Finally getting warm and fuzzy with the new 125 [Archive] - Bay Area Two Stroke

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Dangerous Dave
08-03-2008, 05:46 PM
Well, right out of the box the GPR125R wasn't really everything I had hoped for. Storage space was non-existent. Mirrors were useless as was 6th gear. Speedo ONLY read in kph, despite the owner's manual saying it was switchable. Lots of conversation with guys on the 125cc sportbike forum say I'm not the only one who's come to this sad conclusion, but a sigma bicycle computer solved that problem just fine. Parts and info for this bike here in the U.S. are almost impossible to come by, so I've had to work out alot of stuff on my own. Through help from some of the other forums I'm on and a little experimentation, I've finally gotten this bike to where it's a fun and useful daily driver.

A friend gave me some universal bungee hooks that he had laying around the garage. I did alot of bending on them and got them to where I was able to drill them and screw them to the seat base of the rear "seat" (of course I'm using the word seat very loosely). Now I could actually put something back there with a cargo net, but it still wasn't enough. The plastic tank made a magnetic tank bag not an option and I hate the strap-on bags. A guy on the FJR forum directed me to SW-Mototech who makes gas cap mount tank bags! Turns out this little bugger uses the exact same gas cap as most late model Triumphs, so they had an adapter ring to fit it. I bought one of their bags that's easily big enough to hold my lunchbox and then some, so now I could actually ride it to work and carry some shit with me.

The mirrors are damn sexy (actually discovered at the Barber Motorsports Museum they're the EXACT same mirrors as a Bimota Tesi 3D) but were totally useless. But I found that if I twisted them up a bit I could actually see behind me, now I just had to figure out how to make them stay that way. So I found some thin pieces of black plastic at work that I made into kind of a wedge. I loosened the mounting bolts, inserted the wedges underneath the back edge of the mirrors and bolted them back down (using blue Locktite of course). I won't call them "good" at this point, but at least now it IS possible to see something besides my forearms in them.

But the biggest revelation came this weekend. As I said, 6th gear was useless. The bike would do 83mph in 5th, but shifting to 6th would just cause you to lose speed unless you were going downhill. Power delivery seemed very good on the bike and the Yamaha engine is a peach. I was sure the bike was just overgeared. I got a tip from a guy on the 125 forum that a company in the UK...JT sprockets...made sprockets for this bike. Well, they didn't actually have a listing for the racing model, but I was sure it was the same as the nude, which they did have the listing for. I contacted their US distributor who did NOT want to give me the Parts Unlimited part # so I could order one, but after alot of begging and pleading, she came off of it. So I ordered a 15t front which is one tooth down from stock. $10 bucks and 10 minutes revealed it was a step in the right direction, but not enough to really call an improvement. So I spent another $10 bucks and ten minutes and went down to a 14t front and it absolutely transformed the bike! I rode it 225 miles to the Superbike race at Mid-Ohio yesterday and it was fantastic! The bike feels more relaxed everywhere and will pull strong in any gear. I saw an indicated 86 mph on the Sigma and even uphill and into the wind it would maintain 80 mph. These numbers aren't verified yet, but my buddy who was riding his ZX-12 next to me thinks my Sigma is reading low, but his 12 could just as easily be reading high, so I guess I'll have to let the GPS make the call. Nevertheless, the bike just pulls harder everywhere, goes faster, and struggles less. For the $20 bucks spent on R&D, I'm gonna call that a huge success. Now that I know that the ratio is good, I'll probably order up a sprocket from Sprocket Specialists and go up a few teeth in the rear and go back to the 15t front, so as to put less strain on the chain and slipper.

Kind of funny...there's hardly a Derbi part on this thing. The engine is definately Yamaha. The frame says "Bennelli" plain as day. I also discovered that the Gilera SC125 is the EXACT SAME BIKE with different colors and badges! The current aprilia RS125 is also the EXACT SAME BIKE, but with different front fairings and mirrors. But from the steering head back, it's the same bike. And yet, there's scarcely a single part available for it in the U.S.

Here are a few pics of the mods.

I just love Sigma bicycle computers...they're freakin' accurate!

http://daves_garage1.tripod.com/sigma.jpg.jpg

Tank bag hauls the lunch and never touches the tank!

http://daves_garage1.tripod.com/bag.jpg.jpg

Bag mount is pretty unobtrusive.

http://daves_garage1.tripod.com/bagmount.jpg.jpg

Rim stripes off Ebay are just good cheap Bling!

http://daves_garage1.tripod.com/stripes.jpg.jpg

All in all, she's coming together nicely.
It's taken 4 months...but I'm finally getting happy with this bike!