Have a bike right now with Ultegra Di2 disc groupset. Was looking at getting a backup bike that has Ultegra mechanical with rim brakes.

However, I've had a number of people tell me I'll really regret not spending another $700-1,000 bucks to get similar components on the backup.

The cross-compatibility argument sounds nice in theory, but wondering if anyone has any experience with how useful this actually is? Guess I could see it being nice having the ability to swap wheels in a pinch, but I feel like I'd just end up taking the other bike anyways if there was a wheel issue on the primary.

Is there something else I'm missing here? The backup will spend a bunch of time on the trainer with probably an outside ride here and there. Just don't know if it's worth the extra $ to keep components constant.

Thanks!

It's made life simpler over the long haul to have most things cross-compatible between bikes. Flat tire and it's time to ride? Swap in a spare wheel. Forgot to fix the flat when that one came off the bike? Now it's time for the spare bike. But that's over a dozen years.

Are you going to keep both bikes that long, or will you want a new bike in a couple years?

Without knowing the specifics of this year's groups, I might be thinking about mechanical disc brakes on the "rain" bike so I could switch wheels, and only need one kind of brake pad spares.

I own one disc and one rim brake bike. I find it mildly frustrating that I can't use the same wheelsets on both bikes.
This problem really becomes apparent if you're shopping for a new set of fancy wheels. You have to decide which bike they will be used on. It's like deciding which of your children you like better.

Beyond rim/disc, I wouldn't worry about other components being matched. I can't really imagine a scenario where I'd be swapping other components.

No, I don't collect only Eroica qualified Road Bikes either..

"Keep components the same across bikes?"

Where's the fun in THAT? I've got 2 Shimano bikes(OLD Dura Ace and new 105) and 2 Campy bikes(2006 Chorus and Veloce). I love trading off among them. Each groupset has its own good and bad points.

I can see keeping some similarity across bikes so that you can stock common chains, for example. But really, if the OP is thinking about having spare parts in case a Di2 component fails, then why not simply stock spares?

I'm an Electronic Engineer.
One of the best tools when troubleshooting any issue, is substitution.
Being able to replace a suspect item with a known good one can save hours.

If you work on your own bikes, imagine how useful it might be to have a complete set of spare parts.
You can even take the suspect item and install it on the good bike, just to see if the issue follows the part.

I'd opt to keep the bikes the same.

All the best

Barry

Wait, though - if you're about to ride and you've got a flat and no time to fix it, why not just take another bike? This is the advantage of having 4 bikes all ready to go at any time - if one's got a problem, I have 3 others to choose from, and they each have their own personality.

None of my bikes have the same components.

Why buy a backup bike? Why not buy a new bike and make the current one your backup?

But really, if you just want a bike for the trainer that sometimes gets ridden outside, don't even bother with mechanical Ultegra. Save some money and go with Tiagra or 105. You don't need electronic for a trainer bike.

(I do agree that it is very nice to have wheel and speed compatibility across bikes for easy swapping as needed.)

If I have more than 1 bike (and I do), it has to be different enough to warrant having and additional bike. I can't imagine wanting to have 2 bikes that close to the same.

Spend an extra $700-$1000 just to have a compatible backup?

That is utterly asinine.

The bike I have now is new and pretty nice. The idea with the backup was to have something else I could beat up on the trainer all winter long and take out in a pinch if needed (or if the roads were really crappy one day).

Good points on the groupset though and others have made good comments on the wheels too. Not sure though if I'd actually replace one of my deep section carbon rims on my main bike with the basic alloy rims likely to come on the backup, vs. just taking the backup out.

I should also probably be real with myself in accepting that I actually don't do much work on my own bikes so having all the backup parts might not be as helpful for me

I find it useful. My CX bike, my TT bike, and my son's CX bike are all 10-speed Shimano rim brakes. It's nice to be able to swap wheelsets among the three. Actually, with the TT bike I can also swap wheels with my Campy equipped bike because it has friction bar end shifters.

It's not important. What you ride is less important than riding, and unless you are riding competitively in a team where there are fleet of bikes where it is logical that all the bikes share the same components, you shouldn't worry about it. I have different bikes, they have different components, I don't lose sleep about it.

If you owned two cars why would you want them to be exactly the same? Why should bikes be any different?

I guess I don't get it, what id different between a DI2 rear wheel and a Ultegra mechanical rear wheel? If you have to change the wheels in a pinch, don't you just take it off the backup bike and put it on the Primary bike?

Or if there is a problem with the primary bike, can't you take the backup off the trainer and ride it. I mean, it is a backup. You have to take the bike off the trainer to get the wheel anyways.

My bikes - all rim brakes. (2) 120 mm fix gears, (2) 126 mm, one a 7-speed, the other can do 7-speed or "triple chianline" fix gear. (Slightly dished doubje sided track hub with a single on one side and a double on the other. 3 chainrings and 3 very different gears. (1) 130 mm 9-speed.

I have at least two rear wheels for each of the (4) setups.

Ben

Challenge isn't with Di2 vs. mechanical wheels. It's rim brake vs. disk brake wheels.

Totally agree with just riding the backup bike if there is a problem though.

Really appreciate all the replies. Definitely some things I hadn't thought about originally.

I kinda like the thought of having different bikes with different personalities. Might be nice to have a more traditional rim brake/mechanical setup alongside a Di2 disc. Definitely some food for thought.

R8020 is a mechanical with disc brakes, whats the problem? R8000 is rim brakes, I have that groupset.

Another solution looking for a problem.

start with wheels and tires , then cranks and cassettes , then components !

When I build a bike a start with frame geometry, drivetrain, components, wheels. Normally I try to use some wheels from a different bike to tryout the build.

That never works because then you will need to get a backup for the backup lol.