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Large spur vs small spur
07-20-2021, 08:20 AM
#1
Large spur vs small spur
I have been reading on forums that in modified is best to use as large spur as it is possible while in stock as small spur as it is possible.
Explanations were vague, so I have decided to create a new thread regarding this subject
So which spur size is best and why? Will this decision change depending the size of the track?
Thank you
Explanations were vague, so I have decided to create a new thread regarding this subject
So which spur size is best and why? Will this decision change depending the size of the track?
Thank you
07-20-2021, 08:59 AM
#2
There are so many threads about this.
But here is my summery:
But here is my summery:
If the ratio is the same it doesn't matter what combination of spur / pinion you use. There is no low end high end gain. a 28/60, 35/75 , 42/90 and 49/105 will all give you the same ratio (on an Xray T4 the FDR is: 4.071428571).
The ONLY difference that a normal human will notice is the car's weight balance.
The bigger gear will have a slightly smoother mesh, but unless you have a completely frictionless drive train no one will notice.
The rotational inertia will change but the math has been done and we are talking a 100th of a percent difference. (0.01%)
The ONLY difference that a normal human will notice is the car's weight balance.
The bigger gear will have a slightly smoother mesh, but unless you have a completely frictionless drive train no one will notice.
The rotational inertia will change but the math has been done and we are talking a 100th of a percent difference. (0.01%)
07-20-2021, 09:01 AM
#3
Tech Prophet
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Kinda curious to read what responses you get. I’ve struggled to get my head around gearing. The typical response will be that large/small spur moves the motor location for weight balance. Something along that that.
07-20-2021, 09:10 AM
#4
If keeping gear ratio the same, the bigger difference is weight balance shift. On my pan cars, I like to push the motor as far forward as I can on the pod, so I tend to run larger spurs.
07-20-2021, 11:45 AM
#5
Like mentioned you are shifting the 140-148g motor around by margins but it all accounts for something.
07-22-2021, 05:46 AM
#7
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I know now that it’s the motors now. . Just because a motor is a 17.5 does not mean the same gearing combination will work. I ran into this on clay in November when had to switch last minute from a Reedy to a Tekin motor. I had this again over the weekend with on road. As a last minute switch from a R1 to a Trinity. Same gearing was 2 laps slower with the Trinity.
07-22-2021, 05:55 AM
#8
There have been occasions, especially on my X12's, where the proper ratio for our track and given class, demanded such a large pinion, that I was unable to use the stock spur. In order to achieve the proper ratio, I had to decrease the tooth count on the spur and change the pinion accordingly, Just to get it to fit properly in the pod.
Sometimes physical mechanical constraints will affect gearing, but in general, I mirror the statements in the above posts..... the largest spur that I can and select pinion to suit.
Sometimes physical mechanical constraints will affect gearing, but in general, I mirror the statements in the above posts..... the largest spur that I can and select pinion to suit.
07-22-2021, 07:43 AM
#9
I know now that it’s the motors now. . Just because a motor is a 17.5 does not mean the same gearing combination will work. I ran into this on clay in November when had to switch last minute from a Reedy to a Tekin motor. I had this again over the weekend with on road. As a last minute switch from a R1 to a Trinity. Same gearing was 2 laps slower with the Trinity.
Driving style can also affect gearing. If you can maintain speed through corners well, you wouldn't want the same timing as someone who slows down in the corners more and needs more acceleration.
07-22-2021, 08:57 AM
#11
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Timing also will affect gearing. Higher timing spins faster with lower torque and low timing gives more torque but a lower motor speed.
Driving style can also affect gearing. If you can maintain speed through corners well, you wouldn't want the same timing as someone who slows down in the corners more and needs more acceleration.
Driving style can also affect gearing. If you can maintain speed through corners well, you wouldn't want the same timing as someone who slows down in the corners more and needs more acceleration.
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