mph                      37

                                  50   mph                      46

                                  60  mph                       55

                                  70  mph                       65

                                  80  mph                       75

"At lower speeds, the difference between speedometer and acutal speed is only 2 mph (less than actual).  It increases to 5 mph (less than actual) at 60 mph and then remains constantly off by 5 mph (less than actual).  Just to make sure that my TomTom GPS was good, I tested it against my Toyota Corolla car.  The readings were right on."  
1970's Jawa /  Yezdi
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jjoe256

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Re: C5 and G5 speedometer question
« Reply #3 on: May 01, 2011, 04:09:33 AM »
With my Sigma 1606l dialed in speedo through radar and mileposts, I am consistently 8-10% high. 66 indicated is barely 60. 70 is 63, 87 is 77.5mph on my G-5.

GSS

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Re: C5 and G5 speedometer question
« Reply #4 on: May 01, 2011, 04:51:30 AM »
My curiosity just hit a new high. If the G5 is off by these numbers, the C5 is probably off by even more. No wonder I am being tailgated by the slowest drivers even when I seem to be +5 over the limit! Time to pull out the gps the next time we have sunshine.......!
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It's a Jeep thing......you wouldn't understand.

drbvac

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Re: C5 and G5 speedometer question
« Reply #5 on: May 03, 2011, 09:43:51 PM »
Glad I am always 10 mph over the limit  :D
Dr B

GSS

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Re: C5 and G5 speedometer question
« Reply #6 on: May 08, 2011, 12:54:21 AM »
I used a Garmin GPS with the C5 and stock 18" wheels, and front tire at 18 psi.

RE speedometer          GPS

30 mph                          25-26 mph
55 mph                          50 mph
65 mph                          59-60 mph

It is definitely off by 10-11% and appears to be a bit more optimistic than the numbers seen by others on their G5s with 19" wheels. The C5 should definitely get a bit more accurate with a 19" front wheel conversion.

On that note, what is the largest diameter tire that anyone has safely used on the stock 18" front wheel?

« Last Edit: June 11, 2011, 12:42:50 PM by GSS »
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gashousegorilla

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Re: C5 and G5 speedometer question
« Reply #7 on: May 08, 2011, 01:31:04 AM »
 Don't know why you guys gotta keep ruining the feeling that we are going faster then what we really are!  Who cares!......  My speedo said the Ton!  ::) :D























An thaibhsí atá rattling ag an doras agus tá sé an diabhal sa chathaoir.

GreenMachine

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Re: C5 and G5 speedometer question
« Reply #8 on: May 08, 2011, 01:48:57 AM »
i figure if u going 10 mph faster than the posted, u still not going to get a ticket..
Oh Magoo you done it again

GSS

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Re: C5 and G5 speedometer question
« Reply #9 on: May 08, 2011, 02:03:18 AM »
Don't know why you guys gotta keep ruining the feeling that we are going faster then what we really are!  Who cares!......  My speedo said the Ton!  ::) :D
Ha!  Got 800 miles on mine and made it to "RE 70" for a few seconds today........will try not to post any GPS readings when I get to a ton either.......  :D
« Last Edit: May 08, 2011, 02:05:34 AM by GSS »
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GreenMachine

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Re: C5 and G5 speedometer question
« Reply #10 on: May 08, 2011, 02:11:27 AM »
don't blow it up.... ;D
Oh Magoo you done it again

gashousegorilla

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Re: C5 and G5 speedometer question
« Reply #11 on: May 08, 2011, 02:53:33 AM »
don't blow it up.... ;D
Rev Limiter.......... :-\
An thaibhsí atá rattling ag an doras agus tá sé an diabhal sa chathaoir.

BRADEY

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Re: C5 and G5 speedometer question
« Reply #12 on: May 08, 2011, 05:18:26 AM »
I have said it before, and I still mantain, that more than the speedo, its the Odometer that goes wild. Try to match a distance between two milestones with your Odo, and you will find, it reads 8-10% higher distance than actual  8)

Ducati Scotty

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Re: C5 and G5 speedometer question
« Reply #13 on: May 08, 2011, 12:54:33 PM »
I have said it before, and I still mantain, that more than the speedo, its the Odometer that goes wild. Try to match a distance between two milestones with your Odo, and you will find, it reads 8-10% higher distance than actual  8)

Maybe the speedo and odo are both perfect and we just need to get the correct gearing in the drive unit on the front axle for it all to be accurate.

Scott

GSS

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Re: C5 and G5 speedometer question
« Reply #14 on: May 09, 2011, 12:42:33 AM »
It is indeed an incorrect gear ratio in the front axle hub. There are a dozen different speedometer drive gears available for jeeps where we frequently alter rings and pinions in the differentials to accommodate larger tires for off-roading (newer ones are electronically adjustable).

There has to be a solution for this as well. Maybe our hosts could elaborate as well. Despite our light-hearted comments, it can be a safety issue if you are being tailgated by irate drivers for going "slow".
2014 GT - Red
2010 C5 - Teal
It's a Jeep thing......you wouldn't understand.