Sprocket change for highway

JCW800

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Thanks! Good point. I am going my LBS today to get a new chain and front sprocket (12k miles). If nothing else, I will feel better about protecting the engine case with all new parts. I really want to add the 17 on front, but I just don't want the chain that close to the engine case. I guess as long as it clears it doesn't matter, and if it comes off it doesn't matter either (get out the checkbook). But, that idea will have to grow on me. Thanks again everyone for your comments and advice!
 

guscar65

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angus
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blue/white T120 2018
I love my Tiger, but at 70 mph it is running almost 5k rpms. I'm thinking of dropping the rear sprocket from a 50 to a 47 (the smallest I can find). I don't know why no manufacturer makes 6th gear a road gear.....? Does anyone know of any issues, other than losing a little from 1st gear and spreading out the gearing a little more? Thanks!
As a more recent biker than most in this forum ------I always found it odd that our cars turn over at ,say 2200 at 70 ---but our bikes need to be about twice that. Yes , I know its all about the horses etc. but it does feel odd. In the light of this, 5000 at 70 doesn't sound bad ---both my old Honda CBF1000 and Kawasaki versys were running 6000 at 70. I too am looking at my T120 with a view to re-gearing ---I guess we all have a common goal of making the bike fit our needs as far as possible, for me I should have bought the speed-twin BUT have had to compromise because my wife wants to join in on the occasional ride-out. Don't get me wrong the T120 is lovely and I am fortunate to own it but it is very over geared! as some have noted 6th gear is designed (in this instance) for easy cruising---pretty much what the bike is aimed at. When out with my riding buds --I need to change down to 3rd! to make the fast overtakes that Scottish roads demand , 3rd covers from 30-85 which surprisingly keeps up with the leader who is mounted on a Kawasaki sx1000, (albeit in this limited range). It is not ideal however , having to jump all over the gearbox on a bike designed to cruise! ----SO I am looking at a different rear sprocket. Several owners have changed to a 39T rear as it fits without changing the chain etc. and some have done the research using the gearing charts which are available ---these charts suggest that this gearing matches the bikes power/torque best. I contacted JTS one of many companies who make them but are only available through dealers. These are high quality steel items ----so I don't know how much they cost yet. JTS DID however supply a gearing comparison chart-----the 39T lowers the gearing by a tad over 5%. Doesn't sound much but some report that they feel the difference ----one contributor has fitted one but not been on a long ride yet so maybe will wait until he reports. Certainly at the moment the T120 is tricky at road junction and traffic jam speeds as 1st is too high. So it may make the bike more 'comfortable' overall----but I am reticent to maybe lose the single gear overtake ability that I have presently hmmmmm. choices, choices.
 

2bazookas

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I was curious to see how much difference the sprocket change would make. So, I have started with the front sprocket. I pulled the 16T and installed a JTF52-17RB. I took some before and after pictures of the RPM's at various speeds to compare the difference. There is a slight difference in the RPM's. Where I notice it mostly is in first gear. When doing sharp u turns I need to feather the clutch a little more and when I am taking off from a stop light on a flat road I use first gear now instead of second. It doesn't seem to wind up as quick with the 17T sprocket. Longer legs, if you will, but it is subtle.

16T/25 mph = 2500 rpm/3rd gear
17T/25 mph = 2400 rpm/3rd gear

16T/40 mph = 3400 rpm/4th gear
17T/40 mph = 3200 rpm/4th gear

16T/55 mph = 3900 rpm/6th gear
17T/55 mph = 3600 rpm/6th gear

16T/70 mph = 4900 rpm/6th gear
17T/70 mph = 4700 rpm/6th gear

I am ok with this change. I'm not sure if I want to go a step further with a 47T vs 50T rear sprocket. It would be nice if someone that has done this change could give us some data comparisons to reference. I watched this video on u tube and found it informative. Front & Rear Sprocket change
 

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JCW800

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I made the change to a 47 on the rear, and now I LOVE the Tiger. The gears pull longer and stronger and it’s not screaming at highway speeds. Before it felt so “bottled up” due to the low gearing. Now, it’s free to run. For the haters, leave yours as is. But, I will never go back. Happy New Year! (Yes, I bought a new chain and front sprocket too.)
 

brooke

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Another man of action . Glad to hear you enjoy the change and your thoughts are right in line with mine . The next step would be 1 less on the back and from my experience that could easily be to much . Not worth the bother .
In regards to the highest gears having very close ratios is common and required . Overdrive style gearing works on autos , but they are considerably more aerodynamic than a Tiger 800 with hard luggage . My Can Am 250 was fast enough to win an ice racing championship but when geared for the only half mile of the season shifting from 4th to 5th exposed the issue . It took to long to get it up to speed in 5 probably 75 mph or so . It was faster to reverse the gearing and let it scream its poor little guts out for the last part of the straightaway. Next summer the 250 GP engine was in a Champion frame with six speeds from a 175 cc donor engine which hit the trails in the GP chassis .
 

JCW800

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Brooke, I really think 47 was right, unless you were wanting to totally turn in it into a street bike. I cut about 400-500 rpms at 70 mph, so it still runs 4500ish. I did it to cut rpms at 70 mph, but what I love most is more very strong roll on power from a stop. Right after I did it, I took it on the highway and down the entrance ramp in 5th gear I was doing 80 mph before I knew it. As an old enduro rider, it felt like going from a KTM200 to a KTM300. It feels like it has more power, so I don't believe I lost any noticeable torque on the low end. Whatever works..... Thx
 

brooke

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Exactly my thoughts . I have not changed gearing on the Thruxton R yet but apparently many have . One in particular is a drag racer who is going quicker with taller gearing . It seems the R pulls so hard in first that it’s difficult to make the 1. 2 shift before hitting the rev limit , which makes perfect sense based on my experience.
 

San Jose Tiger

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2018 Tiger 1200XRt
I agree - new sprocket(s) = new chain and vice versa.
My past experience with my Honda 929RR - stock steel sprockets, would contradict that. I had always heard you should change them together, but I went to change out the chain, I bought the new sprockets and after I got the old ones cleaned up, I put one on top of the other and they were identical - no visible wear at all, so I returned them and got my money back. I did 3 chain changes on that bike and got the same mileage out of all 3 chains 16-18K without ever having the change the sprockets. I had a similar experience with my 2 Triumph Sprint 1050 ST's which I was getting 20K per chain and never needed to change the sprockets. Now, I am guessing if you ride in dirt a lot, or don't keep your chain properly lubed, your results may vary... but, I no longer hold to the "new chain must have new sprockets" rule. If a sprocket shows signs of wear, change it. If you doubt your ability to see the wear, buy the new ones, and clean up the old one and compare them and find out before you put install it. If there is no wear, return the new ones and save some money. That said, if you are going with an aluminum rear sprocket to save weight, different story - aluminum wears much faster, especially riding in the dirt.
 

brooke

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Very interesting. Way way back in the day when I was changing chains every day the sprockets , more so the front ,would be so misshaped that using them with a new chain created a noisy marriage . The thought was that the sprockets were worn to adjust to the greater pin to pin distance of the chain or the chain had to stretch to suit the worn sprockets . Those were the days before o rings of course . Had tv though . I get close to 40 k kms on the tiger before reaching the recommended pin to pin measurements. Things seem noisy and snatchy as I approach that limit but I am sure it would go another 10 k before some thing bad occurred . My buddy notices the same on his Weestrom . Would be interesting to hear from more experts on this one .
 
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