Gearing down a TL-01 (Part 1)

With having three Tamiya TL-01 based trucks in the collection ('Blue' 'Red/Yellow' and 'Army'), all of which get used in a variety of environments, it has not escaped my attention that these things are just a bit overgeared for certain styles of off-road running - i.e. going anywhere slowly. It stands to reason really, being as the chassis was originally designed for use in a touring car, and that it's not that difficult to get 40+mph out of a reasonably tuned example.

Not so good if you want to plod around in the woods though - running bigger tyres definitely works against you in this direction as well. Red/Yellow and Army both run the lowest possible gearing, via fitment of a 19 tooth motor pinion (out of a choice of 19, 21 or 23 teeth), but this still doesn't give me much stump-pulling torque. Blue is a litle bit different being as it's currently more of a fast street truck, running a 19 turn motor and a 21 tooth pinion.

On various RC forums I've read that others have managed to get a 16 tooth pinion to work in a TL-01 by drilling new motor mount holes in the correct positions to achieve proper meshing, although I haven't come across any photos showing how this was actually done. Whether plastic had to be removed from the rear gearbox portion of the chassis remains to be seen, but either way, the motor mounting had to be physically relocated in a generally rearwards direction. The change in gearing that this mod gives is simply 16/19 = 0.84210 - therefore a 15.7894% reduction (if my maths is correct).

OK. Change of subject for a few minutes.

Over the last few weeks there have been a huge amount of HPI RC spares appearing on eBay. These include those for Maverick Scout crawlers and HPI Wheely Kings. Of particular interest to me among these was a 87632 HPI WHEELY KING COMPLETE ROCK CRAWLER CONVERSION SET.


Normally retailing for RRP £127.99 and appearing on eBay for one penny less, these started appearing for £39.99 plus £3.95 postage. A quick search on the net found them available direct from Modelsports (in Otley, West Yorkshire) for £32 with £6 for courier delivery.

That's very nice buy I thought to myself. The tyres alone would normally be well over the asking price. And there's plenty more in there to keep my project bench active for quite some time to come! With the first few sets disappearing off eBay quite quickly I felt that I really had to get one before they all went, assuming that the discount is available only because of a temporary overstock situation. As it had happened, my Mum had given me £30 for a new pair of jeans as a Christmas present, I hadn't got them yet and now I'm still going to need to get a pair! Oh well, I guess I'm old enough (52) to choose my own presents!

Anyway, although you can't see it in the photo this kit also includes the #87634 Reduction Gear Box.

Fits Model > 102117 - RTR CRAWLER KING WITH JEEP® WRANGLER® RUBICON BODY

Part: REDUCTION GEAR BOX SET (WHEELY KING)


Description: Transform the Wheely King truck into a rock crawling beast with this Reduction Gear Box Set. This genuine HPI factory approved gear box bolts right into any Wheely King for a perfect fit. It contains a tough metal case, ball bearings and all-metal gears for extra durability. The gear ratio is transformed from 23:1 on the stock truck to a whopping 174:1 after the installation. This Reduction Gear Box Set is perfect for rock crawling because it delivers stump pulling torque and the power to climb any slope. Recommended for use with #87633 Wheely King Crawler Conversion Set, but it can also be used individually or as the basis for a custom project.

Part Category > Car > Car Spares & Options > Specific Car Spares & Options > Drivetrain

Part Number: 87634

Part Area: Drivetrain

Part Type: Optional / Hop Up / Racing

Weight (g): 82

Part Status: Current Part

(Current eBay price £17.32 + £0.99 Standard Delivery)

My first question concerning this lovely little gearbox, even before I'd ordered the kit, was - can one of these be fitted into a TL-01 chassis?

The answer I discovered last night, after two hours fairly fiddly work, is a reasonably qualified 'yes'.

(Being as the camera battery is flat right now and it needs an overnight in the charger, how I did this (first stage of another truck?) will now be the topic for the next post. Coming up ASAP.)