soccerdude28

Hey guys,

First time posting and I am fairly new to the whole Nitro scene.

I have had my hpi firestorm for a couple years but starting enjoying it most this year.

I have added a bumper and replaced a few pieces, however, I would like to further mod this little truck.

Since day 1 I have wanted to add some bigger tires on this truck.

Specifically I was looking at putting some Proline 2.8" tires.

What modifications would I have to do to the gearing to not put as much stress on the little 2 stroke engine?

I was thinking about putting the integy 3 shoe clutch when they get it back in stock and a 21t vented clutch bell.

Anything else??

Thanks!

Rusty22

What motor are you running? You might be fine just slapping the tires on there. 

Sixtysixdeuce

As rusty said, you may not need to do a thing with the gearing, unless your motor is already taxed turning stock size tires. I put 2.8" TRX talons on my RC10GT running a 14T pinion and 54T spur. Of course, I'm using an OFNA Force .32 engine, so my biggest problem is not lack of power but parts breakage.

It's AMAZING how much better these 1/10 stadium trucks do on rough terrain with the larger 5+" tires. And as little as I care for TRX vehicles, the Talons are an awesome tire, especially if you plan to use both on and off pavement.

I've put 2.8" Talons on the front as well since this pic, but this should give you a general idea



I have Proline's 2.8 with the Badlands tires, and I like them for strictly off road, but they wear FAST on pavement or hard pack dirt roads.

PS-

If you do go with the Talons, check your offset. Traxxas offers the wheels in two varieties, and I found the shallower offset necessary for clearance on the rear, since these things are about an inch wider than 2.2" tires.

soccerdude28

Thanks for replying guys.

Everything is stock right now, but its having traction difficulty on some grass terrains so Ive always wanted to throw some bigger tires on it.

Especially on the astro turf. The grass is like plastic and the current tires just make the car spin out a lot of the time.

The clutch bell is 19T right now (stock) - should it be upgraded to the 21t for faster top speed?

The engine is the g3.0 stock engine as well.

I am glad to hear that the 1/10 trucks run much better with the bigger wheels.

My fear is that when I purchase these bigger tires, that they will not have enough clearance on the truck.

Rusty22

Yes that's correct. Think of your gearing like a bicycle... The gears attatched to the pedals are the clutch bell.. Bigger equals Faster but takes more input to turn. The gears attached to the rear wheel are your spurs... Bigger the spur the less stress or input it takes to turn therefore it's "quicker" not "faster".. Make sense? 

soccerdude28

So I bought the badlands yesterday, 2.2 with a bigger outer diameter. The wall is about 1 inch taller than the stock tires. I mounted them on the rims and glued them but have yet to throw them on the car. I read the firestorm official forum and found that it was best to drop a couple of teeth on the clutch bell to compensate for the bigger tires to ease the stress on the motor.

I bought the 17t clutch bell (stock 19). It was a discontinued part of HPI for the firestorm but I found it on ebay for about 12 bucks.

From what I understand, the low end and top end should be about the same because of the change in gearing / bigger wheels.

I was told by the hobby shop owner that I didnt require changing the spur gear if I changed the clutch bell. He said it was kind of an either or.

I am excited to throw these guys on and put it on some grass. Eventually I want to mount them on all 4, but will settle for the rear as of right now.

RC is quite the expensive hobby, but god I love it.

Broke my spoiler yesterday by picking up the truck by it! lol

Sixtysixdeuce

Let us know how it works out.

You can calculate how it will theoretically affect your acceleration & top speed. Find out what your transmission ratio is, then multiply that by your pinon/spur ratio. Then simply apply your tire circumference and you will know how many inches of travel you get per engine revolution.

For instance, the RC10GT has a 2.6:1 transmission ratio and comes stock with 15/66 clutch bell/spur, which is 4.4:1. So the final drive ratio is 11.44:1, or 11.44 engine revs to one wheel rotation. If the stock tire is 3.5" OD, it will cover 11" per revolution. So, each turn of the engine moves the car 0.96". If we go to a 4.5" tire, it will now cover 14.13" per revolution, roughly a 28% increase in distance covered per revolution. To maintain our 0.96" travel per engine revolution, we must increase the final drive ratio by 28%, bringing it to 14.64:1. We have to account for the 2.6 multiplying factor of the transmission ratio, so we divide 14.64 by 2.6, thus telling us we need a 5.6:1 pinion/spur ratio. If we mean to retain the 66T spur, then we divide 66 by 5.6, getting 11.78. So a 12T pinion would be as close as we get. To make the change with spur gear, multiply pinion tooth count by the desired ratio to find the correct spur size, which would be 84 in this case. Of course, neither of these sizes are usually available in nitro, so we have to use combinations, and often settle for a change in grunt & top speed.

Having said this, you can see where your change in clutch bell will probably not fully compensate for a 1" increase in tire OD. The Firestorm 10T is basically an RC10GT clone, except that the transmission ratio is 4.4:1 and the OEM clutch bell/spur is 19T/50T. Your stock final drive ratio is the same as the 10GT at 11.44:1, but they change ratio in spur or pinion are very different. Going from 19T to 17T while retaining the 50T spur is only a 12% change in ratio (2.94 vs. 2.63), which will not compensate for a 25% or 30% increase in tire rolling circumference. To maintain, you'd need a ~3.3:1 ratio, which would require a 14T or 15T bell.

The other thing to remember is that larger tires add unsprung weight and rolling resistance; even if your final drive gives you the same distance per engine rev, you will have slower acceleration and lower top speed (unless your engine is powerful enough to reach maximum RPM regardless). This is a more significant factor in full sized cars, but it does matter with 1/10 cars, too.

In my case, the primary purpose of going to the larger tires was a top speed increase, since that OFNA .32 has more than enough power to spare. I currently have a 9.88:1 final ratio, and cover 1.44" per engine rev. The engine still easily reaches max RPM and I want more speed, so I'll be going from a 14T bell/54T spur to a 20T bell and 50T spur, giving me a 6.5:1 final ratio and covering 2.18" per engine revolution.

For future reference, if you have an SG shaft engine, they are standardized, and you can make just about any clutch bell work. It may require trimming the back a tad or shimming bearings to get proper clearances, though. However, if your car runs a more proprietary set up (like the older AE 3/16 adapters), you may have to stick with bells designed for your car or get creative with adapters.

Spur gears are also pretty easy to adapt if the dedicated part isn't available. My 10GT pictured above is fitted with a Team Durango 54T mod. 1 spur.

Up to the point that you run out of adjustment, yes. If you make a drastic change, it will require both.

soccerdude28

Hey!

Thanks for all the replies.

I read that over once, but am definitly going to have to sit down and really go over all those calculations to fully understand the gearing ratios.

Being new to nitro, I don't want to get into parts that arnt made for the truck, however, I am slowly learning more and more about the nitro cars.

What really helped was reading many pages in the official firestorm thread.

Some of the guys were saying they didn't like the handling of the Firestorm with the bigger tires, but I will definitely let you guys know how it works out.

I ordered the bell of ebay so im assuming it wont be here for 1-2 weeks.

Also waiting for some futaba parts to fix my transmitter for my electric Tamiya TXT-1 for the girl friend to play around with while I do circles around her with the firestorm! HAHA

Thanks for all the help guy. \

Also, would you guys recommend changing the suspension to alloy? Or messing with the springs / oil at all?

Sixtysixdeuce

Just to clarify, your transmission ratio is fixed (with very few exceptions), so ratio changes are done with pinion/spur and tire size. Your primary ratio (pinion/spur) is simply spur gear tooth count divided by pinion (clutch bell) tooth count. Your set-up with the new bell will be 17T/50T, or 2.94:1.

I can understand that. Those of us that do the Frankenstein builds or make totally custom parts are usually after something we can't buy, like to tinker, and generally have many years of experience with many vehicles.

Depends on what you're doing with it. As a stadium truck, the oversize tires will hurt you in every way, from acceleration to cornering to balance in the air. But as a basher, they will give you more ground clearance, more top speed (if the motor can pull it), and better ability to traverse rough terrain.

My stock RC10GT is much better on the track as a stock truck. But for playing around out here in the country, the big power and big tires make my beast GT far superior. It's practically a short wheel base 1/8 scale at this point.


Comparison:



They look better, but most likely will not perform any better (unless you are able to get your hands on some spendy Prolines or similar and make them fit). If your existing shocks are worn, then it's a good time to upgrade to the better look of aluminum. But if your stock shocks are OK, the only real benefit is aesthetic.

soccerdude28

Quick question for you guys! I put on the bigger tires but havnt tried it yet because I'm waiting for the 17t clutch bell. But when I spine them on the car, they wobble quite a bit. Is that going to cause an issue? Is there any way to remedy the problem?

Also I realized that it brings the suspension down a little bit more. Any way you recommend to solve the problem?

Thanks guys!

soccerdude28

See pictures!!! Looks good but tires wobble and are pointed in wards due to the suspension (i think)...

Sixtysixdeuce

What's "quite a bit"? 1/8" runout? 1/4"? Are you watching them with the engine spinning them, or trying to turn them by hand? Because if the latter, it's going to be very difficult to determine if you are causing the whole chassis to wiggle, or if they really aren't spinning true.

That's an illusion. Tires are unsprung weight, won't affect ride height. You'll actually be sitting a little higher if you measure. You're just noticing the decreased distance from top of tire to top of engine, body - whatever reference point you're using

Looks about normal to me. Most stadium trucks have about 3* positive toe on the rear wheels. It will be more noticeable as tire size and aspect ratio (height vs. width) increase. If you were to use a laser down the centerline of each tire, the lines would converge a few yards out (I'm too lazy right now to do the math and tell you exactly how far out, though).