Yokomo YR4-M2 Information and History

Yokomo Information   

Back in the beginning, the YR4 sport sedan started the revolution which was fibergalss. Then, the YR4 special came out which was made of carbon fiber graphite with nurf wings? From that point on, the classic YR4M was released and set the standard for an awsome Yokomo sedan. The first YR4M I saw belonged to William Brown of BBR. The car was on rails! 6 months passed, a new chassis came out which included battery trays and battery hold downs. 2 months later, the YR4MSP was born. This kit included a body also. 2-3 months later, Yokomo came out with a car that looked like a damm FROG. This car was the YR4F2. The car was a totally new design with the motor up front. Masami was unbeatable with this car. He would drive this car with his feet, and still TQ in any track in Japan. If you get the chance to see this car. Look at it carefully. It's a pretty wicked design.

Time passed and another sedan was made. The YR4II. This time Yokomo tried something different. Batteries were on the right side of the car with the electronis on the leftside. Yokomo said " Lets make mini version." then what do you know, the YR4II compact came out. Cameron was the first one to ever have one in the United States. ( Way to go Cam ! ) A year have gone by, and Masami wanted to try something totally different. His dad combined a YR4MSP and a YR4II together. I know you're asking yourself why did he do that? I have a picture of this car which was taken at Hong Kong for a race there. I looked at it and said, " Oh,oh, here's come another sedan !" I decided to copy Masami's new car and try something new also. The only parts that were used was the YR4II top plate, the front diff, and the bulk head covers. The car handled great and I named my car the YR4MSP2.

I raced with it for about 1 month when Yokomo decided to release the YR4M2. This car was the BOMB. A year later, Yokomo decided to make a car for the counrty of Japan. What?!!? The YR4 Type J was born. Knowing the R.C. industry here in the U.S. You know when Yokomo makes something new only for their country, someone is going to make a mistake by sending this car to the U.S. or someone is going to take a trip to Japan for vacation and decides to purchase this car because it's not offered in the states yet. Well this happened. We were purchasing J's from outside the U.S. The car was never seen on any shelves of any hobbyshops in the U.S. Until, R/C California started advertising them in R/C car action. People started buying them and sooner than you know it, the YR4M2 pro was born. Now, Mr. Yokomo releases a sedan for off-road. This car is called the MR-4. From what i've read, you can convert this car either to off or on road. Who knows, maybe someone out there can purchase this car and combine a Type J pro and a MR-4 together to come up with something that may work. I just hope that Yokomo Japan and Yokomo U.S.A decides to keep this car for a long time. But, with technology on the verge of new change, who knows how long this car will last for. 6 months? 1 year? I don't know. Your guess is as good as mine. Just a little history lesson for all of my Yokomo enthusiest. ( I left out the Yokomo gas sedan because I was only refering to electric.) Well, here we go again with a new Yokomo, a new year, new friends, and most importantly, more FUN.

-Roger Serafin

    Ok, here it is, a run down on some of the more common Yokomos. There has been quite a bit of discussion on what is what, so I hope to help you understand what is what, along with their features. 
    First off, all cars share some common ground. The basic suspension arms, dog bones, diffs and bulkheads have been the same for years. although the new Pro cars have new bulkheads.


Shock Types
RC Racing.com - Yokomo Micro Shocks Shown here are the original 'Japanese' micro shocks, found on the original YR4-M2 and older cars.
RC Racing.com - USA Shocks These are the newer full size shocks, also known as 'USA' shocks. You'll find these on all the Type-J's as well as the M2-USA models.


Yokomo YR4-M2 - Japanese/Early US version
YR4-M2 (Click for Larger Image) This is basically the early M2 (less the aluminum suspension arms shown here). These had the micro shocks, different shock towers. Otherwise this is the same car as the later YR4-M2.
RC Racing.com - Yokomo YR4-M2  


Yokomo YR4-M2 - USA version 
Yokomo YR4-M2 USA The M2 USA. This is a follow up to the original shown above. The only changes are the new larger 'USA' shocks and new shock towers. The chassis is the same as the earlier M2. 
The M2 also has a one-way pulley that can be set by simply pulling or replace a pin.


Yokomo YR4-M2 Type - J 
Type-J (Click for Larger Image) The Type J is a completely re-designed chassis for Yokomo. although it still uses the same suspension, bulkheads and shocks as the M2-USA version, the bottom chassis plate has a whole new design that brings the batteries closer together and also allows you to run 4x2, 3x3 or even stick pack batteries if you want.
 Type-J (Click for Larger Image) The Type J also did away with the ever popular battery hold down system found on the original M2, so you'll have to break out your tape for this chassis. The top plate was also completely changed. Gone are the multiple posts down the center. This is replaced with a single post and the typical Yokomo belt tensioner, this time mounted to the rear instead of the front.
The Motor plate also went under changes as well, allowing two different mounting positions for the spur drive shaft and the motor. This comes into play if you need to run a large spur or want to use stick packs. 
The front diff on the Type J is actually a one-way diff, instead of the one-way pulley at the spur drive shaft. This can be replaced with a standard diff, and for most tracks you would want to do this. 
This car only ships with the larger 'USA' type shocks.


Yokomo YR4-M2 - Type - J Pro 
Type J Pro (Click for Larger Image) The Type-J Pro, or as some people have called it, the YR4-M2 Pro. This is in effect the same car as the original Type-J, but with some major improvements. The most note worthy is the all new top plate. The 'Y' design makes the car very stiff. Other improvements include 2' front buck heads instead of the normal 10' as well as making both front and rear's in blue anodized alum. Included as well are blue anodized hardware for the complete 'trick' look. 
The current Team/Japanese version ships with a front one-way diff. The kit that will be available in the USA is said to have a standard diff packaged instead. There are rumors of some other small differences between the current Japanese kit the the USA kit the should hit the shelves in November.
 Type J Pro (Click for Larger Image) This car ships with the larger 'USA' type shocks.


General Information
Gear Ratio Info:
 Gear reduction: 2.2:1 
 Spur / Pinion * 2.2 = Final Drive 

 Base Gear Ratio for a 36' Stock Motor: 
 78 / 28 * 2.2 = 6.129 

 Base Gear Ratio for a 10 turn Triple: 
 81 / 19 * 2.2 = 9.337 
 (These should only be used as a ruff guide. your motor/battery/track combo will effect what gear ratio you would run.)

Suspension Setup 
 Shocks: (front) 
 Length: 71.5 mm 
 Oil: 90wt.  
 Piston: Stock 
 Spring: HPI Blue progressive 

 Shocks: (rear) 
 Length: 69.5 
 Oil: 60wt. 
 Piston: Stock 
 Spring: HPI Red progressive 
 Ride Heigth:  5mm F+R 

 Toe: 1 degree  out 
 Front: 1 deg. 
 Rear: 1 deg. 

Article Date: 01-Jan-99

Date: 01/01/1999
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