How can I make my TBR7 as fast as possible?

[2LZ]

Gearing is key but can only go so far. I over-geared Q and actually lost top speed. She ran out of torque. I dropped a tooth and gained basically 5 mph, though I did gain RPM's in the process. Of course, it was hauling my lard ass.

[shiftclick]

Originally Posted by 2LZ

Gearing is key but can only go so far. I over-geared Q and actually lost top speed. She ran out of torque. I dropped a tooth and gained basically 5 mph, though I did gain RPM's in the process. Of course, it was hauling my lard ass.

Interesting. So if my TBR7 came with a 15t front sprocket and a 46t rear sprocket, installing the 45t would increase my top speed to 75 or 80 mph. Now it might be worth installing (one of the nut's/bolts is stripped on the back 4 wheel hub pressure plates thus the delay).

[Megadan]

Originally Posted by 2LZ

Gearing is key but can only go so far. I over-geared Q and actually lost top speed. She ran out of torque. I dropped a tooth and gained basically 5 mph, though I did gain RPM's in the process. Of course, it was hauling my lard ass.

Agreed, there is a limit to the gearing. It takes X power to make Y bike move Z fast not including variables like wind, tires, etc. Run out of power, and that's all she wrote. That is part of the reason I like to include RPM ranges to try and land in. It helps eliminate a little bit of guess work by giving an area to aim for.

In reality, no CG powered dual sport is ever going to see beyond 75mph, and they have to be geared pretty tall in order to even reach those speeds.

Originally Posted by shiftclick

Interesting. So if my TBR7 came with a 15t front sprocket and a 46t rear sprocket, installing the 45t would increase my top speed to 75 or 80 mph. Now it might be worth installing (one of the nut's/bolts is stripped on the back 4 wheel hub pressure plates thus the delay).

No, if you went from a 46 rear to a 45 rear sprocket and stayed with the 15 front, you would only see about a 2mph gain at 7000rpm.

Now, if you added a 17 front sprocket combined with that 45 rear sprocket, you would then see about a 4.5mph increase at 7000rpm.

The funny thing is, us Hawk guys are actually geared way taller than you TBR7 guys thanks to our larger 18 inch rear wheel and tire setup. Roughly translated our rear sprockets need about 3 to 4 more teeth than your TBR7s to roughly equate to the same overall gearing (Same MPH and RPM).

A very popular Hawk setup has always been a 17 front/45 rear, or a 16 front 43 rear, or 15 front 40 rear. (all basically the same ratio). A 17 front 45 rear on a Hawk will generally yeild about a 65-68mph top speed, and a bike that can comfortably handle 55-60mph without being completely maxed out. It is moderately highway capable without sacrificing too much in the way of acceleration.

For a TBR7 to achieve a similar gearing, you would need a 17 front and 42 rear sprocket.

Now, me personally, for a Hawk that is going to be 80% road and highway, I loved my 17 front 43 rear sprocket setup. With a VM26 clone jetted very well, an exhaust, and a pod filter with more road friendly tires, I could cruise along all day at 60-65 (RPM's right at 6000-6500) and just hit 70mph at 7000rpm where peak power occours. That was about the limit of that bike with my big and tall self in the seat. I could occasionally crawl into the low 70's if the wind was calm, but that was really pushing it hard.

To match that (A perfect match) on a TBR7, it would be a 17 front and 40 rear

There is always a compromise factor though, as with anything. People that live in low altitude flat lands that aren't me sized like JerryHawk, they can get away with even taller gearing and achieve higher top speeds. I live in an area with a lot of decently steep hills, so I have to keep my gearing a bit shorter so I don't struggle to maintain speed up said inclines while my bike is trying to fight the wind resistance and weight of a 6'4'' tall 270lb man. Thus my bike is geared equivalent to a 17 front 45 rear. Will it go faster with taller gearing, sure will. It has the power to do higher top speeds, I even damn near hit 80 once. I compromised on a loss of top speed to be able to climb and accelerate. Going above 70mph on these bikes is honestly something I will leave to the incredibly brave.

Other factors that can translate to different results between our bikes is also the tire diameters. Bikes with a 21 front and 18 inch rear tire have more moment of inertia to overcome and generally have a lower top speed than a bike with a 19 front and 17 rear, which means they have a little more power on tap for acceleration and overall top speed. I know that a Brozz and TBR7 unmodified struggle a lot less to reach past 60mph. A hawk with no mods, even with the right gearing, is hard pressed to go any faster than about 62-63mph.

[JerryHawk250]

Very well said Megadan. Yeah, us light weight flat landers @ sealevel have a slight advantage. To help you understand how tire size plays a big part of gearing. Here's a link to a gear calculator. Load the Hawk data. This will give you the correct information for the TBR7 transmission gearing. Input your rear tire size to replace the Hawk info. You can play around and see what the different gear ratios. https://www.gearingcommander.com/

[A1R 250 bob]

Originally Posted by Tbr2d2

Hey all,
I have a 2020 TBR7. Original top speed b4 the speedo needle fell off was 63 wot. I'm trying to get to 70 wot, that way 60/65 is more comfortable on the engine. I have an aftermarket 27mm carb (iknow its smaller) with a 102 jet that definitely got me higher revs (no I didnt try the 102 in the 30. Will that get me more?). I also switched today to the 17 tooth front. Seemed to gain me a few more mph (guessing by feel) and definitely seemed to take longer b4 I had to shift.

Grease Rat: Like the sign says, "speed's just a question of money. How fast can you go?"

My bike budget is minimal, mainly because the "other one" believes that money is better spent on her ideas. However this 2019 TBR7 can nick 70+ carrying 225 pounds verifying by a GPS phone app. My mods were to un-tamper proof the carb and put in a 110 main, 17 tooth counter sprocket, and drill 3 - 3/8" holes in the muffler around the normal exhaust exit bypassing some of the baffling. Still use the stock chain but baby it with constant cleaning and lube. the crankcase has 10w30. I did buy an 8"x 10" sheet of Plexiglas at Lowes for a windshield.

The elevation average is around 614 feet above sea level.

The bike really does not like to remain at top speed and seemingly prefers 55 to 60 MPH, where the vibration is not as violent.

[NzBrakelathes]

Grand canyon vertical drop - fastest it will ever go.......

[A1R 250 bob]

Originally Posted by NzBrakelathes

Grand canyon vertical drop - fastest it will ever go.......

I bet one could exceed terminal velocity (120 mph) by attaching rockets.

[NoBs]

Originally Posted by shiftclick

2020 TBR7 owner too. Did the 17 up front and threw in a Mikuni knock off and I think the 110 jet. Also threw in a Uni style foam air filter and bypassed the onboard air box. Didn't make a huge difference, but did make a difference. My top speed is probably right around yours although it's new enough I am still breaking it in. There's a youtube video out there somewhere where a guy takes a 250 cc and swaps out the front and rear sprockets for various sizes and gives you a chart showing top speed, fastest 0-60, 40 pull, etc. Let me know if you can't find it.

Which is all well and good if you have the power to take advantage of the taller gearing.. I went one LESS tooth ( 14 ) in the front and seemed to have lost nothing at top end. Of course it will rev a bit higher at the same MPH.. Anemic performance may show its ugly head if one goes overboard on the sprockets..

[Rocket tests]

I decided against building a rocket pack for the tbr7, instead i spent the last 3 evenings porting, polishing port matching, and decking my head.

All I can say is WOW!, what a difference. Hills which would bog down at 45mph are now conquered at 60mph without bogging. I havent changed the factory gearing from the 15 front and 46 rear sprockets. I'm able to hit 70 on a flat road and almost 80 downhill, this is referencing the stock speedo (still waiting for my digi dash). First gear handily lifts the front wheel without need to lean back and I can clutch wheelies in second. I'm 6', 210 lbs and couldn't be happier with the mods.

I recieved an order of various front sprockets today but unfortunately i ordered the wrong center splines. I guess I'll need to rectify this issue by purchasing another bike for them to fit on. The cost of these bikes makes them a blast to mod out.

[JerryHawk250]

Port and decking the head is the best mod I've done on my Hawk.

[Megadan]

Originally Posted by JerryHawk250

Port and decking the head is the best mod I've done on my Hawk.

Especially when paired with a smooth bore carb and an open exhaust.

[shiftclick]

Originally Posted by A1R 250 bob

...and drill 3 - 3/8" holes in the muffler around the normal exhaust exit bypassing some of the baffling.

It's a little different on the 2020 TBR7, but after doing this, I had to adjust the idle screw and I could definitely tell a difference rolling down the road! Guess a performance exhaust is next up for me. Thanks man!

[kb21guru]

Run 140 and 39 jets and run methanol, if those jets let the engine run rich on 100% methanol, add nitro...Nitro bursts into oxygen and will in essence add oxygen to the rich fuel mixture thus leaning it down.

The gearing, the rear gear yields bigger changes than the front, the front gear is for fine tuning. For every rear tooth removed is like adding three teeth up front.
Plus when removing teeth from the rear, if you remove links in the chain...your removing weight too. The quickest way to gain speed is to add lightness.

On my Apollo 125cc RFZ 12/14 inch wheels. Stock gearing was 14/41.

If I run a 16 front gear and a 37 rear with the 12 inch rear wheel I'm running at optimal rpm and torque with a +26%ish gain in top speed but with a -26% torque loss. if I run the same set up with a larger 14 inch rear wheel I am lugging the engine.
Now, if I run the 16 front with the 41 rear gearing on the 14 inch wheel I am at just about the same as the 16/37-12 inch wheel. Why because it takes more power to turn a taller wheel so I have to add teeth to the rear to compensate.

Wheels are probably the best way to add speed. The lighter the wheel is, the less rotating weight (rotating weight is heavier than standing weight). Removing just 2 pounds of front wheel weight is the same as removing 12 pounds of static weight elsewhere on the bike.
But this comes at a huge cost, carbon fiber wheels is about the only way to really see a gain in wheel weight enough to make a difference. Sure alloy rims will remove 1/2 pound but then that's not really much of a difference, rotation wise.

Other ways to make a gain in speed is to do crank work, lightening the crank, angling the leading edge of crank. Working on the conrod (thinning) to limit turbulences and drag internally. And for gosh sake, do not polish anything, just port/match. Why? Polished surfaces create more drag when air and fuel is passing over it, than if it was a rough surface. A rough surface breaks the drag and allows the air/fuel to reach a higher speed.

Intake tuning is a thing too. Air/fuel speeds up in narrow long tunnels and slows down in wide short tunnels.
larger carbs don't always add power. Understanding how air and fuel flow, is a good key.

Simply bolting a large carb and gear is not the only way to go fast. There is many things that when combined will yield a faster bike.

But I don't see anyone really talking about the real way to go fast, just bolt on stuff........

Originally Posted by Tbr2d2

Hey all,
I have a 2020 TBR7. Original top speed b4 the speedo needle fell off was 63 wot. I'm trying to get to 70 wot, that way 60/65 is more comfortable on the engine. I have an aftermarket 27mm carb (iknow its smaller) with a 102 jet that definitely got me higher revs (no I didnt try the 102 in the 30. Will that get me more?). I also switched today to the 17 tooth front. Seemed to gain me a few more mph (guessing by feel) and definitely seemed to take longer b4 I had to shift.

[ChillRider]

Well, my 2c from my experiences with my older Zongshen Sierra chinabike, used as a daily commuter in a daily 25/75% urban/extraurban commute (about 15 miles): with a 15-ish horsepower engine (and less than that to the wheel), those machines ain't built for top anything.

That being said, you can make them more comfortable for open road cruising, with the biggest benefit coming from a sprocket swap giving you a taller gearing. Even that way, calling it "highway cruising" would be a stretch. More like keeping 55-60ish mph for hours without keeping the engine constantly in the redline is more like it. If you push it hard you will get a higher top-speed also, but it's not something you'd like to keep for long. If you manage to get them to the point where you can safely keep up with commuting traffic on extra-urban roads and manage a few overtakes as well, that's really all you can ask of them.

Enhancing fuel/air flow to the engine and keeping valves well-adjusted, esp. on those carbureted chinabikes, will certainly give you more low-end grunt and better acceleration under all circumstances (always welcome), but they simply don't rev all that high to begin with, and their engines + gearboxes are often based on older 5-speed designs, where the lack of a 6th gear really shows.

E.g. the CDI of my Zongshen Sierra is capped at 8000-ish revs I think, while an obscure "performance" version of it claimed to go up to 9000 rpm. Even with a massive increase in power but without increasing revs (like this guy who , same engine), even with the tallest practical gearing, I'd still get no more top speed. Better "pull", yeah, reaching top speed faster, yeah, keeping it while going uphill and riding pillion yeah...but not higher, without more RPM.

With my current setup, in some particularly favourable conditions (e.g. downhill, tailwind, etc. ) I've found myself looking for a 6th gear, feeling the engine screaming and having something more to give... but nope, the revs were already maxed out, and there was no 6th gear

Going to an even taller gearing than what I currently have (14/42) would make the bike suitable only for long distance cruising, but painful to ride in stop & go traffic and hilly areas. Keep in mind, my bike also has the oddball rear 15" cruiser wheel and street-oriented tires.

[TxTaoRider]

As long as we are limited to 5 gears, and not much horsepower, gearing will always be a huge compromise. A 6th gear would sure help.