How many teeth on your front and rear sprocket?

[nicks94tbirdsc]

I did a search to try and find this with very minimal success. As a new team we are just trying to figure if we have our sizes close to what others are using to make sure we are at least in the ballpark. of course the actual ratio you use will vary depending on engine setup and what your curves look like ect. If anyone wants to share how many teeth they use on the motor sprocket and differential sprocket it would be appreciated. Thanks in advance

[Storbeck]

Ours is 14-52. I know I've talked to at least a couple of teams with 14-48.

[Garlic]

I've seen a huge variation over the years. From 60-11 to 45-13. Seems like teams don't put as much thought into final drive as they should IMO, but perhaps they just have differing philospophies about it.

These cars have enough power and gears (generally) that it's not a huge disadvantage if you aren't perfect on this I guess.

[nicks94tbirdsc]

Thanks for all the input so far, although Id still like to hear more if people are willing to share. I think it just depends on your motors numbers and curves whether or not you need to make up for it with steeper gearing.

[jack]

13:39 = 3:1

[Denny Trimble]

Depends on your shift strategy. Many teams launch the car in 2nd gear and only use 2/3/4/5 on the course, avoiding neutral. These teams use a high numerical final drive ratio.

We've been a 1st-gear team for as long as I can remember, launching in 1st, and using 1/2/3 on course with ratios from 13:44 to 13:47 with F4i's and 20" wheels.

The 1-2 shift is interesting, because you go through neutral, and the RPM drop is large.

[nicks94tbirdsc]

Thanks for the input Denny. I believe we are planning on using first gear, but since this is our first car Im sure well play around and see what we like best. Currently on the car we have a 13:52. WE will jsut have to get everything going working properly and decide where we want to go with some testing.

[Frank]

"1st gear team" 13:46

[Daves]

2005 LeTourneau Univ. used 14/65. The drivers wanted to be able to burn out any time.

Speaking of sprockets, I've been looking into chains. Last year, I chose a 428 because it was supposedly lighter than a 520. This year, I realized I made a simple math error. The weight/100 links for a 428 chain and for a 520 chain cannot be directly compared since their pitches are different. Must multiply the 428 value by 5/4 to get the 520 equivalent. Here are the lightest chains from RK, DID, and EK I have found (all weight units are lbs, all strength units are lbs):

Weight/100 links 5-Series Equiv. Strength P/N
1.59 1.99 4300 EK Sport Series 420
1.68 2.10 3580 DID 420V
1.72 2.15 4200 RK "O"� Ring: 420 SO
1.79 2.24 4400 EK Sport Series 428
2.63 2.63 5870 DID 520ERS2
2.13 2.66 5800 RK 428 MXZ
2.2 2.75 5740 DID 428 NZ
2.27 2.84 5500 EK 428SHR
2.84 2.84 6600 EK 520 MRDL
2.84 2.84 7200 RK Heavy Duty: 520 GBTR Gold

You can see that the difference between the lightest 428 and lightest 520 is only 0.39 lbs, but that's for 100 links. Assuming about (60) links, that's only about 0.23 lbs lighter. However, the 428 sprockets are actually slightly wider (5/16" width vs 1/4"), so that 0.23 lbs may be regained in the sprocket weight. So essentially it appears that the 428 sprocket/chain setup maintains about the same weight with considerably less strength (4400 lb chain vs 5870 lb).

Has anybody found the weight/100 links of any titanium 420-series chains (like those made by Sidewinder)?

[Mechanicaldan]

If you haven't made one yet, I suggest you make a thrust chart. Take the torque curve of your engine and multiply it by the gear reduction and drivetrain until it gets to the ground at the contact patch.

It's amazing what an advantage you can gain with the right gearing. 40 ft/lbs can still make 1200 pounds of thrust to push a 450 lbs car into 13th place in acceleration. Only 60 HP. It was 13/50 gears.

This is basic physics. F=m*a F is thrust force from gearing up torque. M is your car mass. A is acceleration. There's 2 things you can do to make your car faster.

If the top speed of the course is 65 mph, then why would you not gear limit your car to around that speed and take advantage of the available thrust?