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View Full Version : DIY wider rear end


Jshwaa
2015.03.07, 09:10 PM
I wanted to try out a wide rear end, so I sacrificed my stock rims and ordered a couple sets of tires and some carbon fiber tubing...

http://i83.photobucket.com/albums/j314/Jshwaa/Mini-Z/DSCN2450.jpg (http://s83.photobucket.com/user/Jshwaa/media/Mini-Z/DSCN2450.jpg.html)

I thought I'd just go double to start out with. If I need to trim down later I can, or just make another set later that's a little narrower (say 15mm or 17mm).

So then I took my stock rims and rigged them up on my dremel and filed them down to size, making sure to check the size from time to time so that I have a snug press fit.

http://i83.photobucket.com/albums/j314/Jshwaa/Mini-Z/DSCN2451.jpg (http://s83.photobucket.com/user/Jshwaa/media/Mini-Z/DSCN2451.jpg.html)

The ID for the carbon fiber tubing was just a hair above 19mm...

http://i83.photobucket.com/albums/j314/Jshwaa/Mini-Z/DSCN2452.jpg (http://s83.photobucket.com/user/Jshwaa/media/Mini-Z/DSCN2452.jpg.html)

When I can get the calipers to fit snug on the rim, I check the press-fit.

http://i83.photobucket.com/albums/j314/Jshwaa/Mini-Z/DSCN2454.jpg (http://s83.photobucket.com/user/Jshwaa/media/Mini-Z/DSCN2454.jpg.html)

I then put the sized rims back on the car and adjust the 20mm carbon fiber sections so that they are balanced with the chassis and body.

http://i83.photobucket.com/albums/j314/Jshwaa/Mini-Z/DSCN2455.jpg (http://s83.photobucket.com/user/Jshwaa/media/Mini-Z/DSCN2455.jpg.html)

http://i83.photobucket.com/albums/j314/Jshwaa/Mini-Z/DSCN2459.jpg (http://s83.photobucket.com/user/Jshwaa/media/Mini-Z/DSCN2459.jpg.html)

I then put a bead of super glue on the joint between the carbon fiber tubing and the rim, on the inside seam...

I'm now ready to install tires....

http://i83.photobucket.com/albums/j314/Jshwaa/Mini-Z/DSCN2462.jpg (http://s83.photobucket.com/user/Jshwaa/media/Mini-Z/DSCN2462.jpg.html)

http://i83.photobucket.com/albums/j314/Jshwaa/Mini-Z/DSCN2467.jpg (http://s83.photobucket.com/user/Jshwaa/media/Mini-Z/DSCN2467.jpg.html)

Some of the added width was offset into the profile of the body, so they don't stick out too bad...

http://i83.photobucket.com/albums/j314/Jshwaa/Mini-Z/DSCN2470.jpg (http://s83.photobucket.com/user/Jshwaa/media/Mini-Z/DSCN2470.jpg.html)

http://i83.photobucket.com/albums/j314/Jshwaa/Mini-Z/DSCN2469.jpg (http://s83.photobucket.com/user/Jshwaa/media/Mini-Z/DSCN2469.jpg.html)

DMALMAD
2015.03.07, 10:12 PM
You could have just added shims on the rear axle. But that works to I guess but probably a little to stiff with the cf, and extra heavy. PN also makes some oversized rear rims that are 14mm wide.

arch2b
2015.03.07, 10:42 PM
extended width wheels have been offered over the years from various manufacturers, none have really taken off.

nice d.i.y. tutorial though :cool:

Jshwaa
2015.03.07, 10:56 PM
You could have just added shims on the rear axle. But that works to I guess but probably a little to stiff with the cf, and extra heavy. PN also makes some oversized rear rims that are 14mm wide.

The carbon fiber may be an additional mass, but I offset it a little with the millimeter or so that I needed to shave off the rim to fit it on. The additional tire is obviously an added mass, but it contributes to 'go power' so I think it's worth an assessment. So far I like how it accelerates and runs more stable on slicker surfaces. You have to try a little harder to induce a spin and lose the rear end a little to help turn quicker, but a little practice and the right motor/gearing will help in that department. Everything needs a little adjustment and getting used to.

Sorry, but I don't understand the comment about shimming the axle. Would that be to widen wheel base? Don't know how that would make the tires wider themselves. I was looking for more surface area to put a little more torque to the ground. I found my mini-z to be a little unstable in the rear when taking off and powering around corners.

And FYI, the mass of the stock back rim and tire was 4.5g and my modified back rims are 6.4g. I added 1.8g of mass overall with this mod, and to put that into perspective, one of my cells weighs 12.5g.

Stiff? Yes, I like rims stiff. Are yours flexible?

DMALMAD
2015.03.08, 01:05 AM
Yes for the shimming I meant for wheel base. However with those protruding wheels when you hit someting you are most likely going to be bending your diff shaft so I would be careful. If you are struggling with grip adding another tire also leads to less of each tire contacting the surface. Assuming you are not truing your tires, your tires are not perfectly round and being positioned differently may also wear at different rates. Just a possibility to think about. Have you taped your tires to your rims? Double sided tire tape like the stuff r246 makes works well. Otherwise you could glue them. Making sure your tires are firmly connected to the rim and perfectly true is very important to gaining more traction. As for the rims being stiff, from my expereince a little softer rim can actually impact grip levels. When we ran rubber tires on carpet which was a lot less grippy I found that the spoked wheels which were more flexible gave a little more grip.

Jshwaa
2015.03.08, 10:31 AM
Yes for the shimming I meant for wheel base. However with those protruding wheels when you hit someting you are most likely going to be bending your diff shaft so I would be careful. If you are struggling with grip adding another tire also leads to less of each tire contacting the surface. Assuming you are not truing your tires, your tires are not perfectly round and being positioned differently may also wear at different rates. Just a possibility to think about. Have you taped your tires to your rims? Double sided tire tape like the stuff r246 makes works well. Otherwise you could glue them. Making sure your tires are firmly connected to the rim and perfectly true is very important to gaining more traction. As for the rims being stiff, from my expereince a little softer rim can actually impact grip levels. When we ran rubber tires on carpet which was a lot less grippy I found that the spoked wheels which were more flexible gave a little more grip.

Interesting about the flexible rims...and yes I was cringing when I smacked the rear against the baseboard of my cabinets earlier, but luckily nothing broke. I do need to be more careful now, as the rear tires are no longer under the protection of the wheel well.

About the tire contact, yes I did think about that. So far the tires have been wearing in nicely. The tread is wearing out a little and so is the seam between the tires, making them look more and more like one big tire. I think I'm gonna stick with it for a bit. It changed everything, and now I want to try different motors and gearing all over again.

Next, I'm aiming at the chassis...

For the price of the X-power, I bought a Dremel Workstation (http://mdm.boschwebservices.com/files/Dremel%20Work%20Station%20Rotary%20Attachments,%20 220-01%20(EN)%20r19891v15.jpg), a Dremel 100 (http://mdm.boschwebservices.com/files/Dremel%20Rotary%20Tool%20100%20Series%20(EN)%20r20 905v15.jpg), plenty of carbide tips (http://www.mcmaster.com/#standard-threaded-standoffs/=w7xm8i), 2 slabs of 3"x12" carbon fiber (http://www.mcmaster.com/#8194k52/=w7xll4), one 1/16" thick, the other 1/32" thick, and all kinds of 2-56 threaded aluminum standoffs (http://www.mcmaster.com/#standard-threaded-standoffs/=w7xm8i) and fastening hardware to craft my own chassis. I got the tools forever now, so if I don't get it right at first, I can try again until I run out of carbon fiber. Because I went with a wider mini-z to begin with, and just widened the rear, I think the next logical step would be to try and widen and lower the chassis just a little bit. As far as I see it, there's nothing wrong with widening a little to approach the width of the wheel base. It 'could' more effectively displace the mass of the middle section a little more across the wheels.

DMALMAD
2015.03.08, 01:02 PM
I have a cad drawing of the mrx bottom plate with all the correct screw hole so if you wanted I could send you a printable version that you could use as a template to make your bottom chassis, then you could just buy the couple of aluminum pieces. However I think it really isn't neccesary for what you are doing. Anyway shoot me a pm. I tried to cut out cf a while back with the template I made with the same dremel stuff but it really didn't turn out too well. The thickness you are most likely going to need is 1/16th and maybe something a little thicker too. the 1/16th is good for the bottom chassis but you need something a little thicker for the upper deck.

Jshwaa
2015.03.08, 01:33 PM
Hey, thanks but I think I'm going to try and wing it.

I ordered a stock chassis to refer to for fitting stuff, so I don't have to take apart my car to get some dimensions and to have a good reference for making parts. I'll make sure everything looks good on it before I actually try and run it. I have some original ideas I'd like to try and implement.

I like the openness of the x-power chassis, and that is what I'm aiming for so-as to allow the power plant to be a little more configurable. Being restricted to 4-cells or 2x1 Kyosho Li-Fe's can be yawn inducing in my opinion. I would really like to get 6 cells to lie flat in the mid section...

So, if we look at what we're dealing with stock, compared to where I'd like to go...

6-cells is definitely within the width of my body...

http://i83.photobucket.com/albums/j314/Jshwaa/Mini-Z/DSCN2475.jpg (http://s83.photobucket.com/user/Jshwaa/media/Mini-Z/DSCN2475.jpg.html)

My wheel base shouldn't be an issue with or without the added rear tire width...

http://i83.photobucket.com/albums/j314/Jshwaa/Mini-Z/DSCN2476.jpg (http://s83.photobucket.com/user/Jshwaa/media/Mini-Z/DSCN2476.jpg.html)

And if we measure the stock width compared to the 6-cell width, you can see that all I really need is a quarter inch on either side.

http://i83.photobucket.com/albums/j314/Jshwaa/Mini-Z/DSCN2478.jpg (http://s83.photobucket.com/user/Jshwaa/media/Mini-Z/DSCN2478.jpg.html)

http://i83.photobucket.com/albums/j314/Jshwaa/Mini-Z/DSCN2479.jpg (http://s83.photobucket.com/user/Jshwaa/media/Mini-Z/DSCN2479.jpg.html)

I think it is definitely doable.

As far as the flexing goes. I plan on strategically placing reinforcement ribs with tiny strips of carbon fiber, in between the gaps of the cells, or wherever space allows. A wide flat piece is flexible, but adding a support rib makes it very rigid. I think that I'm going to find it tricky to get chassis to seamlessly connect to the front and rear ends while keeping it low and maintaining strength. We'll see how it goes. I'm still waiting for the stock chassis to start making measurements...

DMALMAD
2015.03.08, 01:49 PM
The one thing about the MRX that is really excellent is the implimentation of a stock front end on to the cf chassis. Their AL bulkheads for the front end are really good so if there is to be one thing that you buy and try to build the chassis around it would be that. The measurements are the same as a stock chassis and allows the mounting of asc bodies so that would be a good thing to have. Without that I think it would be pretty difficult to put a regular 03 front end onto the chassis unless you had acces to a cnc machine.

Jshwaa
2015.03.09, 07:54 AM
The one thing about the MRX that is really excellent is the implimentation of a stock front end on to the cf chassis. Their AL bulkheads for the front end are really good so if there is to be one thing that you buy and try to build the chassis around it would be that. The measurements are the same as a stock chassis and allows the mounting of asc bodies so that would be a good thing to have. Without that I think it would be pretty difficult to put a regular 03 front end onto the chassis unless you had acces to a cnc machine.

For the price, the MRX better be excellent. Access to a cnc machine is what makes them so expensive. I've spent a fair enough money as it is. I think I'd be crossing a line where I was simply buying my hobby if I was to start purchasing upgrades at the magnitudes of cost that greatly exceed my initial investment. I just can't bring myself to do it...yet.

mleemor60
2015.03.09, 09:27 AM
The MRX is truly a great platform and if properly presented and promoted could likely be the bridge that connects the smaller mini scale to the larger scales.. However, the thought or premise that you have to expend hundreds of dollars on added accessories to make it go is, well, bovine excrement. You are able to take all parts from a stock 03 and mount them to the chassis. The full benefit of the MRX is that you can then add a very wide array of parts from any manufacturer you prefer to get it to the level you want. Since this platform is still in it's infancy the jury is still out on what constitutes the best parts and accessories package to extract all it has to offer. Still. To get the complete chassis and appropriate batteries you are looking at $170ish plus shipping either from the manufacturer or one of the three dealers in the contiguous U.S. Could you produce a viable clone for the same or less and get the quality that it has is a coin toss. It would depend on resources available to you. Would it be worth it? Only you know that.