Oversized Tires on a B4.1: Pros and Cons?

[rapscallion]

Is there a part # for them? Are they ordered directly from JConcepts? What is their overall height/diameter, please?

Go to the JConcepts website and look for J82.

Here's a link directly to the wheels: http://www.jconcepts.net/store/index.php?main_page=index&cPath=4_55

[Jeep-Power]

Thanks!

OK, found the wheels' specs on on Tower.

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXURA5&P=7#tech

now what 1.25" wide x 2.2 rim front ribbed tire comes out to about 3.75" diameter/height... having a hard time finding them on Tower...

searching....

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXWHA2&P=FR#tech

[rapscallion]

now what 1.25" wide x 2.2 rim front ribbed tire comes out to about 3.75" diameter/height... having a hard time finding them on Tower...

As mentioned previously, just search for J82 on the Jconcepts website. Why waste time at Tower when you can buy it directly from the manufacturer for a cheaper listed price?

[Jeep-Power]

As mentioned previously, just search for J82 on the Jconcepts website. Why waste time at Tower when you can buy it directly from the manufacturer for a cheaper listed price?

I was having trouble finding them there-- but I got them. Thanks for the patience & tips!

Rims - PN: 3300

Groove Front Tires - PN: 3000

[rapscallion]

Ok! Finally! I've got all my pieces/parts and assembled the B4.1 with the 1/8 scale buggy wheels/tires.

Initial tests show that top speed seems much improved with the larger diameter tires - which was to be expected; acceleration - though theoretically should be reduced - actually seems better, too, as a result of the significantly better grip provided by the drive tires that have been chosen.

One bad performance characteristic that is immediately evident is the tendency to roll over when cutting corners too sharply at very high speed; with the standard wheels/tires, the car will just slip and slide through the corners - but this configuration will require more careful driving through the turns.

Additionally, the rear wing will need to be modified to make more tire clearance, or possibly just replaced with a smaller wing from the proline wing kit.

Here are some photos to give you an idea of how it looks assembled:





Will run it at the track tomorrow for a complete performance review.

[Coelacanth]

That almost looks like those RC toys that can flip over and keep on drivin'.

[rapscallion]

ok! here's a performance report based on running one full pack (roughly 1 hour) at the track:

Before heading out to the track, I decided to use good ol' Microsoft Excel to create a calculator for Final Drive Ratio, Roll Out and TOP SPEED; TOP SPEED was the thing I was most interested in. Frankly, it seems that most people don't seem to realize that they are grossly over-estimating the speed of their R/C vehicles.

My B4.1 RTR Brushless in total stock configuration with 3.2" diameter tires, 81/21 Spur/Pinion combo, 3300kv Reedy motor and 7.4V Lipo Battery has a mathematical top-speed of roughly 23mph. This is a hard scientifically based fact, yet I've seen many reports online of people claiming anywhere from 28mph to 40mph 'out of the box' with the exact same car in the exact same configuration. Plain and simple, 23mph is as fast as this car can go under perfect conditions - which means that most likely it rarely hits that number and probably comes in a touch slower. Granted, when the 2s battery is fresh from the charger and giving off closer to 8.4v than 7.4v, top speed could approach 26mph - but it wouldn't maintain that speed for long, as the pack voltage would settle down toward its stated 7.4v fairly early in the run.

With the 'Big Wheel' configuration, using 4.5" diameter tires, 87/19 Spur/Pinion combo, 3270kv Bullistorm motor and 7.4v Lipo Battery, mathematical top-speed should be roughly 27mph, with a peak speed during the first bit of the run hitting 31mph thanks to the extra volt the battery pack carries during the first few laps.

The additional 4mph that I was getting from the car was instantly noticeable; 4mph doesn't sound like a lot, but with a 1/10 scale model car, it makes a big difference.

Acceleration was aided greatly by the oversized tires and lower gearing. I could really feel the car grabbing the track and propelling the car forward.

Cornering was much more predictable in the new configuration, with alot less 'dukes of hazzard' going on. Downside here with cornering is the potential for roll-over. Definitely requires more input from the driver to have just the right amount of speed and torque applied to keep you moving through the turn without biting off too much and sending the car flipping; additionally, pouring on the gas as you exit the turn needs to happen a touch later than I'm used to. But after a few laps around the track, I did not roll over anymore and had a good feel for the biting traction.

Stability was improved dramatically. Our local track is peppered with hundreds of tennis-ball-sized pot-holes that usually swallow up my stock tires and send the car careening in crazy directions, but with these 4.5" monsters, the car hardly noticed the holes and rolled smoothly whichever direction I pointed it.

Jumps were much more manageable than ever before. The increased speed combined with better traction allowed me to more confidently approach the jumps without stressing about off-setting any last second shifts in my path that usually occur when the stock tires catch in a hole just before ramp face. Air Time was also much more controlled, with the extra weight on all 4 corners of the car acting as a balance to really level the car neatly through the jump arc. Landings were also smooth; usually, the little car will slip and slide upon landing on the loose layer of dry dirt that makes up the base of our track - but these big tires cut right through the loamy stuff and grab onto the hard pack underneath. Additionally, the one massive cross-over jump that usually proves nearly impossible and occasionally damaging to the 1/10 buggies that run out at our track was no longer a problem; I could easily clear the gap and land without casing the chassis or motor plate.

Overall, I'm very happy with the modifications. Though it might not be perfect for every track condition, it does wonders with the track that I most often visit. For the first time since getting the car, I feel that I can enjoy driving and focus on improving my skills, as opposed to worrying constantly about the impending damage that inevitably occurs when constantly hitting all the holes in the track or casing the chassis on the cross-over jump. Sure, I could have just overgeared the car and left everything else stock in hopes that the higher top speed would get me through the cross-over, or I could have searched for a different tread pattern in stock tire size to help with the loose dry conditions - but neither of those choices would have provided a universal solution to running at this track.

Next up, I'll try to dial things in for better corner handling and smoother dampening over the straight and bumpy stuff.

[Coelacanth]

Nice report, very detailed. I only have one issue with it:

Acceleration was aided greatly by the oversized tires and lower gearing. I could really feel the car grabbing the track and propelling the car forward.

This is a physical impossibility, you can't gain both acceleration AND top speed by up-sizing tires, keeping everything else constant. If that were true, and you kept increasing the tire diameters more and more, do you still think it would continue to show increased acceleration as well as top speed? Perhaps the improvements in acceleration were due to the new tire treads gripping better than the previous tires, as opposed to just being oversized. Unless you tried a tire combo with almost identical tread patterns in 2 different sizes, you can't really make a valid comparison.

Other than that, I enjoyed reading your observations.

EDIT: Some more info on this subject:

http://rusubaru.com/411-gears/

http://www.yotatech.com/f2/tire-size-versus-acceleration-70918/

[rapscallion]

Nice report, very detailed. I only have one issue with it:

Acceleration was aided greatly by the oversized tires and lower gearing. I could really feel the car grabbing the track and propelling the car forward.

This is a physical impossibility, you can't gain both acceleration AND top speed by up-sizing tires, keeping everything else constant.

Hello. Thanks for the comments.

Regarding your 'issue', you would be correct if the only change I had made were tire size - but as the quote clearly states, 'Acceleration was aided greatly by the oversized tires and lower gearing.'

By increasing the spur/pinion ratio from the stock 3.85 (81/21) to 4.58 (87/19), it results in a final drive ratio that is nearly 2 full points higher (from 10.1 all the way to 11.9) - which means MUCH MORE TORQUE. That increase in torque at start-up is definitely adding to the acceleration. And, as suggested, the much more aggressive tire pattern is contributing - but even with matched treads on a stock 3.2 diameter tire, the acceleration of a 10.1 FDR would not compare to an 11.9 with all other things equal.

[Coelacanth]

You're right, and I did say "keeping everything constant". In fact, it was me that suggested going to a lower pinion gear.

If you keep your gearing as it is now and add larger tires, it'll take more work to get them moving. You might want to downsize your pinion gear a few teeth to keep things equal and performing the way you're used to.

Sorry for the confusion.

[rapscallion]

You're right, and I did say "keeping everything constant". In fact, it was me that suggested going to a lower pinion gear.

I actually tried it with the stock gearing (81/21) and it was ridiculously fast According to my 'top speed calculator' it would be hitting 33mph at 7.4v, and topping out around 37mph when the battery just comes off the charger around 8.4v It even seemed to have plenty of pull - but I decided for the sake of safety and finances (can't afford to buy a new esc at the moment) to go more conservatively and use the same stock spur/pinion that come with the SC10.

With this new configuration, motor got only very slightly warm to the touch, and esc was no warmer than the surrounding ambient temperature of the air. I'd say that I can safely gear up a bit without getting too warm, but I sort of like it where it's at for the moment. I much prefer long run-times to high-speed bonanzas

I don't suppose this car would fit into any race-able category as it stands, but it sure would be fun to run it side-by-side with some stock B4.1's.

Thanks again for your input and feedback!

[markt311]

Fun project, and well thought out. Get some spare wheel bearings, I ran 8th scale tires on my SC10 for a short time and the increased loads caused by the heavier tires took out bearings quickly. Especially the drive wheels, it goes without saying to check the bearings for play and smooth feel often.

I practice at a track in a local park that sounds like yours, lots of rocks and ruts caused by rain runoff. mostly 8th scale nitro cars run there, and track work only gets done every few weeks, so it gets pretty rough. I gave up running my buggies there because the rocks ate the chassis up really quick, my Losi SCT is a ton of fun though and it's teaching me some finesse on the throttle.

[rapscallion]

Get some spare wheel bearings, I ran 8th scale tires on my SC10 for a short time and the increased loads caused by the heavier tires took out bearings quickly. Especially the drive wheels, it goes without saying to check the bearings for play and smooth feel often.

Good idea. I think I'm gonna' set aside a full rear drive set-up, including the hub carriers, axles and bearings. Thanks!

[kdog]

I am also running bigger tires on my b4.1 for all the same reasons listed above. I just ordered some sc10 tires/wheels off ebay and bolted them on. With stock gearing, the car is fast as hell and has enough torque to wheely through some sections when it is really hooked up. Motor and esc never seem too hot. (Reedy sc450/3300kv motor/lipo.) As for bearings, I would like to do the rear hub carrier upgrade (b44) with the larger bearings but I figured that a t4.1 uses the same drive parts and brearings as the b4.1 so the bigger tires on my tr/buggy shouldn't tear it up too much. I love how the car handles in the air with the larger momentum tires- sooo stable. No need for ballast weights either. I run with friends on a sweet private track with their sc10's. My car is a pound lighter but has the same tires and clearance.

Other adjustments for this setup: negative camber is really important for the balance of traction/not rolling in every turn, and I made the wheelbase as long as possible with the adjustment shims.

Its a fun ride! I'm glad I'm not the only one playing with this setup.

[rapscallion]

I am also running bigger tires on my b4.1 for all the same reasons listed above. I just ordered some sc10 tires/wheels off ebay and bolted them on. With stock gearing, the car is fast as hell and has enough torque to wheely through some sections when it is really hooked up.

Its a fun ride! I'm glad I'm not the only one playing with this setup.

Thanks for joining in the conversation! I had considered going with the SC10 tires/wheels, but ultimately went with the 1/8 buggy set-up just because it was cheaper and seemed like it would be the most flexible option down the road.

Wheely? Dang I don't seem to be able to get the front tires off the ground in any of the configurations. Kind of surprising, because I've seen lots of other B4.1 rigs running at the track and they almost always lift their wheels when accelerating hard down the main straight - but not mine. Maybe I need to tighten my slipper? I did feel like the front wheels were on the edge of lifting when I ran it for just a few minutes in my front yard using the stock 81/21 gearing, but I changed it to 87/19 before getting it to the track for a true test; now I'm wondering if I should gear up slightly