- Yokomo B-Max2MR - Paul Gill - Weston Park - 16.06.2013 -



Just thought I’d pass on my experiences of running the BMAX2 MR in both mid motor and rear motor on the same day in case anyone else was thinking of trying it.

The track I would be racing on would be at the Weston Park model air show meeting organised by the Telford Model car club. The grass layout had been run on the day before and the track was starting to wear by the time I got to race on the Sunday. The layout consisted of a couple of jumps into corners followed by some on power turns onto the main straight which led into an off camber tightening bend. This followed up with a chicane before the main table top jump in front of the rostrum. Quite tricky to get right but a good feeling when you did!

To begin with I started with my normal mid motor setup but with the car dialled in for a lot of rear grip as I knew there wouldn’t be fresh grass. I was also trying the gear diff again with 2k oil just to see how it worked on this surface as opposed to my normal ball diff.

This was my first weekend of running the alloy rear hubs and this combined with a slight mod to the rear arms meant I got rid of a lot of the slop in the rear of the car. I’ve chosen to run with the 0.5 deg arms as I have now set the rear toe in the car to the 3.5 position. This allows me to run either 3 or 4 degrees depending on the conditions and is quicker to swap over if the weather turns quickly…….

In the open practice after learning the track and trying a few different tyres I settled on sch yellow spikes front and rear.
During the 1st qualifying round I had a reasonable run with a couple of crashes but it wasn’t the best time, 13 in 311 best lap 22.9. Car was ok it just me making mistakes in traffic as usual

2nd round I changed nothing and just concentrated on getting a clean run with a 13 in 306 and a best lap of 22.7.

3 rd qualifying round I managed to improve down to a best lap of 22.61 and a run of 13 in 305.22. The only major change I made was to soften the springs all round for the 3rd round as the track was starting to lose grip
The mid car generated reasonable traction with the gear diff fitted and was ok to drive – had just a little on power push which was controllable with the throttle... Car was still pulling well out of the corners but you couldn’t just plant the power down hard as the track wore away. The ball diff may have been better but I was sticking with the gear diff to see how it got on later

A couple of the others I pit with were already running in rear motor and managed to get 14 laps in during the heats so it would be interesting to compare in the 3 legged finals when I made the change over.

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REAR MOTOR

After qualifying in P7 I made the change over to rear motor, I Velcro my ESC into the car for quicker changes so it took just over 30 minutes from start to finish. I run the car with a shorty pack forwards and the esc tucked in under the rear tower and keep my receiver up front. The rest of the settings I kept from the mid car so as to start from a known point. I even kept on the same rear tyres for a real test of traction!

As it was open practice I took the car out for a quick test and it was very stable into the corners and had much better traction as you would expect. In rear motor I found I could pitch the car in harder than with mid as I had the knowledge the rear wouldn’t step out on me. The slipper was too tight and the car kept wanting to wheelie so had to keep backing it off which meant the car wouldn’t accelerate as hard onto the straight. I added another 10g and increased the wheelbase to help solve this but I will be buying the cream weight next. Unfortunately I suffered my first breakage on the car when I hit a metal rod that held down a pipe and broke the front C hub in half. Luckily someone had a spare so I was able to race the finals and complete the test. I'd found in the practice that the yellow spikes weren’t the right tyre in rear mode so I swapped them out for yellow staggers instead as they felt better in the low speed corners.

So for leg 1 I planted it off the line and nearly joined the jets in the air show on the other side of the park as the slipper was still too tight and the downhill straight made it worse. I had a reasonable run and the car jumped the table top really well for a rear motor car – landing the down ramp almost every time. I had a couple of errors as I adjusted to driving a rear motor car for the first time in 3 years but really enjoyed the way I could attack the corners and get on the power. In the end the run was 13 in 305 but I had improved my best lap by over ½ a second to a 22.07. Id also matched my best mid motor run first time out!

Leg 2 I changed the rear spring back to the std blue from yellow to try and stop the back from sitting down as I couldn’t really back the slipper off more and shortened the rear link on the tower end for a bit more rotation. This was a little better but I still wheeled off the line. This run wasn’t as clean and I made a few errors as the stiffer spring/link change meant the car had more turn in than before and I kept clipping the pipes. Best lap was again a 22.09 though my run was slower.

Leg 3 and I raised the front link by 1mm to take off some steering and gain a bit more on power steering out the corners and also squeezed in an extra 10g of lead onto the front bulkhead to try and keep the front down. I also changed the rear toe in from 4 degrees to 3 degrees to try and free up the rear a bit more in the switchbacks. The start was better this time and managed to get into p4/5 around the first part of the lap. The car was good and much better balanced this time and I was able to push and was having a good race until I got tangled up with another guy’s wing and we lost 8 seconds while being marshalled. However I was able to get back in the groove and ended up finishing in P4 just missing the 14 laps by 2 seconds despite the crash it was nice to know I had found the extra pace. Best lap was a 22.06 and this was still 0.5 better than I managed with the mid car even though the tyres had done another 3 runs.

Conclusion: I think that the modern generation of cars that are built for mid and rear are normally biased to the rear configuration as that is the main market they are aimed at so are now designed around the more modern electronics and lipo batteries. Certainly watching a couple of XXX-CR’s going around yesterday they definitely had less steering overall than the newer cars. The BMAX 2 definitely jumps well and steers well in rear mode and performed no worse than the mid car did on a non high grip surface. It has good steering (although not quite as responsive as a mid car)but despite being rear motor I could just concentrate on picking my lines and not have to worry about exit traction as I knew I would have the grip compared to the mid car. The rear is much easier to drive hard in my opinion. Indoors or high grip days the mid car will always be better as traction is not an issue but when the surface is iffy I’d rather run rear to be safe. The ball diff may also be better but I will have to test that back to back in future.

I did feel that I could push this car harder in rear mode and I’ll be looking forward to testing it on my home track later this week to see how it does on bigger jumps and high grip and refine the setup more. It’s definitely something to consider for outdoor racing especially with the weather we have as if it rains you’re onto a winner – TRY IT AND SEE!!

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Source:

P. Gill