BMW Brat Style vs Bobber Frame Design

INTRODUCTION

Hi there folks. My name is Marcus and welcome to montmoto. This week I’m going to run through the difference between a brat-cafe and a bobber in terms of seating position, frame design and suspension support. Then I’m going to mock up both a brat-style and bobber subframe to see what they might look like on this BMW R80 build and ultimately try to decide what direction to take this build. As always - the different sections are in the timestamp below.

You may have seen my previous blogs on how we got to this point - but as a quick recap I’ve bought a 1979 BMW R80/7 motorcycle and I’m going to break it down into each individual nut and bolt and rebuild it into my ideal custom motorcycle. I’m just not certain what that is yet.

This week I’m going to be focused on ONE key decision - am I building a cafe racer, brat-style or bobber motorcycle? This is one of the most important decisions to make on this build as so many design decisions are impacted by it. So to make sure I’m starting this build on the right path, I’m going to mock up how this build might look with a couple of scenarios before I commit to one. And while I do it, I’m going to talk a bit about each of the motorcycle styles.

First, let’s get the original frame and subframe setup here to see what we’ve got.

Just look at how far back the seat on this subframe goes. The general rule for a cafe racer is that the seat should not extend beyond the rear wheel axle. And just look at this battery holder - it’s an absolute monster so irrespective of which motorcycle frame layout I do, I’m going to switch to a new lithium ion battery. 

Just take a look at the difference in size between the existing Westco 12v battery and this new Shorai 12v battery. It’s really incredible just how far battery technology has come along.

OK, but this isn’t the setup we're exploring here, so let’s first mock up a bobber style custom and I’ll talk to you a bit about the history of this genre motorcycle.

History Bobber Style

The bobber style custom motorcycle first came to be in the US in the 1930’s and is the grandfather of the modern day “chopper”. Originally based on production Harley Davidson motorcycles, the goal was to reduce weight by any means possible, including removing the front fender, shortening the rear and removing all side paneling and accessories. Stylistically the seat tube was lowered or removed entirely and often did not have any rear suspension, aka a hard-tail. I’ve owned choppers and while they are beautiful bikes, and there is a place for them in any garage, but I’m getting to old for no rear suspension - my back just can’t take it.

So I bought this bobber seat on sale a couple of years ago on ebay - it’s made by mother road route 66 customs, and I’ll try and add a link in the description below. I love the color of the leather on this seat but to be honest i didn’t think it would work with this build, but now that I see it mocked up, I have to say that I love it. It looks mean and really fits the look I’m going for. I do have a couple of concerns though. I’m not sure that I’d be comfortable ever trusting a single connection point into the frame to sit on and trust it will hold my 220lb weight directly above a wheel spinning at 60mph. The second thing is I would need to figure out how to mount the suspension in a way that doesn’t ruin the minimalist look - but I can’t do a hard tail these days.

OK - take one last look - time to change this up for a brat style setup.

History Brat Style

Many derivatives of the Cafe Racer have evolved since it’s origins in the 1960’s but in my opinion, one of the most interesting branches in the evolution mutation chain is the Japanese “Brat Style” influence. “Brat Style” a motorcycle modification shop opened in Tokyo in 1993 and has become world famous for not only a specific style, but to some degree, a way of life. Sometimes referred to as “The Japanese Bobber”, in terms of the design, you can probably summarize the Brat Style as a crossover between a bobber and a scrambler motorcycle. Similar to the cafe racer, brat style motorcycles are designed for the urban environment, with emphasis placed on minimalism and function over form - which in itself creates a form that is incredible. Typically Brat Style means slab seating, dirt handlebars, wrapped pipes and knobbly tires. They are aggressive and mean.

History of Cafe Racer

We’ve all likely heard of cafe racers these days, as they have become very popular again in the past 10 years. The cafe racer craze started in London in the 1960’s and was particularly associated with Urban Rockers. At the core of this movement,  production motorcycles were modified by their owners to make them faster over a short distance, so their owners could race each other from cafe to cafe - hence the name. This typically involved removing any weight where possible, and stripping the bikes down to their bare essentials. Mudguards, side panels, fairings and fenders we’re to be discarded. Another typical characteristic, in order for the rider to get low for aerodynamics, is clip on handlebars.

Ok, so now that you’ve seen both options, what direction should I take this build? Would you go with the bobber seat with little to no rear suspension, hovering above the wheel, or would you go for the Japanese style Brat, with bench seat and mongrel looks? I’m not entirely sure myself yet. But there is one more thing to do - cut off all the bits from the frame I don’t need with a smaller battery. 

Next week I’ll be working on the carbs to clean them up and buy me time to get the frame and rims in to get powder coated. So if you’d like to follow along on this project hit subscribe, and I’ll see you in the next one.