blackjohn was referring to my sled.... the difference on the speedo (going from 8T to 9T) was 1/8 or 12.5% lower reading (ie: if 100mph before, now, shows 88mph) that worked well for me, my speedo and radar are very close now....
similarily, if you are going from 9T to 10T that would be 1/9 or 11.1%
Kmer[/quote]
Kmer can you go into a little more detail of how you figure your math? From my experience your right on--the speedo with 8 tooth drivers are exactly 12% off from my GPS. I want to figure out how 9 and 10 tooth drivers change the gearing. I run a 21/40, what gearing would that be equivalent to in a 9 and 10 tooth driver. Thanks WB
similarily, if you are going from 9T to 10T that would be 1/9 or 11.1%
Kmer[/quote]
Kmer can you go into a little more detail of how you figure your math? From my experience your right on--the speedo with 8 tooth drivers are exactly 12% off from my GPS. I want to figure out how 9 and 10 tooth drivers change the gearing. I run a 21/40, what gearing would that be equivalent to in a 9 and 10 tooth driver. Thanks WB
Buckeye
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Speedo
So if you have a shorty with 9 tooth drivers and get a Mtn. speedo you would be right on or damn close? :idea:
So if you have a shorty with 9 tooth drivers and get a Mtn. speedo you would be right on or damn close? :idea:
kmer
Expert
wildbill said:
Changing your gearing won't affect your speedo calibration. No matter what you do to the gearing, you only change the actual speed of the sled... the speedo will still be out by the same percentage.
Notice I said percentage and not speed. If your actual speed drops 10mph then the reported speed will be about 1mph less as well.
1 mph is pretty insignificant at this point so you could easily neglect this effect when calibrating. For our purposes, gearing has nothing to do with calibration of the speedo.
The speedo precision remains relatively constant (ie: always 12% out). Accuracy, however, can be improved through calibration.
The speedo sensor is on the drive axle itself. The only* way to trick (calibrate) your speedo is to either
1) change number of teeth on pickup wheel (ie: by grinding one or two off)
If you start with 15 teeth and grind 1 off, the effect would be 1/15 or 6.7% lower than stock reading on speedo.
Now, if you grind another one off, the effect would be 1/14 (7.1%) lower reading than the last modified reading. It's equivalent to 2/15 (13.4%) lower than stock reading. Depends on how you look at it -- ie: what your initial starting point is.
2) change the number of teeth of the drive axle (driver size)
Remember that driver cogs, whether they are 8T, 9T or 10T are all spaced the same - they have to be to match the standard lugs on your track.
Changing driver effect is opposite to the modifying the speedo pickup wheel. If you start with an 8T driver and go with 9T (ADD 1 tooth), thats a 1/8 (12.5%) decrease in stock speedo reading. From 9T to 10T is 1/9 (11.1%) decrease.
1 tooth added
-
8 tooth initially......1/8 = 0.125....0.125 * 100 = 12.5%
* there are expensive ways/devices to achieve calibration electronically, but hardly seem worth it to me
kmer
Expert
Wildbill,
Are you going to change drivers?
If yes, going from an 8T to a 9T will give the 12% correction you need.
If no, grinding two teeth off the pickup wheel will over correct by about 1 or 2%. Note you should only grind one at a time to verify these calculations. The speedo gear is fairly inexpensive (about $20 i think).
Are you going to change drivers?
If yes, going from an 8T to a 9T will give the 12% correction you need.
If no, grinding two teeth off the pickup wheel will over correct by about 1 or 2%. Note you should only grind one at a time to verify these calculations. The speedo gear is fairly inexpensive (about $20 i think).
kmer
Expert
Re: Speedo
I believe the speedos are the same aren't they?
'03 Part No. is 8FA-83500-00-00 for both mtn and shorty.
*edit - here are the '04 part nos. - they ARE different
'04 Part No. is 8FG-83500-00-00 for shorty.
'04 Part No. is 8EP-83500-20-00 for mtn.
Even the pickup wheels are same, no?
'03 Pickup wheel part no. is 8EK-47715-00-00 for both mtn and shorty.
Buckeye said:
I believe the speedos are the same aren't they?
'03 Part No. is 8FA-83500-00-00 for both mtn and shorty.
*edit - here are the '04 part nos. - they ARE different
'04 Part No. is 8FG-83500-00-00 for shorty.
'04 Part No. is 8EP-83500-20-00 for mtn.
Even the pickup wheels are same, no?
'03 Pickup wheel part no. is 8EK-47715-00-00 for both mtn and shorty.
Kmer thanks that makes sense to me. I have a friend with 9t and one with 10t drivers and am waiting to see how they are in the steep and deep before I decide what to do. Now can it be reasonably assumed that if you go from 8 tooth to 9 tooth it would affect my gearing by 12.5%. In other words if I'm running a 40/21 (1.90) with 8 tooth and swithed to 9 tooth it would decrease 12.5% to a 1.66 gear ratio (10 tooth =1.48)? Or does the gearing not work that way?
kmer
Expert
Wildbill,
No problem. You got it. You would effectively have a taller ratio.
I would like to go to 10T as well. Keep us posted on your findings. What mods to your friends have been done to accommodate the 10T? Mine is at its limit with the 9T, stock skid and 1.25 x 151" track.
No problem. You got it. You would effectively have a taller ratio.
I would like to go to 10T as well. Keep us posted on your findings. What mods to your friends have been done to accommodate the 10T? Mine is at its limit with the 9T, stock skid and 1.25 x 151" track.
Kmer these photos should answer your question. They rolled the chaincase. One is running a 159 x 2 x 15 with 9 tooth the other a 151 x 2 x 16 with 10 tooth.
kmer
Expert
Thanks wildbill. You've answered many questions i had about rolled cases with just those two photos. Perfect.
Thanks again. :wink:
Thanks again. :wink:
