I was running a big track this past weekend (5/16 mile) running a 17/68 turning 6200rpm. I needed more top end speed so I went 17/65 but for some reason I couldn't get the rpm's up, they dropped to 5300. Should I have gone the other direction on the rear or should I have dropped the driver to a 16? Why? I'm new to all of this just my 3rd weekend in a clone.
Starting gear for clone
- Thread starter bullerman
- Start date
I was running a big track this past weekend (5/16 mile) running a 17/68 turning 6200rpm. I needed more top end speed so I went 17/65 but for some reason I couldn't get the rpm's up, they dropped to 5300. Should I have gone the other direction on the rear or should I have dropped the driver to a 16? Why? I'm new to all of this just my 3rd weekend in a clone.
Lightning3
Member
If the track is truly 5/16 of a mile; I can't imagine running a 16 driver and don't know that a 17 is big enough. To answer your question, you would take teeth off the back to increase top speed potential. 3 teeth should not equate to a 900 RPM loss. What were your RPM drops on 17/68 vs 17/65? Did you see or hear of anyone else running that big of a rear gear?
racing promotor
Moderator
Since you were only turning 6200 rpm on a clone when you say you needed more top end, I assume YOU mean you needed MORE rpm, if this is the case you went the wrong way provided the 17/68 was correct ( which I doubt it was ) and since you were already on a 68 rear you would not have went bigger rear, so ya you should of dropped to a 16 driver, and in your case just left the 68 rear on hoping to gain 400 rpm, but as mentioned dropping 3 rear teeth should not have netted 900 rpm lose, you must have made other changes as well.
Some questions in trying to help you up your game, You say Clone meaning SR Clone ? AKRA or NKA ? Do you know your target RPM ?
What made you start on the 17/68 ?
alvin l nunley
Site Supporter
In that gear ratio range, one tooth, more/less, is worth about 100 RPM increase/decrease. You wouldn't think it, but one tooth will show up as far as increase/decrease in RPM.
What this means is, if you add one tooth to the axle, you need to pick up about 100 RPM to be going the same speed. Just the reverse if you take a tooth off. You took off 3 teeth, which, under perfect conditions, would be about a 300 RPM drop to be going the same speed on top. If you lose less than 300 RPM, you're going faster on top.
One tooth on the axle, more/less, is significant.
Losing 900 RPM with a 3 tooth change is unusual. I can't say why you dropped that much RPM. I'm pretty sure it wasn't from the gear change, but what it was, I can't say with any certainty.
What this means is, if you add one tooth to the axle, you need to pick up about 100 RPM to be going the same speed. Just the reverse if you take a tooth off. You took off 3 teeth, which, under perfect conditions, would be about a 300 RPM drop to be going the same speed on top. If you lose less than 300 RPM, you're going faster on top.
One tooth on the axle, more/less, is significant.
Losing 900 RPM with a 3 tooth change is unusual. I can't say why you dropped that much RPM. I'm pretty sure it wasn't from the gear change, but what it was, I can't say with any certainty.
most of the guys were running 16/65 I went up to 17/68 (same basic final drive) hoping for more roll speed and less chain bind. I did find out though that the valve springs went weak on me. I changed springs and the rpms came back up. I was trying something different than everyone else hoping to gain an edge but instead lost the edge.
alvin l nunley
Site Supporter
Here's a gear ratio chart for you.
I always wonder when I see this; are 2 bigger sprockets and a longer, faster moving chain, really faster? This debate has to be at least 10 years old. It'll probably never get settled.
Kj26
Member
I woulda gained the edge by going to a 15/61 if not lower
racing promotor
Moderator
Your not going to gain roll speed with just a gearing change.
I woulda gained the edge by going to a 15/61 if not lower
As I'm learning more I have figured that out. lol