Posted March 22, 201311 yr I'm thinking of replacing the chain and sprockets on my XT 125 X and contemplating whether to go two teeth up on the rear sprocket. I found out that the R model has exactly the same front sprocket and chain length but 50 teeth instead of 48 for the rear. I know I am to expect a little loss in top end but most of my riding is done in city roads so I could do with more bottom end (acceleration). This probably isn't a fair assessment of speed because the R model has a bigger front wheel but just hoping to get a rough idea of its top speed on the road.
March 22, 201311 yr FYI the speedo is recalibrated for the larger front wheel so top speed is what ever it is reguardless of wheel sizehttp://gearingcommander.com/ fillin the info and you will know the difference. get your race out yet?
March 22, 201311 yr Author Yea, that's what I used before but wasn't sure how well that would equate in practice. Theoretically, according to Gearing Commander, I'll be losing around 3mph in 5th gear, which seems fine. Haven't got the race out yet, waiting on a friend to go pick up a heat gun.
March 22, 201311 yr The top speed I have had displayed before running out of road is 57 : ( that was on my original and new speedo
March 22, 201311 yr on the SuMo wheels i got the clock to say 72 once..... that sure was a big hill! and the 10% or so for the clocks being off slightly
March 23, 201311 yr Author 68 on a straight? I need to try out the R rear sprocket on my X! Not sure if the actual sprocket would fit though. //Edit R Sprocket and chain kit ordered along with a brand new rear disk brake and brake pads, £150 all together.
March 25, 201311 yr Author Take into account your weight. I guess a part of making your bike go faster is losing some . I bet BenjiMC weighs 60 ±5 KG.
March 25, 201311 yr Author Dude, 13 stone ≈ 82 KG. Not really surprised if you're only getting 55ish. From your picture and what you've said about your build/weight, you're probably a tall guy, so drag will play its part when riding in an upright posture.
March 25, 201311 yr I'm six foot and when I'm giving it some I tuck my knees and elbows in. There's something wrong with the bike it should do more.
March 26, 201311 yr Author You could try riding like this . But in all seriousness, I think the XT speed correlate with the weight here. BenjiMC - 60kg - 68mph (guessing) Me - 75kg - 60mph (fairly accurate) Grouch - 82kg - 55 mph Not enough data for this graph to be accurate but from what's available, you can see the line of best fit is pretty close to the data points. So, from a statistical point of view, I don't think there is anything wrong with your bike.
March 26, 201311 yr The speed of your XT will no longer matter Grouch when you've got your 2T play-thing...!
March 26, 201311 yr The speed of your XT will no longer matter Grouch when you've got your 2T play-thing...! I know I just can't decide what to get, want a Mito but if I see a nice TZR or RS I'll get it, depends what's about at the time and how much I think it's worth.
April 24, 201311 yr i weigh around 65 KG but often have my uni bag with books etc weighing in a fair bit plus panniers with tool kit and spare shoes to wear around teh library, still will hit over 60 easily on the flat. I do find a lot of extra speed when i tuck being 6ft myself but also how much i tuck too can get that little bit extra out. bear in mind i have the R vs the X which has higher top speed anyway.
April 25, 201311 yr Author Hah, you see that graph, I was pretty close . Not sure if R has a higher top speed, they are the same engine.
April 29, 201311 yr I ride the Xt125R and whent down from 14t to 13t on the engine sprocket lost 5 mph off to end but gained bottom end acceleration/torque the only problem in the chain eats in to the two sprocket bolts
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