520 Upgrade Chain & Sprocket Kit [Conversion] – Hyosung GV125-S EFi Bobber 125 S

13 reviews for 520 Upgrade Chain & Sprocket Kit [Conversion] – Hyosung GV125-S EFi Bobber 125 S

1. 

   Rated 5 out of 5

   Eddie – Mar 20, 2022

   If you are debating whether or not to get the 520 upgrade then the short answer is YES…get it. If you want to know why you should, continue reading……
   I was unsure if the expense would be worth the investment, after all the GV125S in it’s self is a decent cruiser and with the stock sprockets I could achieve 67 mph if the weather was on my side. I found it slow getting there all the same and at top end the bike would be hurting…..you could hear that she didn’t like being redlined. I contacted Hyo Riders and Marcel was so helpful in arranging the upgrade I needed. Once fitted I noticed I was up to speed much, much faster than previous and the gearing and revs seem more in tune. I find that 4th can be a cruising gear….enough pull to get you along and when needed take you to 60 mph , I only really use 5th for when I’m on open carriageways. I have achieved a top end speed with this conversion of 75 MPH and considering I am 12 1/2 stone , the bike has panniers and a topbox and I am fully kitted when riding, I think that is impressive from a upgrade. At this stage I’m sure I have covered most of what is needed to know…..and in fairness , the promises made as to what this 520 upgrade would deliver have been spot on. Well done Hyosung Riders 10/10. Again a big thank you to Marcel for all his help in this, you are a star….

2. 

   Rated 5 out of 5

   Stuart (verified owner) – May 15, 2022

   Really great. Low end acceleration is much better and gets up to 60 in 4th (used to have to use 5th for this). Got it up to 70mph, although it did take a while (previously only got up to 67pmh), but I ran out of road. Pretty sure it would have been up to 75mph+ on a longer carriageway

3. 

   Rated 5 out of 5

   Charlie (verified owner) – Jun 29, 2022

   So got this set few weeks ago as i wanted a bit longer gears. im using it in city, heavy traffic, daily commuting. Before was changing gears like a lunatic 1st to 4th non stop.. this set sorted my problem a lot to be fair. 20-35(40 with screaming engine) mph in 3rd gear. 2nd gear comfortably around 25.. unfortunately havent tried whats the max speed now as grown up life sucks and havent had time to push the bike yet

4. 

   Rated 5 out of 5

   G. Limet – Jul 28, 2023

   What a great kit this is!!
   Delivery to belgium was very quick!
   I’m happy with the result.
   Don’t have to shift as mutch as with the original chain. Lower revs and more accelaration. And a higher top speed. If you buy this kit you won’t regret it!!
   Top notch!
   Thanks marcel!!! Greetz from belgium

5. 

   Rated 5 out of 5

   Koen Schockazer – Jul 29, 2023

   MARCEL ROCKS!
   Not only is this kit is a must have upgrade for your bike, but the support and advice i’ve got from Marcel is amazing!
   You should now that this is my first motorcycle and I really love to make my hands dirty. I love my bike but the acceleration was a bit disappointing. I’ve read about a tooth more or less on the front or back sprocket, but i really didn’t wanted to loose any top speed. It seemed to be one or the other (more acceleration <-> more top speed). I talked to my dealer about this, but I didn’t find any help there.
   So I contacted Marcel. He sent me the kit and the delivery was very fast (I live in Belgium)
   Then came the moment of truth: would I be able to do the upgrade myself? I succeeded with easy with some remote support from Marcel over messenger. His reaction time was very fast and I didn’t loose time with the procedure if i had a question. Many thanks for that Marcel.

   The day after the installation came the second moment of truth. Would this upgrade perform as advertised? In short: IT DID! The test ride with these sprockets / chain exceeded my expectations .

   The acceleration in gears 1-4 is superb now. In second gear i can pull up to 50km/h – in 3th to 70 km/h without going in the red range! The bike pulls really fast now.
   About the top speed, with original chain kit my top speed was 107km/h on a steep downhill. Now on a far less steep one i reached 119 on display and gps speed was 107 !!! Speed record easily broken.

6. 

   Rated 5 out of 5

   C-J – Apr 22, 2024

   Great item arrived well packaged and quickly loved the little notes that Marcel put on the items like the torque pressure thankyou so much hopefully it means I will be able to get my bike back on the road after failing it’s mot

7. 

   Rated 5 out of 5

   Ale (verified owner) – Jul 18, 2024

   It really does make big difference
   I’m just not sure about the front sprocket
   Because I see the one on shop it has 14teeth
   I recited 13teeth
   But I’m very happy about this upgrade
   Thanks Marcel

8. 

   Rated 5 out of 5

   IDunno164 (verified owner) – Oct 13, 2025

   Item arrived quickly, with everything needed. I was sent a 13 tooth front sprocket.
   Have had it installed for a few days and can say while I have not seen the full speed increase (my daily commute to work is along a road with many declines and inclines) I can say that my commute is a bit quicker with this installed and I have seen higher average speeds overall. Also taking off from a stop feels better with the kit installed too. Have seen about a 3 to 5mph (speedo) increase in the gears 1-4.
   First time installing something like this I had all the tools needed (torque wrench, impact gun, socket set and hammer) had it done within 2 hours having read the instructions the day before so it was a straight forward and logical install (mostly need instructions for the torque specs). Only thing I had help with was holding the rear brake while torquing the front sprocket nut.
   Only complaint about the kit on my bike with this is that the chain adjustment needed to be set close to the maximum adjustment to remove excess slack in chain.
   If I have the bike when it comes time to replace the sprockets I will be purchasing this kit again.

9. 

   Rated 5 out of 5

   Lokutes – Oct 19, 2025

   Where do I start? The beginning I guess 😉

   I bought this Beauty, a GV125-S last Month and was not happy with the Power and acceleration, or should I say missing Power of the 14 PS compared to my last ride a Yamaha XV 125 with 11 PS.
   Dont get me wrong I noticed the difference, but she was just laggy, screaming at me, and the Vibrations when going above 8000 Revs. In 5th gear she hit 10-11000 revs and just stopped power wise, not going any faster than 105 Km/h on the dial.

   In the German Group on Facebook it was suggested to upgrade the front Sprocket to one with 15 teeth, which I did, She run a little smoother through the Gears and the Engine sounded a bit quieter and wasnt screaming at me, but the loss in Power in the lower Gears, especially going from 2nd to 3rd, and the Top speed of 110 Km/h, which took me ages to get there, wasnt satisfactory, taking her up into the Red again to get here..

   Then I saw Marcels post in that Group and decided to buy this Upgrade from the UK and have it shipped to Germany, thanks to Marcel here for the support.

   What can I say? I took her out on a 3 Hour ride to test, what a difference!
   The smaller front Sprocket (13) and the Larger Rear Sprocket (Dimension) and 520 Chain is the perfect combination.
   She shoots up through the Gears, no Jerking, no screaming Engine, next to no Vibrations, just smooth and fast, at 9-10000 Revs in 4th Gear she hits 100 Km/h and in 5th I had her at 120 Km/h and felt like there was still more …. plus it was a windy day 😉

   I also ordered the NGK Spark plugs and HT leads which just finishes off a perfect combination.

   Thanks Marcel and Team, Season nears its end and I just cant wait to get out there next year, the Bike is so much fun now and I dont miss my Yamaha at all 😉

10. 

    Rated 5 out of 5

    TomaszG81 – Nov 1, 2025

    The best upgrade you can make on this bike. Those sprockets change everything – acceleration, higher max speed, better rmp/speed ratio. I’m super happy and I’d do it again, anytime. The only suggestion to Marcel I’d have is to offer the front sprocket with rubber to make the chain work quieter with less vibrations. All the rest, 10/10!

11. 

    Rated 5 out of 5

    Bailey (verified owner) – Feb 26, 2026

    I’ve added this upgrade onto my bike it’s perfect only thing I found was that the front sprocket was a little loose even with the washer.

    I’m hearing some noise but unsure if it’s the upgrade so I can hear the chain go more now if if there’s a problem.

    ==============
    Admin Reply: Thanks for your feedback, glad you love it like others do!💎 – If your font sprocket has a rattle, please investigate your drive shaft itself, we don’t know if your own previous sprocket splines caused any issues to it etc, remember the original OEM sprocket from Hyosung is made in China, another owner made his bike chain adjustment too tight and he lost his engine shaft, so it was a mess! (his own fault) but the original sprocket was badly worn even inside the spline teeth connecting to the front engine shaft , so double check your setup! Remember to check chain slack and keep it lubed well!

12. 

    Rated 5 out of 5

    Aaron (verified owner) – Mar 21, 2026

    BUY THIS NOW! I have no regrets, this kit is amazing, amazing, can tell the difference after installing. I had great support and help through the buying, delivery, and installing, and I honestly wish I had done this sooner. And honestly, guys, get this. Ride safe fellow riders!

13. 

    Rated 5 out of 5

    Sheldon – GV125S EFI 2021 – UK (verified owner) – Apr 27, 2026

    After a little bit of a struggle I finally got the kit on! Thanks to the forum post that front sprocket was a right ass to get off!

    The bike feels much nicer to get up to speed, it feels a lot smoother and nicer to ride! So far I’ve noticed an increase of about 5mph on the top speed but I haven’t pushed it to see how far it will go but that extra 5mph gives a more comfortable carriageway experience.

    Highly reccomend!