Aaron Smith Online

TT-R 125L

This page is Aaron Smith's TTR page and after he took it down he was nice enough to let me put it on my web site for everyone to reference. Please understand that this page will not be updated. Aaron would be glad to answer any questions you may have, however. See his new page!

Background

Yamaha introduced the TT-R 125 in 2000 as an entry level bike. It is a 125cc air-cooled fourstroke with a 5 speed manual transmission and suspension and handling far beyond that of Honda’s XR 100. The bike was an immediate success with women and beginner riders, and also with backyard motocrossers (guys who buy them, heavily modify them, and abuse them). Whether you’re a beginner or seasoned pro, you cannot ride this bike without getting a huge smile on your face!

The TT-R 125 is not fast, and no matter how much you modify it, it never will be. Stock it produces 9 hp at the rear wheel. Fully modified you’ll be lucky to get into the low teens. For comparison, a stock KX65 produces 13 hp and weighs at least 50 pounds less. The only bikes you’ll be beating to the first corner are other playbikes. A stock 65cc motorcycle will walk away from the TT-R. But this doesn’t mean it’s not fun! The motor is bulletproof, and can be lugged and trailridden with ease. This is what a playbike is all about.

Why Playbikes?

Playbikes are fun. They are low maintenance, quiet, and a riot to ride. There’s nothing like throwing on your helmet and workboots for a quick moto in the backyard while you wait for your wife or girlfriend to get ready to go to the movies. Should your wife or kids want to give the ‘ol dirtbike a try, they can do it on the TT-R, not your 45hp race bike.

Mods

When looking to improve your ride, start with the chassis. There’s no sense having a fast motor that the chassis can’t handle. The chassis can’t even handle the stock motor! I chose to spend the majority of my money on the chassis to get it up to par first. The motor will have to wait until next year. In the meantime, I can charge as hard as I want to without fear of breaking the bike!

There are plenty of mods available out there. You can easily spend more on mods than you did on the bike. Choose them carefully based on your needs, and do them one at a time. See what works and what doesn’t. Below I share my experiences and opinions on what I have tried and hopefully it will save you some time and money:

Chassis:

YZ 80 Forks See separate page devoted to this conversion. All I can say is that if you can swallow the price, this is a MUST HAVE!
BBR Swingarm In my opinion, this is only really needed if you go for the YZ forks. Otherwise, it is probably not worth the bucks.
Stiff Shock Spring A must-have, whether you go for the YZ forks or not.
BBR Engine Cradle Ties the frame together and prevents stretching or breakage. A must-have.
BBR Chain Guide A must-have. This keeps you from throwing your chain and breaking the engine cases. Don’t ride your bike without this.
Excel Rims Once you square your stock steel wheels (which you will), buy the aluminum Excels from BBR. They’re stronger, look better, and last longer.
Oversize Bars I cut down CR-Mid bend Pro-Tapers for a full-size bike to 30”. A lot of guys run the Tag super-high mini bars, but I had these lying around so I used them.
Front Brakes I installed a CR250 master cylinder, lever, and Fastline brake line. This was necessary due to the YZ forks, but gives the bike incredible front brakes. See YZ Forks page for more details.
Adjust-on-the-Fly Clutch Perch Standard equipment for those who abuse clutches.
Rear Hub I recently took my rear wheel off the bike, and the right side bearing fell right out of the hub! This is bad. If left this way, the hub would eventually fail. When you take your wheel off, check that the bearings are a nice tight fit in the hub. If they’re not, take a pointed punch and make several “burs” in the bearing seat in the hub, then put Loctite on the OD of the bearing and press it in.
Shift Lever Made by Engines Only, this one-piece lever replaces the over-engineered stocker. Definitely improves shifting action. I had some bad luck with mine, though. It took them three weeks to ship it (they said it was in stock) and the very first time I put the bike in gear the lever broke! It was poorly welded. I had a guy at work weld it correctly, and now it works great. Great idea, but questionable quality. Buyer beware!

Engine:

BBR Exhaust Not a cheap mod, but nevertheless a must-have. After installing the exhaust, I was able to clear the 50 foot tabletop at Pro Source. With the stock exhaust I couldn’t even think about trying it. It’s louder, but not too loud. It has the exhaust note of a 250F, but it’s not as deep or loud. I think the system saves 3 pounds over stock.
Airbox mods (cut open the top and right side of the airbox to let the baby breathe!). Also removed the screen behind the air filter. It’s free and makes a big difference. Do it!
BBR Free Flow Air Filter kit BBR claims a noticeable power gain, but I felt the biggest gain by just performing the airbox mods below. The filter is nice, though, because it’s much bigger than stock and seals better. Not a must-have, but it is nice.
Lightened Flywheel I machined 20 ounces from the stock flywheel. It was free (I work at a machine shop) and made a big difference in getting the bike to rev quicker. If you can get it done for free like me, just do it! If you have to pay, but it on your “B list.”
Richer Jetting If you do anything to the airbox and/or exhaust, you’ll need to richen the jetting. Most people leave the needle alone and just opt for a richer main. I’m running a 112.5 (105 stock). Start on the rich side and then go down from there to see what works in your locale. I am going to experiment with a richer pilot to help it start easier. I’ll do an update to tell you how it works.
Gearing Stock gearing is 13/54. With any mods at all, the bike has no trouble pulling a 14 tooth countershaft. This lets each gear pull a little longer. With stock gearing you can hit 5^th gear several times per lap. With the 14T you don’t have to shift quite as much.

A word about the stock suspension: Before converting to the YZ forks, I ran the stock suspension for a while. I had the BBR stiffer springs front and rear with heavier fork oil. This is fine for play riding, but if you’re going to push the bike on an MX track, it’s borderline dangerous. I also had the BBR top triple clamp, which is a must-have if you’re running the stock forks. It keeps them from flexing, and more importantly, sliding up in the clamps. NOBODY should try to ride the bike with the stock springs. Not even a 50 pound kid who’s never ridden a motorcycle before! The modified stock suspension will be more than adequate for many people, but for a full-size adult who’s going to ride the bike hard, it’s not much more money to skip the stock fork mods and go right for the YZ fork conversion. It will save you money in repairs and damages later.