K75 exhaust reroute & tire question

[peteskipslegday]

Soon to commission local custom shop to build a '91 k75 for me.

One of my requests was to re-route the exhaust from the straight parallel pipe to a under-seat or adjacent-to-seat exhaust. However, I've read numerous threads across multiple forums regarding the performance loss with aftermarket exhausts on the K75 in particular. Any one have any additional/recent information regarding this? Has someone stumbled on an aftermarket exhaust system that maintains the bike's performance? (some of those threads were quite old).

What's the fattest rear tire someone's been able to fit on the stock rims? Alternatively, what's the fattest rim anyone has been able to fit on a K bike without having to make major alterations?

I know my question may offend some of the forums' purists, but again it's a project bike and I'm not a fan of the straight pipe. Also, my vacuum sounds better than the stock pipe.

Thanks in advance.

[johnny]

greetings peteskipslegday...

f the purists... the rt motobrick oughtta be bastardized...

a costom shop should be able to getts a custom cut set of wheels on there and a set of low profile car tiors on there for you...

any custom shop can weld up a couple of water hammer mufferlers under the seat... look baddassed and sound rad...

post up some photo as you go...

j o

[peteskipslegday]

J O --

I was not looking to replace the stock BMW wheels (quite fancy them) just wanted to see what the largest tire people were able to fit on them.

What's a water hammer muffler? Had to google it, and I still don't know what that is.

I'll definitely post some photos as it gets built though!

Pete

[Chaos]

What kind of vacuum you got?  Most compare it to a sewing machine, I think a blender nails it.  Nobody makes  a pipe for a K75 anymore.  Staintune and MAC were probably the best if you can find one, I scored a MAC and love it.  They don't add anything performance-wise but all the rubbish about lowering HP came from purists that liked the sound of making smoothies.  The cams, 2V head and CPU pretty much limit what the HP is.

[peteskipslegday]

Got a Dyson. The K75 really lacks a voice, very sterile.

Looks like I might have to take a look into aftermarket slip-ons and just fab headers.

I've seen the dyno charts of aftermarket pipes and the K75 turbo builds, but has anyone found hotter cams, or changed the electronics?

Additionally, I'm sure we're all very familiar with the K100 BEARS build by BSK, can any of their performance enhancements be translated to a K75?

[TimTyler]

Did you buy the K75 with 130k miles on it? Are you having a 3rd party "build" this bike to your specs?

Some might disagree but IMO the old K's are not really "performance" bikes. They excel in reliability, design and touring comfort.

I'm not trying to dissuade your from your objective, but I hope you have realistic expectations.

[bocutter Ed]

What kind of vacuum you got?

Mine's a homebuilt Pentz. Pulls about 1000 cfm, 5 horse power. Dyson based his design on woodworking dust collectors.

[rbm]

What's the fattest rear tire someone's been able to fit on the stock rims?

150/70ZR-17 Bridgestone 020's

Alternatively, what's the fattest rim anyone has been able to fit on a K bike without having to make major alterations?

4.5" K1100 rims are possible without modification to the K75/K100 monolever.  Can fit a 160/60-18 tire. Wider K1200 5" rims are possible be requires modifications to the center stand and possibly changing out the rear end for a K1100 paralever.

[peteskipslegday]

What's the fattest rear tire someone's been able to fit on the stock rims?

150/70ZR-17 Bridgestone 020's

Alternatively, what's the fattest rim anyone has been able to fit on a K bike without having to make major alterations?

4.5" K1100 rims are possible without modification to the K75/K100 monolever.  Can fit a 160/60-18 tire. Wider K1200 5" rims are possible be requires modifications to the center stand and possibly changing out the rear end for a K1100 paralever.

Thanks for the tips. Might have to give the search party a different scent! I've seen the Paralever conversions and they've all raved about eliminating the 'elevator-jacking' effect but I think that's a function of clutch work moreso than the design? Could be wrong....

Did you buy the K75 with 130k miles on it? Are you having a 3rd party "build" this bike to your specs?

Some might disagree but IMO the old K's are not really "performance" bikes. They excel in reliability, design and touring comfort.

I'm not trying to dissuade your from your objective, but I hope you have realistic expectations.

Hey Tim, I would rather have people question my decisions than have people agree with me.

I bought the 130k K75. We found a new tranny (from a K100 i think), everything else upon inspection looked good, so I'm expecting a lot of life out of it. I know the K75 is certainly not a performance bike and I chose it specifically for the reliability the bricks are known for. I fancied me a naked bike and I just couldn't sell myself on a ducati monster, triumph, or even yamaha's new hooligan triple (Fz-09). Instead I thought, hell I want a low maintenance bike, I can strip down, have it look and sound good, and give me the satisfaction of owning a one off bike. That being said, I know the K75 is often referred to as a fairly mild steed and I do love me some low-end torque so I was trying to see if there was any modifications that might add some oomph here or there without involving costly and heavy mods. I already have my sights on a older Ducati 748 and a slightly newer 999 to scratch that itch. Nice to have v. have to haves.