Need higher RPMs through turns

Hi … my kart is a Parolin Le Mans with a Rotax FR125. Gearing is 12/83. The track I go to is about 1,200 meters (4,000’) long with 12 turns, it’s a technical track I guess. The competitive drivers do a 54s lap. My best so far is a mere 58s. I would be very contented with a consistent 56s.

Mychron 5s logs the max RPM at just a smidge under 14,000 RPMs on track but I noticed that I am getting around 5,500 RPMs through the tighter turns. I think that is kinda low as the Rotax FR125 is not allowing me to exit corners well.

I’m informed that the competitive karters with Rotax engines are topping out at just over 14,000 RPM on the longest straight.

I suspect that I am not carrying enough speed through the turns so might lowering the engine sprocket down a tooth help or I am better off improving my driving to carry more speed through the turns? Braking too early? Try a better racing line?

Not had the opportunity to compare data with the better drivers yet. Your thoughts? Thanks!

Its better to gearing up throw the rear gear coz the change with the front sprocket is bigger in gear ratio .

I suggest to start changing a rear sprocket 1 ot 2 theeth up check you stopwatch and continue gearing up as your times gets better .

When you reach the spot that the laptime starts to get slower. Stop and use the rear sprocket size you got just before that size . Thats how im working . After im getting consistency laps on a racetrack

I hear you … 1 tooth of the engine sprocket will take my gear ratio from 6.91 to 7.54. Quite a jump. Just hope that I don’t grind the rear sprocket. Will try to check the amount of clearance. TQ!

While gearing may be the issue and hopefully some of your competitors at the track would help you compare what they are using, more than likely its your driving. 4 seconds off I would guess would put almost a lap down at the end of a race? So when you are running with the faster drivers where do you see them pull away? You have identified some key points. Early or excessive braking will lower your corner speed. The Rotax doesn’t have a lot of grunt so if aren’t maintaining enough corner speed and your RPMS are low this will hurt your exit which in turn lowers your straightaway speed.

Since your max rpms are similar to your competition you likely aren’t too far off on gearing. So work on braking later and increasing corner speed. If you can walk around the track when your class is on the track note where people are braking, especially in that slow corner. Note what line they take and then try to copy all that when you go out.

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I love your frankness. Maybe best to double check my driving first. Gotta also take more videos and see where I’m braking, tracking in etc. Thanks for the advice.

5500 RPM is too low.

Ask a couple of the fast guys what gear they are running add 2 to 4 more and run that rear sprocket. The fast guys have the kart set up so that it free off the corners and the driver has the ability to keep the speed up in the corners and can run a much taller gear than an inexperienced Rotax racer. As you get your kart freed up and your driving improves start pulling teeth off the rear sprocket. You have to drive very smoothly with a Rotax and not scrub any speed, i.e. don’t slide the kart at the same it has to be driven quickly. I’m sure about how the Rotax behaves today but the Rotax carb was weird and you had to roll on throttle and not mash it.

You just need to experiment add 2 teeth then take 2 teeth off your base line.

If you can get a better driver, let’s say 2 seconds faster, have him drive the kart. This will give a baseline data to work from.

Will start to chat with the better drivers. I really need to keep the revs in the mid 6k range at the least. Noticed it starts to come alive around there.

I know this is hard to estimate but might 4 more teeth be too much for a tight track?

So far been feeding throttle in progressively and not mashing it. I did read that the Rotax don’t like to be mashed. Thanks!

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Run the gearing that the others are on, you could ask for their min RPM too.
Hone your driving craft until that min RPM is close.
If the engine still isn’t pulling right then you can look deeper into it.

One tooth on the axle on a 219 pitch chain is (roughly) 100 RPM.

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Thanks for the info. The track owner says most with Rotax engines are running 12/83, which is what I got. My problem is I usually go on weekdays as there are less rentals on track but hardly any private kart owners. :joy:

I guess it’s primarily my driving but will add a few more teeth to the rear sprocket to see what happens. Time to spend more time at the track! :pray:

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Add teeth and see if you go faster. If you go faster then work on your driving and tune the kart and driving so that the kart rolls and does not slide. (interesting that rolls is plural and slide is singular). Experiment each test or race day by trying the taller gear, if it goes slower then go back to the shorter gearing.

Also on weekdays with less karts on the track, there is usually less rubber and therefore less grip and you will have to run a shorter gear and you will go slower than a race day. When there is grip, you can run a taller gear, in general.

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Got that! Will work on it.

4 seconds off the pace is driving. Getting the gearing correct is worth a few tenths at most. Your gearing might be fine, but you’re just simply not using the kart to its max potential in the corners. You can throw more gear at it to band-aid the situation, but the driving is the issue.

Typically, drivers who are learning struggle most with braking. Newer drivers don’t brake nearly hard enough or deep enough into the corner, don’t get the kart slowed down enough, and then have to delay throttle input because of that.

If you’re nearly spot-on on max RPM, but your corner speeds are low and you’re that far off the pace, it’s all driving. You actually already might be geared too high compared to the guys running 54s.


Yup … 4s off the pace is bad news. But I’m kinda new to karting. Am not looking to run with the top drivers though but would love to shave off another 2s - 2.5s per lap.

Will work on my driving as you said. Thanks!

Not bad news. Just learning. Everybody starts somewhere. Keep asking questions and try to apply the feedback you get. Good luck!


Will definitely work on it. Thanks!

Is your kart too tight causing the engine to boog down?


Its not too tight. The cart responds fine to steering input. Not struggling with understeer or oversteer. I think its me. Thanks.

Be more concerned with returning to throttle early than overdriving the entry. Start working on picking up throttle a kart length earlier each time until it’s an issue. You’ll benefit significantly more on the stopwatch entering a 400’ straight 1000 rpm higher (and maintaining that 1000 rpm bump the entire 400’) than you will going fast in to a corner 50’ deeper.

Once you know where you can pick up throttle successfully, setting your brake point and brake duration gets alot easier.


Will bear that in mind. Thanks!

As most have said, driving is most of your issue. You’re new, so that’s not a knock on you. Additionally, the more technical the track is, the more opportunities for a new driver to make mistakes.

As for gearing, I see new karters struggle all of the time when they try to run the same gear ratio as the veteran karters. You have to gear to your current driving ability, and slowly work your way to gearing the same as the vets.

Get a taller rear gear to get you out of the corners faster if that is where your current weakness is. As you get smother in the corners, you can get smaller and smaller on your rear gear.

Seat time! It takes alot of it, especially if you’re not receiving any coaching.

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