Backrest or a top case for 1979 R45

[lauripalokangas]

Hello,

Hope you are all doing well.

I'm considering to buy a 1979 BMW R45. It's sweet, but I've got a predicament with the pillion passenger part. My wife rides quite a lot with me, and she'd feel a lot more comfortable if there was a back rest (sissy bar) or a top case behind her back.

Alas, while it's easy to find either for /6 or /7 models, I've not found them for R45.

The motorcycle I'm considering has original luggage rack and side panniers. Apparently TC30 top case from Siebenrock doesn't fit the short luggage rack in the R45.

Any ideas are appreciated.

[SteveD]

Welcommen.

My first thought was "two up on a R45 " They're generally considered seriously underpowered. I'd seriously reconsider, maybe a R65, or better, a R80.

Apologies for not answering your question.

[barryh]

The problem with the 78-80 R45/R65 is that when the seat hinges up, it takes that tail piece with it, which makes fitting a rack or back rest problematical. On the 81-85 R45/R65 the tail piece stays put which must make fitting a rack or back rest more viable. On the plus side the early model seat is more comfortable particularly for the passenger and it has a grab strap for the passenger to hold onto.

An R45 will certainly be slow two up, but it will get there and only be seriously embarrassed on hills. More power is not necessarily a good thing because you have to stop as well and two up will tax the standard brakes. Unless you are both lightweights, I wouldn't consider using a single disc R45 or R65 two up on braking grounds alone. Riding both fast and two up is not something I'd indulge in anyway, regardless of the available power. My own skin is one thing, but I won't unduly risk someone else's more than necessary.

[lauripalokangas]

Thanks for the considerations - appreciate your useful advise.

What I know of the R45 I'm considering is that it has been upgraded with "800cc parts" but due to the technical reasons, it ends up as 700cc engine. Also, carburetors have been upgraded, as well as the drive train for better gear ratios.

It remains to be seen what impact do those changes have for the suitability to travel 2 up. Naturally I need a proper test drive 2 up with gear and panniers.

[barryh]

If 800cc pistons and barrels have been fitted from a mainstream airhead then the shorter stroke of the R45/R65 will give a capacity of 695cc. That should allay the concern about being short of power provided they also changed the heads for ones with bigger valves. If they went to trouble of fitting bigger carbs I imagine they did replace the heads. If they didn't you'll still have a lot more torque but with a limited top end. The extra power may highlight the braking issue unless they too have been upgraded.

[lauripalokangas]

If they went to trouble of fitting bigger carbs I imagine they did replace the heads.

For what it is worth, they did upgrade the heads too, and used slightly bigger intake valves.

[SteveD]

Sounds like it might be a sleeper. Has it still got R45 decals?

[lauripalokangas]

Sounds like it might be a sleeper. Has it still got R45 decals?

Yes. See attached photo.

[lauripalokangas]

The extra power may highlight the braking issue unless they too have been upgraded.

We're clearly diverting from the original topic, but I take it as we're both guilty and open to it.

I can find retrofit sets to upgrade brakes to a dual disc setup. But I've not seen too many posts nor videos about someone actually doing it. Do you feel the brake upgrade is more a matter of going from single disc to dual disc brakes, or upgrading to Brembo brakes from the later models?

[barryh]

The extra power may highlight the braking issue unless they too have been upgraded.

We're clearly diverting from the original topic, but I take it as we're both guilty and open to it.

I can find retrofit sets to upgrade brakes to a dual disc setup. But I've not seen too many posts nor videos about someone actually doing it. Do you feel the brake upgrade is more a matter of going from single disc to dual disc brakes, or upgrading to Brembo brakes from the later models?

There is no difference between the Ate and 81- 84 R45/65 Brembo caliper in terms of caliper piston diameter both being 36mm so no improvement in braking from that caliper alone. However the Brembo brake fitment in 81 brought with it a welcome reduction in master cylinder piston size from 13mm to 12mm which was a step in the right direction. The later 38mm Brembo caliper used on other airheads would be a further improvement.

Expressed in numbers a stock 79 R45/65 has a fairly abysmal brake piston ratio of 15.3
A 12mm master cylinder from a 81-84 R45/65 improves the ratio to 18
An easily available 38mm caliper improves it further to 20

An Ate caliper is hardly worth re-building as the spares are so expensive, so it makes sense in that scenario to move to a 38 mm Brembo what ever else is done.