losi xxxcr gearing
 

any ideas on wot gearing i shud be using wiv 13.5 iv currently using 25/84 its indoors wiv lipo

Depends on the size of the track but as a starting point go for a FDR of about 7.2, using 28/84 (you will probably be able to go a few pinion sizes higher if the motor isn't getting too warm)

I currenly have 22/82 with a 7.5 motor outdoors and I don't have any overheating issues

gearing
 

thanx mate iwas using 21/84 so its well down then

I thought FDR was meant to be about 9.5 or something? If this has changed it would explain why people are using large pinions compared to the "old" days

Depends what motor you are using. If you are running a 6.5 then and FDR of 9.5 is about right but slower & torquier 13.5T motors will use a higher ratio.

right i see. so my 8.5t should have a FDR of about 8.5? or 10.5?

cheers

in my xxx with a 27t i used 22/78 indoors and with 12t used 21/78 but outdoors on a large flowing track i ran 25/78

I run 25/78 with the timing nudged up from stock the 30' on my Novak 13.5, and it still runs cool. I go up to a 26/78 when I go back to 30'. I find I can keep up to the 10.5's (on my track) because the 13.5 is a little more tractable. I lose a little ground down the straight, but make it back elsewhere. I find this website helpful for quick gearing references.

http://www.comeseethis.com/gearing/Default.aspx

Thats a very nice website! Cheers for posting the link to that...
:thumbsup:

quote..."will use a higher ratio." so a higher ratio than 9.5 would be 12.5 or is it the other way ie: 6.5 is higher

thanks

Its the other way round: a ratio of 12.5:1 means that it takes 12.5 turns of the motor to turn the wheels once, wheras 6.5:1 only takes 6.5 turns of the motor to turn the wheels once, so wheels will spin faster hence higher ratio.

its abit backward....i wont try to understand it, just accept!

Ive got a fdr of 8 in a 2wd with 8.5 turn...about right do you think?

That should work ok, obviously if it is slow on the uptake or gets a bit hot, reduce (increase!) the fdr by using a smaller pinion (maybe to 21/78).

Here is a gear chart that you might find useful

cheers for your help chris

one last question which has been bugging me ages...

whats the advantage/difference going to 21/78 if the ratio would be the same as going to 24/84 (its not the same just an example!)

I thought it was the case that if your motors running hot add a pinion?

cheers!

In practice there won't be any noticeable difference (not that i've noticed anyway). The availability of different spur gears will allow for a bit more flexability in terms of what the mountings will physically take. With the kit 78Tsput, the smallest pinion that will fit is a 21T, any smaller and the teeth wont properly mesh so the alternative is to use the larger spur.

With regards overheating,that can happen because of both over and under gearing. An FDR of 8 for an 8.5 motor is fairly high so you would need a smaller pinion (thus giving an FDR of 9-9.5). If your FDR was say 11, your car may be undergeared so a larger pinion may be needed.

Hope this helps.