1 power meter 2 bikes... (road/cx and MTB)

[flashd]

Hey guys,

This is my first WW post (been observing for a while) so... hello!

I'm looking at getting a power meter, a lot of my training will be on the road but I want to be able to record race data and some intervals on the MTB. Being the cheap-skate that I am, I want to share resources between bikes if possible.

My first thought was to buy a Stages so I would just need to swap the left side crank between bikes. Digging a little deeper it seems that this might be more complex than first thought (difference in q factor, chain line & shifting).

Has anyone found a set-up that works? Any particular disadvantages to this (other than the obvious time taken to swap a crank each ride!)?

FYI the bikes in question are a Cinelli Zydeco CX bike (2x10, 36/46 x 11-28, threaded bb) and Spec Stumpy Evo (1x10, 32t x 11-36, press fit bb but currently run an adapter for threaded/hollowtech bb).

Cheers,
Dave

[mr4fox]

I cant think of any that can be used on both road/CX and mtb. As you said MTB use different cranks so i don't think any current crank or crank arm based meter would work on both.

Power tap hubs wont fit both frames spacings. All the current pedal based systems I've seen are for road pedals, hence road shoes and cleats (Garmin Vector, Powertap P1 and Polar all use Look style cleats i believe) so you wont have any tread on your shoes if you use them off road. I have vectors and am contemplating putting them on my 29er for winter training as i have Ice Spiker Pro tyres mounted so can still train outside. But i would limit this to road use as i'd be paranoid about breaking a pod on rocks or branches when i stack it...which happens a lot lol!

[mentok]

in theory you could buy a spider like a quarq or a p2m rotor or something like that and move it from crankset to crankset, swap rings, etc every ride but that would be a massive hassle and you'd have to sort out your q-factor somehow.

[mrlobber]

Don't bother with PM on MTB, honestly. There is so much of pedalling variability and overall body/core work involved that your average and NP values will never correspond to real effort. Therefore, if you're going measure your MTB training load by power, you are going to seriously underestimate it. To verify this, just look at power / HR relationship on road / on CX / on MTB.

Thus, keep the PM to your road bike and hammer intervals out there on the road. On MTB, go by HR and PE.

[bikerector]

I partly agree with mrlobber, I think PM's are better on road bikes for training but I think they do still have a place for mtb. For mtb though, I think it's more of an observation where you kind of figure out how you should setting up your training vs doing the training. I've always found it incredibly difficult to do a structured interval set on the trails since so much of the intensity gets influenced by the terrain/turns since.

The only one I can think of, and it would require very specific bike setups, is a disc powertap. You would need a disc frame for all of them but the standards can be the same. I've looked into this for 142x12 since many CX bikes have gone that route but ultimately came out that I have too many wheels to try and go back down to just one for CX again.

I have also looked into the powercal from powertap which is roughly an estimated power based on the rate of change of your HR. I came to the conclusion that the only thing it would really end up doing for me is filling in the power slot in my computer and Trainingpeaks but with the hrTSS function in TP, made it a moot point for my application.

[benzebub]

if you really want to do this I would suggest an iBike newton or the newer Powerpod perhaps?

biggest concerns are accuracy vs crank/... based powermeters but I do believe DC rainmaker gave the powerpod a fairly positive review

http://www.powerpodsports.com/

[flashd]

Thanks for the replies guys. Yeh I agree on the MTB intervals being tough, but I think it would be useful to determine the length/intensities of efforts during a race so I can target my training efforts a little better.

Powertap might work actually - both bikes are 9x135mm disc, just need to have a think about cassette options.

The powerpod looks pretty cool but I think it would be pretty inaccurate with mtb tyres and terrain. Guess you can't use it on a trainer either?

[grouk]

my p2m swap between two bikes, during the week i train with a roubaix sl2 in the weekend i put the crank in my venge, only takes two minutes,

[mentok]

but that's road bike to road bike. mtb bbs are wider, chainlines are different, rear hub spacing is different. mtb is weird enough that it becomes a problem.

on second thoughts, someone may have looked at all the shimano and sram crank arms to see similarities - maybe there is 1 combination that is close enough that you could use a road crank on a mtbike or vice versa. this would open up the possibility of using a stages between 2 bikes with only a crank arm and pedal swap required.

[SpeedyChix]

PowerCal works for the mtb, just discount the power output by about 20%
Or run one set of values for that and the other for your road/cx crank-based power meter.
If you wear the PCal unit while on the road bike, compare the data. It'll give you a swag to work with.
Or, just skip it on the mtb.

[stephenjames]

Having used power completely since 2007 I'd completely disagree that's it's not worthwhile on the mtb. In fact the reverse especially if you are predominantly a CX or XC racer. The data you get helps you gear your train much more accurately around the efforts needed to compete at your best in those disciplines.

There are a few options for switching between the two. Disc PT is one of those although it means changing tyre and cassette all the time.

Another is use a MTB width chains on both. If it will fit on the MTB then the Sram with 156q factor is a good happy medium and run single ring on the CX bike too.

Another option which I use a lot is to use a Sram elsa/riken 110mm spider on the CX bike and then swap the spider only onto a Sram MTB chains like the X.0 etc. Single ring in the outer position gives good chain line.

But as I ride for Cannondale it's all a bit easier now because the arms are the same between road, CX and MTB. It's just the axle that alters the q factor. So I use stages arms an swap them between bikes in no time.

In fact, if your bikes are BB30 then switching to the Cannondale chainset on both is a very good option indeed. Have the driveside all setup on both bikes along with axle installed and just swap the NDS stages arm between them.

Steve

[mzlewis]

Hello Steve,

I've just done exactly that with my road bikes and mtb. easily the best and cheapest solution.

Matt