Gearing question re. Shimano XT Di2

Plaxton

I have a full suspension Marin which I love but which has done plenty of miles and needs a bit of an overhaul to the groupset components.

It currently has the original Deore XT 3x9 groupset on it, which has proven fine for my usage - although if anything I'd like the top gearing (44T - 11T) to be a bit higher than it currently is. I know this is probably a strange thing to want in a mountain bike, but the trips I'm using it for (riding around the UK's coast path) are usually half off-road and half on-road - and frequently the road part is on quite hilly roads, to the extent that I have to free-wheel down hills because the gearing isn't high enough to be able to pedal.

The low gearing is fine (22T - 36T I think) as it is and about perfect for what I need.

I'm very happy with the Marin generally and am not looking to upgrade to a different bike. I really like the idea of Di2 though and have pretty-much decided to upgrade to a XT Di2 set-up, but I am confused by the fact that it's only available in 2x11 with a maximum (highest) gearing of 38T - 11T - that's a big drop in gearing from 44T - 11T at a time when I want to be going the other way. I know the XTR Di2 has 3x11 available but even if the cost were the same I'd rather have the more durable XT than the race-intended XTR.

So my question are:

- Am I missing something? Is there any good reason why the top gearing is so much lower on the modern XT set than the older version I currently have?
- Is XT Di2 and XTR Di2 compatible? Could I use a XTR Di2 triple front with a XT rear?
- Could an XT Di2 rear be used with a front triple chainwheel and mechanical derailleur?
- What would actually happen if I used a Di2 front derailleur with a chainring that had more the maximum 38 teeth they recommend?
- Any other comments?

Thanks!

JBA

Mountain bikes aren't intended for fast road down hills. It's as simple as that.

As for the questions about Di2 I have no idea.

You could try a Deore XT Trekking groupset (XT T8000). It's 3x10 and uses a triple chainset with a 48T big ring.

Plaxton

Thanks, and I hadn't come across the Deore XT Trekking set - perhaps my existing bike already has the equivalent of that. My previous mountain bike also had a triple chainwheel as well though and it's strange to me that it's apparently now considered unusual. I'm all for designing a mountain bike to be great off-road but deliberately (and without good reason as far as I can tell) removing the higher gears and making them less good on the road seems a bit bizarre - just as with 4x4 vehicles it's silly to pretend that the vast majority of mountain bikes don't spend a lot of their time being ridden on the
road.

JBA

A 3x system results in some near-duplication of gear ratios. By increasing the number of sprockets it’s possible to reduce the number of chain rings and still have the same spread of gear ratios.
The downside is that you tend to lose top end but for ‘proper’ mountain biking this is not really a problem as you rarely reach such high speeds off road. On my 2x10 bike I can get to about 35mph (38T x 11T) on the road but on my 1x11 bike I struggle to hit 28mph before spinning out (32T x 11T). However, there is only one hill I regularly ride down where such speeds are possible so I don’t care.

If you use THIS GEAR CALCULATOR you can work out what gear ratios you currently have and compare them to any proposed new drive-chain.

Plaxton

That gear calculator is really useful not so much for calculating gearing but because it's preloaded with the details of lots of different manufacturer's cassettes and chainwheels - and I see that some of the cassettes go down to 9 teeth which I hadn't realised was possible. If I could use something like that it would be exactly the answer I'm looking for because 38 - 9 is actually a higher ratio than the 44 - 11 that I have at the moment.

Thanks

Now I have to see if there is a cassette with a 9 tooth sprocket that will match the other parts of my system

JBA

You can get 10- and 11-speed cassettes with a 9T smallest sprocket but they are very expensive.
The e-thirteen TRS+ 9-42 cassette is about £200.
SRAM and Hope make 10-40 and 10-42 cassettes but they are also expensive and you may need to change your freehub.